Anion exchange membrane grafted with crown ether piperidinium cation and preparation method thereof

Abstract

The application belongs to the technical field of basic anion exchange membranes, and provides an anion exchange membrane grafted with crown ether piperidine cations and a preparation method thereof.The anion exchange membrane is a kind of anion exchange membrane with crown ether modified piperidine as a cationic group, with a main chain of a stable crown ether oxygen structure as a polymer main chain, with crown ether modified piperidine as a cationic group grafted on the polymer main chain for modification, with the hydrophilicity of the crown ether increasing the polarity difference between the cationic group and the hydrophobic main chain, and with the micro-phase separation effect being enhanced to improve the conductivity.The novel piperidine cation is synthesized by a method catalyzed by super strong acid, and the crown ether modified piperidine cation can enhance the micro-phase separation of the membrane hydrophilicity, and enhance the conductivity of the membrane.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of fuel cell membrane materials, and relates to an anion exchange membrane with crown ether modified piperidine as a cationic group and a preparation method thereof. BACKGROUND

[0002] In modern society, the rapid development of science and technology makes environmental problems and energy problems increasingly attract people's attention, and the development and use of new energy is imminent. Hydrogen energy, as an ideal energy source with clean source and wide distribution, has attracted special attention. Hydrogen fuel cell, which can directly utilize hydrogen energy, is a high-efficiency and pollution-free device for converting chemical energy into electrical energy.

[0003] Compared with cation exchange membrane fuel cells, the theoretical oxygen reduction reaction kinetics of anion exchange membrane fuel cells is lower, various noble metals required by cation exchange membrane fuel cells are not required, and non-noble metal catalysts such as iron, cobalt and nickel can be used, which has good cost advantage. As one of the core components of fuel cells, anion exchange membrane plays a role in isolating anode and cathode and conducting anions. Although alkaline anion exchange membrane fuel cells have many advantages, anion exchange membranes also have some problems to be solved, such as low conductivity and poor alkali stability.

[0004] The transfer of hydroxyl ions in anion exchange membrane depends on cation exchange groups, so the number of ion exchange groups can be increased, however, too high ion exchange capacity will lead to an increase in membrane water absorption and swelling rate, and the mechanical properties of the membrane will decrease, therefore, under the limited number of ion exchange groups, the cationic groups can be designed to be aggregated and arranged to form a hydrophilic "channel" for the movement of hydroxyl ions, and the hydrophobic region will provide the mechanical properties required by the membrane, which requires increasing the polarity difference between the hydrophilic phase and the hydrophobic phase to realize this microphase separation. SUMMARY

[0005] In view of the above problems of low conductivity and poor alkali stability, the present application proposes an anion exchange membrane with crown ether modified piperidine as a cationic group applied in fuel cells, which takes an alkali-stable oxygen-free polymer as a main chain and crown ether modified piperidine as a cationic group.

[0006] To achieve the above purpose, the technical scheme adopted by the present application is:

[0007] The application discloses a grafting crown ether piperidine cation anion exchange membrane, which is a kind of anion exchange membrane with crown ether modified piperidine as cationic group, is a kind of comb polymer, uses N-methyl piperidine as cationic group, adopts hydrophilic crown ether unit to modify piperidine group, forms microphase separation by the polarity difference between hydrophilic cationic group and hydrophobic main chain, and realizes good alkali stability and high hydroxyl conductivity at a low ion exchange capacity.

[0008] The polymer structure is as follows, wherein x represents the molar percentage of the structural unit of the grafting crown ether piperidine cation:

[0009]

[0010] A preparation method of the grafting crown ether piperidine cation anion exchange membrane comprises the following steps:

[0011] (1) preparing an oxygen-free main chain

[0012] 1.1) dissolving the biphenyl monomer 1 and the ketone-containing monomer 2 in a solvent A, stirring until completely dissolved to obtain a reaction mixture system, wherein the molar ratio of the biphenyl monomer 1 to the ketone-containing monomer 2 is 1:1.1-1.2;

[0013] 1.2) mixing triflic acid and trifluoroacetic acid, then slowly adding the mixture into the reaction mixture system in step 1.1) under an ice bath condition, wherein the volume ratio of the triflic acid to the trifluoroacetic acid is 7-9:1, and the molar ratio of the triflic acid to the biphenyl monomer 1 is 9:1;

[0014] 1.3) after the dropwise addition is completed, with the extension of the reaction time, the viscosity of the reaction system gradually increases, and when the reaction liquid is viscous and the rotor cannot rotate, the reaction liquid is transferred to a solvent B reaction system to precipitate as a solid, and the solid is repeatedly washed with a solvent C until the washing is neutral, to obtain the oxygen-free polymer main chain 1; finally, the oxygen-free polymer main chain is placed in a vacuum drying oven for drying;

[0015] The biphenyl monomer 1 in step (1) is biphenyl, p-terphenyl, m-terphenyl or the like; and the ketone-containing monomer 2 is N-methyl piperidone, 1,1,1-trifluoroacetone or 2,2,2-trifluorophenylacetone or the like.

[0016] The solvent A in step (1) is anhydrous dichloromethane, the solvent B is ethyl acetate, acetone or deionized water, and the solvent C is deionized water.

[0017] The vacuum drying oven in step (1) is 40-80 DEG C, and the time is 24-48 h.

[0018] (2) preparing a crown ether modified piperidine cation

[0019] 2.1) Add benzocrown ether monomer 3 and N-methyl piperidone into solvent D until completely dissolved to obtain a reaction mixture, wherein the molar ratio of benzocrown ether monomer 3 to N-methyl piperidone is 3-4:1;

[0020] 2.2) Mix trifluoromethanesulfonic acid and trifluoroacetic acid, then add into constant pressure dropping funnel, and drop into the reaction mixture of step 2.1) under ice bath, wherein the volume ratio of trifluoromethanesulfonic acid to trifluoroacetic acid is 13-15:1, and the molar ratio of trifluoroacetic acid to N-methyl piperidone is 2:1;

[0021] 2.3) After the drop is completed, keep the ice bath for 12-24 h, and after the reaction is completed, pour the mixture into solvent E, add potassium carbonate until no bubbles are generated, filter out the precipitate, and dry the upper liquid with a rotary evaporator to obtain a solid, which is washed with solvent F and placed in a vacuum drying oven to dry, to obtain a solid, which is crown ether modified piperidine 2;

[0022] The benzocrown ether monomer 3 in step (2) is benzocrown-5 or benzocrown-6.

[0023] The solvent D in step (2) is anhydrous dichloromethane, the solvent E is methanol or ethanol, and the solvent F is dichloromethane.

[0024] The vacuum drying oven in step (2) is 40-60°C, and the time is 24-48 h.

[0025] (3) Preparation of bromooctyl oxygen-free main chain

[0026] Dissolve the oxygen-free polymer main chain 1 in step (1) in solvent G, pour into a constant pressure dropping funnel, and slowly drop into a mixture of solvent G and excess 1,8-dibromo octane, and react at 50-55°C for 48-72 h. After the reaction is completed, pour the reaction mixture into solvent H to generate a large amount of precipitate. The precipitate is filtered and repeatedly washed with solvent H and solvent I, and dried in a vacuum drying oven to obtain a bromooctyl oxygen-free main chain 3. The molar ratio of 1,8-dibromo octane to the structural unit of the oxygen-free polymer main chain 1 is 8-10:1.

[0027] The solvent G in step (3) is dimethyl sulfoxide, the solvent H is ethyl acetate, diethyl ether or acetone, and the solvent I is deionized water.

[0028] The vacuum drying oven in step (3) is 40-80°C, and the time is 24-48 h.

[0029] (4) Synthesis of crown ether modified anion exchange membrane

[0030] The bromooctyl oxygen-free main chain 3 in step (3) is reacted with the crown ether modified piperidine in mixture 2 in step (2); specifically: the bromooctyl oxygen-free main chain 3 is dissolved in solvent J at 60-90°C, an excess of mixture 2 is added, the reaction is stopped after 48-72h, poured into solvent K, a large amount of precipitate is obtained, repeatedly washed with solvent K and solvent L, and dried in a vacuum drying box to obtain polymer 4. The mass ratio of the bromooctyl oxygen-free main chain 3 to the crown ether modified piperidine 2 is 1:3-5.

[0031] In step (4), solvent J is dimethyl sulfoxide; solvent K is ethyl acetate, diethyl ether or acetone; and solvent L is deionized water.

[0032] In step (4), the vacuum drying box is at 40-80°C for 24-48h.

[0033] (5) Casting film

[0034] The polymer synthesized in step (4) is dissolved in solvent L to prepare a 5wt% solution, then the solution is flowed on a clean glass plate, the glass plate is placed horizontally, heated to 60-80°C and left to stand for 24-36h.

[0035] (6) Alkali treatment

[0036] The film obtained in step (5) is peeled off from the surface of the glass plate, immersed in a 1mol / L sodium hydroxide or potassium hydroxide solution for 24-48h, and then the free alkali on the surface is washed away with deionized water to obtain a crown ether modified piperidine grafted anion exchange film.

[0037] The reaction principle of the present application is as follows:

[0038] The biphenyl monomer and the ketone monomer are polymerized into a polymer chain by a Friedel-Crafts reaction catalyzed by a super acid, the ketone monomer and the benzo crown ether monomer are synthesized into a crown ether modified cation, and finally the cation is grafted on the polymer main chain by a Menshutkin reaction.

[0039] The present application has the following beneficial effects:

[0040] (1) A novel piperidine cation is synthesized by a method catalyzed by a super acid.

[0041] (2) The crown ether modified piperidine cation can enhance the hydrophilic microphase separation of the film and enhance the conductivity of the film. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 The present application is a crown ether modified piperidine as a cation of a polyarylene piperidine polymer 4 in the implementation case 1 1 The H NMR spectrum, in which the abscissa is the chemical shift.

[0043] Figure 2 A TEM image of the polyarylpiperidine polymer 4 of Example 1 modified with a crown ether modified piperidinium cation.

[0044] Figure 3 A battery performance graph of Example 1. DETAILED DESCRIPTION

[0045] The application will be further described in connection with specific examples.

[0046] Example 1:

[0047] (1) Preparation of an oxygen-free main chain

[0048] Into 8 ml of dichloromethane, 3.33 g (0.0216 mol) of biphenyl, 1.8 ml (0.0158 mol) of N-methylpiperidone and 0.93 ml (0.0102 mol) of 1,1,1-trifluoroacetone (molar ratio of biphenyl to ketone-containing monomer is 1:1.2) were added, and stirred in an ice bath until completely dissolved. 1.62 ml of trifluoroacetic acid and 13 ml of trifluoromethanesulfonic acid were added into a constant pressure dropping funnel and slowly added to the reaction mixture. Stirring was continued in an ice bath until the rotor could not rotate freely. The entire mixture was poured into deionized water, washed three times with deionized water, and dried in a vacuum oven at 80°C for 24 h to obtain polyarylpiperidine polymer 1.

[0049] (2) Preparation of a crown ether modified piperidinium cation

[0050] Into 4 ml of dichloromethane, 5.63 g (0.021 mol) of benzo 15-crown-5 and 0.8 ml (0.007 mol) of N-methylpiperidone (molar ratio of benzo 15-crown-5 to N-methylpiperidone is 3:1) were added and completely dissolved. 13 ml of trifluoromethanesulfonic acid and 1 ml of trifluoroacetic acid were mixed and added into a constant pressure dropping funnel. The mixture was added dropwise under ice bath. After the addition was completed, the ice bath was maintained for 12 h. After the reaction was completed, the mixture was poured into ethanol, and excess potassium carbonate was added until no bubbles were generated. The precipitate was filtered off, and the upper liquid was spin-dried with a rotary evaporator. The obtained solid was washed with dichloromethane and placed in a vacuum oven at 60°C for 24 h. The final solid product was a crown ether modified piperidinium cation 2.

[0051] (3) Preparation of a bromooctyl oxygen-free main chain

[0052] The polymer 1 in step (1) 2g was dissolved in dimethyl sulfoxide, poured into a constant pressure dropping funnel and slowly added dropwise into a mixture of dimethyl sulfoxide and 5ml 1,8-dibromo octane, the reaction was carried out at 53°C for 36h, after the reaction was completed, the reaction mixture was poured into ethyl acetate, a large amount of precipitate was formed; the precipitate was filtered and repeatedly washed with ethyl acetate and deionized water, and dried in a vacuum oven at 40°C for 48h to obtain a bromo octyl poly (arylene piperidine) main chain 3;

[0053] (4) Synthesis of crown ether modified anion exchange membrane

[0054] The bromo octyl poly (arylene piperidine) main chain 3 in step (3) was reacted with the crown ether modified piperidine cation 2 in step (2); specifically, 1g of the bromo octyl oxygen-free main chain 3 was dissolved in dimethyl sulfoxide at 80°C, 3g of the crown ether modified piperidine cation 2 was added, the reaction was stopped after 36h, and then poured into ethyl acetate to obtain a large amount of precipitate, which was repeatedly washed with ethyl acetate and deionized water, and then dried in a vacuum drying oven at 40°C for 48h to obtain a poly (arylene piperidine) polymer 4 with a crown ether modified piperidine as a cation; Figure 1 TEM image of the poly (arylene piperidine) polymer 4 with a crown ether modified piperidine as a cation, from which it can be seen that the polymer membrane has a good microphase separation morphology; 1 H NMR spectrum, from which it can be seen that the polymer membrane is successfully prepared; Figure 2 TEM image of the poly (arylene piperidine) polymer 4 with a crown ether modified piperidine as a cation, from which it can be seen that the polymer membrane has a good microphase separation morphology;

[0055] (5) Casting film

[0056] The polymer 4 synthesized in step (4) was dissolved in dimethyl sulfoxide to prepare a 5wt% solution, and then flowed onto a clean glass plate, which was placed horizontally and heated to 60°C for 36h;

[0057] (6) Alkali treatment

[0058] The membrane obtained in step (5) was peeled off from the surface of the glass plate, and after being soaked in a 1mol / L sodium hydroxide solution for 36h, the free alkali on the surface of the membrane was washed away with deionized water to obtain an anion exchange membrane with a crown ether modified piperidine as a cationic group.

[0059] Figure 3 Battery performance diagram of Example 1, from which it can be seen that the membrane applied to an alkaline hydrogen-oxygen fuel cell has a high peak power density (558mW cm -2 ) and an open circuit voltage (0.97V).

[0060] Example 2:

[0061] (1) Preparation of oxygen-free main chain

[0062] Into a 4.5 ml dichloromethane, 2.303 g (0.01 mol) of m-terphenyl, 1.254 ml (0.011 mol) of N-methylpiperidone (molar ratio of m-terphenyl to N-methylpiperidone is 1:1.1) were added and stirred in an ice bath until completely dissolved. Into a constant pressure dropping funnel, 1 ml of trifluoroacetic acid and 8 ml of trifluoromethanesulfonic acid were added and slowly added into the reaction mixture. The stirring was continued in an ice bath until the rotor could not rotate freely. The whole mixture was poured into ethyl acetate and the solid was washed with deionized water for three times and dried in a vacuum oven at 60 °C for 36 h to obtain polyarylene piperidine polymer 1.

[0063] (2) Preparation of crown ether modified piperidinium cation

[0064] Into 4 ml of dichloromethane, 7.51 g (0.028 mol) of benzo 15-crown-5 and 0.8 ml (0.007 mol) of N-methylpiperidone (molar ratio of benzo 15-crown-5 to N-methylpiperidone is 4:1) were added and stirred in an ice bath until completely dissolved. Into a constant pressure dropping funnel, 15 ml of trifluoromethanesulfonic acid and 1 ml of trifluoroacetic acid were mixed and added into the mixture in an ice bath drop by drop. After the addition was completed, the ice bath was maintained for 18 h. After the reaction was completed, the mixture was poured into ethanol and excess potassium carbonate was added until no bubbles were generated. The precipitate was filtered off and the upper liquid was rotary evaporated to dryness. The obtained solid was washed with dichloromethane and placed in a vacuum oven at 40 °C for 48 h to obtain the solid product as a crown ether modified piperidinium cation 2.

[0065] (3) Preparation of bromo-octyl oxygen-free backbone

[0066] Into 4 ml of dichloromethane, 7.51 g (0.028 mol) of benzo 15-crown-5 and 0.8 ml (0.007 mol) of N-methylpiperidone (molar ratio of benzo 15-crown-5 to N-methylpiperidone is 4:1) were added and stirred in an ice bath until completely dissolved. Into a constant pressure dropping funnel, 15 ml of trifluoromethanesulfonic acid and 1 ml of trifluoroacetic acid were mixed and added into the mixture in an ice bath drop by drop. After the addition was completed, the ice bath was maintained for 18 h. After the reaction was completed, the mixture was poured into ethanol and excess potassium carbonate was added until no bubbles were generated. The precipitate was filtered off and the upper liquid was rotary evaporated to dryness. The obtained solid was washed with dichloromethane and placed in a vacuum oven at 40 °C for 48 h to obtain the solid product as a crown ether modified piperidinium cation 2.

[0067] (4) Synthesis of crown ether modified anion exchange membrane

[0068] The bromo-octyl polyarylene piperidine backbone 3 in step (3) was reacted with the crown ether modified piperidinium cation 2 in step (2). Specifically, 1 g of bromo-octyl oxygen-free backbone 3 was dissolved in dimethyl sulfoxide at 60 °C, 5 g of crown ether modified piperidinium cation 2 was added, and the reaction was stopped after 72 h of reaction. The reaction mixture was poured into diethyl ether to obtain a large amount of precipitate, which was repeatedly washed with diethyl ether and deionized water, and then dried in a vacuum drying oven at 80 °C for 24 h to obtain a polyarylene piperidine polymer 4 with a crown ether modified piperidinium cation as a cation.

[0069] (5) Casting film

[0070] The polymer 4 synthesized in step (4) was dissolved in dimethyl sulfoxide to form a 5wt% solution, and then was cast on a clean glass plate, horizontally placed, heated to 80°C and left for 24 hours;

[0071] (6) Alkali treatment

[0072] The film obtained in step (5) was peeled off from the surface of the glass plate, and after being soaked in 1 mol / L potassium hydroxide solution for 24 hours, the free alkali on the surface of the film was washed away with deionized water to obtain an anion exchange membrane with crown ether modified piperidine as cationic group.

[0073] Example 3:

[0074] (1) Preparation of oxygen-free main chain

[0075] 2.303 g (0.01 mol) of p-terphenyl, 0.74 ml (0.0065 mol) of N-methyl piperidone and 0.686 ml (0.005 mol) of 2,2,2-trifluoroacetophenone (molar ratio of p-terphenyl to ketone-containing monomer is 1:1.15) were added to 4.5 ml of dichloromethane, stirred in an ice bath until completely dissolved, 1 ml of trifluoroacetic acid and 9 ml of trifluoromethanesulfonic acid were added to a constant pressure dropping funnel and slowly added to the reaction mixture, and the stirring was continued in an ice bath until the rotor could not rotate freely. The whole mixture was poured into acetone, the solid was washed with deionized water for three times, and then dried in a vacuum oven at 40°C for 48 h to obtain polyarylene piperidine polymer 1.

[0076] (2) Preparation of crown ether modified piperidine cation

[0077] 7.65 g (0.0245 mol) of benzo 18-crown-6 and 0.8 ml (0.007 mol) of N-methyl piperidone (molar ratio of benzo 18-crown-6 to N-methyl piperidone is 3.5:1) were added to 4 ml of dichloromethane until completely dissolved. 14 ml of trifluoromethanesulfonic acid and 1 ml of trifluoroacetic acid were mixed and added to a constant pressure dropping funnel, and then added dropwise to the mixture under ice bath. After the addition was completed, the ice bath was maintained for 24 h. After the reaction was completed, the mixture was poured into methanol, and excess potassium carbonate was added until no bubbles were generated. The precipitate was filtered off, and the upper liquid was rotary evaporated to dryness. The obtained solid was washed with dichloromethane and placed in a vacuum oven at 50°C for 36 h. Finally, the solid product obtained was crown ether modified piperidine cation 2.

[0078] (3) Preparation of bromooctyl oxygen-free main chain

[0079] The 2 g of polymer 1 in step (1) was dissolved in dimethyl sulfoxide, poured into a constant pressure dropping funnel and slowly added dropwise to a mixture of dimethyl sulfoxide and 5 ml of 1,8-dibromo octane, and the reaction was carried out at 55°C for 48 h. After the reaction was completed, the reaction mixture was poured into ethyl acetate to form a large amount of precipitate. The precipitate was filtered and repeatedly washed with ethyl acetate and deionized water, and dried in a vacuum oven at 60°C for 36 h to obtain a bromo octyl poly (arylene piperidine) backbone 3.

[0080] (4) Synthesis of crown ether modified anion exchange membrane

[0081] The bromo octyl poly (arylene piperidine) backbone 3 in step (3) was reacted with the crown ether modified piperidine cation 2 in step (2). Specifically, 1 g of bromo octyl oxygen-free backbone 3 was dissolved in dimethyl sulfoxide at 90°C, 4 g of crown ether modified piperidine cation 2 was added, the reaction was stopped after 48 h, poured into acetone to obtain a large amount of precipitate, repeatedly washed with acetone and deionized water, and dried in a vacuum drying oven at 60°C for 36 h to obtain a poly (arylene piperidine) polymer 4 with crown ether modified piperidine as the cation.

[0082] (5) Casting film

[0083] The polymer 4 synthesized in step (4) was dissolved in dimethyl sulfoxide to prepare a 5 wt% solution, and then flowed onto a clean glass plate, placed horizontally, heated to 70°C and left for 30 h;

[0084] (6) Alkali treatment

[0085] The film obtained in step (5) was peeled off from the surface of the glass plate, and after being immersed in a 1 mol / L potassium hydroxide solution for 48 h, the free alkali on the surface of the film was washed off with deionized water to obtain an anion exchange membrane with crown ether modified piperidine as the cationic group.

[0086] The above examples only express the embodiments of the present application, but cannot be understood as limiting the scope of the patent of the present application. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application.

Claims

1. A method for preparing an anion exchange membrane grafted with a crown ether piperidinium cation, characterized by comprising the following steps: (1) Preparation of an oxygen-free main chain 1.1) Dissolve biphenyl monomer 1 and ketone-containing monomer 2 in solvent A, stir until completely dissolved, to obtain a reaction mixture system, wherein, The molar ratio of biphenyl monomer 1 to ketone-containing monomer 2 is 1:1.1-1.2; 1.2) After mixing trifluoromethanesulfonic acid and trifluoroacetic acid, slowly drop them into the reaction mixture of step 1.1) under ice bath, wherein the volume ratio of trifluoromethanesulfonic acid to trifluoroacetic acid is 7-9:1, and the molar ratio of trifluoromethanesulfonic acid to biphenyl monomer 1 is 9:1; 1.3) After the dropwise addition is completed, the viscosity of the reaction system gradually increases with the extension of the reaction time. When the reaction liquid is viscous and the rotor cannot rotate, it is transferred to the solvent B reaction system to precipitate as a solid. Wash repeatedly with solvent C until neutral, to obtain the oxygen-free polymer backbone 1. Finally, place the oxygen-free polymer backbone in a vacuum oven for drying; (2) Preparation of crown ether modified piperidine cation 2.1) Add benzocrown ether monomer 3 and N-methylpiperidone to solvent D until complete dissolution to obtain a reaction mixture, wherein, The molar ratio of benzocrown ether monomer 3 to N-methyl piperidone is 3-4:1; 2.2) After mixing trifluoromethanesulfonic acid and trifluoroacetic acid, add them into a constant pressure dropping funnel, and then drop them into the reaction mixture of step 2.1) under ice bath, wherein the volume ratio of trifluoromethanesulfonic acid to trifluoroacetic acid is 13-15:1, and the molar ratio of trifluoroacetic acid to N-methyl piperidone is 2:1; 2.3) After the dropwise addition is completed, maintain the ice bath state for 12-24h. After the reaction is completed, pour the mixture into solvent E, add potassium carbonate until no bubbles are generated, filter out the precipitate, and then dry the upper liquid with a rotary evaporator. The obtained solid is washed with solvent F and then placed in a vacuum oven for drying to obtain the crown ether modified piperidine 2 in the form of a solid; (3) Preparation of bromooctyl oxygen-free backbone Dissolve the oxygen-free polymer backbone 1 of step (1) in solvent G, pour it into a constant pressure dropping funnel, and then slowly drop it into a mixture of solvent G and excess 1,8-dibromo octane. React at 50-55℃ for 48-72h. After the reaction is completed, pour the reaction mixture into solvent H to generate a large amount of precipitate. Filter the precipitate and then repeatedly wash it with solvent H and solvent I. Dry in a vacuum oven to obtain the bromooctyl oxygen-free backbone 3. The molar ratio of 1,8-dibromo octane to the structural unit of the oxygen-free polymer backbone 1 is 8-10:1; (4) Synthesis of crown ether modified anion exchange membrane React the bromooctyl oxygen-free backbone 3 of step (3) with the crown ether modified piperidine 2 of step (2) to obtain a polymer; (5) Casting film Prepare a 5wt% solution of the polymer synthesized in step (4), and then flow it on a glass plate. Place the glass plate horizontally, heat it to 60-80℃, and then let it stand for 24-36h; (6) Alkali treatment Peel the film obtained in step (5) from the surface of the glass plate, immerse it in a sodium hydroxide or potassium hydroxide solution, and then wash it to obtain a crown ether modified piperidine grafted anion exchange membrane; The ketone-containing monomer 2 is N-methyl piperidone, or a mixture of N-methyl piperidone, 1,1,1-trifluoroacetone and / or 2,2,2-trifluoroacetophenone.

2. The method of claim 1, wherein the step (4) is specifically: dissolving the bromo-octyl oxygen-free backbone 3 in solvent J at 60-90℃, adding excess crown ether modified piperidine 2, stopping the reaction after 48-72h of reaction, pouring into solvent K to obtain a large amount of precipitate, repeatedly washing with solvent K and solvent L, and drying in a vacuum drying oven to obtain the polymer; the mass ratio of the bromo-octyl oxygen-free backbone 3 to the crown ether modified piperidine 2 is 1:3-5.

3. The method for preparing an anion exchange membrane according to claim 1, characterized in that, The biphenyl monomer 1 in step (1) is biphenyl, p-terphenyl, or m-terphenyl.

4. The method for preparing an anion exchange membrane according to claim 1, characterized in that, The benzocrown ether monomer 3 in step (2) is benzocrown-5 or benzocrown-6.

5. The method of claim 1, wherein the anion exchange membrane is prepared by the steps of: (a) dissolving the polymer in a solvent; (b) adding the anion exchange group to the polymer; (c) removing the solvent; and (d) drying the polymer. The solvent A in step (1) is anhydrous dichloromethane, the solvent B is ethyl acetate, acetone or deionized water, and the solvent C is deionized water; the vacuum drying oven in step (1) is at 40-80℃ for 24-48h.

6. The method of claim 1, wherein the anion exchange membrane is prepared by the steps of: The solvent D in step (2) is anhydrous dichloromethane, the solvent E is methanol or ethanol, and the solvent F is dichloromethane; the vacuum drying oven in step (2) is at 40-60℃ for 24-48h.

7. The method for preparing an anion exchange membrane according to claim 1, characterized in that, The solvent G in step (3) is dimethyl sulfoxide, the solvent H is ethyl acetate, diethyl ether or acetone, and the solvent I is deionized water; the vacuum drying oven in step (3) is at 40-80℃ for 24-48h.

8. The method of claim 2, wherein the anion exchange membrane is prepared by the steps of: (a) dissolving the polymer in a solvent; (b) adding the anion exchange group to the polymer; (c) removing the solvent; and (d) drying the polymer. The solvent J in step (4) is dimethyl sulfoxide, the solvent K is ethyl acetate, diethyl ether or acetone, and the solvent L is deionized water; the vacuum drying oven in step (4) is at 40-80℃ for 24-48h.

9. An anion exchange membrane grafted with a crown ether piperidinium cation, characterized by, The anion exchange membrane is prepared by the method of any one of claims 1-8; the anion exchange membrane is a polymer chain without ether oxygen structure as the polymer backbone, N-methyl piperidine as the cationic group, and a hydrophilic crown ether unit for modifying the piperidine group, and the microphase separation is induced by the difference in polarity between the hydrophilic cationic group and the hydrophobic backbone.

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