A fluorine-free polyfluorene ether ketone proton exchange membrane with aromatic side chains and a preparation method thereof

Abstract

The application discloses a kind of aromatic side chain type fluorine-free polyfluorene ether ketone proton exchange membrane and preparation method thereof.The application first carries out one-step polymerization with four methoxy bisphenol fluorene and 4,4'-difluorobenzophenone and bisphenol fluorene, to obtain fluorine-free polyfluorene ether ketone compound containing methoxy, then carries out demethylation reaction to obtain fluorine-free polyfluorene ether ketone compound containing phenolic hydroxyl, then reacts with sodium p-chlorobenzenesulfonate, to obtain aromatic side chain type fluorine-free polyfluorene ether ketone compound containing sodium sulfonate. Film is formed by solution casting method and then acidification, to obtain aromatic side chain type fluorine-free polyfluorene ether ketone proton exchange membrane. The obtained proton exchange membrane has the advantages of low cost, high proton conductivity and excellent solubility, thermal stability, oxidative stability, mechanical properties and the like.

Description

Technical Field

[0001] This invention relates to an aromatic side-chain type fluorine-free polyfluorene ether ketone proton exchange membrane and its preparation method, belonging to the field of organic synthesis technology. Background Technology

[0002] The concept of flow batteries was proposed in the 1970s. As a novel electrochemical energy storage technology, it sparked a surge of research, leading to the development of vanadium redox flow batteries (VFBs). Unlike traditional batteries, VFBs store energy in the active material of the electrolyte, and the inert electrodes themselves do not undergo electrochemical reactions. Therefore, energy storage and power output are relatively independent. With a fixed number of stacks, battery capacity can be increased by increasing the electrolyte volume or concentration. Combined with the flexibility of system design and its safety and environmental friendliness, VFBs are well-suited for large-scale electrochemical energy storage, experiencing rapid development and increasingly broad application prospects in recent years.

[0003] In comparison, as a large-scale energy storage device, flow batteries are cheaper and safer than lithium-ion batteries, and have higher energy efficiency than pumped hydro storage. Among flow batteries, vanadium redox flow batteries are one of the most mature technologies. A vanadium redox flow battery consists of vanadium electrolyte, a storage tank, a pump, graphite plates, carbon felt, clamps, sealing rings, pipes, and a separator. The separator is the most expensive component. It has been reported that there are three types of separators: proton exchange membranes, anion exchange membranes, and porous membranes. Proton exchange membranes have significant advantages due to their high ion selectivity and conductivity. However, the cost of proton exchange membranes remains high. For a 1MW vanadium redox flow battery, approximately 1 million square meters of proton exchange membrane are needed, typically costing between 1 million and 5 million RMB, accounting for more than half of the overall battery cost. Commercially available Nafion membranes are even more expensive. Reducing the cost of proton exchange membranes is the primary task for the commercialization of vanadium redox flow batteries.

[0004] The preparation of proton exchange membranes is divided into two methods: pre-sulfonation and post-sulfonation. Pre-sulfonation involves the direct polymerization of specially prepared sulfonated monomers, while post-sulfonation uses a special polymer precursor. Both steps involve dangerous and expensive special sulfonation processes, hindering commercialization. To improve proton conductivity, some monomers and polymers require carefully designed synthesis, which is even more costly. It is worth noting that there are many conventional, low-cost commercial compounds with sulfonic acid groups. These are often byproducts of certain commodities. Introducing them into polymers to prepare proton exchange membranes would significantly reduce costs compared to specially designed sulfonation methods.

[0005] In terms of performance, introducing multiple sulfonic acid groups onto the monomer, resulting in a dense distribution of sulfonic acid groups, can promote the formation of proton transport channels, thus achieving higher proton conductivity with the same ion exchange capacity (Macromolecules, 2011, 44(18): 7296-7306.). Most existing fluorine-free proton exchange membranes have sodium alkyl sulfonate side chains, which, compared to sodium benzenesulfonate, have poorer stiffness and thermal stability (Rsc Advances, 2017, 7(15): 8994-9001.). Furthermore, most of the reaction conditions are harsh and the steps are cumbersome, making them unsuitable for large-scale industrial production. This invention introduces the sodium benzenesulfonate structure into the side chain, improving both stiffness and thermal stability. The preparation process of this invention is relatively relaxed, simple, and low-cost, making it suitable for large-scale industrial production. It is of great significance for the development and production of high-performance polyfluorene ethers, fuel cells, and flow batteries. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides an aromatic side-chain type fluorine-free polyfluorene ether ketone proton exchange membrane and its preparation method. This membrane not only possesses excellent thermal stability, oxidative stability, and mechanical properties, but also exhibits high proton conductivity.

[0007] To achieve the above objectives, the following technical solution is adopted:

[0008] An aromatic side-chain type fluorine-free polyfluorene ether ketone proton exchange membrane, the chemical structure of which is shown in Formula I.

[0009]

[0010] Where m = 10 to 50 and n = 10 to 80.

[0011] The preparation method of the above-mentioned aromatic side-chain type fluorine-free polyfluorene ether ketone proton exchange membrane includes the following steps:

[0012] (1) Bisphenol fluorene, 4,4'-difluorobenzophenone, and tetramethoxybisphenol fluorene (CAS No.: 1331742-99-4) were added to a three-necked flask, followed by the addition of N,N'-dimethylacetamide and stirring to dissolve. Anhydrous potassium carbonate and toluene were then added. Under nitrogen protection, the system temperature was raised to 140–150 °C and reacted for 2–3 h. Water generated during the reaction was removed using a water separator. The toluene was then distilled off, and the system temperature was raised to 160–170 °C to continue the reaction for 12–36 h. After the reaction, the viscous reactant was poured into deionized water to precipitate a solid. The solid was collected by filtration, redissolved in dichloromethane, and then poured into methanol to precipitate again. The solid was collected by filtration and dried under vacuum at 80 °C for 24–48 h to obtain a methoxy-containing non-fluorinated polyfluorene ether ketone compound. The reaction process is as follows:

[0013]

[0014] Where m = 10 to 50 and n = 10 to 80.

[0015] (2) A methoxyl-containing non-fluorinated polyfluorene ether ketone compound and anhydrous dichloromethane were added to a three-necked flask equipped with a constant-pressure dropping funnel at a mass ratio of 1:10-30. After stirring and dissolving, the temperature was lowered to -40 to -80°C. Then, a 6-12% (w / w) dichloromethane solution of boron tribromide was added dropwise to the constant-pressure dropping funnel and allowed to rise naturally to room temperature. The reaction was allowed to proceed for 24-48 hours. The reactants were then slowly poured into methanol to precipitate the precipitate. The precipitate was collected by filtration, washed 3-5 times with deionized water, and dried under vacuum at 80°C for 24-48 hours to obtain a phenolic hydroxyl-containing non-fluorinated polyfluorene ether ketone compound. The reaction process is as follows:

[0016]

[0017] Where m = 10 to 50 and n = 10 to 80.

[0018] (3) Add the phenolic hydroxyl-containing non-fluorinated polyfluorene ether ketone compound and dimethyl sulfoxide to a three-necked flask, stir to dissolve, then add NaOH and stir for 10-30 minutes. Finally, add sodium p-chlorobenzenesulfonate, and react at 100°C for 24-48 hours under nitrogen protection. Then pour into ethanol to precipitate, filter and collect the precipitate, then wash with deionized water 3-5 times, and dry at 80°C under vacuum for 24-48 hours to obtain the aromatic side-chain type non-fluorinated polyfluorene ether ketone compound containing sodium sulfonate. The reaction process is as follows:

[0019]

[0020] Where m = 10 to 50 and n = 10 to 80.

[0021] (4) Dissolve the aromatic side-chain type fluorine-free polyfluorene ether ketone compound containing sodium sulfonate in N,N'-dimethylacetamide to prepare a concentration of 5-10 wt%. After filtration, cast the solution onto a horizontally placed glass plate and place it in an oven at 80°C for 24-48 hours. Immerse the glass plate in deionized water to allow the membrane to absorb water and detach. Then, immerse the membrane in a 1M sulfuric acid solution and acidify it at 80°C for 24-48 hours. Finally, wash away the residual sulfuric acid in the membrane with deionized water to obtain the aromatic side-chain type fluorine-free polyfluorene ether ketone proton exchange membrane. The reaction process is as follows:

[0022]

[0023] Where m = 10 to 50 and n = 10 to 80.

[0024] Furthermore, in step (1), the sum of the molar amounts of bisphenol fluorene and tetramethoxybisphenol fluorene is equal to the molar amount of 4,4'-difluorobenzophenone; the molar amount of anhydrous potassium carbonate is 2 to 6 times the molar amount of 4,4'-difluorobenzophenone.

[0025] Further, in step (1), the volume of N,N'-dimethylacetamide: the mass of 4,4'-difluorobenzophenone = 10-30 ml: 1 g; the volume of toluene is 10-50% of the volume of N,N'-dimethylacetamide.

[0026] Furthermore, in step (2), the molar ratio of the methoxyl-containing non-fluorinated polyfluorene ether ketone compound to boron tribromide is 1:4 to 6.

[0027] Furthermore, in step (3), the molar ratio of the phenolic hydroxyl-containing non-fluorinated polyfluorene ether ketone compound: NaOH: sodium p-chlorobenzenesulfonate is 1:4-6:4-8.

[0028] The preparation method described in this invention is a preferred embodiment. Reasonable temperature, time and other reaction conditions that can be foreseen by those skilled in the art are within the scope of protection of this invention, and are not limited to the above-mentioned reaction conditions.

[0029] This invention first synthesizes a methoxylated, non-fluorinated polyfluorinated ether ketone compound through polymerization, then demethylates it to synthesize a phenolic hydroxyl-containing non-fluorinated polyfluorinated ether ketone compound, followed by sulfonation to obtain an aromatic side-chain non-fluorinated polyfluorinated ether ketone compound containing sodium sulfonate, and finally obtains an aromatic side-chain non-fluorinated polyfluorinated ether ketone proton exchange membrane through solution casting and acidification. Compared with the prior art, this invention has the following advantages:

[0030] (1) The raw materials used are common chemical raw materials, which are inexpensive and easy to obtain; there are few reaction by-products and the yield is high.

[0031] (2) The experimental process is simple and quick to operate, and is suitable for large-scale industrial production.

[0032] (3) The obtained aromatic side-chain type fluorine-free polyfluorene ether ketone proton exchange membrane has high thermal stability, rigidity and durability, and has broad application prospects in fuel cell vanadium redox flow battery and other fields. Attached Figure Description

[0033] Figure 1 This is the 1H NMR spectrum of the methoxy-containing, fluorine-free polyfluorene ether ketone compound MPAEK in Example 1 of this invention;

[0034] Figure 2 This is the 1H NMR spectrum of HPAEK, a fluorine-free polyfluorene ether ketone compound containing phenolic hydroxyl groups, in Example 2 of this invention.

[0035] Figure 3The infrared spectra of MPAEK, a methoxyl-containing nonfluorinated polyfluorinated ether ketone compound in Example 1, HPAEK, a phenolic hydroxyl-containing nonfluorinated polyfluorinated ether ketone compound in Example 2, AR-SPAEK, an aromatic side-chain nonfluorinated polyfluorinated ether ketone compound containing sodium sulfonate in Example 3, and AL-SPAEK, an aliphatic side-chain nonfluorinated polyfluorinated ether ketone compound containing sodium sulfonate in Comparative Example 1 are shown.

[0036] Figure 4 This is the 1H NMR spectrum of AR-SPAEK, an aromatic side-chain-type non-fluorinated polyfluorene ether ketone compound containing sodium sulfonate, in Example 3 of this invention.

[0037] Figure 5 This is the 1H NMR spectrum of AL-SPAEK, a non-fluorinated polyfluorene ether ketone compound with a fatty side chain containing sodium sulfonate, in Comparative Example 1 of this invention.

[0038] Figure 6 These are the thermogravimetric analysis curves of the aromatic side-chain type fluorine-free polyfluorene ether ketone proton exchange membrane in Example 4 of the present invention and the aliphatic side-chain type fluorine-free polyfluorene ether ketone proton exchange membrane in Comparative Example 2. Detailed Implementation

[0039] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to these embodiments.

[0040] Example 1: Preparation of MPAEK, a methoxyl-containing, fluorine-free polyfluorene ether ketone compound

[0041] 0.9111 g (2.6 mmol) of bisphenol fluorene, 0.8728 g (4 mmol) of 4,4'-difluorobenzophenone, and 0.6587 g (1.4 mmol) of tetramethoxybisphenol fluorene were added to a three-necked flask, followed by 12 ml of N,N'-dimethylacetamide and stirring to dissolve. Then, 1.1056 g (8 mmol) of anhydrous potassium carbonate and 5 ml of toluene were added. Under nitrogen 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. The toluene was then distilled off, and the system temperature was raised to 165 °C and the reaction was continued for 12 h. After the reaction was completed, the viscous reactant was poured into 210 ml of deionized water to precipitate a solid. The solid was collected by filtration, redissolved in 45 ml of dichloromethane, and then poured into methanol to precipitate again. The solid was collected by filtration and dried under vacuum at 80 °C for 24 h to obtain the methoxy-containing fluorinated polyfluorene ether ketone compound MPAEK. Yield: 98%. The proton NMR spectrum of this compound is as follows: Figure 1 As shown: 1H NMR(400MHz,CHCl3,ppm)δ3.61(s,12H),6.54(s,4H),6.93(s,4H),7.01(s,8H) ,7.24(s,4H),7.31(s,4H),7.39(s,4H),7.45(s,4H),7.70(s,8H),7.82(s,4H).

[0042] Example 2: Preparation of HPAEK, a fluorine-free polyfluorene ether ketone compound containing phenolic hydroxyl groups.

[0043] 4.83 g (4 mmol) of the methoxylated, fluorine-free polyfluorene ether ketone compound MPAEK and 72 ml of anhydrous CH2Cl2 were added at a mass ratio of 1:20 to a three-necked flask equipped with a constant-pressure dropping funnel. After stirring and dissolving, the temperature was lowered to -45 °C. Then, 70 ml of a 6% (w / w) CH2Cl2 solution of BBr3 (20 mmol) was added dropwise to the constant-pressure dropping funnel and allowed to rise naturally to room temperature. The reaction was allowed to proceed for 24 h. The reactants were then slowly poured into 1000 ml of methanol to precipitate the product. The precipitate was collected by filtration, washed three times with deionized water, and dried under vacuum at 80 °C for 24 h to obtain the phenolic hydroxyl-containing, fluorine-free polyfluorene ether ketone compound HPAEK. Yield: 98%. The proton NMR spectrum of this compound is shown below. Figure 2 As shown: 1 The -OCH3 proton peak disappeared in the 3.75–3.5 ppm region of the ¹H NMR (400 MHz, DMSO, ppm) spectrum, while a -OH proton peak appeared in the 9.49–9.65 ppm region. This confirms that the methoxy-containing non-fluorinated polyfluorene ether ketone compound MPAEK has been demethylated. The infrared spectrum is as follows: Figure 3 As shown: HPAEK curves of fluorine-free polyfluorene ether ketone compounds containing phenolic hydroxyl groups were observed at 3400 cm⁻¹. -1 The presence of a broad -OH absorption peak confirms the successful demethylation of the methoxyl-containing non-fluorinated polyfluorene ether ketone compound MPAEK.

[0044] Example 3: Preparation of AR-SPAEK, an aromatic side-chain-type fluorinated polyfluorene ether ketone compound containing sodium sulfonate.

[0045] 2.3 g (2 mmol) of the phenolic hydroxyl-containing non-fluorinated polyfluorinated ether ketone compound HPAEK was added to 30 mL of dimethyl sulfoxide in a three-necked flask and stirred to dissolve. Then, 0.32 g (8 mmol) of NaOH was added and stirred for 10 minutes. Finally, 1.72 g (8 mmol) of sodium p-chlorobenzenesulfonate was added. The reaction was carried out at 100 °C for 48 h under nitrogen protection. The precipitate was then poured into ethanol, filtered, collected, washed three times with deionized water, and dried under vacuum at 80 °C for 24 h to obtain the aromatic side-chain non-fluorinated polyfluorinated ether ketone compound AR-SPAEK containing sodium sulfonate. Yield: 98%. Its 1H NMR spectrum is shown below. Figure 4 As shown: the -OH proton peak disappeared at 9.49–9.65 ppm, while new peaks appeared at 7.02 ppm and 7.20 ppm, corresponding to the -CH proton peaks on the benzene ring of sodium p-chlorobenzenesulfonate, respectively. This confirms that the fluorine-free polyfluorene ether ketone compound HPAEK containing phenolic hydroxyl groups has been successfully incorporated into the sodium benzenesulfonate group. The infrared spectrum is as follows: Figure 3 As shown: AR-SPAEK curves of aromatic side-chain type fluorinated polyfluorene ether ketone compounds were observed at 1037 cm⁻¹. -1 The absorption peak at O=S=O also confirms that the fluorine-free polyfluorene ether ketone compound HPAEK containing phenolic hydroxyl groups has been successfully incorporated into sodium benzenesulfonate groups.

[0046] Comparative Example 1: Preparation of AL-SPAEK, a fatty side-chain-type fluorine-free polyfluorene ether ketone compound containing sodium sulfonate

[0047] 2.3 g (2 mmol) of the phenolic hydroxyl-containing non-fluorinated polyfluorinated ether ketone compound HPAEK was added to 30 mL of dimethyl sulfoxide in a three-necked flask and stirred until dissolved. Then, 0.32 g (8 mmol) of NaOH was added and stirred for 10 minutes. Finally, 0.7 mL (8 mmol) of propanesulfonic acid lactone was added. The reaction was carried out at 100 °C for 48 h under nitrogen protection. The precipitate was then poured into ethanol, collected by filtration, washed three times with deionized water, and dried under vacuum at 80 °C for 24 h to obtain the sodium sulfonate-containing aliphatic side-chain non-fluorinated polyfluorinated ether ketone compound AL-SPAEK. Yield: 98%. Its chemical structure is as follows:

[0048]

[0049] Where m = 10 to 50 and n = 10 to 80.

[0050] The 1H NMR spectrum of AL-SPAEK, a non-fluorinated polyfluorene ether ketone compound with a fatty side chain containing sodium sulfonate, is as follows: Figure 5As shown, the -OH proton peak disappeared in the 9.49–9.65 ppm range, while new peaks appeared at 4.17 ppm, 4.12 ppm, and 3.75 ppm, corresponding to the -H proton peaks on propanesulfonate lactone, respectively. This confirms that the fluorine-free polyfluorene ether ketone compound HPAEK containing phenolic hydroxyl groups has been successfully incorporated into sodium propanesulfonate groups. The infrared spectrum is shown below. Figure 3 As shown: From the AL-SPAEK curve, it was observed that at 1075 cm⁻¹... -1 The absorption peak for O=S=O also confirms that the fluorine-free polyfluorene ether ketone compound HPAEK, containing phenolic hydroxyl groups, has been successfully incorporated with sodium propyl sulfonate groups.

[0051] Example 4: Preparation of Aromatic Side-Chain Type Fluorine-Free Polyfluorene Ether Ketone Proton Exchange Membrane

[0052] The aromatic side-chain type fluorine-free polyfluorene ether ketone compound AR-SPAEK containing sodium sulfonate was dissolved in N,N'-dimethylacetamide to prepare a concentration of 5wt%. After filtration, the solution was cast onto a horizontally placed glass plate and placed in an oven at 80℃ for 24 hours. The glass plate was then immersed in deionized water to allow the membrane to absorb water and detach. Subsequently, the membrane was immersed in a 1M sulfuric acid solution and acidified at 80℃ for 24 hours. Finally, the membrane was washed with deionized water to remove the residual sulfuric acid, thus obtaining the aromatic side-chain type fluorine-free polyfluorene ether ketone proton exchange membrane.

[0053] Comparative Example 2: Preparation of Fatty Side-Chain Type Fluorine-Free Polyfluorene Etherketone Proton Exchange Membrane

[0054] A fatty-side-chain, fluorine-free polyfluorene ether ketone (AL-SPAEK) compound containing sodium sulfonate was dissolved in N,N'-dimethylacetamide to prepare a 5wt% concentration. After filtration, the solution was cast onto a horizontally placed glass plate and placed in an oven at 80°C for 24 hours. The glass plate was then immersed in deionized water to allow the membrane to absorb water and detach. Subsequently, the membrane was immersed in a 1M sulfuric acid solution and acidified at 80°C for 24 hours. Finally, the membrane was washed with deionized water to remove residual sulfuric acid, yielding the fatty-side-chain, fluorine-free polyfluorene ether ketone proton exchange membrane. Its chemical structure is as follows:

[0055]

[0056] Where m = 10 to 50 and n = 10 to 80.

[0057] Table 1 shows the basic properties of aromatic side-chain type fluorinated polyfluorene ether ketone (PFEK) proton exchange membranes at different temperatures. With increasing temperature, the proton conductivity of the aromatic side-chain type PFEK proton exchange membrane gradually increases, as do its water absorption and swelling rate. At 80℃, the water absorption rate of the aromatic side-chain type PFEK proton exchange membrane is 35.3%, and its swelling rate is 8.6%. Table 2 shows the basic properties of aliphatic side-chain type PFEK proton exchange membranes at different temperatures. With increasing temperature, the proton conductivity of the aliphatic side-chain type PFEK proton exchange membrane gradually increases, as do its water absorption and swelling rate. At 80℃, the water absorption rate of the aliphatic side-chain type PFEK proton exchange membrane is 42.2%, and its swelling rate is 9.2%. Although there is no significant difference in water absorption and swelling rates between aromatic side-chain type and aliphatic side-chain type fluorinated polyfluorene ether ketone (PFEK) proton exchange membranes, and no significant difference in proton conductivity between 20 and 40°C, the proton conductivity of aromatic side-chain type PFEK proton exchange membranes is significantly higher than that of aliphatic side-chain type PFEK proton exchange membranes at 60 to 80°C.

[0058] Table 3 shows the breakage time and tensile properties of aromatic side-chain type fluorinated polyfluorene ether ketone (PFEK) proton exchange membranes and aliphatic side-chain type PFEK PFEK proton exchange membranes. The membranes were immersed in Fenton's reagent and observed for breakage every 5 hours. The mechanical properties of the membranes were then tested using a tensile test. Testing instrument: SUNS 6502X tensile testing machine. The membranes were cut into dumbbell shapes (5×75mm) and tensile tests were performed at room temperature at a tensile speed of 5mm / min. -1 The tensile strength and elongation were obtained. The aromatic side-chain type fluorinated polyfluorene ether ketone proton exchange membrane had a membrane breakage time of 45 h, a tensile strength of 61.2 MPa, and an elongation of 13.4%, while the aliphatic side-chain type fluorinated polyfluorene ether ketone proton exchange membrane had a membrane breakage time of 35 h, a tensile strength of 58.8 MPa, and an elongation of 9.3%. It is evident that the aromatic side-chain type fluorinated polyfluorene ether ketone proton exchange membrane exhibits higher oxidative stability and mechanical strength than the aliphatic side-chain type.

[0059] The thermogravimetric curves of aromatic side-chain type fluorinated polyfluorene ether ketone proton exchange membranes and aliphatic side-chain type fluorinated polyfluorene ether ketone proton exchange membranes are shown below. Figure 6 As shown, the mass loss of the aromatic side-chain type fluorinated polyfluorene ether ketone proton exchange membrane in each temperature range is lower than that of the aliphatic side-chain type fluorinated polyfluorene ether ketone proton exchange membrane, proving that the thermal stability of the aromatic side-chain type fluorinated polyfluorene ether ketone proton exchange membrane is better than that of the aliphatic side-chain type fluorinated polyfluorene ether ketone proton exchange membrane.

[0060] Table 1. Basic properties of aromatic side-chain type fluorine-free polyfluorene ether ketone proton exchange membranes at different temperatures.

[0061]

[0062] Table 2. Basic properties of fatty side-chain type fluorine-free polyfluorene ether ketone proton exchange membranes at different temperatures.

[0063]

[0064] Table 3. Breakage time and tensile properties of aromatic side-chain type fluorinated polyfluorene ether ketone proton exchange membranes and aliphatic side-chain type fluorinated polyfluorene ether ketone proton exchange membranes.

[0065]

[0066] 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. An aromatic side-chain type fluorine-free polyfluorene ether ketone proton exchange membrane, characterized in that, Its chemical structural formula is shown below: Where m = 10~50 and n = 10~80.

2. The method for preparing the aromatic side-chain type fluorine-free polyfluorene ether ketone proton exchange membrane according to claim 1, characterized in that, Includes the following steps: (1) Add bisphenol fluorene, 4,4'-difluorobenzophenone and tetramethoxybisphenol fluorene to a three-necked flask, then add N,N-dimethylacetamide and stir to dissolve. Then add anhydrous potassium carbonate and toluene. Under nitrogen protection, raise the temperature of the system to 140~150 ℃ and react for 2~3 h. Remove the water generated in the reaction through a water separator. Then distill off the toluene and raise the temperature of the system to 160~170 ℃ to continue the reaction for 12~36 h. After the reaction is completed, pour the viscous reactant into deionized water to precipitate the solid. Filter and collect the solid. Redissolve it in dichloromethane and pour it into methanol to precipitate. Filter and collect the solid. Dry it under vacuum at 80 ℃ for 24~48 h to obtain the methoxy-containing non-fluorinated polyfluorene ether ketone compound. The chemical structural formula of the obtained methoxy-containing non-fluorinated polyfluorene ether ketone compound is shown below: Where m = 10~50, n = 10~80; (2) Add the methoxyl-containing non-fluorinated polyfluorene ether ketone compound and anhydrous dichloromethane at a mass ratio of 1:10~30 to a three-necked flask equipped with a constant pressure dropping funnel. After stirring and dissolving, lower the temperature to -40~-80℃. Then add a dichloromethane solution of boron tribromide with a mass percentage concentration of 6~12% to the constant pressure dropping funnel and add it dropwise to the three-necked flask. Then let the temperature rise naturally to room temperature and react for 24~48 h. Then slowly pour the reactants into methanol to precipitate, filter and collect the precipitate, wash it with deionized water 3~5 times, and dry it under vacuum at 80℃ for 24~48 h to obtain the phenolic hydroxyl-containing non-fluorinated polyfluorene ether ketone compound. The chemical structural formula of the obtained fluorine-free polyfluorene ether ketone compound containing phenolic hydroxyl groups is shown below: Where m = 10~50, n = 10~80; (3) Add the phenolic hydroxyl-containing non-fluorinated polyfluorene ether ketone compound and dimethyl sulfoxide into a three-necked flask, stir to dissolve, then add NaOH and stir for 10-30 minutes, finally add sodium p-chlorobenzenesulfonate, react at 100 °C for 24-48 h under nitrogen protection, then pour into ethanol to precipitate, filter to collect the precipitate, then wash with deionized water 3-5 times, and dry at 80 °C under vacuum for 24-48 h to obtain the aromatic side chain type non-fluorinated polyfluorene ether ketone compound containing sodium sulfonate; The chemical structural formula of the obtained aromatic side-chain-type non-fluorinated polyfluorene ether ketone compound containing sodium sulfonate is shown below: Where m = 10~50, n = 10~80; (4) Dissolve the aromatic side-chain type fluorine-free polyfluorene ether ketone compound containing sodium sulfonate in N,N-dimethylacetamide to prepare a concentration of 5~10 wt%. After filtration, cast it onto a horizontally placed glass plate and place it in an 80 ℃ oven for 24~48 h. Immerse the glass plate in deionized water to allow the membrane to absorb water and detach. Then immerse the membrane in a 1 M sulfuric acid solution and acidify it at 80 ℃ for 24~48 h. Finally, wash away the residual sulfuric acid in the membrane with deionized water to obtain the aromatic side-chain type fluorine-free polyfluorene ether ketone proton exchange membrane.

3. The preparation method according to claim 2, characterized in that, In step (1), the sum of the molar amounts of bisphenol fluorene and tetramethoxybisphenol fluorene is equal to the molar amount of 4,4'-difluorobenzophenone; the molar amount of anhydrous potassium carbonate is 2 to 6 times the molar amount of 4,4'-difluorobenzophenone.

4. The preparation method according to claim 2, characterized in that, In step (1), the volume of N,N-dimethylacetamide and the mass of 4,4'-difluorobenzophenone are 10~30 ml and 1 g respectively; the volume of toluene is 10~50% of the volume of N,N-dimethylacetamide.

5. The preparation method according to claim 2, characterized in that, In step (2), the molar ratio of the methoxyl-containing nonfluorinated polyfluorene ether ketone compound to boron tribromide is 1:4~6.

6. The preparation method according to claim 2, characterized in that, In step (3), the molar ratio of the phenolic hydroxyl-containing non-fluorinated polyfluorene ether ketone compound: NaOH: sodium p-chlorobenzenesulfonate is 1:4~6:4~8.

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