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

Abstract

The invention 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. According to the polybenzimidazole cross-linked polymer provided by the invention, a branched chain group is introduced into a polybenzimidazole main chain, so that the ion selectivity and alkali resistance of a polymer film are ensured; the dithiol is used as a crosslinking group, and the dithiol and hydrogen in a benzene ring on a main chain of the polybenzimidazole are subjected to nucleophilic substitution, so that the main chain of the polybenzimidazole forms an orderly arranged crosslinking structure, the structural stability of the polymer is improved, and the service life of the membrane can be prolonged when the polymer is used as an anion exchange membrane.

Description

Technical Field

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

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

[0003] Polybenzimidazole (PBI) is a type of polymer with benzimidazole groups as repeating units. The benzene rings and benzimidazoles on its main chain have strong rigidity, and intermolecular hydrogen bonds are generated between the nitrogen-hydrogen bonds on the imidazole ring, thereby increasing the intermolecular interaction force. The special molecular structure of polybenzimidazole makes it have very good heat resistance and is not prone to bond breakage even at high temperatures above 300 °C. Therefore, it has become the basic material for anion exchange membranes. However, recent studies have shown that the aryl ether bonds existing in the main chain of polybenzimidazole are easily hydroxylated, resulting in unstable main chain structure and low alkali resistance. In order to improve the alkali resistance of polybenzimidazole, branched chain groups are usually introduced into the main chain of polybenzimidazole, such as quaternization of the main chain of polybenzimidazole, introduction of polybromo branched chains, and phosphoric acid doping. However, introducing branched chain groups can only improve the alkali resistance of the polymer and has no substantial help in improving the structural stability and service life of the polybenzimidazole membrane. After functionalization, the membrane will still slowly deform and lose during use, affecting the use effect and life of the membrane. Summary of the Invention

[0004] The purpose of the present invention is to provide a polybenzimidazole cross-linked polymer, 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 invention purpose, the present invention provides the following technical solutions: The present invention provides a polybenzimidazole cross-linked polymer, including a benzimidazole polymer and a cross-linking group cross-linked between the benzimidazole polymers; the benzimidazole polymer includes a polybenzimidazole main chain and a branched chain group, and the branched chain group is grafted on 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.

[0006] Preferably, the dithiol is terminal dithiol.

[0007] Preferably, the branched groups include one or more of long-chain alkyl groups, halogenated alkyl groups, carbonyl-containing groups, and nitrogen-containing groups.

[0008] Preferably, the molar ratio of the benzimidazole structural units in the polybenzimidazole main chain to the branched groups is 1:(1 - 2).

[0009] Preferably, the molar ratio of the benzimidazole structural units in the polybenzimidazole main chain to the crosslinking groups is (1 - 5):1.

[0010] The present invention also provides a method for preparing the polybenzimidazole crosslinked polymer described in the above technical solution, which includes the following steps: (1) Mix 3,3',4,4'-tetraaminodiphenyl ether, isophthalic acid and a solvent, and then carry out a polycondensation reaction to obtain a polymer solution; (2) Mix the polymer solution obtained in step (1) with a graft monomer and then carry out a graft reaction to obtain a benzimidazole polymer solution; (3) Mix the benzimidazole polymer solution obtained in step (2) with a crosslinking agent and then carry out a crosslinking reaction to obtain a polybenzimidazole crosslinked polymer.

[0011] Preferably, the crosslinking agent in step (3) is 1,4-butanedithiol, 1,6-hexanedithiol or 1,8-octanedithiol.

[0012] Preferably, the temperature of the crosslinking reaction in step (3) is 75 - 85 °C, and the reaction time is 4 - 8 h.

[0013] Preferably, the temperature of the graft reaction in step (2) is 130 - 150 °C, and the reaction time is 10 - 14 h.

[0014] The present invention also provides a polybenzimidazole anion exchange membrane, which is prepared using the polybenzimidazole crosslinked polymer described in the above technical solution or the polybenzimidazole crosslinked polymer prepared by the preparation method described in the above technical solution.

[0015] The present invention provides a polybenzimidazole cross-linked polymer, which comprises a benzimidazole polymer and cross-linking groups cross-linked between the benzimidazole polymers; the benzimidazole polymer comprises a polybenzimidazole main chain and side chain groups, and the side chain groups are grafted on the imino group of the polybenzimidazole main chain; the cross-linking groups are connected to the benzene rings of the polybenzimidazole main chain, and the cross-linking groups are cross-linking groups formed by dithiols. By introducing side chain groups into the polybenzimidazole main chain, the present invention ensures the ion selectivity and alkali resistance of the polymer membrane; using dithiols as cross-linking groups, through the nucleophilic substitution of the hydrogen in the benzene ring on the polybenzimidazole main chain by dithiols, the polybenzimidazole main chain forms a neatly arranged cross-linked structure, improving the structural stability of the polymer, and can improve the service life of the membrane when used as an anion exchange membrane. 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 1 mol / L NaOH solution for 1080 h, the ion exchange capacity is 1.29 mmol / g; after being placed in an oven at 300 °C for 12 h, the ion exchange capacity is 1.67 mmol / g; after being placed in an oven at 300 °C for 24 h, the dimensional change of the membrane is less than 5%. Description of the Drawings

[0016] Figure 1 It is the synthesis route diagram of the benzimidazole polymer in Example 1 of the present invention; Figure 2 It is the structural schematic diagram of the polybenzimidazole anion exchange membrane of Example 2 of the present invention. Detailed Embodiments

[0017] For all raw materials of the present invention, there is no particular limitation on their sources, and they can be purchased on the market or prepared by conventional methods well-known to those skilled in the art.

[0018] For all raw materials of the present invention, there is no particular limitation on their purity, and the present invention preferably uses high-purity raw materials or the raw material purity commonly used in the field of ion exchange membranes.

[0019] The present invention provides a polybenzimidazole cross-linked polymer, which comprises a benzimidazole polymer and cross-linking groups cross-linked between the benzimidazole polymers; the benzimidazole polymer comprises a polybenzimidazole main chain and side chain groups, and the side chain groups are grafted on the imino group of the polybenzimidazole main chain; the cross-linking groups are connected to the benzene rings of the polybenzimidazole main chain, and the cross-linking groups are cross-linking groups formed by dithiols.

[0020] The polybenzimidazole cross-linked polymer provided by the present invention comprises a benzimidazole polymer, and the benzimidazole polymer comprises a polybenzimidazole main chain and side chain groups.

[0021] In the present invention, the branched group preferably includes one or more of long-chain alkyl, haloalkyl, carbonyl-containing group, and nitrogen-containing group, and is more preferably an alkyl chain having 3 to 6 carbon atoms; as an embodiment of the present invention, the branched group may include an alkyl chain having 3 carbon atoms and an alkyl chain having 6 carbon atoms, and the molar ratio of the alkyl chain having 3 carbon atoms to the alkyl chain having 6 carbon atoms may be 1:(0.5 to 2). The branched group having the above structure is beneficial to further improving the alkali resistance of the polymer.

[0022] In the present invention, the branched group is grafted onto the imino group of the polybenzimidazole main chain. In the benzimidazole molecule, the hydrogen atom in the imino group (-NH-) has relatively high activity, which can reduce the grafting difficulty of the branched group.

[0023] In the present invention, the molar ratio of the benzimidazole structural unit in the polybenzimidazole main chain to the branched group is preferably 1:(1 to 2), and more preferably 1:2. When the molar ratio of the benzimidazole structural unit in the polybenzimidazole main chain to the branched group is within the above range, it is beneficial to further improve the alkali resistance and ion selectivity of the polymer.

[0024] The polybenzimidazole crosslinked polymer provided by the present invention further includes a crosslinking group crosslinked between the benzimidazole polymers. By introducing a crosslinking group into the benzimidazole polymer in the present invention, a neatly arranged crosslinked structure can be formed in the polybenzimidazole main chain, improving the structural stability of the polymer, especially the long-term stability. When the polymer is used as an anion exchange membrane, the service life of the membrane can be improved.

[0025] In the present invention, the crosslinking group is a crosslinking group formed by dithiol, and the dithiol is preferably terminal dithiol. In the present invention, the crosslinking group connects the benzene rings in the polybenzimidazole main chain, and terminal dithiol is more conducive to the nucleophilic substitution with the hydrogen on the benzene ring to achieve the crosslinking of the polybenzimidazole main chain.

[0026] In the present invention, the molar ratio of the benzimidazole structural unit in the polybenzimidazole main chain to the crosslinking group is preferably (1 to 5):1, and more preferably (2 to 4):1; as an embodiment of the present invention, the molar ratio of the benzimidazole structural unit in the polybenzimidazole main chain to the crosslinking group may be 1:1, 2:1, 3:1, 4:1, or 5:1. When the molar ratio of the benzimidazole structural unit in the polybenzimidazole main chain to the crosslinking group is within the above range, it is beneficial to further improve the long-term stability of the polymer, and at the same time, excessive crosslinking groups are avoided from reducing the toughness of the polymer, making the polymer hard and brittle.

[0027] By introducing branched-chain groups into the main chain of polybenzimidazole, the present invention ensures the ion selectivity and alkali resistance of the polymer membrane; using dithiol as the cross-linking group, through the nucleophilic substitution of the hydrogen in the benzene ring of the polybenzimidazole main chain by dithiol, a neatly arranged cross-linked structure is formed in the polybenzimidazole main chain, improving the structural stability of the polymer.

[0028] The present invention also provides a preparation method of the polybenzimidazole cross-linked polymer described in the above technical solution, including the following steps: (1) Mix 3,3',4,4'-tetraaminodiphenyl ether, isophthalic acid and a solvent, and then carry out a polycondensation reaction to obtain a polymer solution; (2) Mix the polymer solution obtained in the step (1) with a graft monomer and carry out a graft reaction to obtain a benzimidazole polymer solution; (3) Mix the benzimidazole polymer solution obtained in the step (2) with a cross-linking agent and carry out a cross-linking reaction to obtain a polybenzimidazole cross-linked polymer.

[0029] The present invention mixes 3,3',4,4'-tetraaminodiphenyl ether, isophthalic acid and a solvent, and then carries out a polycondensation reaction to obtain a polymer solution.

[0030] The present invention has no special requirements for the type of the solvent, as long as it can dissolve the reactants. In the examples of the present invention, the solvent is N-methylpyrrolidone (NMP).

[0031] The present invention has no special limitation on the dosage ratio of 3,3',4,4'-tetraaminodiphenyl ether, isophthalic acid to the solvent, as long as the materials can be mixed evenly. As an implementation manner of the present invention, the molar ratio of 3,3',4,4'-tetraaminodiphenyl ether to isophthalic acid can be 1:1, and the relative mass concentration of 3,3',4,4'-tetraaminodiphenyl ether to the solvent can be 70-80%.

[0032] The present invention has no special limitation on the specific parameters of the polycondensation reaction, as long as the polycondensation reaction can proceed normally. As an implementation manner of the present invention, the temperature of the polycondensation reaction can be 60°C, and the reaction time can be 24h.

[0033] After obtaining the polymer solution, the present invention mixes the polymer solution with a graft monomer and carries out a graft reaction to obtain a benzimidazole polymer solution.

[0034] In the present invention, the graft monomer is preferably a 1-bromo-substituted alkyl group, and the alkyl group is preferably an alkyl group having 3 to 6 carbon atoms. As an embodiment of the present invention, the graft monomer may be one or more of 1-bromopropane, 1-bromobutane, 1-bromopentane, and 1-bromohexane. As another embodiment of the present invention, the graft monomer may be 1-bromopropane and 1-bromohexane, and the molar ratio of 1-bromopropane to 1-bromohexane may be 1:(0.5 to 2). Using the above graft monomers is beneficial to further improve the alkali resistance of the polymer.

[0035] In the present invention, the molar ratio of the graft monomer to 3,3',4,4'-tetraaminodiphenyl ether is preferably (2 to 10):1, more preferably (4 to 8):1; as an embodiment of the present invention, the molar ratio of the graft monomer to 3,3',4,4'-tetraaminodiphenyl ether may be 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, or 9:1. When the molar ratio of the graft monomer to 3,3',4,4'-tetraaminodiphenyl ether is within the above range, it is beneficial to graft the graft monomer onto the polybenzimidazole main chain and avoid insufficient grafting.

[0036] In the present invention, the temperature of the graft reaction is preferably 130 to 150 °C, more preferably 135 to 145 °C; as an embodiment of the present invention, the temperature of the graft reaction may be 132 °C, 136 °C, 140 °C, 142 °C, 146 °C, or 148 °C. When the temperature of the graft reaction is within the above range, it is beneficial to carry out the graft reaction.

[0037] In the present invention, the time of the graft reaction is preferably 10 to 14 h, more preferably 11 to 13 h; as an embodiment of the present invention, the time of the graft reaction may be 10.5 h, 11.5 h, 12 h, 12.5 h, 13.5 h, or 14 h. When the time of the graft reaction is within the above range, it is beneficial to carry out the graft reaction.

[0038] As an embodiment of the present invention, when there are two kinds of graft monomers, one graft monomer may be added first for the graft reaction, and after the reaction is completed, the second graft monomer is added for the graft reaction again.

[0039] After obtaining the benzimidazole polymer solution, in the present invention, the benzimidazole polymer solution is mixed with a crosslinking agent and then subjected to a crosslinking reaction to obtain a crosslinked polybenzimidazole polymer.

[0040] In the present invention, the crosslinking agent is preferably 1,4-butanedithiol, 1,6-hexanedithiol, or 1,8-octanedithiol, more preferably 1,6-hexanedithiol. Using the above crosslinking agent is beneficial to further improve the stability of the polymer.

[0041] In the present invention, the molar ratio of the 3,3’,4,4’-tetraaminodiphenyl ether to the crosslinking 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 crosslinking agent can be 1:1, 2:1, 3:1, 4:1 or 5:1. When the molar ratio of the 3,3’,4,4’-tetraaminodiphenyl ether to the crosslinking agent is within the above range, it is beneficial to further improve the long-term stability of the polymer, and it can also avoid excessive crosslinking groups from reducing the physical properties of the polymer, making the polymer hard and brittle.

[0042] In the present invention, the temperature of the crosslinking reaction is preferably 75~85°C, more preferably 78~82°C; as an embodiment of the present invention, the temperature of the crosslinking reaction can be 76°C, 77°C, 79°C, 80°C, 81°C or 83°C. When the temperature of the crosslinking reaction is within the above range, it is beneficial to make the main chain of the polymer arranged neatly and densely, and further improve the stability of the polymer.

[0043] In the present invention, the time of the crosslinking reaction is preferably 4~8 h, more preferably 5~7 h; as an embodiment of the present invention, the time of the crosslinking reaction can be 4.5 h, 5.5 h, 6 h, 6.5 h, 7.5 h or 8 h. When the time of the crosslinking reaction is within the above range, it is beneficial to make the main chain of the polymer arranged neatly and densely, and further improve the stability of the polymer.

[0044] After the crosslinking reaction is completed, the present invention preferably dries the product of the crosslinking reaction to obtain a polybenzimidazole crosslinked polymer. The present invention does not particularly limit the specific method of the drying, as long as the solvent in the product can be removed. In the examples of the present invention, the drying is drying at 80°C for 6 h.

[0045] The preparation method provided by the present invention is simple and easy to implement, and has low cost, which is beneficial to realizing industrial production.

[0046] The present invention also provides a polybenzimidazole anion exchange membrane, which is prepared using the polybenzimidazole crosslinked polymer described in the above technical solution or the polybenzimidazole crosslinked polymer prepared by the preparation method described in the above technical solution.

[0047] The present invention does not particularly limit the preparation method of the polybenzimidazole anion exchange membrane, as long as the polybenzimidazole crosslinked polymer can be prepared into an anion exchange membrane.

[0048] As an embodiment of the present invention, the preparation method of the polybenzimidazole anion exchange membrane may include: Dissolve the polybenzimidazole cross-linked polymer in NMP solvent to obtain a film-forming solution; or directly use the product of the cross-linking reaction during the preparation of the polybenzimidazole cross-linked polymer as the film-forming solution; Pour the film-forming solution onto a substrate and then dry it to obtain a substrate film; Wash the substrate film with alkali to obtain a polybenzimidazole anion exchange membrane.

[0049] As an embodiment of the present invention, the casting thickness of the film-forming solution can be 0.15 - 0.25 mm; after casting, defoaming can be carried out for 15 min under a vacuum of less than 10 -1 MPa; the drying temperature can be 80 °C and the drying time can be 6 h.

[0050] As an embodiment of the present invention, the alkali washing temperature can be 80 °C, the alkali washing time can be 12 h, the alkali solution for alkali washing can be an NaOH aqueous solution, and the concentration of the NaOH aqueous solution can be 1 mol / L; after alkali washing, washing can be carried out with deionized water.

[0051] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0052] Example 1 A polybenzimidazole cross-linked polymer is composed of a PBI main chain, an alkyl side chain, and a cross-linking group connecting the PBI main chain. The alkyl side chain is a propane side chain and a hexane side chain with the same amount of substance. The alkyl side chain is grafted on the imino group of the PBI main chain, and the molar ratio of the alkyl side chain to the benzimidazole structural unit in the PBI main chain is 1:1; the cross-linking group is a cross-linking group formed by 1,6-hexanedithiol, which is connected to the benzene ring of the PBI main chain, and the molar ratio of the cross-linking group to the benzimidazole structural unit in the PBI main chain is 1:1.

[0053] The preparation method of the polybenzimidazole cross-linked polymer specifically comprises the following steps: Synthesize a benzimidazole polymer. The synthesis route diagram is as Figure 1 shown. Mix 0.044 mol of 3,3’,4,4’-tetraaminodiphenyl ether and 0.044 mol of isophthalic acid with 40 mL of NMP and react at 60 °C for 24 h to obtain a polybenzimidazole solution; Add 0.022 mol of 1-bromopropane to the polybenzimidazole solution, react at 140 °C for 12 h, then add 0.022 mol of 1-bromohexane, and react at 140 °C for 12 h to obtain a polybenzimidazole polymer solution; Add 0.044 mol of 1,6-hexanedithiol to the polybenzimidazole polymer solution, react at 80 °C for 6 h, and then dry the reaction product in an oven at 80 °C for 6 h to obtain a crosslinked polybenzimidazole polymer.

[0054] Example 2 A polybenzimidazole anion exchange membrane, the structural schematic diagram is as Figure 2 shown, and the preparation method is as follows: Dissolve the crosslinked polybenzimidazole polymer prepared in Example 1 in 40 mL of NMP to obtain a film-forming solution. Pour the film-forming solution onto a flat glass of 200 mm×200 mm, scrape the film to make its thickness uniform on the flat glass, and the thickness is 0.25 mm; put it into a vacuum oven, the vacuum degree is 10 -2 MPa, defoam for 15 min, then raise the temperature of the vacuum oven to 80 °C, let it stand and dry for 6 h and then take it out to obtain a base film; Put the base film into a 1 mol / L NaOH solution at 80 °C and soak for 12 h to convert Br - to OH - , and then rinse it twice with deionized water to wash away the residual NaOH to obtain a polybenzimidazole anion exchange membrane.

[0055] Comparative Example 1 A polybenzimidazole anion exchange membrane, the preparation method is as follows: Mix 0.044 mol of 3,3’,4,4’-tetraaminodiphenyl ether and 0.044 mol of isophthalic acid with 40 mL of NMP and react at 60 °C for 24 h to obtain a polybenzimidazole solution; Add 0.022 mol of 1-bromopropane to the polybenzimidazole solution, react at 140 °C for 12 h, then add 0.022 mol of 1-bromohexane, and react at 140 °C for 12 h to obtain a film-forming solution of a benzimidazole polymer solution; Pour the film-forming solution onto a flat glass of 200 mm×200 mm, scrape the film to make its thickness uniform on the flat glass; put it into a vacuum oven, the vacuum degree is 10 -2 MPa, defoam for 15 min, then raise the temperature of the vacuum oven to 80 °C, let it stand and dry for 6 h and then take it out to obtain a base film; Put the base film into a 1 mol / L NaOH solution at 80 °C and soak for 12 h to convert Br - to OH -, and then rinse it twice with deionized water to wash away the residual NaOH, obtaining a polybenzimidazole anion exchange membrane.

[0056] Test Example The anion exchange membrane prepared in Example 2 above was tested for ion exchange capacity. The test method was as follows: Cut the anion exchange membrane into 40 mm × 40 mm samples, weigh the mass of the membrane sample after it was completely dried, and record it as m dry , after weighing, immerse the dried membrane in 30 mL of 0.01 mol / L HCl solution, and stir at 30 °C for 24 h to ensure that the OH - in the membrane was completely consumed by H + ; after the ions were completely exchanged, using phenolphthalein as an indicator, titrate the residual H + in the solution with the calibrated 0.01 mol / L NaOH solution. The ion exchange capacity (IEC) was calculated by the following formula: In this formula, V NaOH and V 0,NaOH respectively represent the volumes of the NaOH solution consumed in titrating the experimental sample and the control sample (without anion exchange membrane) of the HCl solution, and C NaOH is the concentration of NaOH calibrated with potassium hydrogen phthalate.

[0057] The ion exchange capacity of the anion exchange membrane prepared in Example 2 was 2.35 mmol / g.

[0058] Immerse the anion exchange membrane prepared in Example 2 in 1 mol / L NaOH solution for 1080 h, take it out and measure the ion exchange capacity to be 1.29 mmol / g.

[0059] Cut the anion exchange membranes prepared in Example 2 and Comparative Example 1 into 40 mm × 40 mm samples and put them into an oven at 300 °C. After 12 h, test the ion exchange capacity of the anion exchange membrane in Example 2 to be 1.67 mmol / g; take it out after 24 h and observe the state of the samples. The size change of the anion exchange membrane prepared in Comparative Example 1 was greater than 25%; the size change of the anion exchange membrane prepared in Example 2 was less than 5%, and the membrane remained intact.

[0060] From the above examples and comparative examples, it can be seen that for the polybenzimidazole anion exchange membrane provided by the present invention, by introducing a cross-linking group into the benzimidazole polymer, the stability of the membrane, especially the long-term stability, is effectively improved, and when used as an anion exchange membrane, the service life of the membrane is increased.

[0061] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A polybenzimidazole cross-linked polymer, characterized in that, It includes a benzimidazole polymer and a crosslinking group crosslinked between the benzimidazole polymers; the benzimidazole polymer includes a polybenzimidazole main chain and a branched chain group, and the branched chain group is grafted on the imino group of the polybenzimidazole main chain; the crosslinking group connects the benzene ring of the polybenzimidazole main chain, and the crosslinking group is a crosslinking group formed by dithiol.

2. The polybenzimidazole crosslinked polymer according to claim 1, wherein The dithiol is a terminal dithiol.

3. The polybenzimidazole cross-linked polymer according to claim 1, wherein The branched chain group includes one or more of a long-chain alkyl group, a halogenated alkyl group, a carbonyl group-containing group, and a nitrogen group-containing group.

4. The polybenzimidazole crosslinked polymer according to claim 1, characterized in that, The molar ratio of the benzimidazole structural unit in the polybenzimidazole main chain to the branched chain group is 1:(1~2).

5. The polybenzimidazole cross-linked polymer according to claim 1, wherein The molar ratio of the benzimidazole structural unit in the polybenzimidazole main chain to the crosslinking group is (1~5):

1.

6. The preparation method of the polybenzimidazole cross-linked polymer according to any one of claims 1 to 5, characterized in that, It includes the following steps: (1) Mix 3,3’,4,4’-tetraaminodiphenyl ether, isophthalic acid and a solvent and then carry out a polycondensation reaction to obtain a polymer solution; (2) Mix the polymer solution obtained in step (1) with a grafting monomer and then carry out a grafting reaction to obtain a benzimidazole polymer solution; (3) Mix the benzimidazole polymer solution obtained in step (2) with a crosslinking agent and then carry out a crosslinking reaction to obtain a polybenzimidazole crosslinked polymer.

7. The preparation method according to claim 6, characterized in that, The crosslinking agent in step (3) is 1,4-butanedithiol, 1,6-hexanedithiol or 1,8-octanedithiol.

8. The preparation method according to claim 6 or 7, characterized in that, The temperature of the crosslinking reaction in step (3) is 75~85 °C, and the reaction time is 4~8 h.

9. The preparation method according to claim 6, characterized in that, The temperature of the grafting reaction in step (2) is 130~150 °C, and the reaction time is 10~14 h.

10. A polybenzimidazole anion exchange membrane, characterized in that, It is prepared by using the polybenzimidazole crosslinked polymer described in any one of claims 1~5 or the polybenzimidazole crosslinked polymer prepared by the preparation method described in any one of claims 6~9.

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