A method for preparing a sulfonated polybenzimidazole proton exchange membrane containing a branched structure

Abstract

The present invention belongs to the technical field of fuel cell proton exchange membranes, and discloses a method for preparing a sulfonated polybenzimidazole proton exchange membrane containing a branched structure. The branched sulfonated polybenzimidazole is prepared by adding a branched monomer (branched aromatic tricarboxylic acid) during the polymerization of raw monomers, and undergoing an imidazole reaction to obtain a novel sulfonated polybenzimidazole containing a branched structure. The sulfonated polybenzimidazole containing a branched structure can be prepared using a solution casting method to obtain a branched sulfonated polybenzimidazole proton exchange membrane. The branched sulfonated polybenzimidazole of the present invention introduces a branched structure, which greatly shortens the reaction time of the polymer, and enables the prepared proton exchange membrane to have a larger microphase space, which is conducive to the construction of a proton transmission channel. The novel sulfonated polybenzimidazole proton exchange membrane containing a branched structure has good application prospects in proton exchange membrane fuel cells.

Description

Technical Field

[0001] The invention belongs to the technical field of fuel cell proton exchange membrane materials, and particularly relates to a sulfonated polybenzimidazole containing a branched structure and a preparation method thereof. The prepared sulfonated polybenzimidazole containing a branched structure can be used for preparing proton exchange membrane materials. Background Art

[0002] Proton exchange membrane is the core material of proton exchange membrane fuel cells. It plays the role of isolating the cathode and anode materials and conducting protons in the battery. Polybenzimidazole (PBI) is a polymer material with good mechanical, chemical and thermal stability. Phosphoric acid can self-ionize and conduct protons in anhydrous state. Polybenzimidazole can conduct protons at an operating temperature of 100-200°C after being doped with phosphoric acid. It is the most promising electrolyte material suitable for high-temperature proton exchange membrane fuel cells. Polybenzimidazole mainly refers to linear heterocyclic compounds containing benzimidazole groups in repeating units, which are polymerized by various tetraamine monomers and diacid monomers.

[0003] Generally, the proton conductivity of phosphoric acid-doped PBI membrane increases with the increase of phosphoric acid (PA) doping content. However, when the original PBI membrane is doped with a large amount of PA, the mechanical strength will drop sharply. Crosslinking is a relatively effective method to increase the mechanical strength, but the conventional covalent crosslinking through ionic crosslinking between NH groups or through heat treatment to bond imidazole groups in the polymer will occupy the phosphate site, resulting in a decrease in phosphate uptake, and the crosslinked PBI is difficult to dissolve in organic solvents. Another method to connect polymer chains is branching. By adding branching monomers during the synthesis of PBI, the polymer chain forms a unique three-dimensional spatial structure, which can connect the long polymer chain without occupying the phosphate binding site, and the branched PBI still has good solubility in organic solvents. The unique spatial structure can also accommodate more phosphoric acid. The phosphoric acid doping level, phosphoric acid retention capacity, proton conductivity and thermal oxidation stability of the membrane containing branched structure synthesized using tricarboxylic acid monomers are all improved compared with the membrane without branched structure. Studies have shown that under the same phosphoric acid doping conditions, PBI containing sulfonic acid groups has higher proton conductivity than PBI without sulfonic acid groups. CN200510111019.4 Hyperbranched polybenzimidazole and its preparation method, CN202210493112.X A HBM-based blended modified PBI proton exchange membrane and its preparation method and application, tricarboxylic acid monomer is polymerized with tetraamino monomer as a carboxyl monomer, and its usage is limited by the ratio of carboxyl to amino group. Hyperbranched molecules are synthesized, and sulfonic acid is only contained in the hyperbranched macromolecular structure. Polybenzimidazole is the main material of the proton exchange membrane, but it itself cannot conduct protons. The hyperbranched macrostructure and PBI are physically blended, and the two parts play their respective roles, which has limited effect on improving the overall proton transfer efficiency of the proton exchange membrane. CN202210774185.6 A polybenzimidazole gel-type high-temperature proton exchange membrane with a functional / branched structure and a preparation method thereof. The polymer membrane is obtained directly through a phase transformation process from a polymer solution to a gel-based membrane. There is no need to consider the re-dissolution process after polymer purification. It can only be in the form of a polymer solution or a proton exchange membrane. Polyphosphoric acid is easily hydrolyzed, which causes more trouble for storage and transportation. Summary of the invention

[0004] In order to overcome the above-mentioned problems in the prior art, the present invention synthesizes a sulfonated polybenzimidazole containing a branched structure from the perspective of optimizing the spatial structure of the polymer, utilizes the branched structure to adjust the spatial distribution of the polymer chain, increases the absorption of phosphoric acid, and uses the sulfonic acid group to assist proton conduction, so as to achieve stable high acid doping and improve the proton conduction performance.

[0005] To achieve the purpose of the present invention, the technical solution adopted by the present invention is:

[0006] The general structural formula of sulfonated polybenzimidazole containing branched structure is:

[0007]

[0008] Where: R1 = Any of;

[0009] R2=

[0010] R3=

[0011] The preparation method of the sulfonated polybenzimidazole proton exchange membrane containing a branched structure comprises the following two steps:

[0012] (1) Synthesis of sulfonated polybenzimidazole with branched structure: branched aromatic tricarboxylic acid, 3,3'-diaminobenzidine, sodium 5-sulfonate of isophthalic acid and 4,4'-dicarboxy diphenyl ether are used as monomers and prepared by solution polycondensation in polyphosphoric acid:

[0013] (2) Preparation of branched sulfonated polybenzimidazole proton exchange membrane: dissolve the sulfonated polybenzimidazole containing a branched structure in an organic solvent to obtain a solution of the sulfonated polybenzimidazole containing a branched structure, pour the solution onto a smooth glass plate, place the glass plate in an environment of 80°C for 24 hours to evaporate the solvent, wash the polymer membrane from the glass plate with deionized water to remove the residual solvent, and then immerse the polymer membrane in a 1M hydrochloric acid solution for proton exchange. After 48 hours, take out the solution and wash off the residual acid on the surface, and dry it at 120°C to obtain the branched sulfonated polybenzimidazole proton exchange membrane.

[0014] Furthermore, the mass ratio of the total mass of the compound monomers to the mass ratio of the polyphosphoric acid is 1:12-13.

[0015] The branched aromatic tricarboxylic acid is 1,3,5-benzenetricarboxylic acid or 1,3,5-tris(4-carboxyphenyl)benzene;

[0016] Furthermore, the molar ratio of 1,3,5-benzenetricarboxylic acid to 3,3'-diaminobenzidine is 1:10-50.

[0017] Furthermore, the molar ratio of 1,3,5-tris(4-carboxyphenyl)benzene to 3,3'-diaminobenzidine is 1:33-100.

[0018] The change of branching ratio will affect the polymerization of the polymer, and different branching structures will also have different effects. Further preferred is: the molar ratio of 1,3,5-benzenetricarboxylic acid to 3,3'-diaminobenzidine is 1:10; the molar ratio of 1,3,5-tris(4-carboxyphenyl)benzene to 3,3'-diaminobenzidine is 1:50.

[0019] Furthermore, the molar ratio of sodium 5-sulfoisophthalate to 4,4'-dicarboxydiphenyl ether is 1:1.

[0020] Furthermore, the molar ratio of the total number of carboxyl groups of 4,4'-dicarboxydiphenyl ether plus sodium 5-sulfoisophthalic acid plus branched aromatic tricarboxylic acid to the total number of amino groups of 3,3'-diaminobenzidine is 1:2.

[0021] Furthermore, the organic solvent is dimethyl sulfoxide or N,N-dimethylacetamide.

[0022] Furthermore, the mass ratio of the sulfonated polybenzimidazole containing a branched structure to the organic solvent is 1:20-50.

[0023] The reaction flow diagram is shown below: Taking 1,3,5-benzenetricarboxylic acid as an example of the branched aromatic tricarboxylic acid.

[0024]

[0025] The molecular weight of the sulfonated polybenzimidazole containing a branched structure is 7000 to 30000.

[0026] The beneficial effects of the present invention are as follows: the sulfonated polybenzimidazole containing a branched structure of the present invention has a long chain containing a sulfonic acid group and a flexible group connected with the branched structure as the core in the polymer. On the one hand, the branched structure can connect the polymer chains together to enhance the stability of the polymer membrane, and on the other hand, it can form a unique spatial structure to increase the absorption rate of phosphoric acid, which is beneficial to the construction of a proton transport channel. The ether bond or sulfone group increases flexibility, making the polymer more soluble in organic solvents. The sulfonic acid group can assist in the construction of a proton transport channel and coordinate phosphoric acid for proton conduction. The sulfonated polybenzimidazole proton exchange membrane containing a branched structure of the present invention has good thermal stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The branched sulfonated polybenzimidazole SPBI-C5 prepared in step (1) of Example 1 1 HNMR (DMSO-d6).

[0028] Figure 2 This is the infrared spectrum of the branched sulfonated polybenzimidazole proton exchange membrane SPBI-C5 prepared in step (2) of Example 1.

[0029] Figure 3 This is the thermogravimetric diagram of the branched sulfonated polybenzimidazole proton exchange membrane SPBI-C5 prepared in step (2) of Example 1.

[0030] Figure 4 The branched sulfonated polybenzimidazole SPBI-B2 prepared in step (1) of Example 4 1 HNMR (DMSO-d6).

[0031] Figure 5 This is a graph showing the proton conductivity of the branched sulfonated polybenzimidazole proton exchange membrane SPBI-B2 prepared in step (2) of Example 4 as a function of temperature at 20% relative humidity. DETAILED DESCRIPTION

[0032] Example 1

[0033] (1) Synthesis of branched sulfonated polybenzimidazole SPBI-C5 with 1,3,5-benzenetricarboxylic acid as branch structure

[0034] Pour 35.118 g of polyphosphoric acid into a 100 mL three-necked flask, stir and heat at 140 ° C for 1 h in a N2 atmosphere to eliminate bubbles, then add 0.063 g (0.30 mmol) of 1,3,5-benzenetricarboxylic acid, 0.744 g (2.775 mmol) of sodium 5-sulfonate of isophthalic acid, 0.717 g (2.775 mmol) of 4,4'-dicarboxydiphenyl ether and 1.286 g (6.00 mmol) of 3,3'-diaminobenzidine in sequence, with an interval of 15 min between each addition. Then cool to 120 ° C, stir and heat for 12 h to fully dissolve, stir and heat at 170 ° C for 1 h for prepolymerization, and stir and heat at 200 ° C for 4 h for reaction. After the reaction is completed, the polymer product is poured into deionized water while hot to wash away most of the acid, the solid is collected by filtration and soaked in a saturated sodium bicarbonate solution until there are no bubbles, filtered, washed with alcohol and deionized water until the solid is neutral, and dried at 120°C for 12h to obtain branched sulfonated polybenzimidazole SPBI-C5. 1 HNMR characterization, see Figure 1 The proton peak H of the branched structure appeared at 8.93ppm in the NMR image. i The attributions of the remaining peaks are indicated in the spectrum, which proves that branched sulfonated polybenzimidazole SPBI-C5 is synthesized with a number average molecular weight Mn of 10043 and a weight average molecular weight Mw of 12992.

[0035]

[0036] (2) Preparation of branched sulfonated polybenzimidazole proton exchange membrane

[0037] Take 1.200gSPBI-C5 and add 24.000g dimethyl sulfoxide, stir and heat at 120℃ for 3h to dissolve a solution with a concentration of 5wt%, centrifuge the solution at 8000r / min for 5min, pour the upper solution onto a flat and smooth glass plate, place it in an 80℃ environment for 18h to allow the solvent to evaporate, then use deionized water to clean the SPBI-C5 proton exchange membrane from the glass plate and wash away the residual organic solvent, soak the SPBI-C5 proton exchange membrane in 1M hydrochloric acid for more than 48h for ion exchange, wash away the attached hydrochloric acid with deionized water, and then dry it at 120℃ for 12h to obtain the SPBI-C5 proton exchange membrane.

[0038] The proton exchange membrane was characterized by infrared spectroscopy. Figure 2 , 1635cm in infrared image -1 is due to the in-plane vibration of the imidazole ring, 1597 cm -1 It is due to the conjugated vibration between imidazole rings, 1486cm -1 It is due to the C=N stretching vibration of the imidazole ring, 1168cm -1 is due to the Ar-O-Ar stretching vibration in the polymer, 1039 cm -1 、1240cm -1 Related to the symmetric and asymmetric vibrations of the sulfonic acid group, 804 cm -1 The proton exchange membrane was characterized by thermogravimetric analysis. Figure 3 , the proton exchange membrane has almost no mass loss within 300°C. The proton conductivity of the membrane was tested at 160°C and 20% relative humidity, and the proton conductivity of the SPBI-C5 proton exchange membrane doped with phosphoric acid was 52.8mS / cm.

[0039] Compared with the SPBI-C5 proton exchange membrane, the preparation method of the SPBI proton exchange membrane without branching structure does not add 1,3,5-benzenetricarboxylic acid and does not stir and heat at 200°C for 8h, while other reaction conditions are the same.

[0040] The proton conductivity of the SPBI proton exchange membrane without branched structure was tested at 160° C. and 20% relative humidity and was 40 mS / cm.

[0041] In addition, the phosphoric acid doping rate in the SPBI-C5 proton exchange membrane prepared in Example 1 is 216.18%, which is higher than the phosphoric acid doping rate (183.24%) of the SPBI proton exchange membrane without a branched structure.

[0042] Example 2

[0043] (1) Synthesis of branched sulfonated polybenzimidazole SPBI-C10 with 1,3,5-benzenetricarboxylic acid as the branching structure

[0044] Pour 34.426 g of polyphosphoric acid into a 100 mL three-necked flask, stir and heat at 140 ° C for 1 h in a N2 atmosphere to eliminate bubbles, then add 0.126 g (0.60 mmol) of 1,3,5-benzenetricarboxylic acid, 0.684 g (2.55 mmol) of sodium 5-sulfonate of isophthalic acid, 0.658 g (2.55 mmol) of 4,4'-dicarboxydiphenyl ether and 1.286 g (6.00 mmol) of 3,3'-diaminobenzidine in sequence, with an interval of 15 min between each addition. Then cool to 120 ° C, stir and heat for 12 h to fully dissolve, stir and heat at 170 ° C for 1 h for prepolymerization, and stir and heat at 200 ° C for 3 h to react. After the reaction is completed, the polymer product is poured into deionized water while hot to wash off most of the acid, the solid is collected by filtration and immersed in a saturated sodium bicarbonate solution until there are no bubbles, filtered, and the solid is washed with alcohol and deionized water until neutral, and then dried at 120°C for 12 hours to obtain branched sulfonated polybenzimidazole SPBI-C10 with a number average molecular weight Mn of 7652 and a weight average molecular weight Mw of 9618.

[0045] (2) Preparation of branched sulfonated polybenzimidazole proton exchange membrane

[0046] Take 1.200gSPBI-C10 and add 60.000gN,N-dimethylacetamide, stir and heat at 120℃ for 2h to dissolve a solution with a concentration of 2wt%, centrifuge the solution at 8000r / min for 5min, pour the upper solution on a flat and smooth glass plate, place it in an 80℃ environment for 24h to evaporate the solvent, then use deionized water to clean the SPBI-C10 proton exchange membrane from the glass plate and wash away the residual organic solvent, soak the SPBI-C10 proton exchange membrane in 1M hydrochloric acid for more than 48h for ion exchange, wash away the attached hydrochloric acid with deionized water, and dry it at 120℃ for 12h to obtain the SPBI-C10 proton exchange membrane. The proton conductivity of the membrane was tested at 160℃ and 20% relative humidity, and the proton conductivity of the SPBI-C10 proton exchange membrane doped with phosphoric acid was 60mS / cm. The phosphoric acid doping rate in the SPBI-C10 proton exchange membrane prepared in Example 2 is 231.30%.

[0047] Example 3

[0048] (1) Synthesis of branched sulfonated polybenzimidazole SPBI-C15 with 1,3,5-benzenetricarboxylic acid as branch structure

[0049] Pour 33.733 g of polyphosphoric acid into a 100 mL three-necked flask, stir and heat at 140 ° C for 1 h in a N2 atmosphere to eliminate bubbles, then add 0.189 g (0.90 mmol) of 1,3,5-benzenetricarboxylic acid, 0.624 g (2.325 mmol) of sodium 5-sulfonate of isophthalic acid, 0.600 g (2.325 mmol) of 4,4'-dicarboxydiphenyl ether and 1.286 g (6.00 mmol) of 3,3'-diaminobenzidine in sequence, with an interval of 15 min between each addition. Then cool to 120 ° C, stir and heat for 12 h to fully dissolve, stir and heat at 170 ° C for 1 h for prepolymerization, and stir and heat at 200 ° C for 3 h to react. After the reaction is completed, the polymer product is poured into deionized water while hot to wash off most of the acid, the solid is collected by filtration and immersed in a saturated sodium bicarbonate solution until there are no bubbles, filtered, and the solid is washed with alcohol and deionized water until neutral, and then dried at 120°C for 12 hours to obtain branched sulfonated polybenzimidazole SPBI-C15.

[0050] (2) Preparation of branched sulfonated polybenzimidazole proton exchange membrane

[0051] Take 1.200g SPBI-C15 and add 60.000g dimethyl sulfoxide, stir and heat at 120°C for 2h to dissolve and prepare a solution with a concentration of 2wt%. After 30min, it becomes gel-like and cannot be stirred by a magnetic rotor, and the polymer cannot be made into a film.

[0052] SPBI-C15 is difficult to dissolve into solution, so the molecular weight cannot be measured. The inability to make membranes with SPBI-C15 may be caused by the high density of branched structures and the molecular chains are intertwined.

[0053] Example 4

[0054] (1) Synthesis of branched sulfonated polybenzimidazole SPBI-B2 with a branched structure of 1,3,5-tri(4-carboxyphenyl)benzene

[0055] Pour 35.876 g of polyphosphoric acid into a 100 mL three-necked flask, stir and heat at 140 ° C for 1 h in a N2 atmosphere to eliminate bubbles, then add 0.053 g (0.12 mmol) of 1,3,5-tri(4-carboxyphenyl)benzene, 0.780 g (2.91 mmol) of sodium 5-sulfonate of isophthalic acid, 0.751 g (2.91 mmol) of 4,4'-dicarboxydiphenyl ether and 1.286 g (6.00 mmol) of 3,3'-diaminobenzidine in sequence, with an interval of 15 min between each addition. Then cool to 120 ° C, stir and heat for 12 h to fully dissolve, stir and heat at 170 ° C for 1 h for prepolymerization, and stir and heat at 200 ° C for 3 h for reaction. After the reaction is completed, the polymer product is poured into deionized water while hot to wash away most of the acid, the solid is collected by filtration and soaked in a saturated sodium bicarbonate solution until there are no bubbles, filtered, washed with alcohol and deionized water until the solid is neutral, and dried at 120°C for 12h to obtain branched sulfonated polybenzimidazole SPBI-B2. 1 HNMR characterization, see Figure 4 The proton peak H of the branched structure appeared at 8.09ppm in the NMR image. i , H j , H k The attributions of the remaining peaks are indicated in the spectrum, which proves that branched sulfonated polybenzimidazole SPBI-B2 is synthesized with a number average molecular weight Mn of 8546 and a weight average molecular weight Mw of 10596.

[0056]

[0057] (2) Preparation of branched sulfonated polybenzimidazole proton exchange membrane

[0058] Take 1.200gSPBI-B2 and add 30.000g dimethyl sulfoxide, stir and heat at 120℃ for 2h to dissolve a solution with a concentration of 4wt%, centrifuge the solution at 8000r / min for 5min, pour the upper solution onto a flat and smooth glass plate, place it in an 80℃ environment for 18h to allow the solvent to evaporate, then use deionized water to clean the SPBI-B2 proton exchange membrane from the glass plate and wash away the residual organic solvent, soak the SPBI-B2 proton exchange membrane in 1M hydrochloric acid for more than 48h for ion exchange, wash away the attached hydrochloric acid with deionized water, and then dry it at 120℃ for 12h to obtain the SPBI-B2 proton exchange membrane.

[0059] The proton conductivity of SPBI-B2 proton exchange membrane changes with temperature at 20% relative humidity. Figure 5 The proton conductivity of the SPBI-B2 membrane after phosphoric acid doping is 70 mS / cm at 160°C and 20% relative humidity. The phosphoric acid doping rate of the SPBI-B2 proton exchange membrane prepared in Example 4 is 197.00%.

[0060] Example 5

[0061] (1) Synthesis of branched sulfonated polybenzimidazole SPBI-B3 with a branched structure of 1,3,5-tri(4-carboxyphenyl)benzene

[0062] Pour 35.909 g of polyphosphoric acid into a 100 mL three-necked flask, stir and heat at 140 ° C for 1 h in a N2 atmosphere to eliminate bubbles, then add 0.079 g (0.18 mmol) of 1,3,5-tri(4-carboxyphenyl)benzene, 0.768 g (2.865 mmol) of sodium 5-sulfonate of isophthalic acid, 0.740 g (2.865 mmol) of 4,4'-dicarboxydiphenyl ether and 1.286 g (6.00 mmol) of 3,3'-diaminobenzidine in sequence, with an interval of 15 min between each addition. Then cool to 120 ° C, stir and heat for 12 h to fully dissolve, stir and heat at 170 ° C for 1 h for prepolymerization, and stir and heat at 200 ° C for 3 h for reaction. After the reaction is completed, the polymer product is poured into deionized water while hot to wash off most of the acid, the solid is collected by filtration and immersed in a saturated sodium bicarbonate solution until there are no bubbles, filtered, and the solid is washed with alcohol and deionized water until neutral, and then dried at 120°C for 12 hours to obtain branched sulfonated polybenzimidazole SPBI-B3 with a number average molecular weight Mn of 6195 and a weight average molecular weight Mw of 8218.

[0063] (2) Preparation of branched sulfonated polybenzimidazole proton exchange membrane

[0064] Take 1.200gSPBI-B3 and add 60.000gN,N-dimethylacetamide, stir and heat at 120℃ for 2h to dissolve a solution with a concentration of 2wt%, centrifuge the solution at 8000r / min for 5min, pour the upper solution on a flat and smooth glass plate, place it in an 80℃ environment for 24h to evaporate the solvent, then use deionized water to clean the SPBI-B3 proton exchange membrane from the glass plate and wash away the residual organic solvent, soak the SPBI-B3 proton exchange membrane in 1M hydrochloric acid for more than 48h for ion exchange, wash away the attached hydrochloric acid with deionized water, and dry it at 120℃ for 12h to obtain the SPBI-B3 proton exchange membrane. The proton conductivity of the membrane was tested at 140℃ and 20% relative humidity, and the proton conductivity of the SPBI-B3 proton exchange membrane doped with phosphoric acid was 54mS / cm. The phosphoric acid doping rate is 209.70%, which is higher than the phosphoric acid doping rate of the proton exchange membrane without branching structure (183.24%).

[0065] Example 6

[0066] (1) Synthesis of branched sulfonated polybenzimidazole SPBI-B4 with a branched structure of 1,3,5-tri(4-carboxyphenyl)benzene

[0067] Pour 35.942 g of polyphosphoric acid into a 100 mL three-necked flask, stir and heat at 140 ° C for 1 h in a N2 atmosphere to eliminate bubbles, then add 0.105 g (0.24 mmol) of 1,3,5-tri(4-carboxyphenyl)benzene, 0.756 g (2.820 mmol) of sodium 5-sulfonate of isophthalic acid, 0.728 g (2.820 mmol) of 4,4'-dicarboxydiphenyl ether and 1.286 g (6.00 mmol) of 3,3'-diaminobenzidine in sequence, with an interval of 15 min between each addition. Then cool to 120 ° C, stir and heat for 12 h to fully dissolve, stir and heat at 170 ° C for 1 h for prepolymerization, and stir and heat at 200 ° C for 2.8 h for reaction. After the reaction is completed, the polymer product is poured into deionized water while hot to wash off most of the acid. The solid is collected by filtration and immersed in a saturated sodium bicarbonate solution until there are no bubbles. The solid is filtered, washed with alcohol and deionized water until neutral, and then dried at 120° C. for 12 h to obtain branched sulfonated polybenzimidazole SPBI-B4.

[0068] (2) Preparation of branched sulfonated polybenzimidazole proton exchange membrane

[0069] Take 1.200g SPBI-B4 and add 30.000g dimethyl sulfoxide. Heat with stirring at 120℃ for 2h to dissolve a solution with a concentration of 4wt%. Centrifuge the solution at 8000r / min for 5min. Most of the solution is gel-like and cannot be used to make membranes. There is very little solution on the upper layer. Pour it onto a flat and smooth glass plate and place it in an 80℃ environment for 24h to allow the solvent to evaporate. Then use deionized water to clean and remove the SPBI-B4 proton exchange membrane from the glass plate. The membrane strength is insufficient and it breaks.

[0070] Example 7

[0071] (1) Synthesis of branched sulfonated polybenzimidazole SPBI-B6 with a branched structure of 1,3,5-tri(4-carboxyphenyl)benzene

[0072] Pour 36.007 g of polyphosphoric acid into a 100 mL three-necked flask, stir and heat at 140 ° C for 1 h in a N2 atmosphere to eliminate bubbles, then add 0.158 g (0.36 mmol) of 1,3,5-tris (4-carboxyphenyl) benzene, 0.732 g (2.730 mmol) of sodium 5-sulfonate of isophthalic acid, 0.705 g (2.730 mmol) of 4,4'-dicarboxydiphenyl ether and 1.286 g (6.00 mmol) of 3,3'-diaminobenzidine in sequence, with an interval of 15 min between each addition. Then cool to 120 ° C, stir and heat for 12 h to fully dissolve, stir and heat at 170 ° C for 1 h for prepolymerization, and stir and heat at 200 ° C for 2.5 h for reaction. After the reaction is completed, the polymer product is poured into deionized water while hot to wash off most of the acid. The solid is collected by filtration and immersed in a saturated sodium bicarbonate solution until there are no bubbles. The solid is filtered, washed with alcohol and deionized water until neutral, and then dried at 120° C. for 12 h to obtain branched sulfonated polybenzimidazole SPBI-B6.

[0073] (2) Preparation of branched sulfonated polybenzimidazole proton exchange membrane

[0074] 1.200 g of SPBI-B6 was added to 30.000 g of dimethyl sulfoxide, and the mixture was heated and stirred at 120° C. to dissolve to prepare a solution with a concentration of 4 wt%. After 30 minutes, the solution became gel-like and could not be stirred by a magnetic rotor, and the polymer could not be made into a film.

Claims

1. A sulfonated polybenzimidazole proton exchange membrane containing a branched structure, characterized in that: The proton exchange membrane is prepared from sulfonated polybenzimidazole containing a branched structure; The general structural formula of sulfonated polybenzimidazole containing branched structure is: Where: R1 = Any of; R2＝ R3＝ The molecular weight of the sulfonated polybenzimidazole containing a branched structure is 7000 to 30000; Synthesis of sulfonated polybenzimidazole with branched structure: branched aromatic tricarboxylic acid, 3,3'-diaminobenzidine, sodium 5-sulfonate of isophthalic acid and 4,4'-dicarboxy diphenyl ether are used as monomers and prepared by solution polycondensation in polyphosphoric acid; The branched aromatic tricarboxylic acid is 1,3,5-benzenetricarboxylic acid or 1,3,5-tris(4-carboxyphenyl)benzene; when the branched aromatic tricarboxylic acid is 1,3,5-benzenetricarboxylic acid, the molar ratio of 1,3,5-benzenetricarboxylic acid to 3,3'-diaminobenzidine is 1:10-50; when the branched aromatic tricarboxylic acid is 1,3,5-tris(4-carboxyphenyl)benzene, the molar ratio of 1,3,5-tris(4-carboxyphenyl)benzene to 3,3'-diaminobenzidine is 1:33-100; The molar ratio of the sodium 5-sulfoisophthalic acid and 4,4'-dicarboxy diphenyl ether is 1:1; the molar ratio of the total carboxyl groups of 4,4'-dicarboxy diphenyl ether, sodium 5-sulfoisophthalic acid, branched aromatic tricarboxylic acid and the total amino groups of 3,3'-diaminobenzidine is 1:

2.

2. The method for preparing a sulfonated polybenzimidazole proton exchange membrane containing a branched structure according to claim 1, characterized in that: The following steps are involved: Preparation of branched sulfonated polybenzimidazole proton exchange membrane: dissolve sulfonated polybenzimidazole containing branched structure in organic solvent to obtain a solution of sulfonated polybenzimidazole containing branched structure, pour the solution on a smooth and flat glass plate, evaporate the solvent to obtain a polymer membrane, wash away the residual solvent, soak the polymer membrane in a hydrochloric acid solution for proton exchange, take out after soaking and wash away the residual acid on the surface, and obtain the branched sulfonated polybenzimidazole proton exchange membrane after drying.

3. The method for preparing a sulfonated polybenzimidazole proton exchange membrane containing a branched structure according to claim 2, characterized in that: The mass ratio of the total mass of the branched aromatic tricarboxylic acid, 3,3'-diaminobenzidine, sodium 5-sulfoisophthalic acid, 4,4'-dicarboxyl diphenyl ether monomer and polyphosphoric acid is 1:12-13.

4. The method for preparing a sulfonated polybenzimidazole proton exchange membrane containing a branched structure according to claim 2, characterized in that: The polycondensation method is to stir and heat at 120°C for 12 hours to fully dissolve, stir and heat at 170°C for 1 hour for prepolymerization, stir and heat at 200°C for 4 hours for reaction, and obtain a polymer product after the reaction.

5. The method for preparing a sulfonated polybenzimidazole proton exchange membrane containing a branched structure according to claim 2, characterized in that: The organic solvent is dimethyl sulfoxide or N,N-dimethylacetamide.

6. The method for preparing a sulfonated polybenzimidazole proton exchange membrane containing a branched structure according to claim 2, characterized in that: In step (2), the mass ratio of the sulfonated polybenzimidazole containing a branched structure to the organic solvent is 1:20 to 50.

Images