Preparation method and application of block polybenzimidazole copolymer containing hydroxyl and sulfonic acid group and proton exchange membrane of block polybenzimidazole copolymer

Abstract

The invention provides a preparation method and application of a block polybenzimidazole copolymer containing hydroxyl groups and sulfonic groups and a proton exchange membrane thereof. In the preparation process, sulfo groups and hydroxyl groups are introduced at the same time to construct a multiple hydrogen bond network with an imidazole ring, and excessive swelling of the membrane in water is inhibited while the conductivity is improved; a good microphase separation structure is formed in the block structure induction membrane, and a continuous and efficient channel is provided for proton transmission; meanwhile, by selecting a series of rigid sulfonated diacid monomers with large steric hindrance, the intermolecular acting force is weakened, the close packing structure of a polymer main chain is destroyed, and the solubility of a high-molecular-weight polymer is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of battery proton exchange membrane preparation, and particularly relates to a block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups and a preparation method and application of a proton exchange membrane thereof. BACKGROUND

[0002] Polybenzimidazole (PBI) is a typical non-fluorine aromatic polymer material, which has excellent mechanical strength and chemical stability, and is widely used in energy storage battery separators. Most PBI materials are prepared by condensation and cyclization of corresponding diamines and carboxylic acids. The molecular chain of PBI is rigid and the interchain interaction force is large, so as to ensure sufficient mechanical properties. However, high molecular weight PBI polymers are usually difficult to dissolve in common organic solvents, which not only leads to the difficulty in synthesizing ultra-high molecular weight PBI through solution method to improve the mechanical properties of the membrane, but also makes it extremely difficult to prepare large-area, defect-free high-quality thin films. For example, although the commercial m-PBI prepared from 3,3'-diaminobenzidine (DAB) and isophthalic acid (IPA) has excellent thermal stability and mechanical strength, the rigidity of its molecular chain and the strong interchain interaction result in the solubility of the PBI in organic solvents decreasing with the increase of the molecular weight, which seriously limits the feasibility of solution processing of the PBI into films.

[0003] In addition, due to the lack of ion exchange groups in PBI materials and the dense structure of PBI itself, the intrinsic conductivity of traditional PBI membranes is extremely low, which cannot meet the operation requirements of batteries. Therefore, the PBI membranes must be doped with strong acid (such as phosphoric acid) to be used as flow battery separators. Although acid doping can improve the conductivity, it will seriously reduce the mechanical strength and stability of the membrane, thereby affecting the overall performance, service life and long-term stability of the battery.

[0004] In order to prepare PBI polymers with high molecular weight, good solubility and high conductivity, researchers have developed a variety of synthesis strategies and modification methods, such as changing the monomer structure, main chain and side chain structure modification, crosslinking network construction, organic-inorganic material blending and porosity treatment, etc., among which sulfonation treatment is one of the effective ways. The existing sulfonated PBI (SPBI) improves the hydrophilicity and proton conductivity of the PBI film by introducing sulfonic acid groups into the main chain, but most of them are limited to introducing sulfonic acid groups as a kind of hydrophilic group, and the number of protons and hydrogen bond sites provided by the sulfonic acid group is limited, and the proton conduction efficiency is not high. In addition, the synthesis of sulfonated PBI usually adopts a random copolymerization method, and the sulfonic acid groups are distributed randomly, which can easily lead to excessive density of local hydrophilic regions and swelling or even dissolution during operation, or excessive size of local hydrophobic regions and hindered proton transmission. At the same time, the traditional sulfonated monomer (such as m-terephthalic acid-5-sulfonic acid sodium) has limited steric hindrance, which is insufficient to destroy the regular accumulation of molecular chains and improve the solubility, and it is difficult to synthesize polymer materials with ultra-high molecular weight, excellent solubility, high proton conductivity, and excellent mechanical strength and stability. SUMMARY

[0005] The present application improves the defects of the existing sulfonated PBI modification scheme, and aims to provide a new kind of block polybenzimidazole copolymer, which fundamentally solves the above problems. The technical principle is: by introducing sulfonic acid groups and hydroxyl groups at the same time, a multiple hydrogen bond network is constructed with the imidazole ring, which can improve the conductivity and inhibit the excessive swelling of the membrane in water; the block structure is used to induce the formation of a good microphase separation structure in the membrane, providing a continuous and efficient channel for proton transmission; a series of rigid sulfonated diacid monomers with large steric hindrance are selected to weaken the intermolecular forces, destroy the close packing structure of the polymer main chain, and improve the solubility of the high molecular weight polymer.

[0006] The first object of the present application is to provide a block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups and a preparation method thereof.

[0007] Another object of the present application 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] In order to achieve the above object, the technical scheme adopted by the present application is as follows:

[0009] In the first aspect of the present application, a block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups is provided, and the general structure formula is:

[0010] ,

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

[0012] In the second aspect of the present application, a synthesis method of the block polybenzimidazole copolymer is provided, and a synthesis route thereof is shown as follows:

[0013]

[0014] The synthesis method is as follows:

[0015] Step (1): In an inert gas atmosphere, Eaton's reagent and 3,3'-diaminobenzidine are added to a reaction kettle, the stirring paddle speed is n1, and the reaction kettle is heated to t1 to dissolve them; then 2,5-dihydroxyterephthalic acid is added to the reaction kettle, the stirring paddle speed is adjusted to n2, and after complete dissolution, the reaction temperature is raised to t2 for 2 h of prepolymerization; then the temperature is lowered to t1, and the sulfonic acid group-containing dicarboxylic acid monomer is added to the reaction kettle, and after complete dissolution, the temperature is raised to t2 for 2 h of prepolymerization, and then the stirring paddle speed is adjusted to n3, and the temperature is raised to t3 for 3 h of polymerization.

[0016] Step (2): After the reaction is completed, the viscous solution is poured into ice water for precipitation after the reaction kettle is cooled to t1, and an alkali solution is added for washing to neutralize the residual acid in the product, and then the product is washed with water and ethanol several times, and finally dried in a vacuum oven at 120°C for 24 hours to obtain the block polybenzimidazole copolymer.

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

[0018] In step (1), the reagent is: Eaton's reagent is a mixture of phosphorus pentoxide and methane sulfonic acid, and the mass fraction of phosphorus pentoxide is 7.2-8.2 wt %;

[0019] The sulfonic acid group-containing dicarboxylic acid monomer is selected from any one of 2,5-disulfonic terephthalic acid, 3,3'-disulfide-[1,1'-biphenyl]-4,4'-dicarboxylic acid, 4,8-disulfonic-2,6-naphthalene dicarboxylic acid, and 4,4'-oxybis[3-(sulfonyl)benzoic acid], preferably 3,3'-disulfide-[1,1'-biphenyl]-4,4'-dicarboxylic acid and 4,8-disulfonic-2,6-naphthalene dicarboxylic acid. The copolymer prepared by sulfonation of the two acids has a larger molecular weight and better solubility in polar solvent DMAC;

[0020] The molar ratio of 3,3'-diaminobenzidine to 2,5-dihydroxyterephthalic acid and the sulfonic acid group-containing dicarboxylic acid monomer is 2:1:1;

[0021] In terms of reaction conditions: the stirring paddle rotation 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 35000-40000 cp;

[0023] The alkali 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 is washed to pH=7.0 using an alkali solution, water, and ethanol.

[0025] The block polybenzimidazole copolymer prepared by the above two steps has an intrinsic viscosity of ≥3.0 dL / g, a weight average molecular weight of 150000-200000 g / mol, and a polydispersity index of 1.5-2.0. Preferably, the structure is as follows:

[0026]

[0027] In a second aspect of the present application, a method for preparing a proton membrane using the above copolymer is provided, as follows: the block polybenzimidazole copolymer is dissolved in an aprotic polar organic solvent to obtain a membrane-forming solution containing the block polybenzimidazole copolymer; then the membrane-forming solution is poured onto a smooth and flat membrane-forming plate, the membrane-forming plate is placed in an 80℃ oven 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 the surface residual acid is washed away with deionized water, and placed in a 100℃ oven for drying for 24 h to obtain a block polybenzimidazole copolymer proton membrane containing hydroxyl and sulfonic acid groups.

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

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

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

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

[0032] In a third aspect, the application provides a proton membrane prepared by the above method.

[0033] Compared with the PBI proton membrane prepared by random copolymerization and the PBI membrane without hydroxyl groups, the proton membrane prepared by the application has more obvious advantages: in terms of solubility, the ultra-high molecular weight polymer has a higher molecular weight, but is more easily soluble in polar solvent DMAC; in terms of hydrophilicity and swelling, the water absorption rate is close to 30%, and the swelling rate is only 15-16%, which is greatly improved compared with the existing PBI membrane; in terms of mechanical properties, the tensile strength of the proton membrane prepared by the application is as high as 124.6 MPa, and the maximum elongation at break is 18.13%, which is greatly improved compared with the existing PBI membrane; the mass retention rate is tested after 24 hours of Fenton reagent oxidation, and the results show that the proton membrane of the application still has a mass retention rate of 92.14% after 24 hours of oxidation test, while the random copolymer and the PBI membrane without hydroxyl groups only have mass retention rates of 82.14% and 80.09%; at the same time, the proton membrane of the application has higher conductivity and lower surface resistance.

[0034] Based on the above comparison, in a fourth aspect, the application provides the use of the above-mentioned hydroxyl and sulfonic acid group-containing block polybenzimidazole copolymer in the preparation of an energy storage battery separator; and simultaneously provides the use of the above-mentioned proton membrane as an energy storage battery separator.

[0035] In a fifth aspect, the application provides an energy storage battery, wherein the separator is prepared from the above-mentioned hydroxyl and sulfonic acid group-containing block polybenzimidazole copolymer, or the above-mentioned proton membrane is used as a battery separator.

[0036] Effects of the application

[0037] The hydroxyl and sulfonic acid group-containing block polybenzimidazole copolymer provided by the application introduces both hydroxyl and sulfonic acid groups into the polymer main chain through precise molecular design, and forms a dense hydrogen bond network with the imidazole ring, which not only provides abundant jumping sites for proton transport and significantly improves the proton conductivity, but also effectively inhibits the excessive swelling of the membrane in water as a dynamic crosslinking site, thereby maintaining the structural stability of the membrane. In addition, the block structure in the membrane promotes the formation of hydrophilic-hydrophobic microphase separation structure, thereby providing a continuous and efficient channel for proton transport.

[0038] The selected series of sulfonated diacid monomers with large steric effect of the application include rigid structures such as biphenyl, naphthalene ring, etc., which can effectively destroy the close packing of polymer molecular chains, reduce the interaction between chains, and increase the free volume, which not only significantly improves the solubility of the polymer in organic solvents, but also enables the synthesis of ultrahigh molecular weight polymers with intrinsic viscosity ≥ 3.0 dL / g.

[0039] The block polybenzimidazole copolymer film containing hydroxyl and sulfonic acid groups prepared by the application effectively improves the proton conductivity without acid doping, and maintains excellent mechanical strength and stability, and has good application prospect in the field of energy storage battery separators. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 The water absorption and swelling rate test results of PBI-1, PBI-2, PBI-3, PBI-4, PBI-5 and PBI-6 films are shown.

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

[0042] Figure 3 The mass retention rate of PBI-1, PBI-2, PBI-3, PBI-4, PBI-5 and PBI-6 films after Fenton reagent oxidation test is shown.

[0043] Figure 4 The proton conductivity and surface resistance of PBI-1, PBI-2, PBI-3, PBI-4, PBI-5 and PBI-6 films are shown.

[0044] Figure 5 The schematic diagram of intramolecular and intermolecular hydrogen bond interaction and proton transport path is shown. DETAILED DESCRIPTION

[0045] The following examples further illustrate the application and are not to be construed as limiting it. The examples do not include detailed descriptions of conventional methods, which are well known to those of ordinary skill in the art and are described in a number of publications.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In addition, any method and material similar or equivalent to those described herein can be used in the practice of the present application, and the preferred methods and materials are described below by way of example.

[0047] The experimental methods in the following examples, unless otherwise specified, are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer.

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

[0049] The synthetic route is as follows:

[0050]

[0051] The specific synthesis method is shown in the following Examples 1-4:

[0052] Example 1

[0053] In this example, 2,5-disulfonic acid terephthalic acid is used as a sulfonating agent, and a preparation method of a block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups and a proton exchange membrane is provided, which comprises the following steps:

[0054] Step one, under the atmosphere of inert gas, 866.6 g of Eaton reagent is added to the reaction kettle, the mass fraction of phosphorus pentoxide in the reagent is 7.7wt% (66.7 g), then 21.4 g (0.1 mol) of 3,3'-diaminobenzidine is added to the reaction kettle, the temperature of the reaction kettle is raised to 80°C under the stirring speed of 160 rpm for 2 h; then 9.9 g (0.05 mol) of 2,5-dihydroxyterephthalic acid is added to the reaction kettle, the stirring speed is adjusted to 100 rpm, and the temperature is raised to 120°C for 2 h; then the temperature is lowered to 80°C, 16.3 g (0.05 mol) of 2,5-disulfonic acid terephthalic acid is added to the reaction kettle, the molar ratio of 3,3'-diaminobenzidine to 2,5-dihydroxyterephthalic acid and 2,5-disulfonic acid terephthalic acid is 2:1:1, after complete dissolution, the reaction kettle is raised to 120°C for 2 h, then the stirring paddle speed is adjusted to 80 rpm, and the temperature is raised to 140°C for 3 h. After the reaction is completed, the kinematic viscosity of the viscous solution in the reaction kettle is measured to be 36642 cp.

[0055] Step two, after the reaction is completed, the viscous solution is poured into ice water for precipitation after the reaction kettle is cooled to 80°C, and saturated sodium bicarbonate is added for washing to neutralize the residual acid in the product. The obtained product is cut and washed with water and ethanol several times until the solution pH is 7.0, and finally the yellow product is placed in a 120°C vacuum oven for drying for 24 hours to obtain the block polybenzimidazole copolymer PBI-1, the yield is 97.6%, the weight average molecular weight of PBI-1 is 164720 g / mol, and the intrinsic viscosity is 3.59 dL / g. The structure of PBI-1 is as follows:

[0056] .

[0057] Step three, 10 g of PBI-1 block copolymer was dissolved in 66.7 g of N,N- dimethylacetamide to obtain a film-forming solution containing 15wt% of the block copolymer, which was then poured onto a smooth glass plate, and the glass plate was placed in an 80℃ oven for solvent evaporation for 24 h to obtain a PBI-1 film with a thickness of 25 μm and a uniform surface. The film was soaked in a 1.0 M sulfuric acid solution for 24 h for proton exchange, then the residual acid on the surface of the film was washed with deionized water, and finally it was placed in a 100℃ oven for drying for 24 h.

[0058] Example 2

[0059] In this embodiment, 3,3'-disulfo-[1,1'-biphenyl]-4,4'-dicarboxylic acid is used as a sulfonating agent, and a block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups and a method for preparing a proton exchange membrane thereof are provided, which comprises the following steps:

[0060] Step one, under an inert gas atmosphere, 866.6 g of Eaton reagent was added to the reaction kettle, and the mass fraction of phosphorus pentoxide in the reagent was 7.7wt% (66.7 g), then 21.4 g (0.1 mol) of 3,3'-diaminobenzidine was added to the reaction kettle, and the temperature of the reaction kettle was raised to 80℃ under a stirring speed of 160 rpm for 2 h; then 9.9 g (0.05 mol) of 2,5-dihydroxyterephthalic acid was added to the reaction kettle, the stirring speed was adjusted to 100 rpm, and the solution was stirred for 2 h, and then the temperature was raised to 120℃ for prepolymerization for 2 h; then the temperature was lowered to 80℃, 20.1 g (0.05 mol) of 3,3'-disulfo-[1,1'-biphenyl]-4,4'-dicarboxylic acid was added to the reaction kettle, and the molar ratio of 3,3'-diaminobenzidine to 2,5-dihydroxyterephthalic acid and 3,3'-disulfo-[1,1'-biphenyl]-4,4'-dicarboxylic acid was 2:1:1, after complete dissolution, the reaction kettle was heated to 120℃ for prepolymerization for 2 h, then the stirring paddle speed was 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 reaction kettle was measured to be 37926 cp.

[0061] Step two, after the reaction is completed, the viscous solution is poured into ice water to precipitate after the reactor is cooled to 80°C, and saturated sodium bicarbonate is added for washing to neutralize the residual acid in the product. The obtained product is cut and washed with water and ethanol several times until the solution pH = 7.0. Finally, the yellow product is placed in a 120°C vacuum oven for drying 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 three, 10 g of PBI-2 block copolymer is dissolved in 66.7 g of N,N-dimethylacetamide to obtain a film-forming solution containing 15wt% of the block copolymer. Then the film-forming solution is poured on a smooth glass plate, and the glass plate is placed in an 80°C oven for solvent evaporation for 24 h to obtain a PBI-2 film with a thickness of 25 μm and a uniform surface. The film is soaked in a 1.0 M sulfuric acid solution for 24 h for proton exchange, and then the residual acid on the surface of the film is washed with deionized water. Finally, it is placed in a 100°C oven for drying for 24 h.

[0064] Example 3

[0065] In this embodiment, 4,8-disulfonic acid-2,6-naphthalene dicarboxylic acid is used as a sulfonating agent to provide a preparation method of a block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups and a proton exchange membrane thereof, which comprises the following steps:

[0066] Step one, under an inert gas atmosphere, 866.6 g of Eaton reagent is added to the reaction kettle, and the mass fraction of phosphorus pentoxide in the reagent is 7.7wt% (66.7 g). Then 21.4 g (0.1 mol) of 3,3'-diaminobenzidine is added to the reaction kettle, and the temperature of the reaction kettle is raised to 80°C under a stirring speed of 160 rpm for 2 h. Then 9.9 g (0.05 mol) of 2,5-dihydroxyterephthalic acid is added to the reaction kettle, and the stirring speed is adjusted to 100 rpm for 2 h. Then the temperature is raised to 120°C for pre-polymerization for 2 h. Then the temperature is lowered to 80°C, and 18.8 g (0.05 mol) of 4,8-disulfonic acid-2,6-naphthalene dicarboxylic acid is added to the reaction kettle. The molar ratio of 3,3'-diaminobenzidine to 2,5-dihydroxyterephthalic acid and 4,8-disulfonic acid-2,6-naphthalene dicarboxylic acid is 2:1:1. After complete dissolution, the reaction kettle is raised to 120°C for pre-polymerization for 2 h, and then the stirring paddle speed is adjusted to 80 rpm, and the temperature is raised to 140°C for polymerization for 3 h. After the reaction is completed, the kinematic viscosity of the viscous solution in the reaction kettle is measured to be 37461 cp.

[0067] Step two, after the reaction is completed, the reaction kettle is cooled to 80°C, then the viscous solution is poured into ice water to precipitate, and saturated sodium bicarbonate is added for washing to neutralize the residual acid in the product. The obtained product is cut and washed with water and ethanol several times until the solution pH = 7.0. Finally, the yellow product is placed in a 120°C vacuum oven for drying 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] Step three, 10 g of PBI-3 block copolymer is dissolved in 66.7 g of N,N-dimethylacetamide to obtain a film-forming solution containing 15wt% of the block copolymer. Then the film-forming solution is poured on a smooth and flat glass plate, and the glass plate is placed in an 80°C oven for solvent evaporation for 24 h to obtain a PBI-3 film with a thickness of 25 μm and a uniform surface. The film is soaked in a 1.0 M sulfuric acid solution for 24 h for proton exchange, then the residual acid on the surface of the film is washed with deionized water, and finally it is placed in a 100°C oven for drying for 24 h.

[0069] Example 4

[0070] In this example, 4,4’-oxybis[3-(sulfonyl)benzoic acid] is used as a sulfonating reagent, and a method for preparing a block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups and a proton exchange membrane thereof is provided, which includes the following steps:

[0071] Step one, under inert gas atmosphere, 866.6 g of Eaton's reagent was added into a reaction kettle, in which the mass fraction of phosphorus pentoxide was 7.7wt% (66.7 g), then 21.4 g (0.1 mol) of 3,3'-diaminobenzidine was added into the reaction kettle, the temperature of the reaction kettle was increased to 80°C under the stirring speed of 160 rpm for 2 h; then 9.9 g (0.05 mol) of 2,5-dihydroxyterephthalic acid was added into the reaction kettle, the stirring speed was adjusted to 100 rpm, and the temperature was increased to 120°C for 2 h for pre-polymerization; then the temperature was decreased to 80°C, 20.9 g (0.05 mol) of 4,4'-oxybis[3-(sulfonyl)benzoic acid] was added into the reaction kettle, the molar ratio of 3,3'-diaminobenzidine to 2,5-dihydroxyterephthalic acid and 4,4'-oxybis[3-(sulfonyl)benzoic acid] was 2:1:1, after complete dissolution, the temperature of the reaction kettle was increased to 120°C for 2 h for pre-polymerization, then the stirring speed of the paddle was adjusted to 80 rpm, and the temperature was increased to 140°C for 3 h for polymerization. After the reaction was completed, the kinematic viscosity of the viscous solution in the reaction kettle was measured to be 35889 cp.

[0072] Step two, after the reaction was completed, the viscous solution was poured into ice water for precipitation after the reaction kettle was cooled to 80°C, and saturated sodium bicarbonate was added for washing to neutralize the residual acid in the product. The obtained product was cut and washed with water and ethanol several times until the solution pH was 7.0, and finally the yellow product was placed in a vacuum oven at 120°C for drying for 24 hours to obtain a block polybenzimidazole copolymer PBI-4, with a yield of 98.1%, a weight average molecular weight of PBI-3 of 154679 g / mol, and a specific viscosity of 3.51 dL / g. The structure of PBI-4 is as follows:

[0073] .

[0074] Step three, 10 g of PBI-4 block copolymer was dissolved in 66.7 g of N,N-dimethylacetamide to obtain a film-forming solution containing 15wt% of the block copolymer, then the film-forming solution was poured onto a smooth glass plate, and the glass plate was placed in an oven at 80°C for solvent evaporation for 24 h to obtain a PBI-3 film with a thickness of 25 μm and a uniform surface. The film was soaked in a 1.0 M sulfuric acid solution for 24 h for proton exchange, then the residual acid on the surface of the film was washed with deionized water, and finally it was placed in an oven at 100°C for drying for 24 h.

[0075] Comparative Example 1

[0076] The reagents used in this comparative example are the same as in Example 1, except that the synthesis is carried out using a random polymerization method. The preparation method of the random polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups and its proton exchange membrane comprises the following steps:

[0077] Step one, under an inert gas atmosphere, 866.6 g of Eaton's reagent is added to the reaction kettle, wherein the mass fraction of phosphorus pentoxide is 7.7wt% (66.7 g), 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 acid terephthalic acid are added to the reaction kettle. The temperature of the reaction kettle is raised to 80°C under a stirring speed of 160 rpm for 2 h. Then the stirring speed is adjusted to 100 rpm, and the temperature is raised to 120°C for 2 h of prepolymerization. Finally, the stirring paddle speed is adjusted to 80 rpm, and the temperature is raised to 140°C for 3 h of polymerization. After the reaction is completed, the kinematic viscosity of the viscous solution in the reaction kettle is measured to be 35461 cp.

[0078] Step two, after the reaction is completed, the viscous solution is poured into ice water for precipitation after the reaction kettle is cooled to 80°C, and saturated sodium bicarbonate is added for washing to neutralize the residual acid in the product. The obtained product is cut and washed with water and ethanol several times until the solution pH is 7.0. Finally, the yellow product is placed in a 120°C vacuum oven for drying for 24 h to obtain the random polybenzimidazole copolymer PBI-5 with a yield of 94.8%, a weight average molecular weight of PBI-5 of 153849 g / mol, and an intrinsic viscosity of 3.48 dL / g.

[0079] Step three, 10 g of the PBI-5 random copolymer is dissolved in 66.7 g of N,N-dimethylacetamide to obtain a film-forming solution containing 15wt% of the random copolymer. Then the film-forming solution is poured onto a smooth and flat glass plate, and the glass plate is placed in an 80°C oven for solvent evaporation for 24 h to obtain a PBI-5 membrane with a thickness of 25 μm and a uniform surface. The membrane is soaked in a 1.0 M sulfuric acid solution for 24 h for proton exchange, and then the residual acid on the membrane surface is washed with deionized water. Finally, it is placed in a 100°C oven for drying for 24 h.

[0080] Comparative Example 2

[0081] The reagents in this comparative example are compared with Example 1, and 2,5-dihydroxyterephthalic acid is not added. The preparation method of a linear sulfonated polybenzimidazole polymer (containing no hydroxyl groups) and its proton exchange membrane comprises the following steps:

[0082] Step one, under inert gas atmosphere, 866.6 g of Eaton's reagent was added into a reaction kettle, in which the mass fraction of phosphorus pentoxide was 7.7wt% (66.7 g), then 21.4 g (0.1 mol) of 3,3'-diaminobenzidine was added into the reaction kettle, the temperature of the reaction kettle was increased to 80℃ under the stirring speed of 160 rpm for 2 h; then 16.3 g (0.05 mol) of 2,5-dicarboxylic acid terephthalic acid was added into the reaction kettle, the stirring speed was adjusted to 100 rpm, and the solution was stirred for 2 h, then the temperature was increased to 120℃ for 2 h of pre-polymerization; then the temperature was decreased to 80℃, 16.3 g (0.05 mol) of 2,5-dicarboxylic acid terephthalic acid was added into the reaction kettle, the molar ratio of 3,3'-diaminobenzidine to 2,5-dicarboxylic acid terephthalic acid was 1:1, after complete dissolution, the reaction kettle was heated to 120℃ for 2 h of pre-polymerization, then the stirring speed of the paddle was adjusted to 80 rpm, and the temperature was increased to 140℃ for 3 h of polymerization. After the reaction was completed, the kinematic viscosity of the viscous solution in the reaction kettle was measured to be 35028 cp.

[0083] Step two, after the reaction was completed, the viscous solution was poured into ice water for precipitation after the reaction kettle was cooled to 80℃, and saturated sodium bicarbonate was added for washing to neutralize the residual acid in the product. The obtained product was cut and washed with water and ethanol several times until the solution pH was 7.0, and finally the yellow product was placed in a 120℃ vacuum oven for drying for 24 hours to obtain a linear polybenzimidazole polymer PBI-6 with a yield of 95.3%, and the weight average molecular weight of PBI-6 was 150247 g / mol and the intrinsic viscosity was 3.42 dL / g.

[0084] Step three, 10 g of PBI-6 linear polymer was dissolved in 66.7 g of N,N-dimethylacetamide to obtain a film-forming solution containing 15wt% of linear polymer, then the film-forming solution was poured onto a smooth glass plate, and the glass plate was placed in an 80℃ oven for solvent evaporation for 24 h to obtain a PBI-6 film with a thickness of 25 μm and a uniform surface. The film was soaked in a 1.0 M sulfuric acid solution for 24 h for proton exchange, then the residual acid on the surface of the film was washed with deionized water, and finally it was placed in a 100℃ oven for drying for 24 h.

[0085] II. Performance test method

[0086] The PBI-1~PBI-4 prepared in Experimental Examples 1-4, and the PBI-5, PBI-6 samples prepared in Comparative Examples 1-2 were tested for kinematic viscosity, intrinsic viscosity, molecular weight, water absorption and swelling rate, mechanical properties, proton conductivity and surface resistance, and the oxidation stability was also investigated. The specific detection methods are as follows:

[0087] 2.1 Kinetic viscosity, intrinsic viscosity, molecular weight

[0088] The kinetic 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; the molecular weight and distribution of the synthesized copolymer were tested by gel permeation chromatography.

[0089] 2.2 Water uptake and swelling ratio

[0090] The prepared film sample was placed in a vacuum drying oven at 60°C for continuous drying for 24 hours. The dry weight of the sample was immediately weighed after taking it out, recorded as M dry , and the diameter of the film at this time was measured, recorded as D dry . Subsequently, the sample was immersed in deionized water for 24 hours. After soaking was completed, the water on the surface of the film was gently absorbed with filter paper, and the wet film mass M wet was quickly weighed, and its wet diameter D wet was measured. To improve the reliability of the experimental results and reduce the operation error, each sample was measured in triplicate, and the final data was the average of the three measurements. The water uptake (WU) and swelling ratio (SR) of the film were calculated according to the following two formulas, respectively:

[0091]

[0092]

[0093] wherein M dry is the dry weight of the film, M wet is the wet weight of the film after water absorption. D dry is the diameter of the film in the dry state, and D wet is the diameter of the film in the wet state.

[0094] 2.3 Mechanical property test

[0095] The mechanical properties of the copolymer film were tested by an electronic universal testing machine. After the film was cut and trimmed to the appropriate test size, its length, width, height, and thickness were measured, and a tensile test was performed at a loading rate of 10 mm / min to obtain the tensile strength and elongation at break of the film.

[0096] 2.4 Proton conductivity and area resistance

[0097] The proton conductivity (σ) and area resistance (AR) of various films were measured by electrochemical impedance spectroscopy. The frequency range of the test was between 10 -2 -10 6 Hz, and the alternating current amplitude was 5 mV. The calculation formulas of the proton conductivity and the area resistance are as follows:

[0098]

[0099] wherein σ is the proton conductivity of the membrane (mS cm -1 ), L is the length of the membrane (cm), A is the cross-sectional area of the membrane sample (cm 2 ), and R is the resistance value obtained by electrochemical impedance spectroscopy fitting (Ω).

[0100] 2.5 Oxidative stability

[0101] The prepared membrane samples were immersed in Fenton reagent (3% H2O2+ 4 ppm Fe 2+ ) at 80°C, and after 24 h, the membranes were taken out and washed with deionized water, and then placed in an 80°C oven to dry for 1 h, and the weight was recorded. The mass retention rate was calculated according to the following formula:

[0102]

[0103] wherein M1 is the mass of the membrane before immersion, and M2 is the mass of the membrane after immersion and drying.

[0104] III. Results analysis

[0105] 3.1 Kinetic viscosity, intrinsic viscosity, molecular weight and solubility

[0106] The test results of the examples and comparative examples are summarized in Table 1 below:

[0107] Table 1 Summary of various parameters of examples and comparative examples

[0108]

[0109] From the data in Table 1, it can be seen that the block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups provided by the present application successfully realizes the controllable synthesis of ultrahigh molecular weight polymer, and the intrinsic viscosity of the copolymer in Examples 1-4 is more than 3.5 dL / g, and the weight average molecular weight reaches more than 150000 g / mol. Examples 2 and 3 with higher molecular weight are more easily soluble in polar solvent DMAC, which is due to the effective destruction of the close packing of the polymer chain by introducing large steric sulfonated monomers, increasing the free volume of the copolymer, thereby maintaining excellent mechanical properties while imparting excellent solution processing properties to the material. In addition, compared with the random copolymer structure of Comparative Example 1, the block structure of the present application can obtain a higher molecular weight; and Comparative Example 2 without hydroxyl is more difficult to dissolve, which also proves the key role of hydroxyl in promoting polymerization and optimizing solubility. The present application provides a new polymer synthesis strategy, which fundamentally solves the technical problem that high molecular weight and excellent solubility are difficult to be compatible, and shows great application potential.

[0110] 3.2 Water absorption and swelling rate

[0111] Figure 1 The results of the water uptake and swelling ratio tests of PBI-1, PBI-2, PBI-3, PBI-4, PBI-5 and PBI-6 membranes are shown in the figure. As shown in the figure, PBI-1~4 have higher water uptake and better swelling resistance than PBI-5~6, among which PBI-2 and PBI-3 have water uptake of 28.97% and 30.28% and swelling ratio of only 15.14% and 16.21% respectively. This is because the block copolymer microphase separation structure forms a size-stable and interconnected hydrophilic region that can absorb a large amount of water molecules, while the film is constrained by the rigid hydrophobic backbone of the polymer, thereby avoiding excessive swelling on a macroscopic scale. In addition, the dynamic hydrogen bond network constructed by hydroxyl, sulfonic acid group and imidazole ring further strengthens the stability of the hydrophilic region and inhibits the swelling of the membrane. The swelling ratio of PBI-5 rises to 25.28%, which indicates that the microstructure formed by random copolymerization is loose and disordered, and cannot maintain size stability after water absorption. PBI-6 shows lower water uptake and higher swelling ratio, which proves that due to the lack of hydroxyl groups, it cannot form an excellent hydrogen bond network, making its hydrophilicity lower and unable to maintain size stability.

[0112] 3.3 Mechanical properties

[0113] Figure 2 The results of the tensile strength and elongation at break tests of PBI-1, PBI-2, PBI-3, PBI-4, PBI-5 and PBI-6 membranes are shown in the figure. As shown in the figure, all examples exhibit better comprehensive mechanical properties than the comparative examples, among which PBI-2 and PBI-3 with rigid biphenyl and naphthalene ring structure have a tensile strength of up to 124.6 MPa and 117.9 MPa; PBI-4 has more flexible ether bonds in the molecule, making the film more ductile and having the highest elongation at break (18.13%). This is due to the successful synthesis of ultrahigh molecular weight copolymer by block design and selection of rigid monomers, and the reinforcing and toughening effect provided by the dense hydrogen bond network.

[0114] 3.4 Oxidative stability

[0115] Figure 3The mass retention of PBI-1, PBI-2, PBI-3, PBI-4, PBI-5 and PBI-6 membranes after Fenton reagent oxidation test is shown. As shown in the figure, PBI-2 still has a mass retention of 92.14% after 24 h oxidation test, while the random copolymer PBI-5 and the PBI-6 without hydroxyl group only have a mass retention of 82.14% and 80.09%, respectively. In the examples, the regular block microphase separation forms a dense and stable polymer aggregate state, which can effectively hinder the penetration and oxidation of the oxidation medium, and in addition, the dynamic hydrogen bond network constructed by hydroxyl, sulfonic acid group and imidazole ring can efficiently neutralize the strong destructive ·OH free radicals generated in the Fenton reaction, significantly delaying the oxidation degradation process of the polymer main chain.

[0116] 3.5 Proton conductivity and area resistance

[0117] Figure 4 The schematic diagram of PBI-1, PBI-2, PBI-3, PBI-4, PBI-5 and PBI-6 membranes is shown. As shown in the figure, all examples exhibit excellent characteristics of high proton conductivity and low area resistance, among which the proton conductivity of PBI-3 membrane reaches 65.47 mS / cm, and its area resistance is as low as 0.061 Ω / cm 2 . This is due to the large steric hindrance effect brought by the naphthalene ring sulfonated monomer, which destroys the close packing of the molecular chain and widens the ion transmission channel. In addition, the synergistic effect of hydroxyl, sulfonic acid group and imidazole ring constructs a dense and continuous hydrogen bond network, providing abundant proton exchange sites, thereby realizing efficient proton conduction. In contrast, PBI-5 (random copolymer) cannot form a connected proton transmission channel due to the disordered distribution of hydrophilic groups, resulting in a significantly lower conductivity of 47.67 mS / cm; and the high resistance (0.132 Ω / cm 2 ) of PBI-6 (without hydroxyl group) also shows that hydroxyl plays an important role in perfecting the hydrogen bond network and optimizing the proton transmission path.

[0118] The above results can be explained by Figure 5 . Figure 5 The multiple hydrogen bond network structure formed in the block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups is shown. As shown in the figure, the phenolic hydroxyl (-OH), sulfonic acid group (-SO3H) and imidazole ring (N-H) in the polymer chain are connected to each other through multiple paths, forming a dense and stable dynamic hydrogen bond network. The proton transmission path indicated in the figure expresses the proton (H +) By means of hydrogen bond network, efficient proton transport is realized through Grotthuss mechanism. This dynamic hydrogen bond network, which is constructed by the synergistic effect of hydroxyl, sulfonic acid group and imidazole ring, not only provides continuous and abundant proton transport channels for protons, significantly improving the proton conductivity, but also acts as a reversible cross-linking structure, effectively inhibiting the excessive swelling of the membrane in water, ensuring the dimensional and mechanical stability of the membrane material during use.

[0119] Therefore, the innovation points of the present application are as follows:

[0120] (1) By precise molecular design, a block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups is synthesized.

[0121] (2) The two hydrophilic groups of hydroxyl and sulfonic acid groups introduced in the polymer main chain cooperatively form a dense hydrogen bond network with the imidazole ring, significantly improving the proton conductivity while maintaining the structural stability of the membrane.

[0122] (3) The sulfonated diacid monomer with large steric effect in the polymer main chain effectively destroys the close packing of the polymer molecular chain, reduces the interchain interaction, and increases the free volume, significantly improving the solubility of the polymer in organic solvents while synthesizing high molecular weight polymers.

[0123] The unexplained part involved in the present application is the same as the prior art or is realized by using the prior art. The applicant declares that the present application illustrates the detailed method of the present application by the above-mentioned embodiments, but the present application is not limited to the above-mentioned detailed method, i.e. it does not mean that the present application must rely on the above-mentioned detailed method to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of each raw material of the product of the present application, addition of auxiliary ingredients, selection of specific methods, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A process for the preparation of a hydroxyl and sulfonic acid group containing block polybenzimidazole copolymer, characterized by, Comprising the following steps: Step (1): under the atmosphere of inert gas, Eaton's reagent and 3,3'-diaminobenzidine are added into a reaction kettle, the stirring paddle speed is set as n1, the reaction kettle is heated to t1 to make it dissolve; then 2,5-dihydroxyterephthalic acid is added into the reaction kettle, the stirring paddle speed is adjusted to n2, after it is completely dissolved, the reaction temperature is raised to t2 for pre-polymerization; Then the temperature is lowered to t1, the sulfonic acid group-containing dicarboxylic acid monomer is added into the reaction kettle, after it is completely dissolved, it is heated to t2 for pre-polymerization, then the stirring paddle speed is adjusted to n3, heated to t3 for polymerization, Wherein, the sulfonic acid group-containing dicarboxylic acid monomer is selected from any one of 2,5-disulfonic terephthalic acid, 3,3'-disulfide-[1,1'-biphenyl]-4,4'-dicarboxylic acid, 4,8-disulfonic-2,6-naphthalene dicarboxylic acid, 4,4'-oxybis[3-(sulfonyl)benzoic acid], The molar ratio of 3,3'-diaminobenzidine to 2,5-dihydroxyterephthalic acid and the sulfonic acid group-containing dicarboxylic acid monomer is 2:1:1, The stirring paddle speed n1 is 150-170 rpm, n2 is 90-110 rpm, n3 is 70-90 rpm; the dissolution temperature t1 is 70-90℃, the pre-polymerization temperature t2 is 110-130℃, and the polymerization temperature t3 is 130-150℃; Step (2): after the reaction is completed, the reaction kettle is cooled to t1 and the viscous solution is poured into ice water for precipitation, and lye is added for washing to neutralize the residual acid in the product, then the solution is washed with water and ethanol for several times, and finally dried in a vacuum oven at 120℃ to obtain a block polybenzimidazole copolymer.

2. The preparation method of the block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups according to claim 1, characterized in that: wherein In step (1), the Eaton's reagent is a mixture of phosphorus pentoxide and methane sulfonic acid, wherein the mass fraction of phosphorus pentoxide is 7.2-8.2 wt %; The pre-polymerization time is 2-3h, and the polymerization time is 3-4h.

3. The preparation method of the block polybenzimidazole copolymer containing hydroxyl and sulfonic acid groups according to claim 1, characterized in that: wherein, In step (2), the kinematic viscosity of the viscous solution is 35000-40000 cp; The lye 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 is washed with lye, water and ethanol until the pH value is 7.0; The drying time is 24h.

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

5. The hydroxyl- and sulfonic acid group-containing block polybenzimidazole copolymer according to claim 4, characterized by, The intrinsic viscosity is ≥3.0 dL / g, the weight average molecular weight is 150000-200000 g / mol, and the polydispersity index is 1.5-2.

0.

6. A method for the preparation of a proton membrane, characterized in that, The hydroxyl and sulfonic acid group-containing block polybenzimidazole copolymer is prepared according to any one of claims 4-5, and the preparation steps are as follows: the block polybenzimidazole copolymer is dissolved in an aprotic polar organic solvent to obtain a film-forming solution containing the block polybenzimidazole copolymer at 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 oven at 80°C for solvent evaporation, after drying, the film is peeled off from the glass plate, then the film is immersed in an acid solution for proton exchange, then the surface residual acid is washed away with deionized water, and the film is dried in an oven at 100°C to obtain a hydroxyl and sulfonic acid group-containing block polybenzimidazole copolymer proton membrane.

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

8. A proton membrane characterized in that, The method for preparing the proton membrane according to claim 6 or 7 is used.

9. An energy storage battery separator, characterized by, The hydroxyl and sulfonic acid group-containing block polybenzimidazole copolymer according to claim 4 or 5 is used, or the proton membrane according to claim 8 is used as an energy storage battery separator.

10. An energy storage cell, characterized by The energy storage battery separator according to claim 9 is used. The energy storage battery separator according to claim 9 is used.

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