Preparation method of cross-linked side chain sulfonated polyfluorene ether ketone proton exchange membrane
By preparing a cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane, sulfonation and cross-linking are achieved using phenolic hydroxyl groups as active sites, thus solving the problems of high cost and insufficient performance of existing membrane materials and realizing efficient and low-cost proton conduction and vanadium ion blocking effects.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-23
- Publication Date
- 2026-04-10
AI Technical Summary
Existing perfluorosulfonic acid proton exchange membranes are expensive and have high vanadium ion permeability in vanadium redox flow batteries, making it difficult to achieve both low vanadium ion permeability and high proton conductivity. Furthermore, existing cross-linked hydrocarbon polymer membranes have cumbersome preparation steps and insufficient stability.
A cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane was prepared by using phenolic hydroxyl groups as common active sites for grafting sulfonic acid groups and cross-linking. Sulfonation and cross-linking were achieved in the same pot through simple reaction steps to prepare a membrane with a rigid polymer backbone and flexible sulfonic acid side chains.
The prepared membrane has high proton conductivity, low vanadium ion permeability, excellent mechanical strength and thermal stability, making it suitable for large-scale production. It is low in cost, produces few by-products, and simplifies the preparation process.
Smart Images
Figure CN121824937A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of organic synthesis technology, and in particular to a method for preparing a cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane. Background Technology
[0002] Vanadium redox flow batteries (VRFBs) possess advantages such as high energy conversion efficiency, long cycle life, safety, and environmental friendliness, and are considered a promising energy storage system. The proton exchange membrane (PEM), as the core component of VRFBs, separates the positive and negative electrolytes while simultaneously conducting protons to form a circuit within the battery. An ideal PEM should possess low vanadium ion permeability, high proton conductivity, excellent chemical stability, and high mechanical strength. While commercially available perfluorosulfonic acid-based PEMs exhibit excellent proton conductivity, their high cost and high vanadium ion permeability limit their application in VRFBs. Therefore, developing novel, proprietary membrane materials that combine low vanadium ion permeability and high proton conductivity is crucial for the development of VRFBs.
[0003] Cross-linked hydrocarbon polymers (PEMs) are a class of PEMs composed of a three-dimensional network of hydrocarbon polymer backbones and ion-conducting groups. They possess advantages such as good anti-swelling properties and high mechanical strength, making them one of the most commercially promising VRFB membranes. Jing et al. (Jing Y, et al. A novel sulfonated polyimide membranes inserting flexible decane chain and rigid triptycene-based crosslinked network for vanadiumredox flow batteries. Journal of Membrane Science 2025, 734, 124454) proposed a semi-rigid / semi-flexible sulfonated polyimide PEM composed of tris(ethylene) units. The resulting membrane exhibits high proton conductivity and low vanadium ion permeability, overcoming the intrinsic challenge of traditional PEM structures that struggle to achieve both high proton conductivity and low vanadium ion permeability. However, its preparation process is complex and the imine structure used is not very stable in strongly acidic vanadium electrolytes. Xia et al. (Xia Y, et al. Crosslinked sulfonated poly(arylene ether sulfone) / sulfonated poly(vinyl alcohol) membrane formed by in situ casting and reaction for vanadium redox flow battery application. Chemical Engineering Journal 2021, 425, 131448) proposed a chloromethylated modified sulfonated polyarylene ether sulfone (PEM) crosslinked with polyvinyl alcohol. The resulting membrane exhibits excellent comprehensive performance and VRFB properties, but its preparation steps are cumbersome and the controllability of the aggregation state of sulfonic acid groups is low. An ideal preparation process for crosslinked hydrocarbon polymer (PEM) should possess characteristics such as wide availability of raw materials, fewer steps, low cost, good compatibility of the crosslinking and polymerization reactions involved, good film-forming properties, easy aggregation of ionic groups into efficient transport channels, good oxidative stability of the crosslinked backbone, and high mechanical strength. This process should improve the membrane's proton conductivity, mechanical strength, and oxidative stability while ensuring low vanadium ion permeability. How to simplify the preparation process while maintaining excellent membrane performance is a bottleneck problem in the commercialization of crosslinked hydrocarbon polymer (PEM). Summary of the Invention
[0004] The purpose of this invention is to provide a method for preparing a cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane, which has the advantages of simple process, no need for complex catalysts and suitability for large-scale production. The resulting membrane has a rigid polymer backbone and flexible sulfonic acid side chains. The rigid backbone can ensure the mechanical strength of the membrane, while the flexible sulfonic acid side chains can promote the movement and conduction of protons.
[0005] To achieve this objective, the present invention adopts the following technical solution: A method for preparing a cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane includes the following steps: (1) Add 2,7-dihydroxy-9-fluorenone to a three-necked flask, then add N,N'-dimethylacetamide, stir until completely dissolved, then add iodomethane and anhydrous potassium carbonate, and under argon protection, raise the temperature of the system to 60-80℃ and react for 8-12 hours. After the reaction is complete, slowly pour the solution into a beaker containing a large amount of deionized water to precipitate. Then filter and collect the precipitate, and dry it in a vacuum oven at 80℃ for 12-24 hours to obtain dimethoxyfluorenone; The structural formula of the obtained dimethoxyfluorenone is shown below:
[0006] (2) Add dimethoxyfluorenone and 2,6-dimethylphenol to a three-necked flask, then add toluene and stir to dissolve. Then, under argon protection, add 3-mercaptopropionic acid, followed by dropwise addition of concentrated sulfuric acid. Then, heat to 60-80℃ and react for 8-12 hours. After the reaction is complete, cool the reactants to room temperature, then pour them into deionized water to precipitate. Filter and collect the precipitate, then dry it in a vacuum oven at 90℃ for 24-48 hours. Finally, recrystallize with dichloromethane to obtain tetramethyldimethoxybisphenol fluorene. The structural formula of the obtained tetramethyldimethoxybisphenol fluorene is shown below:
[0007] (3) Tetramethyldimethoxybisphenol fluorene and 4,4'-difluorobenzophenone were added to a three-necked flask, and then N,N'-dimethylacetamide was added and stirred to dissolve. Then anhydrous potassium carbonate and toluene were added. Under the protection of argon, the system temperature was raised to 140-150℃ and reacted for 2-4 hours. The water generated in the reaction was removed by a water separator. Then the toluene was distilled off. Then the system temperature was raised to 150-170℃ and the reaction was continued for 4-8 hours. After the reaction was completed, the viscous reactants were poured into deionized water to precipitate. The precipitate was collected by filtration and dried at 80℃ under vacuum for 12-24 hours to obtain methoxy-containing polyfluorene ether ketone. The structural formula of the obtained methoxy-containing polyfluorene ether ketone is shown below:
[0008] Where n = 60 to 120; (4) Add the methoxylated polyfluorene ether ketone to a three-necked flask equipped with a constant pressure dropping funnel. Add boron tribromide to the constant pressure dropping funnel and anhydrous dichloromethane to the three-necked flask. After stirring and dissolving, lower the reaction temperature to -80°C under argon protection. Open the constant pressure dropping funnel and add boron tribromide dropwise to the three-necked flask. After the addition is complete, allow the reaction temperature to rise naturally to room temperature. Continue stirring for 18-24 hours. Then, slowly pour the reactants into a large amount of deionized water to precipitate the precipitate. Filter and collect the precipitate. Dry it in a vacuum oven at 80°C for 12-24 hours to obtain the phenolic hydroxyl-containing polyfluorene ether ketone.
[0009] The structural formula of the obtained polyfluorene ether ketone containing phenolic hydroxyl groups is shown below:
[0010] Where n = 60 to 120; (5) Add polyfluorene ether ketone containing phenolic hydroxyl groups to a three-necked flask, then add dimethyl sulfoxide, stir and dissolve under argon protection, then add NaH, stir and react for 30-60 minutes, raise the system temperature to 100-120℃, then add 1,3-propane sulfonyl lactone, stir and react for 4-12 hours, then add 4,4'-difluorobenzophenone, stir and react for 10-30 minutes, then filter the solution, cast it onto a glass plate, and place it horizontally in an oven at 100℃ for 12-24 hours. After drying and forming a membrane, immerse the glass plate in deionized water to allow the membrane to absorb water and detach, then soak the membrane in 1M dilute sulfuric acid and acidify it at 80℃ for 3-8 hours, then wash away the sulfuric acid adsorbed in the membrane with deionized water to obtain a cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane.
[0011] Preferably, in step (1), the molar amount of iodomethane is 2 to 4 times the molar amount of 2,7-dihydroxy-9-fluorenone; the molar amount of anhydrous potassium carbonate is 6 to 10 times the molar amount of 2,7-dihydroxy-9-fluorenone; N,N' Volume of dimethylacetamide: Mass of 2,7-dihydroxy-9-fluorenone = 1 mL: (0.1-0.5) g.
[0012] Preferably, in step (2), the molar ratio of dimethoxyfluorenone to 2,6-xylenol is 1:(5-10); the molar ratio of dimethoxyfluorenone to the volume of toluene to the volume of 3-mercaptopropionic acid to the volume of concentrated sulfuric acid is 1 mol:(500-2000) mL:(30-60) mL:(100-150) mL.
[0013] Preferably, in step (3), the molar amount of tetramethyldimethoxybisphenol fluorene is equal to the molar amount of 4,4'-difluorobenzophenone; the molar amount of anhydrous potassium carbonate is (1 to 4) times the molar amount of tetramethyldimethoxybisphenol fluorene; the volume of N,N'-dimethylacetamide: the mass of tetramethyldimethoxybisphenol fluorene = (5 to 15) mL: 1 g; and the volume of toluene is 5 to 35% of the volume of N,N'-dimethylacetamide.
[0014] Preferably, in step (4), the molar amount of boron tribromide is 10 to 30 times the molar amount of methoxy-containing polyfluorene ether ketone; the mass of methoxy-containing polyfluorene ether ketone: the volume of anhydrous dichloromethane = 1 g : (50 to 200) mL.
[0015] Preferably, in step (5), the molar ratio of polyfluorene ether ketone containing phenolic hydroxyl groups to NaH to 1,3-propanesulfonyl lactone to 4,4'-difluorobenzophenone is 1:(2-5):(1-4):(0.001-0.1); the mass of polyfluorene ether ketone containing phenolic hydroxyl groups to the volume of dimethyl sulfoxide is 1g:(15-25)mL.
[0016] The technical solution provided by this invention may include the following beneficial effects: 1. Raw materials are widely available and low in cost; reaction yield is high and byproducts are few.
[0017] 2. The phenolic hydroxyl group serves as a common active site for both grafting sulfonic acid groups and crosslinking, simplifying the reaction and avoiding compatibility issues between different active sites. For example, the reaction at one site may hinder the reaction at another, and vice versa. Using the phenolic hydroxyl group as a crosslinking site offers higher chemical stability compared to common double bonds, triple bonds, and amino groups. It is less prone to self-crosslinking side reactions, facilitates storage, and allows crosslinking and grafting sulfonic acid groups to proceed at the same temperature and under the same catalyst. Compared to common multi-step reactions, it effectively avoids the waste of solvents and polymers and allows for direct film deposition, simplifying the process.
[0018] 3. The grafting of sulfonic acid groups and the crosslinking of the polymer are combined into one step, followed by filtration and casting into a membrane. This process is simple, low-cost, and suitable for large-scale production. Common multi-step processes require purification of the products at each step, consume large amounts of solvent, and involve multiple drying and re-dissolving processes for membrane laying, which are time-consuming and labor-intensive. This invention effectively avoids the disadvantages of the aforementioned common multi-step processes.
[0019] 4. The polyfluorene ether ketone containing phenolic hydroxyl groups prepared in this invention has excellent grafting and crosslinking activity. Because the phenolic hydroxyl groups are on the fluorene group and there are no substituents on the ortho-benzene ring, the reaction steric hindrance is small, which can ensure the high efficiency of subsequent reactions and solve the problem of large reaction steric hindrance of common phenolic hydroxyl groups. The obtained crosslinked side-chain sulfonated polyfluorene ether ketone proton exchange membrane has a fully rigid polyfluorene ether ketone three-dimensional skeleton with high mechanical strength, good thermal stability and good crosslinking effect. The sulfonic acid groups are suspended in the rigid three-dimensional network through flexible alkyl chains, which has good mobility, is easy to aggregate, and promotes proton transport.
[0020] 5. The obtained cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane has high proton conductivity, low vanadium ion permeability, excellent mechanical stability, thermal stability and antioxidant stability, and has broad application value in the VRFB field. Attached Figure Description
[0021] Figure 1 This is the 1H NMR spectrum of dimethoxyfluorenone in Example 1 of the present invention; Figure 2 This is the 1H NMR spectrum of tetramethyldimethoxybisphenol fluorene in Example 2 of this invention; Figure 3 This is the 1H NMR spectrum of the methoxy-containing polyfluorene ether ketone in Example 3 of the present invention; Figure 4 This is the infrared spectrum of the methoxyl-containing polyfluorene ether ketone in Example 3 of the present invention; Figure 5 This is the thermogravimetric analysis curve of the methoxyl-containing polyfluorene ether ketone in Example 3 of the present invention; Figure 6 This is the 1H NMR spectrum of the polyfluorene ether ketone containing phenolic hydroxyl groups in Example 4 of the present invention; Figure 7 This is the infrared spectrum of the polyfluorene ether ketone containing phenolic hydroxyl groups in Example 4 of the present invention; Figure 8 This is the thermogravimetric analysis curve of polyfluorene ether ketone containing phenolic hydroxyl groups in Example 4 of the present invention; Figure 9 This is the infrared spectrum of the cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane in Example 5 of the present invention; Figure 10 This is the thermogravimetric analysis curve of the cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane in Example 5 of the present invention. Detailed Implementation
[0022] This technical solution provides a method for preparing a cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane. The invention first prepares a polyfluorene ether ketone containing phenolic hydroxyl groups, using the phenolic hydroxyl groups as common active sites for grafting sulfonic acid groups and cross-linking. Then, it reacts with 1,3-propanesulfonyl lactone and 4,4'-difluorobenzophenone in the same reactor. By controlling the reaction temperature, feed ratio, and reaction time, controllable sulfonation and cross-linking are achieved. The membrane is then cast and acidified to obtain the final product. This preparation method has advantages such as simple process, no need for complex catalysts, and suitability for large-scale production. The resulting membrane has a rigid polymer backbone and flexible sulfonic acid side chains. The rigid backbone ensures the mechanical strength of the membrane, while the flexible sulfonic acid side chains promote proton movement and conduction. The above-mentioned method for preparing a cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane includes the following steps: (1) Add 2,7-dihydroxy-9-fluorenone to a three-necked flask, then add N,N'-dimethylacetamide, stir until completely dissolved, then add iodomethane and anhydrous potassium carbonate, and under argon protection, raise the temperature of the system to 60-80℃ and react for 8-12 h. After the reaction is complete, slowly pour the solution into a beaker containing a large amount of deionized water to precipitate. Then filter and collect the precipitate, and dry it in a vacuum oven at 80℃ for 12-24 h to obtain dimethoxyfluorenone. The synthetic route is shown below:
[0023] (2) Dimethoxyfluorenone and 2,6-dimethylphenol were added to a three-necked flask, followed by toluene. The mixture was stirred to dissolve, and then 3-mercaptopropionic acid was added under argon protection. Concentrated sulfuric acid was then added dropwise, and the mixture was heated to 60–80 °C for 8–12 h. After the reaction was complete, the reactants were cooled to room temperature and then poured into deionized water to precipitate the precipitate. The precipitate was collected by filtration and then dried in a vacuum oven at 90 °C for 24–48 h. Finally, it was recrystallized from dichloromethane to obtain tetramethyldimethoxybisphenol fluorene. The synthetic route is shown below:
[0024] (3) Tetramethyldimethoxybisphenol fluorene and 4,4'-difluorobenzophenone were added to a three-necked flask, followed by N,N'-dimethylacetamide and stirring to dissolve. Then, anhydrous potassium carbonate and toluene were added. Under argon protection, the system temperature was raised to 140-150℃ and the reaction was carried out for 2-4 hours. The water generated in the reaction was removed by a water separator, and then the toluene was distilled off. The system temperature was then raised to 150-170℃ and the reaction was continued for 4-8 hours. After the reaction was completed, the viscous reactants were poured into deionized water to precipitate the precipitate. The precipitate was collected by filtration and dried under vacuum at 80℃ for 12-24 hours to obtain methoxy-containing polyfluorene ether ketone. The synthetic route is shown below:
[0025] Where n = 60 to 120.
[0026] (4) Add the methoxylated polyfluorene ether ketone to a three-necked flask equipped with a constant-pressure dropping funnel. Add boron tribromide to the constant-pressure dropping funnel and anhydrous dichloromethane to the three-necked flask. After stirring and dissolving, lower the reaction temperature to -80℃ under argon protection. Open the constant-pressure dropping funnel and add boron tribromide dropwise to the three-necked flask. After the addition is complete, allow the reaction temperature to rise naturally to room temperature. Continue stirring for 18-24 hours. Then, slowly pour the reactants into a large amount of deionized water to precipitate the precipitate. Filter and collect the precipitate, and dry it in a vacuum oven at 80℃ for 12-24 hours to obtain the phenolic hydroxyl-containing polyfluorene ether ketone. The synthetic route is shown below:
[0027] Where n = 60 to 120.
[0028] (5) Add polyfluorene ether ketone containing phenolic hydroxyl groups to a three-necked flask, then add dimethyl sulfoxide, stir and dissolve under argon protection, then add NaH, stir and react for 30-60 minutes, raise the system temperature to 100-120℃, then add 1,3-propane sulfonyl lactone, stir and react for 4-12 hours, then add 4,4'-difluorobenzophenone, stir and react for 10-30 minutes, then filter the solution, cast it onto a glass plate, and place it horizontally in an oven at 100℃ for 12-24 hours. After drying and forming a membrane, immerse the glass plate in deionized water to allow the membrane to absorb water and detach, then soak the membrane in 1M dilute sulfuric acid and acidify it at 80℃ for 3-8 hours, then wash away the sulfuric acid adsorbed in the membrane with deionized water to obtain a cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane.
[0029] Further, in step (1), the molar amount of iodomethane is 2 to 4 times the molar amount of 2,7-dihydroxy-9-fluorenone; the molar amount of anhydrous potassium carbonate is 6 to 10 times the molar amount of 2,7-dihydroxy-9-fluorenone; N,N' Volume of dimethylacetamide: Mass of 2,7-dihydroxy-9-fluorenone = 1 mL: (0.1-0.5) g.
[0030] Further, in step (2), the molar ratio of dimethoxyfluorenone to 2,6-xylenol is 1:(5-10); molar ratio of dimethoxyfluorenone to volume of toluene to volume of 3-mercaptopropionic acid to volume of concentrated sulfuric acid = 1 mol:(500-2000) mL:(30-60) mL:(100-150) mL.
[0031] Further, in step (3), the molar amount of tetramethyldimethoxybisphenol fluorene is equal to the molar amount of 4,4'-difluorobenzophenone; the molar amount of anhydrous potassium carbonate is (1 to 4) times the molar amount of tetramethyldimethoxybisphenol fluorene. The volume of N,N'-dimethylacetamide : mass of tetramethyldimethoxybisphenol fluorene = (5 to 15) mL : 1 g; the volume of toluene is 5 to 35% of the volume of N,N'-dimethylacetamide.
[0032] Furthermore, in step (4), the molar amount of boron tribromide is 10 to 30 times the molar amount of methoxylated polyfluorene ether ketone; the mass of methoxylated polyfluorene ether ketone: the volume of anhydrous dichloromethane = 1 g : (50 to 200) mL.
[0033] Further, in step (5), the molar ratio of polyfluorene ether ketone containing phenolic hydroxyl groups to NaH to 1,3-propanesulfonyl lactone to 4,4'-difluorobenzophenone is 1:(2-5):(1-4):(0.001-0.1); the mass of polyfluorene ether ketone containing phenolic hydroxyl groups to the volume of dimethyl sulfoxide is 1g:(15-25)mL.
[0034] This invention uses phenolic hydroxyl groups as the common active site for grafting sulfonic acid groups and crosslinking, significantly simplifying the compatibility issues of sulfonation and crosslinking processes. During the reaction, attention must be paid to the reaction temperature. Too low a temperature will result in a low grafting rate of sulfonic acid groups, while too high a temperature will trigger side reactions, impairing film-forming properties and the mechanical strength of the product. The order of adding the sulfonating agent and crosslinking agent is also crucial. The sulfonating agent, propanesulfonate lactone, should be added first, followed by the crosslinking agent, 4,4'-difluorobenzophenone. Adding the crosslinking agent first and then the sulfonating agent will lead to insufficient sulfonation and uneven sulfonation distribution. Furthermore, the ratio of sulfonating agent to crosslinking agent must be carefully considered. Too much sulfonating agent will prevent effective crosslinking, while too little will result in insufficient proton conductivity. Similarly, too much crosslinking agent will hinder film formation, while too little will prevent effective crosslinking. Finally, the stirring time after adding the crosslinking agent is also critical. Too long a stirring time will prevent film formation, while too short a stirring time will prevent effective crosslinking. The cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane of the present invention has a rigid aromatic three-dimensional framework and flexible sulfonic acid side chains. Its molecular structure is complex and diverse, and a simplified illustration is shown below:
[0035] The present invention also has the following benefits: (1) The raw materials are widely available and the cost is low; the reaction yield is high and the by-products are few.
[0036] (2) Phenolic hydroxyl groups serve as the common active site for grafting sulfonic acid groups and crosslinking, simplifying the reaction and avoiding compatibility issues between different active sites. For example, the reaction of the first reaction site may hinder the reaction of the second reaction site, and the reaction of the second reaction site may also impair the reaction of the first reaction site. Using phenolic hydroxyl groups as crosslinking sites provides higher chemical stability compared to common crosslinking sites such as double bonds, triple bonds, and amino groups. It is less prone to self-crosslinking side reactions, facilitates storage, and allows crosslinking and grafting sulfonic acid groups to proceed at the same temperature and under the same catalyst. Compared to common multi-step reactions, it effectively avoids the waste of solvents and polymers and simplifies the process by allowing direct film deposition.
[0037] (3) The grafting of sulfonic acid groups and the crosslinking of the polymer are combined into one step, followed by filtration and casting into a membrane. The process is simple, low-cost, and suitable for large-scale production. Common multi-step processes require purification of the products of each step, consume a large amount of solvent, and involve multiple drying and re-dissolving processes for membrane laying, which is time-consuming and labor-intensive. This invention can effectively avoid the disadvantages of the above-mentioned common multi-step processes.
[0038] (4) The polyfluorene ether ketone containing phenolic hydroxyl groups prepared in this invention has excellent grafting and cross-linking activity. Because the phenolic hydroxyl group is on the fluorene group and there are no substituents on the ortho-benzene ring, the reaction steric hindrance is small, which can ensure the high efficiency of subsequent reactions and solve the problem of large reaction steric hindrance of common phenolic hydroxyl groups. The obtained cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane has a fully rigid polyfluorene ether ketone three-dimensional skeleton with high mechanical strength, good thermal stability and good cross-linking effect. The sulfonic acid group is suspended in the rigid three-dimensional network through flexible alkyl chains, which has good mobility, is easy to aggregate, and promotes the transport of protons.
[0039] (5) The obtained cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane has high proton conductivity, low vanadium ion permeability, excellent mechanical stability, thermal stability and antioxidant stability, and has wide application value in the VRFB field.
[0040] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to these embodiments.
[0041] Example 1: Preparation of dimethoxyfluorenone 42.44 g (0.2 mol) of 2,7-dihydroxy-9-fluorenone was added to a three-necked flask, followed by 200 mL of N,N'-dimethylacetamide. The mixture was stirred until completely dissolved, then 70.97 g (0.5 mol) of iodomethane and 207.30 g (1.5 mol) of anhydrous potassium carbonate were added. The system was heated to 80 °C and reacted for 8 h under argon protection. After the reaction was complete, the solution was slowly poured into a beaker containing a large amount of deionized water, causing a precipitate to form. The precipitate was then collected by filtration and dried in a vacuum oven at 80 °C for 24 h to obtain dimethoxyfluorenone, with a yield of 94.7%. The 1H NMR spectrum of the obtained dimethoxyfluorenone is shown below. Figure 1 As shown.
[0042] Example 2: Preparation of tetramethyldimethoxybisphenol fluorene 24.02 g (0.1 mol) of dimethoxyfluorenone and 73.30 g (0.6 mol) of 2,6-dimethylphenol were added to a three-necked flask, followed by 100 mL of toluene. The mixture was stirred to dissolve the fluorene, and then 5 mL of 3-mercaptopropionic acid was added under argon protection. Next, 12 mL of concentrated sulfuric acid was added dropwise, and the mixture was heated to 60 °C and reacted for 12 h. After the reaction was complete, the reactants were cooled to room temperature and then poured into deionized water to precipitate the precipitate. The precipitate was collected by filtration and dried in a vacuum oven at 90 °C for 24 h. Finally, it was recrystallized from dichloromethane to obtain tetramethyldimethoxybisphenol fluorene, with a yield of 96.3%. The 1H NMR spectrum of the obtained tetramethyldimethoxybisphenol fluorene is shown below. Figure 2 As shown.
[0043] Example 3: Preparation of methoxylated polyfluorene ether ketone 2.7972 g (6 mmol) of tetramethyldimethoxybisphenol fluorene and 1.3092 g (6 mmol) of 4,4'-difluorobenzophenone were added to a three-necked flask, followed by 18 mL of N,N'-dimethylacetamide and stirring to dissolve. Then, 2.4877 g (18 mmol) of anhydrous potassium carbonate and 6 mL of toluene were added. Under argon protection, the system temperature was raised to 145 °C and reacted for 2 h. Water generated during the reaction was removed using a water separator, and the toluene was distilled off. The system temperature was then raised to 165 °C and the reaction continued for 6 h. After the reaction was complete, the viscous reactant was poured into deionized water to precipitate the product. The precipitate was collected by filtration and dried under vacuum at 80 °C for 24 h to obtain methoxylated polyfluorene ether ketone with a yield of 94.8%. The 1H NMR spectrum, infrared spectrum, and thermogravimetric analysis curve of the obtained methoxylated polyfluorene ether ketone are shown below. Figure 3 Diagram and Figure 5 As shown.
[0044] Example 4: Preparation of polyfluorene ether ketones containing phenolic hydroxyl groups 3 g (4.65 mmol) of methoxylated polyfluorene ether ketone was added to a three-necked flask equipped with a constant-pressure dropping funnel. 8.96 mL (93 mmol) of boron tribromide was added to the constant-pressure dropping funnel, and 300 mL of anhydrous dichloromethane was added to the three-necked flask. After stirring to dissolve, the reaction temperature was lowered to -80 °C under argon protection. The constant-pressure dropping funnel was opened, and boron tribromide was added dropwise to the three-necked flask. After the addition was complete, the reaction temperature was allowed to rise naturally to room temperature, and the reaction was continued with stirring for 24 h. The reactants were then slowly poured into a large amount of deionized water to precipitate the precipitate. The precipitate was collected by filtration and dried in a vacuum oven at 80 °C for 24 h to obtain phenolic hydroxyl-containing polyfluorene ether ketone, with a yield of 88.7%. The 1H NMR spectrum, infrared spectrum, and thermogravimetric analysis curve of the obtained phenolic hydroxyl-containing polyfluorene ether ketone are shown below. Figure 6 , Figure 7 and Figure 8 As shown.
[0045] Example 5: Preparation of cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane Add 0.5 g (0.81 mmol) of polyfluorene ether ketone containing phenolic hydroxyl groups to a three-necked flask, then add 10 mL of dimethyl sulfoxide. Stir and dissolve under argon protection. Then add 0.13 g (3.24 mol) of NaH and stir for 30 minutes. Raise the temperature of the system to 120 °C, then add 0.21 mL (1.539 mmol) of 1,3-propanesulfonyl lactone and stir for 6 hours. Then add 0.0087 g (0.04 mmol) of 4,4'-difluorobenzophenone and stir for 30 minutes. Filter the solution, cast it onto a glass plate, and place it horizontally in an oven at 100 °C for 24 hours. After drying and forming the membrane, a glass plate was immersed in deionized water to allow the membrane to absorb water and detach. The membrane was then immersed in 1M dilute sulfuric acid and acidified at 80°C for 3 hours. Finally, the adsorbed sulfuric acid was washed away with deionized water to obtain the cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane. The infrared spectrum and thermogravimetric analysis curves of the obtained cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane are shown below. Figure 9 and Figure 10 As shown. From Figure 10 It can be seen that the initial thermal decomposition temperature of the cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane exceeds 200℃, indicating that it has excellent thermal stability.
[0046] Table 1. Water absorption and swelling ratio of cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membranes at different temperatures.
[0047] Table 1 shows the water absorption and swelling rate of the cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane at different temperatures. As can be seen from the table, the water absorption and swelling rate of the cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane gradually increase with increasing temperature. At 80℃, the water absorption and swelling rate of the cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane are 67.4% and 6.4%, respectively. The swelling rate remains at a low level, indicating that limited cross-linking inhibits swelling.
[0048] Table 2. Proton conductivity and VOCs of cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membranes and Nafion 117 membranes at room temperature. 2+ Penetration
[0049] Table 2 shows the proton conductivity and VOCs of cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membranes and Nafion 117 membranes at room temperature. 2+ Permeability. As can be seen from the table, the proton conductivity of the cross-linked side-chain sulfonated proton exchange membrane at room temperature is 86.4 mS / cm. -1 This is higher than the 78.7 mS / cm of the Nafion 117 membrane. -1 This indicates that the prepared cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane possesses excellent proton conductivity. The table also shows that the VOC content of the cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane... 2+ The penetration rate is 2.1 × 10⁻⁶. -13 m 2 s -1 This is lower than the 5.2 × 10⁻⁶ of the Nafion 117 membrane. -12 m 2 s -1 This indicates that the prepared cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane has excellent vanadium permeation blocking performance.
[0050] The tensile strength of the cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane was tested using a universal tensile testing machine. The membrane was immersed in Fenton's reagent (3wt% H2O2 + 2ppm FeSO4) at 80℃, and the oxidation breakage time of the membrane was observed to characterize its oxidation stability. The results are shown in Table 3.
[0051] Table 3 Tensile properties and oxidative breakdown time of cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membranes
[0052] As shown in Table 3, the cross-linked side-chain sulfonated polyfluorenyl ether ketone proton exchange membrane exhibits a tensile strength of 62.1 MPa and an elongation at break of 14.3%. Immersed in Fenton's reagent at 80 °C, the membrane began to oxidize and break down after 522 minutes, exceeding the oxidation and breakdown time of other proton exchange membranes, including the SPFEK / 15%SiO2 membrane described in the literature (Chen DY, et al. Sulfonated poly (fluorenyl ether ketone) membrane with embedded silica rich layer and enhanced proton selectivity for vanadium redoxflow battery. Journal of Power Sources, 2010, 195: 7701-7708). This indicates that the prepared cross-linked side-chain sulfonated polyfluorenyl ether ketone proton exchange membrane possesses excellent oxidative stability.
[0053] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these embodiments will all fall within the scope of protection of the present invention.
Claims
1. A method for preparing a cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane, characterized in that, The method comprises the following steps: (1) adding 2,7-dihydroxy-9-fluorenone into a three-neck flask, then adding N,N'-dimethylacetamide, stirring until completely dissolved, then adding iodomethane and anhydrous potassium carbonate, and increasing the temperature of the system to 60-80 DEG C under the protection of argon to react for 8-12 hours; after the reaction is completed, slowly pouring into a beaker containing a large amount of deionized water to precipitate, then filtering to collect the precipitate, and drying in a vacuum oven at 80 DEG C for 12-24 hours to obtain dimethoxy fluorenone; The structural formula of the obtained dimethoxy fluorenone is as shown in the following formula: (2) adding dimethoxy fluorenone and 2,6-dimethylphenol into a three-neck flask, then adding toluene, stirring and dissolving, then adding 3-mercaptopropionic acid under the protection of argon, then adding concentrated sulfuric acid drop by drop, and then increasing the temperature to 60-80 DEG C to react for 8-12 hours; after the reaction is completed, first cooling the reaction product to room temperature, then pouring into deionized water to precipitate, filtering to collect the precipitate, then drying in a vacuum oven at 90 DEG C for 24-48 hours, and finally recrystallizing with dichloromethane to obtain tetramethyl dimethoxy bisphenol fluorene; The structural formula of the obtained tetramethyl dimethoxy bisphenol fluorene is as shown in the following formula: (3) adding tetramethyl dimethoxy bisphenol fluorene and 4,4'-difluorobenzophenone into a three-neck flask, then adding N,N'-dimethylacetamide, stirring and dissolving, then adding anhydrous potassium carbonate and toluene, increasing the temperature of the system to 140-150 DEG C under the protection of argon to react for 2-4 hours, and removing water generated in the reaction through a water trap, then evaporating toluene, then increasing the temperature of the system to 150-170 DEG C to continue to react for 4-8 hours; after the reaction is completed, pouring the viscous reaction product into deionized water to precipitate, filtering to collect the precipitate, and drying under vacuum at 80 DEG C for 12-24 hours to obtain a methoxy-containing polyfluorene ether ketone; The structural formula of the obtained methoxy-containing polyfluorene ether ketone is as shown in the following formula: Wherein, n=60-120; (4) adding the methoxy-containing polyfluorene ether ketone into a three-neck flask provided with a constant pressure dropping funnel, adding boron tribromide into the constant pressure dropping funnel, adding anhydrous dichloromethane into the three-neck flask, stirring and dissolving, then reducing the reaction temperature to-80 DEG C under the protection of argon; opening the constant pressure dropping funnel to add boron tribromide drop by drop into the three-neck flask, after the drop is completed, naturally increasing the reaction temperature to room temperature, continuing to stir for 18-24 hours, then slowly pouring the reaction product into a large amount of deionized water to precipitate, filtering to collect the precipitate, and drying in a vacuum oven at 80 DEG C for 12-24 hours to obtain a polyfluorene ether ketone containing phenolic hydroxyl groups; The structural formula of the obtained polyfluorene ether ketone containing phenolic hydroxyl groups is as shown in the following formula: Wherein, n=60-120; (5) the phenolic hydroxyl-containing polyfluorene ether ketone is added into a three-necked flask, dimethyl sulfoxide is added, stirring and dissolving under the protection of argon, NaH is added, stirring and reacting for 30-60 minutes, the temperature of the system is raised to 100-120 °C, 1,3-propane sultone is added, stirring and reacting for 4-12 hours, 4,4'-difluorobenzophenone is added, stirring and reacting for 10-30 minutes, then the solution is filtered, cast on a glass plate, horizontally placed in an oven at 100 °C and baked for 12-24 hours; after baking and film forming, the glass plate is immersed in deionized water to make the film absorb water and fall off, then the film is immersed in 1M dilute sulfuric acid and acidified at 80 °C for 3-8 hours, and then the sulfuric acid adsorbed in the film is washed away with deionized water, to obtain a cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane.
2. The method for preparing a cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane according to claim 1, characterized in that, In step (1), the molar amount of iodomethane is 2 to 4 times the molar amount of 2,7-dihydroxy-9-fluorenone; the molar amount of anhydrous potassium carbonate is 6 to 10 times the molar amount of 2,7-dihydroxy-9-fluorenone; the volume of N,N'-dimethylacetamide: mass of 2,7-dihydroxy-9-fluorenone = 1 mL: (0.1 to 0.5) g. In step (1), the molar amount of iodomethane is 2 to 4 times the molar amount of 2,7-dihydroxy-9-fluorenone; the molar amount of anhydrous potassium carbonate is 6 to 10 times the molar amount of 2,7-dihydroxy-9-fluorenone; the volume of N,N'-dimethylacetamide: mass of 2,7-dihydroxy-9-fluorenone = 1 mL: (0.1 to 0.5) g.
3. The method for preparing a cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane according to claim 1, characterized in that, In step (2), the ratio of the molar amount of dimethoxyfluorenone to the molar amount of 2,6-xylenol is 1: (5-10); the molar amount of dimethoxyfluorenone: the volume of toluene: the volume of 3-mercaptopropionic acid: the volume of concentrated sulfuric acid = 1 mol: (500-2000) mL: (30-60) mL: (100-150) mL.
4. The method for preparing a cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane according to claim 1, characterized in that, In step (3), the molar amount of tetramethyl dimethoxy bisphenol fluorene is equal to the molar amount of 4,4'-difluorobenzophenone; the molar amount of anhydrous potassium carbonate is (1-4) times the molar amount of tetramethyl dimethoxy bisphenol fluorene; the volume of N,N'-dimethylacetamide: the mass of tetramethyl dimethoxy bisphenol fluorene = (5-15) mL: 1 g; the volume of toluene is 5-35% of the volume of N,N'-dimethylacetamide.
5. The method for preparing a cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane according to claim 1, characterized in that, In step (4), the molar amount of boron tribromide is 10-30 times the molar amount of methoxy-containing polyfluorene ether ketone; the mass of methoxy-containing polyfluorene ether ketone: the volume of anhydrous dichloromethane = 1 g: (50-200) mL.
6. The method for preparing a cross-linked side-chain sulfonated polyfluorene ether ketone proton exchange membrane according to claim 1, characterized in that, In step (5), the ratio of the molar amount of phenolic hydroxyl-containing polyfluorene ether ketone: the molar amount of NaH: the molar amount of 1,3-propane sultone: the molar amount of 4,4'-difluorobenzophenone is 1: (2-5): (1-4): (0.001-0.1); the mass of phenolic hydroxyl-containing polyfluorene ether ketone: the volume of dimethyl sulfoxide = 1 g: (15-25) mL.