Preparation method and application of large-free-volume polyimide

Abstract

The invention discloses a preparation method and application of large-free-volume polyimide, and belongs to the technical field of polyimide preparation. The preparation method comprises the following steps: firstly, adding two diamine monomers into an aprotic solvent in a specific protective atmosphere to form a uniform solution A; adding a dianhydride monomer into the uniform solution A, controlling the temperature and the stirring speed, and carrying out chemical reaction to generate a polyamide acid solution B; and finally, carrying out imidization on the polyamide acid solution B to prepare the polyimide with the large-free-volume rigid structure. The polyimide prepared by the invention has high rigidity and a large-free-volume chain structure, so that the polyimide has high thermal stability and can better adapt to a high-temperature working environment without being decomposed.

Description

Technical Field

[0001] The invention relates to a preparation method and application of large free volume polyimide, belonging to the technical field of polyimide preparation. Background Art

[0002] Polyimide (PI) is an aromatic heterocyclic polymer containing an imide ring. It has the advantages of high rigidity, good thermal stability, good processing performance and high cost performance. It is widely used in aerospace, semiconductor engineering, waterproof insulation, membrane preparation, liquid crystal display, engineering plastics and other fields. Polyimide can be prepared through a variety of different synthetic routes. Among them, the two-step method is under relatively low temperature conditions. In the first step, the dianhydride and diamine monomers are dissolved in a non-protonic solvent at a molar ratio of 1:1, and the dianhydride and diamine undergo a condensation reaction to form polyamic acid; in the second step, the polyamic acid is dehydrated and cyclized by imidization to form polyimide. The main methods of imidization are chemical imidization and thermal imidization. Chemical imidization, that is, polyimide is generated under the joint action of a catalyst and a dehydrating agent. This method has the advantages of mild reaction conditions and fast reaction speed. The other is thermal imidization, that is, polyamic acid is dehydrated and cyclized under heating conditions to form polyimide. Compared with chemical imidization, thermal imidization does not require catalysts and dehydrating agents, and the reaction system is relatively simple.

[0003] In addition to being affected by reaction conditions such as reaction temperature, reaction time and catalyst, the structure and properties of polyimide are also affected by the physical structure and chemical properties of dianhydride and diamine monomers. By selecting dianhydrides and diamines with different structures, polyimides with different microstructures can be prepared, thereby realizing their wide application in different fields. Based on the side chain relaxation theory, some scholars designed and prepared triphenyldiamine monomers with side groups of different sizes, and polymerized them with pyromellitic dianhydride (PMDA) to obtain polyimides with different structures. The prepared polyimide maintains excellent thermal stability, and the dielectric constant is reduced, and the mechanical properties are gradually improved (European Polymer Journal 211 (2024) 112969). However, this method has a cumbersome preparation process, harsh reaction conditions, and is not easy to industrialize. Therefore, from the perspective of polyimide synthesis, by selecting different raw materials, diamine and dianhydride monomers with large free volume, good thermal stability and strong rigidity are introduced into the polyimide polymer chain, and polyimide with large free volume and high thermal stability is synthesized under simple and mild conditions, so as to adapt to high temperature working environment. Therefore, it is particularly important to develop a polyimide material with good thermal stability and large free volume to adapt to more severe working environment. Summary of the invention

[0004] In order to solve the problem of small free volume and poor thermal stability of polyimide polymer chain, the present invention provides a method for preparing polyimide with large free volume and application thereof from the perspective of molecular structure design.

[0005] The present invention introduces a diamine monomer containing phenyl ether, biphenyl and methylene biphenyl groups on the basis of 3,5-diaminobenzoic acid (DABA) as a diamine monomer, and prepares a polyimide with a large free volume through a polycondensation chemical reaction and an imidization method. The present invention has a simple operation method and introduces a diamine structure containing a long-chain benzene ring, providing a new idea and method for preparing a polyimide with a large free volume.

[0006] The present invention provides a method for preparing a large free volume polyimide, which is carried out according to the following steps:

[0007] (1) Under a specific protective atmosphere, two diamine monomers are added into an aprotic solvent in a certain ratio to form a uniform solution A;

[0008] (2) adding a certain amount of dianhydride monomer to the homogeneous solution A, controlling the temperature and stirring speed, causing a chemical reaction to generate a polyamic acid solution B;

[0009] (3) The polyamic acid solution B is imidized to obtain a polyimide having a large free volume.

[0010] Furthermore, in step (1), the first diamine monomer is 3,5-diaminobenzoic acid (DABA), and its chemical structure is as follows:

[0011]

[0012] The second diamine monomer is any one of the following compounds, and their chemical structural formulas are as follows:

[0013]

[0014]

[0015] Furthermore, in step (2), the dianhydride monomer is any one of the following structures:

[0016]

[0017] Furthermore, in steps (1) and (2), the molar ratio of the first diamine monomer to the second diamine monomer is (1-10):(1-10), and the ratio of the sum of the molar numbers of the two diamine monomers to the molar number of the dianhydride monomer is 1:1.

[0018] Furthermore, the type of the aprotic solvent in step (1) is any one of dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), and tetrahydrofuran (THF).

[0019] Furthermore, the mass fraction of the diamine monomer in solution A of step (1) is 5 to 10 wt %.

[0020] Furthermore, in step (1), the specific protective atmosphere is any one of nitrogen, argon and helium.

[0021] Furthermore, in step (2), the mass fraction of the sum of the dianhydride monomer and the diamine monomer in solution B is 10 to 30 wt%.

[0022] Furthermore, in step (2), the temperature is controlled at -10°C to 30°C, the speed of mechanical stirring is in the range of 100 to 300 rpm, the chemical reaction time is 12 to 72 hours, and the viscosity-average molecular weight of the generated polyamic acid solution B is in the range of 50,000 to 300,000, having the advantages of high rigidity and large free volume.

[0023] Furthermore, the imidization method in step (3) is any one of thermal imidization and chemical imidization.

[0024] Furthermore, in step (3), the thermal imidization method is as follows: the polyamic acid is placed in a forced air drying oven, heated to 70-90°C and maintained for 30-240 min, then the temperature is raised to 130-150°C and maintained for 30-240 min, the temperature is further raised to 190-210°C and maintained for 30-240 min, the temperature is then raised to 250-270°C and maintained for 30-240 min, and finally cooled to room temperature to obtain polyimide.

[0025] Alternatively, the chemical imidization method in step (3) is: adding a dehydrating agent and a catalyst to the polyamic acid solution, and continuing to heat and reflux at 180° C. for 12 to 24 hours to obtain polyimide. The dehydrating agent is acetic anhydride, and the amount of the dehydrating agent added is 0.01% to 10% by mass of the polyamic acid solution; the catalyst is either isoquinoline or pyridine, and the amount of the catalyst added is 0.01% to 10% by mass of the polyamic acid solution.

[0026] The invention provides a polyimide with large free volume prepared by the method.

[0027] The present invention provides the application of the large free volume polyimide in the field of gas separation membranes. The gas separation membrane prepared with the polyimide having high rigidity and large free volume has the advantages of high gas permeability and strong plasticization resistance.

[0028] The present invention also provides applications of the large free volume polyimide in the fields of waterproof insulation, liquid crystal display, engineering plastics, etc.

[0029] Compared with the prior art, the present invention has at least the following beneficial effects:

[0030] (1) The present invention uses dianhydride and diamine to undergo polymerization reaction in an aprotic solvent to generate polyamic acid. Then, imidization is performed to dehydrate and cyclize the polyamic acid to generate polyimide. The method is simple to operate, has mild conditions, and is suitable for large-scale production.

[0031] (2) The polyimide prepared by the present invention not only has a chain structure with a large free volume but also has high thermal stability, and can better adapt to a high-temperature working environment without decomposition.

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments disclosed in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is the general chemical reaction formula for synthesizing the polyimide of the embodiment of the present invention.

[0034] Figure 2 It is the infrared spectra of the polyimide of Examples 1 to 3 of the present invention.

[0035] Figure 3 It is the nuclear magnetic resonance hydrogen spectrum of the polyimide of Examples 1 to 3 of the present invention.

[0036] Figure 4 It is a dynamic thermomechanical analysis curve diagram of the polyimide of Examples 1 to 3 of the present invention.

[0037] Figure 5 It is the thermogravimetric analysis curve of the polyimide of Examples 1 to 3 of the present invention. DETAILED DESCRIPTION

[0038] The present invention is further illustrated by the following examples, but is not limited to the following examples.

[0039] Comparative Example 1

[0040] (1) Under a nitrogen atmosphere, 1 mol (152.15 g) of 3,5-diaminobenzoic acid (DABA) was added to a three-necked flask containing 3379 g of N-methylpyrrolidone (NMP), and the mixture was stirred until the diamine was completely dissolved to obtain a uniform diamine solution A. The mass fraction of the diamine in the solution A was 4.3 wt %.

[0041] (2) The reaction temperature was controlled at 0°C, 1.000 mol (444.24 g) of hexafluorodianhydride (6FDA) was added to solution A, and the mixture was mechanically stirred and reacted for 24 h. The stirring speed was controlled at 200 rpm to obtain a viscous polyamic acid (PAA) solution B with a mass fraction of 15 wt %, a viscosity-average molecular weight of 230,000, and a molar ratio of hexafluorodianhydride to 3,5-diaminobenzoic acid in the polyamic acid of 1:1.

[0042] (3) 0.2 mol (20.42 g) of acetic anhydride and 0.2 mol (25.83 g) of isoquinoline were added to the obtained polyamic acid solution B, and the mixture was heated to reflux at 180° C. for 12 h for chemical imidization to obtain a polyimide (PI) having a rigid structure.

[0043] The test results show that the glass transition temperature of the polyimide is 320° C. and the free volume percentage is 13.1%.

[0044] Example 1

[0045] (1) Under nitrogen atmosphere, 0.900 mol (263.09 g) of 4.4-(1,4-phenylenedioxy) dianiline (TPE-Q) and 0.100 mol (15.21 g) of 3,5-diaminobenzoic acid (DABA) were added sequentially into a three-necked flask containing 4095 g of N-methylpyrrolidone (NMP), and the mixture was stirred until the diamine was completely dissolved to obtain a uniform diamine solution A. The mass fraction of the diamine in the solution A was 6.36 wt%.

[0046] (2) The reaction temperature was controlled at 0°C, 1.000 mol (444.24 g) of hexafluorodianhydride (6FDA) was added to solution A, and the mixture was mechanically stirred and reacted for 24 hours. The stirring speed was controlled at 200 rpm to obtain a viscous polyamic acid (PAA) solution B with a mass fraction of 15 wt % and a viscosity average molecular weight of 170000. The molar ratio of TPE-Q to DABA in the polyamic acid was 9:1, and the molar ratio of dianhydride to diamine monomer was 1:1.

[0047] (3) The obtained polyamic acid is placed in a forced air drying oven and subjected to thermal imidization according to a programmed temperature increase of 80° C. for 80 min, 150° C. for 60 min, 200° C. for 60 min, and 250° C. for 60 min to obtain a polyimide (PI) with a large free volume.

[0048] The test results show that the glass transition temperature of the polyimide is 309° C. and the free volume percentage is 14.5%.

[0049] Example 2

[0050] (1) Under nitrogen atmosphere, 0.800 mol (233.86 g) of 1,3-di(4'-aminophenoxy)benzene (TPE-R) and 0.200 mol (30.45 g) of 3,5-diaminobenzoic acid (DABA) were added sequentially into a three-necked flask containing 4015 g of N-methylpyrrolidone (NMP), and the mixture was stirred until the diamine was completely dissolved to obtain a uniform diamine solution A. The mass fraction of the diamine in the solution A was 6.17 wt%.

[0051] (2) The reaction temperature was controlled at 0°C, 1.000 mol (444.24 g) of hexafluorodianhydride (6FDA) was added to solution A, and the mixture was mechanically stirred and reacted for 24 hours. The stirring speed was controlled at 200 rpm to obtain a viscous polyamic acid (PAA) solution B with a mass fraction of 15 wt % and a viscosity average molecular weight of 157,000. The molar ratio of TPE-R to DABA in the polyamic acid was 8:2, and the molar ratio of dianhydride to diamine was 1:1.

[0052] (3) The obtained polyamic acid is placed in a forced air drying oven and subjected to thermal imidization according to a programmed temperature increase of 80° C. for 80 min, 150° C. for 60 min, 200° C. for 60 min, and 250° C. for 60 min to obtain a polyimide (PI) with a large free volume.

[0053] The test results show that the glass transition temperature of the polyimide is 287° C. and the free volume percentage is 13.7%.

[0054] Example 3

[0055] (1) Under nitrogen atmosphere, 0.700 mol (287.36 g) of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane (BAPP) and 0.300 mol (45.65 g) of 3,5-diaminobenzoic acid (DABA) were added sequentially into a three-necked flask containing 4404.42 g of N-methylpyrrolidone (NMP), and the mixture was stirred until the diamine was completely dissolved to obtain a uniform diamine solution A. The mass fraction of the diamine in the solution A was 7.03 wt%.

[0056] (2) The reaction temperature was controlled at 0°C, 1.000 mol (444.24 g) of hexafluorodianhydride (6FDA) was added to solution A, and the mixture was mechanically stirred and reacted for 24 hours. The stirring speed was controlled at 200 rpm to obtain a viscous polyamic acid (PAA) solution B with a mass fraction of 15 wt % and a viscosity average molecular weight of 126000. The molar ratio of BAPP to DABA in the polyamic acid was 7:3, and the molar ratio of dianhydride to diamine was 1:1.

[0057] (3) The obtained polyamic acid is placed in a forced air drying oven and subjected to thermal imidization according to a programmed temperature increase of 80° C. for 80 min, 150° C. for 60 min, 200° C. for 60 min, and 250° C. for 60 min to obtain a polyimide (PI) with a large free volume.

[0058] The test results show that the glass transition temperature of the polyimide is 286° C. and the free volume percentage is 16.4%.

[0059] Example 4

[0060] (1) Under a helium protective atmosphere, 0.500 mol (214.17 g) of 4,4'-[1,4-phenylbis(oxy)]bis[3-(trifluoromethyl)aniline] (6FAPB) and 0.500 mol (76.08 g) of 3,5-diaminobenzoic acid (DABA) were added sequentially into a three-necked flask containing 4162.11 g of N-methylpyrrolidone (NMP), and the mixture was stirred until the diamine was completely dissolved to obtain a uniform diamine solution A. The mass fraction of the diamine in the solution A was 6.97 wt%.

[0061] (2) The reaction temperature was controlled at -5°C, 1.000 mol (444.24 g) of hexafluorodianhydride (6FDA) was added to solution A, and the mixture was mechanically stirred and reacted for 36 hours. The stirring speed was controlled at 150 rpm to obtain a viscous polyamic acid (PAA) solution B with a mass fraction of 15 wt % and a viscosity average molecular weight of 150000. The molar ratio of 6FAPB to DABA in the polyamic acid was 5:5, and the molar ratio of dianhydride to diamine was 1:1.

[0062] (3) The obtained polyamic acid is placed in a forced air drying oven and subjected to thermal imidization according to a programmed temperature increase of 70° C. for 120 min, 140° C. for 80 min, 200° C. for 80 min, and 250° C. for 120 min to obtain a polyimide (PI) with a large free volume.

[0063] The test results show that the glass transition temperature of the polyimide is 280° C. and the free volume percentage is 18.2%.

[0064] Example 5

[0065] (1) Under an argon protective atmosphere, 0.500 mol (216.24 g) of 4,4'-bis(3-aminophenoxy)diphenyl sulfone (m-BAPS) and 0.500 mol (76.08 g) of 3,5-diaminobenzoic acid (DABA) were added sequentially into a three-necked flask containing 4173.86 g of N-methylpyrrolidone (NMP), and the mixture was stirred until the diamine was completely dissolved to obtain a uniform diamine solution A. The mass fraction of the diamine in the solution A was 6.54 wt%.

[0066] (2) The reaction temperature was controlled at -5°C, 1.000 mol (444.24 g) of hexafluorodianhydride (6FDA) was added to solution A, mechanically stirred and reacted for 36 hours, and the stirring speed was controlled at 150 rpm to obtain a viscous polyamic acid (PAA) solution B with a mass fraction of 15 wt % and a viscosity average molecular weight of 150000. The molar ratio of m-BAPS to DABA in the polyamic acid was 5:5, and the molar ratio of dianhydride to diamine was 1:1.

[0067] (3) The obtained polyamic acid is placed in a forced air drying oven and subjected to thermal imidization according to a programmed temperature increase of 70° C. for 120 min, 140° C. for 80 min, 200° C. for 80 min, and 250° C. for 120 min to obtain a polyimide (PI) with a large free volume.

[0068] The test results show that the glass transition temperature of the polyimide is 252° C. and the free volume percentage is 15.7%.

[0069] Example 6

[0070] (1) Under an argon protective atmosphere, 0.600 mol (192.14 g) of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB) and 0.400 mol (60.86 g) of 3,5-diaminobenzoic acid (DABA) were added sequentially into a three-necked flask containing 3951.03 g of N-methylpyrrolidone (NMP), and the mixture was stirred until the diamine was completely dissolved to obtain a uniform diamine solution A, in which the mass fraction of the diamine in the solution A was 6.01 wt%.

[0071] (2) The reaction temperature was controlled at 0°C, 1.000 mol (444.24 g) of hexafluorodianhydride (6FDA) was added to solution A, and the mixture was mechanically stirred and reacted for 24 hours. The stirring speed was controlled at 200 rpm to obtain a viscous polyamic acid (PAA) solution B with a mass fraction of 15 wt % and a viscosity average molecular weight of 115,000. The molar ratio of TFMB to DABA in the polyamic acid was 6:4, and the molar ratio of dianhydride to diamine was 1:1.

[0072] (3) 0.2 mol (20.42 g) of acetic anhydride and 0.2 mol (25.83 g) of isoquinoline were added to the obtained polyamic acid solution B, and the mixture was heated to reflux at 180° C. for 12 h for chemical imidization to obtain a polyimide (PI) with a large free volume.

[0073] The test results show that the glass transition temperature of the polyimide is 347° C. and the free volume percentage is 17.1%.

[0074] Example 7

[0075] (1) Under nitrogen atmosphere, 0.700 mol (217.34 g) of 4,4'-methylenebis(2,6-diethylaniline) (MDEA) and 0.300 mol (45.65 g) of 3,5-diaminobenzoic acid (DABA) were added into a three-necked flask containing 4007.64 g of N-methylpyrrolidone (NMP) in sequence, and the mixture was stirred until the diamine was completely dissolved to obtain a uniform diamine solution A. The mass fraction of the diamine in the solution A was 6.16 wt%.

[0076] (2) The reaction temperature was controlled at 0°C, 1.000 mol (444.24 g) of hexafluorodianhydride (6FDA) was added to solution A, and the mixture was mechanically stirred and reacted for 24 hours. The stirring speed was controlled at 200 rpm to obtain a viscous polyamic acid (PAA) solution B with a mass fraction of 15 wt % and a viscosity average molecular weight of 150,000. The molar ratio of MDEA to DABA in the polyamic acid was 7:3, and the molar ratio of dianhydride to diamine was 1:1.

[0077] (3) 0.2 mol (20.42 g) of acetic anhydride and 0.2 mol (25.83 g) of isoquinoline were added to the obtained polyamic acid solution B, and the mixture was heated to reflux at 180° C. for 12 h for chemical imidization to obtain a polyimide (PI) with a large free volume.

[0078] The test results show that the glass transition temperature of the polyimide is 324° C. and the free volume percentage is 19.2%.

[0079] Example 8

[0080] (1) Under a nitrogen atmosphere, 0.900 mol (191.06 g) of 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl (m-Tolidine) and 0.100 mol (15.22 g) of 3,5-diaminobenzoic acid (DABA) were added sequentially into a three-necked flask containing 3686.28 g of N-methylpyrrolidone (NMP), and the mixture was stirred until the diamine was completely dissolved to obtain a uniform diamine solution A, in which the mass fraction of the diamine in the solution A was 5.3 wt%.

[0081] (2) The reaction temperature was controlled at 0°C, 1.000 mol (444.24 g) of hexafluorodianhydride (6FDA) was added to solution A, and the mixture was mechanically stirred and reacted for 24 hours. The stirring speed was controlled at 200 rpm to obtain a viscous polyamic acid (PAA) solution B with a mass fraction of 15 wt % and a viscosity average molecular weight of 140000. The molar ratio of m-Tolidine to DABA in the polyamic acid was 9:1, and the molar ratio of dianhydride to diamine was 1:1.

[0082] (3) 0.2 mol (20.42 g) of acetic anhydride and 0.2 mol (25.83 g) of isoquinoline were added to the obtained polyamic acid solution B, and the mixture was heated to reflux at 180° C. for 12 h for chemical imidization to obtain a polyimide (PI) with a large free volume.

[0083] The test results show that the glass transition temperature of the polyimide is 300° C. and the free volume percentage is 15.6%.

[0084] Example 9

[0085] (1) Under nitrogen atmosphere, 0.800 mol (268.98 g) of 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether (6FODA) and 0.200 mol (30.43 g) of 3,5-diaminobenzoic acid (DABA) were added sequentially into a three-necked flask containing 4214 g of N-methylpyrrolidone (NMP), and stirred until the diamine was completely dissolved to obtain a uniform diamine solution A. The mass fraction of the diamine in solution A was 6.63 wt%.

[0086] (2) The reaction temperature was controlled at 0°C, 1.000 mol (444.24 g) of hexafluorodianhydride (6FDA) was added to solution A, and the mixture was mechanically stirred and reacted for 24 hours. The stirring speed was controlled at 200 rpm to obtain a viscous polyamic acid (PAA) solution B with a mass fraction of 15 wt % and a viscosity average molecular weight of 160,000. The molar ratio of 6FODA to DABA in the polyamic acid was 8:2, and the molar ratio of dianhydride to diamine was 1:1.

[0087] (3) 0.2 mol (20.42 g) of acetic anhydride and 0.2 mol (25.83 g) of isoquinoline were added to the obtained polyamic acid solution B, and the mixture was heated to reflux at 180° C. for 12 h for chemical imidization to obtain a polyimide (PI) with a large free volume.

[0088] The test results show that the glass transition temperature of the polyimide is 293° C. and the free volume percentage is 18.3%.

[0089] Example 10

[0090] (1) Under a nitrogen atmosphere, 0.700 mol (166.77 g) of 2,6-diaminoanthracene-9,10-dione (2,6-DAAQ) and 0.300 mol (45.65 g) of 3,5-diaminobenzoic acid (DABA) were added sequentially into a three-necked flask containing 3721 g of N-methylpyrrolidone (NMP), and the mixture was stirred until the diamine was completely dissolved to obtain a uniform diamine solution A. The mass fraction of the diamine in the solution A was 5.4 wt%.

[0091] (2) The reaction temperature was controlled at 0°C, 1.000 mol (444.24 g) of hexafluorodianhydride (6FDA) was added to solution A, and the mixture was mechanically stirred and reacted for 24 hours. The stirring speed was controlled at 200 rpm to obtain a viscous polyamic acid (PAA) solution B with a mass fraction of 15 wt % and a viscosity average molecular weight of 145000. The molar ratio of 2,6-DAAQ to DABA in the polyamic acid was 7:3, and the molar ratio of dianhydride to diamine was 1:1.

[0092] (3) 0.2 mol (20.42 g) of acetic anhydride and 0.2 mol (25.83 g) of isoquinoline were added to the obtained polyamic acid solution B, and the mixture was heated to reflux at 180° C. for 12 h for chemical imidization to obtain a polyimide (PI) with a large free volume.

[0093] The test results show that the glass transition temperature of the polyimide is 290° C. and the free volume percentage is 16.0%.

[0094] Embodiment 11

[0095] (1) Under a nitrogen atmosphere, 0.600 mol (219.76 g) of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP) and 0.400 mol (60.86 g) of 3,5-diaminobenzoic acid (DABA) were added sequentially into a three-necked flask containing 3721 g of N-methylpyrrolidone (NMP), and the mixture was stirred until the diamine was completely dissolved to obtain a uniform diamine solution A. The mass fraction of the diamine in the solution A was 7.01 wt%.

[0096] (2) The reaction temperature was controlled at 0°C, 1.000 mol (444.24 g) of hexafluorodianhydride (6FDA) was added to solution A, and the mixture was mechanically stirred and reacted for 24 hours. The stirring speed was controlled at 200 rpm to obtain a viscous polyamic acid (PAA) solution B with a mass fraction of 15 wt % and a viscosity average molecular weight of 160000. The molar ratio of 6FAP to DABA in the polyamic acid was 6:4, and the molar ratio of dianhydride to diamine was 1:1.

[0097] (3) 0.2 mol (20.42 g) of acetic anhydride and 0.2 mol (25.83 g) of isoquinoline were added to the obtained polyamic acid solution B, and the mixture was heated to reflux at 180° C. for 12 h for chemical imidization to obtain a polyimide (PI) with a large free volume.

[0098] The test results show that the glass transition temperature of the polyimide is 265° C. and the free volume percentage is 18.2%.

[0099] Figure 1 This is the general chemical reaction formula for synthesizing the polyimide provided by the present invention.

[0100] Figure 2 is the infrared spectrum of the polyimide prepared in Examples 1 to 3. In the infrared spectrum of the polyimide obtained in Example 1: 1781cm -1 and 1713cm -1 The symmetrical and asymmetrical stretching vibration peaks of C=O appear at 1380cm -1 The asymmetric stretching vibration peak of -CNC- is 717cm -1 The out-of-plane vibration absorption peak of the imide ring (O=CNC=O) is shown in Figure 2, proving that the polyimide has been successfully prepared. -1 and 1713cm -1 The symmetrical and asymmetrical stretching vibration peaks of C=O appear at 1380cm -1 The asymmetric stretching vibration peak of -CNC- is 717cm -1 The out-of-plane vibration absorption peak of the imide ring (O=CNC=O) strongly proves the successful preparation of polyimide. In the spectrum of the polyimide prepared in Example 3, 1781 cm -1 and 1713cm -1 The symmetrical and asymmetrical stretching vibration peaks of C=O appear at 1380cm -1 The asymmetric stretching vibration peak of -CNC- is 717cm -1 The out-of-plane vibration absorption peak of the imide ring (O=CNC=O) is a strong proof of the successful preparation of polyimide.

[0101] Figure 3It is the hydrogen nuclear magnetic resonance spectrum of the polyimide prepared in Examples 1 to 3. In the spectrum of the polyimide obtained in Example 1, chemical shifts of 7.97ppm, 7.75ppm and 8.17ppm belonging to 6FDA aromatic protons and chemical shifts of 7.86ppm and 8.19ppm belonging to DABA benzene ring aromatic protons were observed; chemical shifts of 7.43ppm, 7.17ppm and 7.18ppm were attributed to aromatic protons on the benzene ring in TPE-Q; indicating that 6FDA, TPE-Q and DABA monomers were successfully introduced into the polyimide polymer chain. In the spectrum of the polyimide prepared in Example 2, chemical shifts attributable to 6FDA aromatic protons at 7.97ppm, 7.75ppm and 8.17ppm and chemical shifts attributable to DABA benzene ring aromatic protons at 7.86ppm and 8.19ppm were observed; chemical shifts attributable to aromatic protons on the benzene ring in TPE-R at 7.46ppm, 7.23ppm, 6.84ppm, 6.88ppm and 7.43ppm were observed; indicating that 6FDA, TPE-R and DABA monomers were successfully introduced into the polyimide polymer chain. In the spectrum of the polyimide prepared in Example 3, chemical shifts attributable to 6FDA aromatic protons at 7.97ppm, 7.75ppm and 8.17ppm and chemical shifts attributable to DABA benzene ring aromatic protons at 7.86ppm and 8.19ppm were observed. The chemical shifts of 7.43ppm, 7.13ppm, 7.28ppm, 7.02ppm and 1.66ppm were attributed to the aromatic protons of the benzene ring and methyl group in BAPP, indicating that 6FDA, BAPP and DABA monomers were successfully introduced into the polyimide polymer chain.

[0102] Figure 4 It is a dynamic mechanical analysis curve diagram of the polyimide prepared in Examples 1 to 3. In the curve diagram of the polyimide obtained in Example 1, the glass transition temperature of 6FDA / TPE-Q:DABA is 309°C. In the curve diagram of the polyimide prepared in Example 2, the glass transition temperature of 6FDA / TPE-R:DABA is 287°C. In the curve diagram of the polyimide prepared in Example 3, the glass transition temperature of 6FDA / BAPP:DABA is 286°C.

[0103] Figure 5It is a thermogravimetric analysis curve of the polyimide prepared in Examples 1 to 3 of the present invention. In the curve of the polyimide obtained in Example 1, the decomposition temperature of the polyimide can reach 370°C and the maximum weight loss rate temperature is 567°C. It shows that 6FDA / TPE-Q:DABA polyimide has good thermal stability. In the curve of the polyimide prepared in Example 2, the decomposition temperature of the polyimide can reach 370°C and the maximum weight loss rate temperature is 563°C. It shows that 6FDA / TPE-R:DABA polyimide has good thermal stability. In the curve of the polyimide prepared in Example 3, the decomposition temperature of the polyimide can reach 370°C and the maximum weight loss rate temperature is 557°C. It shows that 6FDA / BAPP:DABA polyimide has good thermal stability.

[0104] Comparative Examples 1 to 3 show that hexafluorodianhydride is selected as the dianhydride monomer, 3,5-diaminobenzoic acid is selected as one of the diamine monomers, and the other diamine monomers are selected from 4,4'-(1,4-phenylenedioxy) dianiline, 1,3-bis(4'-aminophenoxy)benzene, and 2,2-bis[4-(4-aminophenoxy)phenyl]propane in Examples 1 to 3, respectively, to prepare polyimides with large free volumes, and it is found that the free volume percentages of the three polyimides synthesized in Examples 1 to 3 are all higher than those in Comparative Example 1. Among them, the free volume percentage of Example 3 reaches 16.4%, which is much higher than the free volume percentage of 13.1% in Comparative Example 1.

[0105] Comparative Examples 4 to 5, hexafluorodianhydride is selected as the dianhydride monomer, 3,5-diaminobenzoic acid is selected as one of the diamine monomers, and the other diamine monomers are selected from 4,4'-[1,4-phenylbis(oxy)]bis[3-(trifluoromethyl)aniline] and 4,4'-bis(3-aminophenoxy)diphenylsulfone in Examples 4 to 5, respectively, to prepare polyimides with large free volumes. It is found that the free volume percentages of the two polyimides synthesized in Examples 4 to 5 are both above 15%. In Example 4, when 4,4'-[1,4-phenylbis(oxy)]bis[3-(trifluoromethyl)aniline] is used as one of the diamine monomers, the side group contains a large volume of -CF3, which increases the steric hindrance, limits the rotation of the ortho-phenyl ether bond to a certain extent, and reduces the movement of the chain segment, so it has a higher free body percentage (the value is 18.2%), which is much higher than the free volume percentage of 13.1% in Comparative Example 1.

[0106] Comparative Examples 6 to 8, hexafluorodianhydride is selected as the dianhydride monomer, 3,5-diaminobenzoic acid is selected as one of the diamine monomers, and the other diamine monomers are selected from 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 4,4'-methylenebis(2,6-diethylaniline), and 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl in Examples 6 to 8, respectively, to prepare polyimides with large free volumes. It is found that the free volume percentages of the three polyimides synthesized in Examples 6 to 8 all reach more than 15%. Among them, when 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl is used as one of the monomers in Example 6, because its side group contains a large volume of -CF3, the steric hindrance is increased, and its biphenyl structure increases the rigidity of the polymer chain. The polyimide synthesized in Example 6 has the highest glass transition temperature and the largest free volume, and their values ​​are 347°C and 17.1%, respectively. The glass transition temperature (320°C) and free volume percentage (13.1%) of Comparative Example 1 are much higher than those of Comparative Example 1.

[0107] Comparative Examples 9 to 11, hexafluorodianhydride was selected as the dianhydride monomer, 3,5-diaminobenzoic acid was selected as one of the diamine monomers, and the other monomers were selected from 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether, 2,6-diaminoanthracene-9,10-dione, and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane in Examples 9 to 11, respectively, to prepare polyimides with large free volumes. It was found that the free volume percentages of the three polyimides synthesized in Examples 9 to 11 all reached more than 16%, which was much higher than the free volume percentage of 13.1% in Comparative Example 1.

[0108] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may still be modified, or some or all of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a large free volume polyimide, characterized in that The following steps are involved: (1) Under a protective atmosphere, two diamine monomers are added to an aprotic solvent to form a uniform solution A; The two diamine monomers, the first diamine monomer is 3,5-diaminobenzoic acid, and its chemical structure is as follows: ； The second diamine monomer is any one of the following compounds: ； (2) adding a dianhydride monomer to the homogeneous solution A, controlling the temperature and stirring speed, causing a chemical reaction to generate a polyamic acid solution B; the dianhydride monomer in step (2) is any one of the following structures: ； (3) The polyamic acid solution B is imidized to obtain a polyimide having a large free volume.

2. The method for preparing a large free volume polyimide according to claim 1, characterized in that: In steps (1) and (2), the molar ratio of the first diamine monomer to the second diamine monomer is (1-10):(1-10), and the ratio of the sum of the molar numbers of the two diamine monomers to the molar number of the dianhydride monomer is 1:

1.

3. The method for preparing a large free volume polyimide according to claim 1, characterized in that: The type of the aprotic solvent in step (1) is any one of dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylacetamide, and tetrahydrofuran; the mass fraction of the diamine monomer in solution A of step (1) is 5-10 wt%.

4. The method for preparing a large free volume polyimide according to claim 1, characterized in that: In step (1), the protective atmosphere is any one of nitrogen, argon and helium.

5. The method for preparing a large free volume polyimide according to claim 1, characterized in that: The mass fraction of the sum of the dianhydride monomer and the diamine monomer in solution B in step (2) is 10-30 wt%.

6. The method for preparing a large free volume polyimide according to claim 1, characterized in that: In step (2), the temperature is controlled at -10°C to 30°C, the speed of mechanical stirring is in the range of 100 to 300 rpm, the chemical reaction time is 12 to 72 h, and the viscosity average molecular weight of the generated polyamic acid solution B is in the range of 50,000 to 300,000.

7. The method for preparing a large free volume polyimide according to claim 1, characterized in that: The imidization method in step (3) is any one of thermal imidization and chemical imidization.

8. The method for preparing a large free volume polyimide according to claim 7, characterized in that: In step (3), the thermal imidization method is as follows: the polyamic acid is placed in a forced air drying oven, heated to 70-90°C and maintained for 30-240 min, then the temperature is raised to 130-150°C and maintained for 30-240 min, the temperature is further raised to 190-210°C and maintained for 30-240 min, the temperature is further raised to 250-270°C and maintained for 30-240 min, and finally cooled to room temperature to obtain polyimide.

9. The method for preparing a large free volume polyimide according to claim 7, characterized in that: The chemical imidization method in step (3) is: adding a dehydrating agent and a catalyst to a polyamic acid solution, and continuing to heat and reflux at 180° C. for 12 to 24 hours to obtain polyimide; wherein the dehydrating agent is acetic anhydride, and the amount of the dehydrating agent added is 0.01% to 10% by mass of the polyamic acid solution; the catalyst is either isoquinoline or pyridine, and the amount of the catalyst added is 0.01% to 10% by mass of the polyamic acid solution.

10. Use of a large free volume polyimide prepared by the method according to any one of claims 1 to 9 in the field of gas separation membranes.

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