A method for preparing a block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups and a proton exchange membrane thereof and applications thereof

Abstract

The application provides a preparation method and application of a block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups. In the preparation process, a multiple hydrogen bond network is constructed with the imidazole ring by simultaneously introducing the sulfonic acid group and the hydroxyl group, so that the conductivity is improved and the excessive swelling of the membrane in water is inhibited; the block structure is used to induce the formation of a good microphase separation structure in the membrane, so as to provide a continuous and efficient channel for proton transmission; and a series of rigid sulfonated diacid monomers with large steric hindrance are selected to weaken the intermolecular force, destroy the close packing structure of the polymer main chain, and improve the solubility of the high molecular weight polymer.

Description

Technical Field

[0001] This invention belongs to the field of battery proton exchange membrane preparation technology. Specifically, it relates to a block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups, a method for preparing the proton exchange membrane thereon, and its application. Background Technology

[0002] Polybenzimidazole (PBI), a typical non-fluorinated aromatic polymer material, possesses excellent mechanical strength and chemical stability, making it widely used in energy storage battery separators. Most PBI materials are prepared through the condensation and cyclization of corresponding diamines and carboxylic acids, resulting in rigid molecular chains and strong interchain interactions to ensure sufficient mechanical properties. However, high molecular weight PBI polymers are generally difficult to dissolve in common organic solvents. This not only prevents the synthesis of ultra-high molecular weight PBI via solution methods to improve membrane mechanical properties but also makes the preparation of large-area, defect-free, high-quality films extremely difficult. For example, commercially available m-PBI prepared from 3,3'-diaminobenzidine (DAB) and isophthalic acid (IPA), while exhibiting excellent thermal stability and mechanical strength, suffers from high molecular chain rigidity and strong interchain interactions, leading to a decrease in solubility in organic solvents with increasing molecular weight. This severely limits the feasibility of solution-processing it into films.

[0003] Furthermore, due to the lack of ion exchange groups in PBI materials and their dense structure, traditional PBI membranes exhibit extremely low intrinsic conductivity, making it difficult to meet the operational requirements of batteries. They must be doped with strong acids (such as phosphoric acid) before they can be used as separators in flow batteries. Although acid doping can improve conductivity, it leads to a significant decrease in the membrane's mechanical strength and stability, thereby affecting the overall performance, lifespan, and long-term stability of the battery.

[0004] To prepare high molecular weight PBI polymers with good solubility and high conductivity, researchers have developed various synthetic strategies and modification methods, such as altering monomer structure, modifying main chain and side chain structures, constructing crosslinked networks, blending organic and inorganic materials, and porous treatments. Sulfonation is one of the effective methods. Existing sulfonated PBI (SPBI) improves the hydrophilicity and proton conductivity of PBI membranes by introducing sulfonic acid groups into the main chain. However, most of these methods are limited to introducing only one hydrophilic group, the sulfonic acid group. The proton and hydrogen bond sites provided by the sulfonic acid group are limited, resulting in low proton transport efficiency. In addition, the synthesis of sulfonated PBI usually adopts random copolymerization, resulting in disordered distribution of sulfonic acid groups. This can easily lead to excessively dense local hydrophilic regions that cause swelling or even dissolution during operation, or excessively large local hydrophobic regions that hinder proton transport. At the same time, traditional sulfonated monomers (such as sodium isophthalate-5-sulfonate) have limited steric hindrance and are not effective enough in disrupting the regular packing of molecular chains and improving solubility, making it difficult to synthesize polymer materials that have ultra-high molecular weight, excellent solubility, high proton conductivity and excellent mechanical strength and stability. Summary of the Invention

[0005] This invention addresses the shortcomings of existing sulfonated PBI modification schemes by providing a novel block polybenzimidazole copolymer that fundamentally solves the aforementioned problems. The technical principle is as follows: by simultaneously introducing sulfonic acid groups and hydroxyl groups to construct a multiple hydrogen bond network with the imidazole ring, the conductivity is improved while suppressing excessive swelling of the membrane in water. The block structure induces the formation of a well-defined microphase separation structure within the membrane, providing a continuous and efficient channel for proton transport. A series of rigid sulfonated diacid monomers with high steric hindrance are selected to weaken intermolecular forces, disrupt the close-packed structure of the polymer backbone, and improve the solubility of the high molecular weight polymer.

[0006] The primary objective of this invention is to provide a block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups and a method for preparing the same.

[0007] Another object of the present invention is to provide a proton exchange membrane prepared from the copolymer, so as to prepare a polymer membrane material with high proton conductivity, excellent mechanical strength and good stability.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] In a first aspect, the present invention provides a block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups, the general structural formula of which is:

[0010] ,

[0011] m:n is 3~7:3~7.

[0012] In a second aspect, the present invention provides a method for synthesizing the block polybenzimidazole copolymer described above, the synthetic route of which is shown below:

[0013]

[0014] The synthesis method is as follows:

[0015] Step (1): Under an inert gas atmosphere, Eaton reagent and 3,3'-diaminobenzidine were added to the reactor. The stirring speed was n1, and the reactor was heated to t1 to dissolve them. Then, 2,5-dihydroxyterephthalic acid was added to the reactor, and the stirring speed was adjusted to n2. After it was completely dissolved, the reaction temperature was raised to t2 for prepolymerization for 2 hours. Then, the temperature was lowered to t1, and dicarboxylic acid monomers with sulfonic acid groups were added to the reactor. After they were completely dissolved, the temperature was raised to t2 for prepolymerization for 2 hours. Then, the stirring speed was adjusted to n3, and the temperature was raised to t3 for polymerization for 3 hours.

[0016] Step (2): After the reaction is completed, wait for the reaction vessel to cool down to t1, pour the viscous solution into ice water to precipitate, and add alkali solution to wash in order to neutralize the residual acid in the product. Then wash several times with water and ethanol, and finally dry in a vacuum oven at 120℃ for 24 hours to obtain block polybenzimidazole copolymer.

[0017] The preferred technical solutions for the above two steps are as follows:

[0018] In step (1), regarding the reagents: Eaton reagent is a mixture of phosphorus pentoxide and methanesulfonic acid, wherein the mass fraction of phosphorus pentoxide is 7.2-8.2 wt%.

[0019] The dicarboxylic acid monomer with a sulfonic acid group is selected from any one of 2,5-disulfonic terephthalic acid, 3,3'-disulfonyl-[1,1'-biphenyl]-4,4'-dicarboxylic acid, 4,8-disulfonyl-2,6-naphthalenedicarboxylic acid, and 4,4'-oxobis[3-(sulfonyl)benzoic acid], preferably 3,3'-disulfonyl-[1,1'-biphenyl]-4,4'-dicarboxylic acid and 4,8-disulfonyl-2,6-naphthalenedicarboxylic acid. The copolymer proton exchange membrane prepared by sulfonation with these two acids not only has a larger molecular weight but also exhibits better solubility in the polar solvent DMAC.

[0020] The molar ratio of 3,3'-diaminobenzidine to 2,5-dihydroxyterephthalic acid and dicarboxylic acid monomers with sulfonic acid groups is 2:1:1.

[0021] Regarding reaction conditions: the stirring speed n1 is 150~170 rpm, n2 is 90~110 rpm, and n3 is 70~90 rpm; the dissolution temperature t1 is 70~90℃, the prepolymerization temperature t2 is 110~130℃, and the polymerization temperature t3 is 130~150℃; preferably n1 is 160 rpm, n2 is 100 rpm, and n3 is 80 rpm; the dissolution temperature t1 is 80℃, the prepolymerization temperature t2 is 120℃, and the polymerization temperature t3 is 140℃.

[0022] In step (2), the kinematic viscosity of the viscous solution is 35,000 cp ~ 40,000 cp;

[0023] The alkaline solution is any one of saturated sodium bicarbonate solution, saturated sodium carbonate solution, saturated potassium bicarbonate solution, or saturated potassium carbonate solution.

[0024] The solution was washed with alkali, water and ethanol until the pH reached 7.0.

[0025] The block polybenzimidazole copolymer prepared by the above two steps has an intrinsic viscosity ≥3.0 dL / g, a weight-average molecular weight of 150,000-200,000 g / mol, and a polydispersity index of 1.5-2.0. The preferred structure is as follows:

[0026]

[0027] In a second aspect, the present invention provides a method for preparing a proton exchange membrane using the above-mentioned copolymer, as follows: a block polybenzimidazole copolymer is dissolved in a non-proton polar organic solvent to obtain a membrane-building solution containing the block polybenzimidazole copolymer; the membrane-building solution is then poured onto a smooth and flat membrane-forming plate, the membrane-forming plate is placed in an oven at 80°C for solvent evaporation for 24 h, after drying, the membrane is peeled off from the glass plate, and then immersed in an acid solution for proton exchange for 24 h, then washed with deionized water to remove residual acid from the surface, and then placed in an oven at 100°C for drying for 24 h to obtain a block polybenzimidazole copolymer proton exchange membrane containing hydroxyl and sulfonic acid groups.

[0028] Preferably, the aprotic polar organic solvent is selected from any one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, and tetrahydrofuran;

[0029] The concentration of block polybenzimidazole copolymer in the film-forming solution is 10-20 wt%, preferably 15 wt%; the film-forming plate is preferably a glass plate;

[0030] The acid solution is 1.0 mol / L sulfuric acid;

[0031] The thickness of the block polybenzimidazole copolymer proton exchange membrane containing hydroxyl and sulfonic acid groups is 20-30 μm.

[0032] In a third aspect, this invention provides a proton exchange membrane prepared using the above-described method. Experimental results show that the controllable synthesis of ultra-high molecular weight polymers was successfully achieved using the block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups provided by this invention.

[0033] Compared to PBI proton exchange membranes prepared by random copolymerization and hydroxyl-free PBI membranes, the proton exchange membrane prepared in this invention has more obvious advantages: In terms of solubility, this ultra-high molecular weight polymer has a higher molecular weight, but it is more soluble in the polar solvent DMAC; in terms of hydrophilicity and swelling, the water absorption rate is close to 30%, while the swelling rate is only 15-16%, which is a significant improvement over existing PBI membranes; in terms of mechanical properties, the proton exchange membrane prepared in this invention has a tensile strength as high as 124.6 MPa and a maximum elongation at break of 18.13%, both of which are significantly improved compared to existing PBI membranes; after oxidation with Fenton's reagent for 24 hours, the mass retention rate was tested, and the results showed that the proton exchange membrane of this invention still had a mass retention rate of 92.14% after 24 hours of oxidation, while the random copolymer and hydroxyl-free PBI membranes only had mass retention rates of 82.14% and 80.09%, respectively; at the same time, the proton exchange membrane of this invention has higher conductivity and lower sheet resistance.

[0034] Based on the above comparison, in a fourth aspect, the present invention provides the application of the block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups in the preparation of a battery separator; it also provides the application of the proton exchange membrane described above as a battery separator.

[0035] In a fifth aspect, the present invention provides an energy storage battery in which the separator is prepared using the block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups as described above, or the proton exchange membrane described above is used as the battery separator.

[0036] The role and effect of invention

[0037] The block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups provided by this invention, through precise molecular design, simultaneously introduces two hydrophilic groups, hydroxyl and sulfonic acid groups, into the polymer backbone. These groups, in synergy with the imidazole ring, form a dense hydrogen bond network, providing abundant hopping sites for proton transport and significantly improving proton conductivity. Simultaneously, as dynamic crosslinking sites, they effectively suppress excessive swelling of the membrane in water, maintaining the membrane's structural stability. Furthermore, the block structure within the membrane promotes the formation of a hydrophilic-hydrophobic microphase separation structure, providing a continuous and efficient channel for proton transport.

[0038] The present invention selects a series of sulfonated diacid monomers with large steric hindrance effects, including rigid structures such as biphenyl and naphthalene rings, which can effectively disrupt the tight packing of polymer molecular chains, reduce inter-chain interactions, and increase free volume. This not only significantly improves the solubility of polymers in organic solvents, but also enables the synthesis of ultra-high molecular weight polymers with intrinsic viscosity ≥3.0 dL / g.

[0039] The block polybenzimidazole copolymer membrane containing hydroxyl and sulfonic acid groups prepared by this invention effectively improves proton conductivity without acid doping, while maintaining excellent mechanical strength and stability, and has good application prospects in the field of energy storage battery separators. Attached Figure Description

[0040] Figure 1 The diagram shows the test results of water absorption and swelling rate of PBI-1, PBI-2, PBI-3, PBI-4, PBI-5 and PBI-6 membranes.

[0041] Figure 2 The diagram shows the tensile strength and elongation at break test results of PBI-1, PBI-2, PBI-3, PBI-4, PBI-5 and PBI-6 films.

[0042] Figure 3 The mass retention rates of PBI-1, PBI-2, PBI-3, PBI-4, PBI-5, and PBI-6 membranes after Fenton's reagent oxidation test are shown.

[0043] Figure 4 A schematic diagram showing the proton conductivity and sheet resistance of PBI-1, PBI-2, PBI-3, PBI-4, PBI-5 and PBI-6 films is displayed.

[0044] Figure 5 A schematic diagram showing the intramolecular and intermolecular hydrogen bonding interactions and proton transport pathways of the copolymer is presented. Detailed Implementation

[0045] The following embodiments further illustrate the present invention and should not be construed as limiting the invention. The embodiments do not include a detailed description of conventional methods, which are well known to those skilled in the art and described in numerous publications.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as are familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention, and the preferred embodiments and materials described in the specific implementation are for illustrative purposes only.

[0047] Unless otherwise specified, the experimental methods described in the following examples are generally performed under standard conditions or as recommended by the manufacturer.

[0048] I. Preparation of polybenzimidazole copolymer (PBI)

[0049] The synthesis route is as follows:

[0050]

[0051] For specific synthesis methods, please refer to Examples 1 to 4 below:

[0052] Example 1

[0053] In this embodiment, 2,5-disulfonic acid-terephthalic acid is used as the sulfonating agent. The method for preparing the block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups and its proton exchange membrane includes the following steps:

[0054] Step 1: Under an inert gas atmosphere, 866.6 g of Eaton reagent, containing 7.7 wt% (66.7 g) of phosphorus pentoxide, was added to the reactor. Then, 21.4 g (0.1 mol) of 3,3'-diaminobenzidine was added to the reactor, and the temperature was raised to 80°C at 160 rpm with stirring for 2 h to dissolve. Next, 9.9 g (0.05 mol) of 2,5-dihydroxyterephthalic acid was added to the reactor, and the stirring speed was adjusted to 100 rpm for 2 h to dissolve. The temperature was then raised to 120°C for prepolymerization for 2 h. Finally, the temperature was lowered to 80°C, and 16.3 g of... The molar ratio of 0.05 mol / L 2,5-disulfonic terephthalic acid, 3,3'-diaminobenzidine, 2,5-dihydroxyterephthalic acid, and 2,5-disulfonic terephthalic acid was 2:1:1. After complete dissolution, the reactor was heated to 120°C for prepolymerization for 2 h. Subsequently, the stirring speed was adjusted to 80 rpm, and the temperature was increased to 140°C for polymerization for 3 h. After the reaction, the kinematic viscosity of the viscous solution in the reactor was measured to be 36642 cp.

[0055] Step 2: After the reaction is complete, the viscous solution is poured into ice water to precipitate after the reaction vessel has cooled to 80℃. Saturated sodium bicarbonate is then added for washing to neutralize any residual acid in the product. The resulting product is then shredded and washed several times with water and ethanol until the solution pH reaches 7.0. Finally, the yellow product is dried in a vacuum oven at 120℃ for 24 hours to obtain the block polybenzimidazole copolymer PBI-1, with a yield of 97.6%. The weight-average molecular weight of PBI-1 is 164720 g / mol, and its intrinsic viscosity is 3.59 dL / g. The structure of PBI-1 is as follows:

[0056] .

[0057] Step 3: Dissolve 10 g of PBI-1 block copolymer in 66.7 g of N,N-dimethylacetamide to obtain a film-building solution containing 15 wt% block copolymer. Pour the solution onto a smooth, flat glass plate and place the plate in an 80°C oven for solvent evaporation for 24 h to obtain a PBI-1 membrane with a thickness of 25 μm and a uniform surface. Immerse the membrane in a 1.0 M sulfuric acid solution and allow it to stand for 24 h for proton exchange. Then wash the membrane surface with deionized water to remove residual acid, and finally dry it in a 100°C oven for 24 h.

[0058] Example 2

[0059] In this embodiment, 3,3'-disulfonyl-[1,1'-biphenyl]-4,4'-dicarboxylic acid is used as the sulfonating agent. The method for preparing the block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups and its proton exchange membrane includes the following steps:

[0060] Step 1: Under an inert gas atmosphere, 866.6 g of Eaton reagent, containing 7.7 wt% (66.7 g) phosphorus pentoxide, was added to the reactor. Then, 21.4 g (0.1 mol) of 3,3'-diaminobenzidine was added to the reactor, and the temperature was raised to 80°C at 160 rpm with stirring for 2 h to dissolve. Next, 9.9 g (0.05 mol) of 2,5-dihydroxyterephthalic acid was added to the reactor, and the stirring speed was adjusted to 100 rpm for 2 h to dissolve. The temperature was then raised to 120°C for prepolymerization for 2 h. Finally, the temperature was lowered to 80°C, and 20.1 g of... The molar ratio of 0.05 mol / g 3,3'-disulfonyl-[1,1'-biphenyl]-4,4'-dicarboxylic acid, 3,3'-diaminobenzidine, 2,5-dihydroxyterephthalic acid, and 3,3'-disulfonyl-[1,1'-biphenyl]-4,4'-dicarboxylic acid was 2:1:1. After complete dissolution, the reactor was heated to 120°C for prepolymerization for 2 h. Subsequently, the stirring speed was adjusted to 80 rpm, and the temperature was increased to 140°C for polymerization for 3 h. After the reaction, the kinematic viscosity of the viscous solution in the reactor was measured to be 37926 cp.

[0061] Step 2: After the reaction is complete, wait for the reaction vessel to cool to 80℃, then pour the viscous solution into ice water to precipitate. Add saturated sodium bicarbonate for washing to neutralize any residual acid in the product. Chop the obtained product and wash several times with water and ethanol until the solution pH=7.0. Finally, place the yellow product in a 120℃ vacuum oven and dry for 24 hours to obtain the block polybenzimidazole copolymer PBI-2, with a yield of 98.1%. The weight-average molecular weight of PBI-2 is 176431 g / mol, and the intrinsic viscosity is 3.68 dL / g. The structure of PBI-2 is as follows:

[0062] .

[0063] Step 3: Dissolve 10 g of PBI-2 block copolymer in 66.7 g of N,N-dimethylacetamide to obtain a film-building solution containing 15 wt% block copolymer. Pour the solution onto a smooth, flat glass plate and place the plate in an 80°C oven for solvent evaporation for 24 h, resulting in a 25 μm thick PBI-2 membrane with a uniform surface. Immerse the membrane in a 1.0 M sulfuric acid solution and allow it to stand for 24 h for proton exchange. Then wash the surface of the membrane with deionized water to remove residual acid, and finally dry it in a 100°C oven for 24 h.

[0064] Example 3

[0065] In this embodiment, 4,8-disulfonic acid-2,6-naphthalenedicarboxylic acid is used as the sulfonating agent. The method for preparing the block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups and its proton exchange membrane includes the following steps:

[0066] Step 1: Under an inert gas atmosphere, 866.6 g of Eaton reagent, containing 7.7 wt% (66.7 g) phosphorus pentoxide, was added to the reactor. Then, 21.4 g (0.1 mol) of 3,3'-diaminobenzidine was added to the reactor, and the temperature was raised to 80°C at 160 rpm with stirring for 2 h to dissolve. Next, 9.9 g (0.05 mol) of 2,5-dihydroxyterephthalic acid was added to the reactor, and the stirring speed was adjusted to 100 rpm for 2 h to dissolve. The temperature was then raised to 120°C for prepolymerization for 2 h. Finally, the temperature was lowered to 80°C, and 18.8 g of... The molar ratio of 0.05 mol / L 4,8-disulfonic acid-2,6-naphthalenedicarboxylic acid, 3,3'-diaminobenzidine, 2,5-dihydroxyterephthalic acid, and 4,8-disulfonic acid-2,6-naphthalenedicarboxylic acid was 2:1:1. After complete dissolution, the reactor was heated to 120°C for prepolymerization for 2 h. Subsequently, the stirring speed was adjusted to 80 rpm, and the temperature was increased to 140°C for polymerization for 3 h. After the reaction, the kinematic viscosity of the viscous solution in the reactor was measured to be 37461 cp.

[0067] Step 2: After the reaction is complete, wait for the reaction vessel to cool to 80℃, then pour the viscous solution into ice water to precipitate. Add saturated sodium bicarbonate for washing to neutralize any residual acid in the product. Chop the obtained product and wash several times with water and ethanol until the solution pH=7.0. Finally, place the yellow product in a 120℃ vacuum oven and dry for 24 hours to obtain the block polybenzimidazole copolymer PBI-3, with a yield of 97.2%. The weight-average molecular weight of PBI-3 is 171267 g / mol, and the intrinsic viscosity is 3.65 dL / g. The structure of PBI-3 is as follows:

[0068] .

[0069] Step 3: Dissolve 10 g of PBI-3 block copolymer in 66.7 g of N,N-dimethylacetamide to obtain a film-building solution containing 15 wt% block copolymer. Pour the solution onto a smooth, flat glass plate and place the plate in an 80°C oven for solvent evaporation for 24 h, resulting in a 25 μm thick PBI-3 membrane with a uniform surface. Immerse the membrane in a 1.0 M sulfuric acid solution and allow it to stand for 24 h for proton exchange. Then wash the membrane surface with deionized water to remove residual acid, and finally dry it in a 100°C oven for 24 h.

[0070] Example 4

[0071] In this embodiment, 4,4'-oxobis[3-(sulfonyl)benzoic acid is used as the sulfonating agent. The method for preparing the block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups and its proton exchange membrane includes the following steps:

[0072] Step 1: Under an inert gas atmosphere, 866.6 g of Eaton reagent, containing 7.7 wt% (66.7 g) of phosphorus pentoxide, was added to the reactor. Then, 21.4 g (0.1 mol) of 3,3'-diaminobenzidine was added to the reactor. The reactor temperature was raised to 80°C at 160 rpm, and the mixture was stirred and dissolved for 2 h. Next, 9.9 g (0.05 mol) of 2,5-dihydroxyterephthalic acid was added to the reactor, and the stirring speed was adjusted to 100 rpm. The mixture was stirred and dissolved for 2 h, and then the temperature was raised to 120°C for prepolymerization for 2 h. Finally, the temperature was lowered to 80°C, and 20.9 g of... The molar ratio of 0.05 mol / g 4,4'-oxobis[3-(sulfonyl)benzoic acid], 3,3'-diaminobenzidine, 2,5-dihydroxyterephthalic acid, and 4,4'-oxobis[3-(sulfonyl)benzoic acid] was 2:1:1. After complete dissolution, the reactor was heated to 120°C for prepolymerization for 2 h. Subsequently, the stirring speed was adjusted to 80 rpm, and the temperature was increased to 140°C for polymerization for 3 h. After the reaction, the kinematic viscosity of the viscous solution in the reactor was measured to be 35889 cp.

[0073] Step 2: After the reaction is complete, wait for the reaction vessel to cool to 80℃, then pour the viscous solution into ice water to precipitate. Add saturated sodium bicarbonate for washing to neutralize any residual acid in the product. Chop the obtained product and wash several times with water and ethanol until the solution pH=7.0. Finally, dry the yellow product in a 120℃ vacuum oven for 24 hours to obtain the block polybenzimidazole copolymer PBI-4, with a yield of 98.1%. The weight-average molecular weight of PBI-3 is 154679 g / mol, and the intrinsic viscosity is 3.51 dL / g. The structure of PBI-4 is as follows:

[0074] .

[0075] Step 3: Dissolve 10 g of PBI-4 block copolymer in 66.7 g of N,N-dimethylacetamide to obtain a film-building solution containing 15 wt% block copolymer. Pour the solution onto a smooth, flat glass plate and place the plate in an 80°C oven for solvent evaporation for 24 h, resulting in a 25 μm thick PBI-3 membrane with a uniform surface. Immerse the membrane in a 1.0 M sulfuric acid solution and allow it to stand for 24 h for proton exchange. Then wash the surface of the membrane with deionized water to remove residual acid, and finally dry it in a 100°C oven for 24 h.

[0076] Comparative Example 1

[0077] The reagents used in this comparative example are the same as those in Example 1, the difference being that random polymerization was used for synthesis. The preparation method of this random polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups and its proton exchange membrane includes the following steps:

[0078] Step 1: Under an inert gas atmosphere, 866.6 g of Eaton reagent, containing 7.7 wt% (66.7 g) of phosphorus pentoxide, was added to the reactor. Then, 21.4 g (0.1 mol) of 3,3'-diaminobenzidine, 9.9 g (0.05 mol) of 2,5-dihydroxyterephthalic acid, and 16.3 g (0.05 mol) of 2,5-disulfonic terephthalic acid were added to the reactor. The reactor temperature was raised to 80°C at 160 rpm and stirred for 2 h to dissolve the precipitate. The stirring speed was then adjusted to 100 rpm, and the temperature was raised to 120°C for prepolymerization for 2 h. Finally, the stirring speed was adjusted to 80 rpm, and the temperature was raised to 140°C for polymerization for 3 h. After the reaction, the kinematic viscosity of the viscous solution in the reactor was measured to be 35461 cp.

[0079] Step 2: After the reaction is complete, wait for the reaction vessel to cool to 80℃, then pour the viscous solution into ice water to precipitate. Add saturated sodium bicarbonate for washing to neutralize the residual acid in the product. Cut the obtained product into small pieces and wash it several times with water and ethanol until the solution pH=7.0. Finally, place the yellow product in a vacuum oven at 120℃ and dry for 24 hours to obtain random polybenzimidazole copolymer PBI-5 with a yield of 94.8%. The weight-average molecular weight of PBI-5 is 153849 g / mol, and the intrinsic viscosity is 3.48 dL / g.

[0080] Step 3: Dissolve 10 g of PBI-5 random copolymer in 66.7 g of N,N-dimethylacetamide to obtain a film-building solution containing 15 wt% random copolymer. Pour the solution onto a smooth, flat glass plate and place the plate in an 80°C oven for solvent evaporation for 24 h, resulting in a 25 μm thick PBI-5 membrane with a uniform surface. Immerse the membrane in a 1.0 M sulfuric acid solution and allow it to stand for 24 h for proton exchange. Then wash the membrane surface with deionized water to remove residual acid, and finally dry it in a 100°C oven for 24 h.

[0081] Comparative Example 2

[0082] Compared with the reagents in this comparative example and Example 1, 2,5-dihydroxyterephthalic acid was not added. A method for preparing a linear sulfonated polybenzimidazole polymer (without hydroxyl groups) and its proton exchange membrane includes the following steps:

[0083] Step 1: Under an inert gas atmosphere, 866.6 g of Eaton reagent, containing 7.7 wt% (66.7 g) of phosphorus pentoxide, was added to the reactor. Then, 21.4 g (0.1 mol) of 3,3'-diaminobenzidine was added. The reactor temperature was raised to 80°C at 160 rpm, and the mixture was stirred and dissolved for 2 h. Next, 16.3 g (0.05 mol) of 2,5-disulfonic terephthalic acid was added to the reactor, and the stirring speed was adjusted to 100 rpm. The mixture was stirred and dissolved for 2 h, and then the temperature was raised to 120°C for prepolymerization for 2 h. Then, the temperature was lowered to 80°C, and 16.3 g (0.05 mol) of 2,5-disulfonic terephthalic acid was added to the reactor. The molar ratio of 3,3'-diaminobenzidine to 2,5-disulfonic terephthalic acid was 1:1. After complete dissolution, the reactor temperature was raised to 120°C for prepolymerization for 2 h. The stirring speed was then adjusted to 80 rpm, and the temperature was raised to 140℃ for polymerization for 3 h. After the reaction was completed, the kinematic viscosity of the viscous solution in the reactor was measured to be 35028 cp.

[0084] Step 2: After the reaction is complete, wait for the reaction vessel to cool to 80℃, then pour the viscous solution into ice water to precipitate. Add saturated sodium bicarbonate for washing to neutralize the residual acid in the product. Cut the obtained product into small pieces and wash it several times with water and ethanol until the solution pH=7.0. Finally, place the yellow product in a vacuum oven at 120℃ and dry for 24 hours to obtain the linear polybenzimidazole polymer PBI-6 with a yield of 95.3%. The weight-average molecular weight of PBI-6 is 150247 g / mol, and the intrinsic viscosity is 3.42 dL / g.

[0085] Step 3: Dissolve 10 g of PBI-6 linear polymer in 66.7 g of N,N-dimethylacetamide to obtain a film-building solution containing 15 wt% linear polymer. Pour the solution onto a smooth, flat glass plate and place the plate in an 80°C oven for solvent evaporation for 24 h, resulting in a PBI-6 membrane with a thickness of 25 μm and a uniform surface. Immerse the membrane in a 1.0 M sulfuric acid solution and allow it to stand for 24 h for proton exchange. Then wash the membrane surface with deionized water to remove residual acid, and finally dry it in a 100°C oven for 24 h.

[0086] II. Performance Testing Methods

[0087] Samples PBI-1 to PBI-4 prepared in Experimental Examples 1-4, and PBI-5 and PBI-6 prepared in Comparative Examples 1-2, were subjected to kinematic viscosity, intrinsic viscosity, molecular weight, water absorption and swelling ratio, mechanical properties, proton conductivity, and surface resistivity tests. Oxidative stability was also investigated. Specific testing methods are as follows:

[0088] 2.1 Kinematic viscosity, intrinsic viscosity, molecular weight

[0089] The kinematic viscosity of the viscous solution in the reactor was measured by a vibratory viscometer inserted into the solution; the intrinsic viscosity of the copolymer solution was tested by an Ubbelohde viscometer; and the molecular weight and distribution of the synthesized copolymer were tested by gel permeation chromatography.

[0090] 2.2 Water absorption rate and swelling rate

[0091] The prepared membrane sample was placed in a vacuum drying oven at 60°C and dried continuously for 24 hours. Immediately after removing the sample, its dry weight was measured and recorded as M. dry The diameter of the membrane at this point is measured and denoted as D. dry Subsequently, the sample was immersed in deionized water and allowed to stand for 24 hours. After soaking, the water on the membrane surface was gently blotted off with filter paper, and the mass M of the wet membrane was quickly measured. wet And measure its wet diameter D wet To improve the reliability of the experimental results and reduce operational errors, each sample was measured in triplicate, and the final data was the average of the three measurements. The water absorption rate (WU) and swelling ratio (SR) of the membrane were calculated using the following two formulas:

[0092]

[0093]

[0094] Among them, M dry M is the dry weight of the membrane. wet D is the wet weight of the membrane after it absorbs water. dry D is the diameter of the membrane in its dry state. wet The diameter is the membrane in the wetted state.

[0095] 2.3 Mechanical Performance Testing

[0096] The mechanical properties of the copolymer film were tested using an electronic universal testing machine. After the film was cut to a suitable test size, its length, width, height and thickness were measured. Tensile tests were then performed on it at a loading rate of 10 mm / min to obtain the tensile strength and elongation at break of the film.

[0097] 2.4 Proton conductivity and surface resistance

[0098] The proton conductivity (σ) and sheet resistance (AR) of various membranes were measured using electrochemical impedance spectroscopy. The frequency range of the tests was 10. -2 -10 6 Between Hz, the AC amplitude is 5 mV. The formulas for calculating proton conductivity and surface resistivity are as follows:

[0099]

[0100] Where σ is the proton conductivity of the membrane (mS / cm) -1 L is the length of the membrane (cm), and A is the cross-sectional area of ​​the membrane sample (cm²). 2 R is the resistance value (Ω) obtained by fitting the electrochemical impedance spectroscopy.

[0101] 2.5 Oxidation stability

[0102] The prepared membrane samples were immersed in Fenton's reagent (3% H2O2 + 4 ppm Fe) at 80 degrees Celsius. 2+ After standing for 24 hours, the membrane was removed and washed with deionized water. It was then dried in an 80°C oven for 1 hour, and its weight was recorded. The mass retention rate was calculated using the following formula:

[0103]

[0104] Where M1 is the mass of the membrane before immersion, and M2 is the mass of the membrane after immersion and drying.

[0105] III. Results Analysis

[0106] 3.1 Kinematic viscosity, intrinsic viscosity, molecular weight, and solubility

[0107] The test results of the examples and comparative examples are summarized in Table 1 below:

[0108] Table 1 Summary of parameters for the examples and comparative examples

[0109]

[0110] As can be seen from the data in Table 1, the block polybenzimidazole copolymers containing hydroxyl and sulfonic acid groups provided by this invention successfully achieved the controllable synthesis of ultra-high molecular weight polymers. The intrinsic viscosity of the copolymers in Examples 1-4 all exceeded 3.5 dL / g, and the weight-average molecular weight reached over 150,000 g / mol. Examples 2 and 3, with even higher molecular weights, were more readily soluble in the polar solvent DMAC. This is because the introduction of sterically hindered sulfonated monomers effectively disrupted the close packing of polymer chains, increasing the free volume of the copolymer, thereby endowing the material with excellent solution processability while maintaining superior mechanical properties. Furthermore, compared to the random copolymer structure of Comparative Example 1, the block structure of this invention can achieve a higher molecular weight; while Comparative Example 2, which does not contain hydroxyl groups, is less soluble, demonstrating the crucial role of hydroxyl groups in promoting polymerization and optimizing solubility. This invention provides a novel polymer synthesis strategy, fundamentally solving the technical challenge of balancing high molecular weight and excellent solubility, and exhibits significant application potential.

[0111] 3.2 Water absorption rate and swelling rate

[0112] Figure 1 The diagram shows the test results for PBI-1, PBI-2, PBI-3, PBI-4, PBI-5, and PBI-6 membranes. As shown, PBI-1~4 exhibit higher water absorption rates and better anti-swelling properties compared to PBI-5~6. Specifically, PBI-2 and PBI-3 achieved water absorption rates of 28.97% and 30.28%, respectively, while their swelling rates were only 15.14% and 16.21%. This is because the block copolymer microphase separation structure forms dimensionally stable and interconnected hydrophilic regions, capable of absorbing a large number of water molecules. Simultaneously, the membrane is constrained by the rigid hydrophobic framework of the polymer, thus preventing excessive macroscopic expansion. Furthermore, the dynamic hydrogen bond network constructed from hydroxyl groups, sulfonic acid groups, and imidazole rings further enhances the stability of the hydrophilic regions, inhibiting membrane swelling. The swelling rate of PBI-5 increased to 25.28%, indicating that the microstructure formed through random copolymerization is loose and disordered, unable to maintain dimensional stability after water absorption. PBI-6 exhibits a lower water absorption rate and a higher swelling rate, which demonstrates that due to the lack of hydroxyl groups, it cannot form an excellent hydrogen bond network, resulting in lower hydrophilicity and an inability to maintain dimensional stability.

[0113] 3.3 Mechanical Properties

[0114] Figure 2 The diagram shows the tensile strength and elongation at break test results of PBI-1, PBI-2, PBI-3, PBI-4, PBI-5, and PBI-6 films. As shown, all embodiments exhibit superior overall mechanical properties compared to the comparative examples. PBI-2 and PBI-3, employing rigid biphenyl and naphthalene ring structures, achieve tensile strengths as high as 124.6 MPa and 117.9 MPa, respectively. PBI-4, with its more flexible ether bonds, increases the film's toughness and achieves the highest elongation at break (18.13%). This is attributed to both the successful synthesis of ultra-high molecular weight copolymers through block design and the selection of rigid monomers, and the reinforcing and toughening effects provided by the dense hydrogen bond network.

[0115] 3.4 Oxidative stability

[0116] Figure 3The mass retention rates of PBI-1, PBI-2, PBI-3, PBI-4, PBI-5, and PBI-6 films after Fenton's reagent oxidation test are shown. As shown in the figure, PBI-2 still retained 92.14% of its mass after 24 h of oxidation, while the random copolymer PBI-5 and the hydroxyl-free PBI-6 only retained 82.14% and 80.09% of their respective masses. In the examples, the regular block microphase separation formed a dense and stable polymer aggregate state, which effectively hindered the penetration and oxidation of the oxidizing medium. In addition, the dynamic hydrogen bond network constructed by hydroxyl groups, sulfonic acid groups, and imidazole rings can efficiently neutralize the highly destructive ·OH free radicals generated in the Fenton reaction, significantly delaying the oxidative degradation process of the polymer backbone.

[0117] 3.5 Proton conductivity and surface resistivity

[0118] Figure 4 Schematic diagrams of PBI-1, PBI-2, PBI-3, PBI-4, PBI-5, and PBI-6 films are shown. As illustrated, all embodiments exhibit excellent properties of high proton conductivity and low sheet resistance, with the PBI-3 film achieving a proton conductivity of 65.47 mS / cm and a sheet resistance as low as 0.061 Ω / cm. 2 This is due to the large steric hindrance effect brought about by the naphthalene ring sulfonated monomer used, which disrupts the tight packing of molecular chains and widens the ion transport channels. Furthermore, the synergistic effect of the hydroxyl groups, sulfonic acid groups, and imidazole rings constructs a dense and continuous hydrogen bond network, providing abundant proton exchange sites, thus achieving efficient proton conduction. In contrast, PBI-5 (random copolymer) has a significantly lower conductivity (only 47.67 mS / cm) due to the disordered distribution of hydrophilic groups, which prevents the formation of interconnected proton transport channels; while PBI-6 (hydroxyl-free) has a high electrical resistance (0.132 Ω / cm). 2 This also demonstrates that hydroxyl groups play an important role in perfecting the hydrogen bond network and optimizing the proton transport pathway.

[0119] The above results can be adopted Figure 5 To explain. Figure 5 This paper illustrates the multiple hydrogen bond network structure formed in a block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups. As shown in the figure, the phenolic hydroxyl groups (-OH), sulfonic acid groups (-SO3H), and imidazole rings (NH) in the polymer chain are interconnected through multiple pathways, forming a dense and stable dynamic hydrogen bond network. The proton transport pathways indicated in the figure represent the proton (H) transport pathways. +This membrane utilizes a hydrogen bond network to achieve efficient proton transport via the Grotthuss mechanism. This dynamic hydrogen bond network, constructed through the synergistic interaction of hydroxyl, sulfonic acid, and imidazole rings, not only provides continuous and abundant proton transport channels, significantly improving proton conductivity, but also serves as a reversible cross-linking structure, effectively suppressing excessive swelling of the membrane in water and ensuring the dimensional and mechanical stability of the membrane material during use.

[0120] Therefore, the innovative points of this invention are as follows:

[0121] (1) Block polybenzimidazole copolymers containing hydroxyl and sulfonic acid groups were synthesized through precise molecular design.

[0122] (2) The two hydrophilic groups, hydroxyl and sulfonic acid groups, introduced into the polymer backbone form a dense hydrogen bond network in synergy with the imidazole ring, which significantly improves the proton conductivity while maintaining the structural stability of the membrane.

[0123] (3) The sulfonated diacid monomer with large steric hindrance effect in the polymer backbone effectively disrupts the tight packing of polymer molecular chains, reduces inter-chain interactions, increases free volume, and significantly improves the solubility of polymers in organic solvents while synthesizing high molecular weight polymers.

[0124] The undescribed parts of this invention are the same as or implemented using existing technology. The applicant declares that this invention is illustrated through the above embodiments, but the invention is not limited to the above detailed methods, i.e., it does not mean that the invention must rely on the above detailed methods to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of raw materials for the product of this invention, additions of auxiliary components, and selection of specific methods all fall within the protection and disclosure scope of this invention.

Claims

1. A method for preparing a block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups, characterized in that, Includes the following steps: Step (1): Under an inert gas atmosphere, Eaton reagent and 3,3'-diaminobenzidine are added to the reactor. The stirring speed is set to n1, and the reactor is heated to t1 to dissolve them. Then, 2,5-dihydroxyterephthalic acid is added to the reactor, and the stirring speed is adjusted to n2. After it is completely dissolved, the reaction temperature is raised to t2 for prepolymerization. Then, the temperature was lowered to t1, and a dicarboxylic acid monomer with sulfonic acid groups was added to the reactor. After it was completely dissolved, the temperature was raised to t2 for prepolymerization. Subsequently, the stir bar speed was adjusted to n3, and the temperature was raised to t3 for polymerization. The dicarboxylic acid monomer with a sulfonic acid group is selected from 3,3'-disulfonyl-[1,1'-biphenyl]-4,4'-dicarboxylic acid or 4,8-disulfonic acid-2,6-naphthalenedicarboxylic acid. The molar ratio of 3,3'-diaminobenzidine to 2,5-dihydroxyterephthalic acid and a dicarboxylic acid monomer with a sulfonic acid group is 2:1:

1. The stirring speed n1 is 150~170 rpm, n2 is 90~110 rpm, and n3 is 70~90 rpm; the dissolution temperature t1 is 70~90℃, the prepolymerization temperature t2 is 110~130℃, and the polymerization temperature t3 is 130~150℃. Step (2): After the reaction is completed, the reaction vessel is cooled to t1 and the viscous solution is poured into ice water to precipitate. At the same time, alkali solution is added for washing to neutralize the residual acid in the product. Then, it is washed several times with water and ethanol, and finally dried in a vacuum oven at 120°C to obtain block polybenzimidazole copolymer.

2. The method for preparing the block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups according to claim 1, characterized in that: in, In step (1), the Eaton reagent is a mixture of phosphorus pentoxide and methanesulfonic acid, wherein the mass fraction of phosphorus pentoxide is 7.2-8.2 wt%. The prepolymerization time was 2-3 hours for both processes, and the polymerization time was 3-4 hours.

3. The method for preparing the block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups according to claim 1, characterized in that: in, In step (2), the kinematic viscosity of the viscous solution is 35,000 cp ~ 40,000 cp; The alkaline solution is selected from any one of saturated sodium bicarbonate solution, saturated sodium carbonate solution, saturated potassium bicarbonate solution, and saturated potassium carbonate solution. The solution was washed with alkali, water, and ethanol until the pH reached 7.0; The drying time is 24 hours.

4. A block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups, characterized in that, Prepared by the method according to any one of claims 1 to 3, and selected from any of the following structural formulas: ， m:n=3~7:3~7.

5. The block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups according to claim 4, characterized in that, Its intrinsic viscosity is ≥3.0 dL / g, its weight-average molecular weight is 150,000-200,000 g / mol, and its polydispersity index is 1.5-2.

0.

6. A method for preparing a proton exchange membrane, characterized in that, The preparation method using the block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups as described in any one of claims 4 to 5 is as follows: the block polybenzimidazole copolymer is dissolved in a non-proton polar organic solvent to obtain a film-forming solution containing block polybenzimidazole copolymer with a concentration of 10-20 wt%; then the film-forming solution is poured onto a smooth and flat film-forming plate, the film-forming plate is placed in an 80°C oven for solvent evaporation, after drying, the film is peeled off from the glass plate, then immersed in an acid solution for proton exchange, then washed with deionized water to remove residual acid from the surface, and then dried in a 100°C oven to obtain a block polybenzimidazole copolymer proton exchange membrane containing hydroxyl and sulfonic acid groups.

7. The method for preparing a proton exchange membrane according to claim 6, characterized in that: in, The aprotic polar organic solvent is selected from any one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, and tetrahydrofuran; The concentration of block polybenzimidazole copolymer in the film-forming solution is 15 wt%. The film-forming plate is selected from glass plates; The acid solution is 1.0 mol / L sulfuric acid; The thickness of the block polybenzimidazole copolymer proton membrane containing hydroxyl and sulfonic acid groups is 20-30 μm; The solvent evaporation time was 24 hours, the proton exchange time was 24 hours, and the drying time in the oven was also 24 hours.

8. A proton exchange membrane, characterized in that, It is prepared using the preparation method described in claim 6 or 7.

9. A battery separator for energy storage, characterized in that, The proton exchange membrane can be prepared using the block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups as described in claim 4 or 5, or the proton exchange membrane as described in claim 8 can be used as the separator for the energy storage battery.

10. An energy storage battery, characterized in that, It contains the energy storage battery separator as described in claim 9.

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