Porous polyimide composition and polyamic acid composition

Abstract

To provide a porous polyimide composition with low colorability and high translucency.SOLUTION: A porous polyimide composition is provided, with an average pore diameter (L) of 5 nm or more and 500 nm or less, obtained by the formula: L=4 V / A, based on the pore capacity (V) and the BET specific surface area (A), determined by a gas adsorption method. The porous polyimide composition has a light transmittance of 10% or more and 100% or less at 450 nm with a 1 mm thickness, and a degree of polymerization (n) ranging from 5 or more to less than 40.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to porous polyimide compositions and polyamic acid compositions for obtaining them. [Background technology]

[0002] Aerogels were traditionally defined as porous materials in which the solvent contained in the gel was replaced with a gas by supercritical drying. However, in recent years, they have come to be recognized more broadly as porous materials in which the solvent was removed from a solvent-containing colloid or polymer network while suppressing shrinkage and volume reduction. Due to their fine pore structure, aerogels possess various properties such as low density, high porosity, porousness (mesopores), high specific surface area, high specific strength, high thermal insulation, high electrical insulation, and high sound insulation. Examples of aerogels include silica aerogels, polymer aerogels such as polyimide aerogels, and carbon aerogels.

[0003] Patent documents 1 and 2 describe a crosslinked polyimide aerogel and a method for producing the same. The aerogel has polyamide crosslinks formed using a trioxide crosslinking agent. The aerogel comprises a polyimide oligomer component and a polyamide crosslink, the polyamide crosslink being bonded to the polyimide oligomer component, and the polyimide oligomer component contains the reaction product of a diamine and an acidic dianhydride in the ratio (n+1):n (where n is the number of repeating units of the oligomer).

[0004] Patent Document 3 describes a method for producing polyimide aerogel. It states that the transparency of the polyimide aerogel can be improved by appropriately adjusting the ratio of pyromellitic anhydride and 4,4'-hexafluoroisopropylidene (phthalic anhydride) (6FDA), which are aromatic acid dianhydrides, to a diamine such as 2,2'-dimethyl-4,4'-benzidine.

[0005] Non-patent document 1 describes a method for producing a polyimide aerogel from an amine-cap oligomer crosslinked with 1,3,5-benzenetricarbonyltrichloride (BTC). The aerogel produced by this method is said to have an elastic modulus equivalent to or better than that of crosslinked aerogels of the same density as those previously reported, such as 1,3,5-tris(4-aminophenoxy)benzene (TAPB) and octa(aminophenoxy)silsesquioxane (OAPS).

[0006] Non-patent document 2 describes a polyimide aerogel with improved transparency and a method for producing the same. It states that the transparency of the polyimide aerogel can be improved by appropriately adjusting the ratio of pyromellitic anhydride and 4,4'-hexafluoroisopropylidene (phthalic anhydride) (6FDA) to 2,2'-dimethyl-4,4'-benzidine.

[0007] Non-patent document 3 describes a polyimide aerogel using an alicyclic acid anhydride and a method for producing the same. A polyimide aerogel, in which a polyimide consisting of 1,2,3,4-cyclobutanetetracarboxylic anhydride (CBDA) and 2,2'-bis(trifluoromethyl)-4,4'-benzidine (TFMB) is crosslinked with octa(aminophenyl) silexatene (OAPS), is said to exhibit high hydrophobicity and low dielectric properties.

[0008] Non-patent document 4 describes a method for producing a nanoporous polyimide aerogel. The method includes crosslinking a polyamic acid oligomer capped with an anhydride with an aromatic triamine in solution and chemically imidizing it to obtain a polyimide gel, and then supercritically drying this gel to obtain a nanoporous polyimide aerogel. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] U.S. Patent No. 9434832 [Patent Document 2] U.S. Patent No. 10358539, Specification Patent Document 3 U.S. Patent No. 10800883, Specification Non-Patent Literature

[0010] Non-Patent Literature 1 Mary Ann B. Meador, et al., “Polyimide Aerogels with Amide Cross-Links: A Low Cost Alternative for Mechanically Strong Polymer Aerogels ”, ACS Appl. Mater. Interfaces, (2015), 7(2), 1240-1249 Non-Patent Literature 2 Stephanie L. Vivod, et al., “Toward Improved Optical Transparency of Polyimide Aerogels”, ACS Appl. Mater. Interfaces, (2020), 12, 8622-8633 Non-Patent Literature 3 Dengxiong Shen, et al., “Intrinsically Highly Hydrophobic Semi-alicyclic Fluorinated Polyimide Aerogel”, Chem. Lett., (2013), 42, 1230-1232 Non-Patent Literature 4 Mary Ann B Meador, et al., "Mechanically strong, flexible polyimide aerogels cross-linked with aromatic triamine", ACS Appl. Mater. Interfaces, (2012), 4(2), pp.536-544 Summary of the Invention Problem to be Solved by the Invention

[0011] The polyimide aerogels described in Patent Documents 1 and 2, and Non-Patent Document 1, exhibit a noticeable yellow to orange coloration derived from their aromatic polyimide structure. Furthermore, they are thought to possess a pore structure (macropores) that diffusely reflects light, resulting in low light transmittance.

[0012] The polyimide aerogel described in Non-Patent Document 2, like Non-Patent Document 1, exhibits noticeable yellow to orange coloration derived from its aromatic polyimide structure.

[0013] The polyimide aerogel described in Non-Patent Document 3 uses an alicyclic acid dianhydride, and therefore the polyimide skeleton itself has little coloration. On the other hand, similar to Non-Patent Documents 1 and 2, it is thought to have a pore structure (macropores) that diffusely reflects light, resulting in a white, opaque aerogel.

[0014] The methods described in Patent Document 3 and Non-Patent Document 4 make it difficult to obtain a polyimide aerogel with low coloration and high light transmittance.

[0015] One of the objectives of this disclosure is to provide a porous polyimide composition having low coloration and high light transmittance, and a polyamic acid composition for obtaining the same. [Means for solving the problem]

[0016] Examples of embodiments of this disclosure are listed below. [1] Based on the pore volume (V) and BET specific surface area (A) determined by the gas adsorption method, the following formula is used: L = 4V / A The average pore size (L) obtained by this method is between 5 nm and 500 nm. The light transmittance at a film thickness of 1 mm is between 10% and 100% at 450 nm, and A porous polyimide composition having a degree of polymerization (n) of 5 or more and less than 40. [2] In the desorption curve of the nitrogen adsorption-desorption isotherm at 77K, The porous polyimide composition according to item 1, wherein the ratio of the amount of adsorption at relative pressures of 0.90, 0.85, 0.80, and 0.75 to the amount of adsorption at relative pressure 0.98 is 0.50 or more and 1.0 or less, 0.30 or more and 1.0 or less, 0.25 or more and 0.90 or less, and 0.20 or more and 0.85 or less, respectively. [3] A porous polyimide composition according to item 1 or 2, having a crosslinked polyimide structure obtained by crosslinking a polyamic acid obtained by polymerizing tetracarboxylic dianhydride:diamine in an n+1:n ratio. [4] A porous polyimide composition according to any one of items 1 to 3, wherein the minimum light transmittance between 400 nm and 700 nm at a film thickness of 1 mm is 5% or more. [5] A porous polyimide composition according to any one of items 1 to 4, wherein the difference between the maximum and minimum light transmittance between 400 nm and 700 nm at a film thickness of 1 mm is 1% or more and 80% or less. [6] A porous polyimide composition according to any one of items 1 to 5, wherein the average value of the light transmittance between 400 nm and 700 nm at a film thickness of 1 mm is 30% or more and 100% or less. [7] Bulk density is 0.05 g / cm³ 3 More than 0.50g / cm 3 A porous polyimide composition as described in any one of items 1 to 6 below. [8] A porous polyimide composition according to any one of items 1 to 7, wherein the fracture strain in a three-point bending test is 5% or more. [9] A porous polyimide composition according to any one of items 1 to 8, wherein the bending strength in a three-point bending test is 5 MPa or more.

[10] A porous polyimide composition according to any one of items 1 to 9, wherein the flexural modulus in a three-point bending test is 50 MPa or more.

[11] The BET specific surface area after heat treatment at 200°C for 1 hour is 10 m². 2 / g or more 2,000m 2 A porous polyimide composition according to any one of items 1 to 10, wherein the amount is less than or equal to / g.

[12] A porous polyimide composition having a sheet shape, as described in any one of items 1 to 11.

[13] A porous polyimide composition as described in item 12, having an average thickness of 10 mm or less.

[14] When the light transmittance at 450 nm is LT[%] and the thickness is T[mm], the following formula holds: 0 < (100 - LT) / T ≤ 70 A porous polyimide composition according to any one of items 1 to 13, satisfying the relationship represented by the terms.

[15] The porous polyimide composition according to any one of items 1 to 14, wherein the polyimide constituting the porous polyimide composition has a polyimide main skeleton and a crosslinking structure that crosslinks the polyimide main skeleton.

[16] The porous polyimide composition according to item 15, wherein the crosslinking structure is a structure of trivalent or higher groups derived from a monocyclic or polycyclic aromatic ring which may be substituted, or a group of trivalent or higher groups derived from a linked aromatic ring in which a plurality of substituted aromatic rings are linked to each other by direct bonds or by heteroatom-mediated bonds.

[17] The aforementioned polyimide main skeleton is given by the following general formula (1): [ka] A porous polyimide composition according to item 15, having a molecular chain represented by general formula (1), wherein X and / or Y have a structure including an alicyclic ring, and n is the degree of polymerization of the polyimide.

[18] The polyimide constituting the porous polyimide composition comprises a polymerization product of a polymerization component containing a tetracarboxylic dianhydride, a diamine, and a trifunctional or higher amine. A porous polyimide composition according to any one of items 1 to 17, wherein the ratio of the trifunctional or more amine to 100% by mass of the total of the tetracarboxylic dianhydride, the diamine, and the trifunctional or more amine is 1% by mass or more and 40% by mass or less.

[19] The porous polyimide composition comprises a polymerization product of a polymerization component containing a tetracarboxylic dianhydride, a diamine, and a trifunctional or higher amine, The ratio of the tetracarboxylic dianhydride containing an aromatic ring to the total 100% by mass of the tetracarboxylic dianhydride is less than 50% by mass, and / or The ratio of the diamine containing an aromatic ring to the total 100% by mass of the diamines is less than 50% by mass. A porous polyimide composition as described in any one of items 1 to 18.

[20] A porous polyimide composition according to any one of items 1 to 17, for use as a heat-resistant material with low coloration and high light transmission. [twenty one] A polyamic acid composition comprising a resin precursor and a solvent, for obtaining a heat-resistant material with low coloration and high light transmission, The porous polyimide compositions obtained by adding a crosslinking agent to the aforementioned polyamic acid composition and then chemically imidizing it by immersion in a solution are described below (1) to (2): (1) Based on the pore volume (V) and BET specific surface area (A) determined by the gas adsorption method, the following formula is used: L = 4V / A The average pore size (L) determined by this method must be between 5 nm and 500 nm. (2) The light transmittance at 450 nm is 10% or more with a film thickness of 1 mm. Satisfying the following conditions, A polyamic acid composition in which the degree of polymerization (n) of the polyimide is 5 or more and less than 40. [Effects of the Invention]

[0017] According to this disclosure, porous polyimide compositions having low coloration and high light transmittance, and polyamic acid compositions for obtaining the same may be provided. [Modes for carrying out the invention]

[0018] Hereinafter, one embodiment of the present invention (hereinafter abbreviated as "Embodiment") will be described in detail. It should be noted that the present invention is not limited to the following embodiment, and can be implemented with various modifications within the scope of its gist. In the following description, the upper or lower limits in a numerical range described in stages may be replaced with the upper or lower limits in other numerical ranges described in stages. Also, in the following description, the upper or lower limits in a certain numerical range may be replaced with the values ​​described in the examples. Furthermore, the term "process" in the following description may include not only independent processes but also processes that cannot be clearly distinguished from other processes, as long as the function of that "process" is achieved.

[0019] Porous polyimide composition One aspect of the present invention provides a porous polyimide composition (hereinafter sometimes simply referred to as "porous polyimide") composed of polyimide. In a typical embodiment, the porous polyimide consists of polyimide, but may also contain components other than polyimide, as long as the effects of the present invention are not impaired. The porous polyimide according to one embodiment is calculated based on the pore capacity (V) and BET specific surface area (A) determined by gas adsorption, using the following formula: L = 4V / A The average pore size (L) obtained by this method is between 5 nm and 500 nm. The light transmittance at a film thickness of 1 mm is between 10% and 100% at 450 nm, and The degree of polymerization (n) is 5 or greater and less than 40.

[0020] In one embodiment, the porous polyimide is in sheet form. There are no limitations on the sheet thickness, 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, it may be 0.1 μm or more. Porous polyimide in sheet form, especially in sheet form with an average thickness of 10 mm or less, can be applied as an aerogel sheet to various applications, such as thermal insulation materials, low dielectric materials, filter materials, etc. Alternatively, the average thickness of the sheet may exceed 10 mm, and the porous polyimide may also be in bulk form.

[0021] In one embodiment, porous polyimide is a low-coloration, high-light-transmitting heat-resistant material. Because such porous polyimide efficiently transmits visible light (in one embodiment, light with wavelengths from 400 nm to 700 nm), it is suitable for optical materials (such as window glass), coating materials, interlayer materials, and cover materials in fields requiring heat resistance, such as the aerospace and automotive industries. Alternatively, the porous polyimide according to one embodiment may also be a low-coloration, high-light-transmitting material, and at least one material selected from the group consisting of high electrical insulation materials, high sound insulation materials, and high thermal insulation materials. Further alternatively, the porous polyimide according to one embodiment may also be a low-coloration, high-light-transmitting material, and a high-strength material.

[0022] "Colorability" and "transparency" are not strictly the same concept. Colorability relates, for example, to charge transfer or interaction between the aromatic diamine moiety and the aromatic acid anhydride moiety. "Transparency" relates, for example, to the scattering of visible light (in one embodiment, light with wavelengths from 400 nm to 700 nm) in porous polyimide. Here, the porous polyimide according to one embodiment has low colorability and high light transmittance, as can be seen in the examples. The degree of "colorability" and "light transmittance" that can be seen in the examples corresponds to "low colorability" and "high light transmittance" that are particularly suitable for the above-mentioned applications.

[0023] In one embodiment, the porous polyimide has a light transmittance of 10% to 100% at 450 nm with a film thickness of 1 mm. The fact that the light transmittance is within the above range means that low coloration and high light transmittance are more favorably exhibited. In one embodiment, the light transmittance is preferably 15% or more, 17.5% or more, or 20% or more. Alternatively, in one embodiment, the light transmittance may be 50% or more, or 60% or more. Here, "light transmittance with a film thickness of 1 mm" refers to the light transmittance when the average thickness is 1 mm, or when it is assumed that the average thickness is 1 mm.

[0024] In one embodiment, the porous polyimide has a minimum light transmittance of 5% or more between 400 nm and 700 nm at a film thickness of 1 mm. The fact that the minimum value is within this range means that, in the visible light region (in one embodiment, light with wavelengths of 400 nm to 700 nm), the porous polyimide, regardless of its shape and / or film thickness, has a certain degree of low coloration and light transmittance. In one embodiment, the minimum value is preferably 7% or more, 10% or more, or 15% or more.

[0025] In one embodiment, the porous polyimide has a difference of 1% or more between the maximum and minimum light transmittance between 400 nm and 700 nm at a film thickness of 1 mm. The fact that this difference is within the above range means that, in the visible light region (in one embodiment, light with wavelengths from 400 nm to 700 nm), there is little variation in low coloration and light transmittance in the porous polyimide. In one embodiment, this difference is preferably 1% or more, 5% or more, or 10% or more, and preferably 90% or less, 85% or less, or 80% or less. Alternatively, the difference may be 70% or less.

[0026] In one embodiment, the porous polyimide has an average light transmittance of 30% or more and 100% or less between 400 nm and 700 nm at a film thickness of 1 mm. The fact that the average value is within the above range means that the porous polyimide exhibits low coloration and light transmittance across the entire visible light region (in one embodiment, light with wavelengths from 400 nm to 700 nm). In one embodiment, the average value is preferably 35% or more, 40% or more, or 45% or more. The average light transmittance can be determined by setting the wavelength range to 400 nm to 700 nm and calculating the average of the light transmittance at each wavelength.

[0027] In one embodiment, the porous polyimide has a degree of polymerization (n) of 5 or more and less than 40. The degree of polymerization (n) is also related to "low coloration" and "high light transmittance". From the viewpoint of low coloration and high light transmittance, the degree of polymerization (n) is preferably 30 or less, 25 or less, or 20 or less. Furthermore, if the degree of polymerization (n) is too small, i.e., the degree of crosslinking is too large, the time it takes for the polyamic acid solution to gel is too short, making it difficult to mold the gel into the desired shape. On the other hand, if the degree of polymerization (n) is too large, i.e., the degree of crosslinking is too small, it is difficult to obtain sufficient physical strength in the resulting polyamic acid wet gel, resulting in a tendency for the gel not to gel at all, or for the resulting gel to be brittle and difficult to handle. Therefore, by keeping the degree of polymerization (n) within the above range, it is easier to achieve both sufficient gelation time and sufficient physical strength for handling the resulting wet gel when crosslinking polyamic acid to obtain a polyamic acid wet gel.

[0028] In one embodiment, the porous polyimide exhibits a desorption curve on a nitrogen adsorption-desorption isotherm at 77K where the ratio of adsorption amounts at relative pressures of 0.90, 0.85, 0.80, and 0.75 to the adsorption amount at relative pressures of 0.98 is 0.50 to 1.0, 0.30 to 1.0, 0.25 to 0.90, and 0.20 to 0.85, respectively. Satisfying these conditions means that it is easier to realize a structure that diffusely reflects visible light or a structure with a small contribution from voids, which contributes to the high transparency of the porous polyimide. From the viewpoint of low coloration and high light transmittance, more preferably, the ratio of the amount of adsorption at relative pressures of 0.90, 0.85, 0.80, and 0.75 to the amount of adsorption at relative pressure 0.98 is 0.55 or more and 1.0 or less, 0.35 or more and 1.0 or less, 0.30 or more and 0.90 or less, and 0.20 or more and 0.80 or less, respectively. Even more preferably, the ratio of the amount of adsorption at relative pressures of 0.90, 0.85, 0.80, and 0.75 to the amount of adsorption at relative pressure 0.98 is 0.60 or more and 1.0 or less, 0.40 or more and 1.0 or less, 0.35 or more and 0.90 or less, and 0.25 or more and 0.80 or less, respectively.

[0029] The following points should be considered regarding the shape of the pore size. In conventional techniques, where a crosslinking agent having electrophilic functional groups such as acid chlorides or acid anhydrides is added to a non-gelled polyamic acid, the side chains of the polyamic acid react with the electrophilic functional groups of the crosslinking agent, potentially forming a side-chain crosslinked gel. Such a gel results in a heterogeneous pore structure. On the other hand, in this embodiment, such a heterogeneous pore structure is avoided, making it easier to achieve the pore structure described above.

[0030] In one embodiment, when the light transmittance of a porous polyimide at 450 nm is LT[%] and the thickness is T[mm], the following formula applies: 0 < (100 - LT) / T ≤ 70 satisfies the relationship represented by. When the porous polyimide satisfying the above relationship is a thin film, and even when it is a thick film with a certain thickness, it easily transmits visible light (in one embodiment, light with a wavelength of 450 nm) efficiently, and thus is particularly suitable for the above applications. In one embodiment, the above relationship is preferably 0 or more, 1 or more, or 2 or more, and preferably 80 or less, 75 or less, or 70 or less.

[0031] The porous polyimide according to one embodiment is based on the pore volume (V) determined by a gas adsorption method and the BET specific surface area (A), and is represented by the following formula: L=4V / A The average pore diameter (L) determined by the above formula is 5 nm or more and 500 nm or less. The average pore diameter (L) within this range is an index representing the pore size on the submicron order. The present inventors have focused on controlling the average pore diameter (L) to the pore size on this submicron order, and the resulting porous polyimide according to one embodiment has lower diffuse reflectance of light in the visible light region (in one embodiment, light with a wavelength of 400 nm to 700 nm) compared to porous polyimides having other pore sizes. 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 one embodiment, it 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.

[0032] In one embodiment, the BET specific surface area of the porous polyimide is 10 m 2 / g or more and 2,000 m 2 / g or less. That the BET specific surface area is within the above range is also an index representing the pore size on the submicron order. In one embodiment, the BET specific surface area is 10 m 2 / g or more, or 50 m 2 / g or more, or 100 m 2 / g or more, or 200 m 2 / g or more, or 300 m 2 / g or more, and in one embodiment, it is 2,000 m 2 / g or less, or 1,500 m2 / g or less, or 1,000m 2 / g or less, or 800m 2 It is less than / g.

[0033] In one embodiment, the BET specific surface area of ​​porous polyimide after heat treatment at 200°C for 1 hour is 10 m². 2 / g or more 2,000m 2 The BET specific surface area is less than or equal to / g. The fact that the above BET specific surface area is within the above range means that the porous polyimide maintains its pore structure after the above heat treatment. In one embodiment, the above 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 It is 1 / 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 It is less than / g.

[0034] In one embodiment, the flexural modulus of porous polyimide in a three-point bending test is 50 MPa or higher. Having a flexural modulus within this range is advantageous because it allows porous polyimide to exhibit excellent toughness, making it useful for various applications of aerogel. In one embodiment, the flexural modulus is 100 MPa or higher, 150 MPa or higher, 200 MPa or higher, 300 MPa or higher, or 400 MPa or higher. While there is no upper limit to the flexural modulus, in one embodiment, it may be 1,000 MPa or lower from the viewpoint of ease of manufacturing porous polyimide.

[0035] In one embodiment, the bending strength (flexural strength) of porous polyimide in a three-point bending test is 5 MPa or higher. Having a bending strength within this range is advantageous because it allows porous polyimide to exhibit excellent bending resistance, making it useful for various applications of aerogel. In one embodiment, the bending strength is 7 MPa or higher, 10 MPa or higher, 12 MPa or higher, 13 MPa or higher, 14 MPa or higher, or 15 MPa or higher. While there is no upper limit to the bending strength, in one embodiment, it may be 30 MPa or lower from the viewpoint of ease of manufacturing porous polyimide.

[0036] In one embodiment, the fracture strain in the three-point bending test of porous polyimide is 5% or more. Having the fracture strain within this range is advantageous because it allows the porous polyimide to exhibit excellent flexibility, making it useful for various applications of aerogel. In one embodiment, the fracture strain is 6% or more, 8% or more, 10% or more, 11% or more, 12% or more, 13% or more, 14% or more, or 15% or more. While the upper limit of the fracture strain is not limited, in one embodiment it may be 50% or less from the viewpoint of ease of manufacturing the porous polyimide. The fracture strain can be measured based on the three-point bending test, for example, by the method described in the examples.

[0037] In one embodiment, the bulk density of the porous polyimide is 0.05 g / cm³. 3 More than 0.80g / cm 3 The following applies: The bulk density is within the above range, and it is an indicator representing the pore size on the submicron order. In one embodiment, the bulk density is 0.05 g / cm³. 3 Above, or 0.06 g / cm³ 3 Above, or 0.07 g / cm³ 3 Above, or 0.08 g / cm³ 3 Above or equal to 0.09 g / cm³ 3 Above, or 0.10 g / cm³ 3 The above is true, and in one embodiment, 0.50 g / cm³ 3 The following, or 0.45 g / cm³ 3 The following, or 0.40 g / cm³ 3 The following applies:

[0038] The bulk density of porous polyimide after heat treatment at 200°C for 1 hour is preferably within the same numerical range as the bulk density mentioned above, in that the porous polyimide maintains its pore structure well 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 / cm³. 3 Above, or 0.06 g / cm³ 3 Above, or 0.07 g / cm³ 3 Above, or 0.08 g / cm³ 3 Above or equal to 0.09 g / cm³ 3 Above, or 0.10 g / cm³ 3 The above is true, and in one embodiment, 0.50 g / cm³ 3 The following, or 0.45 g / cm³ 3 The following, or 0.40 g / cm³ 3 The following applies:

[0039] The methods for controlling the above-mentioned structure and properties of porous polyimide within the scope of this embodiment are not limited to the above, but (1) Controlling the molecular structure of polyimide, and / or (2) When manufacturing polyimides, perform gelation before imidation. This can be used as an example.

[0040] <Molecular structure of polyimide> In one embodiment, the polyimide constituting the porous polyimide is a crosslinked polyimide having a polyimide main skeleton and a crosslinking structure that crosslinks the polyimide main skeleton.

[0041] In one embodiment, the polyimide is a polymerization product of a polymerization component comprising a tetracarboxylic dianhydride, a diamine, and a trifunctional or more functional amine. The ratio of the trifunctional or more functional amine to 100% by mass of the total of the tetracarboxylic dianhydride, diamine, and trifunctional or more functional amine is preferably 1% by mass or more, or 1.5% by mass or more, from the viewpoint of obtaining the desired pore structure of the porous polyimide by setting the crosslinking density of the polyimide within an appropriate range, and preferably 40% by mass or less, or 35% by mass or less, or 30% by mass or less.

[0042] In one embodiment, the polyimide has a crosslinked polyimide structure obtained by crosslinking a polyamic acid obtained by polymerizing tetracarboxylic dianhydride:diamine in an n+1:n ratio. This makes it easier to adopt the method described later in "Production of Porous Polyimide," and thus makes it easier to realize a porous polyimide with low coloration and high light transmittance.

[0043] Each of the polyimide main skeleton and the crosslinked structure may have an aliphatic structure (including an alicyclic structure), an aromatic structure, or a combination thereof.

[0044] The main backbone of the polyimide constituting the porous polyimide is preferably the following general formula (1): [ka] The molecular chain is represented by the general formula (1), where X and Y are divalent organic groups and n is the degree of polymerization of the polyimide. In one embodiment, X is a tetravalent organic group derived from a tetracarboxylic dianhydride, Y is a divalent organic group derived from a diamine, and n is a positive integer.

[0045] (Structure including alicyclic rings) In one embodiment, X and / or Y have a structure containing an alicyclic ring (i.e., a cycloalkane structure, an alicyclic structure, etc.). Since the above structure has smaller intermolecular interactions compared to, for example, an aromatic ring, it can suppress discoloration caused by large intermolecular interactions. Furthermore, polyimides obtained from an acid dianhydride having an aromatic ring (an acid dianhydride without an alicyclic structure) and a diamine having an aromatic ring (a diamine without an alicyclic structure) tend to be discolored in a yellowish color due to the structure containing the aromatic ring. However, the porous polyimide according to one embodiment has a structure containing an alicyclic ring, which reduces the proportion of the structure containing the aromatic ring, thereby suppressing such yellowish discoloration.

[0046] In one embodiment, of X and Y, only X may have a structure containing an alicyclic ring, only Y may have a structure containing an alicyclic ring, or both X and Y may have a structure containing an alicyclic ring. If both X and Y have a structure containing an alicyclic ring, their respective "alicyclic rings" may be the same or different. The "alicyclic rings," "diamines having an alicyclic ring (alicyclic diamines)," and "acidic dianhydrides having an alicyclic ring (alicyclic acidic dianhydrides)" may optionally have aromatic rings within the scope of the gist of the present invention. The optionally present "aromatic rings" may have substituents, and the "alicyclic rings" in the "alicyclic rings" may also have substituents.

[0047] To introduce a structure containing an alicyclic ring into X, a polyimide precursor (polyamic acid) can be obtained using an acid dianhydride having the above structure, and then crosslinked and imidized. Specifically, the acid dianhydride having the above structure is: 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, 1,2,3,4-Tetramethyl-1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic acid anhydride, norbornane-2-spiro-2'-cyclopentanone-5'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic dianhydride (CpODA), 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic acid anhydride, 3-(carboxymethyl)-1,2,4-cyclopentanetricarboxylic acid 1,4:2,3-dianhydride (TCA), Bicyclo[2.2.2]octo-7-ene-2,3,5,6-tetracarboxylic dianhydride, Bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic acid 2,3:5,6-dianhydride, Cyclopentanetetracarboxylic dianhydride, Cyclohexanetetracarboxylic acid dianhydride, Meso-butan-1,2,3,4-tetracarboxylic dianhydride 1,1'-Bicyclohexane-3,3',4,4'-tetracarboxylic acid-3,4:3',4'-dianhydride, These are some examples. Preferably, 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), norbornane-2-spiro-2'-cyclopentanone-5'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic dianhydride (CpODA), 3-(carboxymethyl)-1,2,4-cyclopentanetricarboxylic acid 1,4:2,3-dianhydride (TCA) From the viewpoint of polymerization reactivity and the physical strength of the resulting gel, 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) is particularly preferred.

[0048] To introduce a structure containing an alicyclic ring into Y, a polyimide precursor (polyamic acid) can be obtained using a diamine having the above structure, and then crosslinked and imidized. Specifically, the diamine having the above structure is: 1,4-Cyclohexanediamine (CHDA), 1,3-Cyclohexanediamine, 1,2-Cyclohexanediamine, 1,4-bis(aminomethyl)cyclohexane, 1,3-bis(aminomethyl)cyclohexane, Bis(4-aminocyclohexyl)methane, 4,4'-Methylenebis(2-methylcyclohexylamine), 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane, Isophorone diamine, 2,5-Bis(aminomethyl)bicyclo[2.2.1]heptane, These are some examples.

[0049] In one embodiment, a polyimide constituting a porous polyimide, The ratio of tetracarboxylic dianhydrides containing alicyclic rings to 100% by mass of the total tetracarboxylic dianhydrides is 50% by mass or more and 100% by mass or less, and / or the ratio of diamines containing alicyclic rings to 100% by mass of the total diamines is 50% by mass or more and 100% by mass or less. This makes it easier to suppress the increase in intermolecular interactions, and thus a porous polyimide with low coloration and high light transmittance can be suitably obtained.

[0050] In one embodiment, a polyimide constituting a porous polyimide, The ratio of tetracarboxylic dianhydrides containing aromatic rings to 100% by mass of total tetracarboxylic dianhydrides is 0 or more and less than 50% by mass, or greater than 0 and less than 50% by mass, and / or the ratio of diamines containing aromatic rings to 100% by mass of total diamines is 0 or more and less than 50% by mass, or greater than 0 and less than 50% by mass. According to this, the resulting polyimide can be easily subjected to yellow discoloration caused by the aromatic ring skeleton, thus suitably obtaining a porous polyimide with low discoloration and high light transmittance.

[0051] X may have a structure that imparts linearity to the molecular chain of the resulting polyimide, or it may have a structure that imparts flexibility. Preferably, X has a structure that imparts linearity to the molecular chain of the resulting polyimide. In this specification, "imparting linearity" to the molecular chain of polyimide means having a structure in which two single bonds connecting the target monomer unit and two other adjacent monomer units are aligned in a straight line. In this specification, "imparting flexibility" to the molecular chain of polyimide means having a structure in which two single bonds connecting the target monomer unit and two other adjacent monomer units are not aligned in a straight line. By having a structure that imparts linearity to the molecular chain of the resulting polyimide, the heat resistance of the porous polyimide sheet can be controlled to a high degree. Therefore, by having X and / or Y have a "structure containing an alicyclic ring," a "structure that imparts linearity," and / or a "structure that imparts flexibility," the resulting polyimide can obtain the contributions of the "structure containing an alicyclic ring" and the "structure that imparts linearity" and / or the "structure that imparts flexibility."

[0052] (A structure that imparts linearity or flexibility) Examples of X, which has a structure that imparts linearity to the molecular chain of polyimide, include substituted or unsubstituted tetravalent aromatic rings or polycyclic aromatic rings, in which the two acid anhydrides are positioned such that when the two acid anhydrides form imide bonds with the amino group of the diamine, the single bonds of the two imide bonds are aligned in a straight line. Examples of aromatic rings or polycyclic aromatic rings of X include aromatic rings and condensed aromatic rings of benzene, naphthalene, anthracene, phenanthrene, tetracene, triphenylene, chrysene, and pyrene.

[0053] Examples of tetracarboxylic dianhydrides in which X is an aromatic ring or a polycyclic aromatic ring and which have a structure that imparts linearity to the molecular chain of the polyimide include the following general formula: [ka] Examples of compounds represented by the above general formula include: In the above general formula, R may be at least one organic group independently selected from the group consisting of hydrogen, halogen, hydroxyl group, aryl group, and aliphatic hydrocarbon group. The aliphatic hydrocarbon group may be a branched or unbranched, saturated or unsaturated aliphatic hydrocarbon group.

[0054] 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.

[0055] Tetracarboxylic acid dianhydrides having a structure that imparts flexibility to the molecular chain of polyimide include, specifically, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA), 2,3,3',4'-biphenyltetracarboxylic acid dianhydride (α-BPDA), 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride (BTDA), 4,4'-oxydiphthalic acid dianhydride (ODPA), 3,3',4,4'-biphenyl ether tetracarboxylic acid dianhydride, 2,3,3',4'-biphenyl ether tetracarboxylic acid dianhydride, 3,3',4,4'-biphenylsulfonetetracarboxylic acid dianhydride (DSDA), 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropanoic acid dianhydride, 2,2'-bis(3,4-dicarboxyphenyl)propanoic acid dianhydride, and 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 acid-2,6:3,5-Dianhydride (TCA-AH), 4,4'-(Hexafluoroisopropylidene)diphthalic anhydride Examples include (6FDA), bicyclo[2.2.2]octo-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).

[0056] Tetracarboxylic acid dianhydrides having a structure that imparts flexibility to the molecular chain of polyimide are more preferably having an aromatic group, and examples include 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA), 2,3,3',4'-biphenyltetracarboxylic acid dianhydride (α-BPDA), 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride (BTDA), 4,4'-oxydiphthalic acid dianhydride (ODPA), 3,3',4,4'-biphenyl ether tetracarboxylic acid dianhydride, 2,3,3',4'-biphenyl ether tetracarboxylic acid dianhydride, and 3,3',4,4'-biphenylsulfonetetracarboxylic acid dianhydride (DSDA). More preferably is 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA).

[0057] Y may have a structure that imparts linearity to the molecular chains of the resulting polyimide, or it may have a structure that imparts flexibility. Preferably, Y has a structure that imparts linearity to the molecular chains of the resulting polyimide. By having a structure that imparts linearity to the molecular chains of the resulting polyimide, the heat resistance of the porous polyimide sheet can be controlled to a high degree.

[0058] As Y, which has a structure that imparts linearity to the molecular chain of the polyimide, it is preferable that it is a substituted or unsubstituted, divalent aromatic ring or polycyclic aromatic ring, having two amino groups in positions such that when the two amino groups form an imide bond with the acid anhydride group of a tetracarboxylic dianhydride, the single bonds of the two imide bonds are aligned in a straight line. Typically, the position of one amino group may be para relative to the other amino group. Examples of aromatic rings or polycyclic aromatic rings of Y include aromatic rings and condensed aromatic rings of benzene, naphthalene, anthracene, phenanthrene, tetracene, triphenylene, chrysene, and pyrene, as well as ring aggregates of aromatic rings linked by single bonds, such as biphenyl and triphenyl.

[0059] Examples of diamines in which Y is an aromatic ring or a polycyclic aromatic ring and which have a structure that imparts linearity to the molecular chain of the polyimide include the following general formula: [ka] Examples of compounds represented by the above general formula include: In the above general formula, R may be at least one organic group independently selected from the group consisting of hydrogen, halogen, hydroxyl group, aryl group, and aliphatic hydrocarbon group. The aliphatic hydrocarbon group may be a branched or unbranched, saturated or unsaturated aliphatic hydrocarbon group.

[0060] Diamines having a structure that imparts linearity to the molecular chain of polyimide include, specifically, 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 (TMPDA), 4,4'-diaminobiphenyl, 2,2'-dimethylbenzidine (DMBZ), 3,3'-dimethylbenzidine, and 2,2'-bis(trifluoromethyl)benzidine (TFMB).

[0061] Examples of diamines having a structure that imparts flexibility to the molecular chains of polyimides include the following general formula: [ka] Examples of compounds represented by the above general formula include: In the above general formula, R may be at least one organic group independently selected from the group consisting of hydrogen, halogen, hydroxyl group, aryl group, and aliphatic hydrocarbon group. The aliphatic hydrocarbon group may be a branched or unbranched, saturated or unsaturated aliphatic hydrocarbon group.

[0062] Diamines having a structure that imparts flexibility to the molecular chains of polyimides include m-phenylenediamine (MPDA), 2,4-diaminotoluene, 2,4-diaminoxylene, 3,3'-diaminodiphenylsulfone (3DAS), 4,4'-diaminodiphenylsulfone (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 Examples include aromatic diamines such as 2,4,6-trimethyl-1,3-phenylenediamine (TMPDA), 2,2-bis(4-aminophenyl)hexafluoropropane (6FDAm), and 4,4'-oxydianiline (ODA); and aliphatic diamines such as N,N-dimethyl-1,3-propanediamine (DMPDA), 1,4-cyclohexanediamine (trans, cis, or cis-,trans mixture) (CHDA), 1,4-bisaminomethylcyclohexane (trans, cis, or cis-,trans mixture) (14BAC), hexamethylenediamine, 1,3-diaminocyclohexane, 4,4'-diaminodicyclohexane, and 3,3'-diaminodicyclohexane.

[0063] Among diamines having a structure that imparts flexibility, 1,5-diaminonaphthalene (1,5-DAN) is a preferred aromatic diamine.

[0064] (Crosslinked structure) The crosslinked structure is a three- or more functional structure, and in one embodiment, it is derived from a three- or more functional crosslinking agent. The functional groups of the crosslinking agent are groups that are reactive with the acid anhydride group or amino group, which are terminal groups of polyamic acids. As a result, the crosslinking agent has the effect of crosslinking polyamic acids together to form a polyamic acid gel. The crosslinking agent is typically a three- or more functional carboxylic acid or amine, and more typically a three- or more functional amine.

[0065] In one embodiment, the crosslinking agent is given by the following general formula (4): Z-(R) a (4) (In the formula, Z is an a-valent organic group, R is independently either an amino group or a carboxyl group, and a is an integer of 3 or greater.) It is a compound represented by [formula].

[0066] In one embodiment, Z in general formula (4) 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 consist of a carbocyclic and / or heterocyclic ring. The number of carbon atoms in Z is preferably 6 to 24, more preferably 6 to 18, and even more preferably 6 to 12.

[0067] In one embodiment, R consists entirely of amino groups or entirely of carboxyl groups, preferably entirely of amino groups.

[0068] In one embodiment, a is 3 or 4, preferably 3.

[0069] In one embodiment, Z is a trivalent or higher group derived from a monocyclic or polycyclic aromatic ring which may be substituted (i.e., from which three or more hydrogen atoms have been removed), or a trivalent or higher group derived from a linked aromatic ring in which multiple substituted aromatic rings are linked to each other by direct bonds or by heteroatom-mediated bonds (i.e., from which three or more hydrogen atoms have been removed). More specifically, Z may include a monocyclic or polycyclic aromatic ring that may be substituted, or a group with a valency of 3 or more obtained by removing 3 or more hydrogen atoms from a directly bonded, possibly substituted, aromatic ring (e.g., biphenyl) (hereinafter also referred to as a total aromatic group), a group with a valency of 3 or more obtained by removing 3 or more hydrogen atoms from a group of possibly substituted, aromatic rings bonded to each other via heteroatoms (e.g., benzophenone, diphenyl ether, diphenyl sulfone, benzanilide, etc.) (hereinafter also referred to as a heteroskeleton-containing group), and a group with a valency of 3 or more obtained having an aliphatic carbon atom in the molecular skeleton (hereinafter also referred to as an aliphatic skeleton-containing group). The molecular skeleton of the crosslinking agent refers to the sites involved in the bonding of three or more functional groups present in the crosslinking agent. Substituents may include groups containing aliphatic or aromatic atoms, or combinations thereof. The number of carbon atoms in the substituent is preferably 4 or less.

[0070] Examples of crosslinking agents in which Z is a fully 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).

[0071] Examples of crosslinking agents in which Z is a heteroskeleton-containing group include 1,3,5-tris(4-aminophenoxy)benzene.

[0072] Examples of crosslinking agents in which Z is an aliphatic skeleton-containing group include 4,4',4''-(methanetriyl)trisaniline and 4,4',4'',4'''-methanetetrayltetraaniline.

[0073] From the viewpoint of obtaining a porous polyimide with excellent heat resistance, Z is preferably a fully aromatic group or a heteroskeleton-containing group, and more preferably a fully aromatic group.

[0074] In one embodiment, polyimide is given by the following general formula (5): [ka] (In the formulas, X, Y, and Z are the same as the definitions of 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:

[0075] n represents the degree of polymerization of the polyimide, which is preferably 3 or more, or 5 or more, and preferably 40 or less, or 30 or less, or 20 or less.

[0076] From the viewpoint of heat resistance of porous polyimides, preferred combinations of structures X, Y, and Z include combinations in which X is a simple aromatic group and Y and Z are either all aromatic groups or heteroskeleton groups, and combinations in which X is a simple aromatic group or a flexible skeleton-containing group and Y and Z are all aromatic groups.

[0077] <Advantages of this embodiment> The advantages of this embodiment over the prior art will be explained below. For example, the method described in Patent Document 3 makes it difficult to obtain a polyimide aerogel with low coloration and high light transmittance, as in this embodiment.

[0078] Furthermore, in the method described in Patent Document 3, the chemical imidation of polyamic acid using alicyclic acid dianhydride is known to be very slow compared to the chemical imidation of polyamic acid using aromatic acid dianhydride monomers, as described in Patent Documents 1 and 2, and Non-Patent Documents 1 and 2 (Reference: "High-Performance and Functional Design of Polyimides for Corporate Engineers," 1st Edition, 1st Printing, December 25, 2020, Author: Kohei Goto, Publisher: Science & Technology Co., Ltd.). Therefore, it is difficult to obtain an alicyclic polyimide aerogel with a uniform structure using the method described in Patent Document 3.

[0079] Manufacturing of porous polyimides The porous polyimide of this disclosure is, in one embodiment, Polymerization step to obtain a polyamic acid by polymerizing the acid dianhydride of the present disclosure and the diamine of the present disclosure. A gelation step to obtain a polyamidic acid wet gel by crosslinking a polyamidic acid with the crosslinking agent of the present disclosure. An imidization step to obtain a polyimide-wetted gel by imidizing a polyamic acid-wetted gel, and A drying process to obtain porous polyimide, which is a polyimide aerogel, by drying the polyimide wet gel. It can be manufactured by a method that includes [the specified method].

[0080] Polyimide gels are conventionally produced by first imidizing a polyamic acid to obtain polyimide, and then gelling the polyimide. In this method, polyimide tends to aggregate during gelation, which imposes a material selection constraint: in order to stably obtain a polyimide aerogel with the desired pore structure, it is necessary to select a polyimide with a molecular structure that is less prone to aggregation. In particular, if the molecular skeleton of the polyimide is highly rigid, the polyimide tends to aggregate during gelation after imidization, making it difficult to produce a polyimide with the desired pore structure. Furthermore, polyimide gels obtained by gelation after imidization have poor shape retention when heated, and tend to deform significantly, especially under harsh heating conditions such as carbonization, making them often unsuitable for the production of porous carbon.

[0081] On the other hand, the method of imidizing after gelling a polyamic acid offers the advantage of being able to stably form a desired pore structure without being constrained by the molecular structure of the polyimide by appropriately adjusting the gelling conditions. In particular, this method makes it possible to stably produce a polyimide aerogel with a desired pore structure even when the rigidity of the polyimide molecular skeleton is high, and therefore the advantages of this method are especially pronounced when the rigidity of the polyimide molecular skeleton is high. The method of imidizing after gelling a polyamic acid is particularly advantageous in terms of obtaining a porous polyimide with low coloration and high light transmittance when X and / or Y in general formula (2) of this disclosure have a structure containing an alicyclic ring.

[0082] A polyamic acid composition in this disclosure is, in one embodiment, A polyamic acid composition comprising a resin precursor and a solvent, for obtaining a heat-resistant material with low coloration and high light transmission, The porous polyimide obtained by adding a crosslinking agent to the above polyamic acid composition and then chemically imidizing it by immersion in a solution, in this order, is described below (1)~(2): (1) Based on the pore volume (V) and BET specific surface area (A) determined by the gas adsorption method, the following formula is used: L = 4V / A The average pore size (L) determined by this method must be between 5 nm and 500 nm. (2) The light transmittance at 450 nm is 10% or more with a film thickness of 1 mm. Satisfying the following conditions, The degree of polymerization (n) of the polyimide is 5 or greater and less than 40.

[0083] The polyamic acid compositions of this disclosure can suitably provide the polyimide compositions of this disclosure that satisfy the above (1) and (2). The polyamic acid composition according to one embodiment is particularly suitable for applications requiring low coloration, high light transmittance, and heat resistance, such as optical materials (window glass, etc.), coating materials, and cover materials, in fields where heat resistance is required, such as the aerospace and automotive fields. Alternatively, the polyamic acid composition according to one embodiment is particularly suitable for applications requiring low coloration, high light transmittance, and at least one property selected from the group consisting of high electrical insulation, high sound insulation, high heat insulation, and high strength.

[0084] The polyamic acid composition of this disclosure comprises, in one embodiment, a polyamic acid having a structure derived from an acidic dianhydride and a structure derived from a diamine, and a solvent. The polyamic acid composition may contain polymers other than polyamic acid, for example, polyimide. Here, "polyamic acid" refers to a polymer with an imidization rate of less than 20%, i.e., the majority of the repeating units are of the following formula:

[0085] [ka] (In the formula, X and Y are the same as above, and n is a positive integer.) It refers to a polymer that is a polyimide precursor. Polyamic acid is also called "polyimide precursor" or "polyamic acid."

[0086] In one embodiment of a polyamic acid composition, the polyamic acid further comprises a structure derived from a crosslinking agent. The structure derived from the crosslinking agent, i.e., the crosslinked structure, is a structure comprising a trivalent or higher group derived from a monocyclic or polycyclic aromatic ring which may be substituted, or a linked aromatic ring in which a plurality of substituted aromatic rings are linked to each other by direct bonding or by bonding via heteroatoms.

[0087] In one embodiment of the polyamic acid composition, the preferred configuration and properties are basically the same in the case of porous polyimide. Therefore, the polyamic acid composition according to one embodiment is For the resulting porous polyimide, the desorption curves on the nitrogen adsorption / desorption isotherm at 77K may show that the ratio of adsorption amounts at relative pressures of 0.90, 0.85, 0.80, and 0.75 to the adsorption amount at relative pressure 0.98 is between 0.50 and 1.0, 0.30 and 1.0, 0.25 and 0.90, and 0.20 and 0.85, respectively. The structure may have a crosslinked polyamic acid obtained by polymerizing tetracarboxylic dianhydride:diamine in an n+1:n ratio.

[0088] <Polymerization process> In this process, an acidic dianhydride and a diamine are polymerized in a polymerization solvent, and then crosslinked with a crosslinking agent to obtain polyamic acid. As the polymerization solvent, any solvent capable of dissolving polyamic acid can be used, and examples include amide solvents, ether solvents, ester solvents, ketone solvents, phenolic solvents, sulfone solvents, and sulfoxide solvents.

[0089] Examples of amide solvents include N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc).

[0090] 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.

[0091] Examples of ketone solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and cyclopentanone.

[0092] Examples of phenolic solvents include m-cresol.

[0093] Examples of sulfone-based solvents include methyl sulfone, ethylphenyl sulfone, diethyl sulfone, diphenyl sulfone, sulfolane, bisphenol S, sorapsone, dapsone, bisphenol A polysulfone, and sulfolane.

[0094] Examples of sulfoxide solvents include dimethyl sulfoxide (DMSO).

[0095] The boiling point of the solvent is preferably 80°C or higher, or 100°C or higher, or 120°C or higher. Such a high-boiling-point solvent allows the polymerization rate of the polyamic acid and the gelation rate of the polyamic acid or polyimide to be slower compared to the evaporation rate of the solvent, which is advantageous for process control, for example, by enabling polymerization and / or gelation at near room temperature. The high-boiling-point solvent is preferably an amide solvent, and 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.

[0096] In one embodiment, the polymerization temperature may be 10°C or higher, 80°C or lower, 60°C or lower, or 40°C or lower. In a preferred embodiment, the polymerization solvent may be maintained without cooling or heating (i.e., at ambient temperature) throughout the polymerization process.

[0097] <Gelation process> In this step, a polyamic acid wet gel is obtained by adding the crosslinking agent of this disclosure to the polyamic acid solution obtained in the polymerization step. The crosslinking agent may be added to the polyamic acid solution alone or as a solution in a solvent (hereinafter also referred to as the crosslinking agent solvent). Preferred examples of the crosslinking agent solvent are the same as those exemplified for the polymerization solvent above, and the high-boiling point solvents mentioned above are particularly preferred. High-boiling point solvents have a slow evaporation rate relative to the gelation rate, so stable gelation is possible, for example, at a gelation temperature of 10°C or higher and / or without cooling the system. The polymerization solvent and the crosslinking agent solvent may be of the same type or different types, but are preferably of the same type.

[0098] In one embodiment, the above mixture may be cast onto a substrate and allowed to stand to allow gelation to proceed. The thickness of the mixture may be selected according to the desired thickness of the porous polyimide, and in one embodiment, it may be 0.1 μm to 10 mm. The gelation atmosphere is not limited and may be air, an inert gas (e.g., nitrogen), etc.

[0099] The gelation temperature is preferably 10°C or higher from the viewpoint of shortening the gelation time and improving process efficiency, and preferably 80°C or lower, or 60°C or lower, or 40°C or lower from the viewpoint of stably forming the desired pore structure. In a preferred embodiment, the solvent may be maintained without cooling or heating (i.e., under ambient conditions) throughout the gelation process.

[0100] 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 preferably 60 minutes or less, or 30 minutes or less, or 10 minutes or less, from the viewpoint of process efficiency.

[0101] <Imidification process> In this process, a polyimide gel is obtained by imidizing the polyamic acid-wet gel obtained in the gelation process. 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 adjacent carboxyl group of the polyamic acid-wet gel to form an imide bond. The dehydrating imidizing agent is typically a carboxylic acid anhydride and may be used as a mixture with 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.

[0102] In one embodiment, imidation is performed by immersing a polyamic acid-moistened gel in an imidation solution obtained by dissolving a dehydrating imidizing agent and an imidation accelerator in a solvent (hereinafter also referred to as an immersion solvent) in the imidation solution. The total concentration of the dehydrating imidizing agent and the imidation accelerator in 100% by mass of the imidation solution is preferably 1% by mass or more, or 3% by mass or more, from the viewpoint of rapidly promoting imidation, and 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-moistened gel and obtaining a polyimide gel in which the pore structure of the polyamic acid-moistened gel is well maintained.

[0103] Preferred examples of the immersion solvent are the same as those exemplified for the polymerization solvent above. The polymerization solvent and the crosslinking agent solvent may be of the same or different types, but are preferably of the same type. 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.

[0104] The imidation temperature may be, for example, 10°C or higher, 80°C or lower, 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., under ambient conditions) throughout the imidation process.

[0105] As described above, a polyimide wetted gel can be obtained. According to one embodiment of the method, as described above, by performing gelation before imidation, a polyimide wetted gel having dense pores on the submicron order, in which a suitably dispersed polyamic acid composition is chemically crosslinked, can be obtained. The above method according to one embodiment is preferred because a polyimide wetted gel can be suitably obtained even when using alicyclic diamines and / or alicyclic dianhydrides.

[0106] <Drying process> In this step, the polyimide wet gel obtained in the imidation step is dried to obtain a polyimide aerogel. As a drying method, supercritical drying is preferred from the viewpoint of maintaining the polymer network structure of the polyimide wet gel well and stably obtaining a polyimide aerogel having the desired pore structure. An example of a supercritical drying method is to replace the solvent contained in the polyimide wet gel with a ketone solvent such as acetone, or a lower alcohol such as ethanol, and then replace the substituted solvent with an inert gas such as carbon dioxide. A commercially available supercritical drying apparatus can be used for supercritical drying.

[0107] <Advantages of this embodiment> In one embodiment, the porous polyimide of this disclosure is, in one embodiment, the following flow (1): It can be created according to JPEG0007923187000008.jpg36161. In this flow, attention should be paid to the state of the polymer during gelation and the composition of the solvent. In this flow, polyamic acid is basically crosslinked in a good solvent. Therefore, phase separation is less likely to occur. As a result, the resulting porous structure becomes dense and less prone to suspension, which makes it easier to achieve low coloration and high light transmittance.

[0108] Flowchart (1) above is shown in comparison to flows (2) and (3). An example of the comparison between each flow is as follows: [Table 1] [Examples]

[0109] The following describes illustrative embodiments of the present invention with reference to examples, but the present invention is not limited to these examples.

[0110] Measurement and Evaluation Methods <Degree of polymerization (n)> The degree of polymerization (n) was adjusted based on the molar ratio of diamine to dianhydride in the polymerization process. In this disclosure, in Examples 1-4 and Comparative Examples 3-6, the molar ratio of diamine to dianhydride in the polymerization process was n:n+1. In Comparative Examples 1 and 2, the molar ratio of diamine to dianhydride in the polymerization process was n+1:n.

[0111] <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, and 24.8 mmol / L of lithium bromide monohydrate (Wako Pure Chemical Industries, Ltd., 99.5% purity) and 63.2 mmol / L of phosphoric acid (Wako Pure Chemical Industries, Ltd., for high-performance liquid chromatography) were added before measurement. A calibration curve for calculating the weight-average molecular weight was created using standard polystyrene (Tosoh Corporation). Column: Shodex KD-806M (manufactured by Showa Denko Corporation) Flow rate: 1.0mL / min Column temperature: 40℃ Pump: PU-2080Plus (manufactured by JASCO) Detector: RI-2031Plus (RI: Differential Refractometer, manufactured by JASCO) UV-2075Plus (UV-VIS: Ultraviolet-visible absorption spectrometer, manufactured by JASCO)

[0112] <Measurement of average pore size and BET specific surface area of ​​porous polyimide> Approximately 0.2 g of the sample was placed in a glass sample tube and heated and vacuum-degassed for 18 hours at 50°C and below 0.001 mmHg using a sample pretreatment device. After heating and vacuum degassing, the sample weight was measured and used as the sample weight for calculating the specific surface area. The specific surface area was calculated using a multi-sample high-performance specific surface area / pore distribution analyzer (3Flex, Micrometrics) from the adsorption isotherm of nitrogen gas at liquid nitrogen temperature (77 K) using the BET formula, and the intercept and slope of the straight line (BET plot) in the range of relative pressure (P / P0) from 0.05 to 0.30. The pore volume was derived from the adsorption amount at 760 mmHg, and the average pore diameter (L) was calculated using the relationship L = 4V / A, using the pore volume (V) and specific surface area (S). The pore distribution was calculated using the BJH method.

[0113] <Pore size distribution of porous polyimide> The desorption curves on the nitrogen (N2) adsorption / desorption isotherm at 77K, obtained from the measurement of the average pore diameter and BET specific surface area of ​​the above-mentioned porous polyimide, were evaluated according to the following criteria. A: All of the following conditions 1) to 4) must be met. B: Satisfy three or two of the following conditions 1) to 4). C: One of the following conditions 1) to 4) is met, or none of the conditions are met. 1) The ratio of the amount of adsorption at a relative pressure of 0.90 to the amount of adsorption at a relative pressure of 0.98 is 0.50 or more and 1.0 or less. 2) The ratio of the amount of adsorption at a relative pressure of 0.85 to the amount of adsorption at a relative pressure of 0.98 is between 0.30 and 1.0. 3) The ratio of the amount of adsorption at a relative pressure of 0.80 to the amount of adsorption at a relative pressure of 0.98 is 0.25 or more and 0.90 or less. 4) The ratio of the amount of adsorption at a relative pressure of 0.75 to the amount of adsorption at a relative pressure of 0.98 is 0.25 or more and 0.80 or less.

[0114] <Three-point bending modulus and three-point bending strength of porous polyimide> A sample measuring 30 mm wide x 14 mm deep x approximately 2 mm thick (more specifically, 2 mm) was cut from a dried, disc-shaped porous polyimide and subjected to a three-point bending test. The measurement conditions were as follows: Testing machine: Instron 5982 material testing machine Temperature: 23℃ Test speed: 1 mm / min Support span: 20mm

[0115] <Fracture point strain of porous polyimide> A three-point bending test was performed under the same conditions as described above, and the porous polyimide was stretched until it fractured. The strain at the point when the test specimen fractured (when the stress decreased sharply) was defined as the fracture strain. The strain was measured up to a maximum of 15%, and if fracture did not occur, the fracture strain was defined as ">15% (greater than 15%)".

[0116] <Measurement of bulk density of porous polyimide> Let m (g) be the weight, r (cm) be the radius, and h (cm) be the average thickness of the dried, disc-shaped porous polyimide sample. Then, calculate the bulk density d (g / cm³) according to the following formula. 3 ) was calculated. d = m / πhr 2 In the formula, the radius r was calculated by taking 10 measurements of a diameter 2r using a caliper at approximately equal intervals and taking half of the average value. The average thickness h was calculated by taking 20 measurements within the circular surface at approximately equal intervals and taking the average value. Furthermore, the average thickness h is calculated using the following formula: 0 < (100 - LT) / T ≤ 70 This was used as the film thickness T (mm).

[0117] <Measurement of light transmittance of porous polyimide> A sample measuring 30 mm wide x 30 mm deep x 1 mm thick, cut from a dried, disc-shaped porous polyimide, was subjected to light transmittance measurement. The measurement conditions were as follows. Regarding the wavelength range, the measurement itself was performed in the 300-800 nm range, and the 400-750 nm range was used for evaluation. Test machine: UV-2450 manufactured by Shimadzu Corporation Wavelength range: 300~800nm Scan speed: Slow Sampling pitch: 0.5nm Measurement mode: Single S / R switching: Standard Transmittance slit width: 5.0nm Light source switching wavelength: 320nm

[0118] Based on the above light transmittance measurement, 1) Light transmittance at 450nm, 2) Minimum value of light transmittance between 400nm and 700nm, 3) The difference between the maximum and minimum values ​​of light transmittance between 400 nm and 700 nm, and 4) The average value of the light transmittance between 400 nm and 700 nm was calculated. However, for cases that did not meet the criteria in 1) and 2) below, evaluations 3) and 4) were not performed.

[0119] <Evaluation of the transparency of porous polyimides> The transparency of porous polyimide was evaluated according to the following method. Specifically, a sample was placed on a piece of paper containing a single 10mm square mark (letter or symbol), covering one of the marks. The mark was then viewed through the sample from a distance of approximately 30cm, and evaluated according to the evaluation criteria below. This evaluation was conducted under normal indoor lighting conditions. (Evaluation Criteria) A: It was possible to confirm the existence of the mark and to identify 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. The presence of the C: mark could not be confirmed.

[0120] Examples of bulk porous polyimide production methods [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: 35.1 g) by stirring with a magnetic stirrer. Then, 1,2,3,4-cyclobutanetetracarboxylic anhydride (CBDA: 2.09 g; 10.67 mmol) powder was added while stirring. This solution was stirred at room temperature (25°C) until the molecular weight was saturated to obtain a polyamic acid (PAA) solution.

[0121] To the above polyamic acid (PAA) solution, a solution of 1,3,5-tris(4-aminophenyl)benzene (TAB: 0.156 g; 0.444 mmol) dissolved in 3.1 g of NMP in a separate 10 mL glass vial was added and the mixture was stirred for 1 minute. The resulting solution was transferred to a PFA mold (Φ100 mm, depth 30 mm) to a thickness of approximately 1 mm and allowed to stand at room temperature (25°C) for approximately 30 minutes to obtain a non-fluid polyamic acid wet gel (PAA-WG).

[0122] This PAA-WG was left to stand for 24 hours at room temperature (25°C) in a sealed SUS container under an NMP saturated atmosphere. After being removed from the mold, it was immersed for 24 hours at room temperature (25°C) in a mixed solution of acetic anhydride (26.1 g; 256 mmol), triethylamine (TEA: 3.2 g; 32 mmol), and 264 g of NMP to obtain a polyimide wet gel (PI-WG).

[0123] This PI-WG was removed from the above solution, immersed in a solution of acetone:NMP = 1:1 by weight ratio for 24 hours, washed with acetone, and then immersed in acetone for another 24 hours. This process was repeated three times, and then dried using a supercritical drying apparatus (SCRD4, manufactured by Rexxam Co., Ltd.) to obtain porous polyimide (pPI).

[0124] [Examples 2-4] In the same manner as in Example 1, porous polyimide (pPI) was obtained by performing the same procedure as in Example 1, but with the types and amounts of diamine, tetracarboxylic anhydride, crosslinking agent, imidizing reagent (dehydrating imidizing agent and imidizing accelerator), and solvent changed as shown in the table.

[0125] [Comparative Example 1] Based on Non-Patent Document 1, porous polyimide pPI was prepared using the following procedure. In a 100 mL glass vial, 4,4'-oxydianiline (ODA: 2.10 g; 10.5 mmol) was dissolved in N-methyl-2-pyrrolidone (NMP: 44.4 g) by stirring with a magnetic stirrer. Then, 3,3'-4,4'-biphenyltetracarboxylic dianhydride (BPDA: 2.94 g; 10.0 mmol) powder was added, and the mixture was stirred at room temperature (25°C) until the molecular weight was saturated to obtain a polyamic acid (PAA) solution.

[0126] Subsequently, acetic anhydride (8.2 g; 80 mmol) was added to the polyamic acid (PAA) solution while stirring, and the mixture was stirred until homogeneous. Further, triethylamine (1.0 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.

[0127] To the above polyimide (PI) solution, a solution of 1,3,5-benzenetricarbonyl trichloride (BTC: 88 mg; 0.333 mmol), dissolved in 1.8 g of NMP in a separate 10 mL glass vial, was added and stirred at room temperature until homogeneous. After stirring, the resulting solution was transferred to a PFA mold (Φ100 mm, depth 30 mm) to a thickness of approximately 1 mm and allowed to stand at room temperature for 30 minutes to obtain a non-fluid polyimide wet gel (PI-WG).

[0128] The obtained PI-WG was left to stand for 24 hours at room temperature (25°C) in a sealed SUS container under an NMP saturated atmosphere. Then, it was immersed for 24 hours in a solution of acetone:NMP (mass ratio) = 25:75, a solution of acetone:NMP (mass ratio) = 50:50, and a solution of acetone:NMP (mass ratio) = 75:25. After each immersion, the solvent was replaced by repeating the process of washing with acetone and immersing in acetone for 24 hours three times. This acetone-immersed polyimide wet gel was dried using a supercritical drying apparatus (SCRD4, manufactured by Rexxam Co., Ltd.) to obtain porous polyimide (pPI).

[0129] [Comparative Example 2] Based on Non-Patent Document 2, porous polyimide pPI was prepared using the following procedure. In a 100 mL glass vial, 2,2'-dimethylbenzidine (m-Tolidine, DMBZ: 2.17 g; 10.2 mmol) was dissolved in N-methyl-2-pyrrolidone (NMP: 43.9 g) by stirring with a magnetic stirrer. Then, at room temperature, 4,4'-hexafluoroisopropylidene (phthalic anhydride) (6FDA: 1.11 g; 2.5 mmol) powder was added in small amounts over 10 minutes while stirring, and the mixture was stirred until the powder was completely dissolved. After that, pyromellitic anhydride (PMDA: 1.64 g; 7.5 mmol) powder was added to the solution and stirred at room temperature (25°C) for about 10 minutes until homogeneous to obtain a polyamic acid (PAA) solution.

[0130] Subsequently, acetic anhydride (8.2 g; 80 mmol) was added to the polyamic acid (PAA) solution while stirring, and the mixture was stirred until homogeneous. Further, triethylamine (1.0 g; 10 mmol) was added, and the mixture was stirred until homogeneous. After that, the mixture was stirred at room temperature (25°C) for 10 minutes to obtain a polyimide (PI) solution.

[0131] To the above polyimide (PI) solution, a solution of 1,3,5-benzenetricarbonyl trichloride (BTC: 35 mg; 0.133 mmol), dissolved in 0.7 g of NMP in a separate 10 mL glass vial, was added and stirred at room temperature until homogeneous. After stirring, the resulting solution was transferred to a PFA mold (Φ100 mm, depth 30 mm) to a thickness of approximately 1 mm and allowed to stand at room temperature for approximately 120 minutes to obtain a non-fluid polyimide wet gel (PI-WG).

[0132] Porous polyimide (pPI) was obtained by performing solvent substitution and supercritical drying in the same manner as in Comparative Example 1.

[0133] [Comparative Example 3] Based on Non-Patent Document 3, porous polyimide pPI was prepared using the following procedure. In a 100 mL glass vial, 2,2'-bis(trifluoromethyl)-4,4'-benzidine (TFMB: 1.975 g; 6.16 mmol) was dissolved with N-methyl-2-pyrrolidone (NMP: 25.0 g) while stirring with a magnetic stirrer. Then, 1,2,3,4-cyclobutanetetracarboxylic anhydride (CBDA: 1.248 g; 6.36 mmol) powder was added, followed by N-methyl-2-pyrrolidone (NMP: 25.0 g). The mixture was stirred at room temperature (25°C) for approximately 12 hours until the molecular weight was saturated to obtain a polyamic acid (PAA) solution.

[0134] Subsequently, while stirring the polyamic acid (PAA) solution, octa(aminophenoxy)silsesquioxane (OAPS: 58 mg; 0.050 mmol) powder was added. After stirring at room temperature for approximately 12 hours, acetic anhydride (3.2 g; 31.6 mmol) was added and stirred until homogeneous, followed by pyridine (2.5 g; 31.6 mmol) and stirring until homogeneous, and then the mixture was stirred further at room temperature for 30 minutes.

[0135] The above solution was transferred to a PFA mold (Φ100mm, depth 30mm) to a thickness of approximately 1mm, and left to stand at room temperature for approximately 120 minutes to obtain a non-fluid polyimide wet gel (PI-WG). The obtained polyimide wet gel (PI-WG) was a white suspension.

[0136] Porous polyimide (pPI) was obtained by performing solvent substitution and supercritical drying in the same manner as in Comparative Example 1.

[0137] [Comparative Example 4] Based on Patent Document 3, porous polyimide pPI was prepared using the following procedure. In a 100 mL glass vial, 2,2'-dimethylbenzidine (m-Tolidine, DMBZ: 2.17 g; 10.2 mmol) was dissolved in N-methyl-2-pyrrolidone (NMP: 47.2 g) while stirring with a magnetic stirrer. Powdered 1,2,3,4-cyclobutanetetracarboxylic anhydride (CBDA: 1.96 g; 10.0 mmol) was added while stirring at room temperature, and the mixture was stirred at room temperature (25°C) for 4 hours to obtain a polyamic acid (PAA) solution.

[0138] Subsequently, while stirring the polyamic acid (PAA) solution, acetic anhydride (8.2 g; 80 mmol) was added and stirred until homogeneous. Furthermore, triethylamine (1.0 g; 10 mmol) was added and stirred until homogeneous, and then stirred again at room temperature (25°C) for 15 minutes. Furthermore, in this solution, A solution of 1,3,5-benzenetricarbonyl trichloride (BTC: 35 mg; 0.133 mmol), dissolved in 0.7 g of NMP in a separate 10 mL glass vial, was slowly added. As a result, rapid gelation occurred near the NMP solution of BTC, resulting in a heterogeneous system in which droplet-shaped gel and solution were mixed together. Therefore, a homogeneous gel could not be obtained.

[0139] [Comparative example 4A] The results of Comparative Example 4 above are thought to be because the rate of chemical imidation of polyamic acid using alicyclic acid dianhydrides is significantly slower than the rate of chemical imidation of polyamic acid using aromatic acid dianhydrides. In other words, when using the method based on the example in Patent Document 3 (Comparative Example 4A), it is thought that the crosslinking agent is mixed in before the conversion from polyamic acid to polyimide is sufficient. In this case, it is thought that the carboxylic acid moiety of the polyamic acid and the crosslinking agent react rapidly, and as a result, gelation proceeds rapidly around the droplets of the solution containing the crosslinking agent.

[0140] [Comparative Example 5] Bulk porous polyimide pPIr4 was prepared using the following procedure, based on Non-Patent Document 4. Porous polyimide pPI was prepared using the following procedure. In a 100 mL glass vial, 2,2'-dimethylbenzidine (m-Tolidine, DMBZ: 2.12 g; 10.0 mmol) was added to N-methyl-2-pyrrolidone (NMP: 45.4 g) and stirred with a magnetic stirrer until dissolved. 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.

[0141] Subsequently, while stirring the above solution, a solution of 1,3,5-tris(4-aminophenoxy)benzene (TAPB: 0.133 g; 0.333 mmol), dissolved in 2.7 g of NMP in another 20 mL glass vial, was added and stirred at room temperature for 10 minutes. Further, acetic anhydride (8.6 g; 84 mmol) and pyridine (6.6 g; 84 mmol) were added and stirred until homogeneous.

[0142] The above solution was transferred to a PFA mold (Φ100mm, depth 30mm) to a thickness of approximately 1mm, and left to stand at room temperature for about 30 minutes to obtain a non-fluid polyimide wet gel (PI-WG). The obtained polyimide wet gel (PI-WG) was suspended in a yellow color.

[0143] Porous polyimide (pPI) was obtained by performing solvent substitution and supercritical drying in the same manner as in Comparative Example 1.

[0144] [Comparative Example 6] Based on Patent Document 3 and Non-Patent Document 4, porous polyimide pPI was prepared using the following procedure. In a 100 mL glass vial, 2,2'-dimethylbenzidine (m-Tolidine, DMBZ: 2.12 g; 10.0 mmol) was dissolved in N-methyl-2-pyrrolidone (NMP: 46.9 g) while stirring with a magnetic stirrer. 1,2,3,4-cyclobutanetetracarboxylic anhydride (CBDA: 2.06 g; 10.5 mmol) powder was added while stirring at room temperature, and the mixture was stirred at room temperature (25°C) for 4 hours to obtain a polyamic acid (PAA) solution.

[0145] Subsequently, 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 2.7 g of NMP in another 20 mL glass vial, was added and stirred at room temperature for 10 minutes. Then, acetic anhydride (8.6 g; 84 mmol) and pyridine (6.6 g; 84 mmol) were added and stirred for 5 minutes until homogeneous.

[0146] The above solution was transferred to a PFA mold (Φ100mm, depth 30mm) to a thickness of approximately 1mm, and left to stand at room temperature for approximately 300 minutes to obtain a non-fluid polyimide wet gel (PI-WG). The obtained polyimide wet gel (PI-WG) was a white suspension.

[0147] Porous polyimide (pPI) was obtained by performing solvent substitution and supercritical drying in the same manner as in Comparative Example 1.

[0148] [Table 2]

[0149] [Table 3] [Industrial applicability]

[0150] The porous polyimide of this disclosure can be suitably applied to a variety of applications, including heat-resistant materials, particularly those requiring low coloration and high light transmittance, as well as materials for manufacturing porous carbon sheets.

Claims

1. Based on the pore volume (V) and BET specific surface area (A) determined by the gas adsorption method, the following formula is used: L = 4V / A The average pore size (L) obtained by this method is 5 nm or more and 8 nm or less. The light transmittance at a film thickness of 1 mm is between 10% and 100% at 450 nm. In the desorption curves on the nitrogen adsorption / desorption isotherm at 77K, the ratio of the adsorption amount at relative pressures of 0.90, 0.85, 0.80, and 0.75 to the adsorption amount at relative pressure 0.98 is 0.50 or more and 1.0 or less, 0.30 or more and 1.0 or less, 0.25 or more and 0.90 or less, and 0.20 or more and 0.85 or less, respectively, and A porous polyimide composition having a degree of polymerization (n) of 5 or more and less than 40.

2. The porous polyimide composition according to claim 1, having a crosslinked polyimide structure obtained by crosslinking a polyamic acid obtained by polymerizing tetracarboxylic dianhydride:diamine in an n+1:n ratio.

3. The porous polyimide composition according to claim 1 or 2, wherein the minimum value of the light transmittance between 400 nm and 700 nm at a film thickness of 1 mm is 5% or more.

4. The porous polyimide composition according to claim 1 or 2, wherein the difference between the maximum and minimum values ​​of light transmittance between 400 nm and 700 nm at a film thickness of 1 mm is 1% or more and 80% or less.

5. The porous polyimide composition according to claim 1 or 2, wherein the average value of the light transmittance between 400 nm and 700 nm at a film thickness of 1 mm is 30% or more and 100% or less.

6. Bulk density is 0.05 g / cm³ 3 0.50g / cm or more 3 The porous polyimide composition according to claim 1 or 2, which is as follows:

7. The porous polyimide composition according to claim 1 or 2, wherein the fracture strain in a three-point bending test is 5% or more.

8. The porous polyimide composition according to claim 1 or 2, wherein the bending strength in a three-point bending test is 5 MPa or more.

9. The porous polyimide composition according to claim 1 or 2, wherein the flexural modulus in a three-point bending test is 50 MPa or more.

10. The BET specific surface area after heat treatment at 200°C for 1 hour is 10 m². 2 / g or more 2,000m 2 A porous polyimide composition according to claim 1 or 2, wherein the amount is less than or equal to / g.

11. A porous polyimide composition according to claim 1 or 2, having a sheet shape.

12. The porous polyimide composition according to claim 11, wherein the average thickness is 10 mm or less.

13. When the light transmittance at 450 nm is LT [%] and the thickness is T [mm], the following formula is used: 0<(100-LT) / T≦70 A porous polyimide composition according to claim 1 or 2 that satisfies the relationship represented by the expression.

14. The porous polyimide composition according to claim 1 or 2, wherein the polyimide constituting the porous polyimide composition has a polyimide main skeleton and a crosslinking structure that crosslinks the polyimide main skeleton.

15. The porous polyimide composition according to claim 14, wherein the crosslinking structure is a structure of trivalent or higher groups derived from a monocyclic or polycyclic aromatic ring which may be substituted, or a group of trivalent or higher groups derived from a linked aromatic ring in which a plurality of substituted aromatic rings are linked to each other by direct bonds or by bonds via heteroatoms.

16. The polyimide main skeleton is given by the following general formula (1): 【Chemistry 1】 The porous polyimide composition according to claim 14, having a molecular chain represented by the general formula (1), wherein X and / or Y have a structure including an alicyclic ring, and n is the degree of polymerization of the polyimide.

17. The polyimide constituting the porous polyimide composition comprises a polymerization product of a polymerization component containing a tetracarboxylic dianhydride, a diamine, and a trifunctional or higher amine. The porous polyimide composition according to claim 1 or 2, wherein the ratio of the trifunctional or more amine to 100% by mass of the total of the tetracarboxylic dianhydride, the diamine, and the trifunctional or more amine is 1% by mass or more and 40% by mass or less.

18. The porous polyimide composition comprises a polymerization product of a polymerization component containing a tetracarboxylic dianhydride, a diamine, and a trifunctional or higher amine, The ratio of the tetracarboxylic dianhydride containing an aromatic ring to the total 100% by mass of the tetracarboxylic dianhydride is less than 50% by mass, and / or The ratio of the diamine containing an aromatic ring to the total 100% by mass of the diamines is less than 50% by mass. The porous polyimide composition according to claim 1 or 2.

19. A porous polyimide composition according to claim 1 or 2, which is used as a heat-resistant material with low coloration and high light transmission.

20. A polyamic acid composition comprising a resin precursor and a solvent, for obtaining a heat-resistant material with low coloration and high light transmission, The porous polyimide compositions obtained by adding a crosslinking agent to the polyamic acid composition and then chemically imidizing it by immersion in a solution, in this order, are described below (1) to (3): (1) Based on the pore volume (V) and BET specific surface area (A) determined by the gas adsorption method, the following formula is used: L = 4V / A The average pore size (L) determined by this method must be between 5 nm and 8 nm. (2) The light transmittance at a film thickness of 1 mm is 10% or more at 450 nm. (3) In the desorption curves on the nitrogen adsorption-desorption isotherm at 77K, the ratio of the amount of adsorption at relative pressures of 0.90, 0.85, 0.80, and 0.75 to the amount of adsorption at relative pressure 0.98 is 0.50 or more and 1.0 or less, 0.30 or more and 1.0 or less, 0.25 or more and 0.90 or less, and 0.20 or more and 0.85 or less, respectively. Satisfying the following conditions, A polyamic acid composition wherein the degree of polymerization (n) of the polyimide is 5 or more and less than 40.

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