Piperidine functionalized ring-containing polyfluorene ether ketone anion exchange membrane and preparation method thereof

Abstract

The invention relates to a piperidine functionalized ring-containing polyfluorene ether ketone anion exchange membrane and a preparation method thereof. The preparation method comprises the following steps: reacting tetramethyl bisphenol fluorene with excessive 4, 4 '-difluorobenzophenone to generate an ABA type compound containing four methyl groups, performing cyclization reaction on the ABA type compound and tetramethyl dimethoxy bisphenol fluorene in a dilute solution to obtain a dimethoxy group-containing cyclic compound, reacting the dimethoxy group-containing cyclic compound with boron tribromide to prepare a cyclic monomer containing two phenolic hydroxyl groups, and reacting the cyclic monomer with 4, 4'-difluorobenzophenone to obtain a dimethoxy group-containing cyclic monomer. The preparation method comprises the following steps: carrying out polycondensation on 4, 4 '-difluorobenzophenone and bisphenol fluorene at a high temperature to prepare a ring-containing polyfluorene ether ketone compound, brominating methyl in the ring-containing polyfluorene ether ketone compound by utilizing bromination reaction, reacting with N-methylpiperidine to prepare a piperidine functionalized ring-containing polyfluorene ether ketone compound, and carrying out solution casting to obtain the anion exchange membrane. The obtained anion exchange membrane has the advantages of high ion conductivity, low vanadium ion permeability, high mechanical strength and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polymer synthesis, and in particular to a piperidine functionalized cyclic polyfluorene ether ketone anion exchange membrane and a preparation method thereof. BACKGROUND

[0002] Traditional anion exchange membranes have the characteristic of compact structure. However, such membrane materials have the disadvantages of low anion conductivity, low ion selectivity, easy swelling, poor dimensional stability, and the like, and are difficult to meet the development needs of current high-power flow batteries. Microporous ion exchange membranes have a nano-pore structure inside, and have both pore size screening effect and charge repulsion effect, and are the current development hotspot of ion exchange membranes. Zuo et al. (Zuo P, et al. Near-frictionless ion transport within triazine framework membranes. Nature 2023; 617(7960):299-305) developed a self-supporting triazine framework polymer anion exchange membrane with rigid ion channels, and such membrane has high ion conductivity and excellent chemical stability, but the polymerization conditions are relatively harsh and the polymer is not easy to dissolve and film. Lin Yuqing et al. (Chinese Invention Patent 202510288613.8) used 1,3,5-tris(4-aminophenyl)benzene and dimethylol formaldehyde as polymerization monomers to prepare a self-microporous anion exchange membrane, but the rigid twisted molecular structure of the membrane is difficult to form a continuous ion transmission channel, and the functionalization degree and site are not easy to control. How to develop a new three-dimensional topological structure, while maintaining excellent film-forming properties, to obtain an anion exchange membrane with excellent ion selective conductivity performance and easy to control, has important value for the development of all-vanadium redox flow batteries and other membrane fields. SUMMARY

[0003] The purpose of the present application is to overcome the shortcomings of the above-mentioned technologies, and to provide a piperidine functionalized cyclic polyfluorene ether ketone anion exchange membrane and a preparation method thereof. The obtained piperidine functionalized cyclic polyfluorene ether ketone anion exchange membrane has a unique three-dimensional topological structure, and the functionalization degree and the content of the cyclic unit can be adjusted by controlling the monomer feeding ratio, so as to simultaneously control the ion exchange capacity and the composition of the topological structure, so that the membrane has high ion conductivity, thermal stability, excellent mechanical properties and vanadium resistance.

[0004] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: The present application provides a piperidine functionalized cyclic polyfluorene ether ketone anion exchange membrane for all-vanadium redox flow batteries, and the chemical structural formula is as follows:

[0005] In the formula, R represents a piperidine functional group, and n represents an integer of 1-10. For or , m is 10-50, and n is 10-90.

[0006] The preparation method of the piperidine functionalized cyclic polyfluorene ether ketone anion exchange membrane is as follows: (1) Tetramethyl bisphenol fluorene and 4,4'-difluorobenzophenone are added to a polar aprotic solvent, after complete dissolution, anhydrous potassium carbonate is added, the system temperature is raised to 120-150°C under argon protection, and reaction is carried out for 2-3 h, then the precipitate is collected by filtration and dried under vacuum at 80-100°C for 24-48 h, and finally purified by a silica gel chromatographic column, with dichloromethane as the mobile phase, to obtain an ABA type compound containing four methyl groups. The above reaction scheme is as follows: ; (2) 2,7-dihydroxy-9-fluorenone is added to a polar aprotic solvent, after complete dissolution, methyl iodide and anhydrous potassium carbonate are added, the system temperature is raised to 70-80°C under argon protection, and reaction is carried out for 6-8 h, then the precipitate is collected by filtration and dried under vacuum at 90-100°C for 24-48 h, and finally recrystallized with ethanol, to obtain dimethoxy fluorenone. The above reaction scheme is as follows: ; (3) Dimethoxy fluorenone and 2,6-dimethyl phenol are added to toluene, after stirring and dissolving, 3-mercaptopropionic acid is added under argon protection, stirring is carried out for 0.5-1 h, concentrated sulfuric acid is added dropwise to the reaction system, after addition is completed, the system temperature is raised to 30-80°C, and reaction is carried out for 5-10 h, then the precipitate is collected by filtration and dried under vacuum at 90-100°C for 24-48 h, and finally recrystallized with dichloromethane, to obtain tetramethyl dimethoxy bisphenol fluorene. The above reaction scheme is as follows: ; (4) The ABA type compound containing four methyl groups and tetramethyl dimethoxy bisphenol fluorene are added to a polar aprotic solvent, after dissolution, cesium carbonate is added, the system temperature is raised to 40-100°C under argon protection, and reaction is carried out for 5-6 days, then the reaction generated precipitate is collected by filtration and dried under vacuum at 90-100°C for 18-24 h, and finally purified by a silica gel chromatographic column, with dichloromethane as the mobile phase, to obtain a dimethoxy containing cyclic compound. The above reaction scheme is as follows: ; (5) The dimethoxyl-containing cyclic compound was dissolved in anhydrous dichloromethane. Under argon protection, the reaction temperature was lowered to -70 to -80°C. Then, a dichloromethane solution containing boron tribromide at a mass concentration of 6 to 12% was added dropwise. The temperature was then allowed to rise naturally to room temperature, and the reaction was continued for 18 to 24 hours. The reaction was then quenched with deionized water. Finally, the solid was collected by filtration and dried under vacuum at 70 to 80°C for 24 to 48 hours. The solid was recrystallized with ethanol to obtain a cyclic monomer containing two phenolic hydroxyl groups. The above reaction procedure is as follows: ; (6) A cyclic monomer containing two phenolic hydroxyl groups, 4,4'-difluorobenzophenone, and bisphenol fluorene are added to a polar aprotic solvent. Anhydrous potassium carbonate and toluene are added, and the mixture is heated to 120–145 °C under argon protection and reacted for 2–3 h. The water generated in the reaction is removed by a water separator, and then the toluene is distilled off. The system temperature is raised to 150–175 °C and reacted for 5–12 h. The reactants are then poured into deionized water to precipitate the precipitate. The precipitate is collected by filtration and dried under vacuum at 80–120 °C for 24–48 h to obtain a cyclic polyfluorene ether ketone compound. The above reaction process is as follows: ; Where m is 10 to 50 and n is 10 to 90.

[0007] (7) Dissolve the cyclic polyfluorene ether ketone compound in 1,2-dichloroethane to prepare a 1-10 wt.% solution, add N-bromosuccinimide and benzoyl peroxide, heat to 40-60℃ under argon protection and react for 5-8 h, then pour into methanol to precipitate, filter and collect the precipitate, and dry under vacuum at 80-120℃ for 24-48 h to obtain the bromomethylated cyclic polyfluorene ether ketone compound, whose chemical structure is shown below: ; in: for or m is 10 to 50, and n is 10 to 90.

[0008] (8) A 1-10 wt.% solution of a bromomethylated cyclic polyfluorene ether ketone compound was prepared by dissolving it in a polar aprotic solvent. 1-10 times the theoretical content of N-methylpiperidine was slowly added dropwise. The mixture was heated to 40-60°C under argon protection and reacted for 5-8 hours. The mixture was then cast onto a horizontally placed glass plate and baked at 70-80°C for 24-48 hours. Finally, the glass plate was immersed in deionized water to detach the membrane, yielding a piperidine-functionalized cyclic polyfluorene ether ketone anion exchange membrane. Its chemical structure is shown below: ; in: for or m is 10 to 50, and n is 10 to 90.

[0009] Further, in step (1), the molar ratio of tetramethylbisphenol fluorene, 4,4'-difluorobenzophenone and anhydrous potassium carbonate is 1:8-10:3-6, and the volume ratio of the polar aprotic solvent to the molar amount of tetramethylbisphenol fluorene is 3-5 ml:1 mmol.

[0010] Further, in step (2), the molar ratio of 2,7-dihydroxy-9-fluorenone, iodomethane and anhydrous potassium carbonate is 1:3 to 4:3 to 6, and the volume ratio of the polar aprotic solvent to the molar amount of 2,7-dihydroxy-9-fluorenone is 0.3 to 0.5 ml: 1 mmol.

[0011] Further, in step (3), the molar ratio of dimethoxyfluorenone to 2,6-dimethylphenol is 1:2-4, the volume ratio of toluene to the molar amount of dimethoxyfluorenone is 400-800 ml:1 mol, and the molar ratio of 3-mercaptopropionic acid, concentrated sulfuric acid to dimethoxyfluorenone is 10-30 ml:50-100 ml:1 mol.

[0012] Further, in step (4), the molar ratio of the ABA-type compound containing four methyl groups, tetramethyldimethoxybisphenol fluorene, and cesium carbonate is 1:1 to 1.5:1.5 to 3. The volume ratio of the polar aprotic solvent to the molar ratio of tetramethyldimethoxybisphenol fluorene is 1000 ml: 1 to 3 mmol.

[0013] Further, in step (5), the volume ratio of anhydrous dichloromethane to the molar amount of the dimethoxylated cyclic compound is 50-150 ml: 1 mmol, the molar amount of the dimethoxylated cyclic compound to the mass ratio of boron tribromide is 1 mmol: 1-5 g, and the mass ratio of deionized water to boron tribromide is 1-10: 1.

[0014] Further, the sum of the molar amounts of the cyclic monomer containing two phenolic hydroxyl groups and bisphenol fluorene mentioned in step (6) is equal to the molar amount of 4,4'-difluorobenzophenone. The molar amounts of 4,4'-difluorobenzophenone, anhydrous potassium carbonate, and the volume ratio of N-methylpyrrolidone to toluene is 1 mmol: 2-5 mmol: 3-5 ml: 0.5-3 ml.

[0015] Further, in step (7), the molar ratio of N-bromosuccinimide to benzyl group on the cyclic polyfluorene ether ketone compound is 1 to 10:1, the molar ratio of N-bromosuccinimide to benzoyl peroxide is 10 to 30:1, and the volume ratio of methanol to 1,2-dichloroethane used is 5 to 50:1.

[0016] The polar aprotic solvent includes any one of N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and acetonitrile.

[0017] This invention first synthesizes cyclic monomers with special topological structures, then prepares piperidine-functionalized cyclic polyfluorene ether ketone compounds through controlled polymerization, and finally forms a film by solution casting. Compared with the prior art, this invention has the following advantages: (1) The present invention uses low-cost chemical raw materials, has a simple preparation method, does not require precious metal catalysts, and is easy to industrialize.

[0018] (2) Cyclic monomers containing two phenolic hydroxyl groups can not only provide stable molecular-level microporous structures, but also serve as functionalization sites. By adjusting the amount of cyclic monomers with two phenolic hydroxyl groups, polymers with different three-dimensional topologies and ion exchange capacities can be prepared. Ionic groups can be directionally introduced onto the benzyl group of the cyclic monomer, thereby forming a three-dimensional ion transport channel.

[0019] (3) The obtained piperidine-functionalized cyclic polyfluorene ether ketone compound has excellent solubility, is easy to form a film in solution, and the microporous structure remains stable during the film formation process.

[0020] (4) The obtained piperidine-functionalized cyclic polyfluorene ether ketone anion exchange membrane has high ion conductivity, thermal stability, mechanical properties, and low VO2 content. 2+ The penetration rate has broad application prospects in the field of vanadium redox flow batteries. Attached Figure Description

[0021] Figure 1 The above is the 1H NMR spectrum of the ABA-type compound containing four methyl groups prepared in Example 1 of this invention.

[0022] Figure 2 The infrared spectrum is that of the ABA-type compound containing four methyl groups prepared in Example 1 of this invention.

[0023] Figure 3 The nuclear magnetic resonance hydrogen spectrum of dimethoxyfluorenone prepared in Example 2 of this invention.

[0024] Figure 4 The infrared spectrum of dimethoxyfluorenone prepared in Example 2 of this invention.

[0025] Figure 5 The nuclear magnetic resonance hydrogen spectrum of tetramethyldimethoxybisphenol fluorene prepared in Example 3 of this invention.

[0026] Figure 6 The infrared spectrum is that of tetramethyldimethoxybisphenol fluorene prepared in Example 3 of this invention.

[0027] Figure 7 The above is the 1H NMR spectrum of the dimethoxyl-containing cyclic compound prepared in Example 4 of this invention.

[0028] Figure 8 The infrared spectrum is shown for the dimethoxyl-containing cyclic compound prepared in Example 4 of this invention.

[0029] Figure 9 The above is the 1H NMR spectrum of the cyclic monomer containing two phenolic hydroxyl groups prepared in Example 5 of this invention.

[0030] Figure 10 The infrared spectrum is that of the cyclic monomer containing two phenolic hydroxyl groups prepared in Example 5 of this invention.

[0031] Figure 11 This is the mass spectrum of the cyclic monomer containing two phenolic hydroxyl groups prepared in Example 5 of the present invention.

[0032] Figure 12 The above is the 1H NMR spectrum of HPFEK-25 prepared in Example 6 of this invention.

[0033] Figure 13 The infrared spectrum of HPFEK-25 prepared in Example 6 of this invention.

[0034] Figure 14 The nuclear magnetic resonance spectrum of HPFEK-Br-25 prepared in Example 10 of this invention.

[0035] Figure 15 The infrared spectrum of HPFEK-Br-25 prepared in Example 10 of this invention.

[0036] Figure 16 The hydrogen nuclear magnetic resonance spectrum of HPFEK-Pip-25 prepared in Example 14 of this invention.

[0037] Figure 17 The infrared spectrum of HPFEK-Pip-25 prepared in Example 14 of this invention.

[0038] Figure 18 The thermogravimetric curve of HPFEK-Pip-25 prepared in Example 14 of this invention. Detailed Implementation

[0039] To make the content of this invention easier to understand, the technical solution of this invention will be further described below in conjunction with specific embodiments, but this invention is not limited thereto.

[0040] Example 1: Synthesis of an ABA-type compound containing four methyl groups 1.6 g (4 mmol) of tetramethylbisphenol fluorene and 8.7 g (40 mmol) of 4,4'-difluorobenzophenone were added to 16 mL of N,N-dimethylacetamide. After complete dissolution, 1.7 g (12 mmol) of anhydrous potassium carbonate was added. The system was heated to 125 °C and reacted for 3 h under argon protection. The precipitate was then poured into deionized water, filtered, collected, and dried under vacuum at 100 °C for 24 h. Finally, the precipitate was purified by silica gel chromatography with dichloromethane as the mobile phase to obtain an ABA-type compound containing four methyl groups in 91% yield. The 1H NMR spectrum of the obtained ABA-type compound containing four methyl groups is shown below. Figure 1 As shown, the infrared spectrum is as follows Figure 2 As shown.

[0041] Example 2 Synthesis of dimethoxyfluorenone 106 g (0.5 mol) of 2,7-dihydroxy-9-fluorenone was added to 200 mL of N,N-dimethylacetamide and dissolved completely. Then, 93 mL (1.5 mol) of iodomethane and 276.4 g (2 mol) of anhydrous potassium carbonate were added. The mixture was reacted at 75 °C for 7 h under argon protection. The precipitate was then poured into deionized water, filtered, collected, and dried at 100 °C under vacuum for 24 h. Finally, it was recrystallized from ethanol to obtain dimethoxyfluorenone in 95% yield. The 1H NMR spectrum of the obtained dimethoxyfluorenone is shown below. Figure 3 As shown, the infrared spectrum is as follows Figure 4 As shown.

[0042] Example 3 Synthesis of Tetramethyldimethoxybisphenol fluorene 42.4 g (0.2 mol) of dimethoxyfluorenone and 97.7 g (0.8 mol) of 2,6-dimethylphenol were added to 100 mL of toluene and stirred until dissolved. Then, 5 mL of 3-mercaptopropionic acid was added under argon protection, and the mixture was stirred for 1 h. Next, 15 mL of concentrated sulfuric acid was added dropwise to the reaction system. After the addition was complete, the system temperature was raised to 55 °C and the reaction was carried out for 8 h. The precipitate was then poured into deionized water, filtered, collected, and dried under vacuum at 100 °C for 24 h. Finally, it was recrystallized from dichloromethane to obtain tetramethyldimethoxybisphenol fluorene in 95% yield. The 1H NMR spectrum of the obtained tetramethyldimethoxybisphenol fluorene is shown below. Figure 5 As shown, the infrared spectrum is as follows Figure 6 As shown.

[0043] Example 4 Synthesis of dimethoxylated cyclic compounds 32.1 g (40 mol) of an ABA-type compound containing four methyl groups and 18.6 g (40 mmol) of tetramethyldimethoxybisphenol fluorene were added to 20 L of acetonitrile. After dissolution, 39.1 g (120 mmol) of cesium carbonate was added. The system was reacted at 80 °C for 6 days under argon protection, then cooled to room temperature. The precipitate was collected by filtration, dried at 100 °C under vacuum for 24 h, and finally purified by silica gel chromatography with dichloromethane as the mobile phase to obtain a dimethoxy-containing cyclic compound in 85% yield. The 1H NMR spectrum of the obtained dimethoxy-containing cyclic compound is shown below. Figure 7 As shown, the infrared spectrum is as follows Figure 8 As shown.

[0044] Example 5: Synthesis of a cyclic monomer containing two phenolic hydroxyl groups 4 g (3.26 mmol) of a dimethoxylated cyclic compound was dissolved in 400 mL of anhydrous dichloromethane. The reaction temperature was lowered to -78 °C under argon protection. Then, a dichloromethane solution containing 8.9% boron tribromide (prepared by adding 9.8 g BBr3 to 100 g of dichloromethane) was added dropwise. The temperature was then allowed to rise naturally to room temperature, and the reaction continued for 24 h. 40 g of deionized water was then added to quench the reaction. The solid was collected by filtration, dried under vacuum at 80 °C for 24 h, and recrystallized from ethanol to obtain a cyclic monomer containing two phenolic hydroxyl groups. The 1H NMR spectrum of the obtained cyclic monomer containing two phenolic hydroxyl groups is shown below. Figure 9 As shown, the infrared spectrum is as follows Figure 10 As shown, high-resolution mass spectrometry is as follows Figure 11 As shown. Figure 11 A [M+H]+ molecular ion peak appeared at m / z 1201.4601, which is consistent with the theoretical molecular weight (1200.4684).

[0045] Example 6 Synthesis of HPFEK-25, a cyclic polyfluorene ether ketone compound 0.6002 g (0.5 mmol) of a cyclic monomer containing two phenolic hydroxyl groups, 0.4364 g (2 mmol) of 4,4'-difluorobenzophenone, and 0.5256 g (1.5 mmol) of bisphenol fluorene were added to 6 ml of N-methylpyrrolidone, along with 0.8293 g (6 mmol) of anhydrous potassium carbonate and 3 ml of toluene. The mixture was heated to 145 °C under argon protection and reacted for 3 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 reacted for 5 h. The reactants were then poured into deionized water to precipitate the precipitate. The precipitate was collected by filtration and dried under vacuum at 100 °C for 24 h to obtain the cyclic polyfluorene ether ketone compound HPFEK-25, with a yield of 98%. The 1H NMR spectrum of the obtained HPFEK-25 is shown below. Figure 12 As shown, the infrared spectrum is as followsFigure 13 As shown.

[0046] Example 7 Synthesis of HPFEK-15, a cyclic polyfluorene ether ketone compound The amount of cyclic monomer in Example 6 was changed to 0.3601 g (0.3 mmol), the amount of bisphenol fluorene was changed to 0.5957 g (1.7 mmol), and the remaining operations were the same as in Example 6, to obtain the cyclic polyfluorene ether ketone compound HPFEK-15 with a yield of 97%.

[0047] Example 8 Synthesis of HPFEK-20, a cyclic polyfluorene ether ketone compound The amount of cyclic monomer in Example 6 was changed to 0.4802 g (0.4 mmol), the amount of bisphenol fluorene was changed to 0.5607 g (1.6 mmol), and the remaining operations were the same as in Example 6, to obtain the cyclic polyfluorene ether ketone compound HPFEK-20 with a yield of 99%.

[0048] Example 9 Synthesis of HPFEK-30, a cyclic polyfluorene ether ketone compound The amount of cyclic monomer in Example 6 was changed to 0.7203 g (0.6 mmol), the amount of bisphenol fluorene was changed to 0.4906 g (1.4 mmol), and the remaining operations were the same as in Example 6, to obtain the cyclic polyfluorene ether ketone compound HPFEK-30 with a yield of 98%.

[0049] Example 10 Synthesis of the bromomethylated cyclic polyfluorene ether ketone compound HPFEK-Br-25 1 g of the cyclic polyfluorene ether ketone compound HPFEK-25 (1.05 mmol repeating unit, of which 2.10 mmol is benzyl) was dissolved in 20 mL of 1,2-dichloroethane to prepare a 4 wt.% solution. 1.1195 g (6.29 mmol) of N-bromosuccinimide and 0.076 g (0.31 mmol) of benzoyl peroxide were added. The mixture was heated to 50 °C under argon protection and reacted for 5 h. The solution was then poured into 500 mL of methanol to precipitate the precipitate. The precipitate was collected by filtration and dried under vacuum at 100 °C for 24 h to obtain the bromomethylated cyclic polyfluorene ether ketone compound HPFEK-Br-25, with a yield of 99%. The 1H NMR spectrum of the obtained HPFEK-Br-25 is shown below. Figure 14 As shown, the infrared spectrum is as follows Figure 15 As shown.

[0050] Example 11 Synthesis of bromomethylated cyclic polyfluorene ether ketone compound HPFEK-Br-15 1 g of the cyclic polyfluorene ether ketone compound HPFEK-15 (1.28 mmol repeating unit, of which the benzyl content is 1.54 mmol) was dissolved in 20 ml of 1,2-dichloroethane to prepare a 4 wt.% solution. 0.7630 g (4.59 mmol) of N-bromosuccinimide and 0.0371 g (0.23 mmol) of benzoyl peroxide were added, and the remaining operations were performed as in Example 10 to obtain the bromomethylated cyclic polyfluorene ether ketone compound HPFEK-Br-15 in 98% yield.

[0051] Example 12 Synthesis of bromomethylated cyclic polyfluorene ether ketone compound HPFEK-Br-20 1 g of the cyclic polyfluorene ether ketone compound HPFEK-20 (1.15 mmol repeating unit, of which the benzyl content is 1.84 mmol) was dissolved in 20 ml of 1,2-dichloroethane to prepare a 4 wt.% solution. 0.9833 g (5.53 mmol) of N-bromosuccinimide and 0.067 g (0.28 mmol) of benzoyl peroxide were added, and the remaining operations were performed as in Example 10 to obtain the bromomethylated cyclic polyfluorene ether ketone compound HPFEK-Br-20 in 99% yield.

[0052] Example 13 Synthesis of bromomethylated cyclic polyfluorene ether ketone compound HPFEK-Br-30 1 g of the cyclic polyfluorene ether ketone compound HPFEK-30 (0.96 mmol repeating unit, of which the benzyl content is 2.30 mmol) was dissolved in 20 ml of 1,2-dichloroethane to prepare a 4 wt.% solution. 1.2334 g (6.93 mmol) of N-bromosuccinimide and 0.0839 g (0.35 mmol) of benzoyl peroxide were added, and the remaining operations were performed as in Example 10 to obtain the bromomethylated cyclic polyfluorene ether ketone compound HPFEK-Br-30 in 97% yield.

[0053] Example 14 Synthesis of piperidine-functionalized cyclic polyfluorene ether ketone compound HPFEK-Pip-25 1 g of the bromomethylated cyclic polyfluorene ether ketone compound HPFEK-Br-25 (theoretical repeating unit molar number 0.81 mmol, theoretical bromomethyl content 1.62 mmol) was dissolved in 20 ml of N,N-dimethylacetamide to prepare a 5 wt.% solution. 0.49 ml (4.92 mmol) of N-methylpiperidine was slowly added dropwise. The mixture was heated to 50 °C under argon protection and reacted for 5 h. The solution was then cast onto a horizontally placed glass plate and baked at 80 °C for 24 h. Finally, the glass plate was immersed in deionized water to detach the membrane, yielding the piperidine-functionalized cyclic polyfluorene ether ketone anion exchange membrane HPFEK-Pip-25. The proton NMR spectrum of the obtained HPFEK-Pip-25 is shown below.Figure 16 As shown, the infrared spectrum is as follows Figure 17 As shown, the thermogravimetric curve is as follows Figure 18 As shown in the figure, the thermogravimetric analysis curve shows that the initial thermal decomposition temperature of the film is 237℃, indicating good thermal stability, which meets the requirements for use in vanadium redox flow batteries.

[0054] Example 15 Synthesis of piperidine-functionalized cyclic polyfluorene ether ketone compound HPFEK-Pip-15 1 g of the bromomethylated cyclic polyfluorene ether ketone compound HPFEK-Br-15 (theoretical repeating unit molar number of 1.05 mmol, theoretical bromomethyl content of 0.97 mmol) was dissolved in 20 ml of N,N-dimethylacetamide to prepare a 5 wt.% solution. 0.381 m (3.821 mmol) of N-methylpiperidine was slowly added dropwise, and the remaining operations were performed according to Example 14 to obtain the piperidine-functionalized cyclic polyfluorene ether ketone anion exchange membrane HPFEK-Pip-15.

[0055] Example 16 Synthesis of piperidine-functionalized cyclic polyfluorene ether ketone compound HPFEK-Pip-20 1 g of the bromomethylated cyclic polyfluorene ether ketone compound HPFEK-Br-20 (theoretical repeating unit molar number of 0.91 mmol, theoretical bromomethyl content of 1.46 mmol) was dissolved in 20 ml of N,N-dimethylacetamide to prepare a 5 wt.% solution. 0.44 ml (4.44 mmol) of N-methylpiperidine was slowly added dropwise, and the remaining operations were performed according to Example 14 to obtain the piperidine-functionalized cyclic polyfluorene ether ketone anion exchange membrane HPFEK-Pip-20.

[0056] Example 17 Synthesis of piperidine-functionalized cyclic polyfluorene ether ketone compound HPFEK-Pip-30 1 g of the bromomethylated cyclic polyfluorene ether ketone compound HPFEK-Br-30 (theoretical repeating unit molar number of 0.73 mmol, theoretical bromomethyl content of 1.75 mmol) was dissolved in 20 ml of N,N-dimethylacetamide to prepare a 5 wt.% solution. 0.53 ml (5.34 mmol) of N-methylpiperidine was slowly added dropwise, and the remaining operations were performed according to Example 14 to obtain the piperidine-functionalized cyclic polyfluorene ether ketone anion exchange membrane HPFEK-Pip-30.

[0057] Example 18 Performance testing of piperidine-functionalized cyclic polyfluorene ether ketone anion exchange membrane Ion exchange capacity was tested by titration, ionic conductivity was tested by AC impedance spectroscopy, tensile properties were tested by a universal testing machine, and the osmotic concentration of VOSO4 was determined by a UV-Vis spectrophotometer. The VOSO4 concentration was then calculated. 2+ Permeability is used to characterize the vanadium ion permeation performance.

[0058] The properties of piperidine-functionalized cyclic polyfluorene ether ketone (PFEK) anion exchange membranes at room temperature are shown in Table 1. It can be seen that all prepared membranes exhibit high tensile strength; for example, HPFEK-Pip-30 has a tensile strength of 79.2 MPa, which is higher than the 14.5 MPa of commercially available Nafion 212 under the same conditions. The obtained piperidine-functionalized PFEK anion exchange membranes all exhibit high ionic conductivity; for example, HPFEK-Pip-15 has a Br- conductivity of 18.46 mS·cm. -1 The value is greater than 2.98 mS·cm for QA-PAEK-20 in the literature (Chen D, et al. IonClustering in Quaternary Ammonium Functionalized Benzylmethyl Containing Poly(arylene ether ketone)s. Macromolecules, 2013, 46(23):9270-9278). -1 Generally, ionic conductivity increases with increasing water absorption rate. HPFEK-Pip-15 has a water absorption rate of 7.8%, lower than the 14% water absorption rate of QA-PAEK-20 in the literature. This shows that the high ionic conductivity of HPFEK-Pip-15 is achieved with a lower water absorption rate, representing a significant advancement. This is likely due to the introduction of the cyclic structure, which promotes ion transport. The prepared piperidine-functionalized cyclic polyfluorene ether ketone anion exchange membranes all exhibit low vanadium ion permeability. For example, HPFEK-Pip-20 (ion exchange capacity of 1.84 mmol / g) has a vanadium ion permeability of 0.98 × 10⁻¹⁴ m³. 2 ·s -1 , smaller than the 8×10-14 m of DQA-PFE-C6 in the literature (Chen Y, et al. Fluorinated poly(fluorenyl ether)s with linear multi-cationicside chains for vanadium redox flow batteries. Science China Materials, 2021,64(2): 349-361) 2 ·s -1 And it is much smaller than Nafion212's 5.36 × 10⁻¹² m under the same conditions. 2 ·s -1 This indicates that the membrane has excellent vanadium blocking properties.

[0059] Table 1 Performance of piperidine-functionalized polyfluorene ether ketone anion exchange membranes at room temperature

[0060] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A piperidine functionalized cyclopolymacrolide ether ketone anion exchange membrane, characterized in that, The chemical structural formula is shown as follows: wherein: is or m is 10 to 50 and n is 10 to 90.

2. A method for preparing a piperidine-functionalized cyclopolymacrolide ether ketone anion exchange membrane according to claim 1, characterized in that, The method comprises the following steps: (1) adding tetramethyl diphenyl fluorene and 4,4'-difluorobenzophenone into a polar aprotic solvent, dissolving completely, then adding anhydrous potassium carbonate, and raising the temperature of the system to 120-150 DEG C under argon protection for 2-3 hours, then pouring into deionized water to precipitate, collecting the precipitate by filtration, and drying at 80-100 DEG C under vacuum for 24-48 hours, finally purifying by a silica gel chromatographic column, and using dichloromethane as the mobile phase to obtain the ABA type compound containing four methyl groups; The chemical structural formula of the obtained ABA type compound containing four methyl groups is shown as follows: ； (2) adding 2,7-dihydroxy-9-fluorenone into a polar aprotic solvent, dissolving completely, then adding methyl iodide and anhydrous potassium carbonate, raising the temperature of the system to 70-80 DEG C under argon protection for 6-8 hours, then pouring into deionized water to precipitate, collecting the precipitate by filtration, drying at 90-100 DEG C under vacuum for 24-48 hours, finally recrystallizing with ethanol to obtain dimethoxy fluorenone; The chemical structural formula of the obtained dimethoxy fluorenone is shown as follows: ； (3) adding dimethoxy fluorenone and 2,6-dimethyl phenol into toluene, stirring and dissolving, then adding 3-mercaptopropionic acid under argon protection, stirring for 0.5-1 hour, then adding concentrated sulfuric acid drop by drop into the reaction system, raising the temperature of the system to 30-80 DEG C after the addition is completed for 5-10 hours, then pouring into deionized water to precipitate, collecting the precipitate by filtration, drying at 90-100 DEG C under vacuum for 24-48 hours, finally recrystallizing with dichloromethane to obtain tetramethyl dimethoxy diphenyl fluorene; The chemical structural formula of the obtained tetramethyl dimethoxy diphenyl fluorene is shown as follows: ； (4) adding the ABA type compound containing four methyl groups and tetramethyl dimethoxy diphenyl fluorene into a polar aprotic solvent, dissolving, then adding cesium carbonate, raising the temperature of the system to 40-100 DEG C under argon protection for 5-6 days, then cooling to room temperature, collecting the precipitate generated in the reaction by filtration, drying at 90-100 DEG C under vacuum for 18-24 hours, finally purifying by a silica gel chromatographic column, and using dichloromethane as the mobile phase to obtain the cyclic compound containing dimethoxy groups; The chemical structural formula of the obtained cyclic compound containing dimethoxy groups is shown as follows: (5) dissolving the cyclic compound containing dimethoxy groups in anhydrous dichloromethane, lowering the reaction temperature to -70 to -80 DEG C under argon protection, then adding a boron tribromide solution with a mass concentration of 6-12% in dichloromethane drop by drop, then allowing the temperature to rise to room temperature naturally, continuing to react for 18-24 hours, then adding deionized water to quench the reaction, finally collecting the solid by filtration, drying at 70-80 DEG C under vacuum for 24-48 hours, recrystallizing with ethanol to obtain the cyclic monomer containing two phenolic hydroxyl groups; The chemical structural formula of the obtained cyclic monomer containing two phenolic hydroxyl groups is shown as follows: (6) The cyclic monomer containing two phenolic hydroxyl groups, 4,4'-difluorobenzophenone, and bisphenol fluorene are added to a polar aprotic solvent, anhydrous potassium carbonate and toluene are added, and the system is heated to 120-145°C under argon protection for 2-3 hours. The water generated in the reaction is removed by a water trap, and then the toluene is distilled off. The temperature of the system is raised to 150-175°C for 5-12 hours. Then the reaction product is poured into deionized water to precipitate, and the precipitate is collected by filtration and dried at 80-120°C under vacuum for 24-48 hours to obtain a cyclic polyfluorene ether ketone compound; The structure of the obtained cyclic polyfluorene ether ketone compound is as shown in the following formula: wherein m is 10-50, and n is 10-90. (7) The cyclic polyfluorene ether ketone compound is dissolved in 1,2-dichloroethane to prepare a 1-10 wt.% solution, N-bromosuccinimide and benzoyl peroxide are added, and the system is heated to 40-60°C under argon protection for 5-8 hours. Then the reaction product is poured into methanol to precipitate, and the precipitate is collected by filtration and dried at 80-120°C under vacuum for 24-48 hours to obtain a bromomethylated cyclic polyfluorene ether ketone compound. The structure of the obtained bromomethylated cyclic polyfluorene ether ketone compound is as shown in the following formula: wherein: is or m is 10 to 50 and n is 10 to 90; (8) The bromomethylated cyclic polyfluorene ether ketone compound is dissolved in a polar aprotic solvent to prepare a 1-10 wt.% solution, and 1-10 times the theoretical amount of N-methylpiperidine is slowly added dropwise. The system is heated to 40-60°C under argon protection for 5-8 hours. Then the reaction product is cast on a horizontally placed flat glass plate, and the glass plate is baked at 70-80°C for 24-48 hours. Finally, the glass plate is soaked in deionized water to make the membrane fall off, and a piperidine functionalized cyclic polyfluorene ether ketone anion exchange membrane is obtained.

3. The method of claim 2, wherein, In step (1), the molar ratio of the tetramethyl bisphenol fluorene, 4,4'-difluorobenzophenone, and anhydrous potassium carbonate is 1:8-10:3-6, and the volume of the polar aprotic solvent to the molar amount of the tetramethyl bisphenol fluorene is 3-5 ml:1 mmol.

4. The preparation method according to claim 2, characterized in that, In step (2), the molar ratio of the 2,7-dihydroxy-9-fluorenone, iodomethane, and anhydrous potassium carbonate is 1:3-4:3-6, and the volume of the polar aprotic solvent to the molar amount of the 2,7-dihydroxy-9-fluorenone is 0.3-0.5 ml:1 mmol.

5. The preparation method according to claim 2, characterized in that, In step (3), the molar ratio of the dimethoxy fluorenone and 2,6-dimethylphenol is 1:2-4, the volume of toluene to the molar amount of the dimethoxy fluorenone is 400-800 ml:1 mol, and the molar ratio of 3-mercaptopropionic acid, concentrated sulfuric acid, and dimethoxy fluorenone is 10-30 ml:50-100 ml:1 mol.

6. The preparation method according to claim 2, characterized in that, In step (4), the molar ratio of the ABA type compound containing four methyl groups, tetramethyl dimethoxy bisphenol fluorene, and cesium carbonate is 1:1-1.5:1.5-3, and the volume of the polar aprotic solvent to the molar amount of the tetramethyl dimethoxy bisphenol fluorene is 1000 ml:1-3 mmol.

7. The preparation method according to claim 2, characterized in that, The ratio of the volume of the anhydrous dichloromethane to the molar amount of the dimethoxy-containing cyclic compound in step (5) is 50 to 150 ml: 1 mmol, the ratio of the molar amount of the dimethoxy-containing cyclic compound to the mass of the boron tribromide is 1 mmol: 1 to 5 g, and the ratio of the deionized water to the mass of the boron tribromide is 1 to 10:

1.

8. The preparation method according to claim 2, characterized in that, The sum of the molar amounts of the cyclic monomer containing two phenolic hydroxyl groups and the bisphenol fluorene in step (6) is equal to the molar amount of 4,4'-difluorobenzophenone; the ratio of the molar amount of 4,4'-difluorobenzophenone, the molar amount of anhydrous potassium carbonate, the volume of N-methylpyrrolidone, and the volume of toluene is 1 mmol: 2 to 5 mmol: 3 to 5 ml: 0.5 to 3 ml.

9. The preparation method according to claim 2, characterized in that, The molar ratio of the N-bromosuccinimide to the benzyl group on the cyclic polyfluorene ether ketone compound in step (7) is 1 to 10: 1, the molar ratio of the N-bromosuccinimide to the benzoyl peroxide is 10 to 30: 1, and the volume ratio of the methanol to the 1,2-dichloroethane is 5 to 50:

1.

10. The method of claim 2, wherein, The polar aprotic solvent includes any one of N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, or acetonitrile.

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