Sulfonated diamine monomer, sulfonated polyimide copolymer, proton exchange membrane, preparation method and application

Abstract

The invention discloses a sulfonated diamine monomer, a sulfonated polyimide copolymer, a proton exchange membrane, a preparation method and application. The sulfonated diamine monomer provided by the invention has a sulfonated aromatic side chain, and is structurally characterized in that a sulfonic acid group is connected to the aromatic side chain, and a main chain adopts a quaterphenyl structure, so that a material is endowed with excellent chemical stability. Compared with the existing sulfonated polyimide material, the sulfonated polyimide copolymer prepared by the invention is easier to form a stable hydrophilic-hydrophobic microphase separation structure, and the prepared proton exchange membrane shows excellent proton conductivity and long-term durability under the conditions of high temperature and low relative humidity; the method has a wide application prospect and an important practical value in the field of electrochemical energy sources such as proton exchange membrane fuel cells.

Description

Technical Field

[0001] The present invention relates to the field of energy batteries, and in particular to a sulfonated diamine monomer, a sulfonated polyimide copolymer, a proton exchange membrane, a preparation method and applications. Background Art

[0002] Proton exchange membrane fuel cells (PEMFC) have the advantages of high efficiency, cleanliness, and low noise, and have broad application prospects in electric vehicles, electronic devices, home distributed power generation systems, aerospace and other fields. Especially in the field of electric vehicles, its application can reduce dependence on petroleum resources and play an important role in promoting sustainable development and environmental protection. The proton exchange membrane is one of the core components of the fuel cell, and its performance and stability directly affect the power generation efficiency and service life of the fuel cell. From the perspective of practical application, the proton exchange membrane should meet the following basic requirements: 1) low cost and suitable for large-scale commercial applications; 2) high proton conductivity to improve the electrochemical performance of the fuel cell; 3) high mechanical strength and toughness to ensure that the membrane maintains structural integrity during long-term operation; 4) low swelling rate to reduce the impact of membrane size changes on battery performance; 5) excellent chemical stability, especially good free radical oxidation stability, to improve the durability of the membrane; 6) low fuel and oxygen permeability to reduce gas cross leakage and improve energy conversion efficiency; 7) good thermal stability, which can maintain stable performance within the operating temperature range of the fuel cell. Produced by DuPont, USA Perfluorosulfonic acid membrane is one of the most typical proton exchange membranes, with excellent chemical stability and high proton conductivity. However, this membrane still has the following shortcomings in fuel cell applications: 1) high cost; 2) low operating temperature ( The glass transition temperature of the fuel cell is only about 105 ° C, and the operating temperature of the fuel cell must be much lower than its glass transition temperature); 3) high swelling rate; 4) high fuel permeability; 5) poor high temperature water retention (Guan PP, Zou YC, Zhang M, et al. High-temperature low-humidity protonexchange membrane with "stream-reservoir" ionic channels for high-power-density fuel cells [J]. Science Advances, 2023, 9 (17): eadh1386.). The above problems seriously limit the Therefore, in the past two decades, researchers have been committed to developing sulfonated hydrocarbon polymer proton exchange membranes with lower cost and better performance to replace The goal is to reduce production costs while increasing the operating temperature of fuel cells, reducing fuel permeability, and improving the mechanical stability and durability of the membrane.

[0003] Among them, sulfonated polynaphthalimide (SPI) has attracted widespread attention due to its low cost, high mechanical strength, excellent thermal stability, strong gas barrier ability, and controllable chemical structure. However, the stability of SPI membranes in fuel cells under high temperature and high humidity conditions cannot be ignored. The main reason is that the electron cloud density of the imide bond is low, which is easily attacked by nucleophilic water molecules, resulting in hydrolysis and ring opening, and even main chain rupture, affecting the structural stability of the membrane. Studies have shown that by regulating the monomer structure and increasing the electron cloud density of nitrogen atoms and carbonyl carbon atoms, the hydrolytic stability of sulfonated polyimide proton exchange membranes (PEMs) can be effectively improved (Fang JH, Guo XX, Xu HJ, et al. Sulfonated polyimides: Synthesis, proton conductivity and water stability [J]. Journal of Power Sources, 2006, 159 (1): 4-11.). Common methods include introducing electron-pushing groups such as ether bonds at the ortho or para position of the amino group. For example, K. Okamoto et al. studied sulfonated copolyimide (SPI) synthesized from 4,4′-bis(4-aminophenoxy)biphenyl-3,3′-disulfonic acid (PBAPBDS) and evaluated its hydrolytic stability under high temperature and high humidity (Watari T, Fang JH, Tanaka K, et al. Synthesis, water stability and proton conductivity of novel sulfonated polyimides from 4,4'-bis(4-aminophenoxy)biphenyl-3,3'-disulfonic acid[J]. Journal of Membrane Science, 2004, 230(1):111-120.). The experimental results showed that the SPI membrane could still maintain high mechanical strength after aging in 130°C water for 192 hours, showing excellent hydrolytic stability. However, the introduced electron-donating groups containing heteroatoms (such as ether bonds) are susceptible to attack by hydroxyl radicals, resulting in reduced oxidative stability of the proton exchange membrane during fuel cell operation. Therefore, how to improve the hydrolysis stability of polyimide while taking into account its oxidation stability remains an important challenge facing current material design and optimization.

[0004] In addition, the power generation performance of sulfonated polyimide proton exchange membrane fuel cells is heavily dependent on external humidification conditions, and excellent electrochemical performance can only be achieved in a high humidity environment. Under low relative humidity (<30%) conditions, the output power of SPI proton exchange membrane fuel cells drops significantly, or even completely loses its power generation capability (Yaguchi K, Chen KC, Endo N, et al. Crosslinked membranes of sulfonated polyimides for polymer electrolyte fuel cell applications [J]. Journal of Power Sources, 2010, 195 (15): 4676-4684.). Currently, researchers are paying extensive attention to the microscopic phase separation behavior of proton exchange membranes and their influence on proton transport performance. Studies have shown that the degree of phase separation and the water channel network induced by it are key factors in determining the proton conduction capacity of proton exchange membranes (PEMs). Compared with the SPI membrane, the SPI proton exchange membrane shows significant differences in microstructure, mainly in terms of composition elements, backbone rigidity and spatial distribution of sulfonic acid groups. In particular, the microphase separation degree of the SPI proton exchange membrane is much lower than that of the SPI membrane. This is mainly attributed to the reduced mobility of the sulfonic acid groups and the presence of hydrogen bonding sites even in hydrophobic regions, which inhibits the formation of continuous water channels and significantly affects proton transport efficiency. Therefore, the development of proton exchange membranes that can maintain high proton conductivity in high temperature and low relative humidity environments has become a key research direction for improving the performance and durability of fuel cells under actual operating conditions. Summary of the Invention

[0005] In response to the above-mentioned defects in the prior art, the present invention aims to overcome the contradiction between the hydrolytic stability and oxidative stability of sulfonated polyimide proton exchange membranes, and at the same time improve the proton conductivity of sulfonated copolymer proton exchange membranes under high temperature and low relative humidity conditions, thereby improving the electrochemical performance of fuel cells. In order to achieve the above-mentioned goals, the present invention provides a synthesis of a new sulfonated diamine monomer and further prepares a series of sulfonated polyimide copolymer proton exchange membranes. The copolymer membrane has excellent hydrolytic stability and anti-free radical oxidation stability, and can still maintain a high proton conductivity under low humidity conditions. The fuel cell assembled based on this membrane shows good power generation performance under high temperature and low relative humidity conditions, effectively solving the problem of low output power of existing sulfonated polymer proton exchange membrane fuel cells under high temperature and low relative humidity conditions.

[0006] The present invention provides a sulfonated diamine monomer, the general structural formula of which is shown in formula (1):

[0007]

[0008] wherein R1 represents a sulfonated aromatic group containing a carbonyl group or a sulfonyl group, and R2 represents a monovalent group;

[0009] R1 is selected from any one of the following groups:

[0010]

[0011] R2 is selected from any one of the following groups: -H, -CH3, -CF3.

[0012] The present invention also provides a method for preparing the above-mentioned sulfonated diamine monomer, comprising the following steps:

[0013] Step 1) Under N2 protection, a dibromoaryl compound containing a carboxylic acid or sulfonic acid group and thionyl chloride or oxalyl chloride are sequentially added to a dry three-necked flask, and heated to react at 0-100°C for 1-30 hours. After the reaction, the thionyl chloride or oxalyl chloride is removed to obtain a dibromo compound containing an acyl chloride or sulfonyl chloride group; benzene or a benzene derivative and a Lewis acid are sequentially added to the above reaction system, and the reaction is carried out at 20-150°C for 1-50 hours to obtain a dibromo compound containing a carbonyl or sulfonyl group. The reaction is carried out according to the following chemical reaction equation (1):

[0014]

[0015] Where z is 0 or 1;

[0016] R4 is selected from any one of the following groups: -COOH, -SO3H;

[0017] R5 is selected from any one of the following groups: -COCl, -SO2Cl;

[0018] R6 is selected from any one of the following groups: -O-, -SO2-;

[0019] R7 is selected from any one of the following groups:

[0020]

[0021] Step 2) The dibromo compound containing a carbonyl or sulfonyl group obtained in step 1 is added to a dry three-necked flask, and concentrated sulfuric acid and fuming sulfuric acid are added in sequence. The mixture is heated at 20-150° C. for 1-30 hours to obtain a sulfonated dibromo compound containing a carbonyl or sulfonyl group. The reaction is carried out according to the following chemical reaction equation (2):

[0022]

[0023] wherein R1 and R7 are as defined above;

[0024] Step 3) The sulfonated dibromo compound containing a carbonyl or sulfonyl group obtained in step 2, an amino-containing end-capping agent, a base, a palladium catalyst, a ligand, an organic solvent, and water are sequentially added to a three-necked flask and reacted at 20 to 150° C. for 1 to 30 hours to obtain a sulfonated diamine monomer. The reaction is carried out according to the following chemical reaction equation (3):

[0025]

[0026] wherein R1, R2, and R7 are as defined above, and R8 represents a monovalent boronic acid or a derivative thereof;

[0027] R8 is selected from any one of the following groups:

[0028]

[0029] In one embodiment of the present invention, in step 1), after the reaction system is cooled to room temperature, ice water is added and stirred to precipitate. The resulting solid is washed with deionized water until neutral, filtered, and vacuum dried at 100°C for 20 hours to obtain a dry dibromo compound containing a carbonyl or sulfonyl group. Subsequently, the resulting product is dissolved in an organic solvent, recrystallized at 50-120°C, filtered, and dried to obtain the target compound.

[0030] In one embodiment of the present invention, in step 1), the Lewis acid is selected from one or more of CF3SO3H, trifluoroacetic acid, and AlCl3.

[0031] In one embodiment of the present invention, in step 1), the molar ratio of the thionyl chloride or oxalyl chloride to the dibromoaryl compound containing a carboxylic acid or sulfonic acid group is 1:1 to 1:100. The molar ratio of the benzene or diphenyl ether to the dibromoaryl compound containing a carboxylic acid or sulfonic acid group is 1:1 to 1:100. The molar ratio of the Lewis acid to the dibromoaryl compound containing a carboxylic acid or sulfonic acid group is 1:1 to 1:100.

[0032] In one embodiment of the present invention, in step 2), the molar ratio of the concentrated sulfuric acid to the dibromo compound containing a carbonyl group or a sulfonyl group is 1:1 to 1:100. The molar ratio of the fuming sulfuric acid to the dibromo compound containing a carbonyl group or a sulfonyl group is 1:1 to 1:100.

[0033] In one embodiment of the present invention, in step 3), the reaction system is cooled to room temperature, an acid solution is added to neutralize the reaction system, a light brown precipitate is collected by centrifugation, and the precipitate is washed three times with water, filtered, and the solid is collected and vacuum dried at 80° C. for 12 hours to obtain the target product.

[0034] In one embodiment of the present invention, in step 3), the molar ratio of the base to the dibromo compound containing a carbonyl or sulfonyl group is 0:1 to 20:1. The molar ratio of the palladium catalyst to the dibromo compound containing a carbonyl or sulfonyl group is 0:1 to 1:1. The molar ratio of the ligand to the dibromo compound containing a carbonyl or sulfonyl group is 0:1 to 1:1. The molar ratio of the organic solvent to water is 0:1 to 100:1. The solid content of the reaction system is 0.1 to 100% (mass / volume percentage, w / v%).

[0035] In one embodiment of the present invention, in step 3), the organic solvent is selected from one or more of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, methanol, ethanol, tetrahydrofuran, and toluene.

[0036] In one embodiment of the present invention, in step 3), the amino-containing end-capping agent is selected from one or more of 4-aminophenylboronic acid hydrochloride, 4-aminophenylboronic acid pinacol ester, 4-aminophenylboronic acid, 3-aminophenylboronic acid pinacol ester, 3-aminophenylboronic acid, and 2-fluoro-5-aminophenylboronic acid.

[0037] In one embodiment of the present invention, in step 3), the palladium catalyst is selected from one or more of Pd(OAc)2, Pd(PPh3)4, and Pd(dppf)Cl2.

[0038] In one embodiment of the present invention, in step 3), the base is selected from one or more of Na2CO3, K2CO3, K3PO4, triethylamine, tetramethylammonium hydroxide, and tetrabutylammonium hydroxide.

[0039] In one embodiment of the present invention, in step 3), the ligand is selected from one or more of PPh3, n-Bu3P, 1,2-bis(diphenylphosphino)ethane, 1,3-bis(diphenylphosphino)propane, and 1,1′-bis(diphenylphosphino)ferrocene.

[0040] The present invention also provides a sulfonated polyimide block copolymer, which is obtained by block copolymerization of one or more diamine monomers and one or more dianhydride monomers, and its general structural formula is represented by Formula 2:

[0041]

[0042] wherein R1 and R2 are as defined above, Ar1 and Ar2 represent a tetravalent aromatic group, R3 represents a divalent aromatic group, an alkyl group or an aromatic aliphatic group, and m and n are integers of 5 to 100;

[0043] Ar1 and Ar2 are each selected from any one of the following groups:

[0044]

[0045] R3 is selected from any one of the following groups:

[0046]

[0047] The present invention also provides a method for preparing a sulfonated polyimide block copolymer, comprising the following steps:

[0048] Step 1) Ar2-type dianhydride monomer, hydrophobic R3-type diamine monomer and phenolic solvent are added to a three-necked flask, heated to 50-140° C., reacted at this temperature for 1-10 hours, and then the reaction temperature is further increased to 150-200° C., and reacted at this temperature for 2-30 hours to obtain a polyimide hydrophobic block oligomer. The reaction is carried out according to the following chemical equation (4):

[0049]

[0050] Wherein, Ar2, R3, and n are as defined above;

[0051] Step 2) Add Ar1 type dianhydride monomer, hydrophilic sulfonated diamine monomer, organic base and phenolic solvent into another three-necked flask, heat and react at 50-140°C for 1-10 hours, then increase the temperature to 150-200°C and continue the reaction for 2-30 hours to obtain a polyimide hydrophilic block oligomer solution, wherein the reaction is carried out according to the following chemical equation (5):

[0052]

[0053] Wherein, Ar1, R1, R2, and m are as defined above;

[0054] Step 3) adding the polyimide hydrophobic block oligomer obtained in step 1 and a phenolic solvent into the three-necked flask obtained in step 2) and reacting at 150-200° C. for 2-72 hours to obtain a sulfonated polyimide block copolymer. The reaction is carried out according to the following chemical reaction equation (6):

[0055]

[0056] Wherein, Ar1, Ar2, R1, R2, R3, m, and n are as defined above.

[0057] In one embodiment of the present invention, in the step 1), after the reaction system is cooled to room temperature, it is added to an organic poor solvent to obtain a first precipitate, which is then filtered and dried under vacuum at 160°C for 20 hours to obtain a dry polyimide hydrophobic block oligomer; in the step 3), after the reaction system is cooled to room temperature, it is added to an organic poor solvent to obtain a second precipitate, which is then filtered and dried under vacuum at 100°C for 20 hours to obtain a dry polyimide block copolymer.

[0058] In one embodiment of the present invention, in step 1) and step 3), the organic solvent is selected from one or more of methanol, ethanol, isopropanol, acetone, and ethyl acetate.

[0059] In one embodiment of the present invention, in step 1), the molar ratio of the Ar2 type dianhydride monomer to the hydrophobic R3 type diamine monomer is greater than 1; in step 2), the molar ratio of the hydrophilic sulfonated diamine monomer to the Ar1 type dianhydride is greater than 1.

[0060] In one embodiment of the present invention, in step 1), the molar ratio of the Ar2 type dianhydride to the hydrophobic R3 type diamine is less than 1; and in step 2), the molar ratio of the hydrophilic sulfonated diamine monomer to the Ar1 type dianhydride is less than 1.

[0061] In one embodiment of the present invention, in step 2), the organic base reacts with the sulfonated diamine monomer, and the organic base is selected from one or more of triethylamine, trimethylamine, pyridine, or 4-(N,N-dimethylamino)pyridine.

[0062] In one embodiment of the present invention, the phenolic solvent is selected from one or more of m-cresol, o-cresol, p-cresol, m-chlorocresol, o-chlorocresol or p-chlorocresol.

[0063] In one embodiment of the present invention, the catalyst is selected from one or more of acetic acid, benzoic acid, chlorobenzoic acid, hydroxybenzoic acid, quinoline, isoquinoline or pyridine.

[0064] In one embodiment of the present invention, the solid content of the imide in the phenolic solvent is 5-40 w / v %; in step 4, the solid content of the polyimide in the phenolic solvent is 0.5-25 w / v %.

[0065] In one embodiment of the present invention, the terminal groups of the hydrophilic oligomers are all amino groups; and in step 2), the terminal groups of the hydrophobic oligomers are all anhydride groups.

[0066] In one embodiment of the present invention, the terminal groups of the hydrophilic oligomers are all anhydride groups; and in step 2), the terminal groups of the hydrophobic oligomers are all amino groups.

[0067] In one embodiment of the present invention, the synthesis of steps 1) to 3) is carried out in a reaction solution with a solid content of 1 to 50 w / v%.

[0068] In one embodiment of the present invention, the reaction temperature of steps 1) to 3) is 40 to 250°C.

[0069] The present invention also provides a sulfonated polyimide sequential copolymer, which is prepared by sequential copolymerization of one or more diamine monomers and one or more dianhydride monomers, and its general structural formula is represented by Formula 3-1 and Formula 3-2:

[0070]

[0071] Wherein, Ar1, Ar2, R1, R2, R3, and m are defined as above, x, y, and z are decimals ranging from 0 to 1, and x+y+z=1.

[0072] The present invention also provides a method for preparing a sulfonated polyimide sequence copolymer (Formula 3-1), comprising the following steps:

[0073] Step 1) Add Ar1-type dianhydride monomer, sulfonated diamine monomer, organic base and phenolic solvent into a three-necked flask and heat to react at 50-140°C for 1-10 hours; then raise the temperature to 150-200°C and continue to react at this temperature for 2-30 hours to obtain a hydrophilic sulfonated polyimide oligomer solution. The reaction proceeds according to the following chemical reaction equation (7):

[0074]

[0075] Wherein, Ar1, Ar2, R1, R2, R3, and m are as defined above;

[0076] Step 2) adding the Ar2-type dianhydride monomer, the hydrophobic R3-type diamine monomer, and the phenolic solvent to the reaction system obtained in step 1, heating the reaction at 150-200° C. for 2-72 hours to obtain a sulfonated polyimide sequence copolymer; the reaction proceeds according to the following chemical reaction equation (8):

[0077]

[0078] Wherein, Ar1, Ar2, R1, R2, R3, m, x, y, and z are as defined above.

[0079] In one embodiment of the present invention, in step 1) and step 2), the molar ratio of the sulfonated diamine monomer to the Ar1-type dianhydride monomer is greater than 1, and the molar ratio of the Ar2-type dianhydride monomer to the hydrophobic R3-type diamine monomer is greater than 1; in step 1) and step 2), the molar ratio of the total dianhydride monomer to the total diamine monomer is equal to 1.

[0080] In one embodiment of the present invention, in step 1) and step 2), the molar ratio of the sulfonated diamine monomer to the Ar1-type dianhydride monomer is less than 1, and the molar ratio of the Ar2-type dianhydride monomer to the hydrophobic R3-type diamine monomer is less than 1; and in step 1) and step 2), the molar ratio of the total dianhydride monomer to the total diamine monomer is equal to 1.

[0081] In one embodiment of the present invention, in step 1), the terminal groups of the hydrophilic sulfonated polyimide oligomers are all amino groups.

[0082] In one embodiment of the present invention, in step 1), the terminal groups of the hydrophilic sulfonated polyimide oligomer are all anhydride groups.

[0083] In one embodiment of the present invention, in step 1), an organic base may react with the sulfonated diamine monomer, and the organic base is selected from one or more of triethylamine, trimethylamine, pyridine, and 4-(N,N-dimethylamino)pyridine.

[0084] In one embodiment of the present invention, in step 2), the reaction system is cooled to room temperature and then poured into an organic poor solvent to form a filamentous precipitate. After washing three times with the organic poor solvent, the solid is vacuum dried at 100° C. for 20 hours to obtain a dry sulfonated polyimide sequence copolymer.

[0085] In one embodiment of the present invention, in step 2), the organic poor solvent is selected from one or more of methanol, ethanol, isopropanol, acetone, and ethyl acetate.

[0086] In one embodiment of the present invention, in step 1) and step 2), the catalyst is selected from one or more of acetic acid, benzoic acid, chlorobenzoic acid, hydroxybenzoic acid, quinoline, isoquinoline, and pyridine.

[0087] In one embodiment of the present invention, in step 1) and step 2), the synthesis is carried out in a reaction solution with a solid content of 1 to 50 w / v%.

[0088] In one embodiment of the present invention, the reaction temperature in step 1) and step 2) is 40-250°C.

[0089] In one embodiment of the present invention, in step 3), the process for preparing the sulfonated polyimide sequence copolymer membrane is as follows: dissolving the sulfonated polyimide block copolymer in a phenolic solvent to form a uniform sulfonated polyimide block copolymer solution, then uniformly coating the solution on the surface of a glass plate, and drying at a temperature of 90 to 110° C. for 5 to 15 hours to obtain a thin film; and finally peeling the thin film from the glass plate.

[0090] In one embodiment of the present invention, in steps 1) to 3), the phenolic solvent is selected from one or more of m-cresol, o-cresol, p-cresol, m-chlorocresol, o-chlorocresol, and p-chlorocresol.

[0091] In one embodiment of the present invention, in steps 1) to 2), the solid content of the polyimide in the phenolic solvent is 5 to 40 w / v%; in step 3, the solid content of the polyimide in the phenolic solvent is 0.5 to 25 w / v%.

[0092] The present invention also provides a method for preparing a sulfonated polyimide sequence copolymer (Formula 3-2), comprising the following steps:

[0093] Step 1) Ar2-type dianhydride monomer, hydrophobic R3-type diamine monomer and phenolic solvent are added to a three-necked flask, reacted at 50-140° C. for 1-10 hours, then heated to 150-200° C. and reacted at this temperature for 2-30 hours to obtain a hydrophobic polyimide oligomer solution, wherein the reaction is carried out according to the following chemical reaction equation (9):

[0094]

[0095] Wherein, Ar2, R3, and m are as defined above;

[0096] Step 2) Adding Ar1-type dianhydride monomer, sulfonated diamine monomer, organic base, and phenolic solvent to the reaction system obtained in step 1) and heating at 150-200° C. for 2-72 hours to obtain a sulfonated polyimide sequence copolymer. The reaction proceeds according to the following chemical reaction equation (10):

[0097]

[0098] Wherein, Ar1, Ar2, R1, R2, R3, m, x, y, and z are as defined above.

[0099] In one embodiment of the present invention, in steps 1) to 2), the molar ratio of the sulfonated diamine monomer to the Ar1-type dianhydride monomer is greater than 1, and the molar ratio of the Ar2-type dianhydride monomer to the hydrophobic R3-type diamine monomer is greater than 1; and the molar ratio of the total dianhydride monomer to the total diamine monomer in steps 1) to 2) is equal to 1.

[0100] In one embodiment of the present invention, in steps 1) to 2), the molar ratio of the sulfonated diamine monomer to the Ar1-type dianhydride monomer is less than 1, and the molar ratio of the Ar2-type dianhydride monomer to the hydrophobic R3-type diamine monomer is less than 1; and the molar ratio of the total dianhydride monomer to the total diamine monomer in steps 1) to 2) is equal to 1.

[0101] In one embodiment of the present invention, in step 1), the terminal groups of the hydrophobic sulfonated polyimide oligomers are all amino groups.

[0102] In one embodiment of the present invention, in step 1), the terminal groups of the hydrophobic sulfonated polyimide oligomer are all anhydride groups.

[0103] In one embodiment of the present invention, in step 2), an organic base may react with the sulfonated diamine monomer, and the organic base is selected from one or more of triethylamine, trimethylamine, pyridine, and 4-(N,N-dimethylamino)pyridine.

[0104] In one embodiment of the present invention, in step 2), the reaction system is cooled to room temperature and then poured into an organic poor solvent to form a filamentous precipitate. After washing three times with the organic poor solvent, the solid is vacuum dried at 100° C. for 20 hours to obtain a dry sulfonated polyimide sequence copolymer.

[0105] In one embodiment of the present invention, in step 2), the organic poor solvent is selected from one or more of methanol, ethanol, isopropanol, acetone, and ethyl acetate.

[0106] In one embodiment of the present invention, in steps 1) to 2), the catalyst is selected from one or more of acetic acid, benzoic acid, chlorobenzoic acid, hydroxybenzoic acid, quinoline, isoquinoline, and pyridine.

[0107] The synthesis of steps 1) to 2) is carried out in a reaction solution with a solid content of 1 to 50 w / v%.

[0108] In one embodiment of the present invention, in steps 1) to 2), the reaction temperature is 40 to 250°C.

[0109] In one embodiment of the present invention, in steps 1) to 3), the phenolic solvent is selected from one or more of m-cresol, o-cresol, p-cresol, m-chlorocresol, o-chlorocresol, and p-chlorocresol.

[0110] In one embodiment of the present invention, in steps 1) to 2), the solid content of the polyimide in the phenolic solvent is 5 to 40 w / v%; in step 3, the solid content of the polyimide in the phenolic solvent is 0.5 to 25 w / v%.

[0111] The present invention also provides a sulfonated polyimide random copolymer, the general structural formula of which is represented by Formula 4:

[0112]

[0113] Wherein, Ar1, R1, R2, and R3 are defined as above, a, b, c, and d are decimals ranging from 0 to 1, and a+b+c+d=1.

[0114] The present invention also provides a method for preparing a sulfonated polyimide random copolymer, comprising the following steps:

[0115] Step 1) adding a sulfonated diamine monomer, an Ar1-type dianhydride monomer, a hydrophobic R3-type diamine monomer, an Ar2-type dianhydride monomer, an organic base and a phenolic solvent into a three-necked flask, reacting at 50-140° C. for 1-10 hours, then heating to 150-200° C. and continuing the reaction for 2-30 hours to obtain a sulfonated polyimide random copolymer. The reaction is carried out according to the following chemical reaction equation (11):

[0116]

[0117] Wherein, Ar1, R1, R2, R3, a, b, c, and d are defined as above.

[0118] In one embodiment of the present invention, in step 1), after the reaction system is cooled to room temperature, an organic poor solvent is added to form a filamentous precipitate of the product. After washing three times with the organic poor solvent, the solid is vacuum dried at 100° C. for 20 hours to obtain a dry sulfonated polyimide random copolymer.

[0119] In one embodiment of the present invention, in step 1), the organic poor solvent is selected from one or more of methanol, ethanol, isopropanol, acetone, and ethyl acetate.

[0120] In one embodiment of the present invention, in step 1), the molar ratio of the sulfonated diamine monomer to the Ar1 type dianhydride is less than 1, and the molar ratio of the Ar2 type dianhydride to the hydrophobic R3 type diamine monomer is less than 1; and the molar ratio of the total dianhydride to the total diamine is equal to 1.

[0121] In one embodiment of the present invention, in step 1), the molar ratio of the sulfonated diamine monomer to the Ar1 type dianhydride is greater than 1, the molar ratio of the Ar2 type dianhydride to the hydrophobic R3 type diamine monomer is greater than 1; and the molar ratio of the total dianhydride to the total diamine is equal to 1.

[0122] In one embodiment of the present invention, in step 1), the organic base is selected from one or more of triethylamine, trimethylamine, pyridine, and 4-(N,N-dimethylamino)pyridine.

[0123] In one embodiment of the present invention, in step 1), the catalyst is selected from one or more of acetic acid, benzoic acid, chlorobenzoic acid, hydroxybenzoic acid, quinoline, isoquinoline, and pyridine.

[0124] In one embodiment of the present invention, in step 1), the reaction temperature is 40-250°C.

[0125] In one embodiment of the present invention, in step 2), the process for preparing the sulfonated polyimide random copolymer film is as follows: dissolving the sulfonated polyimide random copolymer in a phenolic solvent to form a uniform sulfonated polyimide random copolymer solution, then uniformly coating the solution on the surface of a glass plate, and drying at a temperature of 90 to 110° C. for 5 to 15 hours to obtain a thin film; and finally peeling the thin film from the glass plate.

[0126] In one embodiment of the present invention, in steps 1) to 2), the phenolic solvent used is selected from one or more of m-cresol, o-cresol, p-cresol, m-chlorocresol, o-chlorocresol, and p-chlorocresol.

[0127] In one embodiment of the present invention, in steps 1) to 2), the solid content of the sulfonated polyimide random copolymer in the phenolic solvent is 0.5 to 25 w / v%.

[0128] The present invention also provides a proton exchange membrane made of the sulfonated polyimide block copolymer, the sulfonated polyimide sequence copolymer or the sulfonated polyimide random copolymer.

[0129] In one embodiment of the present invention, the method for preparing the proton exchange membrane includes: dissolving a copolymer in a phenolic solvent to form a uniform copolymer solution, then uniformly coating the solution on the surface of a glass plate, and drying it at a temperature of 90 to 110° C. for 5 to 15 hours to obtain a thin film; and finally peeling the thin film from the glass plate.

[0130] In one embodiment of the present invention, the membrane is immersed in alcohol to remove residual solvent in the membrane, and then the membrane is immersed in a protonic acid solution to perform proton exchange.

[0131] In one embodiment of the present invention, the membrane after proton exchange is washed with water until it becomes neutral, and then vacuum dried at a drying temperature of 50 to 150° C. for 2 to 30 hours.

[0132] The present invention also provides an application of a proton exchange membrane made of a sulfonated polyimide copolymer in a battery, wherein the battery includes but is not limited to a fuel cell.

[0133] Technical Effects

[0134] (1) The present invention designs and synthesizes a new type of sulfonated diamine monomer with a conjugated skeleton structure and a molecularly regulated sulfonated polyimide copolymer, which effectively solves the problem of balancing hydrolytic stability and oxidative stability in existing sulfonated polyimide proton exchange membranes. By synergistically regulating the main chain and side chain structures, the membrane material is endowed with:

[0135] Excellent hydrolytic stability: Main chain structure remains intact under high temperature and high humidity conditions;

[0136] Higher oxidative stability: Strong resistance to free radical oxidative degradation;

[0137] Optimized microphase separation structure: conducive to the formation of continuous water channels and enhanced proton conductivity under low humidity conditions.

[0138] This structural design concept can be extended to a variety of aromatic sulfonated polymer systems and has good technical versatility and iterative development potential.

[0139] (2) The sulfonated polyimide block copolymer proton exchange membrane NS provided by the present invention 30 -b-ND 10 In terms of key performance indicators such as proton conductivity, power generation performance, hydrolysis and oxidation stability, mechanical strength and dimensional stability, it shows better comprehensive performance than existing SPI membrane materials and Nafion 212 membranes, and is suitable for the use requirements of fuel cell systems under high temperature and low humidity conditions. Typical performance indicators are as follows:

[0140] 1) Proton conductivity

[0141] At 80℃, 100%RH, NS 30 -b-ND 10 The proton conductivity can reach 0.137S / cm, which is better than Nafion 212 (0.133S / cm).

[0142] 2) Membrane electrode power generation efficiency

[0143] NS 30 -b-ND 10 The peak power density of the assembled single cell reached 1.97 W / cm 2 (90℃, 100%RH), 1.587W / cm 2 (90℃, 30%RH), while the peak power density of the Nafion polymer assembled single cell is only 1.04W / cm 2 (90°C, 100% RH), 0.93W / cm 2 (90°C, 30% RH).

[0144] 3) Hydrolytic stability

[0145] After aging in distilled water at 120℃ for 24h, NS 30 -b-ND 10 The quality retention rate of the membrane is higher than 96%, which is comparable to the traditional SPI containing ether bonds (Comparative Example NB 15 -b-ND 10 )quite.

[0146] 4) Oxidation stability

[0147] NS 30 -b-ND 10 The initial dissolution time of the membrane in Fenton's reagent (80°C, 3% H2O2, 3ppm FeSO4) was more than 160 minutes, which was significantly better than that of the traditional SPI containing ether bonds (Comparative Example NB 15 -b-ND 10 ), the initial dissolution time of the latter is less than 120 minutes.

[0148] 5) Mechanical properties

[0149] NS 30 -b-ND 10 The membrane has a tensile strength of 200 MPa and an elongation at break of 34%, making it suitable for MEA processing. It maintains good toughness even in the water-absorbing state, making it suitable for actual assembly needs.

[0150] 6) Swelling rate and dimensional stability

[0151] NS 30 -b-ND 10 The volume swelling ratio of the membrane in 25°C water is controlled at 54%, which is comparable to the volume swelling ratio of Nafion 212 (52%).

[0152] 7) Film thickness uniformity and film forming properties

[0153] It is suitable for solution casting process, and the film produced has uniform thickness (30-40μm), smooth surface, no obvious defects, and has the basis for mass production.

[0154] The membrane material of the present invention reaches or exceeds the performance level of existing commercial membranes in many key properties such as proton conductivity, power generation performance and mechanical stability, and has good practicality and industrial application potential.

[0155] (3) The synthetic route of the present invention is based on scalable sulfonated aromatic diamines and commercially available dianhydride raw materials. The synthetic steps can be successfully implemented under laboratory and pilot-scale conditions. The sulfonation reaction and polyimide condensation process used is mature, controllable, and easy to scale up, and has the following industrial advantages:

[0156] ●The monomers used are low-cost and the synthesis route is green;

[0157] ●Can smoothly replace existing film production lines (solution casting or extrusion);

[0158] ●The membrane material has high physical strength and good mechanical processing performance and can be directly applied to membrane electrode assemblies (MEAs);

[0159] ●The technical route can be extended to other nitrogen-containing aromatic backbone copolymers, which is conducive to technology licensing and horizontal expansion.

[0160] In addition, the membrane material is particularly suitable for fuel cell systems under high temperature and low humidity conditions, such as:

[0161] ●On-board fuel cell without external humidification system (suitable for commercial vehicles and heavy trucks);

[0162] Aerospace power systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0163] Figure 1 For the sulfonated precursor SDBrBP 1 H NMR spectrum (solvent: DMSO-d6);

[0164] Figure 2 The sulfonated diamine monomer SBPDA of Example 1 1 H NMR spectrum (solvent: DMSO-d6+Et3N);

[0165] Figure 3 For Example 2 (NS 20 -b-ND 10 ) and Example 3 (NS 30 -b-ND 10 )’s infrared absorption spectrum;

[0166] Figure 4 For Example 2 (NS 20 -b-ND 10 ) and Example 3 (NS 30 -b-ND 10 )’s stress-strain curve;

[0167] Figure 5 For Example 2 (NS 20 -b-ND 10 ), Example 3 (NS 30 -b-ND 10 ) and X-ray diffraction (XRD) patterns of Nafion 212;

[0168] Figure 6 (a) is Example 2 (NS 20 -b-ND 10 ) and (b) are from Example 3 (NS 30 -b-ND 10 ) transmission electron microscopy (TEM) images;

[0169] Figure 7-1 For Example 3 (NS 30 -b-ND 10Polarization curves of a single cell assembled with 212 nanoparticles (100 nm) and Nafion 212 at 90°C, a back pressure of 150 kPa, and a relative humidity of 100%;

[0170] Figure 7-2 For Example 3 (NS 30 -b-ND 10 Polarization curves of a single cell assembled with ) and Nafion 212 at 90 °C, back pressure 150 kPa and relative humidity 30%;

[0171] Figure 8 For Example 3 (NS 30 -b-ND 10 ) OCV durability test of the assembled single cell at 90°C, back pressure 0 kPa and relative humidity 50%. DETAILED DESCRIPTION

[0172] The following describes several preferred embodiments of the present invention with reference to the accompanying drawings to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms of embodiments, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0173] Example 1: Sulfonated diamine monomer SBPDA

[0174] The synthesis of the sulfonated diamine monomer SBPDA is divided into three steps: the first step is the synthesis of the dibromo precursor (4,4′-dibromo-[1,1′-biphenyl]-2,2′-diyl) bis(phenyl ketone) (DBrBP); the second step is the synthesis of the sulfonated dibromo precursor sodium 3,3′-(4,4′-dibromo-[1,1′-biphenyl]-2,2′-dicarbonyl) dibenzenesulfonate (SDBrBP); and the third step is the synthesis of the sulfonated diamine monomer 3,3′-[4,4″′-diamino-[1,1′:4′,1″:4″,1″′-tetraphenyl]-2″,3′-diacyl] dibenzenesulfonic acid (SBPDA). The detailed synthesis steps are as follows:

[0175] Synthesis of (4,4′-dibromo-[1,1′-biphenyl]-2,2′-diyl)bis(phenyl ketone) (DBrBP): 4,4′-dibromo-[1,1′-biphenyl]-2,2′-dicarboxylic acid (25.0 g, 62.5 mmol) and thionyl chloride (250 mL) were added to a dry three-necked flask and heated to 80°C for 6 hours with stirring. After completion of the reaction, the mixture was cooled to room temperature, and the thionyl chloride was evaporated under reduced pressure to obtain a crude intermediate. Subsequently, the intermediate was dissolved in benzene (56 mL), cooled in an ice bath (0-5°C), and trifluoromethanesulfonic acid (CF3SO3H, 66.4 mL, 750 mmol) was slowly added dropwise. After the addition was complete, the temperature was gradually increased to 85°C, and the reaction was continued for 20 hours to complete the Friedel-Crafts acylation reaction. After completion of the reaction, the reaction solution was slowly poured into 500 mL of ice water to quench the reaction and stirred to precipitate a solid. The resulting precipitate was collected by filtration under reduced pressure and washed three times with deionized water. The wet cake was dried under reduced pressure and then purified by recrystallization using ethyl acetate as solvent to obtain 27.6 g of a white solid product (DBrBP) with a yield of 85%.

[0176] Synthesis of sodium 3,3′-(4,4′-dibromo-[1,1′-biphenyl]-2,2′-dicarbonyl)dibenzenesulfonate (SDBrBP): To a dry 100 mL three-necked flask, add (4,4′-dibromo-[1,1′-biphenyl]-2,2′-diyl)bis(phenyl ketone) (15 g, 28.8 mmol, DBrBP). The mixture was stirred in an ice bath and cooled. Concentrated sulfuric acid (98%, 15 mL) was slowly added dropwise. Once the reactants were completely dissolved, fuming sulfuric acid (50 wt %, 22.5 mL) was slowly added dropwise. The mixture was stirred at room temperature for 1 hour, then heated to 50°C and reacted for 3 hours. After the reaction, the reaction system was cooled to room temperature and slowly poured into 120 mL of ice water. The solution was adjusted to neutrality with cooled 30 wt % aqueous NaOH. Subsequently, solid NaCl (35 g) was added and stirred to precipitate a white precipitate. The precipitate was collected by centrifugation and dried in vacuo at 80°C. The dried solid was dissolved in 40 mL of DMSO, and the light brown supernatant was collected by centrifugation. The supernatant was concentrated by evaporation under reduced pressure, and the resulting concentrate was slowly added dropwise to ethanol. The precipitate was collected by centrifugation. The resulting precipitate was dried under vacuum at 80°C to obtain a crude product. The crude product was purified by recrystallization from water to obtain 17.7 g of a white solid (SDBrBP) powder, with a yield of 85%.

[0177] Synthesis of 3,3′-[4,4″′-diamino-[1,1′:4′,1″:4″,1″′-tetraphenyl]-2″,3′-diacyl]dibenzenesulfonic acid (SBPDA): Under nitrogen protection, sodium 3,3′-(4,4′-dibromo-[1,1′-biphenyl]-2,2′-dicarbonyl)dibenzenesulfonate (5.21 g, 7.2 mmol, SDBrBP), 4-aminophenylborate hydrochloride (2.62 g, 15.1 mmol), 2.4 M Na2CO3 aqueous solution (54 mL), DMF (23 mL), Pd(OAc)2 (0.047 g). The reaction system was subjected to freeze-evacuation-thaw cycles three times to remove oxygen, then heated to 85°C and stirred for 24 hours. After the reaction was completed, it was cooled to room temperature, filtered to remove the black precipitate, and the filtrate was adjusted to pH = 7 with dilute hydrochloric acid solution. The resulting precipitate was collected by centrifugation, washed three times with water, and dried in vacuo at 80°C for 12 hours to obtain 4.82 g of the product with a yield of 95%.

[0178] Example 2 NS 20 -b-ND 10 Block copolymer proton exchange membrane

[0179] Under nitrogen protection, 1,4,5,8-naphthalenetetracarboxylic anhydride (NTDA) (2.95g, 11mmol), 1,12-diaminododecane (DDA) (2.004g, 10mmol), benzoic acid (2.687g, 2.2mmol), 3.0mL isoquinoline and 40mL meta-cresol were added to a 100mL dry three-necked flask in sequence. Stir at room temperature for 1 hour, then heat to 80°C for 4 hours, and then heat to 180°C for 20 hours. After the reaction is completed, cool to room temperature, and slowly pour the reaction system into 150mL methanol to precipitate an orange solid powder. The obtained solid was repeatedly washed with methanol, filtered, and extracted with acetone until the eluent was colorless. Finally, it was vacuum dried at 160°C for 20 hours to obtain anhydride-terminated polyimide oligomer ND 10 .

[0180] Under nitrogen protection, SBPDA (1.4800 g, 2.1 mmol), 10 mL of m-cresol and triethylamine (468 mg) were added to a 100 mL dry three-necked flask in sequence and mechanically stirred at room temperature until SBPDA was completely dissolved. Subsequently, NTDA (0.5364 g, 2.0 mmol), benzoic acid (0.514 g, 4.2 mmol) and isoquinoline (0.543 mg, 4.2 mmol) were added in sequence. The resulting reaction system was mechanically stirred at room temperature for 1 hour, then slowly heated to 80 ° C for 4 hours, and then heated to 180 ° C for 20 hours. After the reaction was completed, the resulting reaction system was cooled to room temperature and the ND synthesized in the previous step was added to the three-necked flask. 10 (0.4593 g, 0.1 mmol) and 6.4 mL of m-cresol. The resulting mixture was stirred at room temperature for 1 hour, and then heated to 180°C for 20 hours. After the reaction, the resulting mixture was cooled to 80°C and quickly poured into 150 mL of methanol to form a filamentous precipitate. The resulting precipitate was repeatedly washed with methanol and filtered to collect the solid product. Finally, the solid product was vacuum dried at 100°C for 20 hours to obtain a crystalline sulfonated polyimide block copolymer NS with an average hydrophobic block length of 10 and an average hydrophilic block length of 20. 20 -b-ND 10 .

[0181] NS 20 -b-ND 10 The polymer solution was dissolved in m-cresol to prepare a polymer solution with a solid content of 5 w / v%. The resulting solution was vacuum degassed, cast onto a clean glass plate, and dried in a forced-air oven at 110°C for 5 hours to form a polymer membrane. After drying, the membrane was peeled from the glass plate and soaked in methanol for 24 hours to remove residual m-cresol. Subsequently, the membrane was placed in 50 mL of a 1.0 M sulfuric acid solution and soaked at room temperature for 72 hours for proton exchange treatment. The proton-exchanged membrane was washed with deionized water until neutral and vacuum dried at 120°C for 20 hours to obtain a proton exchange membrane made of a crystalline sulfonated polyimide block copolymer.

[0182] Example 3NS 30 -b-ND 10 Block copolymer proton exchange membrane

[0183] Under nitrogen protection, SBPDA (2.1848 g, 3.1 mmol), 15 mL of m-cresol and triethylamine (691 mg) were added to a 100 mL dry three-necked flask in sequence and mechanically stirred at room temperature until SBPDA was completely dissolved. Subsequently, NTDA (0.8046 g, 3.0 mmol), benzoic acid (0.7590 g, 6.2 mmol) and isoquinoline (0.8020 g, 6.2 mmol) were added in sequence. The resulting reaction system was mechanically stirred at room temperature for 1 hour, then slowly heated to 80°C for 4 hours, and then heated to 180°C for 20 hours. After the reaction was completed, the resulting reaction system was cooled to room temperature, and ND synthesized in Example 2 was added to the three-necked flask. 10 (0.4593 g, 0.1 mmol) and 6.4 mL of m-cresol. The resulting mixture was stirred at room temperature for 1 hour, and then heated to 180°C for 20 hours. After the reaction, the resulting mixture was cooled to 80°C and quickly poured into 150 mL of methanol to form a filamentous precipitate. The resulting precipitate was repeatedly washed with methanol and filtered to collect the solid product. Finally, the solid product was vacuum dried at 100°C for 20 hours to obtain a crystalline sulfonated polyimide block copolymer NS with an average hydrophobic block length of 10 and an average hydrophilic block length of 20. 30 -b-ND 10 .

[0184] NS 30 -b-ND 10 The polymer solution was dissolved in m-cresol to prepare a polymer solution with a solid content of 5 w / v%. The resulting solution was vacuum degassed, cast onto a clean glass plate, and dried in a forced-air oven at 110°C for 5 hours to form a polymer membrane. After drying, the membrane was peeled from the glass plate and soaked in methanol for 24 hours to remove residual m-cresol. Subsequently, the membrane was placed in 50 mL of a 1.0 M sulfuric acid solution and soaked at room temperature for 72 hours for proton exchange treatment. The proton-exchanged membrane was washed with deionized water until neutral and vacuum dried at 120°C for 20 hours to obtain a proton exchange membrane made of a crystalline sulfonated polyimide block copolymer.

[0185] Example 4r-N:S:D (41:31:10) random copolymer proton exchange membrane

[0186] Under nitrogen, NTDA (1.1000 g, 4.1 mmol), SBPDA (2.1848 g, 3.1 mmol), DDA (0.2004 g, 1 mmol), triethylamine (691 mg), 55 mL of m-cresol, benzoic acid (1.0259 g, 8.2 mmol), and isoquinoline (1.0849 g, 8.2 mmol) were added sequentially to a 100 mL dry three-necked flask. The reaction system was mechanically stirred at room temperature for 1 hour, then slowly heated to 80°C for 4 hours, and then raised to 180°C for a further 20 hours. After the reaction, the mixture was cooled to 80°C and quickly poured into 150 mL of methanol, forming a filamentous precipitate. The precipitate was repeatedly washed with methanol and filtered to collect the solid product. Finally, the solid product was vacuum-dried at 100°C for 20 hours to obtain a sulfonated polyimide random copolymer rN:S:D (41:31:10).

[0187] rN:S:D (41:31:10) was dissolved in m-cresol to prepare a polymer solution with a solid content of 5 w / v%. The resulting solution was vacuum degassed, cast onto a clean glass plate, and dried in a forced-air oven at 110°C for 5 hours to form a polymer membrane. After drying, the membrane was peeled from the glass plate and soaked in methanol for 24 hours to remove residual m-cresol. Subsequently, the membrane was placed in 50 mL of 1.0 M sulfuric acid solution at room temperature for 72 hours to undergo proton exchange treatment. The proton-exchanged membrane was washed with deionized water until neutral and vacuum dried at 120°C for 20 hours to obtain a proton exchange membrane made of a sulfonated polyimide random copolymer.

[0188] Comparative Example 1NB 15 -b-ND 10 Block copolymer proton exchange membrane

[0189] Under nitrogen protection, 1,4,5,8-naphthalenetetracarboxylic anhydride (NTDA) (2.95g, 11mmol), 1,12-diaminododecane (DDA) (2.004g, 10mmol), benzoic acid (2.687g, 2.2mmol), 3.0mL isoquinoline and 40mL meta-cresol were added to a 100mL dry three-necked flask in sequence. Stir at room temperature for 1 hour, then heat to 80°C for 4 hours, and then heat to 180°C for 20 hours. After the reaction is completed, cool to room temperature, and slowly pour the reaction system into 150mL methanol to precipitate an orange solid powder. The obtained solid was repeatedly washed with methanol, filtered, and extracted with acetone until the eluent was colorless. Finally, it was vacuum dried at 160°C for 20 hours to obtain anhydride-terminated polyimide oligomer ND 10 .

[0190] Under nitrogen protection, 4,4′-bis(4-aminophenoxy)biphenyl-3,3′-disulfonic acid (BAPBDS) (0.846 g, 1.6 mmol), 8.3 mL of m-cresol and 0.7 mL of triethylamine were added to a 100 mL dry three-necked flask in sequence and mechanically stirred at room temperature until BAPBDS was completely dissolved. Subsequently, NTDA (0.402 g, 1.5 mmol), benzoic acid (0.5366 g, 3.0 mmol) and 0.7 mL of isoquinoline were added in sequence. The resulting reaction system was mechanically stirred at room temperature for 1 hour, then slowly heated to 80°C for 4 hours, and then heated to 180°C for 20 hours. After the reaction was completed, the resulting reaction system was cooled to room temperature, and the ND synthesized in the previous step was added to the three-necked flask. 10 (0.4593 g, 0.1 mmol) and 3 mL of m-cresol. The resulting mixture was stirred at room temperature for 1 hour and then heated to 180°C for 20 hours. After the reaction, the resulting mixture was cooled to 80°C and quickly poured into 150 mL of methanol to form a filamentous precipitate. The resulting precipitate was repeatedly washed with methanol and filtered to collect the solid product. Finally, the solid product was vacuum dried at 100°C for 20 hours to obtain a crystalline sulfonated polyimide block copolymer NB with an average hydrophobic block length of 10 and an average hydrophilic block length of 20. 15 -b-ND 10 .

[0191] NB 15 -b-ND 10 The polymer solution was dissolved in m-cresol to prepare a polymer solution with a solid content of 5 w / v%. The resulting solution was vacuum degassed, cast onto a clean glass plate, and dried in a forced-air oven at 110°C for 5 hours to form a polymer membrane. After drying, the membrane was peeled from the glass plate and soaked in methanol for 24 hours to remove residual m-cresol. Subsequently, the membrane was placed in 50 mL of a 1.0 M sulfuric acid solution and soaked at room temperature for 72 hours for proton exchange treatment. The proton-exchanged membrane was washed with deionized water until neutral and vacuum dried at 120°C for 20 hours to obtain a proton exchange membrane made of a crystalline sulfonated polyimide block copolymer.

[0192] Structural Characterization of Sulfonated Diamine Monomers and Polymers

[0193] Figure 1 For the sulfonated dibromo precursor SDBrBP 1H NMR spectrum. Peaks a (7.91 ppm) and b (7.82 ppm) correspond to the ortho and para hydrogens of the sodium sulfonate on the side-chain sulfonated benzene ring, respectively; peak c (7.69 ppm) is attributed to the para-position hydrogen of the carbonyl group on the main-chain biphenyl ring; peak d (7.61 ppm) is attributed to the para-position hydrogen of the carbonyl group on the side-chain sulfonated benzene ring; peak e (7.56 ppm) is attributed to the ortho-position hydrogen of the carbonyl group on the main-chain biphenyl ring; peak f (7.44 ppm) is attributed to the meta-position hydrogen of the carbonyl group on the side-chain sulfonated benzene ring; and peak g (7.20 ppm) corresponds to the meta-position hydrogen of the carbonyl group on the main-chain biphenyl ring. The integrated ratios and chemical shifts of all peaks are consistent with the predicted structure, confirming the successful synthesis of the sulfonated dibromo precursor SDBrBP.

[0194] Figure 2 It is the sulfonated diamine monomer SBPDA neutralized with triethylamine. 1 H NMR spectrum. Compared to the sulfonated dibromo precursor SDBrBP, the newly emerged peak j (5.32 ppm) is attributed to the amino group at the main chain terminal; the newly emerged peaks h (7.35 ppm) and i (6.60 ppm) are attributed to the protons at the meta and ortho positions of the amino group on the main chain terminal benzene ring, respectively. The integrated ratios and chemical shifts of all signals are highly consistent with the expected structure, confirming the successful synthesis of the sulfonated diamine monomer.

[0195] Figure 3 Example 2 (NS 20 -b-ND 10 ) (dashed line) and Example 3 (NS 30 -b-ND 10 (Solid line) FT-IR spectrum of block copolymer proton exchange membrane. 2847-2929 cm -1 The peak in the region is the absorption peak of -CH2 in the alkyl chain, which proves the existence of fatty chains in the block copolymer. -1 and 1715cm -1 The typical imide-C=O asymmetric and symmetric stretching vibration absorption peaks appear at 1580cm, proving the successful formation of the polyimide skeleton. -1 and 1520cm -1 The characteristic absorption peak of benzene ring C=C is at 1030-1080cm -1 The symmetric and asymmetric stretching vibration peaks of the sulfonic acid groups can be observed in the region. FT-IR spectra confirmed the expected chemical structures of the two block copolymers.

[0196] Ion exchange capacity (IEC) and proton conductivity σ test

[0197] Ion exchange capacity test method: Accurately weigh 0.2-0.3g of dried proton exchange membrane, cut it into pieces and place it in 50mL of saturated sodium chloride solution. Stir it at room temperature for 3 days. Then remove the membrane and wash it three times with a small amount of deionized water. Collect all the eluate and combine it with the original saturated sodium chloride solution. Titrate it with a sodium hydroxide solution of known concentration to determine the H in the solution. + Content. Ion exchange capacity (IEC) is calculated according to the following formula:

[0198]

[0199] Among them, C NaOH is the concentration of NaOH solution (unit: mmol / L), V NaOH is the volume of NaOH solution consumed during the titration (unit: L), and m represents the mass of the polymer membrane (unit: g).

[0200] Proton conductivity testing method: Proton conductivity was tested for Examples 2-4, Comparative Example 1, and Nafion 212 proton exchange membrane using the AC impedance spectroscopy method. A Hioki 3553 Hitester AC impedance meter was used under the following test conditions: test frequency 42 Hz to 5 MHz; test medium: ultrapure water; test temperature: 40°C or 80°C. Proton conductivity σ (unit: S / cm) was calculated according to the following formula:

[0201]

[0202] Where D is the distance between the two electrodes (5 mm), L is the width of the membrane sample (5 mm), B is the thickness of the membrane sample (30-50 μm), and R is the impedance of the test sample (unit: Ω).

[0203] Table 1 lists three copolymer film examples 2 (NS 20 -b-ND 10 ), Example 3 (NS 30 -b-ND 10 ), Example 4 (rN:S:D (41:31:10)) and Nafion 212 in terms of ion exchange capacity (IEC), proton conductivity, water absorption and swelling rate.

[0204] The IEC of Example 2 is 1.75meq / g, and that of Example 3 and Example 4 is 1.86meq / g, which are significantly higher than Nafion 212 (0.91meq / g). At 80°C, the proton conductivity of Example 2 is 0.131S / cm, and the conductivities of Examples 3 and 4 are 0.137 and 0.134S / cm, respectively, both slightly higher than Nafion 212 (0.133S / cm). The proton conductivity of Example 3 is slightly higher than that of Example 4, indicating that the block copolymerization method makes the sulfonic acid groups more aggregated to form continuous hydrophilic channels compared to random copolymerization, thereby improving the proton conductivity. At 40°C, the conductivity of the three (0.0615-0.0684S / cm) is equivalent to that of Nafion (0.0685S / cm). It can be seen that the improvement of IEC directly increases the concentration of mobile protons in the membrane, thereby maintaining conductive properties comparable to or better than the commercial membrane Nafion 212 under high temperature conditions.

[0205] The three sulfonated polyimide copolymer membranes shown in Table 1 exhibit significant anisotropy in their in-plane (Δl) and through-thickness (Δt) swelling rates. Their linear in-plane swelling rates are all as low as 3%, far less than the 15% of Nafion 212, while the through-thickness swelling rate increases with the degree of sulfonation, from 31% to 50%. This is due to the highly rigid aromatic units in the copolymer backbone being arranged in the membrane plane through π-π stacking. In-plane interchain forces significantly suppress dimensional changes in the membrane in the in-plane direction. Unlike in the membrane plane, the through-thickness direction lacks continuous segment orientation and stacking constraints. Hydrophilic sulfonic acid groups can freely expand along the membrane interlayers after water absorption, resulting in a much larger Δt than Δl. As the degree of sulfonation increases, the water absorption rate increases from 28% in Example 2 to 55% in Example 3, further increasing the through-thickness swelling, while in-plane swelling remains limited by backbone rigidity and interchain interactions. Under the condition of the same degree of sulfonation (IEC = 1.86meq / g), Example 3 has a lower swelling rate and water absorption rate than Example 4 using random copolymerization due to the use of block copolymerization. The low swelling rate in the planar direction ensures the dimensional stability and mechanical integrity of the membrane during MEA assembly and operation, and avoids interfacial debonding or microcracks caused by expansion stress. Moderate thickness expansion is conducive to the formation of a more continuous water phase channel network, thereby improving the proton transfer efficiency. In summary, this swelling anisotropy reflects that the block copolymer achieves an organic combination of planar structural stability and functional expansion in the thickness direction through molecular-level orientation and interchain interaction, providing an ideal structural basis for the mechanical durability and conductive properties of high-temperature and low-humidity proton exchange membranes.

[0206] Table 1. Ion exchange capacity, proton conductivity, water absorption, and swelling rate of proton exchange membranes

[0207]

[0208] Oxidative and hydrolytic stability testing

[0209] The oxidative stability of the proton exchange membrane was characterized by its initial dissolution time and complete dissolution time in Fenton's reagent (80°C, 3% H2O2, 3ppm FeSO4). As shown in Table 2, the initial dissolution time of the membranes of Examples 2 to 4 in Fenton's reagent exceeded 160 minutes, which was significantly better than that of Comparative Example 1 (NB containing ether bonds). 15 -b-ND 10 ), the initial dissolution time of the latter is less than 120 minutes. Examples 2 to 4 exhibit excellent oxidative stability due to the use of wholly aromatic sulfonated diamines.

[0210] In a pressurized, sealed autoclave, membrane samples with a thickness of 30 μm were placed in 140°C water for 24 hours. The hydrolytic stability of the samples was assessed by weighing the dry mass before and after treatment. Table 2 shows that after the accelerated hydrolytic stability test, the weight of the membranes in Examples 2-4 remained above 95% of their initial weight, demonstrating their high hydrolytic stability. These experimental results demonstrate that the structural adjustment of the sulfonated diamine monomer not only effectively maintains the hydrolytic stability of the sulfonated polyimide proton exchange membrane but also enhances its resistance to free radical oxidation.

[0211] Table 2. Anti-radical oxidation stability and hydrolytic stability of proton exchange membranes

[0212]

[0213] Mechanical properties testing

[0214] Figure 4 For Example 2 (NS 20 -b-ND 10 ) and Example 3 (NS 30 -b-ND 10 ) Stress-strain curve of sulfonated polyimide block copolymer membrane. The mechanical behavior of the two membranes is highly consistent. 20 -b-ND 10 and NS 30 -b-ND 10 The tensile strengths of NS are 185MPa and 190MPa respectively. 30 -b-ND 10 Breaking at ε≈34%, NS 20 -b-ND 10The elongation at break is approximately 35%. The tensile strength (≈190 MPa) and excellent elongation at break (≈35%) demonstrate that the polyimide prepared by the block copolymerization strategy has both extremely high resistance to stress failure and high toughness, meeting the mechanical performance requirements for membrane electrode assembly (MEA) and the practical application requirements of fuel cell MEAs.

[0215] X-ray diffraction (XRD) test

[0216] Figure 5 The commercial Nafion 212 and two sulfonated polyimide block copolymer membranes prepared in this study (NS 20 -b-ND 10 and NS 30 -b-ND 10 ) X-ray diffraction (XRD) spectrum of Nafion 212. The diffraction signal of Nafion 212 is mainly concentrated in the range of 15-20° (2θ), corresponding to the amorphous and partially oriented stacking of the main chain or side chain of perfluorosulfonic acid. In contrast, NS 20 -b-ND 10 and NS 30 -b-ND 10 Both exhibit a sharp diffraction peak at 2θ = 5° (d ≈ 1.7 nm), which is consistent with the repeating unit length of the hydrophobic block in both materials (~1.5 nm). This low-angle peak originates from the crystalline arrangement of the hydrophobic segments along the chain axis. The crystallinity of the hydrophobic regions facilitates the formation of continuous proton conduction channels within the amorphous hydrophilic regions, contributing to the membrane electrode's power generation efficiency and mechanical stability under high-temperature, low-humidity conditions.

[0217] Transmission electron microscopy (TEM) testing

[0218] Transmission electron microscopy was used to characterize the block copolymer proton exchange membrane NS 20 -b-ND 10 and NS 30 -b-ND 10 To enhance the electron contrast in TEM images, Pb was introduced during sample preparation. 2+ Ion exchange step. Pb 2+ The high atomic number of the α-Hydroxy-Phenyl-Ion (PI) significantly increases the electron density in the hydrophilic phase, resulting in stronger contrast in the dark regions (hydrophilic clusters) under TEM. Both samples exhibit alternating dark and bright regions, corresponding to the hydrophilic ion clusters (sulfonated PI segments) and the hydrophobic polyimide phase, respectively. Figure 6 (a) NS 20 -b-ND 10 The ion clusters are small and dispersed, with an average size of 4 to 6 nm, resulting in a discontinuous distribution of water channels; Figure 6 (b) NS 30-b-ND 10 The ionic clusters grow to 6-8 nm and form an interconnected network. As the degree of sulfonation increases, the Flory–Huggins interaction parameter χN increases, the driving force for microphase separation strengthens, and the size and connectivity of the hydrophilic clusters increase simultaneously. 30 -b-ND 10 The constructed coherent hydrophilic channel network enables the assembled membrane electrode to exhibit excellent proton conductivity and power generation performance under low relative humidity (<30% RH) conditions, proving that by regulating the block ratio and sulfonation degree, the phase separation degree of the membrane can be optimized, thereby improving the proton transport performance of the membrane material and the power generation performance of the fuel cell.

[0219] Power generation performance test

[0220] Preparation method of membrane electrode (MEA): 40wt% Pt / C (Johnson) was used as the electrode catalyst and Nafion was used as the binder. The catalyst ink was evenly sprayed on both sides of the proton exchange membrane, with an effective area of ​​5cm on each side. 2 The platinum catalyst loadings at the anode and cathode were 0.3 mg / cm 2 and 0.7 mg / cm 2 .

[0221] The power generation performance of single cells assembled with the proton exchange membranes prepared in Examples 2-4 and Comparative Example 1 and Nafion 212 membrane was tested using a Scribner 850e fuel cell tester (USA). The test conditions were as follows: (1) Gas supply: Hydrogen and oxygen flow rates were both 200 mL / min; (2) Test temperature: 90°C; (3) Back pressure: 150 kPa; (4) Humidification conditions: Gas relative humidity was 100%, 80%, 50%, or 30%.

[0222] Compared with the single cell assembled with Nafion 212 proton exchange membrane, the single cell assembled with the sulfonated polyimide block copolymer proton exchange membrane prepared in Example 3 not only has a higher open circuit voltage, but also has an improved peak power density, indicating that the membrane has better electrochemical performance and energy output characteristics in the field of fuel cells. Under high relative humidity conditions (90°C, 100% RH), at a current density below 700 mA / cm 2 The performance of the single cell assembled in Example 3 is comparable to that of the single cell assembled with Nafion polymer. However, at higher current density, the performance of the single cell assembled in Example 3 is further improved, and the resistance is reduced, indicating that it has better conductivity and energy conversion efficiency under high load operating conditions. The test results show that at a current density of 4076 mA / cm 2 When the peak power density of the single cell assembled in Example 3 reaches 1.97 W / cm2 , while the Nafion polymer assembled single cell was 3196mA / cm 2 The peak power density is only 1.587W / cm 2 Therefore, the peak power density of the single cell assembled in Example 3 is 25% higher than that of the single cell assembled with Nafion polymer (e.g. Figure 7-1 shown). Figure 7-2 The polarization curve of the single cell assembled with Example 3 and Nafion 212 at 90°C and low relative humidity (30% RH) is shown. The test results show that under these conditions, the peak power density of the single cell assembled with Example 3 is 1.04 W / cm 2 (corresponding to a current density of 2.1A / cm 2 ), while the peak power density of the single cell assembled with Nafion is 0.93W / cm 2 (corresponding to a current density of 2.1A / cm 2 ). Therefore, the peak power density of the single cell assembled in Example 3 is approximately 12% higher than that of the single cell assembled with Nafion 212. The above results show that the single cell assembled with the sulfonated polyimide block copolymer proton exchange membrane prepared in Example 3 exhibits better power generation performance than the single cell assembled with Nafion 212 under both high and low humidity conditions, further demonstrating the applicability of the membrane material of the present invention in different humidity environments, reducing dependence on external humidification systems, and thus improving the energy efficiency and overall operational stability of the fuel cell system.

[0223] like Figure 8 As shown, the stability of the proton exchange membrane (PEM) was evaluated by open circuit voltage (OCV) durability testing under 90°C and 50% RH conditions. The test results show that the OCV of the single cell assembled in Example 3 remained stable during the 50-hour continuous test without significant attenuation, indicating that the membrane has excellent durability and chemical stability under these conditions. Further analysis shows that the sulfonated polyimide block copolymer proton exchange membrane provided by the present invention can effectively inhibit performance degradation caused by hydrolysis or oxidation during long-term operation, thereby improving the stability and service life of the fuel cell.

[0224] The preferred embodiments of the present invention have been described in detail above. It should be understood that numerous modifications and variations based on the concepts of the present invention are possible without inventive effort by those skilled in the art. Therefore, any technical solution that can be derived by one skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A sulfonated diamine monomer, characterized in that Its general structural formula is shown in formula (1): wherein R1 represents a sulfonated aromatic group containing a carbonyl group or a sulfonyl group, and R2 represents a monovalent group; R1 is selected from any one of the following groups: R2 is selected from any one of the following groups: -H, -CH3, -CF3.

2. A method for preparing a sulfonated diamine monomer as claimed in claim 1, characterized in that: The method comprises the following steps: step 1) under N2 protection, adding a dibromoaryl compound containing a carboxylic acid or sulfonic acid group and thionyl chloride or oxalyl chloride in sequence into a dry three-necked flask, heating and reacting at 0-100°C for 1-30 hours, removing thionyl chloride or oxalyl chloride after the reaction to obtain a dibromo compound containing an acyl chloride or sulfonyl chloride group; adding benzene or a benzene derivative and a Lewis acid in sequence into the reaction system, reacting at 20-150°C for 1-50 hours to obtain a dibromo compound containing a carbonyl or sulfonyl group, wherein the reaction is carried out according to the following chemical reaction equation (1): Reaction equation (1) Where z is 0 or 1; R4 is selected from any one of the following groups: -COOH, -SO3H; R5 is selected from any one of the following groups: -COCl, -SO2Cl; R6 is selected from any one of the following groups: -O-, -SO2-; R7 is selected from any one of the following groups: Step 2) The dibromo compound containing a carbonyl or sulfonyl group obtained in step 1 is added to a dry three-necked flask, and concentrated sulfuric acid and fuming sulfuric acid are added in sequence. The mixture is heated at 20-150° C. for 1-30 hours to obtain a sulfonated dibromo compound containing a carbonyl or sulfonyl group. The reaction is carried out according to the following chemical reaction equation (2): Reaction equation (2) wherein R1 and R7 are as defined above; Step 3) The sulfonated dibromo compound containing a carbonyl or sulfonyl group obtained in step 2, an amino-containing end-capping agent, a base, a palladium catalyst, a ligand, an organic solvent, and water are sequentially added to a three-necked flask and reacted at 20 to 150° C. for 1 to 30 hours to obtain a sulfonated diamine monomer. The reaction is carried out according to the following chemical reaction equation (3): Reaction equation (3) wherein R1, R2, and R7 are as defined above, and R8 represents a monovalent boronic acid or a derivative thereof; R8 is selected from any one of the following groups:

3. The method for preparing a sulfonated diamine monomer according to claim 2, wherein: In the step 1), the molar ratio of the thionyl chloride or the oxalyl chloride to the dibromoaryl compound containing a carboxylic acid or sulfonic acid group is 1:1 to 1:100; the molar ratio of the benzene or diphenyl ether to the dibromoaryl compound containing a carboxylic acid or sulfonic acid group is 1:1 to 1:100; and the molar ratio of the Lewis acid to the dibromoaryl compound containing a carboxylic acid or sulfonic acid group is 1:1 to 1:

100.

4. The method for preparing a sulfonated diamine monomer according to claim 2, wherein: In the step 2), the molar ratio of the concentrated sulfuric acid to the dibromo compound containing a carbonyl group or a sulfonyl group is 1:1 to 1:100; the molar ratio of the fuming sulfuric acid to the dibromo compound containing a carbonyl group or a sulfonyl group is 1:1 to 1:

100.

5. A sulfonated polyimide block copolymer, characterized in that: Its general structure is represented by Formula 2: wherein R1 and R2 are as defined above, Ar1 and Ar2 represent a tetravalent aromatic group, R3 represents a divalent aromatic group, an alkyl group or an aromatic aliphatic group, and m and n are integers of 5 to 100; Ar1 and Ar2 are each selected from any one of the following groups: R3 is selected from any one of the following groups:

6. A sulfonated polyimide sequence copolymer, characterized in that: Its general structural formula is represented by Formula 3-1 and Formula 3-2: Wherein, Ar1, Ar2, R1, R2, R3, and m are defined as above, x, y, and z are decimals ranging from 0 to 1, and x+y+z=1.

7. A sulfonated polyimide random copolymer, characterized in that: Its general structural formula is represented by Formula 4: Wherein, Ar1, R1, R2, and R3 are defined as above, a, b, c, and d are decimals ranging from 0 to 1, and a+b+c+d=1.

8. A method for preparing the sulfonated polyimide block copolymer according to claim 5, the sulfonated polyimide sequential copolymer according to claim 6, or the sulfonated polyimide random copolymer according to claim 7.

9. A proton exchange membrane made of the sulfonated polyimide block copolymer according to claim 5, the sulfonated polyimide sequential copolymer according to claim 6, or the sulfonated polyimide random copolymer according to claim 7.

10. Use of the proton exchange membrane according to claim 9 in preparing a battery.

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