CN113773472A

CN113773472A - Side chain type anion exchange membrane based on polyfluorene and preparation method thereof

Info

Publication number: CN113773472A
Application number: CN202110905594.0A
Authority: CN
Inventors: 丁建宁; 徐斐; 林本才; 李泾; 陈燕波; 袁宁一
Original assignee: Changzhou University
Current assignee: Changzhou University
Priority date: 2021-08-06
Filing date: 2021-08-06
Publication date: 2021-12-10

Abstract

The invention relates to a polymer anion exchange membrane and a preparation method thereof, in particular to a polyfluorene-based side chain type anion exchange membrane and a preparation method thereof. A series of polyfluorene base high polymer materials without weak bonds are synthesized through Suzuki coupling reaction to be used as a main chain framework of AEMs, in order to keep the strength of the AEMs, stable alkyl chain segments are introduced into the main chain of the polyfluorene, the chain flexibility and the solubility of the polyfluorene are adjusted, the distance between quaternary ammonium cations and aromatic rings on the main chain is adjusted, the polarization effect of the cations on the main chain is reduced, and the alkali resistance of the AEMs is improved; preparing a polyfluorene-based polymer, and constructing a microphase separation structure to improve the ionic conductivity of the polymer film. The whole preparation process is simple and efficient.

Description

Side chain type anion exchange membrane based on polyfluorene and preparation method thereof

Technical Field

The invention relates to a polymer anion exchange membrane and a preparation method thereof, in particular to a polyfluorene-based side chain type anion exchange membrane and a preparation method thereof.

Background

In recent years, environmental pollution and energy shortage have become serious. Fuel cells have attracted considerable attention as a new, efficient and clean energy conversion device. There are many fuel cells, among which polymer electrolyte membrane fuel cells have a higher power density and stronger CO by replacing an electrolyte with a solid electrolyte membrane₂Tolerance has become a research hotspot in recent decades. Polymer electrolyte membrane fuel cells are generally classified into Proton Exchange Membrane Fuel Cells (PEMFCs) and alkaline Anion Exchange Membrane Fuel Cells (AEMFCs) according to the electrolyte membrane used. Compared to PEMFCs. AEMFCs have higher cathode reaction kinetics speed, can get rid of the dependence on noble metal catalysts, and thus are widely concerned by people.

Anion Exchange Membranes (AEMs) serve as the core component of AEMFCs, serving the dual purpose of separating fuel from oxygen, and conducting ions. The performance of the AEMFCs will affect the performance and life of the AEMFCs during operation. In order to satisfy the normal operation of AEMFCs, ideal AEM must have high ionic conductivity, good thermal stability, excellent dimensional stability, mechanical strength, and excellent alkali resistance stability, etc. Typical AEMs are composed of a polymer main chain framework and quaternary ammonium cationic groups, researches on AEMs and AEMFCs have been greatly advanced through the efforts of researchers in recent years, however, the situation that AEMs are poor in alkali resistance and low in ionic conductivity causes that no commercialized AEMFCs appear at present, and the key for popularizing and using AEMFCs is to solve the two problems.

To increase the ionic conductivity of AEMs, it is most common practice to increase the Ion Exchange Capacity (IEC) of the polymer electrolyte membrane, however, an increase in IEC inevitably leads to a large amount of water uptake into the membrane, which in turn leads to a drastic decrease in the dimensional stability of the membrane. The introduction of the cross-linked structure can effectively improve the dimensional stability and mechanical strength of the membrane, and can limit the ionic conduction at the same time. Recent research finds that an hydrophilic/hydrophobic phase microphase separation structure is constructed in the polymer electrolyte membrane, so that a rapid channel can be provided for the transmission of ions, and the ion conductivity of the membrane can be effectively improved. Meanwhile, the hydrophobic phase in the polymer can effectively limit the swelling of the membrane and enhance the mechanical property of the membrane. The general methods for constructing microphase separation include ion cluster, comb-shaped side chain, block, cation suspension, etc. Improving the alkali resistance stability of the polymer is another difficulty in promoting the AEMFCs. During the work of AEMs, cations serving as conductive groups are attacked by OH-nucleophilicity under high-temperature and high-alkaline environment, so that the cations are degraded and destroyed. Further studies have found that when the polymer main chain contains a weak bond such as an ether bond, the polymer is degraded by OH-attack. Therefore, in the preparation of high alkali resistance AEMs, the comprehensive consideration of the polymer backbone and the alkali resistance stability of the cationic groups is necessary, and the induction effect of quaternary ammonium cations on the polymer backbone cannot be ignored.

Disclosure of Invention

According to the invention, a series of polyfluorene base high polymer materials without weak bonds are synthesized through Suzuki coupling reaction and used as a main chain framework of AEMs, in order to keep the strength of the AEMs, a stable alkyl chain segment is introduced into a polyfluorene main chain, the chain flexibility and the solubility of the polyfluorene are adjusted, the distance between quaternary ammonium cations and an aromatic ring on the main chain is adjusted, the polarization effect of the cations on the main chain is reduced, and the alkali resistance of the AEMs is improved; preparing a polyfluorene-based polymer, and constructing a microphase separation structure to improve the ionic conductivity of the polymer film. The whole preparation process is simple and efficient.

In order to achieve the purpose of the invention, the technical scheme adopted by the invention is as follows: an anionic polymer having a repeating unit as shown below:

wherein n is a degree of polymerization, is an integer and is not 0; x is an integer of 1-12; y is an integer of 2-12; r is cation such as quaternary ammonium, spiro quaternary ammonium, imidazolium, piperidinium, pyridinium and pyrrolium.

The invention also provides a preparation method of the polyfluorene-based side chain type anion exchange membrane, which comprises the following steps:

step (1): preparation of 9, 9-dibromoalkyl-2, 7-dibromofluorene monomer.

Dissolving 2, 7-dibromofluorene and 1, x-dibromoalkane in tetrahydrofuran, taking tetrabutylammonium bromide (TBAB) as a phase transfer agent and 50 wt% NaOH as an alkali source, and stirring and reacting at 60-100 ℃ for 24-36 hours under the protection of nitrogen. And extracting the obtained crude product by using dichloromethane, taking an organic layer for drying, and then carrying out column chromatography separation and purification to obtain a target product, namely the 9, 9-dibromoalkyl-2, 7-dibromofluorene monomer.

Wherein, the stationary phase used in the column chromatography separation is silica gel, and the eluant is normal hexane or petroleum ether.

Step (2): preparation of fluorenyl monomers terminated with boroxanes.

Stirring and dissolving the 9, 9-dibromoalkyl-2, 7-dibromofluorene monomer synthesized in the step (1) and excessive bis (pinacol and) diboron in a certain volume of toluene, taking potassium acetate as an alkali source, and taking [1,1' -bis (diphenylphosphine) ferrocene]Palladium dichloride dichloromethane complex (PdCl)₂(dppf)) is used as a catalyst, and is stirred and reacted for 36-48 hours at the temperature of 80-100 ℃ under the protection of nitrogen. And extracting the obtained solution by using dichloromethane, taking an organic layer for drying, and then carrying out column chromatography separation and purification on a crude product to obtain the target product, namely the fluorenyl monomer with the end group of the borosiloxane.

Wherein, the stationary phase used in the column chromatography separation is silica gel, and the eluant is a mixed solution of normal hexane and ethyl acetate.

And (3): and (3) preparing a fluorenyl polymer.

Stirring and dissolving the fluorenyl monomer synthesized in the step (2) and dibromobenzene alkane in toluene, and dissolving with tetrakis (triphenylphosphine palladium) (Pd (pph)₃)₄) As a catalyst, 2M K₂CO₃The method is characterized in that the method is used as an alkali source, and stirring reaction is carried out for 48-120 hours at 80-100 ℃ under the protection of nitrogen through Suzuki coupling reaction. After the reaction is finished, the reaction solution is poured into an ethanol/hydrochloric acid mixed solution for precipitation and cleaning, and then the polymer is washed to be neutral by deionized water and dried. Finally, the dried crude product was loaded into a soxhlet extractor and purified with dichloromethane. Finally obtaining the target fluorenyl polymer.

And (4): and (3) preparing a side chain type anion exchange membrane of polyfluorene.

Dissolving the fluorenyl polymer prepared in the step (3) in N-methylpyrrolidone, adding trimethylamine or N heterocycle (such as 1, 2-dimethylimidazole, N-methylpiperidine, N-methylpyrrolidine and the like) with 2 times of molar mass, stirring and reacting at 60-80 ℃ for 24 hours, and carrying out quaternization. And after the reaction is finished, pouring the reaction solution into a clean polytetrafluoroethylene mold, and drying the reaction solution at 80 ℃ in vacuum to form a film so as to obtain the corresponding halogen type polymer electrolyte film. And soaking the electrolyte membrane in an alkaline solution for ion exchange to obtain the polyfluorene side chain type anion exchange membrane.

Wherein the alkaline solution is 1M KOH or NaOH solution.

The side chain type anion exchange membrane of the polyether-free polyfluorene prepared by the invention can be applied to the fields of fuel cells, flow batteries, electrolysis, electrodialysis or separation membranes and the like.

Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages:

(1): the 9 th site of fluorene is grafted with an alkane side chain, and cations are suspended outside the main chain of the polymer, so that the distance between the cations and the main chain is increased, the induction effect of the cations on the main chain framework is reduced, and the nucleophilic attack of OH < - > on the main chain is weakened.

(2): the introduction of a methylene soft segment into the polyfluorene main chain effectively improves the main chain flexibility and solubility of the polyfluorene. In addition, the introduction of the aliphatic soft segment enhances the flexibility of the polymer, which is beneficial to the formation of hydrophilic/hydrophobic phase microphase separation, thereby constructing a high-speed channel for the transmission of ions.

(3): fluorene has a highly conjugated structure and has excellent chemical stability. The prepared fluorenyl polymer without weak bonds (such as ether bonds) has excellent alkali resistance stability.

Description of the drawings:

FIG. 1 shows the preparation of side-chain type anion exchange membrane polymer (A) based on polyether-bond-free polyfluorene prepared in example 1 and the corresponding halogen type polymer (B) quaternized with N-methylpiperidine¹H NMR spectrum.

Detailed Description

The present invention will be further described with reference to the following embodiments.

Example 1

2, 7-dibromofluorene (5.0g,15mmol), 1, 6-dibromohexane (30ml) and tetrabutylammonium bromide (0.1g) were dissolved in tetrahydrofuran with heating and stirring at 60 ℃. NaOH solution (30ml,50 wt%) was slowly added under nitrogen. The mixture was reacted for 8 hours. The reaction solution was then extracted with dichloromethane, and the dried organic layer was collected. And (3) carrying out column chromatography separation and purification on the crude product by using normal hexane to obtain 9, 9-dibromohexyl-2, 7-dibromofluorene with the yield of 82%.

9, 9-dibromohexyl-2, 7-dibromofluorene, bis (pinacol and) diboron (3.0g,12mmol), potassium acetate (3.5g,35.5mmol) and (PdCl)₂) (dppf) (250mg) was dissolved in 50ml of toluene. The reaction was stirred at 85 ℃ for 24 hours under nitrogen protection. The reaction solution was extracted with dichloromethane and water, and the dried organic layer was collected. The crude product is separated and purified by column chromatography with n-hexane/ethyl acetate (20:1v/v) to obtain fluorenyl monomer with the end group of borosiloxane, the yield is 82 percent, and the structural formula is shown in the specification

Fluorenyl monomer terminated with boroxine (0.744g,1mmol) and 1, 2-bis (4-bromophenyl) ethane (0.34g,1mmol) were dissolved in 30ml of degassed toluene and 10ml of 2M potassium carbonate and Pd (PPh) were slowly added under nitrogen₃)₄(54 mg). The reaction solution is heated and stirred for reaction for 120 hours at 100 ℃ under the protection of nitrogen. The reaction solution was cooled to room temperature, and slowly poured into an ethanol/hydrochloric acid (1:1v/v) solution to wash the precipitate. The precipitated solid was washed to neutrality with deionized water and dried. Finally, the crude product was loaded into a soxhlet extractor, washed with dichloromethane and dried. Pure polymer was obtained. The structural formula is

The polymer is dissolved in N-methyl pyrrolidone to form a 5 wt% solution, and 2 times of molar mass of N-methyl piperidine is added. The reaction was stirred at 80 ℃ for 12 hours. And pouring the solution after reaction into a clean polytetrafluoroethylene mold, and drying the solution in a vacuum drying oven at 80 ℃ to form a film so as to obtain the halogen type polymer electrolyte film. And finally, soaking the membrane in a 1M NaOH solution at 60 ℃ for ion replacement to obtain the target OH-type anion exchange membrane.

The prepared side chain type anion exchange membrane based on polyfluorene has the ionic conductivity of 80.44mS cm at 80 DEG C^-1The swelling degree at 80 ℃ is only 9.42%. When the membrane is soaked in a 2M KOH solution at 80 ℃ for 30 days, the conductivity is only lost by 6 percent, and excellent alkali-resistant stability is shown.

Example 2

This example is similar to example 1, except that the 9-position of fluorene is substituted and grafted by 1, 4-dibromobutane, and the structure of the polyfluorene-based side chain anion exchange membrane finally prepared is as follows:

the prepared side chain type anion exchange membrane based on polyfluorene has the ionic conductivity of 70.24mS cm at the temperature of 80 DEG C^-1The swelling degree at 80 ℃ is only 8.48%. When the membrane is soaked in a 2M KOH solution at 80 ℃ for 30 days, the conductivity is only lost by 8 percent, and excellent alkali-resistant stability is shown.

Example 3

This example is similar to example 1, except that the final quaternization procedure, using 1, 2-dimethylimidazole, resulted in a polyfluorene-based side-chain anion exchange membrane having the structure:

the prepared side chain type anion exchange membrane based on polyfluorene has the ionic conductivity of 78.24mS cm at the temperature of 80 DEG C^-1The swelling degree at 80 ℃ is only 7.18%. When the membrane is soaked in a 2M KOH solution at 80 ℃ for 30 days, the conductivity is only lost by 8 percent, and excellent alkali-resistant stability is shown.

Example 4

This example is similar to example 2, except that trimethylamine is selected for the final quaternization process, and the resulting polyfluorene-based side-chain anion exchange membrane has the following structure:

the prepared polyfluorene-based side chain type anion exchange membrane has the ionic conductivity of 83.66mS cm at 80 DEG C^-1The swelling degree at 80 ℃ is only 10.56%. When the membrane is soaked in a 2M KOH solution at 80 ℃ for 30 days, the conductivity is only lost by 10 percent, and excellent alkali-resistant stability is shown.

Example 5

This example is similar to example 1, except that in the case of the Suzuki coupled polymerization, the reaction is carried out in the presence of a catalyst

The structure of the polyfluorene-based side chain type anion exchange membrane prepared finally by replacing 1, 2-bis (4-bromophenyl) ethane is as follows:

the prepared polyfluorene-based side chain type anion exchange membrane has the ionic conductivity of 92.24mS cm at 80 DEG C^-1The swelling degree at 80 ℃ is only 11.16%. When the membrane is soaked in a 2M KOH solution at 80 ℃ for 30 days, the conductivity is only lost by 6 percent, and excellent alkali-resistant stability is shown.

Example 6

Example 6 similar to example 5, except that N-methylpyrrolidine was selected for the final quaternization, the resulting polyfluorene-based side-chain anion exchange membrane was prepared with the following structure:

the prepared side chain type anion exchange membrane based on polyfluorene has the ionic conductivity of 88.98mS cm at 80 DEG C^-1The swelling degree at 80 ℃ is only 11.78%. When the membrane is soaked in a 2M KOH solution at 80 ℃ for 30 days, the conductivity is only lost by 6 percent, and excellent alkali-resistant stability is shown.

The above embodiments are merely illustrative of the technical concept and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the content of the present invention and implement the invention, and not to limit the scope of the invention, and all equivalent changes or modifications made according to the spirit of the present invention should be covered by the scope of the present invention.

Claims

1. A polyfluorene-based side chain type anion exchange membrane is characterized in that the structural formula of the polyfluorene-based side chain type anion exchange membrane is as follows:

wherein n is a degree of polymerization, is an integer and is not 0; x is an integer of 1-12; y is an integer of 2-12; r is quaternary ammonium, spiro quaternary ammonium, imidazolium, piperidinium, pyridinium or pyrrolium cation.

2. A preparation method of a polyfluorene-based side chain type anion exchange membrane is characterized by comprising the following specific steps:

(1) preparing a 9, 9-dibromoalkyl-2, 7-dibromofluorene monomer;

(2) preparing fluorenyl monomer with a borosiloxane as a terminal group;

(3) preparing a fluorenyl polymer;

(4) and (3) preparing a side chain type anion exchange membrane of polyfluorene.

3. The preparation method of the polyfluorene-based side chain anion exchange membrane according to claim 2, wherein in the step (1), 2, 7-dibromofluorene and 1, x-dibromoalkane are dissolved in tetrahydrofuran, tetrabutylammonium bromide (TBAB) is used as a phase transfer agent, 50 wt% NaOH is used as an alkali source, the mixture is stirred and reacted for 24-36 hours at 60-100 ℃ under the protection of nitrogen, the obtained crude product is extracted by dichloromethane, an organic layer is taken and dried, and then column chromatography separation and purification are carried out, so that the target 9, 9-dibromoalkyl-2, 7-dibromofluorene monomer is obtained.

4. The method for preparing the polyfluorene-based side chain anion exchange membrane according to claim 2, wherein the step (2) is to dissolve the 9, 9-dibromoalkyl-2, 7-dibromofluorene monomer synthesized in the step (1) and excess bis (pinacol and) diboron in toluene with stirring, and to dissolve the monomer in toluene with potassium acetate as an alkali source and [1,1' -bis (diphenylphosphino) ferrocene]Palladium dichloride dichloromethane complex (PdCl)₂(dppf)) is used as a catalyst, stirring and reacting at 80-100 ℃ for 36-48 hours under the protection of nitrogen, extracting the obtained solution with dichloromethane, taking an organic layer for drying, and then carrying out column chromatography separation and purification on a crude product to obtain a target product.

5. The method for preparing the polyfluorene-based side chain anion exchange membrane according to claim 2, wherein the step (3) is to dissolve the fluorenyl monomer synthesized in the step (2) and dibromobenzene alkane in toluene with stirring to obtain tetrakis (triphenylphosphine palladium) (Pd (pph)₃)₄) As a catalyst, 2M K₂CO₃The method comprises the following steps of taking the raw materials as an alkali source, conducting Suzuki coupling reaction, stirring and reacting for 48-120 hours at 80-100 ℃ under the protection of nitrogen, pouring reaction liquid into an ethanol/hydrochloric acid mixed solution after the reaction is finished, precipitating and cleaning, washing a polymer to be neutral by deionized water, drying, and finally filling a dried crude product into a Soxhlet extractor to be purified by dichloromethane. Finally obtaining the target fluorenyl polymer.

6. The preparation method of the polyfluorene-based side chain anion exchange membrane according to claim 2, wherein in the step (4), the fluorenyl polymer prepared in the step (3) is dissolved in N-methyl pyrrolidone, 2 times of molar mass of trimethylamine or 1, 2-dimethylimidazole, N-methylpiperidine and N-methylpyrrolidine is added, the mixture is stirred and reacted for 24 hours at 60-80 ℃, quaternization is carried out, after the reaction is finished, the reaction solution is poured into a clean polytetrafluoroethylene mold, vacuum drying is carried out at 80 ℃ to form a membrane, a corresponding halogen type polymer electrolyte membrane is obtained, and the membrane is soaked in an alkaline solution for ion exchange, so that the polyfluorene-based side chain anion exchange membrane is obtained.

7. Use of a polyfluorene-based side-chain anion exchange membrane according to claim 1 in a fuel cell, a flow battery, electrolysis, electrodialysis or separation membrane.