Porous polyimide with highly uniform nanostructure

Abstract

The present invention provides a porous polyimide or polyimide wet gel with excellent physical properties. One aspect provides a porous polyimide in which an average pore size (d) obtained by using small-angle x-ray scattering is 1.0 nm to 7.0 nm. One aspect provides a porous polyimide in which the minimum value of the differential coefficient when the logarithmic value log[I(q)] of the scattering intensity I(q) is differentiated by the logarithmic value log[q] of the scattering vector q is -1.0 to 0.0 within a range in which the size of the scattering vector q in small-angle x-ray scattering is 0.025 nm-1 to 0.075 nm-1.

Description

[Technical Field]

[0001] The present disclosure relates to porous polyimides having highly uniform nanostructures, and further to polyimide wet gels and porous carbon sheets. [Background technology]

[0002] Traditionally, aerogel has been defined as a porous material in which the solvent contained in the gel has been replaced with a gas by supercritical drying. However, in recent years, it has been recognized in a broader sense as a porous material in which the solvent has been removed from a solvent-containing colloid or polymer network while suppressing shrinkage, volume loss, etc. Due to its fine pore structure, aerogel has various properties, such as low density, high porosity, porosity (mesopores), high specific surface area, high specific strength, high thermal insulation, high electrical insulation, and high soundproofing. Known types of aerogel include organic and inorganic aerogels, such as silica aerogel, polymer aerogel (e.g., polyimide aerogel), and carbon aerogel.

[0003] For example, polymer aerogels are known as porous materials obtained by removing a solvent from a colloid or polymer network without shrinkage or volume loss. Among polymer aerogels, polyimide aerogels can be useful in various applications requiring heat resistance due to the inherently good heat resistance of polyimides.

[0004] Patent Documents 1 and 2 describe crosslinked polyimide aerogels and methods for their manufacture. The aerogels have polyamide crosslinks formed using a triacid chloride crosslinker. The aerogels include polyimide oligomer components and polyamide crosslinks, which are bonded to the polyimide oligomer components. The polyimide oligomer components contain reaction products of diamines and acid dianhydrides in a ratio of (n+1):n, where n is the number of repeating units in the oligomer.

[0005] Patent Document 3 describes a method for producing crosslinked polyimide aerogels, which involves synthesizing polyamic acid by polycondensation using acid dianhydride and diamine as monomers, forming a polyimide wet gel by low-temperature osmotic imidization using polyamino monomer as a crosslinker, and then producing crosslinked polyimide aerogels by a supercritical drying process.

[0006] Non-Patent Document 1 describes a method for producing polyimide aerogels from amine-capped oligomers crosslinked with 1,3,5-benzenetricarbonyl trichloride (BTC). The aerogels produced by this method are said to have a modulus equal to or greater than those of previously reported aerogels with the same crosslink density, such as 1,3,5-tris(4-aminophenoxy)benzene (TAPB) or octa(aminophenoxy)silsesquioxane (OAPS).

[0007] Non-Patent Documents 2 and 3 report polyimide aerogels in which a linear aliphatic skeleton is introduced into the polyimide main chain, using polyamic acid as a raw material, which is composed of diamines linked by linear aliphatic groups and acid dianhydrides. These documents describe that the polyimide aerogels have flexibility derived from the linear aliphatic structure, and that sheet-like polyimide aerogels can be produced.

[0008] Non-Patent Document 4 describes hyperbranched polyimides synthesized from dianhydrides and triisocyanates.

[0009] Non-Patent Document 5 describes a method for producing nanoporous polyimide aerogels, which involves crosslinking anhydride-capped polyamic acid oligomers with aromatic triamines in solution, chemically imidizing them to obtain polyimide gels, and then supercritically drying the gels to obtain nanoporous polyimide aerogels.

[0010] Non-Patent Document 6 describes polyimide aerogels synthesized from a combination of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and 4,4'-oxydianiline (ODA), or a combination of 4,4'-oxydianiline (ODA) and 9,9'-bis(4-aminophenyl)fluorene (BAPF), and crosslinked with 1,3,5-benzenetricarbonyl trichloride (BTC).

[0011] Non-Patent Document 7 describes the relationship between the structure and properties of polyimide aerogels with various diamine fractions, which have pyromellitic dianhydride (PMDA) and biphenyltetracarboxylic dianhydride (BPDA) as their backbones.

[0012] Non-Patent Document 8 describes a rigid polymer network in which the backbone of an aromatic polyimide (PI) is end-linked with a symmetrical crosslinker. The crosslinker is 1,3,5-tris(4-aminophenyl)benzene (TAB) or tetra(4-aminophenyl)methane (TAPM), and a polyamic acid network is produced by end-linking a polyamic acid precursor with TAB or TAPM.

[0013] Furthermore, porous carbon materials have properties such as high electrical conductivity, adsorptivity, and chemical stability, and are therefore widely used as electrode materials, catalyst supports, etc. Known porous carbon materials include, for example, porous carbon materials having nano-order pores, such as molecular sieve carbon, activated carbon, carbon nanotubes, carbon nanofibers, and template carbon produced from a zeolite template, etc.; porous carbon materials having submicron-order pores, such as vapor-grown carbon and carbon aerogel; and porous carbon materials having micron-order pores, such as carbon foam, woven carbon fiber fabric, and reticulated vitreous carbon.

[0014] Porous carbon materials with nano-order pores are generally formed by chemical approaches and come in a variety of shapes, including powder (zero-dimensional), fiber (one-dimensional), relatively thin sheet (two-dimensional), relatively thick sheet, and various bulk (three-dimensional) shapes such as block. Porous carbon materials with relatively large pores on the micron order can generally be formed by physical approaches such as foaming and are often produced in shapes ranging from fiber to bulk. Porous carbon materials with submicron order pores are difficult to produce by either chemical or physical approaches; for example, only powdered vapor-grown carbon and carbon aerogels, and bulk carbon aerogels, etc., are known. Carbon aerogels can be produced, for example, by carbonizing polymer aerogels such as resorcinol-based phenolic resins at high temperatures.

[0015] Non-Patent Documents 1 to 7 contain the above-mentioned descriptions. Non-Patent Document 4 describes a method for synthesizing a monolithic multiscale micro / meso / macroporous polymer based on a hyperbranched polyimide synthesized from an acid dianhydride and triisocyanate. It is described that the microporous polymer is an inherent property of the molecular network, and is resistant to thermal decomposition and transitions into a multiscale nanoporous carbon material with mesoporosity and macroporosity. Non-Patent Document 6 describes that shrinkage can be suppressed by incorporating bulky moieties into the polymer skeleton.

[0016] In addition, Non-Patent Document 9 reports that when resorcinol and formaldehyde are polycondensed under alkaline conditions, clusters of surface-functionalized phenolic resins are formed, and a gel is generated by crosslinking these clusters with covalent bonds. This gel is then treated in a supercritical state to produce a low-density organic aerogel (0.1 g / cm). 3 ) can be obtained. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] U.S. Patent No. 9,434,832 [Patent Document 2] U.S. Patent No. 10,358,539 [Patent Document 3] China Patent No. 108203516 Detailed Information

Non-licensed literature

[0018]

Non-patent document 1

Non-patent document 2

Non-patent document 3

Non-patent document 4

Direct Environment 5

Outdoor Configuration6

Direct Environment 7

Outdoor Track 8

Outdoor Tools9

[0019] However, none of the above-mentioned conventional techniques has been able to achieve excellent physical properties in porous polyimide, polyimide wet gel, or porous carbon sheet.

[0020] First, the polyimide aerogels described in Patent Documents 1 and 2 and Non-Patent Documents 1 to 6 are believed to have a pore structure (macropores) that diffuses light, resulting in low light transmittance. Furthermore, the pore structure includes micropores in addition to macropores, resulting in a broad pore size distribution. This tends to result in low uniformity of the polyimide backbone structure and poor mechanical strength, particularly in low flexural modulus, flexural strength, and strain at break in bending tests. The polyimide aerogels described in Non-Patent Documents 2 and 3 are crosslinked from polyimides with linear aliphatic structures, which makes the aerogels highly flexible, but tend to have poor mechanical strength, particularly in low flexural modulus or flexural strength in bending tests. Furthermore, like the polyimide aerogels described in Patent Documents 1 and 2 and Non-Patent Document 1, the polyimide aerogels described in Non-Patent Documents 2 and 3 also tend to have poor uniformity of the polyimide backbone structure.

[0021] Second, in recent years, the range of applications desired for polyimide aerogels has become broader, and applications such as heat insulating materials, low dielectric materials, and filter materials are being considered. Porous carbon sheets can also be useful as catalyst supports, electrode materials, and filter materials. However, the aerogels described in Patent Documents 1 and 2 have low toughness (and therefore resistance to bending) and are not suitable for a wide range of applications.

[0022] Third, in recent years, the range of applications desired for polyimide aerogels has become more diverse, and their use as flexible, highly heat-resistant insulating materials, for example, has been explored. However, the aerogels described in Patent Documents 1 and 2 lack sufficient heat resistance during heat processing, resulting in problems such as deformation of the aerogel and loss of its pore structure. While polyimide aerogels prepared by the methods described in Non-Patent Documents 1, 5-7 can in principle be molded into sheets, they suffer from insufficient heat resistance and shrinkage at high temperatures. Non-Patent Documents 2 and 3 achieve sheet-shape molding by introducing an aliphatic skeleton into the main chain of the polyimide aerogel. However, the introduction of a linear aliphatic structure, which generally has lower heat resistance than an aromatic skeleton, results in insufficient heat resistance, as in Non-Patent Documents 1, 5-7. The method described in Non-Patent Document 4 polymerizes and gels polyimide using triisocyanate. However, this method requires high-temperature and long-term reaction conditions for polymerization and gelation. Therefore, even if the polymerization solution is spread into a sheet, the evaporation rate of the solvent is overwhelmingly faster than the polymerization and gelation rates, and a sheet-like wet gel cannot be formed, so a sheet-like porous polyimide cannot be obtained.

[0023] Fourth, in conventional methods such as those described in Patent Documents 1 and 2 and Non-Patent Documents 1, 6, and 7, polyimide wet gels are obtained by imidizing polyamic acid in solution to obtain a polyimide solution, and then introducing crosslinking sites to gel the polyimide. However, polyimides are poorly soluble in commonly used organic solvents and are prone to aggregation, precipitation, and sedimentation in solution during gelation. Furthermore, in conventional methods such as those described in Patent Document 3 and Non-Patent Document 8, polyamic acid is first gelled to obtain a polyamic acid wet gel, and then the polyamic acid wet gel is imidized to obtain a polyimide wet gel. However, polyamic acid wet gels tend to deform in solution during imidization, and this can result in failure to obtain a polyimide wet gel. For example, Patent Document 3 describes performing imidization at a low temperature of -30°C to 5°C for a long period of time, while Non-Patent Document 8 describes performing imidization at a low temperature and narrowing the molecular weight distribution of the polyamic acid. However, these conventional techniques have made it difficult to produce polyimide wet gels with excellent physical strength.

[0024] Fifth, in conventional methods such as those described in Patent Documents 1 and 2 and Non-Patent Documents 1, 6, and 7, polyimide wet gels are obtained by imidizing polyamic acid in solution to obtain a polyimide solution, and then introducing crosslinking sites to gel the polyimide. However, polyimides are poorly soluble in commonly used organic solvents and are prone to aggregation, precipitation, and sedimentation in solution during gelation. This limits the structure of polyamic acid that can be used. In conventional methods such as those described in Patent Document 3 and Non-Patent Document 8, polyamic acid wet gels are obtained by first gelling polyamic acid to obtain a polyamic acid wet gel, and then imidizing the polyamic acid wet gel. However, polyamic acid wet gels are prone to deformation in solution during imidization, and polyimide wet gels may not be obtained. For this reason, for example, imidization is performed for a long period of time at low temperatures of -30°C to 5°C as described in Patent Document 3, and Non-Patent Document 8 shows that when polyamic acid wet gels are imidized in a mixture of acetic anhydride and pyridine, the shape of the sample is significantly deformed.

[0025] Sixth, it has been difficult to produce porous carbon materials with submicron-order pores in a sheet-like shape. Polyimide aerogels are known, as described in Non-Patent Documents 1, 5, 6, 7, and 8. Non-Patent Documents 2 and 3 also report polyimide aerogel sheets, which are formed by developing these into sheets. Commercially available polyimide aerogel sheets include AeroZero (product name) manufactured by BlueShift. However, these conventional polyimide aerogel sheets have low heat resistance, and their pore structure collapses under carbonization conditions, making it impossible to obtain porous carbon sheets. The method described in Non-Patent Document 4 involves polymerizing and gelling polyimide using triisocyanate, which is then carbonized. The method described in Non-Patent Document 9 involves reacting resorcinol with formaldehyde to polymerize and gel a phenolic resin. However, these methods require high-temperature and long-term reaction conditions for polymerization and gelation. Therefore, even if the polymerization solution is spread into a sheet, the evaporation rate of the solvent is overwhelmingly faster than the polymerization and gelation rates, and a sheet-like wet gel cannot be formed, and a porous carbon sheet cannot be obtained.

[0026] The present disclosure aims to provide a porous polyimide, a polyimide wet gel, or a porous carbon sheet that can solve one or more of the above problems. More specifically, the first and second aspects of the present disclosure aim to provide a porous polyimide having good toughness. The third aspect of the present disclosure aims to provide a sheet-like porous polyimide having good heat resistance. The fourth aspect of the present disclosure aims to provide a polyimide wet gel having excellent physical strength. The fifth aspect of the present disclosure aims to provide a method for producing a polyimide wet gel and a porous polyimide that can suppress deformation of the polyamic acid wet gel during imidization. The sixth aspect of the present disclosure aims to provide a porous carbon sheet having submicron-order pores and a method for producing the same. [Means for solving the problem]

[0027] This disclosure encompasses the following items: [1] A porous polyimide having an average pore size (D) of 1.0 nm or more and 7.0 nm or less, as determined by small-angle X-ray scattering. [2] The magnitude of the scattering vector q of small-angle X-ray scattering is 0.025 nm -1 More than 0.075nm -1 2. The porous polyimide according to item 1, wherein the minimum value of the differential coefficient when the logarithm of the scattering intensity I(q) log[I(q)] is differentiated by the logarithm of the scattering vector q log[q] is -1.0 or more and 0.0 or less in the following range: [3] Based on the pore volume (V) and BET specific surface area (A) determined by gas adsorption, the following formula: L=4V / A 3. The porous polyimide according to item 1 or 2, wherein the average pore diameter (L) obtained by [4] The porous polyimide according to any one of items 1 to 3, which has a flexural modulus of 100 MPa or more in a three-point bending test. [5] The porous polyimide according to any one of items 1 to 4, which has a flexural modulus of 200 MPa or more in a three-point bending test. [6] The porous polyimide according to any one of items 1 to 5, which has a bending strength of 5 MPa or more in a three-point bending test. [7] The porous polyimide according to any one of items 1 to 6, which has a bending strength of 10 MPa or more in a three-point bending test. [8] Bulk density of 0.05 g / cm 3 More than 0.50g / cm 3 8. A porous polyimide according to any one of the above items 1 to 7, which is as follows: [9] BET specific surface area is 100m 2 / g or more 2,000m 2 9. The porous polyimide according to any one of items 1 to 8, wherein the porous polyimide has a viscosity of 1 / g or less.

[10] The porous polyimide according to any one of items 1 to 9 above, which has a sheet shape.

[11] The porous polyimide according to any one of items 1 to 10, wherein the polyimide constituting the porous polyimide has a polyimide main skeleton and a crosslinking structure that crosslinks the polyimide main skeleton.

[12] Based on the pore volume (V) and BET specific surface area (A) determined by gas adsorption, the following formula: L=4V / A The average pore diameter (L) calculated by is 5 nm or more and 500 nm or less, Porous polyimide with a flexural modulus of 150 MPa or more in a three-point bending test.

[13] The porous polyimide according to item 12, having a flexural modulus of 200 MPa or more in a three-point bending test.

[14] Based on the pore volume (V) and BET specific surface area (A) determined by gas adsorption, the following formula: L=4V / A The average pore diameter (L) calculated by is 5 nm or more and 500 nm or less, A porous polyimide having a bending strength of 10 MPa or more in a three-point bending test.

[15] The porous polyimide according to any one of items 12 to 14, wherein the polyimide constituting the porous polyimide has a polyimide main skeleton and a crosslinking structure that crosslinks the polyimide main skeleton.

[16] Based on the pore volume (V) and BET specific surface area (A) determined by gas adsorption, the following formula: L=4V / A The average pore diameter (L) calculated by is 5 nm or more and 500 nm or less, The bending modulus in a three-point bending test is 50 MPa or more, A porous polyimide comprising a polyimide main skeleton having an aromatic group in the molecular skeleton and a crosslinked structure having an aromatic group in the molecular skeleton.

[17] Bulk density of 0.05 g / cm 3 More than 0.50g / cm 3 17. The porous polyimide according to any one of the above items 12 to 16, wherein:

[18] BET specific surface area is 10m 2 / g or more 2,000m 218. The porous polyimide according to any one of items 12 to 17, wherein the porous polyimide has a viscosity of 1 / g or less.

[19] The porous polyimide according to any one of items 12 to 18, wherein the ratio of the number of carbonyl carbon atoms to the total number of carbon atoms in the polyimide constituting the porous polyimide is 13.5% or more.

[20] Based on the pore volume (V) and BET specific surface area (A) determined by gas adsorption, the following formula: L=4V / A The average pore diameter (L) calculated by is 5 nm or more and 500 nm or less, After heat treatment at 300°C for 1 hour, the BET specific surface area is 10m 2 / g or more 2,000m 2 / g or less.

[21] Bulk density of 0.05 g / cm 3 More than 0.50g / cm 3 21. The porous polyimide according to item 20, which is:

[22] The porous polyimide according to item 20 or 21, wherein the ratio of the number of carbonyl carbon atoms to the total number of carbon atoms in the polyimide constituting the porous polyimide is 13.5% or more.

[23] The porous polyimide according to any one of items 20 to 22, wherein the polyimide constituting the porous polyimide has a polyimide main skeleton and a crosslinking structure that crosslinks the polyimide main skeleton.

[24] The porous polyimide according to any one of items 1 to 23, wherein the crosslinked structure is a structure formed by a trivalent or higher group derived from an optionally substituted monocyclic or polycyclic aromatic ring, or a trivalent or higher group derived from a linked aromatic ring in which multiple optionally substituted aromatic rings are linked to each other by direct bonds or bonds via heteroatoms.

[25] The polyimide main skeleton is represented by the following general formula (1): [ka] (In the formula, X is a tetravalent organic group; Y is a divalent organic group, provided that: X is a tetravalent group derived from an optionally substituted monocyclic or polycyclic aromatic ring, or a tetravalent group derived from a linked aromatic ring in which multiple optionally substituted aromatic rings are linked to each other by direct bonds or bonds via heteroatoms, and / or Y is a divalent group derived from an optionally substituted monocyclic or polycyclic aromatic ring, or a divalent group derived from a linked aromatic ring in which multiple optionally substituted aromatic rings are linked to each other by a direct bond or a bond via a heteroatom, n is a positive integer.) 25. The porous polyimide according to any one of items 1 to 24, having a structure represented by the following formula (1): wherein the degree of polymerization of the polyimide main skeleton is n in the general formula (1).

[26] The porous polyimide according to any one of items 1 to 25, wherein the polyimide constituting the porous polyimide comprises a polymerization product of polymerization components including a tetracarboxylic dianhydride, a diamine, and a trifunctional or higher functional amine, and the ratio of the trifunctional or higher functional amine to a total of 100% by mass of the tetracarboxylic dianhydride, the diamine, and the trifunctional or higher functional amine is 1% by mass or more and 40% by mass or less.

[27] The porous polyimide according to any one of items 1 to 26, having an average thickness of 10 mm or less.

[28] The polyimide constituting the porous polyimide includes a polymerization product of polymerization components including a tetracarboxylic dianhydride and a diamine, 50 mol % or more of the tetracarboxylic dianhydride is pyromellitic anhydride, 28. The porous polyimide according to any one of items 1 to 27, wherein the terminal of the polyimide is an anhydride structure derived from pyromellitic anhydride.

[29] When plotting the scattering vector q of small-angle X-ray scattering, the scattering intensity I(q) multiplied by q, qI(q), the scattering vector q of small-angle X-ray scattering, the scattering vector qI(q) is 0.04 nm. -1 <q<2.0nm -1 The average pore size D calculated from the peak position of qI(q) has a maximum value in the range w The polyimide wet gel has a particle size of 0.8 nm or more and 8.0 nm or less.

[30] The magnitude of the scattering vector q of small-angle X-ray scattering is 0.080 nm -1 More than 0.12nm -1 30. The polyimide wet gel according to item 29, wherein the minimum value of the differential coefficient when the logarithm log[I(q)] of the scattering intensity I(q) is differentiated by the logarithm log[q] of the scattering vector q is −1.0 or more and 0.0 or less in the following range:

[31] The polyimide wet gel according to item 29 or 30, which has a breaking strain of 10% or more in a three-point bending test.

[32] The polyimide constituting the polyimide wet gel is represented by the following general formula (1): [ka] (In the formula, X is a tetravalent organic group, Y is a divalent organic group, and n is a positive integer.) wherein in general formula (1), X and / or Y have a structure that imparts linearity to the molecular chain, and n is the degree of polymerization of the polyimide.

[33] The polyimide constituting the polyimide wet gel is represented by the following general formula (1): [ka] (In the formula, X is a tetravalent organic group, Y is a divalent organic group, and n is a positive integer.) wherein the ratio of structures derived from pyromellitic anhydride among X present in the molecular chain is 50 mol % or more, and the terminal of the molecular chain is derived from pyromellitic anhydride.

[34] The polyimide wet gel according to any one of items 29 to 33, which has a sheet shape.

[35] The porous polyimide obtained by substituting the solvent in the polyimide wet gel with acetone and then drying with supercritical carbon dioxide is BET specific surface area: 100m 2 / g or more 2,000m 2 / g or less, Bulk density: 0.05g / cm 3 More than 0.50g / cm 3 below, Bending strength: 5 MPa or more, Flexural modulus: 100 MPa or more, and Average pore size (D) determined by small-angle X-ray scattering: 1.0 nm or more and 7.0 nm or less; 35. The polyimide wet gel according to any one of items 29 to 34, wherein

[36] Adding a crosslinker having three or more functional groups to a polyamic acid solution to obtain a polyamic acid wet gel; a step of immersing the polyamic acid wet gel in a solution containing a dehydrating imidizing agent to obtain a polyimide wet gel; Including, The method for producing a polyimide wet gel, wherein the concentration of the dehydrating imidizing agent in the solution is 1% by weight or more and 50% by weight or less.

[37] The method according to item 36, wherein the temperature in the step of obtaining a polyamic acid wet gel and the step of obtaining a polyimide wet gel is maintained at 10°C or higher.

[38] The method according to item 36 or 37, wherein the temperature in the step of obtaining a polyamic acid wet gel and the step of obtaining a polyimide wet gel is maintained at 120°C or lower.

[39] The method according to any one of items 36 to 38, wherein the step of obtaining the polyamic acid wet gel is carried out by adding the crosslinking agent having three or more functional groups to the polyamic acid solution and spreading the mixture into a sheet.

[40] The method according to any one of items 36 to 39, wherein the dehydrating imidizing agent is a combination of acetic anhydride and triethylamine.

[41] The porous polyimide constituting the polyimide wet gel has a BET specific surface area of 10 m after heat treatment at 300 °C for 1 hour. 2 / g or more 2,000m 2 / g or less.

[42] The method according to any one of items 36 to 41, wherein the porous polyimide constituting the polyimide wet gel has a bending strength of 10 MPa or more and a bending modulus of 100 MPa or more in a three-point bending test.

[43] The method according to any one of items 36 to 42, wherein the average pore size (D) of the porous polyimide constituting the polyimide wet gel, as determined by small-angle X-ray scattering, is 1.0 nm or more and 7.0 nm or less.

[44] The polyimide constituting the polyimide wet gel is represented by the following general formula (1): [ka] (In the formula, X is a tetravalent organic group, Y is a divalent organic group, and n is a positive integer.) wherein in general formula (1), X and / or Y have a structure that imparts linearity to the molecular chain, and n is the degree of polymerization of the polyimide.

[45] A step of obtaining the polyimide wet gel by the method according to any one of items 36 to 44 above; removing the solution from the polyimide wet gel to obtain a porous polyimide; A method for producing a porous polyimide, comprising:

[46] A porous carbon sheet which is a carbonized product of the porous polyimide according to any one of items 1 to 28, Based on the pore volume (V) and BET specific surface area (A) determined by gas adsorption, the following formula: L=4V / A A porous carbon sheet having an average pore diameter (L) determined by the above formula (1) of 5 nm or more and 500 nm or less.

[47] Bulk density of 0.01 g / cm 3 More than 0.80g / cm 3 47. The porous carbon sheet according to item 46, wherein:

[48] The porous carbon sheet according to item 46 or 47, having an average thickness of 10 mm or less.

[49] BET specific surface area is 10 m 2 More than 2,000m 249. A porous carbon sheet according to any one of the above items 46 to 48, which is:

[50] A method for producing a porous carbon sheet, comprising the step of heating a sheet of the porous polyimide according to any one of items 1 to 28 to 400°C or higher to carbonize it, thereby obtaining a porous carbon sheet, The porous carbon sheet has a pore volume (V) and a BET specific surface area (A) determined by a gas adsorption method, and the pore volume (V) and the BET specific surface area (A) are determined by the following formula: L=4V / A The method according to claim 1, wherein the average pore diameter (L) obtained by the above method is 5 nm or more and 500 nm or less.

[51] A step of obtaining a porous polyimide sheet by the method described in Item 45 above; A method for producing a porous carbon sheet, comprising: a step of heating the sheet to 400°C or higher to carbonize it, thereby obtaining a porous carbon sheet, The porous carbon sheet has a pore volume (V) and a BET specific surface area (A) determined by a gas adsorption method, and the pore volume (V) and the BET specific surface area (A) are determined by the following formula: L=4V / A The method according to claim 1, wherein the average pore diameter (L) obtained by the above method is 5 nm or more and 500 nm or less. [Effects of the Invention]

[0028] According to the first and second aspects of the present disclosure, a porous polyimide having excellent toughness can be provided. Furthermore, according to the third aspect of the present disclosure, a sheet-like porous polyimide having good heat resistance can be provided. Furthermore, according to the fourth aspect of the present disclosure, a polyimide wet gel having excellent physical strength can be provided. Furthermore, according to the fifth aspect of the present disclosure, a method for producing a polyimide wet gel and a porous polyimide that can suppress deformation of the polyamic acid wet gel during imidization is provided. Furthermore, according to the sixth aspect of the present disclosure, a porous carbon sheet having pores on the submicron order and a method for producing the same are provided. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1 is a diagram illustrating small-angle X-ray scattering measurement. DETAILED DESCRIPTION OF THE INVENTION

[0030] An embodiment of the present invention (hereinafter abbreviated as "embodiment") will be described in detail below. The present invention is not limited to the following embodiment, and various modifications can be made within the scope of the gist of the present invention. Unless otherwise specified, the characteristic values referred to in this disclosure are values described in the "Examples" section of the present disclosure or values measured using methods that are understood to be equivalent to those described in the "Examples" section of the present disclosure.

[0031] <<<Porous Polyimide>>> One aspect of the present invention provides a porous polyimide (also referred to as a porous polyimide composition) composed of polyimide. In a typical embodiment, the porous polyimide is composed of polyimide, but may contain components other than polyimide as long as the effects of the present invention are not impaired.

[0032] First Aspect In a porous polyimide according to one embodiment, the average pore size (D) determined by small-angle X-ray scattering is, in one embodiment, 1.0 nm or more, or 1.5 nm or more, or 2.0 nm or more, from the viewpoint of having a pore structure suitable for an aerogel; and, in one embodiment, is 7.0 nm or less, or 6.0 nm or less, or 5.0 nm or less, from the viewpoint of obtaining a good flexural modulus, flexural strength, and strain at break.

[0033] In the small-angle X-ray scattering intensity profile from a large-sized structure, the scattering intensity is high in regions with small scattering vectors q and low in regions with large q. On the other hand, if the structure size is sufficiently smaller than the reciprocal of the observed q, the scattering intensity does not show q dependence and remains a constant value. Therefore, if the change in X-ray scattering intensity per unit change in scattering vector q in the ultra-small-angle region is small, there are few structural portions of a size that cause diffuse reflection of visible light, which is thought to be advantageous in terms of transparency.

[0034] In one embodiment, the magnitude of the scattering vector q of the small-angle X-ray scattering is 0.025 nm -1More than 0.075nm -1 In the following ranges, the minimum value of the differential coefficient (also simply referred to as the minimum differential coefficient) when the logarithm of the scattering intensity I(q) log[I(q)] is differentiated by the logarithm of the scattering vector q log[q] is preferably -1.0 or more, -0.95 or more, or -0.90 or more. The absolute value of the minimum differential coefficient is preferably as close to zero as possible, and in one embodiment, it is 0.0 or less. However, from the viewpoint of ease of production of the porous polyimide, in one embodiment, it may be -0.01 or less, or -0.05 or less. When a porous polyimide has an average pore size (D) within the range of the present disclosure and a minimum differential coefficient within the above range, it is believed that the porous polyimide contains many micropores and few large-sized structural portions. Such porous polyimides have a desired pore structure and excellent structural uniformity, and therefore can achieve both good toughness (more specifically, flexural modulus, flexural strength, and strain at break) and good transparency.

[0035] In small-angle X-ray scattering measurements, X-rays are incident on the surface of a thin piece cut from a porous polyimide. In one embodiment, the surface of the thin piece is a cross section of the porous polyimide in the direction in which the outer diameter is smallest (for example, the thickness direction of the sheet). Calculation of the average pore size (D) and quantification of structural heterogeneity can be performed as follows.

[0036] <Calculation of average pore size (D)> The scattering pattern I(2θ,φ) in small-angle X-ray scattering (SAXS) measurement is calculated using the following formula (1):

number

[0037] The one-dimensional profile calculated by the above formula (1) includes scattering from the sample as well as scattering from sources other than the sample, such as the window material and air.

number

[0038] The pores in the porous material are randomly located, and the influence of interference between pores is considered to be small. In this case, the scattering vector q = 4π sinθ / λ (λ: incident X-ray wavelength) and the scattering intensity I(q) are calculated by the following formula (3):

number

number

[0039] q 2When I(q) is plotted against q, 2 Point q where I(q) takes a maximum value peak From the value of , the average pore size (D) = 3 1 / 2 / q peak Calculate.

[0040] Calculation of the minimum differential coefficient (quantification of structural heterogeneity) Polymer gels generally have heterogeneity in crosslink density or in the concentration of polymers frozen by crosslinking. Therefore, in the scattering profile of polymer gels, excess scattering due to structural heterogeneity is often observed in the region where q is small. Scattering due to structural heterogeneity is expressed as, for example, I(q)=exp[-Ξ 2 q 2 ] (Ξ: correlation length of structural heterogeneity), and the intensity of this excess scattering reflects the magnitude of the structural heterogeneity of the polymer gel (see M. Shibayama et al., J. Chem. Phys. 1992, 97, 6829).

[0041] In excess scattering, the scattering intensity tends to increase rapidly as the scattering vector q becomes smaller, which is often expressed as the "rise of the small-angle region." I(q) ∝ q -α In this case, the "small-angle region rises" in the log-log plot of I(q) versus q corresponds to the exponent α becoming rapidly larger in the small-angle region. I(q) ∝ q -α When Derivative coefficient dlog[I(q)] / dlog[q]=-α Therefore, the magnitude of the rise of the small angle can be quantified from the q dependence of dlog[I(q)] / dlog[q].

[0042] dlog[I(q)] / dlog[q] is calculated using the circular average profile of the porous polyimide. Specifically, using Igor Pro 8.0 (Wavemetrics), the following equation (5) is used:

number

[0043] The obtained dlog[I(q)] / dlog[q] is 0.025 nm -1 ≦q≦0.075nm -1 The minimum value at is calculated to obtain the minimum differential coefficient of the porous polyimide of the present disclosure as an index of the structural heterogeneity of the porous polyimide.

[0044] The porous polyimide according to one embodiment has a pore volume (V) and a BET specific surface area (A) determined by a gas adsorption method, and the pore volume (V) and the BET specific surface area (A) are expressed by the following formula: L=4V / A The average pore diameter (L) calculated by the above formula is 5 nm or more and 500 nm or less. Such a pore diameter is an index representing the pore size characteristic of the aerogel. In one embodiment, the average pore diameter (L) is 5 nm or more, or 6 nm or more, or 7 nm or more, or 8 nm or more, or 9 nm or more, or 10 nm or more, and in another embodiment, is 500 nm or less, or 300 nm or less, or 200 nm or less, or 100 nm or less, or 50 nm or less, or 30 nm or less, or 20 nm or less.

[0045] In one embodiment, the flexural modulus of the porous polyimide in a three-point bending test is 100 MPa or more. A flexural modulus within the above range is advantageous in that the porous polyimide can exhibit excellent toughness that is useful for various aerogel applications. In one embodiment, the flexural modulus is 100 MPa or more, 150 MPa or more, or 200 MPa or more. There is no upper limit to the flexural modulus, but in one embodiment, it may be 1,000 MPa or less from the viewpoint of ease of production of the porous polyimide.

[0046] In one embodiment, the porous polyimide is composed of a polyimide main skeleton having aromatic groups in the molecular skeleton (also referred to in the present disclosure as an aromatic polyimide main skeleton) and a crosslinked structure having aromatic groups in the molecular skeleton (also referred to in the present disclosure as an aromatic crosslinked structure), and has a flexural modulus of 50 MPa or more in a three-point bending test. When the porous polyimide is composed of an aromatic polyimide main skeleton and an aromatic crosslinked structure, the aromatic structure imparts rigidity to the molecule. Therefore, in this case, even if the flexural modulus is relatively low, the porous polyimide can exhibit excellent toughness that makes it useful for various aerogel applications. From the above perspective, when the porous polyimide is composed of an aromatic polyimide main skeleton and an aromatic crosslinked structure, the flexural modulus of the porous polyimide is, in one embodiment, 50 MPa or more, 100 MPa or more, 200 MPa or more, 300 MPa or more, or 400 MPa or more. When a porous polyimide is composed of an aromatic polyimide main skeleton and an aromatic crosslinked structure, the upper limit of the flexural modulus of the porous polyimide is not limited, but in one embodiment, from the viewpoint of ease of production of the porous polyimide, it may be 1,000 MPa or less.

[0047] In one embodiment, the flexural strength of the porous polyimide in a three-point bending test is 5 MPa or more. A flexural strength within the above range is advantageous in that the porous polyimide can exhibit excellent bending resistance that is useful for various aerogel applications. In one embodiment, the flexural strength is 5 MPa or more, or 10 MPa or more. There is no upper limit to the flexural strength, but from the viewpoint of ease of production of the porous polyimide, in one embodiment, it may be 100 MPa or less, 50 MPa or less, or 30 MPa or less.

[0048] In one embodiment, the porous polyimide has a bulk density of 0.05 g / cm 3 More than 0.50g / cm 3 The bulk density being within the above range means that the porous polyimide can have a pore size characteristic of an aerogel. In one embodiment, the bulk density is 0.05 g / cm or less. 3 or more, or 0.06 g / cm 3or more, or 0.07 g / cm 3 or more, or 0.08g / cm 3 or more, or 0.09 g / cm 3 or more, or 0.10 g / cm 3 or more, and in one embodiment, 0.50 g / cm 3 or less, or 0.40 g / cm 3 or less, or 0.30 g / cm 3 The following is the result.

[0049] <<Second Aspect>> The porous polyimide according to the second embodiment has a pore volume (V) and a BET specific surface area (A) determined by a gas adsorption method, and the pore volume (V) and the BET specific surface area (A) are expressed by the following formula: L=4V / A The average pore diameter (L) calculated by the above formula is 5 nm or more and 500 nm or less. Such a pore diameter is an index representing the pore size characteristic of the aerogel. In one embodiment, the average pore diameter (L) is 5 nm or more, or 6 nm or more, or 7 nm or more, or 8 nm or more, or 9 nm or more, or 10 nm or more, and in another embodiment, is 500 nm or less, or 300 nm or less, or 200 nm or less, or 100 nm or less, or 50 nm or less, or 30 nm or less, or 20 nm or less.

[0050] In one embodiment, the BET specific surface area of the porous polyimide is 10 m 2 / g or more 2,000m 2 / g or less. The BET specific surface area within the above range means that the porous polyimide has a pore structure suitable for aerogel. In one embodiment, the BET specific surface area is 10 m 2 / g or more, or 50m 2 / g or more, or 100m 2 / g or more, or 200m 2 / g or more, or 300m 2 / g or more, and in one embodiment, 2,000m 2 / g or less, or 1,500m 2 / g or less, or 1,000m 2 / g or less, or 800m 2 / g or less.

[0051] In one embodiment, the flexural modulus of the porous polyimide in a three-point bending test is 150 MPa or more. A flexural modulus within the above range is advantageous in that the porous polyimide can exhibit excellent toughness that is useful for various aerogel applications. In one embodiment, the flexural modulus is 150 MPa or more, or 200 MPa or more, or 300 MPa or more, or 400 MPa or more. There is no upper limit to the flexural modulus, but in one embodiment, it may be 1,000 MPa or less from the viewpoint of ease of production of the porous polyimide.

[0052] In one embodiment, the porous polyimide is composed of a polyimide main skeleton having aromatic groups in the molecular skeleton (also referred to in the present disclosure as an aromatic polyimide main skeleton) and a crosslinked structure having aromatic groups in the molecular skeleton (also referred to in the present disclosure as an aromatic crosslinked structure), and has a flexural modulus of 50 MPa or more in a three-point bending test. When the porous polyimide is composed of an aromatic polyimide main skeleton and an aromatic crosslinked structure, the aromatic structure imparts rigidity to the molecule. Therefore, in this case, even if the flexural modulus is relatively low, the porous polyimide can exhibit excellent toughness that makes it useful for various aerogel applications. From the above perspective, when the porous polyimide is composed of an aromatic polyimide main skeleton and an aromatic crosslinked structure, the flexural modulus of the porous polyimide is, in one embodiment, 50 MPa or more, 100 MPa or more, 200 MPa or more, 300 MPa or more, or 400 MPa or more. When a porous polyimide is composed of an aromatic polyimide main skeleton and an aromatic crosslinked structure, the upper limit of the flexural modulus of the porous polyimide is not limited, but in one embodiment, from the viewpoint of ease of production of the porous polyimide, it may be 1,000 MPa or less.

[0053] In one embodiment, the flexural strength of the porous polyimide in a three-point bending test is 10 MPa or more. Having a flexural strength within the above range is advantageous in that the porous polyimide can exhibit excellent flexural resistance that is useful for various aerogel applications. In one embodiment, the flexural strength is 10 MPa or more, or 12 MPa or more, or 13 MPa or more, or 14 MPa or more, or 15 MPa or more. While there is no upper limit to the flexural strength, in one embodiment, from the viewpoint of ease of production of the porous polyimide, it may be 100 MPa or less, or 50 MPa or less, or 30 MPa or less.

[0054] In one embodiment, the porous polyimide has a bulk density of 0.05 g / cm 3 More than 0.80g / cm 3 The bulk density being within the above range means that the porous polyimide can have a pore size characteristic of an aerogel. In one embodiment, the bulk density is 0.05 g / cm or less. 3 or more, or 0.06 g / cm 3 or more, or 0.07 g / cm 3 or more, or 0.08g / cm 3 or more, or 0.09 g / cm 3 or more, or 0.10 g / cm 3 or more, and in one embodiment, 0.80 g / cm 3 or less, or 0.70 g / cm 3 or less than 0.60 g / cm 3 or less, or 0.50 g / cm 3 or less, or 0.40 g / cm 3 The following is the result.

[0055] <Third Aspect> The porous polyimide according to the third embodiment has a pore volume (V) and a BET specific surface area (A) determined by a gas adsorption method, and the pore volume (V) and the BET specific surface area (A) are expressed by the following formula: L=4V / A The average pore diameter (L) calculated by the above formula is 5 nm or more and 500 nm or less. Such a pore diameter is an index representing the pore size characteristic of the aerogel. In one embodiment, the average pore diameter (L) is 5 nm or more, or 6 nm or more, or 7 nm or more, or 8 nm or more, or 9 nm or more, or 10 nm or more, and in another embodiment, is 500 nm or less, or 300 nm or less, or 200 nm or less, or 100 nm or less, or 50 nm or less, or 30 nm or less, or 20 nm or less.

[0056] In one embodiment, the BET specific surface area of the porous polyimide is 10 m 2 / g or more 2,000m 2 / g or less. The BET specific surface area within the above range means that the porous polyimide has a pore structure suitable for aerogel. In one embodiment, the BET specific surface area is 10 m 2 / g or more, or 50m 2 / g or more, or 100m 2 / g or more, or 200m 2 / g or more, or 300m 2 / g or more, and in one embodiment, 2,000m 2 / g or less, or 1,500m 2 / g or less, or 1,000m 2 / g or less, or 800m 2 / g or less.

[0057] In one embodiment, the BET specific surface area of the porous polyimide after heat treatment at 300° C. for 1 hour is 10 m 2 / g or more 2,000m 2 / g or less. The BET specific surface area being within the above range means that the porous polyimide maintains its pore structure after the heat treatment. In one embodiment, the BET specific surface area is 10 m 2 / g or more, or 50m 2 / g or more, or 100m 2 / g or more, or 200m 2 / g or more, or 300m 2 / g or more, and in one embodiment, 2,000m 2 / g or less, or 1,500m2 / g or less, or 1,000m 2 / g or less, or 800m 2 / g or less.

[0058] In one embodiment, the porous polyimide has a bulk density of 0.05 g / cm 3 More than 0.80g / cm 3 The bulk density being within the above range means that the porous polyimide can have a pore size characteristic of an aerogel. In one embodiment, the bulk density is 0.05 g / cm or less. 3 or more, or 0.06 g / cm 3 or more, or 0.07 g / cm 3 or more, or 0.08g / cm 3 or more, or 0.09 g / cm 3 or more, or 0.10 g / cm 3 or more, and in one embodiment, 0.80 g / cm 3 or less, or 0.70 g / cm 3 or less than 0.60 g / cm 3 or less, or 0.50 g / cm 3 or less, or 0.40 g / cm 3 The following is the result.

[0059] The bulk density of the porous polyimide after heat treatment at 300°C for 1 hour is preferably in the same range as the above bulk density, in that the porous polyimide maintains a good pore structure even after heat treatment. That is, in one embodiment, the bulk density after heat treatment at 300°C for 1 hour is 0.05 g / cm 3 or more, or 0.06 g / cm 3 or more, or 0.07 g / cm 3 or more, or 0.08g / cm 3 or more, or 0.09 g / cm 3 or more, or 0.10 g / cm 3 or more, and in one embodiment, 0.80 g / cm 3 or less, or 0.70 g / cm 3 or less than 0.60 g / cm 3 or less, or 0.50 g / cm 3 or less, or 0.40 g / cm 3 The following is the result.

[0060] <Structure of porous polyimides according to first to third embodiments> Below, preferred examples of the structure of the porous polyimide according to the first to third aspects will be explained, and the structures explained below are common to the first to third aspects unless otherwise specified. In the first to third embodiments, the porous polyimide is in a sheet form in one embodiment. The thickness of the sheet is not limited, but in one embodiment, the average thickness may be 10 mm or less, or 8 mm or less, or 5 mm or less, or 3 mm or less, or 1 mm or less, or 500 μm or less, or 400 μm or less, or 300 μm or less, and in one embodiment, may be 0.1 μm or more. Porous polyimides in a sheet form, particularly those in a sheet form with an average thickness of 10 mm or less, can be used as an aerogel sheet in various applications, such as heat insulating materials, low dielectric materials, and filter materials.

[0061] In the present disclosure, means for controlling the average pore size (D), average pore diameter (L), minimum differential coefficient, BET specific surface area, and bulk density within the range of this embodiment include, but are not limited to, (1) Controlling the molecular structure of the polyimide, and / or (2) When producing polyimides, gelation is carried out before imidization; Examples include:

[0062] <Polyimide molecular structure> In one embodiment, the polyimide constituting the porous polyimide of the first to third embodiments is a crosslinked polyimide having a polyimide main skeleton and a crosslinking structure that crosslinks the polyimide main skeleton.

[0063] In one embodiment, the polyimide comprises or is a polymerization product of polymerization components including a tetracarboxylic dianhydride, a diamine, and a trifunctional or higher functional amine. The ratio of the trifunctional or higher functional amine to the total of 100% by mass of the tetracarboxylic dianhydride, the diamine, and the trifunctional or higher functional amine is preferably 1% by mass or more, or 1.5% by mass or more, from the viewpoint of achieving a desired pore structure of the porous polyimide by controlling the crosslink density of the polyimide within an appropriate range, and from the same viewpoint, is preferably 40% by mass or less, or 35% by mass or less, or 30% by mass or less.

[0064] The polyimide backbone and crosslinked structure may each have an aliphatic structure or an aromatic structure, or a combination thereof. The polyimides according to the first and second aspects preferably have an aromatic structure in the molecular skeleton. The polyimide according to the third embodiment preferably does not have any aliphatic carbon atoms in the molecular skeleton (ie, in the main chain).

[0065] [Carbonyl carbon ratio] In polyimides, a high ratio of the number of carbonyl carbons to the number of carbon atoms in the molecule is an indicator of a high ratio of imide rings. When the ratio of imide rings is high, the interaction between atoms in the molecular skeleton is strong, so the toughness of the porous polyimide tends to be high in the first and second embodiments, and the heat resistance tends to be high in the third embodiment. The ratio of carbonyl carbons to the total number of carbons in the polyimide molecule (also referred to as the carbonyl carbon ratio in the present disclosure) is preferably 13.5% or more, or 14% or more, or 15% or more, or 16% or more, or 17% or more, or 18% or more, or 19% or more, or 20% or more, and preferably 40% or less, or 35% or less, or 30% or less. In particular, when the molecular skeleton of the polyimide contains aliphatic carbon atoms, the carbonyl carbon ratio is preferably 18% or more, or 19% or more. The carbonyl carbon ratio is 13 Using CNMR (nuclear magnetic resonance), it can be determined from the ratio of the sum of the integral values of the peaks attributed to the carbon atoms of the polyimide molecular skeleton to the integral value of the peaks attributed to the carbonyl carbon.

[0066] [Polyimide main skeleton] The polyimide backbone may have an aliphatic or aromatic structure or a combination thereof. The polyimide according to the third aspect preferably does not have any aliphatic carbon atoms in its molecular skeleton. Aliphatic carbon atoms in the molecular skeleton tend to reduce the inherent rigidity of the polyimide molecule. Therefore, from the viewpoint of suppressing deformation of the pore structure during heat treatment of the porous polyimide, it is preferable that no aliphatic carbon atoms are present in the molecular skeleton. Aliphatic carbon atoms present in a portion other than the molecular skeleton (i.e., as a substituent) do not cause the problem of reducing the rigidity of the polyimide, and therefore there is no problem even if aliphatic carbon atoms are present in a portion other than the molecular skeleton.

[0067] In one embodiment, the polyimide has the following general formula (1): [ka] (In the formula, X is a tetravalent organic group, Y is a divalent organic group, and n is a positive integer.) In this disclosure, the organic group refers to a group having one or more carbon atoms. In one embodiment, n is the degree of polymerization of the polyamide main skeleton.

[0068] In one embodiment, the polyimide main skeleton has the following general formula (2): [ka] (wherein X is a tetravalent organic group.) and a tetracarboxylic acid dianhydride represented by the following general formula (3): H2N-Y-NH2(3) (In the formula, Y is a divalent organic group.) In a preferred embodiment, X is a tetravalent group derived from an optionally substituted monocyclic or polycyclic aromatic ring (i.e., formed by removing four hydrogen atoms from the ring), or a tetravalent group derived from a linked aromatic ring in which multiple aromatic rings, which may be substituted, are connected to each other by direct bonds or bonds via heteroatoms (i.e., formed by removing four hydrogen atoms from the ring), and / or Y is a divalent group derived from an optionally substituted monocyclic or polycyclic aromatic ring (i.e., formed by removing two hydrogen atoms from the ring), or a divalent group derived from a linked aromatic ring in which multiple aromatic rings, which may be substituted, are connected to each other by direct bonds or bonds via heteroatoms (i.e., formed by removing two hydrogen atoms from the ring). In this case, the polyimide main skeleton has a rigid structure, so that in the first and second embodiments, a highly tough porous polyimide can be obtained, and in the third embodiment, deformation of the pore structure of the porous polyimide during heat treatment can be suppressed.

[0069] (Tetracarboxylic acid dianhydride) In one aspect, X in the above general formula (2) includes a substituted or unsubstituted aliphatic group, an aromatic group, or a combination thereof. The aliphatic group may be linear or cyclic, branched or unbranched, saturated or unsaturated. The aromatic group may be composed of a carbon ring and / or a heterocycle (heterocycle). The number of carbon atoms in X may preferably be 6 or more, or 8 or more, or 10 or more, and may preferably be 50 or less, or 36 or less, or 18 or less, or 12 or less. From the viewpoint of obtaining a porous polyimide having excellent toughness in the first and second aspects, or from the viewpoint of obtaining a porous polyimide having excellent heat resistance in the third aspect, it is preferable that at least a portion of the molecular skeleton of the tetracarboxylic dianhydride is composed of an aromatic group.

[0070] Examples of tetracarboxylic dianhydrides having an aromatic group include 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-cyclohexene-1,2 dicarboxylic anhydride, pyromellitic dianhydride (PMDA), 1,2,3,4-benzenetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 2,2',3,3'-benzophenonetetracarboxylic dianhydride, and 3,3',4,4'-biphenyltetracarboxylic dianhydride. carboxylic dianhydride (BPDA), 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA), 2,2',3,3'-biphenyltetracarboxylic dianhydride, methylene-4,4'-diphthalic dianhydride, 1,1-ethylidene-4,4'-diphthalic dianhydride, 2,2-propylidene-4,4'-diphthalic dianhydride, 1,2-ethylene-4,4'-diphthalic dianhydride, 1,3-trimethylene-4,4'-diphthalic dianhydride, 1,4-tetramethylene-4,4'-diphthalic dianhydride, 1,5-pentamethylene-4,4'-diphthalic dianhydride Phthalic dianhydride, 4,4'-oxydiphthalic dianhydride (ODPA), thio-4,4'-diphthalic dianhydride, sulfonyl-4,4'-diphthalic dianhydride, 1,3-bis(3,4-dicarboxyphenyl)benzene dianhydride, 1,3-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 1,3-bis[2-(3,4-dicarboxyphenyl)-2-propyl]benzene dianhydride, 1,4-bis[2-(3,4-dicarboxyphenyl)-2-propyl]benzene Dianhydride, bis[3-(3,4-dicarboxyphenoxy)phenyl]methane dianhydride, bis[4-(3,4-dicarboxyphenoxy)phenyl]methane dianhydride, 2,2-bis[3-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), bis(3,4-dicarboxyphenoxy)dimethylsilane dianhydride, 1,3-bis(3,4-dicarboxyphenyl)-1,1,3,3-tetramethyldisiloxane dianhydride, 2,3,6,Examples of the dianhydride include 7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, and 1,2,7,8-phenanthrenetetracarboxylic dianhydride.

[0071] In one embodiment, X is a tetravalent group obtained by removing four hydrogen atoms from an optionally substituted monocyclic or polycyclic aromatic ring (also referred to in the present disclosure as a simple aromatic group), or a tetravalent group obtained by removing four hydrogen atoms from a linked aromatic ring in which multiple optionally substituted aromatic rings are linked to each other by direct bonds or bonds via heteroatoms (also referred to in the present disclosure as a flexible backbone-containing group). Examples of the substituent include aliphatic or aromatic groups, or groups containing a combination thereof. The number of carbon atoms in the substituent is preferably 4 or less. In another embodiment, X is a group having a freely rotatable structure (in one embodiment, an aliphatic carbon atom) in the molecular backbone (also referred to in the present disclosure as a freely rotatable group).

[0072] The fact that X is a simple aromatic group is advantageous in the first and second embodiments in that it allows for the production of a highly tough porous polyimide, and in the third embodiment in that it allows for the production of a porous polyimide having excellent heat resistance, such that the desired pore structure is well maintained even after heat treatment. X, which is a simple aromatic group, is preferably a tetrayl group formed by removing four hydrogen atoms from a benzene ring or its fused ring, i.e., an arenetetrayl group. The fused ring may be a naphthalene ring, an anthracene ring, or the like. Suitable acid dianhydrides in which X is a simple aromatic group include pyromellitic dianhydride (PMDA), 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA), and 2,3,6,7-naphthalenetetracarboxylic dianhydride, with pyromellitic dianhydride (PMDA) being particularly preferred.

[0073] When X is a flexible backbone-containing group, from the viewpoint of obtaining a highly tough porous polyimide in the first and second embodiments, and from the viewpoint of obtaining a porous polyimide having excellent heat resistance such that the desired pore structure is well maintained even when heat-treated in the third embodiment, X is preferably a tetravalent group obtained by removing four hydrogen atoms from a compound in which two benzene rings are bonded to each other directly or via a heteroatom, such as biphenyl, benzophenone, diphenyl ether, or diphenyl sulfone.

[0074] Examples of acid anhydrides in which X is a group derived from biphenyl include 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (α-BPDA), Examples of acid anhydrides in which X is a group derived from benzophenone include 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), Examples of acid anhydrides in which X is a group derived from diphenyl ether include 4,4'-oxydiphthalic dianhydride (ODPA), 3,3',4,4'-biphenyl ether tetracarboxylic dianhydride, 2,3,3',4'-biphenyl ether tetracarboxylic dianhydride, Examples of acid anhydrides in which X is a group derived from diphenyl sulfone include 3,3',4,4'-biphenylsulfonetetracarboxylic dianhydride (DSDA), are listed below.

[0075] In the first and second embodiments, when X is a freely rotatable group, in one embodiment, X is a tetravalent group obtained by removing four hydrogen atoms from an aromatic compound in which aromatic rings (particularly benzene rings) are single-bonded to each other via an aliphatic carbon atom (in one embodiment, via a substituted or unsubstituted aliphatic hydrocarbon group).

[0076] In the third embodiment, when X is a freely rotating group, the porous polyimide tends to be easily deformed during heat treatment. Therefore, in the polyimide using an acid dianhydride having such a freely rotating group, it is desirable to increase the carbonyl carbon ratio (i.e., increase the ratio of imide rings), more specifically, to set the carbonyl carbon ratio to 18% or more, thereby suppressing deformation during heat treatment.

[0077] Examples of the acid dianhydride when X is a freely rotatable group include 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropanoic dianhydride and 2,2'-bis(3,4-dicarboxyphenyl)propanoic dianhydride.

[0078] In order to obtain a porous polyimide having excellent toughness in the first and second embodiments, and excellent heat resistance in the third embodiment, X is preferably a simple aromatic group or a flexible backbone-containing group, and more preferably a simple aromatic group.

[0079] (diamine) In one embodiment, Y in the above general formula (3) includes a substituted or unsubstituted aliphatic group or aromatic group, or a combination thereof. The aliphatic group may be linear or cyclic, branched or unbranched, saturated or unsaturated. The aromatic group may be composed of a carbon ring and / or a heterocycle (heterocycle). It is preferable that at least a portion of the molecular skeleton of the diamine is composed of an aromatic group. The number of carbon atoms in Y is preferably 6 to 24, more preferably 6 to 18, and even more preferably 6 to 12. The molecular skeleton of the diamine in the third embodiment preferably does not have any aliphatic carbon atoms.

[0080] Diamines include 4,4-(diaminodiphenyl) sulfone (4,4-DAS), 3,4-(diaminodiphenyl) sulfone, 3,3-(diaminodiphenyl) sulfone (3,3-DAS), 2,2'-bis(trifluoromethyl)benzidine (TFMB), 2,2'-dimethyl-4,4'-diaminobiphenyl (DMBZ), 1,4-diaminobenzene (PPDA), 1,3-diaminobenzene (MPDA), 4-aminophenyl 4'-aminobenzoate (APAB), 4,4'-diaminobenzoate (DABA), 4,4' -(or 3,4'-, 3,3'-, 2,4'-)diaminodiphenyl ether, 4,4'-(or 3,3'-)diaminodiphenyl sulfone, 4,4'-(or 3,3'-)diaminodiphenyl sulfide, 4,4'-benzophenonediamine, 3,3'-benzophenonediamine, 4,4'-di(4-aminophenoxy)phenylsulfone, 4,4'-di(3-aminophenoxy)phenylsulfone, 4,4'-bis(4-aminophenoxy)biphenyl, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4 -aminophenoxy)benzene, 2,2-bis{4-(4-aminophenoxy)phenyl}propane, 4,4'-diaminodiphenylmethane (4,4'-DADPM), 3,3',5,5'-tetramethyl-4,4'-diaminodiphenylmethane, 2,2'-bis(4-aminophenyl)propane, 2,2',6,6'-tetramethyl-4,4'-diaminobiphenyl, 2,2',6,6'-tetratrifluoromethyl-4,4'-diaminobiphenyl, bis{(4-aminophenyl)-2-propyl}1,4-benzene, 9,9-biphenyl Bis(4-aminophenyl)fluorene, 9,9-bis(4-aminophenoxyphenyl)fluorene, 3,3'-dimethylbenzidine, 3,3'-dimethoxybenzidine and 3,5-diaminobenzoic acid, 2,6-diaminopyridine, 2,4-diaminopyridine, bis(4-aminophenyl-2-propyl)-1,4-benzene, 3,3'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (3,3'-TFDB), 2,2'-bis[3(3-aminophenoxy)phenyl]hexafluoropropane (3-BDAF), 2,Examples include 2'-bis[4(4-aminophenoxy)phenyl]hexafluoropropane (4-BDAF), 2,2'-bis(3-aminophenyl)hexafluoropropane (3,3'-6F), 2,2'-bis(4-aminophenyl)hexafluoropropane (4,4'-6F), and 1,5-diaminonaphthalene (1,5-DAN).

[0081] In one embodiment, Y is a divalent group derived from an optionally substituted monocyclic or polycyclic aromatic ring (i.e., formed by removing two hydrogen atoms from the ring), or a divalent group derived from linked aromatic rings in which multiple optionally substituted aromatic rings are connected to each other by direct bonds or bonds via heteroatoms (i.e., formed by removing two hydrogen atoms from the rings). More specifically, Y includes a divalent group (also referred to as a wholly aromatic group in the present disclosure) formed by removing two hydrogen atoms from an optionally substituted monocyclic or polycyclic aromatic ring or multiple directly bonded optionally substituted aromatic rings (e.g., biphenyl), a divalent group (also referred to as a heteroskeleton-containing group in the present disclosure) formed by removing two hydrogen atoms from multiple optionally substituted aromatic rings connected to each other via heteroatoms (e.g., benzophenone, diphenyl ether, diphenyl sulfone, benzanilide, etc.), and a divalent group having an aliphatic carbon atom in the molecular skeleton (also referred to as an aliphatic skeleton-containing group in the present disclosure). The substituent may be an aliphatic or aromatic group, or a group containing a combination thereof. The number of carbon atoms in the substituent is preferably 4 or less.

[0082] The aromatic ring constituting the wholly aromatic group may be a carbocyclic ring or a heterocyclic ring, or a combination thereof. Examples of diamines in which Y is a wholly aromatic group include p-phenylenediamine (PPDA), m-phenylenediamine (MPDA), 2,4-diaminotoluene, 2,5-diaminotoluene, 2,4-diaminoxylene, 2,5-diaminoxylene (2,5-dimethyl-p-phenylenediamine (DMPDA)), 2,5-dihydroxy-1,4-phenylenediamine, 2,4,6-trimethyl-1,3-phenylenediamine, 1,5-diaminonaphthalene (1,5-DAN), 3,6-diaminodurene (2,3,5,6-tetramethyl-p-phenylenediamine (TMPDA)), benzidine, 2,2'-dimethylbenzidine (DMBZ), 3,3'-dimethylbenzidine, 2,2'-bis(trifluoromethyl)benzidine (TFMB), Examples of the benzophenone-4-one include 3,3'-dihydroxy-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 5-amino-2-(4-aminophenyl)-benzimidazole (ABI), and the like. Preferably, the benzophenone-4-one is one or more selected from the group consisting of p-phenylenediamine (PPDA), m-phenylenediamine (MPDA), 2,5-diaminotoluene, 2,5-dimethyl-p-phenylenediamine (DMPDA), 2,3,5,6-tetramethyl-p-phenylenediamine (TMPDA), 1,5-diaminonaphthalene (1,5-DAN), benzidine, 2,2'-dimethylbenzidine (DMBZ), 3,3'-dimethylbenzidine, and 2,2'-bis(trifluoromethyl)benzidine (TFMB).

[0083] Examples of diamines in which Y is a hetero skeleton-containing group include 3,3'-diaminodiphenyl sulfone (3DAS), 4,4'-diaminodiphenyl sulfone (4DAS), 4,4'-diaminobenzophenone (4,4'-DABP), 3,3'-diaminobenzophenone (3,3'-DABP), 4,4'-diaminobenzanilide (DABA), and 4,4'-oxydianiline (ODA).

[0084] Examples of diamines in which Y is an aliphatic skeleton-containing group include 9,9-bis(4-aminophenyl)fluorene, 9,9-bis(4-aminophenoxyphenyl)fluorene, N,N-dimethyl-1,3-propanediamine, 2,2-bis(4-aminophenyl)hexafluoropropane (6FDA), hexamethylenediamine, 4,4'-diaminodiphenylmethane (4,4'-DADPM), 1,4-bis(4-aminophenoxy)butane (BAP4), and 1,3-bis(4-aminophenoxy)-2,2-dimethylpropane (BAPN).

[0085] In the first and second aspects, from the viewpoint of obtaining a porous polyimide having excellent toughness, and in the third aspect, from the viewpoint of obtaining a porous polyimide having excellent heat resistance, Y is preferably a wholly aromatic group or a heteroskeleton-containing group, and more preferably a wholly aromatic group.

[0086] During imidization, an isoimide skeleton may be by-produced in addition to the imide skeleton. In the polyimide main skeleton of the present disclosure, it is desirable that the ratio of the isoimide skeleton to the imide skeleton is as small as possible. [ka] (wherein A is a structure that provides X of the present disclosure, and R is a structure that provides Y of the present disclosure.) As shown in the figure, the isoimide skeleton (general formula (β)) is generally considered to be less stable than the imide skeleton (general formula (α)), and has a flexible structure (i.e., the A structure and the R structure are not on a straight line). When the polyimide main skeleton in a porous polyimide contains a large number of isoimide skeletons, the porous polyimide tends to be easily shrunk or deformed during imidization and drying, and the heat resistance of the porous polyimide tends to be poor. It is known that an isoimide skeleton is formed when acetic anhydride-pyridine, a typical dehydration imidization reagent, is reacted with an amic acid. However, it is known that when acetic anhydride-triethylamine is reacted, the isoimide skeleton is not produced and only the imide skeleton is rapidly produced (see, for example, "Latest Polyimides - Fundamentals and Applications," edited by Yoshio Imai and Tsutomu Yokota, edited by the Japan Polyimide Research Association, 2002, published by NTS Co., Ltd., and RJ Angelo et al., "Recent Advances in Polyimide Science and Technology," eds., W.D. Weber and M.R. Gupta, (1987), pp. 67-91, Soc. Plast. Eng., New York). The ratio of isoimide skeletons to imide skeletons in the polyimide main skeleton of the present disclosure can be measured by infrared spectroscopy (see, for example, Non-Patent Document 2 of the present disclosure). In one embodiment, the proportion of isoimide skeletons in the imide main skeleton relative to the total of imide skeletons and isoimide skeletons (100 mol %) is preferably 10 mol % or less.

[0087] [Crosslinked structure] The crosslinked structure is a trifunctional or higher functional structure, and in one embodiment, is derived from a trifunctional or higher functional crosslinker. The functional group of the crosslinker is a group reactive with the acid anhydride group or amino group, which is the terminal group of the polyamic acid. This allows the crosslinker to crosslink polyamic acids to form a polyamic acid gel. The crosslinker is typically a trifunctional or higher functional carboxylic acid or amine, more typically a trifunctional or higher functional amine. In the first aspect, the crosslinked structure is a structure formed by a trivalent or higher group derived from an optionally substituted monocyclic or polycyclic aromatic ring, or a trivalent or higher group derived from a linked aromatic ring in which multiple optionally substituted aromatic rings are linked to each other by direct bonds or bonds via heteroatoms.

[0088] In one embodiment, the crosslinking agent has the following general formula (4): Z-(R) a (4) (In the formula, Z is an a-valent organic group, each R is independently an amino group or a carboxy group, and a is an integer of 3 or more.) It is a compound represented by the formula:

[0089] In one embodiment, Z in general formula (4) comprises a substituted or unsubstituted aliphatic group, aromatic group, or a combination thereof. In the first embodiment, Z preferably comprises an aromatic group. The aliphatic group may be linear or cyclic, branched or unbranched, saturated or unsaturated. The aromatic group may be composed of a carbon ring and / or a heterocycle (heterocycle). Z preferably has 6 to 24 carbon atoms, more preferably 6 to 18 carbon atoms, and even more preferably 6 to 12 carbon atoms.

[0090] In one embodiment, all of the R's are amino groups or all of the R's are carboxy groups, and preferably all of the R's are amino groups.

[0091] In one embodiment, a is 3 or 4, preferably 3.

[0092] In one embodiment, Z is a trivalent or higher valent group derived from an optionally substituted monocyclic or polycyclic aromatic ring (i.e., formed by removing three or more hydrogen atoms from the ring), or a trivalent or higher valent group derived from a linked aromatic ring in which multiple optionally substituted aromatic rings are linked to each other by direct bonds or bonds via heteroatoms (i.e., formed by removing three or more hydrogen atoms from the ring). More specifically, Z may be a trivalent or higher valent group (also referred to as a wholly aromatic group in the present disclosure) formed by removing three or more hydrogen atoms from an optionally substituted monocyclic or polycyclic aromatic ring or from multiple directly bonded, optionally substituted aromatic rings (e.g., biphenyl); a trivalent or higher valent group (also referred to as a heteroskeleton-containing group in the present disclosure) formed by removing three or more hydrogen atoms from multiple, optionally substituted aromatic rings bonded to each other via heteroatoms (e.g., benzophenone, diphenyl ether, diphenyl sulfone, benzanilide, etc.); or a trivalent or higher valent group having an aliphatic carbon atom in the molecular skeleton (also referred to as an aliphatic skeleton-containing group in the present disclosure). The molecular skeleton of the crosslinking agent refers to the portion involved in the bonding of three or more functional groups present in the crosslinking agent. Examples of the substituent include aliphatic or aromatic groups, or groups containing a combination thereof. The number of carbon atoms in the substituent is preferably four or less.

[0093] Examples of crosslinking agents in which Z is a wholly aromatic group include 1,3,5-tris(4-aminophenyl)benzene (TAB), 2,4,6-tris(4-aminophenyl)pyridine (TAPP), and 1,3,5-benzenetricarbonyl trichloride (BTC).

[0094] Examples of crosslinking agents in which Z is a hetero skeleton-containing group include 1,3,5-tris(4-aminophenoxy)benzene (TAPB).

[0095] Examples of crosslinking agents in which Z is an aliphatic skeleton-containing group include 4,4',4''-(methanetriyl)trisaniline, 4,4',4'',4''-methanetetrayltetraaniline, and the like.

[0096] In the first and second aspects, from the viewpoint of obtaining a porous polyimide having excellent toughness, and in the third aspect, from the viewpoint of obtaining a porous polyimide having excellent heat resistance, Z is preferably a wholly aromatic group or a heteroskeleton-containing group, and more preferably a wholly aromatic group.

[0097] In one embodiment, the polyimide is represented by the following general formula (5): [ka] (In the formula, X, Y, and Z are defined as X in general formula (2), Y in general formula (3), and Z in general formula (4), respectively, and n is a positive integer.) It has a structure represented by the following formula:

[0098] n refers to the degree of polymerization of the main skeleton of the polyimide, and is preferably 5 or more, more preferably 6 or more, and even more preferably 7 or more. When n is 5 or more, particularly 7 or more, the time required from adding a crosslinking agent to a polymer precursor solution until gelation tends to provide a sufficient time from casting the solution to forming a desired shape. Furthermore, the degree of polymerization n is preferably 30 or less, more preferably 25 or less, and even more preferably 20 or less. When n is 30 or less, particularly 20 or less, a polyimide wet gel with excellent physical strength and ease of handling tends to be obtained.

[0099] From the viewpoint of the toughness (for the first and second embodiments) or the heat resistance (for the third embodiment) of the porous polyimide, preferred structural combinations of X, Y, and Z include a combination in which X is a simple aromatic group and Y and Z are each a wholly aromatic group or a heteroskeleton group, and a combination in which X is a simple aromatic group or a flexible skeleton-containing group and Y and Z are wholly aromatic groups. In a particularly preferred embodiment of the first embodiment, the polyimide main skeleton has a terminal derived from pyromellitic dianhydride (PMDA), and the crosslinked structure is derived from a trifunctional or higher functional amine.

[0100] In a preferred embodiment, the polyimide comprises a polymerization product of polymerization components including tetracarboxylic dianhydride and diamine, wherein 50 mol % or more, 75 mol % or more, 90 mol % or more, or 100 mol % of the tetracarboxylic dianhydride is pyromellitic anhydride, and the polyimide has an anhydride structure derived from pyromellitic anhydride at its terminal. Pyromellitic anhydride has excellent reactivity with crosslinkers, contributing to rapid gelation and high physical strength of the gel.

[0101] <Production of porous polyimide> In one embodiment, the porous polyimide of the present disclosure comprises: a polymerization step of polymerizing the acid dianhydride of the present disclosure with the diamine of the present disclosure to obtain a polyamic acid; a gelling step of crosslinking the polyamic acid with the crosslinking agent of the present disclosure to obtain a polyamic acid wet gel; an imidization step of imidizing the polyamic acid wet gel to obtain a polyimide wet gel; and a drying step of drying the polyimide wet gel to obtain a porous polyimide aerogel; It can be produced by a method including:

[0102] Conventionally, polyimide gels have been produced by imidizing polyamic acid to obtain polyimide, followed by gelation of the polyimide. This method places constraints on material selection, since polyimides tend to aggregate during gelation. Therefore, to consistently obtain polyimide aerogels with the desired pore structure, it is necessary to select polyimides with molecular structures that are less susceptible to aggregation. In particular, when the molecular skeleton of a polyimide is highly rigid, the polyimide tends to aggregate during gelation after imidization, making it difficult to produce polyimides with the desired pore structure. Furthermore, in the first and second aspects, the polyimide gels obtained by gelation after imidization tend to have poor toughness, making them unsuitable for various desired aerogel applications. Furthermore, in the third aspect, the polyimide gels obtained by gelation after imidization tend to have poor shape retention during heating, and are prone to significant deformation, particularly under harsh heating conditions such as carbonization, making them unsuitable for the production of porous carbon.

[0103] On the other hand, the method of gelling polyamic acid and then imidizing it has the advantage that by appropriately adjusting the gelling conditions, the desired pore structure can be stably formed without being restricted by the molecular structure of the polyimide. In particular, this method allows for the stable production of polyimide aerogels with the desired pore structure even when the polyimide molecular skeleton is highly rigid. Therefore, the advantages of this method are particularly pronounced when the polyimide molecular skeleton is highly rigid. From this perspective, the method of gelling polyamic acid and then imidizing it is particularly advantageous when the polyimide constituting the porous polyimide is a combination in which X in general formula (2) of the present disclosure is a simple aromatic group, and Y in general formula (3) and Z in general formula (4) are each a wholly aromatic group or a heteroskeleton group, or a combination in which X is a simple aromatic group or a flexible skeleton-containing group, and Y and Z are both wholly aromatic groups.

[0104] <Polymerization process> In this step, a polyamic acid is obtained by polymerizing an acid dianhydride and a diamine in a polymerization solvent. The polymerization solvent can be a solvent capable of dissolving polyamic acid, and examples of the polymerization solvent include amide solvents, ether solvents, ester solvents, ketone solvents, phenol solvents, sulfone solvents, and sulfoxide solvents.

[0105] Examples of amide solvents include N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc).

[0106] Examples of ester solvents include cyclic esters (for example, lactones such as γ-butyrolactone (GBL), δ-valerolactone, ε-caprolactone, γ-crotonolactone, γ-hexanolactone, α-methyl-γ-butyrolactone, γ-valerolactone, α-acetyl-γ-butyrolactone, and δ-hexanolactone), methyl acetate, ethyl acetate, butyl acetate, and dimethyl carbonate.

[0107] Examples of the ketone solvent include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and cyclopentanone.

[0108] Phenol-based solvents include m-cresol.

[0109] Examples of sulfone solvents include methyl sulfone, ethyl phenyl sulfone, diethyl sulfone, diphenyl sulfone, sulfolane, bisphenol S, sorapsone, dapsone, bisphenol A polysulfone, and sulfolane.

[0110] Examples of sulfoxide solvents include dimethyl sulfoxide (DMSO).

[0111] The boiling point of the solvent may preferably be 80°C or higher, 100°C or higher, or 120°C or higher. Such high-boiling-point solvents can slow the polymerization rate of polyamic acid and the gelation rate of polyamic acid or polyimide relative to the evaporation rate of the solvent, which is advantageous from the viewpoint of process control, for example, making it possible to carry out polymerization and / or gelation at temperatures near room temperature. The high-boiling-point solvent is preferably an amide solvent, more preferably at least one selected from the group consisting of N-methyl-2-pyrrolidone (NMP, boiling point 202°C), N,N-dimethylformamide (DMF, boiling point 153°C), and N,N-dimethylacetamide (DMAc, boiling point 165°C), with N-methyl-2-pyrrolidone (NMP) being particularly preferred.

[0112] The polymerization temperature, in one embodiment, may be 10° C. or higher, and may be 80° C. or lower, or 60° C. or lower, or 40° C. or lower. In a preferred embodiment, the polymerization medium may be maintained without cooling or heating (i.e., at ambient conditions) throughout the polymerization process.

[0113] <Gelling process> In this step, a crosslinking agent according to the present disclosure is added to the polyamic acid solution obtained in the polymerization step to obtain a polyamic acid wet gel. The crosslinking agent may be added to the polyamic acid solution alone or as a solution in a solvent (also referred to as a crosslinker solvent in this disclosure). Suitable examples of crosslinker solvents are the same as those exemplified for the polymerization solvents described above, with the aforementioned high-boiling point solvents being particularly preferred. High-boiling point solvents have a slow evaporation rate relative to the gelation rate, allowing stable gelation at a gelation temperature of 10°C or higher and / or without the need for a cooling operation of the system. The polymerization solvent and crosslinker solvent may be the same or different, but are preferably the same.

[0114] In one embodiment, the mixture may be cast onto a substrate and allowed to stand to allow gelation to proceed. The thickness of the mixture may be selected depending on the desired thickness of the porous polyimide, and in one embodiment, may be 0.1 μm to 10 mm. The gelation atmosphere is not limited and may be air, an inert gas (e.g., nitrogen), or the like.

[0115] The gelation temperature is preferably 10° C. or higher from the viewpoint of shortening the gelation time and improving the process efficiency, and is preferably 80° C. or lower, or 60° C. or lower, or 40° C. or lower from the viewpoint of stably forming a desired pore structure. In a preferred embodiment, the solvent may be maintained without cooling or heating (i.e., in an ambient environment) throughout the gelation step.

[0116] The gelation time is preferably 1 minute or more, or 2 minutes or more, from the viewpoint of stably forming the desired pore structure, and is preferably 60 minutes or less, or 30 minutes or less, or 10 minutes or less, from the viewpoint of process efficiency.

[0117] <Imidization process> In this step, the polyamic acid wet gel obtained in the gelation step is imidized to obtain a polyimide gel. In one embodiment, a dehydrating imidizing agent is used for imidization. The dehydrating imidizing agent is not particularly limited as long as it can dehydrate and cyclize the amide bond and the adjacent carboxy group in the polyamic acid wet gel to form an imide bond. The dehydrating imidizing agent may typically be a mixture of a dehydrating agent (such as a carboxylic acid anhydride) and an imidization accelerator (such as an amine). Examples of carboxylic acid anhydrides include acetic anhydride, and examples of amines include tertiary amines such as triethylamine and heterocyclic aromatic amines such as pyridine. Among these, a combination of acetic anhydride and triethylamine or a combination of acetic anhydride and pyridine is preferred. Among these, a combination of acetic anhydride and triethylamine is more preferred from the viewpoint of suppressing the formation of isoimide groups, which are considered to be inferior in heat resistance and physical strength to imide groups.

[0118] In one embodiment, imidization is performed by immersing a polyamic acid wet gel in an imidization solution prepared by dissolving a dehydrating imidization agent (more specifically, a combination of a dehydrating agent and an imidization accelerator) in a solvent (also referred to as an immersion solvent in the present disclosure). The total concentration of the dehydrating agent and the imidization accelerator in 100% by mass of the imidization solution is preferably 1% by mass or more, or 3% by mass or more, from the viewpoint of rapidly progressing the imidization, and is preferably 50% by mass or less, or 40% by mass or less, or 30% by mass or less, or 20% by mass or less, from the viewpoint of suppressing deformation of the polyamic acid wet gel and obtaining a polyimide gel in which the pore structure of the polyamic acid wet gel is well maintained.

[0119] Suitable examples of the immersion solvent are the same as those exemplified for the polymerization solvent. The polymerization solvent and the crosslinker solvent may be the same or different, but are preferably the same. The immersion solvent is preferably an amide solvent, more preferably at least one selected from the group consisting of NMP, DMF, and DMAc, and even more preferably NMP.

[0120] The imidization temperature may be, for example, 10° C. or higher. In the first and second embodiments, the imidization temperature may be 120° C. or lower, or 100° C. or lower, or 80° C. or lower, or 60° C. or lower, or 40° C. or lower, and in the third embodiment, 80° C. or lower, or 60° C. or lower, or 40° C. or lower. In a preferred embodiment, the immersion solvent may be maintained without cooling or heating (i.e., at ambient temperature) throughout the imidization step.

[0121] In this manner, a polyimide wet gel can be obtained.

[0122] <Drying process> In this process, the polyimide wet gel obtained in the imidization process is dried to obtain a polyimide aerogel. Supercritical drying is preferred as a drying method, as it maintains the polymer network structure of the polyimide wet gel well and stably produces a polyimide aerogel with the desired pore structure. Examples of supercritical drying methods include replacing the solvent contained in the polyimide wet gel with a ketone solvent such as acetone or a lower alcohol, e.g., ethanol, and then replacing the solvent with an inert gas such as carbon dioxide. A commercially available supercritical drying device can be used for supercritical drying.

[0123] <<<Polyimide wet gel>>> A fourth aspect provides a polyimide wet gel. The polyimide wet gel according to one aspect may be a precursor of the porous polyimide according to any one of the first to third aspects. That is, the porous polyimide according to any one of the first to third aspects may be obtained by removing the solvent from the polyimide wet gel according to the fourth aspect. Alternatively, the polyimide wet gel according to one aspect may be a polyimide wet gel produced by the method for producing a polyimide wet gel according to the fifth aspect. In a typical aspect, the polyimide wet gel comprises a polyimide and a solvent, but may contain other components as long as the effects of the present invention are not impaired.

[0124] The solvent in the polyimide wet gel may be one exemplified as an immersion solvent in the present disclosure. In one embodiment, the solid content of the polyimide wet gel is 3% by mass or more, or 4% by mass or more, or 5% by mass or more, and in another embodiment, 20% by mass or less, or 15% by mass or less, or 10% by mass or less. The solid content of the polyimide wet gel may be considered to be the solid content of the polyimide wet gel when it is produced.

[0125] In one embodiment, the polyimide wet gel according to the fourth embodiment has a small angle X-ray scattering vector q of which qI(q) is 0.04 nm when the scattering intensity I(q) is multiplied by q and plotted against the scattering vector q of the small angle X-ray scattering. -1 <q<2.0nm -1 The average pore size D calculated from the peak position of qI(q) has a maximum value in the rangew The average size D is 0.8 nm or more and 8.0 nm or less. w is, in one aspect, 0.8 nm or more, or 0.9 nm or more, or 1.0 nm or more, from the viewpoint of having a pore structure suitable for a wet gel, and is, in one aspect, 8.0 nm or less, or 7.0 nm or less, or 6.0 nm or less, from the viewpoint of obtaining a good flexural modulus, flexural strength, and breaking strain of the polyimide wet gel.

[0126] In the small-angle X-ray scattering intensity profile from a large-sized structure, the scattering intensity is high in the region where the scattering vector q is small, and low in the region where q is large. On the other hand, if the structure size is sufficiently smaller than the reciprocal of the observed q, the scattering intensity does not show q dependence and takes a constant value. Therefore, when qI(q) is 0.04 nm -1 <q<2.0nm -1 When the polyimide has a maximum value in the range of 1.0, there are fewer large structural portions that cause a decrease in the physical strength of the polyimide wet gel, which is advantageous in terms of physical strength, particularly flexural modulus, flexural strength, or breaking strain.

[0127] In one embodiment, the magnitude of the scattering vector q of the small-angle X-ray scattering is 0.080 nm -1 More than 0.12nm -1 In the following ranges, the minimum value of the differential coefficient (also simply referred to as the minimum differential coefficient) when the logarithm of the scattering intensity I(q) log[I(q)] is differentiated by the logarithm of the scattering vector q log[q] is preferably -1.0 or more, or -0.95 or more, or -0.90 or more. The absolute value of the minimum differential coefficient is preferably as close to zero as possible, and in one embodiment, it is 0.0 or less. However, from the viewpoint of ease of production of the polyimide wet gel, in one embodiment, it may be -0.01 or less, or -0.05 or less. When the polyimide wet gel has an average pore size (D w) and the minimum differential coefficient value within the above range, the polyimide wet gel is considered to have a large number of micropores and few large structural portions. Such a polyimide wet gel has a desired pore structure and excellent structural uniformity, and therefore can have good physical strength (in one aspect, good flexural modulus, flexural strength, and / or break strain) and / or good transparency.

[0128] In small-angle X-ray scattering measurement, X-rays are incident on the surface of a thin piece cut out from a polyimide wet gel. In one embodiment, the surface of the thin piece is a cross section in the direction in which the outer diameter of the polyimide wet gel is smallest (for example, the thickness direction of the sheet). The average pore size (D w ) and quantification of structural heterogeneity can be performed as follows.

[0129] <Average pore size (D w ) calculation> For the scattering pattern I(2θ, φ) in small-angle X-ray scattering (SAXS) measurement, the following formula (a):

number

[0130] The one-dimensional profile calculated by the above formula (a) includes scattering from the sample as well as scattering from sources other than the sample, such as the window material and air.

number

[0131] The scattering intensity of a wet gel includes the scattering of the solvent as a background, as shown in the following equation (c): I(q) = I gel (q) - (1-φ)I solv (q) (c) I gel (q), I solv (q): Scattering intensity of wet gel and solvent after correction by equation (b) φ: Solid volume fraction The solvent scattering is subtracted by

[0132] The pores in the porous material are randomly located, and the influence of interference between pores is considered to be small. In this case, the scattering vector q = 4π sinθ / λ (λ: incident X-ray wavelength) and the scattering intensity I(q) are calculated by the following formula (d):

number

number

[0133] <Calculation of the minimum differential coefficient (quantification of structural heterogeneity)> Polymer gels generally have heterogeneity in crosslink density or in the concentration of polymers frozen by crosslinking. Therefore, in the scattering profile of polymer gels, excess scattering due to structural heterogeneity is often observed in the region where q is small. Scattering due to structural heterogeneity is expressed as, for example, I(q)=exp[-Ξ 2 q 2 ] (Ξ: correlation length of structural heterogeneity), and the intensity of this excess scattering reflects the magnitude of the structural heterogeneity of the polymer gel (see M. Shibayama et al., J. Chem. Phys. 1992, 97, 6829).

[0134] In excess scattering, the scattering intensity tends to increase rapidly as the scattering vector q becomes smaller, which is often expressed as the "rise of the small-angle region." I(q) ∝ q -α In this case, the "small-angle region rises" in the log-log plot of I(q) versus q corresponds to the exponent α becoming rapidly larger in the small-angle region. I(q) ∝ q -α When Derivative coefficient dlog[I(q)] / dlog[q]=-α Therefore, the magnitude of the rise of the small angle can be quantified from the q dependence of dlog[I(q)] / dlog[q].

[0135] dlog[I(q)] / dlog[q] is calculated using the circular average profile of the polyimide wet gel. First, at each measurement point of log[I(q)], the moving average of ±1 point before and after is taken and smoothed ("Boxcar" smoothing). That is, the smoothed value is log[I(q i )] s As, log[I(q i )] s =(log[I(q i-1 )]+log[I(qi )]+log[I(q i+1 )]) / 3 The obtained log[I(q i )] s Using the following formula (f):

number

[0136] Smoothing and numerical differentiation were performed using Igor Pro 8.0 (Wavemetrics). The obtained dlog[I(q)] / dlog[q] was 0.080 nm. -1 ≦q≦0.12nm -1 The minimum value at is calculated to obtain the minimum differential coefficient of the polyimide wet gel of the present disclosure as an index of the structural heterogeneity of the polyimide wet gel.

[0137] In one embodiment, the strain at break in a three-point bending test of the polyimide wet gel is 10% or more, 12% or more, or 15% or more. A large strain at break is an indicator of good toughness of the polyimide wet gel. The upper limit of the strain at break is not limited, but in one embodiment, it may be 100%.

[0138] The polyimide constituting the polyimide wet gel according to the fourth aspect may be the same as those exemplified in the first to third or fifth aspects. In one aspect, the polyimide constituting the polyimide wet gel is represented by the following general formula (1): [ka] (In the formula, X is a tetravalent organic group, Y is a divalent organic group, and n is a positive integer.) It has a molecular chain represented by the formula:

[0139] In one embodiment, in general formula (1), X and / or Y have a structure that imparts linearity to the molecular chain, and n is the degree of polymerization of the polyimide. The structure that imparts linearity to the molecular chain will be described later in the fifth embodiment.

[0140] Of the X's present in the molecular chain represented by general formula (1), the proportion of structures derived from pyromellitic anhydride is preferably 50 mol% or more, or 75 mol% or more, or 90 mol% or more, and in one embodiment, 100 mol%. In this case, it is preferable that the terminal of the molecular chain is derived from pyromellitic anhydride. Pyromellitic anhydride has excellent reactivity with crosslinking agents, contributing to rapid gelation and high physical strength of the gel.

[0141] The polyimide wet gel may be in any form, including bulk, sheet, and particles. To take advantage of the excellent physical strength (especially toughness) of the polyimide wet gel, a typical preferred form is a bulk or sheet, particularly a sheet. The thickness of the sheet is preferably 10 mm or less, or 5 mm or less, or 3 mm or less, or 1 mm or less, or 500 μm or less, or 400 μm or less, or 300 μm or less. The thickness of the sheet can be, for example, 50 μm or more.

[0142] In one embodiment, the solvent in the polyimide wet gel is replaced with acetone, and then the resulting porous polyimide (i.e., porous polyimide for evaluation) is dried with supercritical carbon dioxide. BET specific surface area: 100m 2 / g or more 2,000m 2 / g or less, Bulk density: 0.05g / cm 3 More than 0.50g / cm 3 below, Bending strength: 5 MPa or more, Flexural modulus: 100 MPa or more, and Average pore size (D) determined by small-angle X-ray scattering: 1.0 nm or more and 7.0 nm or less; The porous polyimide for evaluation has one or more of the following characteristics, preferably all of them. More specifically, the porous polyimide for evaluation is prepared by the following procedure: A polyimide wet gel is immersed in a solution of acetone:NMP = 1:1 by weight for 24 hours, and then washed with acetone and immersed in acetone for 24 hours is repeated three times. The resulting gel is dried in a supercritical dryer (manufactured by Rexxam Co., Ltd., "SCRD6") to obtain a porous polyimide for evaluation.

[0143] The BET specific surface area within the above range means that the polyimide wet gel of the present embodiment can easily form a porous polyimide having a pore structure suitable for aerogel. 2 / g or more, or 200m 2 / g or more, or 300m 2 / g or more, and in one embodiment, 2,000m 2 / g or less, or 1,500m 2 / g or less, or 1,000m 2 / g or less, or 800m 2 / g or less.

[0144] The bulk density within the above range means that the polyimide wet gel of this embodiment can easily form a porous polyimide having a pore size characteristic of an aerogel. In one embodiment, the bulk density is 0.05 g / cm. 3 or more, or 0.06 g / cm 3 or more, or 0.07 g / cm 3 or more, or 0.08g / cm 3 or more, or 0.09 g / cm 3 or more, or 0.10 g / cm 3 or more, and in one embodiment, 0.50 g / cm 3 or less, or 0.40 g / cm 3 or less, or 0.30 g / cm 3 The following is the result.

[0145] The bending strength within the above range means that the polyimide wet gel of this embodiment can easily form a porous polyimide having physical strength suitable for aerogel. In one aspect, the bending strength is 5 MPa or more, or 10 MPa or more. There is no upper limit to the bending strength, but in one aspect, it may be 100 MPa or less from the viewpoint of ease of production of the porous polyimide.

[0146] The flexural modulus within the above range means that the polyimide wet gel of this embodiment can easily form a porous polyimide having physical strength suitable for aerogel. In one aspect, the flexural modulus is 100 MPa or more, or 150 MPa or more, or 200 MPa or more, or 300 MPa or more, or 400 MPa or more, and in another aspect, 1,000 MPa or less.

[0147] The average pore size (D) determined by the small-angle X-ray scattering is, in one aspect, 1.0 nm or more, or 1.5 nm or more, or 2.0 nm or more, in that the polyimide wet gel of this embodiment can easily form a porous polyimide having a pore structure suitable for an aerogel, and, in another aspect, is 7.0 nm or less, or 6.0 nm or less, or 5.0 nm or less, in that the polyimide wet gel of this embodiment can easily form a porous polyimide having a good flexural modulus, flexural strength, and strain at break.

[0148] <<<Polyimide Wet Gel Manufacturing Method>>> Fifth Aspect A fifth aspect provides a method for producing a polyimide wet gel. The method includes, in this order, a step of obtaining a polyamic acid wet gel and a step of obtaining a polyimide wet gel. In one aspect, the polyimide wet gel according to the fourth aspect may be obtained by the method according to the fifth aspect. In one aspect, the polyamic acid wet gel obtained by the method according to the fifth aspect may be dried to obtain the porous polyimide according to the first to third aspects. In one aspect, the drying may be performed by the drying step described above with respect to the first to third aspects.

[0149] <Step of Obtaining Polyamic Acid Wet Gel> The step of obtaining a polyamic acid wet gel includes adding a crosslinker having three or more functional groups to a polyamic acid solution to obtain a polyamic acid wet gel (PAA-WG).

[0150] The polyamic acid preferably contains a tetracarboxylic dianhydride (also simply referred to as "acid dianhydride") and a diamine as monomer units. The polyamic acid can be obtained, for example, by dissolving a diamine and a tetracarboxylic dianhydride in a solvent and polymerizing the resulting solution. The polyamic acid solution obtained by polymerization can be used as is as a polyamic acid solution.

[0151] (Tetracarboxylic acid dianhydride) The tetracarboxylic dianhydride is a compound having two structures in which two carboxy groups are condensed in one molecule. The tetracarboxylic dianhydride is preferably represented by the following general formula (2): [ka] {In general formula (2), X is a tetravalent organic group.} The tetracarboxylic dianhydride may be, for example, a cyclic or acyclic, branched or unbranched, substituted or unsubstituted aliphatic or aromatic hydrocarbon group. The aliphatic hydrocarbon group may be saturated or unsaturated. X is preferably a tetravalent organic group having an aromatic group. The number of carbon atoms in X is preferably 6 to 24, more preferably 6 to 18, and even more preferably 6 to 12.

[0152] (diamine) The diamine is a compound having two amino groups in one molecule, and is preferably represented by the following general formula (3): H2N-Y-NH2(3) {In formula (3), Y is a divalent organic group.} The diamine can be, for example, a cyclic or acyclic, branched or unbranched, substituted or unsubstituted aliphatic or aromatic hydrocarbon group. The aliphatic hydrocarbon group may be saturated or unsaturated. Y is preferably a divalent organic group having an aromatic group. The number of carbon atoms in Y is preferably 6 to 24, more preferably 6 to 18, and even more preferably 6 to 12.

[0153] (Polymerization solvent) As a solvent for polymerizing polyamic acid (also referred to as "polymerization solvent"), a solvent capable of dissolving the resulting polyamic acid can be used. Examples of the solvent include amide solvents, and solvents having a cyclic ester, an ester group, an ether group, a ketone group, a hydroxyl group, a sulfone group, and a sulfinyl group.

[0154] Examples of amide solvents include N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc). Examples of cyclic esters include lactone solvents such as γ-butyrolactone (GBL), δ-valerolactone, ε-caprolactone, γ-crotonolactone, γ-hexanolactone, α-methyl-γ-butyrolactone, γ-valerolactone, α-acetyl-γ-butyrolactone, and δ-hexanolactone. Examples of solvents having an ester group include ester solvents such as methyl acetate, ethyl acetate, butyl acetate, and dimethyl carbonate. Examples of solvents having a ketone group include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and cyclopentanone. Examples of solvents having a hydroxyl group include phenol solvents such as m-cresol. Examples of solvents having a sulfone group include methyl sulfone, ethyl phenyl sulfone, diethyl sulfone, diphenyl sulfone, sulfolane, bisphenol S, sorapsone, dapsone, bisphenol A polysulfone, and sulfolane. Examples of solvents having a sulfinyl group include sulfoxide solvents such as dimethyl sulfoxide (DMSO).

[0155] The solvent is preferably a high-boiling solvent, more preferably a solvent having a boiling point higher than 80°C, even more preferably 100°C or higher, and even more preferably 120°C or higher. The use of a high-boiling solvent can slow the polymerization and gelation rate of the polyamic acid relative to the evaporation rate of the solvent, allowing the formation of a polyamic acid wet gel sheet, described below, to be carried out at around room temperature. The high-boiling solvent is preferably an amide solvent, more preferably at least one selected from the group consisting of N-methyl-2-pyrrolidone (NMP, boiling point 202°C), N,N-dimethylformamide (DMF, boiling point 153°C), and N,N-dimethylacetamide (DMAc, boiling point 165°C), with N-methyl-2-pyrrolidone (NMP) being particularly preferred.

[0156] (Polymerization temperature) The temperature during polymerization of the polyamic acid is preferably maintained at 10° C. or higher. The upper limit of the temperature is preferably maintained at 120° C. or lower, 100° C. or lower, 80° C. or lower, 60° C. or lower, or 40° C. or lower. It is particularly preferred that the polymerization be carried out under ambient conditions without cooling or heating the polymerization solvent.

[0157] (Crosslinking agent) By adding a crosslinking agent to a polyamic acid solution, the polyamic acid can be gelled to obtain a polyamic acid wet gel. The crosslinking agent is not particularly limited as long as it has three or more functional groups. The three or more functional groups of the crosslinking agent can react with the amine terminals and / or acid anhydride terminals of the polyamic acid to crosslink the molecular chains of the polyamic acid and form a polymer network structure.

[0158] The crosslinking agent having three or more functional groups is preferably represented by the following general formula (4): Z(-R) a (4) {In general formula (4), Z is at least a trivalent organic group.} R is a group capable of forming a bond with the amine end and / or acid anhydride end of the polyamic acid, and a is an integer of 3 or more, corresponding to the valence of Z. Z can be, for example, a cyclic or acyclic, branched or unbranched, substituted or unsubstituted aliphatic or aromatic hydrocarbon group. The aliphatic hydrocarbon group may be saturated or unsaturated. Z is preferably a trivalent organic group (a=3) having an aromatic group. Z preferably has 6 to 24 carbon atoms, more preferably 6 to 18, and even more preferably 6 to 12. Examples of R include a carboxy group, an amino group, and combinations thereof.

[0159] The crosslinking agent preferably has the following general formula: Z(—NH2)3, where Z is a trivalent organic group having an aromatic group, and Z preferably has 6 to 24 carbon atoms, more preferably 6 to 18 carbon atoms, and even more preferably 6 to 12 carbon atoms. Specific examples of such crosslinking agents include 1,3,5-tris(4-aminophenyl)benzene (TAB), 1,3,5-tris(4-aminophenoxy)benzene (TAPB), and 2,4,6-tris(4-aminophenyl)pyridine (TAPP).

[0160] The crosslinking agent may have the following general formula: Z(—COOH)3, where Z is a trivalent organic group having an aromatic group, and Z preferably has 6 to 24 carbon atoms, more preferably 6 to 18 carbon atoms, and even more preferably 6 to 12 carbon atoms. Specific examples of such crosslinking agents include 1,3,5-benzenetricarboxylic acid (BTC).

[0161] (crosslinker solvent) In the process of adding a crosslinker to a polyamic acid solution to obtain a polyamic acid wet gel, the crosslinker may be added alone to the polyamic acid solution, or the crosslinker may be dissolved in a solvent in a system separate from the polyamic acid solution to form a crosslinker solution, which may then be added to the polyamic acid solution. In this specification, the solvent for the crosslinker solution is also referred to as the "crosslinker solvent." The crosslinker solvent may be the same as the solvent described in the "Polymerization Solvent" section above. The crosslinker solvent is preferably an amide-based solvent, more preferably at least one selected from the group consisting of NMP, DMF, and DMAc, and even more preferably NMP. The crosslinker solvent may be different from the polymerization solvent, but preferably the same solvent as the polymerization solvent is used. In a preferred embodiment, both the polymerization solvent and the crosslinker solvent are NMP.

[0162] (gelation temperature) The temperature in the step of obtaining a polyamic acid wet gel is preferably maintained at 10°C or higher. This allows the polyamic acid wet gel to be obtained in a short time. The upper limit of the temperature is not limited, but is preferably 120°C or lower, 100°C or lower, 80°C or lower, 60°C or lower, or 40°C or lower. It is particularly preferred that the gelation be carried out under ambient conditions without cooling or heating the solvent.

[0163] (Gelation time) The reaction time (standing time) in the step of obtaining a polyamic acid wet gel is preferably 1 minute or more and 60 minutes or less, more preferably 1 minute or more and 30 minutes or less, and even more preferably 2 minutes or more and 10 minutes or less.

[0164] (Formation of Polyamic Acid Wet Gel Sheet) The step of obtaining a polyamic acid wet gel may be carried out by spreading the mixture containing the crosslinker into a sheet. The spread mixture into a sheet and allowing it to stand for a period of time to allow gelation to proceed, thereby obtaining a polyamic acid wet gel sheet (PAA-WGs). In this specification, the term "sheet-like" is not limited, but preferably refers to a planar shape with an average thickness of 10 mm or less. The average thickness of the spread mixture into a sheet is preferably 10 mm or less, 5 mm or less, 3 mm or less, 1 mm or less, 500 μm or less, more preferably 400 μm or less, and even more preferably 300 μm or less. The lower limit of the average thickness of the spread mixture into a sheet is not limited, but can be, for example, 50 μm or more. The average thickness of the polyimide wet gel sheet obtained after gelation is preferably 10 mm or less, 5 mm or less, 3 mm or less, 1 mm or less, 500 μm or less, more preferably 400 μm or less, and even more preferably 300 μm or less. The lower limit of the average thickness of the obtained polyimide wet gel sheet is not limited, but can be, for example, 50 μm or more.

[0165] Conventional methods for producing polyimide wet gels have been difficult to form polyimide wet gel sheets. Specifically, in conventional methods involving imidizing polyamic acid in a solution to obtain a polyimide solution and then introducing crosslinking sites to gel the polyimide, polyimides are poorly soluble in commonly used organic solvents and are prone to aggregation, precipitation, and sedimentation in the solution during gelation. This makes it difficult to form polyimide wet gel sheets. Furthermore, in conventional methods involving first gelling polyamic acid to obtain a polyamic acid wet gel and then imidizing the polyamic acid wet gel, the polyamic acid wet gel is prone to deformation during imidization, making it difficult to form polyimide wet gels with small dimensions, such as sheets. In contrast, the method disclosed herein uses a solution with a low concentration of dehydrating imidizing agent during imidization, as described below, which can suppress deformation of the polyamic acid wet gel, making it easy to form polyimide wet gel sheets.

[0166] When forming a polyamic acid wet gel sheet, it is preferable to use the high-boiling point solvents listed above as the solvent. Because the evaporation rate of high-boiling point solvents is slower than the gelation rate, a polyamic acid wet gel sheet can be formed preferably by maintaining the solvent at 10°C or higher, or more preferably under ambient conditions without cooling the solvent.

[0167] <Step of Obtaining Polyimide Wet Gel> The step of obtaining a polyimide wet gel includes obtaining a polyimide wet gel (PI-WG) by immersing a polyamic acid wet gel in a solution containing a dehydrating imidization agent. The polyimide wet gel sheet (PI-WGs) may be obtained using the polyamic acid wet gel sheet.

[0168] (Dehydrating imidizing agent) The dehydrating imidizing agent is not particularly limited as long as it can dehydrate and cyclize the amide bond and the adjacent carboxyl group of the polyamic acid wet gel to form an imide bond. A typical example of the dehydrating imidizing agent is a mixture of a dehydrating agent (such as a carboxylic acid anhydride) and an imidization accelerator (such as an amine). Examples of the carboxylic acid anhydride include acetic anhydride, and examples of the amine include tertiary amines such as triethylamine and heterocyclic aromatic amines such as pyridine. A preferred dehydrating imidizing agent is a combination of acetic anhydride and triethylamine, or a combination of acetic anhydride and pyridine. Among these, a combination of acetic anhydride and triethylamine is more preferred from the viewpoint of suppressing the formation of isoimide groups, which are considered to be inferior in heat resistance and physical strength to imide groups.

[0169] (Concentration of dehydrating imidizing agent) In one embodiment, the concentration of the dehydrating imidizing agent in the solution into which the polyamic acid wet gel is immersed during imidization (more specifically, the total concentration of the dehydrating agent and imidization accelerator) is 1% by weight or more and 50% by weight or less, based on the total weight of the solution (imidization solution). Without being limited by theory, it is believed that deformation of the polyamic acid wet gel during imidization is partly due to exposure to the dehydrating imidizing agent, which is a poor solvent for the polyamic acid wet gel. By using 50% by weight or more and 99% by weight or less of a solvent that is a good solvent for polyamic acid and polyimide, the solution (imidization solution) is more likely to penetrate into the gel, which is believed to improve the imidization rate or the imidization rate of the product. On the other hand, if the proportion of the poor solvent containing the dehydrating agent and imidization accelerator exceeds 50% by weight, it is believed that the solution (imidization solution) is less likely to penetrate into the gel, which is believed to reduce the imidization rate or the imidization rate of the product. Therefore, it is believed that deformation of the polyamic acid wet gel can be suppressed by keeping the concentration of the dehydrating imidizing agent at 50% by weight or less during the imidization. When the concentration of the dehydrating imidizing agent is 1% by weight or more, the imidization proceeds more quickly, and the polyimide wet gel can be obtained in a shorter time. The concentration of the dehydrating imidizing agent is preferably 1% by weight or more and 40% by weight or less, more preferably 1% by weight or more and 30% by weight or less, even more preferably 1% by weight or more and 20% by weight or less, and even more preferably 3% by weight or more and 20% by weight or less.

[0170] (immersion solvent) The solvent in the solution in which the polyamic acid wet gel is immersed during imidization (also referred to as the "immersion solvent") is not limited, but the same solvents as those described in the "polymerization solvent" section above can be used. The immersion solvent is preferably an amide solvent, more preferably at least one selected from the group consisting of NMP, DMF, and DMAc, and even more preferably NMP. The immersion solvent may be different from the polymerization solvent and the crosslinker solvent, but preferably the same solvent as the polymerization solvent and the crosslinker solvent can be used.

[0171] (soaking temperature) The temperature in the step of obtaining a polyimide wet gel is preferably maintained at 10°C or higher. This allows the polyimide wet gel to be obtained in a shorter time. Among conventional methods, in which gelation is performed first and imidization is performed later, the polyamic acid wet gel is prone to deformation during imidization, so it was necessary to perform the imidization at a low temperature. In contrast, in the method of the present disclosure, the concentration of the dehydrating imidization agent is 50% by weight or less, so that deformation of the polyamic acid wet gel can be suppressed, preferably by maintaining the temperature at 10°C or higher, and more preferably even in an ambient environment without cooling.

[0172] The upper limit of the temperature in the step of obtaining a polyimide wet gel is not limited, but is preferably 120° C. or less, 100° C. or less, 80° C. or less, 60° C. or less, or 40° C. or less. It is particularly preferred that the imidization be carried out under ambient conditions without cooling or heating the immersion solution.

[0173] The temperatures in both the step of obtaining a polyamic acid wet gel and the step of obtaining a polyimide wet gel are preferably maintained at 10° C. or higher. The temperatures in both the step of obtaining a polyamic acid wet gel and the step of obtaining a polyimide wet gel are preferably maintained at 120° C. or lower, 100° C. or lower, 80° C. or lower, 60° C. or lower, or 40° C. or lower. It is particularly preferred that the step of obtaining a polyamic acid wet gel and the step of obtaining a polyimide wet gel are both carried out in an ambient environment without cooling or heating the system.

[0174] <Method for producing porous polyimide> The method for producing a porous polyimide of the present disclosure further includes a step of removing the solution from the polyimide wet gel to obtain a porous polyimide (pPI).The porous polyimide sheets (pPIs) can be obtained by using the polyimide wet gel sheets (PI-WGs).

[0175] <Solvent Removal Process> The method for removing the solution from the polyimide wet gel is not particularly limited as long as it can maintain at least a portion of the polymer network structure of the polyimide wet gel and produce a porous polyimide. The method for removing the solution is not particularly limited as long as it can dry the porous polyimide while maintaining its pore structure. Freeze drying or supercritical drying is preferred, and supercritical drying is more preferred. Supercritical drying can be performed, for example, by replacing the solvent contained in the polyimide wet gel with a replacement solvent such as acetone or a lower alcohol, e.g., ethanol, and then replacing the replacement solvent with an inert gas such as carbon dioxide. A commercially available supercritical drying device can be used for supercritical drying.

[0176] <Porous polyimide> <Molecular structure> The polyimide constituting the porous polyimide is preferably represented by the following general formula (1): [ka] It has a molecular chain represented by the formula: {In general formula (1), X is a tetravalent organic group, Y is a divalent organic group, and n is a positive integer.} X and Y in general formula (1) correspond to X in general formula (2) and Y in general formula (3), respectively.

[0177] X may have a structure that imparts linearity or flexibility to the molecular chain of the resulting polyimide. X preferably has a structure that imparts linearity to the molecular chain of the resulting polyimide. In the present disclosure, "imparting linearity" to the molecular chain of the polyimide refers to a structure in which the two single bonds connecting the target monomer unit and the two other adjacent monomer units are aligned in a straight line. In the present disclosure, "imparting flexibility" to the molecular chain of the polyimide refers to a structure in which the two single bonds connecting the target monomer unit and the two other adjacent monomer units are not aligned in a straight line. By imparting linearity to the molecular chain of the polyimide, deformation of the polyamic acid wet gel during imidization can be further suppressed, and a porous polyimide with high heat resistance can be provided.

[0178] X, which has a structure that imparts linearity to the molecular chain of the polyimide, is preferably, for example, a substituted or unsubstituted, tetravalent aromatic ring (monocyclic aromatic ring) or polycyclic aromatic ring, which has two anhydride groups positioned so that when the two anhydride groups form imide bonds with the amino groups of the diamine, the single bonds of the two imide bonds are aligned in a straight line. Examples of the aromatic ring or polycyclic aromatic ring of X include aromatic rings and fused aromatic rings such as benzene, naphthalene, anthracene, phenanthrene, tetracene, triphenylene, chrysene, and pyrene.

[0179] Examples of tetracarboxylic acid dianhydrides in which X is an aromatic ring or a polycyclic aromatic ring and has a structure that imparts linearity to the molecular chain of the polyimide include those represented by the following general formula: [ka] In the above general formula, each R may independently represent a group selected from the group consisting of hydrogen, halogen, a hydroxyl group, an aryl group, and an aliphatic hydrocarbon group. The aliphatic hydrocarbon group may be branched or unbranched, saturated or unsaturated.

[0180] Specific examples of tetracarboxylic dianhydrides having a structure that imparts linearity to the molecular chain of polyimide include pyromellitic dianhydride (PMDA), 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA), and 2,3,6,7-naphthalenetetracarboxylic dianhydride, with pyromellitic dianhydride (PMDA) being particularly preferred.

[0181] Specific examples of tetracarboxylic dianhydrides having a structure that imparts flexibility to the molecular chain of polyimide include 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (α-BPDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 4,4'-oxydiphthalic dianhydride (ODPA), 3,3',4,4'-biphenylethertetracarboxylic dianhydride, 2,3,3',4'-biphenylethertetracarboxylic dianhydride, 3,3',4,4'-biphenylsulfonetetracarboxylic dianhydride (DSDA), 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropanoic dianhydride, 2,2'-bis(3,4-dicarboxyphenyl)propanoic dianhydride, 1,2,4 ,5-Cyclohexanetetracarboxylic dianhydride (HPMDA), 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), 1-carboxymethyl-2,3,5-cyclopentanetricarboxylic-2,6:3,5-dianhydride (TCA-AH), 4,4'-(hexafluoroisopropylidene)diphthalic anhydride Examples include 6FDA, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BTA), bicyclo[2,2,1]heptane-2,3,5,6-tetracarboxylic dianhydride (NBDAn), and 1,3,3a,4,5,9b-hexahydro-5-(tetrahydro-2,5-dioxo-3-furanyl)naphtho[1,2-c]furan-1,3-dione (TDA).

[0182] The tetracarboxylic dianhydride having a structure that imparts flexibility to the molecular chain of the polyimide preferably has an aromatic group, and examples thereof include 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (α-BPDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 4,4'-oxydiphthalic dianhydride (ODPA), 3,3',4,4'-biphenylethertetracarboxylic dianhydride, 2,3,3',4'-biphenylethertetracarboxylic dianhydride, and 3,3',4,4'-biphenylsulfonetetracarboxylic dianhydride (DSDA). 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) is more preferred.

[0183] Y may have a structure that imparts linearity or flexibility to the molecular chain of the resulting polyimide. Y preferably has a structure that imparts linearity to the molecular chain of the resulting polyimide. By imparting linearity to the molecular chain of the polyimide, deformation of the polyamic acid wet gel during imidization can be further suppressed, and a porous polyimide with high heat resistance can be provided.

[0184] Y, which has a structure that imparts linearity to the molecular chain of the polyimide, is preferably, for example, a substituted or unsubstituted, divalent aromatic ring or polycyclic aromatic ring, having two amino groups positioned so that when the two amino groups form imide bonds with the anhydride groups of the tetracarboxylic dianhydride, the single bonds of the two imide bonds are aligned in a straight line. Typically, one amino group may be positioned para to the other amino group. Examples of the aromatic ring or polycyclic aromatic ring of Y include aromatic rings and fused aromatic rings such as benzene, naphthalene, anthracene, phenanthrene, tetracene, triphenylene, chrysene, and pyrene, as well as ring assemblies of aromatic rings bonded via single bonds, such as biphenyl and triphenyl.

[0185] Examples of diamines having a structure that imparts linearity to the molecular chain of a polyimide in which Y is an aromatic ring or a polycyclic aromatic ring and Y is an aromatic ring or a polycyclic aromatic ring, include diamines having a structure that imparts linearity to the molecular chain of a polyimide, such as diamines having a structure of the following general formula: [ka] In the above general formula, each R may independently represent a group selected from the group consisting of hydrogen, halogen, a hydroxyl group, an aryl group, and an aliphatic hydrocarbon group. The aliphatic hydrocarbon group may be branched or unbranched, saturated or unsaturated.

[0186] Specific examples of diamines having a structure that imparts linearity to the molecular chain of polyimide include p-phenylenediamine (PPDA), 2,5-dimethyl-p-phenylenediamine (DMPDA), 2,3,5,6-tetramethyl-p-phenylenediamine (TMPDA), 4,4'-diaminobiphenyl, 2,2'-dimethylbenzidine (DMBZ), 3,3'-dimethylbenzidine, 2,2'-bis(trifluoromethyl)benzidine (TFMB), 2,5-diaminotoluene, 2,5-dihydroxy-1,4-phenylenediamine, o-tolidine, 3,3'-dihydroxy-4,4'-diaminobiphenyl, and 3,3'-dimethoxy-4,4'-diaminobiphenyl. The diamine having a structure that imparts linearity to the molecular chain of the polyimide is preferably at least one selected from the group consisting of p-phenylenediamine (PPDA), 2,5-dimethyl-p-phenylenediamine (DMPDA), 2,3,5,6-tetramethyl-p-phenylenediamine (TPMDA), 4,4'-diaminobiphenyl, 2,2'-dimethylbenzidine (DMBZ), 3,3'-dimethylbenzidine, and 2,2'-bis(trifluoromethyl)benzidine (TFMB).

[0187] Diamines having a structure that imparts flexibility to the molecular chain of polyimide include m-phenylenediamine (MPDA), 2,4-diaminotoluene, 2,4-diaminoxylene, 3,3'-diaminodiphenyl sulfone (3DAS), 4,4'-diaminodiphenyl sulfone (4DAS), 4,4'-diaminobenzophenone (4,4'-DABP), 3,3'-diaminobenzophenone (3,3'-DABP), 1,5-diaminonaphthalene (1,5-DAN), m-tolidine, 5-amino-2-(4-aminophenyl)-benzimidazole (ABI), 4,4'-diaminobenzanilide (DABA), 9,9-bis(4-aminophenyl)fluorene, and 9,9-bis(4-aminophenoxyphenyl)fluorene. and aliphatic diamines such as N,N-dimethyl-1,3-propanediamine (DMPDA), 2,4,6-trimethyl-1,3-phenylenediamine (TMPDA), 2,2-bis(4-aminophenyl)hexafluoropropane (6FDAm), 1,4-cyclohexanediamine (trans isomer, cis isomer, or a cis-, trans-mixture) (CHDA), 1,4-bisaminomethylcyclohexane (trans isomer, cis isomer, or a cis-, trans-mixture) (14BAC), 4,4'-oxydianiline (ODA), hexamethylenediamine, 1,3-diaminocyclohexane, 4,4'-diaminodicyclohexane, and 3,3'-diaminodicyclohexane.

[0188] Among the diamines having a structure that imparts flexibility, a preferred example of the aromatic diamine is 1,5-diaminonaphthalene (1,5-DAN).

[0189] (Combination of Monomers) The combination of tetracarboxylic dianhydride and diamine is such that when the resulting polyimide is heat-treated at 300°C for 1 hour, the BET specific surface area of the polyimide is 10 m 2 / g or more 2,000m 2 / g or less. The BET specific surface area within the above range means that the porous polyimide maintains its pore structure after the heat treatment, and a porous polyimide having high heat resistance can be obtained. In one embodiment, the BET specific surface area is 10 m 2 / g or more, 50m 2 / g or more, 100m 2 / g or more, 200m 2 / g or more, or 300m 2 / g or more, and in one embodiment, 2,000m 2 / g or less, 1,500m 2 / g or less, 1,000m 2 / g or less, or 800m 2 / g or less.

[0190] In the combination of tetracarboxylic dianhydride and diamine, it is preferable that the X and / or Y have a structure that imparts linearity to the molecular chain of the polyimide, and it is more preferable that both the X and Y have a structure that imparts linearity to the molecular chain of the obtained polyimide. Without being limited by theory, it is believed that imparting linearity to the molecular chain makes the molecular chain more rigid, and that deformation of the polyamic acid wet gel during imidization can be more effectively suppressed. Furthermore, by imparting linearity to the molecular chain, it is possible to increase the BET specific surface area of the obtained polyimide after heat treatment at 300°C for 1 hour to 10 m 2 / g or more 2,000m 2 / g or less, and a porous polyimide with high heat resistance can be obtained. In conventional methods for producing polyimide wet gels, imidization is performed first and then gelation is performed later. However, if the polyimide molecular chain has linearity, the polyimide is more likely to aggregate, precipitate, and sediment, making it difficult to use a monomer that imparts linearity to such molecular chains. In contrast, the method of the present disclosure performs gelation first and then imidization, making it possible to use a monomer that imparts linearity to such molecular chains.

[0191] The polyimide constituting the porous polyimide is more preferably a polyimide represented by the following general formula (5): [ka] It has a molecular structure represented by the following formula: {In general formula (5), X, Y, and Z are defined as X in general formula (2), Y in general formula (3), and Z in general formula (4), respectively, and n is a positive integer.}

[0192] In the general formulas (1) and (5), n represents the degree of polymerization of the polyimide. The degree of polymerization (n) of the polyimide is preferably 3 to 50, more preferably 3 to 40, even more preferably 5 to 30, and still more preferably 5 to 20.

[0193] Other physical properties The average pore size of the porous polyimide may be in the submicron to nano order, preferably 1 nm or more and 1 μm or less, more preferably 1 nm or more and 100 nm or less, and even more preferably 1 nm or more and 50 nm or less. The BET specific surface area of the porous polyimide before heat treatment at 300° C. for 1 hour is preferably 10 m 2 / g~2000m 2 The BET specific surface area of the porous polyimide before heat treatment at 300°C for 1 hour is more preferably about 10 m 2 / g or more, 50m 2 / g or more, 100m 2 / g or more, 200m 2 / g or more, 300m 2 / g or more, or 400m 2 / g or more, more preferably 2,000m 2 / g or less, 1,500m 2 / g or less, 1,000m 2 / g or less, or 800m 2 The bulk density of the porous polyimide is preferably 0.1 to 0.5 g / cm 3 It may be to some extent.

[0194] <<<Porous carbon sheet>>> <Sixth Aspect> A sixth aspect provides a porous carbon sheet. The porous carbon sheet may have the following properties. In one aspect, the porous carbon sheet may be produced using the porous polyimide according to any one of the first to third aspects. In one aspect, the porous carbon sheet may be produced using the polyimide wet gel according to the fourth aspect, or the method for producing a polyimide wet gel or a porous polyimide according to the fifth aspect.

[0195] <Average pore diameter (L)> The porous carbon sheet according to the present disclosure has a pore volume (V) and a BET specific surface area (A) determined by a gas adsorption method, and the pore volume (V) and the BET specific surface area (A) are calculated based on the following formula: L=4V / A The average pore diameter (L) calculated by is 5 nm or more and 500 nm or less. An average pore diameter (L) in this range is an index representing pore sizes on the submicron order, and is a range that is difficult to produce by either chemical or physical approaches. With conventional methods, it has been difficult to produce a porous carbon sheet having an average pore diameter (L) in this range. Without being limited by theory, this is thought to be because the porous resin sheet used to produce the porous carbon sheet has low heat resistance, causing the pores to collapse during carbonization. The average pore diameter (L) of the porous carbon sheet is preferably 5 nm or more, 5.5 nm or more, or 6 nm or more, and preferably 300 nm or less, 200 nm or less, 100 nm or less, 50 nm or less, 30 nm or less, or 20 nm or less.

[0196] <Bulk density> The bulk density of the porous carbon sheet is 0.01 g / cm 3 More than 0.80g / cm 3It is preferable that the bulk density is 0.05 g / cm or less. A bulk density within the above range is also an indicator of a pore size on the submicron order, which is a range that is difficult to produce by either chemical or physical approaches. With conventional methods, it has been difficult to produce a porous carbon sheet having a bulk density in this range. Without being limited by theory, it is thought that this is because the porous resin sheet used to produce the porous carbon sheet has low heat resistance, and the pores collapse during carbonization. The bulk density of the porous carbon sheet is preferably 0.05 g / cm or less. 3 More than 0.06g / cm 3 More than 0.07g / cm 3 More than 0.08g / cm 3 More than 0.09g / cm 3 or more, or 0.10 g / cm 3 or more, preferably 0.80 g / cm 3 Below, 0.70g / cm 3 Below 0.60g / cm 3 Below 0.50g / cm 3 or less, or 0.40 g / cm 3 The following is the result.

[0197] <BET specific surface area> The BET specific surface area of the porous carbon sheet is 10m 2 More than 2,000m 2 It is preferable that the BET specific surface area is less than 10 m. The BET specific surface area being within the above range is also an indicator of a pore size on the submicron order, which is a range that is difficult to produce by either chemical or physical approaches. With conventional methods, it has been difficult to produce a porous carbon sheet having a BET specific surface area in this range. Without being limited by theory, it is thought that this is because the porous resin sheet used to produce the porous carbon sheet has low heat resistance, and the pores collapse during carbonization. The BET specific surface area of the porous carbon sheet is preferably less than 10 m. 2 / g or more, 50m 2 / g or more, 100m 2 / g or more, 200m 2 / g or more, or 300m 2 / g or more, preferably 2,000m2 / g or less, 1,500m 2 / g or less, 1,000m 2 / g or less, or 800m 2 / g or less.

[0198] <Seat shape> The average thickness of the porous carbon sheet is not limited, but is preferably 10 mm or less. Without being bound by theory, in the case of a sheet, the porous resin sheet shrinks due to heating during carbonization, and the pores tend to collapse, making it difficult to produce a porous carbon sheet in a sheet shape with pores on the submicron order using conventional methods. The average thickness is more preferably 5 mm or less, 3 mm or less, 2 mm or less, 1 mm or less, 800 μm or less, 500 μm or less, 300 μm or less, 200 μm or less, or 100 μm or less. The lower limit of the average thickness is not limited, but may be, for example, 10 μm or more, 20 μm or more, or 50 μm or more.

[0199] <<Method for manufacturing porous carbon sheet>> The method for producing a porous carbon sheet according to the present disclosure includes a step of carbonizing a porous resin sheet by heating it to 400°C or higher to obtain a porous carbon sheet. The obtained porous carbon sheet has a pore volume (V) and a BET specific surface area (A) determined by a gas adsorption method, and the pore volume (V) and the BET specific surface area (A) are expressed by the following formula: L=4V / A The average pore diameter (L) calculated by the above formula is 5 nm or more and 500 nm or less.

[0200] <Carbonization> The heating temperature during carbonization (hereinafter referred to as "carbonization temperature") is preferably 500°C or higher, 600°C or higher, 700°C or higher, 800°C or higher, 900°C or higher, or 1000°C or higher. The upper limit of the carbonization temperature is not limited, but may be, for example, 2000°C or lower, 1500°C or lower, or 1300°C or lower. If the carbonization temperature is within this range, the shape and pores of the porous resin sheet are less likely to collapse, and it is easy to obtain a porous carbon sheet.

[0201] The heating time for carbonization at the desired carbonization temperature is preferably 30 minutes or more, 40 minutes or more, 50 minutes or more, or 60 minutes or more, and preferably 300 minutes or less, 180 minutes or less, or 120 minutes or less. If the heating time is within this range, the shape and pores of the porous resin sheet are less likely to collapse, and it is easy to obtain a porous carbon sheet.

[0202] Before heating to the desired carbonization temperature, the porous resin sheet may be subjected to a pretreatment in which the temperature is gradually increased. In the pretreatment, the temperature can be increased to the desired carbonization temperature at a temperature increase rate of preferably 1°C / min or more, 2°C / min or more, or 3°C / min or more, and preferably 30°C / min or less, 20°C / min or less, or 10°C / min or less. If the temperature increase rate is within this range, the shape and pores of the porous resin sheet are less likely to collapse, and it is easy to obtain a porous carbon sheet.

[0203] After maintaining the desired carbonization temperature for the desired heating time, the porous resin sheet may be subjected to a post-treatment in which the temperature is gradually lowered. In the post-treatment, the temperature can be lowered to the desired temperature at a temperature lowering rate of preferably 1°C / min or more, 2°C / min or more, or 3°C / min or more, and preferably 30°C / min or less, 20°C / min or less, or 10°C / min or less. If the temperature lowering rate is within this range, the shape and pores of the porous resin sheet are less likely to collapse, and it is easy to obtain a porous carbon sheet.

[0204] The pretreatment, carbonization, and post-treatment can be carried out under any atmosphere. The pretreatment, carbonization, and post-treatment can be carried out, for example, under air or an inert gas, preferably under an inert gas, and more preferably under a nitrogen atmosphere. If carried out under an inert gas, the shape and pores of the porous resin sheet are less likely to collapse, making it easier to obtain a porous carbon sheet, and also suppressing carbon dioxide emission.

[0205] <Porous resin sheet> The porous resin sheet has heat resistance to such an extent that a porous carbon sheet having an average pore diameter (L) of 5 nm or more and 500 nm or less can be obtained by carbonizing the porous resin sheet. In order to control the heat resistance of the porous resin sheet to a high level, for example, the molecular structure of the resin can be controlled.

[0206] The average pore diameter (L) of the porous resin sheet is calculated based on the pore volume (V) and BET specific surface area (A) determined by a gas adsorption method using the following formula: L=4V / A The average pore diameter (L) of the porous resin sheet is preferably 5 nm or more and 500 nm or less. The average pore diameter (L) of the porous resin sheet is more preferably 3 nm or more, 4 nm or more, 5 nm or more, 6 nm or more, or 7 nm or more, and more preferably 300 nm or less, 200 nm or less, or 150 nm or less. When carbonized at 1100°C for 1 hour, the porous resin sheet has a pore size (L) of 1.0 mm or less calculated by the following formula: Average pore diameter (L) retention rate = L after carbonization / L before carbonization × 100 (%) The retention rate of the average pore diameter (L) calculated by is preferably 60% or more, 70% or more, 75% or more, or 80% or more. When the retention rate of the average pore diameter (L) is within this range, it is easier to obtain the porous carbon sheet of the present disclosure.

[0207] The bulk density of the porous resin sheet is 0.01 g / cm 3 More than 0.80g / cm 3 The bulk density of the porous resin sheet is preferably 0.05 g / cm or less. 3 More than 0.06g / cm 3 More than 0.07g / cm 3 More than 0.08g / cm 3 More than 0.09g / cm 3 or more, or 0.10 g / cm 3 or more, preferably 0.80 g / cm 3 Below, 0.70g / cm 3 Below 0.60g / cm 3 Below 0.50g / cm 3 or less, or 0.40 g / cm 3When the porous resin sheet was carbonized at 1100°C for 1 hour, the following formula was obtained: Bulk density increase rate = (bulk density after carbonization - bulk density before carbonization) / bulk density before carbonization × 100 (%) The increase in bulk density calculated by the following formula is preferably 50% or less, 45% or less, or 40% or less. When the increase in bulk density due to carbonization is at this level, it is easier to obtain the porous carbon sheet of the present disclosure.

[0208] The BET specific surface area of the porous resin sheet is 10m 2 / g or more 2,000m 2 The BET specific surface area of the porous resin sheet is preferably 10 m / g or less. 2 / g or more, 50m 2 / g or more, 100m 2 / g or more, or 200m 2 / g or more, preferably 2,000m 2 / g or less, 1,500m 2 / g or less, 1,000m 2 / g or less, or 800m 2 When the porous resin sheet was carbonized at 1100° C. for 1 hour, the porous resin sheet had a molecular weight of 1.01g or less, and the molecular weight of the porous resin sheet was 1.01g or less. BET specific surface area retention rate = BET specific surface area after carbonization / BET specific surface area before carbonization × 100 (%) The retention rate of the BET specific surface area calculated by is preferably 50% or more, 60% or more, or 65% or more. When the retention rate of the BET specific surface area is within this range, it is easier to obtain the porous carbon sheet of the present disclosure.

[0209] The porous resin sheet is preferably at least one selected from the group consisting of a porous polyimide sheet and a porous polyvinylidene fluoride (PVDF) sheet. By using such a porous resin sheet, it is easier to obtain the porous carbon sheet of the present disclosure.

[0210] (porous polyimide sheet) The polyimide constituting the porous polyimide sheet is preferably a polyimide represented by the following general formula (1): [ka] It has a molecular chain represented by the following general formula (1): {In general formula (1), X is a tetravalent organic group, Y is a divalent organic group, and n is a positive integer.} X is derived from a tetracarboxylic dianhydride, and Y is derived from a diamine.

[0211] X may have a structure that imparts linearity or flexibility to the molecular chain of the resulting polyimide. X preferably has a structure that imparts linearity to the molecular chain of the resulting polyimide. When X has a structure that imparts linearity to the molecular chain of the resulting polyimide, the heat resistance of the porous polyimide sheet can be highly controlled. Suitable examples of X having a structure that imparts linearity to the molecular chain of the polyimide and X having a structure that imparts flexibility to the molecular chain of the polyimide are the same as those described above in relation to the fifth aspect.

[0212] Y may have a structure that imparts linearity or flexibility to the molecular chain of the resulting polyimide. Y preferably has a structure that imparts linearity to the molecular chain of the resulting polyimide. When Y has a structure that imparts linearity to the molecular chain of the resulting polyimide, the heat resistance of the porous polyimide sheet can be highly controlled. Suitable examples of Y having a structure that imparts linearity to the molecular chain of the polyimide and Y having a structure that imparts flexibility to the molecular chain of the polyimide are the same as those described above in relation to the fifth aspect.

[0213] The average pore diameter (L) of the porous polyimide sheet is calculated based on the pore volume (V) and BET specific surface area (A) determined by a gas adsorption method using the following formula: L=4V / A The average pore diameter (L) of the porous polyimide sheet is preferably 3 nm or more, 4 nm or more, 5 nm or more, 6 nm or more, or 7 nm or more, and is preferably 500 nm or less, 300 nm or less, 200 nm or less, 100 nm or less, 50 nm or less, 30 nm or less, or 20 nm or less. When carbonized at 1100°C for 1 hour, the porous polyimide sheet has a pore size (L) of 3 nm or more calculated by the following formula: Average pore diameter (L) retention rate = L after carbonization / L before carbonization × 100 (%) The retention rate of the average pore diameter (L) calculated by is preferably 60% or more, 70% or more, 75% or more, or 80% or more. When the retention rate of the average pore diameter (L) is within this range, it is easier to obtain the porous carbon sheet of the present disclosure.

[0214] The bulk density of the porous polyimide sheet is 0.01 g / cm 3 More than 0.80g / cm 3 The bulk density of the porous polyimide sheet is preferably 0.01 g / cm or less. 3 More than 0.05g / cm 3 More than 0.06g / cm 3 More than 0.07g / cm 3 More than 0.08g / cm 3 More than 0.09g / cm 3 More than 0.10g / cm 3 or more, preferably 0.80 g / cm 3 Below, 0.70g / cm 3 Below 0.60g / cm 3 Below 0.50g / cm 3 or less, or 0.40 g / cm 3 When the porous polyimide sheet was carbonized at 1100°C for 1 hour, the following formula was obtained: Bulk density increase rate = (bulk density after carbonization - bulk density before carbonization) / bulk density before carbonization × 100 (%) The increase in bulk density calculated by the following formula is preferably 50% or less, 45% or less, or 40% or less. When the increase in bulk density due to carbonization is at this level, it is easier to obtain the porous carbon sheet of the present disclosure.

[0215] The BET specific surface area of the porous polyimide sheet is 10m 2 / g or more 2,000m 2 The BET specific surface area of the porous polyimide sheet is preferably 10 m / g or less. 2 / g or more, 50m 2 / g or more, 100m 2 / g or more, 200m 2 / g or more, 300m 2 / g or more, or 400m 2 / g or more, preferably 2,000m 2 / g or less, 1,500m 2 / g or less, 1,000m 2 / g or less, or 800m 2 When the porous polyimide sheet was carbonized at 1100° C. for 1 hour, the molecular weight of the porous polyimide sheet was determined to be 1000 kJ / g or less. BET specific surface area retention rate = BET specific surface area after carbonization / BET specific surface area before carbonization × 100 (%) The retention rate of the BET specific surface area calculated by is preferably 50% or more, 60% or more, or 65% or more. When the retention rate of the BET specific surface area is within this range, it is easier to obtain the porous carbon sheet of the present disclosure.

[0216] Methods for producing porous polyimide sheets are not limited, and examples include (1) a method in which a polyamic acid solution is gelled and spread into a sheet, followed by imidization, and then the solvent is removed; and (2) a method in which a polyamic acid solution is imidized, gelled, spread into a sheet, and then the solvent is removed. The method for producing porous polyimide sheets is preferably method (1), which more preferably includes, for example, a step of gelling a polyamic acid solution and spreading it into a sheet to obtain a polyamic acid wet gel sheet, a step of imidizing the obtained polyamic acid wet gel sheet by immersing it in a solution containing a dehydrating imidizing agent to obtain a polyimide wet gel sheet, and a step of removing the solvent from the obtained polyimide wet gel sheet to obtain a porous polyimide sheet. The concentration of the dehydrating imidizing agent in the solution in which the polyamic acid wet gel is immersed is particularly preferably 1% by weight or more and 50% by weight or less, based on the total weight of the solution. Method (1) allows for the formation of a porous polyimide sheet using a monomer having a structure that imparts linearity to the polyimide molecular chain as X and / or Y, thereby making it easier to produce porous polyimide sheets with high heat resistance. The method for removing the solvent is not particularly limited as long as it is a method that can dry the porous polyimide while maintaining the pore structure of the porous polyimide, but supercritical drying is preferred.

[0217] (Porous PVDF sheet) The method for producing a porous PVDF sheet is not limited, but examples include a method in which a polyvinylidene fluoride (PVDF) solution is spread into a sheet, gelled, and then the solvent is removed. More specifically, examples include a method in which PVDF is dissolved in an arbitrary solvent and spread into a sheet to obtain a PVDF gel sheet, the resulting PVDF gel sheet is dehydrofluorinated (de-HF) under strong alkaline conditions to obtain a HF-free PVDF gel sheet, and the solvent is removed from the resulting HF-free PVDF gel sheet to obtain a porous PVDF sheet. The method for removing the solvent is not particularly limited as long as it is a method that can dry the porous polyimide while maintaining its pore structure, but supercritical drying is preferred.

[0218] The average pore diameter (L) of the porous PVDF sheet is calculated based on the pore volume (V) and BET specific surface area (A) determined by a gas adsorption method using the following formula: L=4V / A The average pore diameter (L) of the porous PVDF sheet is preferably 3 nm or more, 4 nm or more, 5 nm or more, 6 nm or more, or 7 nm or more, and preferably 500 nm or less, 300 nm or less, 200 nm or less, or 150 nm or less. When the porous PVDF sheet is carbonized at 1100°C for 1 hour, the average pore diameter (L) of the porous PVDF sheet is determined by the following formula: Average pore diameter (L) retention rate = L after carbonization / L before carbonization × 100 (%) The retention rate of the average pore diameter (L) calculated by is preferably 60% or more, 70% or more, 75% or more, or 80% or more. When the retention rate of the average pore diameter (L) is within this range, it is easier to obtain the porous carbon sheet of the present disclosure.

[0219] The bulk density of the porous PVDF sheet is 0.01 g / cm 3 More than 0.80g / cm 3 The bulk density of the porous PVDF sheet is preferably 0.05 g / cm or less. 3 More than 0.06g / cm 3 More than 0.07g / cm 3 More than 0.08g / cm 3 More than 0.09g / cm 3 or more, or 0.10 g / cm 3 or more, preferably 0.80 g / cm 3 Below, 0.70g / cm 3 Below 0.60g / cm 3 Below 0.50g / cm 3 or less, or 0.40 g / cm 3 When the porous PVDF sheet was carbonized at 1100°C for 1 hour, the following formula was obtained: Bulk density increase rate = (bulk density after carbonization - bulk density before carbonization) / bulk density before carbonization × 100 (%) The increase in bulk density calculated by the following formula is preferably 50% or less, 45% or less, or 40% or less. When the increase in bulk density due to carbonization is at this level, it is easier to obtain the porous carbon sheet of the present disclosure.

[0220] The BET specific surface area of the porous PVDF sheet is 10m 2 / g or more 2,000m 2 The BET specific surface area of the porous PVDF sheet is preferably 10 m / g or less. 2 / g or more, 50m 2 / g or more, 100m 2 / g or more, or 200m 2 / g or more, preferably 2,000m 2 / g or less, 1,500m 2 / g or less, 1,000m 2 / g or less, or 800m 2 When the porous PVDF sheet was carbonized at 1100°C for 1 hour, the carbonyl group of the porous PVDF sheet was determined to be 0.01g or less by the following formula: BET specific surface area retention rate = BET specific surface area after carbonization / BET specific surface area before carbonization × 100 (%) The retention rate of the BET specific surface area calculated by is preferably 50% or more, 60% or more, or 65% or more. When the retention rate of the BET specific surface area is within this range, it is easier to obtain the porous carbon sheet of the present disclosure.

[0221] <<<Examples of embodiments of the present disclosure>>> Examples of embodiments of the present disclosure are listed below. First Aspect [1] A porous polyimide having an average pore size (D) of 1.0 nm or more and 7.0 nm or less, as determined by small-angle X-ray scattering. [2] The magnitude of the scattering vector q of small-angle X-ray scattering is 0.025 nm -1 More than 0.075nm -1 2. The porous polyimide according to item 1, wherein the minimum value of the differential coefficient when the logarithm of the scattering intensity I(q) log[I(q)] is differentiated by the logarithm of the scattering vector q log[q] is -1.0 or more and 0.0 or less in the following range: [3] Based on the pore volume (V) and BET specific surface area (A) determined by gas adsorption, the following formula: L=4V / A 3. The porous polyimide according to item 1 or 2, wherein the average pore diameter (L) obtained by [4] The porous polyimide according to any one of items 1 to 3, which has a flexural modulus of 100 MPa or more in a three-point bending test. [5] The porous polyimide according to any one of items 1 to 4, which has a flexural modulus of 200 MPa or more in a three-point bending test. [6] The porous polyimide according to any one of items 1 to 5, which has a bending strength of 5 MPa or more in a three-point bending test. [7] The porous polyimide according to any one of items 1 to 6, which has a bending strength of 10 MPa or more in a three-point bending test. [8] Bulk density of 0.05 g / cm 3 More than 0.50g / cm 3 8. A porous polyimide according to any one of the above items 1 to 7, which is as follows: [9] BET specific surface area is 100m 2 / g or more 2,000m 2 9. The porous polyimide according to any one of items 1 to 8, wherein the porous polyimide has a viscosity of 1 / g or less.

[10] The porous polyimide according to any one of items 1 to 9 above, which has a sheet shape.

[11] The porous polyimide according to item 10, having an average thickness of 10 mm or less.

[12] The porous polyimide according to any one of items 1 to 11, wherein the polyimide constituting the porous polyimide has a polyimide main skeleton and a crosslinking structure that crosslinks the polyimide main skeleton.

[13] The porous polyimide according to item 12, wherein the crosslinked structure is a structure formed by a trivalent or higher group derived from an optionally substituted monocyclic or polycyclic aromatic ring, or a trivalent or higher group derived from a linked aromatic ring in which multiple optionally substituted aromatic rings are linked to each other by direct bonds or bonds via heteroatoms.

[14] The polyimide main skeleton is represented by the following general formula (1): [ka] (In the formula, X is a tetravalent organic group; Y is a divalent organic group, provided that: X is a tetravalent group derived from an optionally substituted monocyclic or polycyclic aromatic ring, or a tetravalent group derived from a linked aromatic ring in which multiple optionally substituted aromatic rings are linked to each other by direct bonds or bonds via heteroatoms, and / or Y is a divalent group derived from an optionally substituted monocyclic or polycyclic aromatic ring, or a divalent group derived from a linked aromatic ring in which multiple optionally substituted aromatic rings are linked to each other by a direct bond or a bond via a heteroatom, n is a positive integer.) 14. The porous polyimide according to item 12 or 13, having a structure represented by the following formula (1): wherein the degree of polymerization of the polyimide main skeleton is n in general formula (1).

[15] The porous polyimide according to any one of items 1 to 14, wherein the polyimide constituting the porous polyimide comprises a polymerization product of polymerization components including a tetracarboxylic dianhydride, a diamine, and a trifunctional or higher functional amine, and the ratio of the trifunctional or higher functional amine to a total of 100% by mass of the tetracarboxylic dianhydride, the diamine, and the trifunctional or higher functional amine is 1% by mass or more and 40% by mass or less.

[0222] <<Second Aspect>> [1] Based on the pore volume (V) and BET specific surface area (A) determined by gas adsorption, the following formula: L=4V / A The average pore diameter (L) calculated by is 5 nm or more and 500 nm or less, Porous polyimide with a flexural modulus of 150 MPa or more in a three-point bending test. [2] The porous polyimide according to the above aspect 1, which has a flexural modulus of 200 MPa or more in a three-point bending test. [3] Based on the pore volume (V) and BET specific surface area (A) determined by gas adsorption, the following formula: L=4V / A The average pore diameter (L) calculated by is 5 nm or more and 500 nm or less, A porous polyimide having a bending strength of 10 MPa or more in a three-point bending test. [4] The porous polyimide according to any one of the above aspects 1 to 3, wherein the polyimide constituting the porous polyimide has a polyimide main skeleton and a crosslinking structure that crosslinks the polyimide main skeleton. [5] Based on the pore volume (V) and BET specific surface area (A) determined by gas adsorption, the following formula: L=4V / A The average pore diameter (L) calculated by is 5 nm or more and 500 nm or less, The bending modulus in a three-point bending test is 50 MPa or more, A porous polyimide comprising a polyimide main skeleton having an aromatic group in the molecular skeleton and a crosslinked structure having an aromatic group in the molecular skeleton. [6] The polyimide main skeleton is represented by the following general formula (1): [ka] (In the formula, X is a tetravalent organic group; Y is a divalent organic group, provided that: X is a tetravalent group derived from an optionally substituted monocyclic or polycyclic aromatic ring, or a tetravalent group derived from a linked aromatic ring in which multiple optionally substituted aromatic rings are linked to each other by direct bonds or bonds via heteroatoms, and / or Y is a divalent group derived from an optionally substituted monocyclic or polycyclic aromatic ring, or a divalent group derived from a linked aromatic ring in which multiple optionally substituted aromatic rings are linked to each other by a direct bond or a bond via a heteroatom, n is a positive integer.) 6. The porous polyimide according to aspect 4 or 5, having a structure represented by the following formula: [7] Bulk density of 0.05 g / cm 3 More than 0.80g / cm 3 The porous polyimide according to any one of the above-mentioned embodiments 1 to 6, which is as follows: [8] BET specific surface area is 10m 2 / g or more 2,000m 2 The porous polyimide according to any one of the above aspects 1 to 7, wherein the porous polyimide has a viscosity of 1 / g or less. [9] The porous polyimide according to any one of the above aspects 1 to 8, which is in the form of a sheet having an average thickness of 10 mm or less.

[10] The porous polyimide according to any one of the above aspects 1 to 9, wherein the ratio of the number of carbonyl carbon atoms to the total number of carbon atoms in the polyimide constituting the porous polyimide is 13.5% or more.

[0223] <Third Aspect> [1] Based on the pore volume (V) and BET specific surface area (A) determined by gas adsorption, the following formula: L=4V / A The average pore diameter (L) calculated by is 5 nm or more and 500 nm or less, After heat treatment at 300°C for 1 hour, the BET specific surface area is 10m 2 / g or more 2,000m 2 / g or less. [2] Bulk density of 0.05 g / cm 3 More than 0.80g / cm 3 The porous polyimide according to Aspect 1, wherein: [3] The porous polyimide according to the first or second aspect, wherein the ratio of the number of carbonyl carbon atoms to the total number of carbon atoms in the polyimide constituting the porous polyimide is 13.5% or more. [4] The porous polyimide according to any one of the above aspects 1 to 3, having an average thickness of 10 mm or less. [5] The porous polyimide according to any one of the above aspects 1 to 4, wherein the polyimide constituting the porous polyimide has a polyimide main skeleton and a crosslinking structure that crosslinks the polyimide main skeleton. [6] The polyimide main skeleton is represented by the following general formula (1): [ka] (In the formula, X is a tetravalent organic group; Y is a divalent organic group, provided that: X is a tetravalent group derived from an optionally substituted monocyclic or polycyclic aromatic ring, or a tetravalent group derived from a linked aromatic ring in which multiple optionally substituted aromatic rings are linked to each other by direct bonds or bonds via heteroatoms, and / or Y is a divalent group derived from an optionally substituted monocyclic or polycyclic aromatic ring, or a divalent group derived from a linked aromatic ring in which multiple optionally substituted aromatic rings are linked to each other by a direct bond or a bond via a heteroatom, n is a positive integer.) The porous polyimide according to the above-mentioned embodiment 5, having a structure represented by the following formula: [7] The porous polyimide according to aspect 5 or 6, wherein the crosslinked structure is a trivalent or higher group derived from an optionally substituted monocyclic or polycyclic aromatic ring, or a trivalent or higher group derived from a linked aromatic ring in which multiple optionally substituted aromatic rings are linked to each other by direct bonds or bonds via heteroatoms. [8] The polyimide constituting the porous polyimide is a polymerization product of polymerization components including a tetracarboxylic dianhydride, a diamine, and a trifunctional or higher functional amine, A porous polyimide according to any one of Aspects 1 to 7, wherein the ratio of the tri- or higher functional amine to the total of 100% by mass of the tetracarboxylic dianhydride, the diamine, and the tri- or higher functional amine is 1% by mass or more and 40% by mass or less.

[0224] <Fourth Aspect> [1] When plotting the scattering vector q of small-angle X-ray scattering, the scattering intensity I(q) multiplied by q, qI(q), the value of which is 0.04 nm -1 <q<2.0nm -1 The average pore size D calculated from the peak position of qI(q) has a maximum value in the range wThe polyimide wet gel has a particle size of 0.8 nm or more and 8.0 nm or less. [2] The magnitude of the scattering vector q of small-angle X-ray scattering is 0.080 nm -1 More than 0.12nm -1 Item 2. The polyimide wet gel according to item 1, wherein the minimum value of the differential coefficient when the logarithm log[I(q)] of the scattering intensity I(q) is differentiated by the logarithm log[q] of the scattering vector q is −1.0 or more and 0.0 or less in the following range: [3] The polyimide wet gel according to item 1 or 2, which has a breaking strain of 10% or more in a three-point bending test. [4] The polyimide constituting the polyimide wet gel is represented by the following general formula (1): [ka] (In the formula, X is a tetravalent organic group, Y is a divalent organic group, and n is a positive integer.) wherein in general formula (1), X and / or Y have a structure that imparts linearity to the molecular chain, and n is the degree of polymerization of the polyimide. [5] The polyimide constituting the polyimide wet gel is represented by the following general formula (1): [ka] (In the formula, X is a tetravalent organic group, Y is a divalent organic group, and n is a positive integer.) wherein the ratio of structures derived from pyromellitic anhydride among X present in the molecular chain is 50 mol % or more, and the terminal of the molecular chain is derived from pyromellitic anhydride. [6] The polyimide wet gel according to any one of items 1 to 5, which has a sheet shape. [7] The porous polyimide obtained by substituting the solvent in the polyimide wet gel with acetone and then drying with supercritical carbon dioxide is BET specific surface area: 100m 2 / g or more 2,000m 2 / g or less, Bulk density: 0.05g / cm 3 More than 0.50g / cm 3 below, Bending strength: 5 MPa or more, Flexural modulus: 100 MPa or more, and Average pore size (D) determined by small-angle X-ray scattering: 1.0 nm or more and 7.0 nm or less; 7. The polyimide wet gel according to any one of items 1 to 6, having:

[0225] Fifth Aspect [1] A step of adding a crosslinker having three or more functional groups to a polyamic acid solution to obtain a polyamic acid wet gel; a step of immersing the polyamic acid wet gel in a solution containing a dehydrating imidizing agent to obtain a polyimide wet gel; Including, The method for producing a polyimide wet gel, wherein the concentration of the dehydrating imidizing agent in the solution is 1% by weight or more and 50% by weight or less. [2] The method according to Item 1, wherein the temperature in the step of obtaining the polyamic acid wet gel and the step of obtaining the polyimide wet gel is maintained at 10°C or higher. [3] The method according to item 1 or 2, wherein the temperature in the step of obtaining the polyamic acid wet gel and the step of obtaining the polyimide wet gel is maintained at 120°C or lower. [4] The method according to any one of items 1 to 3, wherein the step of obtaining the polyamic acid wet gel is carried out by adding the crosslinking agent having three or more functional groups to the polyamic acid solution and spreading the mixture into a sheet. [5] The porous polyimide constituting the polyimide wet gel has a BET specific surface area of 10 m after heat treatment at 300°C for 1 hour. 2 / g or more 2,000m 2 / g or less. [6] The porous polyimide constituting the polyimide wet gel is represented by the following general formula (1): [ka] (In the formula, X is a tetravalent organic group, Y is a divalent organic group, and n is a positive integer.) wherein in general formula (1), X and / or Y have a structure that imparts linearity to the molecular chain, and n is the degree of polymerization of the polyimide. [7] A step of obtaining the polyimide wet gel by the method according to any one of items 1 to 6; removing the solution from the polyimide wet gel to obtain a porous polyimide; A method for producing a porous polyimide, comprising:

[0226] <Sixth Aspect> [1] Based on the pore volume (V) and BET specific surface area (A) determined by gas adsorption, the following formula: L=4V / A A porous carbon sheet having an average pore diameter (L) determined by the above formula (1) of 5 nm or more and 500 nm or less. [2] Bulk density of 0.01 g / cm 3 More than 0.80g / cm 3 Item 2. The porous carbon sheet according to item 1, wherein: [3] The porous carbon sheet according to item 1 or 2, having an average thickness of 10 mm or less. [4] BET specific surface area is 10m 2 More than 2,000m 2 A porous carbon sheet according to any one of items 1 to 3, which is: [5] A method for producing a porous carbon sheet, comprising a step of heating a porous resin sheet to 400°C or higher to carbonize it, thereby obtaining a porous carbon sheet, The porous carbon sheet has a pore volume (V) and a BET specific surface area (A) determined by a gas adsorption method, and the pore volume (V) and the BET specific surface area (A) are determined by the following formula: L=4V / A The method according to claim 1, wherein the average pore diameter (L) obtained by the above method is 5 nm or more and 500 nm or less. [6] The method according to Item 5, wherein the porous resin sheet is at least one selected from the group consisting of a porous polyimide sheet and a porous PVDF sheet. [Example]

[0227] The following examples further illustrate exemplary embodiments of the present invention, but the present invention is not limited to these examples.

[0228] <<<Example I: First embodiment>>> <<Measurement and Evaluation Methods>> <Degree of polymerization (n)> The degree of polymerization (n) was adjusted based on the molar ratio of diamine to acid dianhydride in the polymerization step. In the present disclosure, in Examples 1 to 7 and Comparative Examples 2, 5, 6, and 7, the molar ratio of diamine to acid dianhydride in the polymerization step was n:n+1. In Comparative Examples 1, 3, and 4, the molar ratio of diamine to acid dianhydride in the polymerization step was n+1:n.

[0229] (Measurement of weight average molecular weight) The weight-average molecular weight (Mw) was measured by gel permeation chromatography (GPC) under the following conditions. N,N-dimethylformamide (Wako Pure Chemical Industries, Ltd., for high-performance liquid chromatography) was used as the solvent, to which 24.8 mmol / L of lithium bromide monohydrate (Wako Pure Chemical Industries, Ltd., purity 99.5%) and 63.2 mmol / L of phosphoric acid (Wako Pure Chemical Industries, Ltd., for high-performance liquid chromatography) were added prior to measurement. A calibration curve for calculating the weight-average molecular weight was prepared using standard polystyrene (Tosoh Corporation). Column: Shodex KD-806M (Showa Denko) Flow rate: 1.0mL / min Column temperature: 40℃ Pump: PU-2080Plus (JASCO) Detector: RI-2031Plus (RI: differential refractometer, manufactured by JASCO) UV-2075Plus (UV-VIS: Ultraviolet-visible absorption spectrometer, manufactured by JASCO)

[0230] <Measurement of average pore size and BET specific surface area of porous polyimide> Approximately 0.2 g of sample was placed in a glass sample tube and heated and vacuum-degassed for 18 hours at 50°C and a pressure of 0.001 mmHg or less using a sample pretreatment device. The sample weight was measured after heating and vacuum degassing and used as the sample weight for calculating the specific surface area. The specific surface area was calculated using a multi-analyte high-performance specific surface area / pore size distribution analyzer (3Flex, Micrometrics) from the nitrogen gas adsorption isotherm at liquid nitrogen temperature (77 K) using the BET equation. The intercept and slope of the line (BET plot) for relative pressures (P / P) ranging from 0.05 to 0.30 were used. The pore volume was determined from the adsorption amount at 760 mmHg, and the average pore diameter (L) was calculated using the pore volume (V) and specific surface area (A) using the equation L = 4V / A. The pore size distribution was calculated using the BJH method.

[0231] (Three-point bending modulus and three-point bending strength of porous polyimide) After drying, a sample measuring 30 mm wide x 14 mm deep x approximately 2 mm thick was cut out from the disk-shaped porous polyimide and subjected to a three-point bending test under the following conditions. Testing machine: Instron material testing machine 5982 Temperature: Room temperature (23℃) Test speed: 1mm / min Support span: 20mm

[0232] <Measurement of strain at break of porous polyimide> A three-point bending test was performed under the same conditions as above, and the porous polyimide was stretched until it broke. The strain at which the test piece broke (the stress suddenly decreased) was taken as the breaking strain. The strain was measured up to a maximum of 15%, and if the specimen did not break, the breaking strain was recorded as ">15% (over 15%)."

[0233] <Measurement of Bulk Density of Porous Polyimide> The weight of the dried disk-shaped porous polyimide sample is m (g), the radius is r (mm), and the average thickness is h (mm). The bulk density d (g / cm) is calculated according to the following formula: 3 ) was calculated.

[0234] d=m / πhr2 In the formula, the radius r was calculated as half the average of 10 measurements of the diameter 2r taken with a vernier caliper at approximately equal intervals, and the average thickness h was calculated as the average of 20 measurements taken at approximately equal intervals within the circular surface.

[0235] <Small angle X-ray scattering measurement> Referring to Figure 1, Sample 1, which is a disk-shaped porous polyimide, was cut using a double-edged razor blade into a slice 1A with a thickness of approximately 0.5 mm to 1.0 mm and subjected to measurement. As shown in Figure 1, the incident direction of X-rays L was the cross-sectional direction of Sample 1, and scattering was detected by Detector 2. The measurement was carried out at the synchrotron radiation facility SPring-8 under the following conditions. The measurement environment was room temperature (25°C). Equipment: SPring-8, BL03XU beamline second hatch X-ray wavelength λ: 0.200nm Detector: PILATUS 1M Camera length: 4255mm Exposure time: 1s Damping plate: 100 μm thick aluminum plate

[0236] In this measurement, the attenuation plate and exposure time are not particularly specified. The incident X-rays were attenuated using an appropriate attenuation plate, and the measurement was performed under conditions where there was no sample damage, i.e., the SAXS pattern did not change when the sample was repeatedly irradiated with X-rays. For the scattering pattern I(2θ, φ) measured by the two-dimensional detector, the following equation (1):

number

[0237] The one-dimensional profile calculated by the above formula (1) includes scattering from the sample as well as scattering from sources other than the sample, such as the window material and air.

number

[0238] <Calculation method for average pore size (D)> The pores in the porous material are randomly located, and the influence of interference between pores is considered to be small. In this case, the scattering vector q = 4π sinθ / λ (λ: incident X-ray wavelength) and the scattering intensity I(q) are calculated by the following formula (3):

number

number

[0239] q 2 When I(q) is plotted against q, 2 Point q where I(q) takes a maximum value peakFrom the value of , the average pore size (D) = 3 1 / 2 / q peak was calculated.

[0240] <Method for quantifying structural heterogeneity> Using the circularly averaged profile, dlog[I(q)] / dlog[q] was calculated using the following equation (5) using Igor Pro 8.0 (Wavemetrics).

number

[0241] The obtained dlog[I(q)] / dlog[q] is 0.025 nm -1 ≦q≦0.075nm -1 The minimum value (minimum differential coefficient) at the σ was calculated and used as an index of the structural heterogeneity of the porous polyimide.

[0242] <Production examples of porous polyimide in bulk (thick sheet) and thin sheet forms> [Example 1] In a 100 mL glass vial, p-phenylenediamine (PPDA: 1.08 g; 10.0 mmol) was dissolved in N-methyl-2-pyrrolidone (NMP: 45.5 g) with magnetic stirring. Then, pyromellitic anhydride (PMDA: 2.49 g; 11.4 mmol) powder was added with stirring. The resulting solution was stirred at room temperature (25 °C) until the molecular weight reached saturation, yielding a polyamic acid (PAA) solution. This molecular weight saturation was confirmed by gel permeation chromatography.

[0243] To the polyamic acid (PAA) solution, a solution of 1,3,5-tris(4-aminophenyl)benzene (TAB: 0.335 g; 0.952 mmol) dissolved in 6.4 g of NMP in another 10 mL glass vial was added, and the mixture was stirred for 1 minute. Bulk polyamic acid wet gel (PAA-WG) was prepared by transferring a portion of the solution obtained above into a PFA mold (φ50 mm, depth 30 mm) to a thickness of approximately 3 mm and leaving it to stand at room temperature (25°C) for approximately 30 minutes, thereby obtaining a non-fluid polyamic acid wet gel (PAA-WG). Thin polyamic acid wet gel sheets (PAA-WGs) were prepared by applying a portion of the solution obtained above onto a Kapton® film (manufactured by Toray DuPont Co., Ltd., 250 mm × 600 mm) using a bar coater (manufactured by Matsuo Sangyo Co., Ltd., bar No. 200, wet film thickness approximately 300 μm) (coating area: width approximately 200 mm × length approximately 500 mm). The film was then left to stand at room temperature (25°C) for 10 minutes to obtain polyamic acid wet gel sheets (PAA-WGs).

[0244] The PAA-WG was left standing in a sealed SUS container saturated with NMP at room temperature (25°C) for 24 hours, then removed from the mold and immersed in a mixed solution of acetic anhydride (28.0 g; 274 mmol), triethylamine (3.5 g; 34.3 mmol), and 283 g of NMP at room temperature (25°C) for 24 hours to obtain a polyimide wet gel (PI-WG). The PAA-WGs were then left to stand in an NMP-saturated atmosphere in a sealed stainless steel container at room temperature (25°C) for 24 hours, and then immersed in a mixed solution of acetic anhydride (28.0 g; 274 mmol), triethylamine (3.5 g; 34.3 mmol), and 283 g of NMP at room temperature (25°C) for 24 hours to obtain polyimide wet gels (PI-WGs).

[0245] The PI-WG was removed from the solution, immersed in a solution of acetone:NMP = 1:1 by weight for 24 hours, washed with acetone, and immersed in acetone for another 24 hours three times. The PI-WG was then dried using a supercritical dryer (manufactured by Rexxam Co., Ltd., "SCRD6") to obtain porous polyimide (pPI). In addition, after peeling the PAA-WGs from the Kapton film, the porous polyimide sheets (pPIs) were obtained by solvent substitution and supercritical drying in the same manner as for the PAA-WG.

[0246] [Examples 2 to 7] Bulk porous polyimide (pPI) and thin sheet porous polyimide (pPIs) were obtained in the same manner as in Example 1, except that the diamine, tetracarboxylic acid anhydride, crosslinking agent, amount of imidization reagent, and solvent were changed to those shown in Table 1. The physical properties of the obtained pPIs are shown in Table 1.

[0247] [Comparative Example 1] Bulk porous polyimide (pPI) was prepared using the following procedure, based on Non-Patent Document 1 (ACS Appl. Mater. Interfaces, (2015), 7(2), pp. 1240-1249). In a 100 mL glass vial, 2,2'-dimethylbenzidine (DMBZ: 2.23 g; 10.5 mmol) was mixed with N-methyl-2-pyrrolidone (NMP: 45.7 g) and dissolved under magnetic stirring. Then, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 2.94 g; 10.0 mmol) powder was added and stirred at room temperature (25 °C) until the molecular weight reached saturation, yielding a polyamic acid (PAA) solution.

[0248] Then, acetic anhydride (8.16 g; 80 mmol) was added to the polyamic acid (PAA) solution while stirring, and the mixture was stirred until homogeneous. Triethylamine (1.0 g; 10 mmol) was then added, and the mixture was stirred until homogeneous. After that, the mixture was stirred at room temperature (25°C) for 15 minutes to obtain a polyimide (PI) solution.

[0249] A solution of 1,3,5-benzenetricarbonyl trichloride (BTC: 89 mg; 0.333 mmol) dissolved in 1.7 g of NMP in a 10 mL glass vial was added to the polyimide (PI) solution and stirred at room temperature until homogeneous. After stirring, a portion of the resulting solution was transferred to a PFA mold (φ50 mm, depth 30 mm) to a thickness of approximately 3 mm and allowed to stand at room temperature for 120 minutes to obtain a non-flowable bulk polyimide wet gel (PI-WG).

[0250] The resulting PI-WG was placed in a sealed stainless steel container saturated with NMP at room temperature (25°C) for 24 hours. It was then immersed in a solution of acetone:NMP (mass ratio) = 25:75 for 24 hours, a solution of acetone:NMP (mass ratio) = 50:50 for 24 hours, and a solution of acetone:NMP (mass ratio) = 75:25 for 24 hours. The solvent was then exchanged by repeating acetone washing and 24-hour immersion three times. The acetone-immersed bulk polyimide wet gel was then dried using the supercritical drying apparatus described above to obtain bulk porous polyimide (pPI).

[0251] Comparative Example 2 With reference to Non-Patent Document 5 (ACS Appl. Mater. Interfaces, (2012), 4, pp. 536-544), bulk porous polyimide pPI was prepared by the following procedure.

[0252] In a 100 mL glass vial, 2,2'-dimethylbenzidine (DMBZ: 2.13 g; 10.0 mmol) was mixed with N-methyl-2-pyrrolidone (NMP: 41.6 g) and dissolved by magnetic stirring. Then, while stirring the solution, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 3.09 g; 10.5 mmol) powder was added and stirred at room temperature until the molecular weight was saturated.

[0253] Thereafter, while stirring the above solution, a solution of 1,3,5-tris(4-aminophenoxy)benzene (TAPB: 0.133 g; 0.333 mmol) dissolved in 10 g of NMP in another 20 mL glass vial was added, and the mixture was stirred at room temperature for 10 minutes.

[0254] Acetic anhydride (8.58 g; 84 mmol) and pyridine (6.64 g; 84 mmol) were then added and stirred until homogenous. The solution was then transferred to a PFA mold (φ50 mm, depth 30 mm) to a thickness of approximately 3 mm and allowed to stand at room temperature for 30 minutes to obtain a non-fluid bulk polyimide wet gel (PI-WG).

[0255] Thereafter, solvent substitution and supercritical drying were carried out in the same manner as in Comparative Example 1 to obtain a bulk porous polyimide (pPI). The physical properties of the obtained bulk porous polyimide (pPI) are shown in Table 2.

[0256] Comparative Example 3 Similar to Comparative Example 1, a bulk porous polyimide was obtained using the diamine, tetracarboxylic acid anhydride, crosslinking agent, and their amounts as shown in Table 2, with reference to Non-Patent Document 7 (Polymer, (2019), 176, pp. 213-226). The physical properties of the resulting bulk porous polyimide (pPI) are shown in Table 2.

[0257] Comparative Example 4 Bulk porous polyimide (pPI) was prepared using the following procedure, based on Non-Patent Document 6 (ACS Appl. Mater. Interfaces, (2017), 9, pp. 8287-8296). In a 100 mL glass vial, 4,4'-oxydianiline (ODA: 1.05 g; 5.25 mmol) was added to N-methyl-2-pyrrolidone (NMP: 48 g) and dissolved using a magnetic stirrer. After stirring the solution, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 2.94 g; 10.0 mmol) powder was added and stirred at room temperature until the molecular weight was saturated. To the homogeneous solution, 9,9'-bis(4-aminophenyl)fluorene (BAFL: 1.83 g; 5.25 mmol) was added and stirred at room temperature for 30 minutes.

[0258] Acetic anhydride (8.15 g; 80 mmol) was then added to the above solution while stirring, and the mixture was stirred until homogenized. Triethylamine (1.0 g; 10 mmol) was then added, and the mixture was stirred until homogenized. After that, the mixture was stirred at room temperature for 15 minutes. In another 10 mL glass vial, a solution of 1,3,5-benzenetricarbonyl trichloride (BTC: 88 mg; 0.333 mmol) dissolved in 5 g of NMP was added, and the mixture was stirred at room temperature until homogenized.

[0259] After stirring, the solution was transferred to a PFA mold (φ50 mm, depth 30 mm) to a thickness of approximately 3 mm and allowed to stand at room temperature for 30 minutes to obtain a non-fluid bulk polyimide wet gel (PI-WG).

[0260] Subsequently, gelation, solvent substitution, and supercritical drying were carried out in the same manner as in Comparative Example 1 to obtain a bulk porous polyimide. Table 2 shows the physical properties of the obtained bulk porous polyimide.

[0261] Comparative Example 5 Bulk porous polyimide was prepared using the following procedure, based on Non-Patent Document 3 (ACS Appl. Mater. Interfaces, (2019), 11, pp. 9425-9437). In a 100 mL glass vial, 1,4-bis(4-aminophenoxy)butane (BAP4: 2.04 g; 7.5 mmol) was mixed with N-methyl-2-pyrrolidone (NMP: 45 g) and dissolved using a magnetic stirrer. After stirring the solution, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 3.04 g; 10.33 mmol) powder was added and stirred at room temperature for 2 hours. To the homogeneous solution, 2,2'-dimethylbenzidine (DMBZ: 0.53 g; 2.5 mmol) was added and stirred at room temperature for 30 minutes to obtain a polyamic acid (PAA) solution.

[0262] Next, while stirring the polyamic acid (PAA) solution, a solution of 1,3,5-tris(4-aminophenoxy)benzene (TAPB: 0.089 g; 0.222 mmol) dissolved in 6.3 g of NMP was added to another 20 mL glass vial and stirred at room temperature for 10 minutes. Acetic anhydride (8.44 g; 82.7 mmol) was then added and stirred until homogenous. Then, triethylamine (3.13 g; 31 mmol) was added and stirred until homogenous.

[0263] Subsequently, gelation, solvent substitution, and supercritical drying were carried out in the same manner as in Comparative Example 1 to obtain a bulk porous polyimide. Table 2 shows the physical properties of the obtained bulk porous polyimide.

[0264] Comparative Example 6 Referring to Non-Patent Document 2 (ACS Appl. Polym. Mater., (2020), 2, pp. 2179-2189), bulk porous polyimide was prepared using the following procedure. In a 100 mL glass vial, 2,2'-dimethylbenzidine (DMBZ: 0.53 g; 2.5 mmol) was added to N-methyl-2-pyrrolidone (NMP: 45 g) and stirred using a magnetic stirrer to dissolve. Then, while stirring the solution, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 2.99 g; 10.17 mmol) powder was added and stirred at 40 ° C until homogenous. To the homogenized solution, 1,3-bis(4-aminophenoxy)-2,2-dimethylpropane (BAPN: 2.15 g; 7.5 mmol) was added and stirred at 40 ° C until homogenous, yielding a polyamic acid (PAA) solution.

[0265] Next, while stirring the polyamic acid (PAA) solution, a solution of 1,3,5-tris(4-aminophenoxy)benzene (TAPB: 0.044 g; 0.111 mmol) dissolved in 6.4 g of NMP was added to another 20 mL glass vial and stirred at room temperature for 10 minutes. Acetic anhydride (8.3 g; 81.3 mmol) was then added and stirred until homogenous. Then, triethylamine (2.05 g; 20.3 mmol) was added and stirred until homogenous.

[0266] Subsequently, gelation, solvent substitution, and supercritical drying were carried out in the same manner as in Comparative Example 1 to obtain a bulk porous polyimide. Table 2 shows the physical properties of the obtained bulk porous polyimide.

[0267] Comparative Example 7 Bulk porous polyimide was prepared with reference to Patent Document 3 (China Patent No. 108203516) as follows: In a 100 mL glass vial, 2,2'-dimethylbenzidine (DMBZ: 2.03 g; 9.55 mmol) was mixed with N-methyl-2-pyrrolidone (NMP: 96.8 g) and dissolved by magnetic stirring. Then, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 2.94 g; 10.0 mmol) powder was added while stirring the solution, and the mixture was stirred at 25°C for 24 hours to obtain a polyamic acid (PAA) solution.

[0268] Then, while stirring the polyamic acid (PAA) solution, a solution of 1,3,5-tris(4-aminophenoxy)benzene (TAPB: 0.12 g; 0.3 mmol) dissolved in 3.0 g of NMP in another 20 mL glass vial was added and stirred for 5 minutes at 25° C. A portion of the resulting solution was transferred to a PFA mold (φ50 mm, depth 30 mm) to a thickness of approximately 3 mm and allowed to stand at 25° C. for approximately 60 minutes to obtain a non-fluid bulk polyamic acid wet gel (PAA-WG).

[0269] This PAA-WG was left standing at 60°C for 24 hours in a SUS sealed container saturated with NMP, then removed from the mold and immersed in a mixed solution of acetic anhydride (90.0 g; 0.88 mol), pyridine (90 g; 1.14 mol), and 120 g of NMP at -5°C for 8 hours. The solution was then heated to 25°C and left standing for 6 hours, then heated to 80°C and left standing for 10 hours to obtain a bulk polyimide wet gel (PI-WG).

[0270] The PI-WG was removed from the solution, washed with ethanol, and then immersed in ethanol for 24 hours three times. This was then dried using a supercritical drying apparatus (manufactured by Rexxam Co., Ltd., "SCRD6") to obtain a bulk porous polyimide (pPI). The supercritical drying conditions were as described in Patent Document 3: a temperature of 40°C, a pressure of 15 MPa, and a drying time of 8 hours. The physical properties of the obtained bulk porous polyimide are shown in Table 2.

[0271] [Table 1]

[0272] [Table 2]

[0273] <<<Example II: Second embodiment>>> <Evaluation method> (average pore diameter of porous polyimide) The measurement was carried out in the same manner as in Example I.

[0274] (Three-point bending modulus and three-point bending strength of porous polyimide) The measurement was carried out in the same manner as in Example I.

[0275] (Bulk density of porous polyimide) The measurement was carried out in the same manner as in Example I.

[0276] (Carbonyl carbon mass ratio) The ratio of carbonyl carbon to total carbon in the porous polyimide was 13 It was calculated from the ratio of the integral values of the C-NMR signals. Solid state NMR measurement conditions: Equipment: Bruker Avance 500 Observed nucleus: 13C Observation frequency: 125.8MHz Pulse program: hpdec(DDMAS) Rotation speed: 9kHz or 11kHz Repeat pulse waiting time: 300sec Accumulation count: 500 times Measurement temperature: room temperature Sample tube: 4mmφ Shift standard: Glycine = 176.03 ppm Broadening factor: 50Hz

[0277] <Production of porous polyimide> [Example 1] (Preparation of bulk (thick sheet) polyamic acid wet gel) In a 100 mL glass vial, 1,4-phenylenediamine (PPDA: 1.08 g; 10.0 mmol) was dissolved in N-methyl-2-pyrrolidone (NMP: 29.0 g) with magnetic stirring. Pyromellitic anhydride (PMDA: 2.34 g; 11.0 mmol) powder was then added with stirring. After stirring for 1 hour at 25 °C, a solution of 1,3,5-tris(4-aminophenyl)benzene (TAB: 0.234 g; 0.667 mmol) dissolved in 4.5 g of NMP was added to a separate 10 mL glass vial and stirred for 1 minute. The resulting solution was transferred to a PFA mold (φ100 mm, depth 30 mm) to a thickness of approximately 3 mm and allowed to stand at room temperature for 10 minutes to yield a non-flowable bulk polyamic acid wet gel, PAA-WG1.

[0278] (Preparation of bulk polyimide wet gel) This PAA-WG1 was left at room temperature for 24 hours in a sealed SUS container saturated with NMP, then removed from the mold and immersed in a mixed solution of acetic anhydride (27.0 g; 264 mmol), triethylamine (3.3 g; 33 mmol), and 270 g of NMP at 25°C for 6 hours to obtain a bulk polyimide wet gel PI-WG1.

[0279] (Preparation of bulk porous polyimide) PI-WG1 was then immersed in a 1:1 (mass ratio) solution of acetone and NMP for 24 hours, washed with acetone, and immersed in acetone for 24 hours three times. The bulk porous polyimide pPI1 was obtained by drying using the supercritical dryer described above. The physical properties of the obtained pPI1 are shown in Table 3.

[0280] [Examples 2 to 10] Bulk porous polyimides pPI2 to 10 were obtained in the same manner as in Example 1, except that the diamine, tetracarboxylic acid anhydride, crosslinking agent, imidizing agent, solvent, and amounts thereof were as shown in Table 3.

[0281] [Comparative Example 1] With reference to Non-Patent Document 1 (ACS Appl. Mater. Interfaces, (2015), 7, pp. 1240-1249), bulk porous polyimide pPIr1 was prepared by the following procedure.

[0282] (Preparation of Polyamic Acid) In a 100 mL glass vial, 4,4'-oxydianiline (ODA: 2.10 g; 10.5 mmol) was dissolved in N-methyl-2-pyrrolidone (NMP: 41 g) while stirring using a magnetic stirrer. Then, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 2.94 g; 10.0 mmol) powder was added and stirred at room temperature for 2 hours.

[0283] (Imidization and gelation) Acetic anhydride (8.15 g; 80 mmol) was then added to the above solution while stirring, and the mixture was stirred until homogenous. Furthermore, triethylamine (1.0 g; 10 mmol) was added, and the mixture was stirred until homogenous. After stirring for 15 minutes at room temperature, a solution of 1,3,5-benzenetricarbonyl trichloride (BTC: 88 mg; 0.333 mmol) dissolved in 5 g of NMP was added to another 10 mL glass vial and stirred at room temperature until homogenous. After stirring, the solution was transferred to a PFA mold (Φ100 mm, depth 30 mm) to a thickness of approximately 3 mm and allowed to stand at room temperature for 30 minutes to obtain a non-flowable bulk polyimide wet gel, PI-WGr1.

[0284] The resulting PI-WGr1 was placed in a sealed stainless steel container saturated with NMP at room temperature for 24 hours. It was then immersed in a 25:75 acetone:NMP (mass ratio) solution for 24 hours, a 50:50 acetone:NMP (mass ratio) solution for 24 hours, and a 75:25 acetone:NMP (mass ratio) solution for 24 hours. The solvent was then exchanged by washing with acetone and immersing in acetone for 24 hours three times. The acetone-immersed bulk polyimide wet gel was dried using the supercritical drying apparatus described above to obtain the bulk porous polyimide pPIr1. The physical properties of the resulting pPIr1 are shown in Table 4.

[0285] Comparative Example 2 In the same manner as in Comparative Example 1, the diamine, tetracarboxylic acid anhydride, crosslinking agent, imidizing agent, and solvent were added in amounts as shown in Table 4, and the same operation as in Comparative Example 1 was carried out to obtain bulk porous polyimide pPIr2.

[0286] Comparative Example 3 With reference to Non-Patent Document 6 (ACS Appl. Mater. Interfaces, (2017), 9, pp. 8287-8296), bulk porous polyimide pPIr3 was prepared by the following procedure.

[0287] (Preparation of Polyamic Acid) In a 100 mL glass vial, 4,4'-oxydianiline (ODA: 1.05 g; 5.25 mmol) was added to N-methyl-2-pyrrolidone (NMP: 48 g) and dissolved by stirring using a magnetic stirrer. Then, while stirring the solution, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 2.94 g; 10.0 mmol) powder was added and stirred at room temperature for 2 hours.

[0288] (Imidization and gelation) To the homogenized solution, 9,9'-bis(4-aminophenyl)fluorene (BAFL: 1.83 g; 5.25 mmol) was added, and the mixture was stirred at room temperature for 30 minutes. Thereafter, acetic anhydride (8.15 g; 80 mmol) was added to the above solution while stirring, and the mixture was stirred until it became homogeneous. Further, triethylamine (1.0 g; 10 mmol) was added and stirred until homogenized, followed by stirring at room temperature for 15 minutes. A solution of 1,3,5-benzenetricarbonyl trichloride (BTC: 88 mg; 0.333 mmol) dissolved in 5 g of NMP in another 10 mL glass vial was added, followed by stirring at room temperature until homogenized.

[0289] After stirring, the solution was transferred to a PFA mold (φ100 mm, depth 30 mm) to a thickness of approximately 3 mm and allowed to stand at room temperature for 30 minutes to obtain a non-fluid bulk polyimide wet gel PI-WGr3. The solvent substitution and supercritical drying were carried out in the same manner as in Comparative Example 1 to obtain a bulk porous polyimide pPIr3. The physical properties of the obtained pPIr3 are shown in Table 4.

[0290] Comparative Example 4 With reference to Non-Patent Document 5 (ACS Appl. Mater. Interfaces, (2012), 4, pp. 536-544), bulk porous polyimide pPIr4 was prepared by the following procedure.

[0291] (Preparation of Polyamic Acid) In a 100 mL glass vial, 4,4'-oxydianiline (ODA: 2.00 g; 10.0 mmol) was added to N-methyl-2-pyrrolidone (NMP: 40.5 g) and dissolved by stirring using a magnetic stirrer. Then, while stirring the solution, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 3.09 g; 10.5 mmol) powder was added and stirred at room temperature for 2 hours.

[0292] (Gelation and Imidization) Thereafter, while stirring the above solution, a solution of 1,3,5-tris(4-aminophenoxy)benzene (TAPB: 0.133 g; 0.333 mmol) dissolved in 10 g of NMP in another 20 mL glass vial was added, and the mixture was stirred at room temperature for 10 minutes.

[0293] Acetic anhydride (8.58 g; 84 mmol) and pyridine (6.64 g; 84 mmol) were then added and stirred until homogenous. The solution was then transferred to a PFA mold (Φ100 mm, depth 30 mm) to a thickness of approximately 3 mm and allowed to stand at room temperature for 30 minutes to obtain a non-fluid bulk polyimide wet gel, PI-WGr4. The solvent substitution and supercritical drying were carried out in the same manner as in Comparative Example 1 to obtain a bulk porous polyimide pPIr4. The physical properties of the obtained pPIr4 are shown in Table 4.

[0294] Comparative Example 5 The bulky porous polyimide pPIr5 was obtained in the same manner as in Comparative Example 1, except that the diamine, tetracarboxylic acid anhydride, crosslinking agent, and their amounts were as shown in Table 4, and the same procedure as in Comparative Example 4 was carried out. The physical properties of the obtained pPIr5 are shown in Table 4.

[0295] Comparative Example 6 Similar to Comparative Example 1, the diamine, tetracarboxylic acid anhydride, crosslinker, and their amounts were as shown in Table 4 with reference to Non-Patent Document 7 (Polymer, (2019), 176, pp. 213-226), and the same procedure as in Comparative Example 1 was carried out to obtain bulky porous polyimide pPIr6. The physical properties of the obtained pPIr6 are shown in Table 4.

[0296] Comparative Example 7 Similar to Comparative Example 1, the diamine, tetracarboxylic acid anhydride, crosslinker, and their amounts were as shown in Table 4 with reference to Non-Patent Document 7 (Polymer, (2019), 176, pp. 213-226), and the bulk porous polyimide pPIr7 was obtained by the same procedure as in Comparative Example 1. The physical properties of the obtained pPIr7 are shown in Table 4.

[0297] [Comparative Example 8] Bulk porous polyimides (pPIs) were prepared using the following procedure, based on Non-Patent Document 3 (ACS Appl. Mater. Interfaces, (2019), 11, pp. 9425-9437). In a 100 mL glass vial, 1,4-bis(4-aminophenoxy)butane (BAP4: 2.04 g; 7.5 mmol) was mixed with N-methyl-2-pyrrolidone (NMP: 45 g) and dissolved using a magnetic stirrer. After stirring the solution, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 3.04 g; 10.33 mmol) powder was added and stirred at room temperature for 2 hours. To the homogenized solution, 2,2'-dimethylbenzidine (DMBZ: 0.53 g; 2.5 mmol) was added and stirred at room temperature for 30 minutes to obtain a polyamic acid (PAA) solution.

[0298] Next, while stirring the polyamic acid (PAA) solution, a solution of 1,3,5-tris(4-aminophenoxy)benzene (TAPB: 0.089 g; 0.222 mmol) dissolved in 6.3 g of NMP was added to another 20 mL glass vial and stirred at room temperature for 10 minutes. Acetic anhydride (8.44 g; 82.7 mmol) was then added and stirred until homogenous. Then, triethylamine (3.13 g; 31 mmol) was added and stirred until homogenous.

[0299] Subsequently, gelation, solvent substitution, and supercritical drying were carried out in the same manner as in Comparative Example 1 to obtain a bulk porous polyimide (pPIs). The physical properties of the obtained pPIr8 are shown in Table 4.

[0300] Comparative Example 9 Based on Non-Patent Document 2 (ACS Appl. Polym. Mater., (2020), 2, pp. 2179-2189), porous polyimide sheets (pPIs) were prepared using the following procedure. In a 100 mL glass vial, 2,2'-dimethylbenzidine (DMBZ: 0.53 g; 2.5 mmol) was added to N-methyl-2-pyrrolidone (NMP: 45 g) and stirred using a magnetic stirrer to dissolve. Then, while stirring the solution, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 2.99 g; 10.17 mmol) powder was added and stirred at 40 ° C until homogenous. 1,3-bis(4-aminophenoxy)-2,2-dimethylpropane (BAPN: 2.15 g; 7.5 mmol) was added to the homogenized solution, and the mixture was stirred at 40 ° C until homogenous, yielding a polyamic acid (PAA) solution.

[0301] Next, while stirring the polyamic acid (PAA) solution, a solution of 1,3,5-tris(4-aminophenoxy)benzene (TAPB: 0.044 g; 0.111 mmol) dissolved in 6.4 g of NMP was added to another 20 mL glass vial and stirred at room temperature for 10 minutes. Acetic anhydride (8.3 g; 81.3 mmol) was then added and stirred until homogenous. Then, triethylamine (2.05 g; 20.3 mmol) was added and stirred until homogenous.

[0302] Subsequently, gelation, solvent substitution, and supercritical drying were carried out in the same manner as in Comparative Example 1 to obtain a bulk porous polyimide (pPIs). The physical properties of the obtained pPIr9 are shown in Table 4.

[0303] [Comparative Example 10] A bulk porous polyimide (pPIs) was obtained by the same procedure as in Comparative Example 7 of Example I. The physical properties of the obtained pPIr10 are shown in Table 4.

[0304] [Table 3]

[0305] [Table 4]

[0306] In each example, a porous polyimide was produced that showed little deformation from the template during gel formation and had excellent toughness. On the other hand, in Comparative Examples 1 to 10, which were examples in which gelation was performed after imidization, the toughness of the porous polyimide was insufficient.

[0307] <<<Example III: Third embodiment>>> <Evaluation method> (average pore diameter of porous polyimide) The measurement was carried out in the same manner as in Example I.

[0308] (Bulk density of porous polyimide) The measurement was carried out in the same manner as in Example I.

[0309] (Preparation of 300℃ heat-treated sample) 0.2 g of porous polyimide was heated to 300°C at a rate of 5°C / min in a vertical curing oven (Koyo Lindberg, model VF-2000B) under a nitrogen atmosphere, held at that temperature for 1 hour, and then cooled to 50°C at a rate of 5°C / min to obtain a heat-treated sample.

[0310] (Carbonyl carbon mass ratio) Measurement was carried out in the same manner as in Example II.

[0311] <Production of porous polyimide> [Example 1] The porous polyimide pPI1 was obtained in the same manner as in Example 1 of Example II. The physical properties of the obtained pPI1 are shown in Table 5.

[0312] [Examples 2 to 9] In the same manner as in Example 1, the diamine, tetracarboxylic acid anhydride, crosslinking agent, imidizing agent, solvent, and amounts thereof added were changed as shown in Table 5, and the same operation as in Example 1 was carried out to obtain porous polyimides pPI2 to 9.

[0313] [Comparative Example 1] Porous polyimide pPIr1 was prepared in the same manner as in Comparative Example 1 of Example II. The physical properties of the obtained pPIr1 are shown in Table 6.

[0314] Comparative Example 2 In the same manner as in Comparative Example 1, the diamine, tetracarboxylic acid anhydride, crosslinking agent, imidizing agent, and solvent were added in amounts as shown in Table 6, and the same operation as in Comparative Example 1 was carried out to obtain porous polyimide pPI2.

[0315] Comparative Example 3 Porous polyimide pPIr3 was prepared in the same manner as in Comparative Example 3 of Example II. The physical properties of the obtained pPIr3 are shown in Table 6.

[0316] Comparative Example 4 Porous polyimide pPIr4 was prepared in the same manner as in Comparative Example 4 of Example II. The physical properties of the obtained pPIr4 are shown in Table 6.

[0317] Comparative Example 5 The same procedure as in Comparative Example 4 was carried out to obtain porous polyimide pPIr5, except that the diamine, tetracarboxylic acid anhydride, crosslinking agent, and their amounts were as shown in Table 6. The physical properties of the obtained pPIr5 are shown in Table 6.

[0318] Comparative Example 6 In the same manner as in Comparative Example 1, the diamine, tetracarboxylic anhydride, crosslinker, and their amounts added were as shown in Table 6 with reference to Non-Patent Document 7 (Polymer, (2019), 176, pp. 213-226), and the same procedure as in Comparative Example 1 was carried out to obtain porous polyimide pPIr6. The physical properties of the obtained pPIr6 are shown in Table 6.

[0319] Comparative Example 7 In the same manner as in Comparative Example 1, the diamine, tetracarboxylic anhydride, crosslinker, and their amounts added were as shown in Table 7 with reference to Non-Patent Document 7 (Polymer, (2019), 176, pp. 213-226), and the same procedure as in Comparative Example 1 was carried out to obtain porous polyimide pPIr7. The physical properties of the obtained pPIr7 are shown in Table 7.

[0320] [Comparative Example 8] As in Comparative Example 1, the diamine, tetracarboxylic acid anhydride, crosslinking agent, and their amounts added were changed as shown in Table 7, and the same procedure as in Comparative Example 4 was carried out to attempt to obtain porous polyimide pPIr8. In a 100 mL glass vial, 1,4-phenylenediamine (PPDA: 1.08 g; 10.0 mmol) was mixed with N-methyl-2-pyrrolidone (NMP: 29.0 g) and dissolved by magnetic stirring. Then, while stirring the solution, pyromellitic anhydride (PMDA: 2.40 g; 11.0 mmol) powder was added. Thereafter, acetic anhydride (8.16 g; 80 mmol) was added to the above solution while stirring, and the mixture was stirred until homogenized. Triethylamine (1.0 g; 10 mmol) was then added, and the solution suddenly thickened, making it difficult to stir.

[0321] Comparative Example 9 As in Comparative Example 1, the diamine, tetracarboxylic acid anhydride, crosslinking agent, and their amounts added were changed as shown in Table 7, and the same procedure as in Comparative Example 4 was carried out to attempt to obtain porous polyimide pPIr9. In a 100 mL glass vial, 3,3'-dimethylbenzidine (DMBZ: 2.12 g; 10.0 mmol) was mixed with N-methyl-2-pyrrolidone (NMP: 38.3 g) and dissolved by stirring using a magnetic stirrer. Then, while stirring the solution, pyromellitic anhydride (PMDA: 2.40 g; 11.0 mmol) powder was added. Thereafter, acetic anhydride (8.16 g; 80 mmol) was added to the above solution while stirring, and the mixture was stirred until homogenized. Triethylamine (1.0 g; 10 mmol) was then added, and the solution suddenly thickened, making it difficult to stir.

[0322] [Comparative Example 10] A porous polyimide sheet (pPIs) was prepared in the same manner as in Comparative Example 8 of Example II. However, when the pPIs was heat-treated at 300°C, the sample shape changed significantly, as in Comparative Example 1. The properties of the obtained pPIs and the greatly deformed porous polyimide sheet are shown in Table 7.

[0323] [Comparative Example 11] Based on Non-Patent Document 2 (ACS Appl. Polym. Mater., (2020), 2, pp. 2179-2189), porous polyimide sheets (pPIs) were prepared using the following procedure. In a 100 mL glass vial, 2,2'-dimethylbenzidine (DMBZ: 0.53 g; 2.5 mmol) was added to N-methyl-2-pyrrolidone (NMP: 45 g) and stirred using a magnetic stirrer to dissolve. Then, while stirring the solution, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 2.99 g; 10.17 mmol) powder was added and stirred at 40 ° C until homogeneous. 1,3-bis(4-aminophenoxy)-2,2-dimethylpropane (BAPN: 2.15 g; 5.5 mmol) was added to the homogeneous solution and stirred at 40 ° C until homogeneous, obtaining a polyamic acid (PAA) solution.

[0324] Next, while stirring the polyamic acid (PAA) solution, a solution of 1,3,5-tris(4-aminophenoxy)benzene (TAPB: 0.044 g; 0.111 mmol) dissolved in 6.4 g of NMP was added to another 20 mL glass vial and stirred at room temperature for 10 minutes. Acetic anhydride (8.3 g; 81.3 mmol) was then added and stirred until homogenous. Then, triethylamine (2.05 g; 20.3 mmol) was added and stirred until homogenous.

[0325] Subsequently, sheet molding, gelation, solvent substitution, and supercritical drying were carried out in the same manner as in Comparative Example 1 to obtain a porous polyimide sheet (pPIs). However, when the pPIs was heat-treated at 300°C, the sample shape changed significantly, as in Comparative Example 1. The properties of the obtained pPIs and the highly deformed porous polyimide sheet are shown in Table 7.

[0326] [Comparative Example 12] A porous polyimide sheet (pPIs) was obtained by the same procedure as in Comparative Example 7 of Example I. The properties of the obtained porous polyimide sheet are shown in Table 7.

[0327] [Table 5]

[0328] [Table 6]

[0329] [Table 7]

[0330] According to each example, a porous polyimide was produced that showed little deformation from the mold during gel formation and maintained its pore structure well even after heating at 300° C., i.e., had excellent heat resistance. On the other hand, Comparative Examples 1 to 11 are examples in which gelation was performed after imidization, and Comparative Example 12 is an example in which gelation was performed before imidization, but in both cases the heat resistance of the porous polyimide was insufficient.

[0331] <<<Example IV: Fourth embodiment>>> <Degree of polymerization (n)> The measurement was carried out in the same manner as in Example I.

[0332] <Small angle X-ray scattering measurement> Referring to Figure 1, Sample 1, a disk-shaped porous polyimide wet gel, was cut into slices 1A with a thickness of approximately 0.5 mm to 1.0 mm using a double-edged razor blade, which were then sealed in a sealed cell for measurement. To prevent solvent evaporation, the sample was immersed in a petri dish filled with solvent and cut into slices with a thickness of approximately 1 mm using a razor blade, and a 30 μm thick cover glass was used as a window material. As shown in Figure 1, the incident direction of X-rays L was in the cross-sectional direction of Sample 1, and scattering was detected by Detector 2. Measurements were performed under the following conditions. The measurement environment was 25°C. Equipment: Rigaku Corporation NANOPIX X-ray wavelength λ: 0.154nm Optical system: Point collimation "2PHR" mode (1st: 0.55 mm, 2nd: Open, Guard: 0.35 mm) Detector: Hypix-6000 (2D semiconductor detector) Camera length: 1307mm Exposure time: 30 min / sample

[0333] For the scattering pattern I(2θ, φ) in small-angle X-ray scattering (SAXS) measurement, the following formula (a):

number

[0334] The one-dimensional profile calculated by the above formula (a) includes scattering from the sample as well as scattering from sources other than the sample, such as the window material and air.

number

[0335] The scattering intensity of a wet gel includes the scattering of the solvent as a background, as shown in the following equation (c): I(q) = I gel (q) - (1-φ)I solv (q) (c) I gel (q), I solv (q): Scattering intensity of wet gel and solvent after correction by equation (b) φ: Solid volume fraction The solvent scattering was subtracted by

[0336] <Average pore size (D w ) Calculation method> The pores in the porous material are randomly located, and the influence of interference between pores is considered to be small. In this case, the scattering vector q = 4π sinθ / λ (λ: incident X-ray wavelength) and the scattering intensity I(q) are calculated by the following formula (d):

number

number

[0337] When qI(q) is plotted against q, the point q where qI(q) takes a maximum value peak From the value of , the average pore size (D w )=(3 / 2) 1 / 2 / q peak was calculated.

[0338] <Method for quantifying structural heterogeneity> Using the circularly averaged profile of the polyimide wet gel, dlog[I(q)] / dlog[q] was calculated. First, at each measurement point of log[I(q)], the moving average of ±1 point before and after was smoothed ("Boxcar" smoothing). That is, the smoothed value was expressed as log[I(q i )] s As, log[I(q i )] s =(log[I(q i-1 )]+log[I(q i )]+log[I(q i+1 )]) / 3 The obtained log[I(q i )] s Using the following formula (f):

number

[0339] Smoothing and numerical differentiation were performed using Igor Pro 8.0 (Wavemetrics). The obtained dlog[I(q)] / dlog[q] was 0.080 nm. -1 ≦q≦0.12nm -1 The minimum value at σ was calculated and used as an index of the structural heterogeneity of the polyimide wet gel.

[0340] <Measurement of Polyimide Wet Gel Thickness> The thickness of the disc-shaped polyimide wet gel was measured at 20 points with a thickness meter at approximately equal intervals within the circular surface, and the average value was taken as the gel thickness.

[0341] <Measurement of strain at break of wet polyimide gel> A sample measuring 30 mm wide x 14 mm deep x 2 mm thick was cut out from the polyimide wet gel in the solvent it was immersed in and subjected to a three-point bending test under the following conditions: Testing machine: Instron material testing machine 5982 Temperature: Room temperature (23℃) Test speed: 1mm / min Support span: 20mm Time from removal from solvent to testing: Within 3 minutes

[0342] Under the above conditions, the polyimide wet gel was stretched until it broke. The strain at which the test piece broke (the stress suddenly decreased) was taken as the breaking strain. The strain was measured up to a maximum of 15%, and if the specimen did not break, the breaking strain was recorded as ">15% (more than 15%)."

[0343] <Wrapping test of wet polyimide gel sheet> A strip-shaped wet gel sheet measuring 30 mm wide x 100 mm deep x approximately 300 μm thick was cut from a polyimide NMP wet gel sheet impregnated in NMP. The sheet was removed from the NMP and wrapped around a SUS rod measuring 30 mm in diameter and 200 mm in length. This wrapping was maintained for at least 5 seconds, after which the wet gel sheet was turned over and wrapped around the SUS rod in the same manner. After wrapping the wet gel sheet both ways as described above, the wet gel sheet was again impregnated in NMP. This wrapping was carried out at 25°C within 3 minutes from the time the sheet was removed from NMP until it was again impregnated in NMP after the test. This operation was repeated 10 times, and the wet gel sheet was evaluated according to the following criteria. (Evaluation criteria) A: There was no breakage of the sheet and no warping was observed. B: Part of the sheet was torn or warped. C: The sheet broke.

[0344] <Determination of transparency of polyimide wet gel> The transparency of the polyimide wet gel was evaluated according to the following method. Specifically, on a piece of paper bearing a randomly selected 10 mm square mark (letter or symbol), multiple sheet-like samples were placed one on top of the other so that the sample thickness was 1.0 mm or more and covered the mark. Then, from a distance of approximately 30 cm, an attempt was made to visually recognize the mark through the sample, and the evaluation was performed according to the following criteria. This evaluation was performed under normal room light. (Evaluation criteria) A: The presence of the mark was confirmed and it was possible to determine what kind of mark it was. B: The presence of a mark was confirmed, but it was impossible to determine what kind of mark it was. C: The presence of the mark could not be confirmed.

[0345] <Measurements of BET specific surface area, bulk density, flexural strength, flexural modulus, and average pore size (D) of porous polyimide> The following bulk polyimide NMP wet gel (PI-WG-NMP) was immersed in a solution of acetone:NMP = 1:1 by weight for 24 hours, followed by washing with acetone and 24-hour acetone immersion three times. The resulting gel was dried in a supercritical dryer (Rexxam Corporation, "SCRD6") to obtain a bulk porous polyimide. This bulk porous polyimide was measured using the same procedures as in Example I.

[0346] <Production of bulk (thick sheet) and thin sheet polyimide wet gel> [Example 1] In a 100 mL glass vial, p-phenylenediamine (PPDA: 1.08 g; 10.0 mmol) was dissolved in N-methyl-2-pyrrolidone (NMP: 44.1 g) by magnetic stirring. Then, pyromellitic anhydride (PMDA: 2.29 g; 10.5 mmol) powder was added while stirring. The solution was stirred at room temperature (25 °C) for 1 hour to obtain a polyamic acid (PAA) solution.

[0347] To the polyamic acid (PAA) solution, a solution of 1,3,5-tris(4-aminophenyl)benzene (TAB: 0.117 g; 0.333 mmol) dissolved in 2.2 g of NMP in another 10 mL glass vial was added, and the mixture was stirred for 1 minute to become homogeneous.

[0348] Bulk polyamic acid wet gel (PAA-WG) was prepared by transferring the solution obtained above into a PFA mold (φ100 mm, depth 30 mm) to a thickness of approximately 3 mm and allowing it to stand at room temperature for 10 minutes to obtain non-flowable polyamic acid wet gel PAA-WG1. Thin polyamic acid wet gel sheets (PAA-WGs) were prepared by applying the solution obtained above to a Kapton® film (Toray-DuPont Co., Ltd., 250 mm × 600 mm) as a substrate film using a bar coater (Matsuo Sangyo Co., Ltd., bar No. 200, wet film thickness approximately 300 μm) (coating area: approximately 200 mm wide × approximately 500 mm long) and allowing it to stand at room temperature (25 °C) for 10 minutes to obtain thin polyamic acid wet gel sheets (PI-WGs).

[0349] This PAA-WG or PAA-WGs was left to stand in an NMP-saturated atmosphere in a sealed SUS container at room temperature (25°C) for 24 hours, and then immersed in a mixed solution of acetic anhydride (25.7 g; 252 mmol), triethylamine (3.2 g; 32 mmol), and 260 g of NMP at 25°C for 72 hours to obtain bulk polyimide wet gel (PI-WG) or thin sheet polyimide wet gel (PI-WGs).

[0350] The PI-WGs was washed with NMP, immersed in NMP for 24 hours, then washed with NMP and immersed in fresh NMP three times, and peeled from the Kapton film to obtain a polyimide NMP wet gel sheet (PI-WGs-NMP). Similarly, PAA-WG was washed with NMP, immersed in NMP for 24 hours, washed with NMP and immersed in fresh NMP three times to obtain a bulk polyimide NMP wet gel (PI-WG-NMP). The physical properties of the resulting PI-WG-NMP and PI-WGs-NMP are shown in Table 8.

[0351] [Examples 2 to 6] A bulk polyimide NMP wet gel (PI-WG-NMP) and a polyimide NMP wet gel sheet (PI-WGs-NMP) were obtained in the same manner as in Example 1, except that the diamine, tetracarboxylic anhydride, crosslinking agent, imidizing agent, solvent, and their amounts were as shown in Table 8. The physical properties of the obtained PI-WG-NMP and PI-WGs-NMP are shown in Table 8.

[0352] [Comparative Example 1] Bulk polyimide NMP wet gel (PI-WG-NMP) and bulk polyimide NMP wet gel (PI-WGs-NMP) were prepared using the following procedure, based on Non-Patent Document 1 (ACS Appl. Mater. Interfaces, (2015), 7(2), pp. 1240-1249). In a 100 mL glass vial, 2,2'-diaminobenzidine (m-Tolidine; DMBZ: 2.23 g; 10.5 mmol) was added to N-methyl-2-pyrrolidone (NMP: 45.7 g) and dissolved under magnetic stirring. Then, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 2.942 g; 10.0 mmol) powder was added and stirred at room temperature (25 °C) for 2 hours to obtain a polyamic acid (PAA) solution.

[0353] Then, acetic anhydride (8.16 g; 80 mmol) was added to the polyamic acid (PAA) solution while stirring, and the mixture was stirred until homogeneous. Further, triethylamine (1.01 g; 10 mmol) was added, and the mixture was stirred until homogeneous. After that, the mixture was stirred at room temperature (25°C) for 15 minutes to obtain a polyimide (PI) solution.

[0354] To the polyimide (PI) solution, a solution of 1,3,5-benzenetricarbonyl trichloride (BTC: 89 mg; 0.333 mmol) dissolved in 1.68 g of NMP in another 10 mL glass vial was added, and the mixture was stirred at room temperature for 5 minutes until the mixture became homogeneous.

[0355] Thin polyimide wet gel sheets (PI-WGs) were prepared by applying the resulting solution to a Kapton® film (250 mm x 600 mm, Toray-DuPont Co., Ltd.) substrate film using a bar coater (Matsuo Sangyo Co., Ltd., bar No. 200, wet film thickness approximately 300 μm) (coating area: approximately 200 mm wide x 500 mm long). The entire coated surface was then covered with a plastic container and allowed to stand at room temperature (25 °C) for 1 hour to obtain polyimide wet gel sheets (PI-WGs). Bulk polyimide wet gels were prepared by transferring the solution to a PFA mold (100 mm diameter, 30 mm deep) to a thickness of approximately 3 mm and allowing it to stand at room temperature for 30 minutes to obtain bulk polyimide wet gels (PI-WGs).

[0356] Thereafter, solvent substitution was carried out in the same manner as in Example 1 to obtain a thin polyimide NMP wet gel sheet (PI-WGs-NMP) and a bulk polyimide NMP wet gel (PI-WG-NMP). The physical properties of the obtained PI-WG-NMP and PI-WGs-NMP are shown in Table 8.

[0357] Comparative Example 2 Based on Non-Patent Document 5 (ACS Appl. Mater. Interfaces, (2012), 4, pp. 536-544), bulk polyimide NMP wet gel (PI-WG-NMP) and bulk polyimide NMP wet gel (PI-WGs-NMP) were prepared as follows: In a 100 mL glass vial, 2,2'-dimethylbenzidine (DMBZ: 2.13 g; 10.0 mmol) was mixed with N-methyl-2-pyrrolidone (NMP: 41.6 g) and dissolved by magnetic stirring. Then, while stirring, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 3.09 g; 10.5 mmol) powder was added and stirred at room temperature until the molecular weight reached saturation.

[0358] Then, while stirring the above solution, a solution of 1,3,5-tris(4-aminophenoxy)benzene (TAPB: 0.133 g; 0.333 mmol) dissolved in 10 g of NMP in another 20 mL glass vial was added and stirred at room temperature for 10 minutes, followed by the addition of acetic anhydride (8.58 g; 84 mmol) and pyridine (6.64 g; 84 mmol) and stirring until the mixture was homogenous.

[0359] Bulk polyimide wet gels (PI-WG) were prepared by transferring the solution obtained above into a PFA mold (φ50 mm, depth 30 mm) to a thickness of approximately 3 mm and allowing it to stand at room temperature for 30 minutes. A non-flowable bulk polyimide wet gel (PI-WG) was obtained. Thin sheet polyimide wet gels (PI-WGs) were prepared by applying the solution obtained above to a Kapton® film (Toray-DuPont Co., Ltd., 250 mm x 600 mm) as a substrate film using a bar coater (Matsuo Sangyo Co., Ltd., bar No. 200, wet film thickness approximately 300 μm) (coating area: approximately 200 mm wide x 500 mm long). The entire coated surface was then covered with a plastic container and allowed to stand at room temperature (25 °C) for 1 hour to obtain thin sheet polyimide wet gels (PI-WGs).

[0360] Thereafter, solvent substitution was carried out in the same manner as in Example 1 to obtain a thin polyimide NMP wet gel sheet (PI-WGs-NMP) and a bulk polyimide NMP wet gel (PI-WG-NMP). The physical properties of the obtained PI-WG-NMP and PI-WGs-NMP are shown in Table 9.

[0361] Comparative Example 3 Based on Non-Patent Document 1 (ACS Appl. Mater. Interfaces, (2015), 7, pp. 1240-1249), bulk polyimide NMP wet gel (PI-WG-NMP) and bulk polyimide NMP wet gel (PI-WGs-NMP) were prepared as follows: In a 100 mL glass vial, 4,4'-oxydianiline (ODA: 2.10 g; 10.5 mmol) was added to N-methyl-2-pyrrolidone (NMP: 41 g) and dissolved under magnetic stirring. Then, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 2.94 g; 10.0 mmol) powder was added and stirred at room temperature for 2 hours.

[0362] Acetic anhydride (8.15 g; 80 mmol) was then added to the above solution while stirring, and the mixture was stirred until homogenized. Triethylamine (1.0 g; 10 mmol) was then added, and the mixture was stirred until homogenized. After that, the mixture was stirred at room temperature for 15 minutes. In another 10 mL glass vial, a solution of 1,3,5-benzenetricarbonyl trichloride (BTC: 88 mg; 0.333 mmol) dissolved in 5 g of NMP was added, and the mixture was stirred at room temperature until homogenized.

[0363] Subsequently, a bulk polyimide NMP wet gel (PI-WG-NMP) and a polyimide NMP wet gel sheet (PI-WGs-NMP) were obtained by the same procedure as in Comparative Example 1. The physical properties of the obtained PI-WG-NMP and PI-WGs-NMP are shown in Table 9.

[0364] Comparative Example 4 With reference to Non-Patent Document 6 (ACS Appl. Mater. Interfaces, (2017), 9, pp. 8287-8296), bulk polyimide NMP wet gel (PI-WG-NMP) and bulk polyimide NMP wet gel (PI-WGs-NMP) were prepared according to the following procedure.

[0365] In a 100 mL glass vial, 4,4'-oxydianiline (ODA: 1.05 g; 5.25 mmol) was dissolved in N-methyl-2-pyrrolidone (NMP: 48 g) and stirred using a magnetic stirrer. 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 2.94 g; 10.0 mmol) powder was added while stirring the solution, and the mixture was stirred at room temperature for 2 hours. 9,9'-bis(4-aminophenyl)fluorene (BAFL: 1.83 g; 5.25 mmol) was added to the homogenized solution, and the mixture was stirred at room temperature for 30 minutes.

[0366] Acetic anhydride (8.15 g; 80 mmol) was then added to the above solution while stirring, and the mixture was stirred until homogenized. Triethylamine (1.0 g; 10 mmol) was then added, and the mixture was stirred until homogenized. After that, the mixture was stirred at room temperature for 15 minutes. In another 10 mL glass vial, a solution of 1,3,5-benzenetricarbonyl trichloride (BTC: 88 mg; 0.333 mmol) dissolved in 5 g of NMP was added, and the mixture was stirred at room temperature until homogenized.

[0367] Subsequently, a bulk polyimide NMP wet gel (PI-WG-NMP) and a polyimide NMP wet gel sheet (PI-WGs-NMP) were obtained by the same procedure as in Comparative Example 1. The physical properties of the obtained PI-WG-NMP and PI-WGs-NMP are shown in Table 9.

[0368] Comparative Example 5 Based on Non-Patent Document 3 (ACS Appl. Mater. Interfaces, (2019), 11, pp. 9425-9437), bulk polyimide NMP wet gel (PI-WG-NMP) and bulk polyimide NMP wet gel (PI-WGs-NMP) were prepared as follows. In a 100 mL glass vial, 1,4-bis(4-aminophenoxy)butane (BAP4: 2.04 g; 7.5 mmol) was added to N-methyl-2-pyrrolidone (NMP: 45 g) and stirred with a magnetic stirrer to dissolve. Then, while stirring the solution, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 3.04 g; 10.33 mmol) powder was added and stirred at room temperature for 2 hours. To the homogenized solution, 2,2'-dimethylbenzidine (DMBZ: 0.53 g; 2.5 mmol) was added, and the mixture was stirred at room temperature for 30 minutes to obtain a polyamic acid (PAA) solution.

[0369] Next, while stirring the polyamic acid (PAA) solution, a solution of 1,3,5-tris(4-aminophenoxy)benzene (TAPB: 0.089 g; 0.222 mmol) dissolved in 6.3 g of NMP was added to another 20 mL glass vial and stirred at room temperature for 10 minutes. Acetic anhydride (8.44 g; 82.7 mmol) was then added and stirred until homogenous. Then, triethylamine (3.13 g; 31 mmol) was added and stirred until homogenous.

[0370] Thereafter, sheet formation, molding, gelation, and solvent substitution were carried out in the same manner as in Comparative Example 1 to obtain a thin sheet-like polyimide NMP wet gel (PI-WGs-NMP) and a bulk polyimide NMP wet gel (PI-WG-NMP). The physical properties of the obtained thin sheet-like polyimide NMP wet gel (PI-WGs-NMP) and bulk polyimide NMP wet gel (PI-WG-NMP) are shown in Table 9.

[0371] Comparative Example 6 Non-Patent Document 2 (ACS Appl. Polym. Mater., (2020), 2, pp. 2179-2189) was used as a reference to prepare bulk polyimide NMP wet gel (PI-WG-NMP) and bulk polyimide NMP wet gel (PI-WGs-NMP) according to the following procedure. In a 100 mL glass vial, 2,2'-dimethylbenzidine (DMBZ: 0.53 g; 2.5 mmol) was added to N-methyl-2-pyrrolidone (NMP: 45 g) and stirred using a magnetic stirrer to dissolve. Then, while stirring the solution, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 2.99 g; 10.17 mmol) powder was added and stirred at 40 ° C until homogeneous. To the homogenized solution, 1,3-bis(4-aminophenoxy)-2,2-dimethylpropane (BAPN: 2.15 g; 7.5 mmol) was added, and the mixture was stirred at 40° C. until homogenized, to obtain a polyamic acid (PAA) solution.

[0372] Next, while stirring the polyamic acid (PAA) solution, a solution of 1,3,5-tris(4-aminophenoxy)benzene (TAPB: 0.044 g; 0.111 mmol) dissolved in 6.4 g of NMP was added to another 20 mL glass vial and stirred at room temperature for 10 minutes. Acetic anhydride (8.3 g; 81.3 mmol) was then added and stirred until homogenous. Then, triethylamine (2.05 g; 20.3 mmol) was added and stirred until homogenous.

[0373] Thereafter, sheet formation, molding, gelation, and solvent substitution were carried out in the same manner as in Comparative Example 1 to obtain a thin sheet-like polyimide NMP wet gel (PI-WGs-NMP) and a bulk polyimide NMP wet gel (PI-WG-NMP). The physical properties of the obtained thin sheet-like polyimide NMP wet gel (PI-WGs-NMP) and bulk polyimide NMP wet gel (PI-WG-NMP) are shown in Table 9.

[0374] Comparative Example 7 A porous polyimide was prepared using the following procedure, based on Patent Document 3 (China Patent No. 108203516): In a 100 mL glass vial, 2,2'-dimethylbenzidine (DMBZ: 2.03 g; 9.55 mmol) was mixed with N-methyl-2-pyrrolidone (NMP: 96.8 g) and dissolved by magnetic stirring. Then, while stirring, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 2.94 g; 10.0 mmol) powder was added and stirred at 25°C for 24 hours to obtain a polyamic acid (PAA) solution.

[0375] Then, while stirring the polyamic acid (PAA) solution, a solution of 1,3,5-tris(4-aminophenoxy)benzene (TAPB: 0.12 g; 0.3 mmol) dissolved in 3.0 g of NMP in another 20 mL glass vial was added, and the mixture was stirred at 25° C. for 5 minutes.

[0376] Bulk polyamic acid wet gels (PAA-WG) were prepared by transferring the solution obtained above into a PFA mold (φ100 mm, depth 30 mm) to a thickness of approximately 3 mm and allowing it to stand at room temperature for 10 minutes. Thin polyamic acid wet gel sheets (PAA-WGs) were prepared by applying the solution obtained above to a Kapton® film (Toray-DuPont Co., Ltd., 250 mm × 600 mm) as a substrate film using a bar coater (Matsuo Sangyo Co., Ltd., bar No. 200, wet film thickness approximately 300 μm) (coating area: approximately 200 mm wide × approximately 500 mm long) and allowing it to stand at room temperature (25 °C) for 10 minutes.

[0377] This PAA-WG was left standing at 60°C for 24 hours in a SUS sealed container saturated with NMP, then removed from the mold and immersed in a mixed solution of acetic anhydride (90.0 g; 0.88 mol), pyridine (90 g; 1.14 mol), and 120 g of NMP at -5°C for 8 hours. The solution was then heated to 25°C and left standing for 6 hours, then heated to 80°C and left standing for 10 hours to obtain bulk polyimide wet gels (PI-WG) or thin sheet polyimide wet gels (PI-WGs).

[0378] Thereafter, solvent substitution was carried out in the same manner as in Comparative Example 1 to obtain a thin sheet-like polyimide NMP wet gel (PI-WGs-NMP) and a bulk polyimide NMP wet gel (PI-WG-NMP). The physical properties of the obtained thin sheet-like polyimide NMP wet gel (PI-WGs-NMP) and bulk polyimide NMP wet gel (PI-WG-NMP) are shown in Table 9.

[0379] [Table 8]

[0380] [Table 9]

[0381] <<<Example V: Fifth embodiment>>> <<Measurement and Evaluation Methods>> <Degree of polymerization (n)> The degree of polymerization (n) was adjusted based on the molar ratio of diamine to acid dianhydride in the polymerization step. In the present disclosure, in Examples 1 to 16 and Comparative Examples 2 and 5 to 7, the molar ratio of diamine to acid dianhydride in the polymerization step was n:n+1. In Comparative Examples 1, 3, and 4, the molar ratio of diamine to acid dianhydride in the polymerization step was n+1:n.

[0382] <Solid content> The solid content of the charged components was considered to be the solid content (%) of the polyamic acid wet gel (PAA-WG).

[0383] <Measurement of average pore size and BET specific surface area of porous polyimide> The measurement was carried out in the same manner as in Example I.

[0384] <Measurement of Bulk Density of Porous Polyimide> The measurement was carried out in the same manner as in Example I.

[0385] <Preparation of 300°C heat-treated samples> It was prepared in the same manner as in Example III.

[0386] <Production example of bulk (thick sheet) porous polyimide> [Example 1] In a 100 mL glass vial, p-phenylenediamine (PPDA: 1.08 g; 10.0 mmol) was dissolved in N-methyl-2-pyrrolidone (NMP: 29.0 g) with magnetic stirring. Then, pyromellitic anhydride (PMDA: 2.4 g; 11.0 mmol) powder was added with stirring. The solution was stirred at room temperature (25 °C) for 1 hour to obtain a polyamic acid (PAA) solution.

[0387] A solution of 1,3,5-tris(4-aminophenyl)benzene (TAB: 0.234 g; 0.667 mmol) dissolved in 4.5 g of NMP was added to the polyamic acid (PAA) solution in a separate 10 mL glass vial and stirred for 1 minute. The resulting solution was transferred to a PTA mold (Φ100 mm, depth 30 mm) to a thickness of approximately 3 mm and allowed to stand at room temperature (25 °C) for 10 minutes to obtain a non-flowable polyamic acid wet gel (PAA-WG).

[0388] This PAA-WG was left to stand in a sealed SUS container saturated with NMP at room temperature (25°C) for 24 hours, then removed from the mold and immersed in a mixed solution of acetic anhydride (27.0 g; 264 mmol), triethylamine (3.3 g; 33 mmol), and 270 g of NMP at room temperature (25°C) for 6 hours to obtain a polyimide wet gel (PI-WG).

[0389] This PI-WG was immersed in a solution of acetone:NMP = 1:1 by weight for 24 hours, washed with acetone, and then immersed in acetone for another 24 hours three times. The PI-WG was then dried using a supercritical dryer (manufactured by Rexxam Co., Ltd., "SCRD6") to obtain porous polyimide (pPI).

[0390] [Examples 2 to 8, 10 to 12] Porous polyimide (pPI) was obtained in the same manner as in Example 1, except that the diamine, tetracarboxylic acid anhydride, crosslinking agent, amount of imidization reagent, and solvent were changed to those shown in Tables 10 and 11, respectively.

[0391] [Example 9] A porous polyimide (pPI) was obtained in the same manner as in Example 1, except that the conditions for chemical imidization by immersion in the solution were 60° C. and 1 hour.

[0392] [Examples 13 to 16] The same procedure as in Example 12 was carried out except that the conditions for chemical imidization by solution immersion were set as shown in Table 11, to obtain porous polyimide (pPI).

[0393] [Comparative Example 1] Based on Non-Patent Document 1 (ACS Appl. Mater. Interfaces, (2015), 7(2), 1240-1249), porous polyimide pPI was prepared as follows: In a 100 mL glass vial, 2,2'-diaminobenzidine (m-Tolidine; DMBZ: 2.23 g; 10.5 mmol) was added to N-methyl-2-pyrrolidone (NMP: 45.7 g) and dissolved while stirring using a magnetic stirrer. Then, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 2.942 g; 10.0 mmol) powder was added and stirred at room temperature (25 °C) for 2 hours to obtain a polyamic acid (PAA) solution.

[0394] Then, acetic anhydride (8.16 g; 80 mmol) was added to the polyamic acid (PAA) solution while stirring, and the mixture was stirred until homogeneous. Further, triethylamine (1.01 g; 10 mmol) was added, and the mixture was stirred until homogeneous. After that, the mixture was stirred at room temperature (25°C) for 15 minutes to obtain a polyimide (PI) solution.

[0395] A solution of 1,3,5-benzenetricarbonyl trichloride (BTC: 89 mg; 0.333 mmol) dissolved in 1.68 g of NMP in a separate 10 mL glass vial was added to the polyimide (PI) solution and stirred at room temperature until homogeneous. After stirring, the solution was transferred to a PTFE mold (Φ100 mm, depth 30 mm) and allowed to stand at room temperature for 30 minutes to obtain a non-flowable polyimide wet gel (PI-WG).

[0396] The resulting PI-WG was placed in a sealed stainless steel container saturated with NMP at room temperature (25°C) for 24 hours, then immersed in a solution of acetone:NMP (mass ratio) = 25:75 for 24 hours, a solution of acetone:NMP (mass ratio) = 50:50 for 24 hours, and a solution of acetone:NMP (mass ratio) = 75:25 for 24 hours. The solvent was then replaced by washing with acetone and immersion in acetone for 24 hours three times. The acetone-immersed wet polyimide gel was dried using the supercritical drying apparatus described above to obtain porous polyimide (pPI).

[0397] Comparative Example 2 A porous polyimide (pPI) was prepared using the following procedure, based on Non-Patent Document 5 (ACS Appl. Mater. Interfaces, (2012), 4(2), 536-544). In a 100 mL glass vial, 2,2'-diaminobenzidine (m-Tolidine; DMBZ: 2.123 g; 10.0 mmol) was mixed with N-methyl-2-pyrrolidone (NMP: 41.6 g) and dissolved by magnetic stirring. While stirring, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 3.09 g; 10.5 mmol) powder was added and stirred at room temperature for 2 hours to obtain a polyamic acid (PAA) solution.

[0398] Next, while stirring the PAA solution, a solution of 1,3,5-tris(4-aminophenoxy)benzene (TAPB: 0.133 g; 0.333 mmol) dissolved in 6.5 g of NMP was added to a 20 mL glass vial and stirred at room temperature. After 10 minutes, acetic anhydride (8.58 g; 84 mmol) and pyridine (6.64 g; 84 mmol) were added to the solution and stirred until homogeneous. The solution was then transferred to a PFA mold (Φ100 mm, depth 30 mm) to a thickness of approximately 3 mm and allowed to stand at room temperature for 30 minutes to obtain a non-flowable polyimide wet gel (PI-WG).

[0399] Solvent substitution and supercritical drying were carried out in the same manner as in Comparative Example 1, to obtain a porous polyimide (pPI).

[0400] Comparative Example 3 Referring to Non-Patent Document 7 (Polymer, (2019), 176(2), 213-226), the diamine, tetracarboxylic acid anhydride, crosslinker, and their added weights were changed to those shown in Table 12, and the same procedure as in Comparative Example 1 was carried out to obtain porous polyimide pPI.

[0401] Comparative Example 4 Referring to Non-Patent Document 7 (Polymer, (2019), 176(2), 213-226), the diamine, tetracarboxylic acid anhydride, crosslinker, and their added weights were changed to those shown in Table 12, and the same procedure as in Comparative Example 1 was carried out to obtain a porous polyimide (pPI).

[0402] Comparative Example 5 The same procedure as in Comparative Example 1 was repeated to obtain porous polyimide pPI, except that the diamine, tetracarboxylic anhydride, crosslinker, and their weight amounts were changed to those listed in Table 13. In a 100 mL glass vial, p-phenylenediamine (PPDA: 1.08 g; 10.0 mmol) was added to N-methyl-2-pyrrolidone (NMP: 29.0 g) and dissolved using a magnetic stirrer. Then, pyromellitic anhydride (PMDA: 2.40 g; 11.0 mmol) powder was added while stirring. Subsequently, acetic anhydride (8.16 g; 80 mmol) was added to the solution while stirring, and the mixture was stirred until homogeneous. Triethylamine (1.01 g; 10 mmol) was added, and the solution rapidly thickened, making it difficult to stir.

[0403] Comparative Example 6 The same procedure as in Comparative Example 1 was repeated to obtain porous polyimide pPI, except that the diamine, tetracarboxylic acid anhydride, crosslinker, and their weight amounts were changed to those listed in Table 13. In a 100 mL glass vial, 2,2'-dimethylbenzidine (DMBZ: 2.12 g; 10.0 mmol) was added to N-methyl-2-pyrrolidone (NMP: 38.4 g) and dissolved using a magnetic stirrer. Then, while stirring, pyromellitic anhydride (PMDA: 2.40 g; 11.0 mmol) powder was added. Subsequently, acetic anhydride (8.16 g; 80 mmol) was added to the solution while stirring, and the mixture was stirred until homogeneous. Triethylamine (1.0 g; 10 mmol) was added, and the solution rapidly thickened, making it difficult to stir.

[0404] Comparative Example 7 We attempted to obtain porous polyimide pPI by referring to Patent Document 5 (ACS Appl. Mater. Interfaces, (2012), 4(2), 536-544), changing the diamine, tetracarboxylic anhydride, crosslinker, and their weight amounts to those listed in Table 13. In a 100 mL glass vial, 2,2'-dimethylbenzidine (DMBZ: 2.03 g; 9.55 mmol) was added to N-methyl-2-pyrrolidone (NMP: 96.8 g) and stirred with a magnetic stirrer to dissolve. Then, while stirring, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 2.94 g; 10.0 mmol) powder was added and stirred at 25 °C for 24 hours to obtain a polyamic acid (PAA) solution.

[0405] To the resulting polyamic acid (PAA) solution, a solution of 1,3,5-tris(4-aminophenoxy)benzene (TAPB: 0.120 g; 0.30 mmol) dissolved in 3.0 g of NMP was added in another 20 mL glass vial, and the mixture was stirred for 5 minutes at 25° C. The resulting solution was transferred to a sealable PFA mold (Φ100 mm, depth 30 mm) to a thickness of approximately 3 mm, and allowed to stand at 60° C. for 24 hours to obtain a non-flowable polyamic acid wet gel (PAA-WG).

[0406] This PAA-WG was immersed in a mixed solution of acetic anhydride (90.0 g; 882 mmol), pyridine (90.0 g; 1138 mmol), and NMP (120 g) at 25°C for 6 hours to obtain a polyimide wet gel (PI-WG). During this process, the shape of the wet gel was significantly deformed from the disk-like shape of the mold to a shape closer to a bowl.

[0407] Further, solvent substitution and supercritical drying were carried out in the same manner as in Example 1 to obtain porous polyimide (pPI).

[0408] [Table 10]

[0409] [Table 11]

[0410] [Table 12]

[0411] [Table 13]

[0412] Samples of the examples and comparative examples that were heat-treated at 300°C were prepared by the method described above in "Preparation of samples that were heat-treated at 300°C." The changes in physical properties before and after heating are shown in Tables 14 to 16 below.

[0413] [Table 14]

[0414] [Table 15]

[0415] [Table 16]

[0416] <Production example of thin porous polyimide sheet> [Example 17] In a 100 mL glass vial, p-phenylenediamine (PPDA: 1.08 g; 10.0 mmol) was dissolved in N-methyl-2-pyrrolidone (NMP: 29.0 g) by magnetic stirring. Then, pyromellitic anhydride (PMDA: 2.34 g; 11.0 mmol) powder was added while stirring. The solution was stirred at room temperature (25 °C) for 1 hour to obtain a polyamic acid (PAA) solution.

[0417] To the polyamic acid (PAA) solution, a solution of 1,3,5-tris(4-aminophenyl)benzene (TAB: 0.234 g; 0.667 mmol) dissolved in 4.5 g of NMP was added to a separate 10 mL glass vial and stirred for 1 minute to homogenize. The resulting solution was applied to a Kapton® film (Toray-DuPont Co., Ltd., 250 mm x 600 mm) substrate film (coated area: approximately 200 mm wide x 500 mm long) using a bar coater (Matsuo Sangyo Co., Ltd., Bar No. 200, wet film thickness approximately 100 μm). The resulting solution was then allowed to stand at room temperature (25 °C) for 5 minutes to yield polyamic acid wet gel sheets (PAA-WGs).

[0418] The PAA-WGs were left standing in a sealed stainless steel container saturated with NMP at room temperature (25°C) for 24 hours, and then immersed in a mixed solution of acetic anhydride (27.0 g; 264 mmol), triethylamine (3.3 g; 33 mmol), and 540 g of NMP at 25°C for 6 hours to obtain polyimide wet gel (PI-WG).

[0419] This PI-WG was immersed in a solution of acetone:NMP = 1:1 by mass for 24 hours, then washed with acetone and immersed in acetone for 24 hours three times. After peeling it off from the Kapton film, it was dried using the above-mentioned supercritical drying apparatus to obtain a porous polyimide sheet (pPIs).

[0420] [Comparative Example 8] In a 100 mL glass vial, 2,2'-diaminobenzidine (m-Tolidine; DMBZ: 2.23 g; 10.5 mmol) was added to N-methyl-2-pyrrolidone (NMP: 45.7 g) and dissolved under magnetic stirring. Then, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 2.942 g; 10.0 mmol) powder was added and stirred at room temperature (25°C) for 2 hours to obtain a polyamic acid (PAA) solution.

[0421] Then, acetic anhydride (8.16 g; 80 mmol) was added to the polyamic acid (PAA) solution while stirring, and the mixture was stirred until homogeneous. Further, triethylamine (1.01 g; 10 mmol) was added, and the mixture was stirred until homogeneous. After that, the mixture was stirred at room temperature (25°C) for 15 minutes to obtain a polyimide (PI) solution.

[0422] A solution of 1,3,5-benzenetricarbonyl trichloride (BTC: 89 mg; 0.333 mmol) dissolved in 1.68 g of NMP was added to the polyimide (PI) solution in a separate 10 mL glass vial and stirred at room temperature until homogeneous. After 5 minutes, the resulting solution was applied to a Kapton® film (Toray-DuPont Co., Ltd., 250 mm x 600 mm) substrate film (coated area: approximately 200 mm wide x 500 mm long) using a bar coater (Matsuo Sangyo Co., Ltd., Bar No. 200, wet film thickness approximately 100 μm). After 25 minutes at room temperature (25 °C), the coated film cracked when an attempt was made to remove the Kapton film. A polyimide wet gel sheet could not be obtained.

[0423] [Table 17]

[0424] [Table 18]

[0425] <<<Example VI: Sixth embodiment>>> <<Measurement and Evaluation Methods>> <Measurement of Degree of Polymerization (n)> The degree of polymerization (n) was adjusted based on the molar ratio of diamine to acid dianhydride in the polymerization step. In the present disclosure, in Examples 1 to 7 and Comparative Examples 2, 6, and 7, the molar ratio of diamine to acid dianhydride in the polymerization step was set to n:n+1. In Comparative Examples 1 and 3 to 5, the molar ratio of diamine to acid dianhydride in the polymerization step was set to n+1:1.

[0426] <Solid content> The solid content of the charged components was considered to be the solid content (%) of the polyamic acid wet gel (PAA-WG).

[0427] <Measurement of average pore size and BET specific surface area of porous resin sheet> The measurement was carried out in the same manner as in Example I.

[0428] <Measurement of Bulk Density of Porous Resin Sheet> The bulk density of the porous polyimide in Example I was measured in the same manner.

[0429] <Carbonization of porous resin sheet> A porous resin sheet (50 mm x 50 mm) was heated to 1100°C at a heating rate of 5°C / min in a horizontal circular furnace manufactured by Koyo Thermo Co., Ltd. under a nitrogen atmosphere, held at 1100°C for 1 hour, and then cooled to 50°C at a cooling rate of 5°C / min to obtain a porous carbon sheet.

[0430] <Measurement of average pore size, BET specific surface area, and bulk density of porous carbon sheet> The average pore diameter, specific surface area and bulk density of the porous carbon sheet were measured in the same manner as in the measurement of the average pore diameter, specific surface area and bulk density of the porous resin sheet.

[0431] Examples and Comparative Examples [Example 1] In a 100 mL glass vial, p-phenylenediamine (PPDA: 1.08 g; 10.0 mmol) was dissolved in N-methyl-2-pyrrolidone (NMP: 29.0 g) by magnetic stirring. Then, pyromellitic anhydride (PMDA: 2.40 g; 11.0 mmol) powder was added while stirring. The solution was stirred at room temperature (25 °C) for 1 hour to obtain a polyamic acid (PAA) solution.

[0432] To the polyamic acid (PAA) solution, a solution of 1,3,5-tris(4-aminophenyl)benzene (TAB: 0.234 g; 0.667 mmol) dissolved in 4.5 g of NMP was added to a separate 10 mL glass vial and stirred for 1 minute to achieve uniformity. The resulting solution was applied to a Kapton® film (Toray-DuPont Co., Ltd., 250 mm x 600 mm) substrate film (coated area: approximately 200 mm wide x 500 mm long) using a bar coater (Matsuo Sangyo Co., Ltd., Bar No. 200, wet film thickness approximately 100 μm). The resulting solution was then allowed to stand at room temperature (25 °C) for 5 minutes to yield polyamic acid wet gel sheets (PAA-WGs).

[0433] The PAA-WGs were left standing in a sealed stainless steel container saturated with NMP at room temperature (25°C) for 24 hours, and then immersed in a mixed solution of acetic anhydride (27.0 g; 264 mmol), triethylamine (3.3 g; 33 mmol), and 270 g of NMP at 25°C for 6 hours to obtain polyimide wet gel (PI-WG).

[0434] This PI-WG was immersed in a solution of acetone:NMP = 1:1 by weight for 24 hours, washed with acetone, and immersed in acetone for 24 hours three times. After peeling it off from the Kapton film, it was dried using a supercritical dryer (Rexxam Co., Ltd., "SCRD6") to obtain a porous polyimide sheet (pPIs). The BET specific surface area of the resulting pPIs was 512 m. 2 / g.

[0435] The obtained pPIs was cut into a 50 mm × 50 mm piece and carbonized under the above carbonization conditions to obtain a porous carbon sheet pCs. The BET specific surface area of the obtained pCs was 448 m 2 / g.

[0436] [Examples 2 to 8] In the same manner as in Example 1, the diamine, tetracarboxylic acid anhydride, crosslinking agent, amount of imidization reagent, and solvent were changed to those shown in Table 19, and the same operations as in Example 1 were carried out to obtain a porous polyimide sheet pPIs and a porous carbon sheet pCs.

[0437] [Comparative Example 1] Porous polyimide sheets (pPIs) were prepared using the following procedure, based on Non-Patent Document 6 (ACS Appl. Mater. Interfaces, (2017), 9(9), 8287-8296). In a 100 mL glass vial, 4,4'-oxydianiline (ODA: 1.05 g; 5.25 mmol) was added to N-methyl-2-pyrrolidone (NMP: 51.5 g) and dissolved under magnetic stirring. Then, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 2.94 g; 10.0 mmol) powder was added and stirred at room temperature (25 °C) for 2 hours. To the homogenized solution, 9,9'-bis(4-aminophenyl)fluorene (BAFL: 1.83 g; 5.25 mmol) was added and stirred at room temperature for 30 minutes to obtain a polyamic acid (PAA) solution.

[0438] Then, acetic anhydride (8.16 g; 80 mmol) was added to the polyamic acid (PAA) solution while stirring, and the mixture was stirred until homogeneous. Further, triethylamine (1.01 g; 10 mmol) was added, and the mixture was stirred until homogeneous. After that, the mixture was stirred at room temperature (25°C) for 15 minutes to obtain a polyimide (PI) solution.

[0439] A solution of 1,3,5-benzenetricarbonyl trichloride (BTC: 89 mg; 0.333 mmol) dissolved in 1.68 g of NMP was added to the polyimide (PI) solution in a separate 10 mL glass vial and stirred at room temperature until homogenous. The resulting solution was applied to a Kapton® film (Toray-DuPont Co., Ltd., 250 mm x 600 mm) substrate film (coated area: approximately 200 mm wide x 500 mm long) using a bar coater (Matsuo Sangyo Co., Ltd., Bar No. 200, wet film thickness approximately 300 μm). The resulting solution was then allowed to stand at room temperature (25 °C) for 1 hour to yield polyimide wet gel sheets (PI-WGs).

[0440] The resulting PI-WGs were placed in a sealed SUS container saturated with NMP at room temperature (25°C) for 24 hours. They were then immersed in a solution of acetone:NMP = 25:75 (mass ratio) for 24 hours, a solution of acetone:NMP (mass ratio) = 50:50 for 24 hours, and a solution of acetone:NMP (mass ratio) = 75:25 for 24 hours. The solvent was then replaced by repeating washing with acetone and immersion in acetone for 24 hours three times. The acetone-immersed polyimide wet gel sheet was dried using the supercritical drying apparatus described above to obtain a porous polyimide sheet (pPIs). The BET specific surface area of the resulting pPIs was 472 m. 2 / g.

[0441] The obtained pPIs was cut into a piece of 50 mm x 50 mm, and carbonization was attempted under the same carbonization conditions as in Example 1. However, the sheet shape was significantly deformed, and a porous carbon sheet could not be obtained. The BET specific surface area of the significantly deformed carbonized product was below the lower limit of the above-mentioned measuring device (10 m 2 / g or less).

[0442] Comparative Example 2 Porous polyimide sheets (pPIs) were prepared using the following procedure, based on Non-Patent Document 5 (ACS Appl. Mater. Interfaces, (2012), 4(2), 536-544). In a 100 mL glass vial, 2,2'-dimethylbenzidine (m-tolidine; DMBZ: 2.123 g; 10.0 mmol) was added to N-methyl-2-pyrrolidone (NMP: 41.6 g) and dissolved under magnetic stirring. Then, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 3.09 g; 10.5 mmol) powder was added and stirred at room temperature (25°C) for 2 hours to obtain a polyamic acid (PAA) solution.

[0443] Then, while stirring the polyamic acid (PAA) solution, a solution of 1,3,5-tris(4-aminophenoxy)benzene (TAPB: 0.133 g; 0.333 mmol) dissolved in 6.5 g of NMP in another 20 mL glass vial was added and stirred at room temperature for 10 minutes. After that, acetic anhydride (8.58 g; 84 mmol) and pyridine (6.6 g; 84 mmol) were added and stirred for 5 minutes until the mixture became homogeneous.

[0444] Thereafter, sheet forming, gelation, solvent substitution, and supercritical drying were carried out in the same manner as in Comparative Example 1 to obtain a porous polyimide sheet (pPIs). However, during carbonization of the pPIs, the sample shape changed significantly, as in Comparative Example 1, and a porous carbon sheet could not be obtained. The physical properties of the obtained pPIs and the significantly deformed carbonized product are shown in Table 20.

[0445] Comparative Example 3 As in Comparative Example 1, the diamine, tetracarboxylic anhydride, crosslinker, and their added weights were changed to those shown in Table 20 with reference to Non-Patent Document 7 (Polymer, (2019), 176(2), 213-226), and the same procedure as in Comparative Example 1 was performed to obtain a porous polyimide sheet (pPIs). However, during carbonization, as in Comparative Example 1, the sample shape changed significantly, and a porous carbon sheet could not be obtained. The physical properties of the obtained pPIs and the significantly deformed carbonized product are shown in Table 20.

[0446] Comparative Example 4 As in Comparative Example 1, the diamine, tetracarboxylic anhydride, crosslinker, and their added weights were changed to those shown in Table 21 with reference to Non-Patent Document 7 (Polymer, (2019), 176(2), 213-226), and the same procedure as in Comparative Example 1 was carried out to obtain a porous polyimide sheet (pPIs). However, as in Comparative Example 1, the sample shape changed significantly during carbonization of the pPIs, and a porous carbon sheet could not be obtained. The physical properties of the obtained pPIs and the significantly deformed carbonized product are shown in Table 21.

[0447] Comparative Example 5 Porous polyimide sheets (pPIs) were obtained in the same manner as in Example 1, except that the diamine, tetracarboxylic anhydride, crosslinking agent, and their added weights were changed to those shown in Table 21. However, during carbonization of the pPIs, the sample shape changed significantly, as in Comparative Example 1, and a porous carbon sheet could not be obtained. The physical properties of the obtained pPIs and the significantly deformed carbonized product are shown in Table 21.

[0448] Comparative Example 6 Based on Non-Patent Document 3 (ACS Appl. Mater. Interfaces, (2019), 11, 9425-9437), porous polyimide sheets (pPIs) were prepared using the following procedure. In a 100 mL glass vial, 1,4-bis(4-aminophenoxy)butane (BAP4: 2.04 g; 7.5 mmol) was added to N-methyl-2-pyrrolidone (NMP: 45 g) and stirred using a magnetic stirrer to dissolve. Then, while stirring the solution, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 3.04 g; 10.33 mmol) powder was added and stirred at room temperature for 2 hours. To the homogeneous solution, 2,2'-dimethylbenzidine (DMBZ: 0.53 g; 2.5 mmol) was added and stirred at room temperature for 30 minutes to obtain a polyamic acid (PAA) solution.

[0449] Next, while stirring the polyamic acid (PAA) solution, a solution of 1,3,5-tris(4-aminophenoxy)benzene (TAPB: 0.089 g; 0.222 mmol) dissolved in 6.3 g of NMP was added to another 20 mL glass vial and stirred at room temperature for 10 minutes. Acetic anhydride (8.44 g; 82.7 mmol) was then added and stirred until homogenous. Then, triethylamine (3.13 g; 31 mmol) was added and stirred until homogenous.

[0450] Thereafter, sheet forming, gelation, solvent substitution, and supercritical drying were carried out in the same manner as in Comparative Example 1 to obtain a porous polyimide sheet (pPIs). However, in carbonizing the pPIs, the sample shape changed significantly, as in Comparative Example 1, and a porous carbon sheet could not be obtained. The physical properties of the obtained pPIs and the significantly deformed carbonized product are shown in Table 21.

[0451] Comparative Example 7 Based on Non-Patent Document 2 (ACS Appl. Polym. Mater., (2020), 2, 2179-2189), porous polyimide sheets (pPIs) were prepared using the following procedure. In a 100 mL glass vial, 2,2'-dimethylbenzidine (DMBZ: 0.53 g; 2.5 mmol) was added to N-methyl-2-pyrrolidone (NMP: 45 g) and stirred using a magnetic stirrer to dissolve. Then, while stirring the solution, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA: 2.99 g; 10.17 mmol) powder was added and stirred at 40 ° C until homogenous. 1,3-bis(4-aminophenoxy)-2,2-dimethylpropane (BAPN: 2.15 g; 7.5 mmol) was added to the homogenized solution and stirred at 40 ° C until homogenous, obtaining a polyamic acid (PAA) solution.

[0452] Next, while stirring the polyamic acid (PAA) solution, a solution of 1,3,5-tris(4-aminophenoxy)benzene (TAPB: 0.044 g; 0.111 mmol) dissolved in 6.4 g of NMP was added to another 20 mL glass vial and stirred at room temperature for 10 minutes. Acetic anhydride (8.3 g; 81.3 mmol) was then added and stirred until homogenous. Then, triethylamine (2.05 g; 20.3 mmol) was added and stirred until homogenous.

[0453] Thereafter, sheet forming, gelation, solvent substitution, and supercritical drying were carried out in the same manner as in Comparative Example 1 to obtain a porous polyimide sheet (pPIs). However, in carbonizing the pPIs, the sample shape changed significantly, as in Comparative Example 1, and a porous carbon sheet could not be obtained. The physical properties of the obtained pPIs and the significantly deformed carbonized product are shown in Table 21.

[0454] [Table 19]

[0455] [Table 20]

[0456] [Table 21]

[0457] [Example 9] A polyvinylidene fluoride (PVDF) gel sheet was dehydrofluorinated (de-HF), and the resulting HF-depleted PVDF gel sheet was subjected to supercritical drying to produce a porous PVDF sheet. The resulting porous PVDF sheet was then carbonized to produce a porous carbon sheet. The specific procedure is as follows.

[0458] First, 35 ml of propylene carbonate (PC) was added to a 100 ml three-necked flask equipped with a condenser and a thermometer, and 2.33 g of PVDF powder (Solef6020, manufactured by Solvay) was added while stirring with a magnetic stirrer.

[0459] The flask was immersed in a warm bath and heated to 90°C while stirring to dissolve the PVDF powder. The heated PVDF PC solution was transferred onto a Kapton film substrate and spread to a width of approximately 200 mm and a length of approximately 500 mm using a bar coater (wet film thickness approximately 100 μm), and then allowed to stand at room temperature. After approximately 3 minutes, the solution gelled, yielding a PVDF wet gel sheet.

[0460] The obtained PVDF wet gel sheet was immersed in a solution of 1,8-diazabicyclo[5.4.0]-7-undecene (DBU), a strong organic base, to remove HF. Specifically, the PVDF wet gel sheet, still attached to the Kapton film, was immersed in approximately 50 ml of a 1 M DBU solution in a mixture of PC and ethanol (PC / EtOH = 75 / 25 vol) at room temperature for 24 hours. Subsequently, the sheet was immersed at 70°C for 24 hours to obtain a HF-free PVDF wet gel sheet.

[0461] The resulting HF-free PVDF wet gel sheet was immersed in ethanol, and the ethanol was replaced every 24 hours, a total of three times, to replace the solvent in the gel. The solvent-substituted HF-free PVDF wet gel sheet was peeled off from the Kapton film and subjected to supercritical drying under the same conditions as for the polyimide wet gel sheet, yielding a porous PVDF sheet. The BET specific surface area, bulk density, and average pore diameter of the resulting porous PVDF sheet were 256 m². 2 / g, 0.11g / cm 3 , and 131 nm.

[0462] The obtained porous PVDF sheet was carbonized under the same conditions as the porous polyimide sheet to obtain a porous carbon sheet. The BET specific surface area, bulk density, and average pore diameter of the obtained porous carbon sheet were 237 m 2 / g (retention rate 92.6%), 0.13g / cm 3 (increase rate 18.1%), and 119nm (maintenance rate 90.8%). [Industrial Applicability]

[0463] The porous polyimide according to one embodiment of the present disclosure can be suitably applied to various uses such as a material for producing a porous carbon sheet. The method according to one aspect of the present disclosure can be used to produce polyimide wet gels and porous polyimides. A porous carbon sheet according to one embodiment of the present disclosure has pores on the submicron order and can be used in fields such as catalyst supports, electrode materials, and filter materials.

Claims

1. A porous polyimide having an average pore size (D) determined by small-angle X-ray scattering of 1.0 nm or more and 7.0 nm or less, the polyimide constituting the porous polyimide has a polyimide main skeleton and a crosslinking structure that crosslinks the polyimide main skeleton, The porous polyimide has a crosslinked structure formed by a trivalent or higher group derived from an optionally substituted monocyclic or polycyclic aromatic ring, or a trivalent or higher group derived from a linked aromatic ring in which a plurality of optionally substituted aromatic rings are linked to each other by a direct bond or a bond via a heteroatom.

2. The magnitude of the scattering vector q of small-angle X-ray scattering is 0.025 nm -1 More than 0.075 nm -1 2. The porous polyimide according to claim 1, wherein the minimum value of the differential coefficient when the logarithm of the scattering intensity I(q) log[I(q)] is differentiated by the logarithm of the scattering vector q log[q] is -1.0 or more and 0.0 or less in the following range:

3. Based on the pore volume (V) and BET specific surface area (A) determined by gas adsorption method, the following formula: L=4V / A 2. The porous polyimide according to claim 1, wherein the average pore diameter (L) obtained by the following formula is 5 nm or more and 500 nm or less.

4. 2. The porous polyimide according to claim 1, which has a flexural modulus of elasticity of 100 MPa or more in a three-point bending test.

5. 2. The porous polyimide according to claim 1, which has a flexural modulus of elasticity of 200 MPa or more in a three-point bending test.

6. 2. The porous polyimide according to claim 1, which has a bending strength of 5 MPa or more in a three-point bending test.

7. 2. The porous polyimide according to claim 1, which has a bending strength of 10 MPa or more in a three-point bending test.

8. Bulk density is 0.05 g / cm 3 0.50g / cm or more 3 2. The porous polyimide of claim 1, wherein:

9. BET specific surface area is 100m 2 / g or more 2,000m 2 2. The porous polyimide according to claim 1, wherein the molecular weight of the porous polyimide is 1 / g or less

10. The porous polyimide according to claim 1 , which has a sheet shape.

11. Based on the pore volume (V) and BET specific surface area (A) determined by gas adsorption method, the following formula: L=4V / A The average pore diameter (L) obtained by A porous polyimide having a flexural modulus of 150 MPa or more in a three-point bending test, the polyimide constituting the porous polyimide has a polyimide main skeleton and a crosslinking structure that crosslinks the polyimide main skeleton, The porous polyimide has a crosslinked structure formed by a trivalent or higher group derived from an optionally substituted monocyclic or polycyclic aromatic ring, or a trivalent or higher group derived from a linked aromatic ring in which a plurality of optionally substituted aromatic rings are linked to each other by a direct bond or a bond via a heteroatom.

12. 12. The porous polyimide according to claim 11, which has a flexural modulus of elasticity of 200 MPa or more in a three-point bending test.

13. Based on the pore volume (V) and BET specific surface area (A) determined by gas adsorption method, the following formula: L=4V / A The average pore diameter (L) obtained by A porous polyimide having a bending strength of 10 MPa or more in a three-point bending test, the polyimide constituting the porous polyimide has a polyimide main skeleton and a crosslinking structure that crosslinks the polyimide main skeleton, The porous polyimide has a crosslinked structure formed by a trivalent or higher group derived from an optionally substituted monocyclic or polycyclic aromatic ring, or a trivalent or higher group derived from a linked aromatic ring in which a plurality of optionally substituted aromatic rings are linked to each other by a direct bond or a bond via a heteroatom.

14. Based on the pore volume (V) and BET specific surface area (A) determined by gas adsorption method, the following formula: L=4V / A The average pore diameter (L) obtained by The bending modulus in a three-point bending test is 50 MPa or more, It is composed of a polyimide main skeleton having an aromatic group in the molecular skeleton and a crosslinked structure having an aromatic group in the molecular skeleton. The porous polyimide has a crosslinked structure formed by a trivalent or higher group derived from an optionally substituted monocyclic or polycyclic aromatic ring, or a trivalent or higher group derived from a linked aromatic ring in which a plurality of optionally substituted aromatic rings are linked to each other by a direct bond or a bond via a heteroatom.

15. Bulk density is 0.05 g / cm 3 0.50g / cm or more 3 15. The porous polyimide according to claim 11, 13 or 14, wherein:

16. BET specific surface area is 10m 2 / g or more 2,000m 2 15. The porous polyimide according to claim 11, 13 or 14, wherein the molecular weight is 1 / g or less.

17. 15. The porous polyimide according to claim 11, 13 or 14, wherein the ratio of the number of carbonyl carbon atoms to the total number of carbon atoms in the polyimide constituting said porous polyimide is 13.5% or more.

18. Based on the pore volume (V) and BET specific surface area (A) determined by gas adsorption method, the following formula: L=4V / A The average pore diameter (L) calculated by is 5 nm or more and 500 nm or less, After heat treatment at 300°C for 1 hour, the BET specific surface area is 10 m 2 / g or more 2,000m 2 / g or less, the polyimide constituting the porous polyimide has a polyimide main skeleton and a crosslinking structure that crosslinks the polyimide main skeleton, the crosslinked structure is a structure formed by a trivalent or higher group derived from an optionally substituted monocyclic or polycyclic aromatic ring, or a trivalent or higher group derived from a linked aromatic ring in which a plurality of optionally substituted aromatic rings are linked to each other by a direct bond or a bond via a hetero atom; Porous polyimide sheet.

19. Bulk density is 0.05 g / cm 3 0.50g / cm or more 3 19. The porous polyimide of claim 18, wherein:

20. 19. The porous polyimide according to claim 18, wherein the ratio of the number of carbonyl carbon atoms to the total number of carbon atoms in the polyimide constituting said porous polyimide is 13.5% or more.

21. The polyimide main skeleton is represented by the following general formula (1): 【Chemical 1】 (In the formula, X is a tetravalent organic group; Y is a divalent organic group, X is a tetravalent group derived from an optionally substituted monocyclic or polycyclic aromatic ring, or a tetravalent group derived from a linked aromatic ring in which a plurality of optionally substituted aromatic rings are linked to each other by a direct bond or a bond via a heteroatom, and / or Y is a divalent group derived from an optionally substituted monocyclic or polycyclic aromatic ring, or a divalent group derived from a linked aromatic ring in which a plurality of optionally substituted aromatic rings are linked to each other by a direct bond or a bond via a hetero atom, n is a positive integer.) 19. The porous polyimide according to claim 1, 11, 13, 14 or 18, having a structure represented by the following formula (1): wherein the degree of polymerization of the polyimide main skeleton is n in the general formula (1).

22. 19. The porous polyimide according to claim 1, 11, 13, 14 or 18, wherein the polyimide constituting the porous polyimide comprises a polymerization product of polymerization components including a tetracarboxylic dianhydride, a diamine, and a trifunctional or higher functional amine, and the ratio of the trifunctional or higher functional amine to a total of 100 mass% of the tetracarboxylic dianhydride, the diamine, and the trifunctional or higher functional amine is 1 mass% or more and 40 mass% or less.

23. 19. The porous polyimide according to claim 1, 11, 13, 14 or 18, having an average thickness of 10 mm or less.

24. the polyimide constituting the porous polyimide contains a polymerization product of polymerization components containing a tetracarboxylic dianhydride and a diamine, 50 mol % or more of the tetracarboxylic dianhydride is pyromellitic anhydride, 19. The porous polyimide according to claim 1, 11, 13, 14 or 18, wherein the terminal of the polyimide is an anhydride structure derived from pyromellitic anhydride.

25. When plotting the scattering vector q of small-angle X-ray scattering, the scattering intensity I(q) multiplied by q, qI(q), the value of which is 0.04 nm -1 <q<2.0 nm -1 and the average pore size D calculated from the peak position of qI(q) w A polyimide wet gel having a particle size of 0.8 nm or more and 8.0 nm or less, the polyimide constituting the polyimide wet gel has a polyimide main skeleton and a crosslinking structure that crosslinks the polyimide main skeleton, the crosslinked structure is a structure formed by a trivalent or higher group derived from an optionally substituted monocyclic or polycyclic aromatic ring, or a trivalent or higher group derived from a linked aromatic ring in which a plurality of optionally substituted aromatic rings are linked to each other by a direct bond or a bond via a hetero atom; Polyimide wet gel.

26. The magnitude of the scattering vector q of small-angle X-ray scattering is 0.080 nm -1 0.12nm or more -1 26. The polyimide wet gel according to claim 25, wherein the minimum value of the differential coefficient when the logarithm of the scattering intensity I(q) log[I(q)] is differentiated by the logarithm of the scattering vector q log[q] is -1.0 or more and 0.0 or less in the following range:

27. 26. The polyimide wet gel according to claim 25, wherein the strain at break in a three-point bending test is 10% or more.

28. The polyimide constituting the polyimide wet gel is represented by the following general formula (1): 【Chemistry 2】 (In the formula, X is a tetravalent organic group, Y is a divalent organic group, and n is a positive integer.) wherein in general formula (1), X and / or Y have a structure that imparts linearity to the molecular chain, and n is a degree of polymerization of the polyimide.

29. The polyimide constituting the polyimide wet gel is represented by the following general formula (1): 【Chemistry 3】 (In the formula, X is a tetravalent organic group, Y is a divalent organic group, and n is a positive integer.) wherein the ratio of structures derived from pyromellitic anhydride among X present in the molecular chain is 50 mol % or more, and the terminal of the molecular chain is derived from pyromellitic anhydride.

30. 26. The polyimide wet gel of claim 25, having a sheet shape.

31. The solvent in the polyimide wet gel is replaced with acetone, and then the polyimide is dried with supercritical carbon dioxide to obtain a porous polyimide. BET specific surface area: 100m 2 / g above 2,000m 2 / g or less, Bulk density: 0.05 g / cm 3 0.50g / cm or more 3 below, Bending strength: 5 MPa or more, Flexural modulus: 100 MPa or more, and Average pore size (D) determined by small-angle X-ray scattering: 1.0 nm or more and 7.0 nm or less; 26. The polyimide wet gel of claim 25, having

32. a step of adding a crosslinking agent having three or more functional groups to a polyamic acid solution to obtain a polyamic acid wet gel; a step of immersing the polyamic acid wet gel in a solution containing a dehydrating imidizing agent to obtain a polyimide wet gel; Including, A method for producing a polyimide wet gel, wherein a concentration of the dehydrating imidizing agent in the solution is 1% by weight or more and 50% by weight or less, the polyimide constituting the polyimide wet gel has a polyimide main skeleton and a crosslinking structure that crosslinks the polyimide main skeleton, the crosslinked structure is a structure formed by a trivalent or higher group derived from an optionally substituted monocyclic or polycyclic aromatic ring, or a trivalent or higher group derived from a linked aromatic ring in which a plurality of optionally substituted aromatic rings are linked to each other by a direct bond or a bond via a hetero atom, The method for producing a polyimide wet gel, wherein the porous polyimide constituting the polyimide wet gel has an average pore size (D) of 1.0 nm or more and 7.0 nm or less as determined by small-angle X-ray scattering.

33. 33. The method of claim 32, wherein the temperature of the steps of obtaining the polyamic acid wet gel and obtaining the polyimide wet gel is maintained at 10°C or higher.

34. 33. The method of claim 32, wherein the temperature of the steps of obtaining the polyamic acid wet gel and obtaining the polyimide wet gel is maintained at 120°C or less.

35. 33. The method according to claim 32, wherein the step of obtaining the polyamic acid wet gel is carried out by spreading a mixture of the polyamic acid solution and the crosslinking agent having three or more functional groups into a sheet.

36. 33. The method of claim 32, wherein the dehydrating imidization agent is a combination of acetic anhydride and triethylamine.

37. The porous polyimide constituting the polyimide wet gel has a BET specific surface area of 10 m after heat treatment at 300° C. for 1 hour. 2 / g or more 2,000m 2 33. The method of claim 32, wherein the .alpha.-hydroxybenzoate is 0.15g or less.

38. 33. The method according to claim 32, wherein the porous polyimide constituting the polyimide wet gel has a bending strength of 10 MPa or more and a bending modulus of elasticity of 100 MPa or more in a three-point bending test.

39. The polyimide constituting the polyimide wet gel is represented by the following general formula (1): 【Chemistry 4】 (In the formula, X is a tetravalent organic group, Y is a divalent organic group, and n is a positive integer.) wherein in general formula (1), X and / or Y have a structure that imparts linearity to the molecular chain, and n is the degree of polymerization of the polyimide.

40. Obtaining the polyimide wet gel by the method according to any one of claims 32 to 39; removing the solution from the polyimide wet gel to obtain a porous polyimide; A method for producing a porous polyimide, comprising:

41. A porous carbon sheet which is a carbonized product of the porous polyimide according to claim 1, 11, 13, 14 or 18, Based on the pore volume (V) and BET specific surface area (A) determined by gas adsorption method, the following formula: L=4V / A The porous carbon sheet has an average pore diameter (L) calculated by the above method of 5 nm to 500 nm.

42. Bulk density is 0.01 g / cm 3 0.80g / cm or more 3 42. The porous carbon sheet according to claim 41, wherein:

43. 42. The porous carbon sheet according to claim 41, having an average thickness of 10 mm or less.

44. BET specific surface area is 10m 2 More than 2,000m 2 42. The porous carbon sheet according to claim 41, wherein:

45. A method for producing a porous carbon sheet, comprising a step of heating a sheet that is the porous polyimide according to claim 1, 11, 13, 14 or 18 to 400°C or higher to carbonize it, thereby obtaining a porous carbon sheet, The porous carbon sheet has a pore volume (V) and a BET specific surface area (A) determined by a gas adsorption method, and the pore volume (V) and the BET specific surface area (A) are determined by the following formula: L=4V / A The method according to claim 1, wherein the average pore diameter (L) obtained by the above method is 5 nm or more and 500 nm or less.

46. Obtaining a porous polyimide sheet by the method of claim 40; A method for producing a porous carbon sheet, comprising: a step of heating the sheet to 400°C or higher to carbonize it, thereby obtaining a porous carbon sheet, The porous carbon sheet has a pore volume (V) and a BET specific surface area (A) determined by a gas adsorption method, and the pore volume (V) and the BET specific surface area (A) are determined by the following formula: L=4V / A The method according to claim 1, wherein the average pore diameter (L) obtained by the above method is 5 nm or more and 500 nm or less.

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