A polybenzimidazole cross-linked polymer, a preparation method thereof and a polybenzimidazole anion exchange membrane

Abstract

The application provides a polybenzimidazole cross-linked polymer, a preparation method thereof and a polybenzimidazole anion exchange membrane, and belongs to the technical field of ion exchange membranes.The polybenzimidazole cross-linked polymer provided by the application introduces branched groups into a polybenzimidazole main chain, thereby ensuring the ion selectivity and alkali resistance of the polymer membrane; a dithiol is used as a cross-linking group, nucleophilic substitution occurs between the dithiol and hydrogen in a benzene ring on the polybenzimidazole main chain, the polybenzimidazole main chain forms a cross-linked structure arranged in an orderly manner, the structural stability of the polymer is improved, and when the polymer is used as an anion exchange membrane, the service life of the membrane can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of ion exchange membranes, and in particular relates to a polybenzimidazole cross-linked polymer and a preparation method thereof, and a polybenzimidazole anion exchange membrane. Background Art

[0002] Anion exchange membrane is a polymer membrane containing alkaline active groups and having selective permeability to anions. Due to its high ion selectivity and other characteristics, it is widely used in water treatment, fuel cells, electrochemical analysis and other fields.

[0003] Polybenzimidazole (PBI) is a class of polymers with benzimidazole as repeating units. The benzene rings and benzimidazoles in its backbone possess strong rigidity, and the nitrogen-hydrogen bonds on the imidazole rings generate intermolecular hydrogen bonds, thereby enhancing intermolecular interactions. The unique molecular structure of PBI imparts excellent heat resistance, making it resistant to bond breakage even at temperatures exceeding 300°C. Therefore, it has become a fundamental material for anion exchange membranes. However, recent studies have shown that the aromatic ether bonds in the PBI backbone are susceptible to hydrogen oxidation, resulting in structural instability and poor alkali resistance. To improve the alkali resistance of PBI, branching groups are commonly introduced into the PBI backbone, such as through quaternization, polybrominated branches, and phosphoric acid doping. However, the introduction of branching groups only improves the polymer's alkali resistance and does not substantially enhance the structural stability or service life of PBI membranes. Even after functionalization, the membranes can still slowly deform and deteriorate during use, impacting their performance and lifespan. Summary of the Invention

[0004] The purpose of the present invention is to provide a polybenzimidazole cross-linked polymer and a preparation method thereof and a polybenzimidazole anion exchange membrane. The anion exchange membrane prepared using the polybenzimidazole cross-linked polymer provided by the present invention has long-term stability and good ion exchange capacity.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a polybenzimidazole cross-linked polymer, comprising a benzimidazole polymer and a cross-linking group cross-linking the benzimidazole polymer; the benzimidazole polymer comprises a polybenzimidazole main chain and a branching group, wherein the branching group is grafted onto the imino group of the polybenzimidazole main chain; the cross-linking group connects the benzene ring of the polybenzimidazole main chain, and the cross-linking group is a cross-linking group formed by dithiol.

[0007] Preferably, the dithiol is a terminal dithiol.

[0008] Preferably, the branched groups include one or more of long-chain alkyl groups, halogenated alkyl groups, carbonyl-containing groups and nitrogen-containing groups.

[0009] Preferably, the molar ratio of the benzimidazole structural unit in the polybenzimidazole main chain to the branched group is 1:(1-2).

[0010] Preferably, the molar ratio of the benzimidazole structural unit in the polybenzimidazole main chain to the cross-linking group is (1-5):1.

[0011] The present invention also provides a method for preparing the polybenzimidazole cross-linked polymer described in the above technical solution, comprising the following steps:

[0012] (1) mixing 3,3',4,4'-tetraaminodiphenyl ether, isophthalic acid and a solvent and performing a polycondensation reaction to obtain a polymer solution;

[0013] (2) mixing the polymer solution obtained in step (1) with a grafting monomer and performing a grafting reaction to obtain a benzimidazole polymer solution;

[0014] (3) The benzimidazole polymer solution obtained in step (2) is mixed with a crosslinking agent and subjected to a crosslinking reaction to obtain a polybenzimidazole crosslinked polymer.

[0015] Preferably, the cross-linking agent in step (3) is 1,4-butanedithiol, 1,6-hexanedithiol or 1,8-octanedithiol.

[0016] Preferably, the temperature of the cross-linking reaction in step (3) is 75-85° C., and the reaction time is 4-8 hours.

[0017] Preferably, the temperature of the grafting reaction in step (2) is 130-150° C., and the reaction time is 10-14 h.

[0018] The present invention also provides a polybenzimidazole anion exchange membrane, which is prepared using the polybenzimidazole cross-linked polymer described in the above technical solution or the polybenzimidazole cross-linked polymer prepared by the preparation method described in the above technical solution.

[0019] The present invention provides a cross-linked polybenzimidazole polymer, comprising a benzimidazole polymer and a cross-linking group cross-linking the benzimidazole polymer. The benzimidazole polymer comprises a polybenzimidazole main chain and a branching group, wherein the branching group is grafted onto an imino group of the polybenzimidazole main chain. The cross-linking group connects to the benzene rings of the polybenzimidazole main chain, and the cross-linking group is a dithiol cross-linking group. By introducing the branching group into the polybenzimidazole main chain, the present invention ensures the ion selectivity and alkali resistance of the polymer membrane. Using the dithiol as the cross-linking group, the dithiol undergoes nucleophilic substitution with hydrogen atoms in the benzene rings of the polybenzimidazole main chain, thereby forming a neatly arranged cross-linked structure in the polybenzimidazole main chain. This improves the structural stability of the polymer and, when used as an anion exchange membrane, can extend the membrane's service life. The results of the examples show that the anion exchange membrane prepared from the polybenzimidazole cross-linked polymer provided by the present invention has an ion exchange capacity of 2.35 mmol / g; after being immersed in a 1 mol / L NaOH solution for 1080 hours, the ion exchange capacity is 1.29 mmol / g; after being placed in a 300°C oven for 12 hours, the ion exchange capacity is 1.67 mmol / g; and after being placed in a 300°C oven for 24 hours, the dimensional change of the membrane is less than 5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 1 is a synthetic route diagram of the benzimidazole polymer in Example 1 of the present invention;

[0021] Figure 2 Schematic diagram of the structure of the polybenzimidazole anion exchange membrane of Example 2 of the present invention. DETAILED DESCRIPTION

[0022] All raw materials of the present invention are not particularly limited in their sources and can be purchased from the market or prepared according to conventional methods well known to those skilled in the art.

[0023] There is no particular limitation on the purity of all raw materials in the present invention. The present invention preferably uses high-purity raw materials or raw materials with a purity commonly used in the field of ion exchange membranes.

[0024] The present invention provides a polybenzimidazole cross-linked polymer, comprising a benzimidazole polymer and a cross-linking group cross-linking the benzimidazole polymer; the benzimidazole polymer comprises a polybenzimidazole main chain and a branching group, wherein the branching group is grafted onto the imino group of the polybenzimidazole main chain; the cross-linking group connects the benzene ring of the polybenzimidazole main chain, and the cross-linking group is a cross-linking group formed by dithiol.

[0025] The polybenzimidazole cross-linked polymer provided by the present invention comprises a benzimidazole polymer, and the benzimidazole polymer comprises a polybenzimidazole main chain and a branched group.

[0026] In the present invention, the branched groups preferably include one or more of long-chain alkyl groups, halogenated alkyl groups, carbonyl-containing groups, and nitrogen-containing groups, and more preferably include alkyl chains of 3 to 6 carbon atoms. As one embodiment of the present invention, the branched groups may include alkyl chains of 3 carbon atoms and alkyl chains of 6 carbon atoms, and the molar ratio of the alkyl chains of 3 carbon atoms to the alkyl chains of 6 carbon atoms may be 1:(0.5-2). The branched groups of the above structure are beneficial for further improving the alkali resistance of the polymer.

[0027] In the present invention, the branching groups are grafted onto the imino groups of the polybenzimidazole main chain. The hydrogen atoms in the imino groups (-NH-) in the benzimidazole molecule have high activity, which can reduce the difficulty of grafting the branching groups.

[0028] In the present invention, the molar ratio of the benzimidazole structural units in the polybenzimidazole backbone to the side chain groups is preferably 1:(1-2), more preferably 1:2. A molar ratio of the benzimidazole structural units in the polybenzimidazole backbone to the side chain groups within the above range is beneficial for further improving the alkali resistance and ion selectivity of the polymer.

[0029] The cross-linked polybenzimidazole polymer provided by the present invention also includes cross-linking groups that cross-link the benzimidazole polymers. By introducing cross-linking groups into the benzimidazole polymer, the present invention enables the polybenzimidazole main chain to form a neatly arranged cross-linked structure, thereby improving the structural stability of the polymer, especially its long-term stability. When the polymer is used in an anion exchange membrane, the membrane's service life can be extended.

[0030] In the present invention, the crosslinking group is a crosslinking group formed by a dithiol, and the dithiol is preferably a terminal dithiol. In the present invention, the crosslinking group connects the benzene rings in the polybenzimidazole backbone. The terminal dithiol is more conducive to nucleophilic substitution with hydrogen on the benzene ring to achieve crosslinking of the polybenzimidazole backbone.

[0031] In the present invention, the molar ratio of the benzimidazole structural units in the polybenzimidazole backbone to the crosslinking groups is preferably (1-5):1, more preferably (2-4):1. As one embodiment of the present invention, the molar ratio of the benzimidazole structural units in the polybenzimidazole backbone to the crosslinking groups can be 1:1, 2:1, 3:1, 4:1, or 5:1. When the molar ratio of the benzimidazole structural units in the polybenzimidazole backbone to the crosslinking groups is within the above range, it is beneficial to further improve the long-term stability of the polymer while avoiding excessive crosslinking groups that reduce the toughness of the polymer and make it hard and brittle.

[0032] The present invention ensures the ion selectivity and alkali resistance of the polymer membrane by introducing branched groups into the polybenzimidazole main chain; uses dithiol as a cross-linking group, and forms a neatly arranged cross-linked structure in the polybenzimidazole main chain through nucleophilic substitution of dithiol with hydrogen in the benzene ring on the polybenzimidazole main chain, thereby improving the structural stability of the polymer.

[0033] The present invention also provides a method for preparing the polybenzimidazole cross-linked polymer described in the above technical solution, comprising the following steps:

[0034] (1) mixing 3,3',4,4'-tetraaminodiphenyl ether, isophthalic acid and a solvent and performing a polycondensation reaction to obtain a polymer solution;

[0035] (2) mixing the polymer solution obtained in step (1) with a grafting monomer and performing a grafting reaction to obtain a benzimidazole polymer solution;

[0036] (3) The benzimidazole polymer solution obtained in step (2) is mixed with a crosslinking agent and subjected to a crosslinking reaction to obtain a polybenzimidazole crosslinked polymer.

[0037] The invention mixes 3,3',4,4'-tetraaminodiphenyl ether, isophthalic acid and a solvent and then carries out polycondensation reaction to obtain a polymer solution.

[0038] The present invention has no particular requirements on the type of the solvent, as long as it can dissolve the reactants. In an embodiment of the present invention, the solvent is N-methylpyrrolidone (NMP).

[0039] The present invention does not particularly limit the ratio of the amount of the 3,3',4,4'-tetraaminodiphenyl ether, isophthalic acid, and solvent, as long as the materials can be evenly mixed. As one embodiment of the present invention, the molar ratio of the 3,3',4,4'-tetraaminodiphenyl ether to isophthalic acid can be 1:1, and the relative mass concentration of the 3,3',4,4'-tetraaminodiphenyl ether to the solvent can be 70-80%.

[0040] The present invention has no particular limitation on the specific parameters of the polycondensation reaction, as long as the polycondensation reaction can proceed normally. As an embodiment of the present invention, the temperature of the polycondensation reaction can be 60° C. and the reaction time can be 24 hours.

[0041] After obtaining the polymer solution, the present invention mixes the polymer solution with a grafting monomer to carry out a grafting reaction to obtain a benzimidazole polymer solution.

[0042] In the present invention, the grafting monomer is preferably a 1-bromo-substituted alkyl group, and the alkyl group is preferably a C3-C6 alkyl group. As one embodiment of the present invention, the grafting monomer can be one or more of 1-bromopropane, 1-bromobutane, 1-bromopentane, and 1-bromohexane. As another embodiment of the present invention, the grafting monomer can be 1-bromopropane and 1-bromohexane, and the molar ratio of the 1-bromopropane to the 1-bromohexane can be 1:(0.5-2). The use of the above grafting monomers is conducive to further improving the alkali resistance of the polymer.

[0043] In the present invention, the molar ratio of the grafting monomer to 3,3',4,4'-tetraaminodiphenyl ether is preferably (2-10):1, more preferably (4-8):1. As one embodiment of the present invention, the molar ratio of the grafting monomer to 3,3',4,4'-tetraaminodiphenyl ether can be 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, or 9:1. A molar ratio of the grafting monomer to 3,3',4,4'-tetraaminodiphenyl ether within the above range facilitates grafting of the grafting monomer to the polybenzimidazole backbone, preventing insufficient grafting.

[0044] In the present invention, the temperature of the grafting reaction is preferably 130-150° C., more preferably 135-145° C.; as an embodiment of the present invention, the temperature of the grafting reaction can be 132° C., 136° C., 140° C., 142° C., 146° C., or 148° C. The grafting reaction temperature within the above range is conducive to the progress of the grafting reaction.

[0045] In the present invention, the grafting reaction time is preferably 10 to 14 hours, more preferably 11 to 13 hours. As an embodiment of the present invention, the grafting reaction time can be 10.5 hours, 11.5 hours, 12 hours, 12.5 hours, 13.5 hours, or 14 hours. The grafting reaction time within the above range is conducive to the progress of the grafting reaction.

[0046] As an embodiment of the present invention, when there are two grafting monomers, one grafting monomer may be added first to carry out the grafting reaction. After the reaction is completed, the second grafting monomer may be added to carry out the grafting reaction again.

[0047] After obtaining the benzimidazole polymer solution, the present invention mixes the benzimidazole polymer solution with a crosslinking agent and then performs a crosslinking reaction to obtain a polybenzimidazole crosslinked polymer.

[0048] In the present invention, the crosslinking agent is preferably 1,4-butanedithiol, 1,6-hexanedithiol or 1,8-octanedithiol, more preferably 1,6-hexanedithiol. The use of the above crosslinking agents is beneficial to further improve the stability of the polymer.

[0049] In the present invention, the molar ratio of the 3,3',4,4'-tetraaminodiphenyl ether to the cross-linking agent is preferably (1~5):1, more preferably (2~4):1; as an embodiment of the present invention, the molar ratio of the 3,3',4,4'-tetraaminodiphenyl ether to the cross-linking agent may be 1:1, 2:1, 3:1, 4:1 or 5:1. The molar ratio of 3,3',4,4'-tetraaminodiphenyl ether to the cross-linking agent within the above range is beneficial to further improve the long-term stability of the polymer, and can also avoid excessive cross-linking groups reducing the physical properties of the polymer, making the polymer hard and brittle.

[0050] In the present invention, the cross-linking reaction temperature is preferably 75-85°C, more preferably 78-82°C. As one embodiment of the present invention, the cross-linking reaction temperature can be 76°C, 77°C, 79°C, 80°C, 81°C, or 83°C. A cross-linking reaction temperature within the above range is conducive to aligning and compacting the polymer backbone, further improving the stability of the polymer.

[0051] In the present invention, the cross-linking reaction time is preferably 4 to 8 hours, more preferably 5 to 7 hours. As one embodiment of the present invention, the cross-linking reaction time can be 4.5 hours, 5.5 hours, 6 hours, 6.5 hours, 7.5 hours, or 8 hours. The cross-linking reaction time within the above range is conducive to aligning the polymer backbone and further improving the stability of the polymer.

[0052] After the cross-linking reaction is complete, the cross-linking reaction product is preferably dried to obtain a polybenzimidazole cross-linked polymer. The present invention does not particularly limit the specific method of drying, as long as the solvent in the product can be removed. In an embodiment of the present invention, the drying is performed at 80°C for 6 hours.

[0053] The preparation method provided by the present invention is simple, easy to implement, low in cost, and is conducive to industrial production.

[0054] The present invention also provides a polybenzimidazole anion exchange membrane, which is prepared using the polybenzimidazole cross-linked polymer described in the above technical solution or the polybenzimidazole cross-linked polymer prepared by the preparation method described in the above technical solution.

[0055] The present invention has no particular limitation on the preparation method of the polybenzimidazole anion exchange membrane, as long as the polybenzimidazole cross-linked polymer is prepared into an anion exchange membrane.

[0056] As an embodiment of the present invention, the preparation method of the polybenzimidazole anion exchange membrane may include:

[0057] Dissolving the polybenzimidazole cross-linked polymer in NMP solvent to obtain a membrane-building solution; or using the cross-linking reaction product in the preparation process of the polybenzimidazole cross-linked polymer directly as the membrane-building solution;

[0058] pouring the membrane-building liquid onto a substrate and then drying it to obtain a basement membrane;

[0059] The base membrane is subjected to alkali washing to obtain a polybenzimidazole anion exchange membrane.

[0060] As an embodiment of the present invention, the casting thickness of the membrane-building liquid can be 0.15~0.25mm; after the casting is completed, the membrane-building liquid can be cast in a vacuum degree of less than 10 -1 MPa conditions for defoaming for 15 min; the drying temperature can be 80° C., and the drying time can be 6 h.

[0061] As an embodiment of the present invention, the temperature of the alkali washing can be 80°C, the time of the alkali washing can be 12 hours, the alkali solution of the alkali washing can be a NaOH aqueous solution, and the concentration of the NaOH aqueous solution can be 1 mol / L; after the alkali washing, deionized water can be used for washing.

[0062] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0063] Example 1

[0064] A polybenzimidazole crosslinked polymer comprises a PBI backbone, alkyl side chains, and crosslinking groups connecting the PBI backbone. The alkyl side chains are propane and hexane side chains of equal molar mass, grafted onto the imino groups of the PBI backbone, with the molar ratio of the alkyl side chains to the benzimidazole structural units in the PBI backbone being 1:1. The crosslinking groups are crosslinking groups formed from 1,6-hexanedithiol, connected to the benzene rings of the PBI backbone, with the molar ratio of the crosslinking groups to the benzimidazole structural units in the PBI backbone being 1:1.

[0065] The preparation method of the polybenzimidazole cross-linked polymer comprises the following specific steps:

[0066] Synthesis of benzimidazole polymers, the synthesis route is shown in the figure Figure 1 As shown, 0.044 mol of 3,3',4,4'-tetraaminodiphenyl ether and 0.044 mol of isophthalic acid were mixed with 40 mL of NMP and reacted at 60 °C for 24 h to obtain a polybenzimidazole solution;

[0067] 0.022 mol of 1-bromopropane was added to the polybenzimidazole solution, and the mixture was reacted at 140° C. for 12 h. Then, 0.022 mol of 1-bromohexane was added, and the mixture was reacted at 140° C. for 12 h to obtain a benzimidazole polymer solution.

[0068] 0.044 mol of 1,6-hexanedithiol was added to the benzimidazole polymer solution, and the mixture was reacted at 80° C. for 6 h. The reaction product was dried in an oven at 80° C. for 6 h to obtain a polybenzimidazole cross-linked polymer.

[0069] Example 2

[0070] A polybenzimidazole anion exchange membrane, the structural diagram of which is shown in FIG. Figure 2 As shown, the preparation method is as follows:

[0071] The polybenzimidazole cross-linked polymer prepared in Example 1 was dissolved in 40 mL of NMP to obtain a film-forming solution. The film-forming solution was poured onto a 200 mm × 200 mm flat glass and scraped to maintain a uniform thickness of 0.25 mm on the flat glass. The film was placed in a vacuum oven with a vacuum degree of 10 -2 MPa, defoam for 15 min, then raise the vacuum oven temperature to 80 °C, let it stand and dry for 6 h, then take it out to obtain a basement membrane;

[0072] Place the basement membrane in 1 mol / L NaOH solution at 80°C and soak for 12 hours to allow Br - Converted to OH - , and then rinsed twice with deionized water to wash away residual NaOH to obtain a polybenzimidazole anion exchange membrane.

[0073] Comparative Example 1

[0074] A polybenzimidazole anion exchange membrane, the preparation method is as follows:

[0075] 0.044 mol of 3,3',4,4'-tetraaminodiphenyl ether and 0.044 mol of isophthalic acid were mixed with 40 mL of NMP and reacted at 60°C for 24 h to obtain a polybenzimidazole solution;

[0076] 0.022 mol of 1-bromopropane was added to the polybenzimidazole solution, and the mixture was reacted at 140°C for 12 h. Then, 0.022 mol of 1-bromohexane was added and the mixture was reacted at 140°C for 12 h to obtain a benzimidazole polymer solution for membrane formation.

[0077] The film-forming liquid was poured onto a 200mm×200mm flat glass, and the film was scraped to keep the thickness uniform on the flat glass; the film was placed in a vacuum oven with a vacuum degree of 10 -2MPa, defoam for 15 min, then raise the vacuum oven temperature to 80 °C, let it stand and dry for 6 h, then take it out to obtain a basement membrane;

[0078] Place the basement membrane in 1 mol / L NaOH solution at 80°C and soak for 12 hours to allow Br - Converted to OH - , and then rinsed twice with deionized water to wash away residual NaOH to obtain a polybenzimidazole anion exchange membrane.

[0079] Test Case

[0080] The anion exchange membrane prepared in Example 2 was tested for ion exchange capacity. The test method was as follows: the anion exchange membrane was cut into 40 mm × 40 mm samples, and the membrane samples were completely dried and weighed, and the mass was recorded as m dry After weighing, the dried membrane was immersed in 30 mL of 0.01 mol / L HCl solution and stirred at 30 ° C for 24 h to ensure that the OH in the membrane - Completely H + After the ion exchange is complete, the residual H + The titration was performed and the ion exchange capacity (IEC) was calculated using the following formula:

[0081]

[0082] In this formula, V NaOH and V 0,NaOH Respectively represent the volume of NaOH solution consumed by titrating the HCl solution experimental sample and the control sample (without anion exchange membrane), C NaOH is the concentration of NaOH after standardization with potassium hydrogen phthalate.

[0083] The ion exchange capacity of the anion exchange membrane prepared in Example 2 is 2.35 mmol / g.

[0084] The anion exchange membrane prepared in Example 2 was immersed in a 1 mol / L NaOH solution for 1080 h, and the ion exchange capacity was measured to be 1.29 mmol / g.

[0085] The anion exchange membranes prepared in Example 2 and Comparative Example 1 were respectively cut into 40 mm × 40 mm samples and placed in a 300°C oven. After 12 hours, the ion exchange capacity of the anion exchange membrane of Example 2 was tested to be 1.67 mmol / g. After 24 hours, the samples were taken out and the state of the samples was observed. The dimensional change of the anion exchange membrane prepared in Comparative Example 1 was greater than 25%; the dimensional change of the anion exchange membrane prepared in Example 2 was less than 5%, and the membrane was still intact.

[0086] From the above examples and comparative examples, it can be seen that the polybenzimidazole anion exchange membrane provided by the present invention effectively improves the stability of the membrane, especially the long-term stability, by introducing cross-linking groups into the benzimidazole polymer, and increases the service life of the membrane when used as an anion exchange membrane.

[0087] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A polybenzimidazole cross-linked polymer, characterized in that The invention comprises a benzimidazole polymer and a cross-linking group cross-linking the benzimidazole polymer; the benzimidazole polymer comprises a polybenzimidazole main chain and a branching group, wherein the branching group is grafted onto the imino group of the polybenzimidazole main chain; the cross-linking group connects the benzene ring of the polybenzimidazole main chain, and the cross-linking group is a cross-linking group formed by dithiol; The dithiol is a terminal dithiol; The branched group is an alkyl chain of 3 to 6 carbon atoms; The method for preparing the polybenzimidazole cross-linked polymer is characterized by comprising the following steps: (1) mixing 3,3',4,4'-tetraaminodiphenyl ether, isophthalic acid and a solvent and performing a polycondensation reaction to obtain a polymer solution; (2) mixing the polymer solution obtained in step (1) with a grafting monomer and performing a grafting reaction to obtain a benzimidazole polymer solution; (3) mixing the benzimidazole polymer solution obtained in step (2) with a crosslinking agent and performing a crosslinking reaction to obtain a polybenzimidazole crosslinked polymer; In step (3), the cross-linking agent is 1,4-butanedithiol, 1,6-hexanedithiol or 1,8-octanedithiol; The temperature of the cross-linking reaction in step (3) is 75-85° C., and the reaction time is 4-8 hours.

2. The polybenzimidazole cross-linked polymer according to claim 1, characterized in that The ratio of the amount of the benzimidazole structural unit in the polybenzimidazole main chain to the amount of the branched group is 1:(1-2).

3. The polybenzimidazole cross-linked polymer according to claim 1, characterized in that The ratio of the amount of benzimidazole structural units in the polybenzimidazole main chain to the amount of the cross-linking group is (1-5):

1.

4. The method for preparing the polybenzimidazole cross-linked polymer according to any one of claims 1 to 3, characterized in that: The steps include: (1) mixing 3,3',4,4'-tetraaminodiphenyl ether, isophthalic acid and a solvent and performing a polycondensation reaction to obtain a polymer solution; (2) mixing the polymer solution obtained in step (1) with a grafting monomer and performing a grafting reaction to obtain a benzimidazole polymer solution; (3) mixing the benzimidazole polymer solution obtained in step (2) with a crosslinking agent and performing a crosslinking reaction to obtain a polybenzimidazole crosslinked polymer; In step (3), the cross-linking agent is 1,4-butanedithiol, 1,6-hexanedithiol or 1,8-octanedithiol; The temperature of the cross-linking reaction in step (3) is 75-85° C., and the reaction time is 4-8 hours.

5. The preparation method according to claim 4, characterized in that The temperature of the grafting reaction in step (2) is 130-150° C., and the reaction time is 10-14 h.

6. A polybenzimidazole anion exchange membrane, characterized in that The method is prepared by using the polybenzimidazole cross-linked polymer described in any one of claims 1 to 3 or the polybenzimidazole cross-linked polymer prepared by the preparation method described in any one of claims 4 to 5.

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