A kind of polyimide film material of side group benzene ring high-substitution graft imidazole group and its preparation method

Abstract

The application belongs to the field of chemistry and chemical engineering, and discloses a polyimide film material with a side group benzene ring and a high substitution grafted imidazole group and a preparation method thereof.The key of the preparation method of the polyimide film material is that the aromatic diamine monomer for synthesizing a polyimide main chain contains a side group benzene ring structure, and the side group benzene ring structure has at least one electron-donating group.The electron cloud density of the benzene ring structure is improved through the electron-donating group, the difficulty of a secondary chloromethylation reaction is reduced, and the side group benzene ring is high-substitution grafted with the imidazole group.Based on the technical scheme of the application, a kind of polyimide film material is synthesized, the main chain of which is synthesized from 4,4'-(hexafluoroisopropylene) diphthalic anhydride and bis(4-amin-3,5-dimethylphenyl) toluene methane, and the carbon dioxide permeation coefficient reaches 59.3 Barrer at normal temperature, the selectivity reaches 118.6, and the polyimide film material exhibits excellent natural gas decarburization performance.

Description

Technical Field

[0001] This invention belongs to the fields of chemistry and chemical engineering, and relates to a polyimide membrane material with highly substituted side-chain benzene rings grafted with imidazole groups and its preparation method. Background Technology

[0002] Natural gas is a clean fuel that meets the "dual carbon" goals and sustainable development needs, with emissions of carbon dioxide and air pollutants far lower than coal and oil for the same calorific value. Carbon dioxide is the most common harmful impurity in natural gas, causing problems such as reduced calorific value, decreased transmission capacity, and corrosion of pipelines and equipment. According to the national standard GB17820-2018, the carbon dioxide concentration of Class I natural gas must not exceed 3.0 mol%, and the carbon dioxide concentration of Class II natural gas must not exceed 4.0 mol%. The carbon dioxide concentration of newly extracted natural gas typically exceeds 20.0 mol%, and the carbon dioxide concentration of some unconventional gas sources even exceeds 70.0 mol%. In conclusion, efficient and low-cost decarbonization is a key step in natural gas processing.

[0003] Membrane technology achieves separation based on differences in permeation rates, independent of phase equilibrium under high pressure and low temperature conditions, and holds promise for significantly reducing the cost of natural gas decarbonization. Polyimide is a commonly used industrial membrane material for natural gas decarbonization. Most aromatic polyimides exhibit good solution processing properties and can be used to prepare asymmetric membranes with ultra-thin, dense skins through phase inversion, while also possessing excellent mechanical properties. Permeability and selectivity are two key indicators for membrane materials. Higher permeability requires a smaller membrane area to process the same amount of natural gas; higher selectivity requires less energy to achieve the same natural gas separation target. In summary, polyimide membrane materials with both high permeability and high selectivity are fundamental to achieving efficient and low-cost decarbonization.

[0004] Commercially available polyimide membrane material Matrimid 5218 has a carbon dioxide permeation coefficient of approximately 8.9 Barrer and an ideal carbon dioxide / methane selectivity of approximately 41.1; P84 has a carbon dioxide permeation coefficient of less than 2.0 Barrer and an ideal carbon dioxide / methane selectivity of approximately 50.0. In the laboratory, an asymmetric resistance composite membrane prepared using Matrimid 5218 through phase inversion showed a carbon dioxide permeation rate of only 60.0 GPU, with selectivity slightly below its intrinsic level. Using simulated natural gas at a pressure of 4.0 MPaG and a carbon dioxide content of 50.0 mol%, and producing Class I natural gas according to the national standard GB17820-2018, the methane loss in the primary membrane separation system exceeded 25%, and the natural gas production capacity per square meter of membrane module was only 0.47 standard cubic meters per hour. In summary, the separation performance of existing polyimide membrane products is insufficient to meet the requirements for efficient and low-cost decarbonization of natural gas.

[0005] Introducing side-chain groups with stereochemical structures (enhancing carbon dioxide diffusion coefficient and selectivity in membrane materials by controlling segment spacing through steric hindrance) and positive charge properties (enhancing competitive adsorption through affinity, thus improving carbon dioxide solubility coefficient and solubility selectivity in membrane materials) onto polymer segments is a crucial strategy for significantly improving the natural gas decarbonization performance of polyimide membrane materials. The benzene ring in the polyimide molecule has a high electron cloud density, making it susceptible to attack by electrophilic reagents and capable of substitution reactions. For example, it undergoes substitution reactions with chloromethylating agents such as chloromethyl ether under the catalysis of Lewis acids. Based on this, side-chain groups with stereochemical structures and carbon dioxide affinity can be introduced. It is noteworthy that after the benzene ring in the polyimide molecule is replaced by chloromethyl groups, the electron cloud density decreases, significantly inhibiting secondary chloromethylation reactions and making it difficult to achieve highly substituted imidazole group grafting functionalization modification.

[0006] Addressing the critical issue that existing polyimide membrane products cannot meet the decarbonization requirements of natural gas, this invention, starting from the mechanism of chloromethylation's influence on the electron cloud density of the benzene ring, innovatively proposes a polyimide membrane material with highly substituted side-chain benzene rings grafted with imidazole groups and its preparation method. The key to the preparation method of the polyimide membrane material described in this invention lies in the fact that the aromatic diamine monomer used to synthesize the polyimide backbone contains a side-chain benzene ring structure, and this side-chain benzene ring structure has at least one electron-donating group. By specifically increasing the electron cloud density of the benzene ring structure through the electron-donating group, the difficulty of the secondary chloromethylation reaction is reduced, providing reaction sites for the highly substituted side-chain benzene rings in the polyimide membrane material to be grafted with imidazole groups. Summary of the Invention

[0007] The purpose of this invention is to provide a polyimide membrane material with highly substituted side-chain benzene rings grafted with imidazole groups and its preparation method. The method for preparing the polyimide membrane material of this invention preferably involves an aromatic diamine monomer containing a side-chain benzene ring structure with at least one electron-donating group, which is then synthesized into an aromatic polyimide backbone structure via a polycondensation reaction with an aromatic dianhydride monomer. Two chloromethyl active groups are then introduced onto the side-chain benzene ring structure via an electrophilic substitution reaction. Finally, 1-methylimidazolium is grafted onto the chloromethyl active groups to form a polyimide membrane material with highly substituted side-chain benzene rings grafted with imidazole groups, thereby improving the decarbonization performance of natural gas.

[0008] The technical solution of the present invention: A polyimide film material with highly substituted side-chain benzene rings grafted with imidazole groups has the following repeating unit structure: Wherein, A is an aromatic compound that simultaneously links two acid anhydrides, including benzene, biphenyl, 2,2-diphenylpropane, 2,2-diphenylhexafluoropropane, and diphenylmethane; B represents an aromatic compound that simultaneously connects two amino groups, including structures such as benzene, biphenyl, and diphenylmethane, but not limited to the above aromatic compounds; R is an electron-donating group with a low carbon number and a straight-chain structure, including methyl, ethyl, propyl, etc. n is the number of repeating units in the polyimide molecular chain segment.

[0009] A method for preparing a polyimide film material with highly substituted benzene rings grafted with imidazole groups, comprising the following steps: 1) Synthesis of polyimide backbone structure: An aromatic diamine monomer containing a side benzene ring structure with at least one electron-donating group is polymerized with an aromatic dianhydride monomer to form an aromatic polyimide backbone structure; the aromatic diamine monomer and the aromatic dianhydride monomer are purified by recrystallization and sublimation to a purity exceeding 99.5%; the preferred diamine monomer and dianhydride monomer are fully dissolved in an aprotic polar solvent with a boiling point exceeding 180 °C in a dry and inert atmosphere to prepare a polymerization reaction solution, with the molar ratio of the two monomers controlled in the range of 0.99 to 1.01, and the total concentration of the two monomers controlled in the range of 15.0 wt% to 45.0 wt%; one of pyridine, isoquinoline, 3-methylpyridine, m-cresol, benzoic acid, or triethanolamine is added to the polymerization reaction solution as a catalyst, with a concentration not exceeding 1.50 wt%; after the catalyst is added dropwise, the temperature of the polymerization reaction solution is raised to 120 °C to 150 °C. Within a certain temperature range, the reaction is stirred for 10 to 15 hours, then the temperature is increased to 180°C to 200°C, and the reaction is stirred for at least 5 hours. After the reaction is complete, heating is stopped and the mixture is cooled to room temperature. The polymerization solution is then slowly poured into anhydrous ethanol, precipitating fibrous polyimide. After precipitation, the fibers are soaked in anhydrous ethanol for more than 12 hours, then transferred to deionized water for more than 12 hours. After thorough washing, the polyimide fibers are vacuum dried at a temperature range of 120°C to 150°C. The schematic structure of the repeating unit of polyimide is shown below: 2) Chloromethylation of the side-chain benzene ring: The polyimide synthesized in the first step is fully dissolved in a polar chloroalkane solvent under a dry, inert atmosphere to prepare a chloromethylation reaction solution. The polyimide concentration is controlled within the range of 10.0 wt% to 20.0 wt%. A chloromethylation reagent and a catalyst, tin tetrachloride, are slowly added dropwise to the chloromethylation reaction solution. The amount of chloromethylation reagent added is no less than four times the stoichiometric amount required for complete substitution of the active benzene ring. The catalyst concentration is controlled within the range of 1.0 wt% to 3.0 wt%. After the catalyst is added, the temperature of the chloromethylation reaction solution is raised to 40 ℃ to 60 ℃. The reaction was carried out with stirring for more than 12 hours within a certain temperature range. After the reaction was completed, heating was stopped and the mixture was cooled to room temperature. The solution was then slowly poured into anhydrous ethanol, with the volume of anhydrous ethanol exceeding 10 times the volume of the chloromethylation reaction solution, causing fibrous chloromethylated polyimide to precipitate. After precipitation, the fibers were soaked in anhydrous ethanol for more than 12 hours, and then transferred to deionized water for more than 12 hours. After thorough washing, the polyimide fibers were vacuum dried within a temperature range of 40 °C to 60 °C. The schematic structure of the repeating unit of chloromethylated polyimide is shown below: 3) Imidazole intumization of chloromethylated polyimide: The chloromethylated polyimide synthesized in the second step is fully dissolved in an aprotic polar solvent under a dry, inert atmosphere, and then 1-methylimidazole is added to prepare an imidazole intumization reaction solution. The concentration of chloromethylated polyimide is controlled within the range of 5.0 wt% to 10.0 wt%, and the amount of 1-methylimidazole added is not less than 5.0 times the amount of reagent required for complete imidazole intumization of chloromethylated polyimide. The temperature of the imidazole intumization reaction solution is raised to 60 ℃ to 100 ℃. The reaction was stirred for more than 8 hours within a certain temperature range. After the reaction was completed, heating was stopped and the mixture was cooled to room temperature. Then, the imidazole intumination reaction solution was slowly poured into ethyl acetate, with the volume of ethyl acetate exceeding 10 times the volume of the imidazole intumination reaction solution, causing powdered imidazole intuminated polyimide to precipitate. After precipitation, the powder was transferred to deionized water for soaking and washing for more than 12 hours. The thoroughly washed imidazole intuminated polyimide powder was then vacuum dried within a temperature range of 80 °C to 100 °C. The schematic structure of the repeating unit of imidazole intuminated polyimide is shown below: The beneficial effects of this invention are as follows: The preparation method of this invention introduces two imidazole groups into the side benzene ring structure of polyimide through chloromethylation and imidazole ononization, which significantly improves the natural gas decarbonization performance of the membrane material through segment affinity and configuration regulation. Compared with the direct use of aromatic diamine monomers with the target structure, the post-modification functionalization strategy based on chloromethylation and imidazole ononization can significantly reduce the preparation cost of high-performance polyimide membrane materials. The preferred side benzene ring structure has at least one electron-donating group, which significantly reduces the difficulty of secondary chloromethylation reaction of the side benzene ring structure, achieves high substitution grafting of imidazole groups, and can better improve the natural gas decarbonization performance of polyimide membrane materials. An aromatic polyimide membrane material with highly substituted benzene rings grafted with imidazole groups, designed and synthesized based on the technical solution described in this invention, uses bis(4-amino-3,5-dimethylphenyl)-1-tolylmethane as the diamine monomer in the main chain and 4,4'-(hexafluoroisopropene)phthalic anhydride as the dianhydride monomer. The degree of imidazole ondenylation reaction can reach more than 150%. Under the conditions of 25 °C and 0.2 MPaG, the carbon dioxide permeability coefficient is measured to be 59.31 Barrer, and the carbon dioxide / methane permeability selectivity reaches 118.62, showing extremely high potential for natural gas decarbonization. Detailed Implementation

[0010] The specific embodiments of the present invention will be further described below in conjunction with the technical solution.

[0011] Example 1 Example 1 describes the synthesis of o-methyl polyimide from (2-methylphenyl)bis(4-amino-3,5-dimethylphenyl)methane (BAPM-o) and 4,4′-(hexafluoroisopropene)phthalic anhydride (6FDA), which was then converted into o-methylimidazolium-substituted polyimide membrane material via chloromethylation and imidazoliumization. The specific synthesis steps of the membrane material are as follows: 1) Chloromethylation of o-methyl polyimide: Under an argon atmosphere, o-methyl polyimide was dissolved in completely dehydrated 1,2-dichloroethane, with a polyimide concentration of 20.0 wt%. The reaction solution was heated and stirred at 40 °C. Chloromethyl ethyl ether and tin tetrachloride catalyst were slowly added dropwise to the preheated polyimide solution, with the amount of chloromethylated polyimide added being twice the molar amount of o-methyl polyimide, and the catalyst concentration being 1.0 wt%. The reaction system was maintained at 40 °C with stirring and heating for 24 hours. After the reaction was completed, heating was stopped and the system was cooled to room temperature. The solution was then slowly poured into anhydrous ethanol at a volume ratio of 1:10, precipitating flocculent chloromethylated polyimide. Subsequently, the chloromethylated polyimide was repeatedly soaked and washed with anhydrous ethanol and deionized water to remove the reagents remaining on the solid surface. The filtered chloromethylated product was then heated at 40 °C. Vacuum drying at ℃ yields the final chloromethylated polyimide product; the schematic structure of the repeating unit of chloromethylated polyimide is shown below: 2) Imidazole entropy of chloromethylated polyimide: Under an argon atmosphere, chloromethylated o-methyl polyimide was dissolved in completely dehydrated N,N-dimethylformamide (DMF) at a concentration of 5.0 wt%. Then, 1-methylimidazole was added to the solution at an amount 5.0 times the amount of 1-methylimidazole required for complete imidazole entropy of the chloromethylated polyimide. The polyimide solution was heated and stirred at 80 °C for a total reaction time of 8 hours. After the reaction was complete, heating was stopped and the solution was cooled to room temperature. The solution was then slowly poured into ethyl acetate at a volume ratio of 1:10. Powdered or blocky imidazole entropy polyimide membrane material precipitated out. The imidazole entropy polyimide was then repeatedly soaked and washed with deionized water. Finally, the imidazole entropy polyimide membrane material was separated by filtration and heated at 80 °C. Vacuum drying at ℃ yields the final imidazolium-indium polyimide product; the schematic structure of the repeating unit of the imidazolium-indium polyimide is shown below: The total imidazole substitution degree of the polyimide membrane material with side-group benzimidazole functionalized by the design and synthesis in Example 1 was 153% as determined by 1H NMR spectroscopy. A dense, defect-free homogeneous membrane with an average thickness of 40 μm was prepared by solution casting. The intrinsic separation performance of the membrane material was then tested by constant pressure variable volume method. The results showed that under the conditions of 25 °C and 0.2 MPa, the carbon dioxide permeability coefficient was 49.90 Barrer and the selectivity for methane was 116.05, exhibiting extremely high potential for natural gas decarbonization.

[0012] Example 2 Example 2 uses m-methyl polyimide synthesized by polymerization of (3-methylphenyl)bis(4-amino-3,5-dimethylphenyl)methane (BAPM-m) and 4,4′-(hexafluoroisopropene)phthalic anhydride (6FDA), which is then converted into m-methylimidazolium-substituted polyimide membrane material via chloromethylation and imidazoliumization. The specific synthesis steps of the membrane material are as follows: 1) Chloromethylation of m-methyl polyimide: Under an argon atmosphere, m-methyl polyimide was dissolved in completely dehydrated 1,2-dichloroethane, with a polyimide concentration of 20.0 wt%. The reaction solution was heated and stirred at 40 °C. Chloromethyl ethyl ether and tin tetrachloride catalyst were slowly added dropwise to the preheated polyimide solution, with the amount of chloromethylated polyimide added being twice the molar amount of m-methyl polyimide, and the catalyst concentration being 1.0 wt%. The reaction system was maintained at 40 °C with stirring and heating for 24 hours. After the reaction was completed, heating was stopped and the system was cooled to room temperature. The solution was then slowly poured into anhydrous ethanol at a volume ratio of 1:10, precipitating flocculent chloromethylated polyimide. Subsequently, the chloromethylated polyimide was repeatedly soaked and washed with anhydrous ethanol and deionized water to remove the reagents remaining on the solid surface. The filtered chloromethylated product was then heated at 40 °C. Vacuum drying at ℃ yields the final chloromethylated polyimide product; the schematic structure of the repeating unit of chloromethylated polyimide is shown below: 2) Imidazole entropy of chloromethylated polyimide: Under an argon atmosphere, chloromethylated m-methyl polyimide was dissolved in completely dehydrated N,N-dimethylformamide (DMF) at a concentration of 5.0 wt%. Then, 1-methylimidazole was added to the solution at an amount 5.0 times the amount of 1-methylimidazole required for complete imidazole entropy of the chloromethylated polyimide. The polyimide solution was heated and stirred at 80 °C for a total reaction time of 8 hours. After the reaction was complete, heating was stopped and the solution was cooled to room temperature. The solution was then slowly poured into ethyl acetate at a volume ratio of 1:10. Powdered or blocky imidazole entropy polyimide membrane material precipitated out. The imidazole entropy polyimide was then repeatedly soaked and washed with deionized water. Finally, the imidazole entropy polyimide membrane material was separated by filtration and heated at 80 °C. Vacuum drying at ℃ yields the final imidazolium-indium polyimide product; the schematic structure of the repeating unit of the imidazolium-indium polyimide is shown below: The total imidazole substitution degree of the benzimidazole-functionalized polyimide membrane material designed and synthesized in Example 2 was determined to be 156% by 1H NMR spectroscopy. A dense, defect-free homogeneous membrane with an average thickness of 40 μm was prepared by solution casting. The intrinsic separation performance of the membrane material was then tested by constant pressure variable volume method. The results showed that under the conditions of 25 °C and 0.2 MPa, the carbon dioxide permeability coefficient was 59.31 Barrer and the selectivity for methane was 118.62, exhibiting extremely high potential for natural gas decarbonization.

[0013] Example 3 Example 3 uses p-methyl polyimide synthesized from (4-methylphenyl)bis(4-amino-3,5-dimethylphenyl)methane (BAPM-p) and 4,4′-(hexafluoroisopropene)phthalic anhydride (6FDA), which is then converted into m-methylimidazolium-modified polyimide membrane material via chloromethylation and imidazoliumization. The specific synthesis steps of the membrane material are as follows: 1) Chloromethylation of p-methyl polyimide: Under an argon atmosphere, p-methyl polyimide was dissolved in completely dehydrated 1,2-dichloroethane, with a polyimide concentration of 20.0 wt%. The reaction solution was heated and stirred at 40 °C. Chloromethyl ethyl ether and tin tetrachloride catalyst were slowly added dropwise to the preheated polyimide solution, with the amount of chloromethylated polyimide added being twice the molar amount of m-methyl polyimide, and the catalyst concentration being 1.0 wt%. The reaction system was maintained at 40 °C with stirring and heating for 24 hours. After the reaction was completed, heating was stopped and the system was cooled to room temperature. The solution was then slowly poured into anhydrous ethanol at a volume ratio of 1:10, precipitating flocculent chloromethylated polyimide. Subsequently, the chloromethylated polyimide was repeatedly soaked and washed with anhydrous ethanol and deionized water to remove the reagents remaining on the solid surface. The filtered chloromethylated product was then heated at 40 °C. Vacuum drying at ℃ yields the final chloromethylated polyimide product; the schematic structure of the repeating unit of chloromethylated polyimide is shown below: 2) Imidazole entropy of chloromethylated polyimide: Under an argon atmosphere, chloromethylated m-methyl polyimide was dissolved in completely dehydrated N,N-dimethylformamide (DMF) at a concentration of 5.0 wt%. Then, 1-methylimidazole was added to the solution at an amount 5.0 times the amount of 1-methylimidazole required for complete imidazole entropy of the chloromethylated polyimide. The polyimide solution was heated and stirred at 80 °C for a total reaction time of 8 hours. After the reaction was complete, heating was stopped and the solution was cooled to room temperature. The solution was then slowly poured into ethyl acetate at a volume ratio of 1:10. Powdered or blocky imidazole entropy polyimide membrane material precipitated out. The imidazole entropy polyimide was then repeatedly soaked and washed with deionized water. Finally, the imidazole entropy polyimide membrane material was separated by filtration and heated at 80 °C. Vacuum drying at ℃ yields the final imidazolium-indium polyimide product; the schematic structure of the repeating unit of the imidazolium-indium polyimide is shown below: The total imidazole substitution degree of the polyimide membrane material with side-chain benzimidazole functionalized by the design and synthesis in Example 3 was 148% as determined by 1H NMR spectroscopy. A dense, defect-free homogeneous membrane with an average thickness of 40 μm was prepared by solution casting. The intrinsic separation performance of the membrane material was then tested by constant pressure variable volume method. The results showed that under the conditions of 25 °C and 0.2 MPa, the carbon dioxide permeability coefficient was 47.56 Barrer and the selectivity for methane was 96.26, showing extremely high potential for natural gas decarbonization.

[0014] Comparative Example 1 Comparative Example 1 used p-methyl polyimide synthesized by polymerization of (4-methylphenyl)bis(4-amino-3,5-dimethylphenyl)methane (BAPM-p) and 4,4′-(hexafluoroisopropene)phthalic anhydride (6FDA), which was then converted into m-methylimidazolium-modified polyimide membrane material via chloromethylation and imidazoliumization. The specific synthesis steps of the membrane material are as follows: 1) Chloromethylation of p-methyl polyimide: Under an argon atmosphere, p-methyl polyimide was dissolved in completely dehydrated 1,2-dichloroethane, with a polyimide concentration of 20.0 wt%. The reaction solution was heated and stirred at 40 °C. Chloromethyl ethyl ether and tin tetrachloride catalyst were slowly added dropwise to the preheated polyimide solution, with the amount of chloromethylated polyimide added being twice the molar amount of m-methyl polyimide, and the catalyst concentration being 1.0 wt%. The reaction system was maintained at 40 °C with stirring and heating for 24 hours. After the reaction was completed, heating was stopped and the system was cooled to room temperature. The solution was then slowly poured into anhydrous ethanol at a volume ratio of 1:10, precipitating flocculent chloromethylated polyimide. Subsequently, the chloromethylated polyimide was repeatedly soaked and washed with anhydrous ethanol and deionized water to remove the reagents remaining on the solid surface. The filtered chloromethylated product was then heated at 40 °C. Vacuum drying at ℃ yields the final chloromethylated polyimide product; the schematic structure of the repeating unit of chloromethylated polyimide is shown below: 2) Chloromethylated polyimide imidazole entropy: Under an argon atmosphere, chloromethylated p-methyl polyimide was dissolved in completely dehydrated N,N-dimethylformamide (DMF) at a concentration of 5.0 wt%. Then, 1-methylimidazole was added to the solution at an amount 5.0 times the amount of 1-methylimidazole required for complete imidazole entropy of the chloromethylated polyimide. The polyimide solution was heated and stirred at 80 °C for a total of 8 hours. After the reaction was complete, heating was stopped and the solution was cooled to room temperature. The solution was then slowly poured into ethyl acetate at a volume ratio of 1:10. Powdered or blocky imidazole entropy polyimide membrane material precipitated out. The imidazole entropy polyimide was then repeatedly soaked and washed with deionized water. Finally, the imidazole entropy polyimide membrane material was separated by filtration and heated at 80 °C. Vacuum drying at ℃ yields the final imidazolium-indium polyimide product; the schematic structure of the repeating unit of the imidazolium-indium polyimide is shown below: The total imidazole substitution degree of the polyimide membrane material with side-group benzyl methyl groups synthesized in Comparative Example 1 was determined to be 95% by 1H NMR spectroscopy. A dense, defect-free homogeneous membrane with an average thickness of 40 μm was prepared by solution casting. The intrinsic separation performance of the membrane material was then tested by constant pressure variable volume method. The results showed that under the conditions of 25 ℃ and 0.2 MPa, the carbon dioxide permeability coefficient was 46.73 Barrer and the selectivity for methane was 80.17. Due to the limitation of the total imidazole substitution degree, the overall performance was much lower than that of the imidazole functionalized polyimide membrane materials with side-group benzyl methyl groups containing electron-donating methyl groups prepared in the three examples.

Claims

1. A polyimide film material with highly substituted benzene rings grafted with imidazole groups, characterized in that, The repeating unit structure of the polyimide film material with highly substituted benzene rings grafted with imidazole groups is as follows: Among them, structure A is an aromatic compound that simultaneously links two acid anhydrides; Structure B is an aromatic compound that simultaneously connects two amino groups; Structure R is an electron-donating group with a low number of carbon atoms and a straight-chain structure, including methyl, ethyl, propyl, etc. n is the number of repeating units in the polyimide molecular chain segment.

2. The polyimide film material with highly substituted side-chain benzene rings grafted with imidazole groups according to claim 1, characterized in that, Structure A is benzene, biphenyl, 2,2-diphenylpropane, 2,2-diphenylhexafluoropropane, or diphenylmethane.

3. The polyimide film material with highly substituted side-chain benzene rings grafted with imidazole groups according to claim 1, characterized in that, Structure B is benzene, biphenyl, or diphenylmethane.

4. The polyimide film material with highly substituted side-chain benzene rings grafted with imidazole groups according to claim 1, characterized in that, The structure R is methyl, ethyl, or propyl.

5. A method for preparing a polyimide film material with highly substituted side-chain benzene rings grafted with imidazole groups as described in any one of claims 1-4, characterized in that, The steps are as follows: 1) Synthesis of polyimide backbone structure: Aromatic diamine monomers containing side benzene ring structures with at least one electron-donating group are polymerized with aromatic dianhydride monomers to form aromatic polyimide backbone structure. In a dry, inert atmosphere, aromatic diamine monomers and aromatic dianhydride monomers are fully dissolved in an aprotic polar solvent with a boiling point exceeding 180 °C to form a polymerization reaction solution. Pyridine, isoquinoline, 3-methylpyridine, m-cresol, benzoic acid, or triethanolamine are added to the polymerization reaction solution as a catalyst. After the catalyst is added dropwise, the temperature of the polymerization reaction solution is raised to 120 °C-150 °C, and the reaction is stirred for 10-15 hours. Then, the temperature is raised to 180 °C-200 °C, and the reaction is stirred for at least 5 hours. After the reaction is complete, heating is stopped and the solution is cooled to room temperature. The polymerization reaction solution is then slowly poured into anhydrous ethanol, precipitating polyimide fibers. The polyimide fibers are immersed in anhydrous ethanol for more than 12 hours, then transferred to deionized water for more than 12 hours. After thorough washing, the polyimide fibers are vacuum dried at 120 °C-150 °C. The repeating unit structure of the polyimide fibers is as follows: 2) Chloromethylation of the side-chain benzene ring structure: The polyimide fiber synthesized in step 1) was fully dissolved in a polar chloroalkane solvent under a dry and inert atmosphere to prepare a chloromethylation reaction solution; chloromethylation reagent and catalyst tin tetrachloride were slowly added dropwise to the chloromethylation reaction solution; after the catalyst was added, the temperature of the chloromethylation reaction solution was raised to the range of 40 ℃-60 ℃, and the reaction was stirred for more than 12 hours; After the reaction was complete, heating was stopped and the mixture was cooled to room temperature. The chloromethylation reaction solution was then slowly poured into anhydrous ethanol, with the volume of the anhydrous ethanol exceeding 10 times the volume of the chloromethylation reaction solution. This caused fibrous chloromethylated polyimide to precipitate. The chloromethylated polyimide was then immersed in anhydrous ethanol for more than 12 hours, followed by immersion in deionized water for more than 12 hours. After thorough washing, the chloromethylated polyimide was vacuum-dried at 40℃-60℃. The repeating unit structure of the chloromethylated polyimide is as follows: 3) Imidazole intumization of chloromethylated polyimide: The chloromethylated polyimide synthesized in step 2) was fully dissolved in an aprotic polar solvent under a dry, inert atmosphere, and then 1-methylimidazole was added to prepare an imidazole intumization reaction solution. The temperature of the imidazole intumization reaction solution was raised to 60 ℃-100 ℃, and the reaction was stirred for more than 8 hours. After the reaction was completed, heating was stopped and the solution was cooled to room temperature. Then, the imidazole intumization reaction solution was slowly poured into ethyl acetate, with the volume of ethyl acetate exceeding 10 times the volume of the imidazole intumization reaction solution, precipitating out powdered imidazole intumized polyimide. The imidazole intumized polyimide was transferred to deionized water for immersion and washing for more than 12 hours. After thorough washing, the imidazole intumized polyimide was vacuum dried at a temperature of 80 ℃-100 ℃ to obtain a polyimide film material with highly substituted benzene rings grafted with imidazole groups. The repeating unit structure of the imidazole intumized polyimide is as follows: 。 6. The preparation method according to claim 5, characterized in that, In step 1), The molar ratio of aromatic diamine monomer to aromatic dianhydride monomer is controlled within the range of 0.99-1.01, and the total concentration of aromatic diamine monomer and aromatic dianhydride monomer is controlled within the range of 15.0 wt%-45.0 wt%. The concentration of the catalyst does not exceed 1.50 wt%.

7. The preparation method according to claim 5, characterized in that, In step 2), The concentration of polyimide fiber is controlled within the range of 10.0 wt%-20.0 wt%. The amount of chloromethylating agent added shall be no less than four times the stoichiometric amount required for complete replacement of the active benzene ring; The catalyst concentration is controlled within the range of 1.0 wt% to 3.0 wt%.

8. The preparation method according to claim 5, characterized in that, In step 3), The concentration of chloromethylated polyimide was controlled within the range of 5.0 wt%-10.0 wt%. The amount of 1-methylimidazole added shall be no less than 5.0 times the amount of reagent required for the complete imidazoleization of chloromethylated polyimide.

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