A polybenzimidazole and a method for preparing and using the same

Abstract

The present application relates to the technical field of polymer preparation, and provides a polybenzimidazole and a preparation method and application thereof.The present application forms a mixed solvent system by compounding PPA and MSA, improves the viscosity problem of a traditional single solvent system by the synergistic effect of a phosphorus pentoxide cosolvent, improves the solubility and mass transfer efficiency of the reaction system to diamine and diacid monomers, and lays a foundation for the full performance of polycondensation reaction; the mixed solvent system formed by compounding PPA and MSA not only solves the inherent defects of the pure PPA system, such as high viscosity, high reaction temperature and limited monomer diffusion, but also makes up for the short board of the pure MSA system, such as insufficient catalytic activity, realizes the synergistic balance of catalytic activity and mass transfer efficiency, completes the polycondensation under relatively low temperature conditions, significantly reduces the process energy consumption, greatly improves the product molecular weight and batch consistency, and the obtained polybenzimidazole can be used in the fields of proton exchange membranes, diaphragms and the like.

Description

Technical Field

[0001] This invention relates to the field of polymer preparation technology, and in particular to a polybenzimidazole, its preparation method, and its applications. Background Technology

[0002] Polybenzimidazole (PBI) is a class of aromatic heterocyclic high-performance polymers containing imidazole rings. The imidazole rings in its molecular structure endow the material with excellent heat resistance, chemical corrosion resistance, electrical insulation and mechanical strength. The material is non-flammable and can work stably in high-temperature environments. It is a core membrane material for high-temperature proton exchange membrane fuel cells, flow batteries and water electrolysis for hydrogen production. It also has important application value in aerospace, chemical corrosion protection, and electronic and electrical fields.

[0003] Traditional synthesis processes for polybenzimidazoles (such as mPBI, ABPBI, and pPBI) are based on a single solvent system, the most representative of which is the pure polyphosphoric acid (PPA) system. For example, patents such as CN202310677056.X disclose a process for polycondensation of 3,3',4,4'-biphenyltetramine with diacid monomers at 180-250℃ using pure polyphosphoric acid as the reaction medium. Although this method can achieve the synthesis of polybenzimidazole, it has significant technical defects: First, the viscosity of the pure PPA system is extremely high, resulting in low mass transfer efficiency during the reaction, limited solid content of the reactants, low production efficiency, and difficulty in adapting to large-scale continuous production; Second, pure PPA has poor compatibility with some diacid monomers, especially those containing electron-withdrawing groups, which easily leads to incomplete reaction and affects product yield and purity; Third, the excessive viscosity of the reaction system makes product collection difficult and subsequent post-processing steps such as neutralization and washing cumbersome, increasing the cost of commercial production; Fourth, the excessive viscosity of the reaction system also makes it difficult to increase the molecular weight of PBI, affecting the mechanical tensile properties of the membrane products.

[0004] In summary, existing polybenzimidazole synthesis processes using single solvent systems generally suffer from low mass transfer efficiency, poor monomer compatibility, cumbersome post-processing, and high production costs, severely limiting the large-scale application and market promotion of polybenzimidazole materials. To address these technical problems, it is urgent to develop a new polybenzimidazole synthesis method that optimizes the reaction solvent system, overcomes the performance bottlenecks of single solvents, improves reaction mass transfer efficiency and monomer compatibility, and achieves high-performance, high-yield, and efficient synthesis of the product.

[0005] Based on this, this patent application is filed. Summary of the Invention

[0006] This invention addresses the technical problems of excessive viscosity, low mass transfer efficiency, and limited reaction conditions inherent in traditional polybenzimidazole synthesis processes using single solvent systems. It provides a polybenzimidazole synthesis method based on a polyphosphoric acid-methanesulfonic acid mixed solvent. By constructing a mixed solvent system using polyphosphoric acid (PPA) and methanesulfonic acid (MSA), the viscosity of the reaction system is precisely controlled. This solves the inherent defects of the pure PPA system, such as high viscosity, high reaction temperature, and limited monomer diffusion, while also compensating for the insufficient catalytic activity of the pure MSA system. This achieves a synergistic balance between catalytic activity and mass transfer efficiency, enabling polycondensation to be completed at relatively low temperatures, significantly reducing process energy consumption, and greatly improving the molecular weight and batch consistency of the product. The resulting polybenzimidazole, such as mPBI, can reach a molecular weight of up to 84211 g / mol.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing polybenzimidazole, comprising the following steps:

[0009] Using diamine and diacid as reactants, polyphosphoric acid and methanesulfonic acid as solvents, and phosphorus pentoxide as a co-solvent, polybenzimidazole was obtained by polycondensation reaction under a protective atmosphere, followed by water precipitation, washing, and drying.

[0010] The mass ratio of the polyphosphoric acid to the methanesulfonic acid is (2~8):(2~8).

[0011] Preferably, the method for preparing the polybenzimidazole includes the following steps:

[0012] Polyphosphoric acid is mixed with methanesulfonic acid to obtain a solvent;

[0013] Add phosphorus pentoxide to the solvent and stir until the phosphorus pentoxide dissolves to obtain a mixture;

[0014] Diamine and diacid are added to the mixture, and polycondensation reaction is carried out under a protective atmosphere to obtain the polycondensation product. The polycondensation product is added to water, and water precipitation is used to obtain the crude product. The crude product is washed and dried to obtain polybenzimidazole.

[0015] Preferably, the polycondensation reaction temperature is 80~220℃ and the time is 1~25 h.

[0016] Preferably, the diamine includes at least one of 3,3',4,4'-biphenyltetramine and 3,4-diaminobenzoic acid;

[0017] The dicarboxylic acid includes at least one of isophthalic acid, terephthalic acid, 4,4'-diphenyl ether dicarboxylic acid, pyridine-3,5-dicarboxylic acid, pyridine-2,5-dicarboxylic acid, pyridine-2,6-dicarboxylic acid, pyridine-3,4-dicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2-sulfonic acid terephthalic acid, 2,5-dihydroxyterephthalic acid, 2-aminoterephthalic acid, 4,4'-diphenyl sulfone dicarboxylic acid, 4,4'-(hexafluoroisopropyl)dibenzoic acid, alkane dicarboxylic acid with 4 to 16 carbon atoms, and fluorinated alkane dicarboxylic acid with 4 to 16 carbon atoms.

[0018] Preferably, the mass-to-volume ratio of phosphorus pentoxide to solvent is (50~200) g:1 L.

[0019] Preferably, the molar ratio of the diamine to the diacid is 1:1, and the sum of the masses of the diamine and the diacid to the volume ratio of the solvent is (20~300) g:1 L.

[0020] Preferably, the crude product is washed sequentially with sodium bicarbonate aqueous solution and deionized water until neutral, and then dried to obtain polybenzimidazole.

[0021] Preferably, the drying temperature is 80~200℃ and the drying time is 1~50 h;

[0022] The protective atmosphere includes at least one of nitrogen, helium, neon, and argon.

[0023] Secondly, the present invention also provides a polybenzimidazole, which is prepared by the aforementioned preparation method.

[0024] Thirdly, the present invention also provides the application of the aforementioned polybenzimidazole in the preparation of proton exchange membranes, membrane materials, vanadium redox batteries, insulating materials, high-temperature resistant protective coatings, and corrosion-resistant sealing materials.

[0025] The method for preparing polybenzimidazole of the present invention has the following advantages compared with the prior art:

[0026] The method for preparing polybenzimidazole of the present invention utilizes a mixed solvent system formed by compounding polyphosphoric acid (PPA) and methanesulfonic acid (MSA). Combined with the synergistic effect of phosphorus pentoxide as a co-solvent, this method improves the viscosity problem of traditional single solvent systems, enhances the solubility and mass transfer efficiency of the reaction system for diamine and diacid monomers, and lays the foundation for the full conduct of the polycondensation reaction. The mixed solvent system constructed by compounding PPA and MSA precisely controls the viscosity of the reaction system, solving the inherent defects of high viscosity, high reaction temperature, and limited monomer diffusion in the pure PPA system, while also compensating for the insufficient catalytic activity of the pure MSA system. This achieves a synergistic balance between catalytic activity and mass transfer efficiency, enabling polycondensation to be completed at relatively low temperatures, significantly reducing process energy consumption, and greatly improving the molecular weight and batch consistency of the product. Furthermore, the heating polycondensation is carried out under a protective atmosphere, effectively preventing oxidation of the reaction system and monomers, ensuring the directional conduction of the polycondensation reaction. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 The mPBI resin synthesized in Example 1 of this invention 1 HNMR spectrum;

[0029] Figure 2 This is a photograph of the mPBI resin synthesized in Example 1 of the present invention.

[0030] Figure 3 This is a photograph of the membrane prepared using mPBI resin in Example 4 of the present invention.

[0031] Figure 4 Thermogravimetric analysis (TGA) results of the pPBI resin synthesized in Example 3 of this invention;

[0032] Figure 5 This is a particle size distribution diagram of the mPBI resin synthesized in Example 1 of the present invention after grinding.

[0033] Figure 6 The all-vanadium redox flow battery assembled using the membrane prepared with mPBI resin in Example 4 of this invention operates at 40 mA cm⁻¹. -2 80 mA cm -2 and 160 mA cm -2 Charge-discharge curves at current density. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0035] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single digits within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0036] This application provides a method for preparing polybenzimidazole, comprising the following steps:

[0037] Using diamine and diacid as reactants, polyphosphoric acid and methanesulfonic acid as solvents, and phosphorus pentoxide as a co-solvent, polybenzimidazole was obtained by polycondensation reaction under a protective atmosphere, followed by water precipitation, washing, and drying.

[0038] The mass ratio of polyphosphoric acid to methanesulfonic acid is (2~8):(2~8). By adjusting the ratio of the two, the physicochemical properties of the solvent system are optimized to meet the requirements of polybenzimidazole polycondensation reaction.

[0039] This invention uses a mixed solvent of polyphosphoric acid (PPA) and methanesulfonic acid (MSA) as the reaction medium and phosphorus pentoxide as the co-solvent. Polybenzimidazole is obtained through heating, polycondensation, precipitation, washing, and drying. Compared with traditional single-solvent systems of pure PPA and pure MSA, the mixed solvent system of this invention significantly reduces system viscosity, improves mass transfer efficiency, and increases monomer solubility. It can prepare various PBI resins such as high molecular weight, highly uniform mPBI, ABPBI, and pPBI, with a shorter reaction time, making it suitable for large-scale industrial production. The obtained polybenzimidazole can be used in high-temperature proton exchange membrane fuel cells, flow batteries, water electrolysis for hydrogen production, aerospace, and chemical corrosion protection.

[0040] This invention addresses the technical problems of excessive viscosity, low mass transfer efficiency, and limited reaction conditions inherent in traditional polybenzimidazole synthesis processes using single solvent systems. It provides a polybenzimidazole synthesis method based on a polyphosphoric acid-methanesulfonic acid mixed solvent. By combining polyphosphoric acid (PPA) and methanesulfonic acid (MSA) to form a mixed solvent system, and combining this with the synergistic effect of phosphorus pentoxide as a co-solvent, the viscosity problem of traditional single solvent systems is improved. This enhances the solubility and mass transfer efficiency of the reaction system for diamine and diacid monomers, laying the foundation for the full conduct of the polycondensation reaction. The mixed solvent system constructed by combining PPA and MSA precisely controls the viscosity of the reaction system, solving the inherent defects of high viscosity, high reaction temperature, and limited monomer diffusion in the pure PPA system, while also compensating for the insufficient catalytic activity of the pure MSA system. This achieves a synergistic balance between catalytic activity and mass transfer efficiency, enabling polycondensation to be completed at relatively low temperatures, significantly reducing process energy consumption, and greatly improving product molecular weight and batch consistency. Furthermore, the heating polycondensation is carried out under a protective atmosphere, effectively preventing oxidation of the reaction system and monomers, ensuring the directional conduction of the polycondensation reaction.

[0041] In some embodiments, the preparation method of polybenzimidazole includes the following steps:

[0042] Polyphosphoric acid is mixed with methanesulfonic acid to obtain a solvent;

[0043] Add phosphorus pentoxide to the solvent and stir until the phosphorus pentoxide dissolves to obtain a mixture;

[0044] Diamine and diacid are added to the mixture, and polycondensation reaction is carried out under a protective atmosphere to obtain the polycondensation product. The polycondensation product is added to water, and water precipitation is used to obtain the crude product. The crude product is washed and dried to obtain polybenzimidazole.

[0045] In some embodiments, the polycondensation reaction temperature is 80~220℃ and the time is 1~25 h. The heating method can be either oil bath heating or microwave heating, which can be flexibly selected according to actual production needs to achieve uniform and controllable reaction temperature.

[0046] In some embodiments, the mass-volume ratio of phosphorus pentoxide to solvent is (50~200) g:1 L. Phosphorus pentoxide acts as a co-solvent, which helps to improve the reaction compatibility of the solvent system and promotes the dissolution and polycondensation reaction of the reactants.

[0047] In some embodiments, the molar ratio of diamine to diacid is 1:1, and the sum of the masses of diamine and diacid to the volume ratio of solvent is (20~300) g:1L. The monomer feeding ratio and solid content are precisely controlled to ensure the sufficiency and controllability of the polycondensation reaction.

[0048] In some embodiments, the crude product is washed sequentially with an aqueous sodium bicarbonate solution (5-6% by mass) and deionized water until neutral, and then dried to obtain polybenzimidazole.

[0049] In some embodiments, the drying temperature is 80~200℃ and the drying time is 1~50 h;

[0050] In some embodiments, the protective atmosphere includes at least one of nitrogen, helium, neon, and argon.

[0051] This invention standardizes and controls the synthesis process of polybenzimidazole by regulating and limiting the parameters of the entire process, including solvent ratio, co-solvent addition, monomer feeding ratio, polycondensation reaction temperature, washing and drying processes. Different types of polybenzimidazole can be efficiently prepared by this process, and the parameter ranges of each step of the process are widely adaptable. They can be flexibly adjusted according to actual production needs and target product characteristics, combining process stability and practicality.

[0052] In some embodiments, different polybenzimidazoles are prepared by adjusting the monomers. Specifically, the repeating structural units of polybenzimidazoles are shown below:

[0053]

[0054] In some embodiments, the diamine includes at least one of 3,3',4,4'-biphenyltetramine and 3,4-diaminobenzoic acid;

[0055] Dicarboxylic acids include at least one of isophthalic acid, terephthalic acid, 4,4'-diphenyl ether dicarboxylic acid, pyridine-3,5-dicarboxylic acid, pyridine-2,5-dicarboxylic acid, pyridine-2,6-dicarboxylic acid, pyridine-3,4-dicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2-sulfonic acid terephthalic acid, 2,5-dihydroxyterephthalic acid, 2-aminoterephthalic acid, 4,4'-diphenyl sulfone dicarboxylic acid, 4,4'-(hexafluoroisopropyl)dibenzoic acid, straight-chain (branched) alkane dicarboxylic acids with 4 to 16 carbon atoms, and straight-chain (branched) fluorinated alkane dicarboxylic acids with 4 to 16 carbon atoms.

[0056] Based on the same inventive concept, the present invention also provides a polybenzimidazole, which is prepared by the above-described preparation method.

[0057] Based on the same inventive concept, the present invention also provides an application of the above-mentioned polybenzimidazole in the preparation of proton exchange membranes, membrane materials, vanadium redox flow batteries, insulating materials, high-temperature resistant protective coatings, and corrosion-resistant sealing materials.

[0058] In some embodiments, the preparation of a membrane using the polybenzimidazole synthesized according to the present invention includes the following steps:

[0059] S1. The polybenzimidazole synthesized in this invention is mixed with N,N-dimethylacetamide (DMAc) and stirred at 70-80°C for 20-30 hours. Vacuum degassing is then performed to obtain a polybenzimidazole slurry; wherein the mass fraction of polybenzimidazole in the polybenzimidazole slurry is 10-15%.

[0060] S2. Pour the polybenzimidazole slurry from step S1 into a mold, use a scraper to coat it to form a uniform liquid film, and dry it to remove the solvent to obtain a polybenzimidazole film.

[0061] Specifically, the polybenzimidazole slurry from step S1 is poured into a mold and coated with a scraper to form a uniform liquid film. It is first dried at 60-65℃ for 2-3 hours, then at 80-85℃ for 2-3 hours, then at 100-105℃ for 4-5 hours, and finally at 120-125℃ for 2-3 hours. The solvent is removed by drying under normal pressure in a gradient process. After cooling to room temperature, it is slowly demolded. The peeled film is placed at room temperature for 24 hours to eliminate internal stress, resulting in a continuous, crack-free polybenzimidazole film with a smooth surface.

[0062] The polybenzimidazole membrane of the present invention can be used to prepare an all-vanadium redox flow battery.

[0063] The following detailed embodiments further illustrate the polybenzimidazole and its preparation method of this application. This section, in conjunction with specific embodiments, further explains the content of the present invention, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0064] The polyphosphoric acid used in the following examples is a commercially available product, specifically P815555 polyphosphoric acid purchased from Maclean's Reagents.

[0065] Example 1

[0066] This embodiment provides a method for preparing polybenzimidazole (synthesis of poly[2,2'-(m-phenylene)-5,5'-dibenzimidazole] (mPBI), including the following steps:

[0067] S1. Take 1L of polyphosphoric acid (PPA) and methanesulfonic acid (MSA) and add them to a three-necked flask to form PPA / MSA mixed solvents with mass ratios of 7:3, 5:5 and 3:7 respectively.

[0068] S2. Add 120 g of phosphorus pentoxide (phosphorus pentoxide mass-volume concentration of 120 g·L⁻¹) to the mixed solvent in step S1. -1 Under nitrogen protection, turn on the heating device (oil bath heating), raise the temperature to 120°C and stir continuously until phosphorus pentoxide is completely dissolved to obtain a uniform and transparent mixture.

[0069] S3. Add 3,3',4,4'-biphenyltetramine (CAS No. 91-95-2, chemical formula C) to the mixture from step S2 at a molar ratio of 1:1. 12 H 14 N4) and isophthalic acid (CAS No. 121-91-5, chemical formula C8H6O4), with a total mass-volume concentration of 200 g·L⁻¹. -1 Under nitrogen protection, the temperature was raised to 160-180℃ and the reaction was stirred for 14-15 hours. The system gradually became a viscous liquid, yielding the mPBI stock solution. The mPBI stock solution was poured into deionized water, and the crude product was obtained by water precipitation. The crude product was washed three times with a 5% sodium bicarbonate aqueous solution, and then repeatedly washed with deionized water until the washing water was neutral. The washed product was placed in a 100℃ oven and dried under normal pressure for 24 hours, and then dried under reduced pressure for 12 hours. After grinding, the mPBI solid product was obtained.

[0070] Furthermore, following the above method, pure polyphosphoric acid (PPA) and methanesulfonic acid (MSA) were used instead of the mixed solvent, and the polycondensation reaction temperature and time were changed. The amounts of other raw materials were the same as in Example 1. The PPA:MSA mass ratios of 7:3, 5:5, and 3:7 were designated as Experiment 1, Experiment 2, and Experiment 3, respectively. The experiments using pure polyphosphoric acid (PPA) and methanesulfonic acid (MSA) were designated as Comparative Experiment 1 and Comparative Experiment 2. The polycondensation reaction temperatures and times for each experiment are shown in Table 1 below. The viscosity of the PPA / MSA mixed solvent with different mass ratios and the molecular weight of the mPBI finally prepared using the PPA / MSA mixed solvent with different mass ratios are shown in Table 2 below.

[0071] Table 1 - Temperature and time of polycondensation reaction in each experiment

[0072]

[0073] Table 2 - Viscosities of PPA / MSA mixed solvents with different mass ratios and molecular weights of the final prepared mPBI

[0074]

[0075] As shown in Table 2 above, this invention uses a mixed solvent formed by compounding PPA and MSA to precisely control the viscosity of the reaction system: as the proportion of MSA increases, the viscosity of the system decreases linearly. The pure PPA system has the highest viscosity (3210 cp), while the pure MSA system has the lowest viscosity (39 cp). (Pure MSA has a low boiling point, which strictly limits the polycondensation reaction temperature, resulting in low reaction efficiency, insufficient degree of polymerization, and difficulty in obtaining high molecular weight products, thus failing to meet the performance requirements of high-performance membrane materials and structural components.) The viscosities of the mixed systems with mass ratios of 7:3, 5:5, and 3:7 are 2252 cp, 1619 cp, and 987 cp, respectively. The system viscosity is positively correlated with the polycondensation reaction conditions. The higher the viscosity, the higher the required reaction temperature. The pure PPA system requires a reaction temperature of 200℃, while the mixed solvent system can reduce the reaction temperature to 160~180℃. Medium viscosity ratios (5:5, 3:7) can also shorten the reaction time from 15h to 14h, significantly optimizing the process conditions and reducing energy consumption. Meanwhile, the molecular weight of the product first increases and then decreases with the viscosity of the system. Under the optimal ratio of PPA:MSA of 5:5 (viscosity 1619 cp), the molecular weight of the product reaches a peak of 84211 g / mol, which is much higher than that of pure PPA (69678 g / mol) and pure MSA (78547 g / mol) single solvent systems. This achieves a synergistic balance between catalytic activity and diffusion resistance, and combines the advantages of process economy and high product performance.

[0076] Example 2

[0077] This embodiment provides a method for preparing polybenzimidazole (synthesis of poly-2,5-benzimidazole (ABPBI)), including the following steps:

[0078] S1. Take 1L of polyphosphoric acid (PPA) and methanesulfonic acid (MSA) and add them to a three-necked flask to form a PPA / MSA mixed solvent with a mass ratio of 1:1.

[0079] S2. Add 100 g of phosphorus pentoxide (phosphorus pentoxide mass-volume concentration of 100 g·L⁻¹) to the mixed solvent in step S1. -1 Under nitrogen protection, turn on the heating device (oil bath heating), raise the temperature to 160°C and stir continuously until phosphorus pentoxide is completely dissolved to obtain a uniform and transparent mixture.

[0080] S3. Add 3,4-diaminobenzoic acid (CAS No. 619-05-6, chemical formula C7H8N2O2) and terephthalic acid (CAS No. 100-21-0, chemical formula C8H6O4) in a molar ratio of 1:1 to the mixture from step S2, with a total mass-volume concentration of 150 g·L⁻¹. -1Under nitrogen protection, the temperature was raised to 190℃ and the reaction was stirred for 12 hours to obtain a viscous ABPBI stock solution. The ABPBI stock solution was poured into deionized water, and the precipitate was obtained by water precipitation to obtain a crude product. The crude product was washed three times with a 5% sodium bicarbonate aqueous solution, and then repeatedly washed with deionized water until the washing water was neutral. The washed product was placed in a 100℃ oven and dried under normal pressure for 24 hours, and then dried under reduced pressure for 12 hours. After grinding, the solid ABPBI product was obtained.

[0081] Example 3

[0082] This embodiment provides a method for preparing polybenzimidazole (synthesis of poly[2,2'-(p-phenylene)-5,5'-dibenzimidazole] (pPBI), including the following steps:

[0083] S1. Take 1L of polyphosphoric acid (PPA) and methanesulfonic acid (MSA) and add them to a three-necked flask to form a PPA / MSA mixed solvent with a mass ratio of 4:6;

[0084] S2. Add 80 g of phosphorus pentoxide (phosphorus pentoxide mass-volume concentration of 100 g·L⁻¹) to the mixed solvent in step S1. -1 Under nitrogen protection, turn on the heating device (oil bath heating), raise the temperature to 170°C and stir continuously until phosphorus pentoxide is completely dissolved to obtain a uniform and transparent mixture.

[0085] S3. Add 3,3',4,4'-biphenyltetramine and terephthalic acid in a molar ratio of 1:1 to the mixture from step S2, with a total mass-volume concentration of 180 g·L⁻¹. -1 Under nitrogen protection, the temperature was raised to 210℃ and the reaction was stirred for 20 hours to obtain a viscous pPBI stock solution. The pPBI stock solution was poured into deionized water, and the crude product was obtained by water precipitation. The crude product was washed three times with a 5% sodium bicarbonate aqueous solution, and then repeatedly washed with deionized water until the washing water was neutral. The washed product was placed in a 100℃ oven and dried under normal pressure for 24 hours, and then dried under reduced pressure for 12 hours. After grinding, the pPBI solid product was obtained.

[0086] Example 4

[0087] This embodiment provides a method for preparing a membrane using polybenzimidazole synthesized according to the present invention, comprising the following steps:

[0088] S1. mPBI was prepared using a PPA / MSA mixed solvent with a mass ratio of 5:5 as described in Example 1.

[0089] mPBI resin and N,N-dimethylacetamide (DMAc) after drying and dehydration of molecular sieves were added to a dry three-necked flask at a mass ratio of 12.5:87.5. The flask was placed in a 70℃ constant temperature water bath and stirred and dispersed at 500 r / min for 24 h. Then, vacuum degassing was performed for 60 min to remove air bubbles from the slurry, resulting in a uniform, bubble-free mPBI slurry with good flowability. The solution of 12.5% ​​mPBI in DMAc was a brown transparent solution with high viscosity, making it easy to cast into a film.

[0090] S2. Wipe the polytetrafluoroethylene mold clean with anhydrous ethanol and dry it at 60°C to constant weight. Pour the 12.5% ​​mPBI slurry from step S1 into the mold, adjust the thickness to 30 μm with a scraper and spread it evenly to form a uniform liquid film. Place the mold in a 60°C oven and dry it for 6 h until the liquid film is initially formed. Then transfer the film and the mold to a vacuum drying oven and dry it at atmospheric pressure in a gradient program of 60°C (drying for 2 h), 80°C (drying for 2 h), 100°C (drying for 4 h), and 120°C (drying for 2 h) to remove solvent. After cooling to room temperature, slowly demold the film and place it at room temperature for 24 h to eliminate internal stress, thus obtaining a continuous, crack-free, and smooth polybenzimidazole film.

[0091] Performance testing

[0092] Figure 1 The mPBI resin synthesized in Example 1 of this invention using a PPA / MSA mixed solvent at a mass ratio of 5:5 1 HNMR spectrum.

[0093] from Figure 1 As can be seen, the characteristic peak at 13.0 ppm corresponds to the NH proton of the imidazole ring, and the multiple peaks in the range of 7.0~9.0 ppm correspond to the aromatic hydrogen of the main chain benzene ring. All signals are completely consistent with the target polymer structure, and there are no obvious impurity peaks, which proves that a polybenzimidazole resin with regular structure and excellent purity has been successfully synthesized.

[0094] Figure 2 This is a photograph of the mPBI resin synthesized using a PPA / MSA mixed solvent with a mass ratio of 5:5 in Example 1 of this invention. Figure 2 As can be seen from the data, the synthesized mPBI resin is a brown powder.

[0095] Figure 3 This is a photograph of the membrane prepared using mPBI resin in Example 4 of the present invention; from Figure 3 As can be seen from the data, the mPBI film is a brown transparent film.

[0096] Figure 4The thermogravimetric analysis (TGA) results show that pPBI resin synthesized in Example 3 of this invention undergoes only minor weight loss (mainly due to the evaporation of adsorbed water and residual solvent) in the 0~500℃ range, exhibiting excellent thermal stability. After 500℃, it gradually undergoes thermal decomposition, yet still maintains an ultra-high char rate of approximately 84% at 800℃, fully demonstrating its excellent high-temperature resistance and char-forming ability, meeting the stringent requirements of applications such as high-temperature proton exchange membranes.

[0097] Figure 5 This is the particle size distribution diagram of the mPBI resin synthesized in Example 1 of the present invention using a PPA / MSA mixed solvent with a mass ratio of 5:5, after grinding. Specifically, the mPBI synthesized in Example 1 was fed into a high-speed universal pulverizer, first coarsely pulverized at 2500 r / min for 3 min, then finely pulverized at 3500 r / min for 6 min, and then wet-sieved using a 300-mesh standard sieve with anhydrous ethanol as the dispersion medium. The sieved material was collected and dried in a vacuum drying oven at 60℃ for 6 h to remove the ethanol, finally obtaining uniformly sized mPBI fine powder. The particle size distribution results are shown below. Figure 5 And as shown in Table 3.

[0098] Table 3 - Particle size distribution of mPBI resin

[0099]

[0100] from Figure 5 As can be seen, the particle size of mPBI powder exhibits a unimodal normal distribution, with the main peak concentrated in the 10~20μm range. The particle size distribution is concentrated and exhibits excellent uniformity. From the particle size distribution data in Table 3, it can be seen that the cumulative proportion of particles smaller than 45μm reaches 87.19%, the cumulative proportion of particles smaller than 100μm reaches 98.86%, and the cumulative proportion of particles smaller than 300μm is 100%. The overall particle size is small and there are no large particle impurities. This fine and uniform particle size characteristic can significantly improve the flowability and filling properties of the powder during the hot pressing process, effectively reduce the internal porosity of the profile, and ensure the density, mechanical properties, and structural uniformity of the mPBI profile after hot pressing, fully meeting the process requirements for powder particle size in the preparation of hot-pressed profiles.

[0101] Figure 6 The vanadium redox flow battery assembled using a membrane prepared with mPBI resin, as shown in Example 4 of this invention, operates at 40 mAcm. -2 80 mA cm -2 and 160 mA cm -2 Charge-discharge curves at current density. The test procedure is as follows: First, the mPBI membrane prepared in Example 4 was immersed in a 3 M H2SO4 solution at 40°C for 24 h, and then the battery was assembled after removal; wherein, both the negative and positive electrodes are carbon felt, with an effective active area of ​​16 cm².2 The negative and positive electrodes were each immersed in 30 mL of solution containing 1.5 MV. 2+ / V 3+ 3 M H2SO4 solution and 30 mL of solution containing 1.5 M VO 2+ / VO2 + A 3 M H₂SO₄ solution. At a current density from 40 mA cm⁻¹. -2 Up to 160 mA cm -2 Within the specified range, with a voltage window from 0.8 V to 1.7 V, battery performance was tested, and the results are as follows: Figure 6 As shown.

[0102] from Figure 6 As can be seen, the battery exhibits clear and stable charge-discharge voltage plateaus at all three current density gradients, with significant distinction between the charge and discharge curves, demonstrating excellent electrochemical stability and charge-discharge reversibility under different operating conditions. With current density increasing from 40 mA cm⁻¹... -2 Increased to 160 mA cm -2 The difference between the charge and discharge curves gradually widens, the charging cutoff voltage continuously increases, and the discharging cutoff voltage decreases accordingly. Even at 160 mA cm⁻¹ -2 Under high current density conditions, the battery can still maintain a relatively stable voltage platform and retain a high usable capacity, demonstrating its low polarization resistance and excellent proton conduction capability. This effectively reduces internal ohmic losses and ensures stable output of the battery under high load.

[0103] It is understood that the technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0104] The above are merely preferred embodiments of this application, and only specifically describe the technical principles of this application. These descriptions are only for explaining the principles of this application and should not be construed as limiting the scope of protection of this application in any way. Based on this explanation, any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, as well as other specific embodiments of this application that can be conceived by those skilled in the art without creative effort, should be included within the scope of protection of this application.

Claims

1. A method for preparing polybenzimidazole, characterized in that, Includes the following steps: Polyphosphoric acid is mixed with methanesulfonic acid to obtain a solvent; Add phosphorus pentoxide to the solvent and stir until the phosphorus pentoxide dissolves to obtain a mixture; Diamine and diacid are added to the mixture, and polycondensation reaction is carried out under a protective atmosphere to obtain the polycondensation product; the polycondensation product is added to water, and water precipitation is used to obtain the crude product; the crude product is washed and dried to obtain polybenzimidazole. The mass ratio of the polyphosphoric acid to the methanesulfonic acid is (3~7):(3~7).

2. The method for preparing polybenzimidazole according to claim 1, characterized in that, The mass ratio of polyphosphoric acid to methanesulfonic acid is 5:

5.

3. The method for preparing polybenzimidazole as described in claim 1, characterized in that, The polycondensation reaction temperature is 80~220℃, and the time is 1~25 h.

4. The method for preparing polybenzimidazole according to claim 1, characterized in that, The diamine includes at least one of 3,3',4,4'-biphenyltetramine and 3,4-diaminobenzoic acid; The dicarboxylic acid includes at least one of isophthalic acid, terephthalic acid, 4,4'-diphenyl ether dicarboxylic acid, pyridine-3,5-dicarboxylic acid, pyridine-2,5-dicarboxylic acid, pyridine-2,6-dicarboxylic acid, pyridine-3,4-dicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2-sulfonic acid terephthalic acid, 2,5-dihydroxyterephthalic acid, 2-aminoterephthalic acid, 4,4'-diphenyl sulfone dicarboxylic acid, 4,4'-(hexafluoroisopropyl)dibenzoic acid, alkane dicarboxylic acid with 4 to 16 carbon atoms, and fluorinated alkane dicarboxylic acid with 4 to 16 carbon atoms.

5. The method for preparing polybenzimidazole according to claim 1, characterized in that, The mass-to-volume ratio of phosphorus pentoxide to solvent is (50~200) g:1 L.

6. The method for preparing polybenzimidazole according to claim 1, characterized in that, The molar ratio of the diamine to the diacid is 1:1, and the sum of the masses of the diamine and the diacid to the volume ratio of the solvent is (20~300) g:1 L.

7. The method for preparing polybenzimidazole according to claim 1, characterized in that, The crude product was washed sequentially with sodium bicarbonate aqueous solution and deionized water until neutral, and then dried to obtain polybenzimidazole.

8. The method for preparing polybenzimidazole according to claim 1, characterized in that, The drying temperature is 80~200℃, and the drying time is 1~50 h; The protective atmosphere includes at least one of nitrogen, helium, neon, and argon.

9. A polybenzimidazole, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 8.

10. The application of the polybenzimidazole as described in claim 9 in the preparation of proton exchange membranes, membrane materials, vanadium redox flow batteries, insulating materials, high-temperature protective coatings, and corrosion-resistant sealing materials.

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