阅读说明：本技术 一种基于无醚键聚芴的主链型碱性阴离子交换膜及其制备方法 (Main chain type alkaline anion exchange membrane based on ether bond-free polyfluorene and preparation method thereof ) 是由 林本才 徐斐 丁建宁 陈燕波 李泾 于 2021-08-06 设计创作，主要内容包括：本发明涉及一种聚合物阴离子交换膜及其制备方法,尤其涉及一种基于无醚键聚芴的主链型碱性阴离子交换膜及其制备方法。本发明选用耐碱稳定性优异的哌啶阳离子,设计合成出9号位不同尺寸的亚甲基侧链取代的芴基单体。通过酸催化的Friedel-Crafts聚合制备出不含醚键的芴基聚合物,以提高阴离子膜的化学稳定性。整个制备过程简单,高效。在聚合物主链的疏水段引入亚甲基侧链,促进膜内部微相分离的形成,为离子的传输提供高速通道从而进一步提高膜的电导率。(The invention relates to a polymer anion exchange membrane and a preparation method thereof, in particular to a main chain type alkaline anion exchange membrane based on ether bond-free polyfluorene and a preparation method thereof. The invention selects piperidine cations with excellent alkali-resistant stability to design and synthesize the 9-position methylene side chain substituted fluorenyl monomer with different sizes. The fluorenyl polymer without ether bonds is prepared by acid-catalyzed Friedel-Crafts polymerization to improve the chemical stability of the anionic membrane. The whole preparation process is simple and efficient. A methylene side chain is introduced into a hydrophobic section of a polymer main chain, so that the formation of micro-phase separation inside the membrane is promoted, and a high-speed channel is provided for the transmission of ions, thereby further improving the conductivity of the membrane.)

1. A main chain type alkaline anion exchange membrane based on ether bond-free polyfluorene is characterized in that the repeating unit of the anion exchange membrane polymer 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 1-12; r is methyl or H.

2. A preparation method of a main chain type alkaline anion exchange membrane based on ether bond-free polyfluorene is characterized by comprising the following steps:

(1) synthesizing a 9, 9-dialkyl-2, 7-diphenylfluorene monomer;

(2) preparing a non-ether bond fluorenyl polymer;

(3) preparing a main chain type alkaline anion exchange membrane based on ether bond-free polyfluorene.

3. The method for preparing a main chain type basic anion exchange membrane based on polyether bond-free polyfluorene as claimed in claim 2, wherein the step (1) is that 9, 9-dialkyl-2, 7-dibromo fluorene and excess phenylboronic acid are stirred and dissolved in toluene to obtain 1M K₂CO₃Adding Pd (pph) as an alkali source under the protection of nitrogen₃)₄And stirring and reacting for 36-48 hours at 80-100 ℃, 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 a target product 9, 9-dialkyl-2, 7-diphenylfluorene monomer.

4. The method for preparing a main chain type basic anion exchange membrane based on polyether bond-free polyfluorene as claimed in claim 2, wherein the step (2) is to mix 9, 9-dialkyl-2, 7-diphenylfluorene and N-methylStirring and dissolving-4-piperidone in dichloromethane, adding trifluoroacetic acid and trifluoromethanesulfonic acid in sequence in an ice-water bath to enable the mass fraction of 9, 9-dialkyl-2, 7-diphenylfluorene and N-methyl-4-piperidone to be 10-30 wt%, mechanically stirring the mixture at 0-20 ℃ for 24-48 hours until the solution becomes highly viscous, and adding Na in sequence to the crude product₂CO₃And deionized water is used for ultrasonic cleaning until the polymer is washed to be neutral, filtered and dried in vacuum.

5. The preparation method of the main chain type alkaline anion-exchange membrane based on the ether bond-free polyfluorene as claimed in claim 2, wherein the step (3) is that the ether bond-free fluorenyl polymer prepared in the step (2) is stirred and dissolved in an organic solvent to form a 5 wt% solution, then alkyl halide is added, the reaction is carried out for 12-24 hours at 20-60 ℃ for quaternization, the reaction solution is poured into a clean tetrafluoroethylene mold, and the film is dried in a vacuum drying oven to form a halogen type polymer film; and soaking the halogen type polymer membrane in 1M alkali solution for ion exchange to finally obtain the OH-type anion exchange membrane.

6. Use of a main chain type alkaline anion exchange membrane based on a polyfluorene without ether linkage according to claim 1, wherein the polyfluorene alkaline anion exchange membrane without ether linkage is used in fuel cells, flow batteries, electrolysis, electrodialysis or separation membranes.

Technical Field

The invention relates to a polymer anion exchange membrane and a preparation method thereof, in particular to a main chain type alkaline anion exchange membrane based on ether bond-free polyfluorene and a preparation method thereof.

Background

As a new energy conversion device, fuel cells have received much attention in recent years due to their high efficiency and cleanliness. The fuel cell is of a wide variety, and the polymer electrolyte membrane fuel cell is a research hotspot due to its higher output power and solves the problem of electrolyte leakage of the traditional fuel cell. Polymer fuel cells are generally classified into proton exchange membrane fuel cells and anion exchange membrane fuel cells, depending on the electrolyte membrane used. Anion Exchange Membrane Fuel Cell (AEMFC) technology has the following advantages compared to proton exchange membrane fuel cells: (1) the catalyst has lower requirements, and silver or nickel can be used as the catalyst to replace noble metal platinum; (2) cations in the alkaline anion exchange membrane are all fixed on a polymer chain, free salt does not exist in a liquid phase, and the phenomenon that the conventional alkaline liquid electrolyte of the alkaline fuel cell is easy to react with CO can be avoided₂The effect of the reaction; (3) the transmission direction of the conductive ions in the membrane is opposite to the diffusion direction of the fuel, so that the permeation of the fuel in the membrane is favorably inhibited.

Anion Exchange Membranes (AEMs) serve as core components of AEMFCs, and the performance of the AEMFCs directly determines the performance and service life of the AEMFCs during operation. However, due to OH as a conductive ion in the anion exchange membrane^-The dissociation degree and mobility of the self are lower than that of H⁺The conductivity of the AEMs is lower. In addition, quaternary ammonium cation groups of the conductive groups can be subjected to OH in a high-temperature and high-alkaline environment^-Such as Hofmann degradation and Ylide reaction, resulting in the destruction of quaternary ammonium cationic groups.

Polyfluorene (PF) is a highly conjugated, very rigid, fully aromatic polymer that exhibits good thermal and chemical stability. However, PF structures are currently used in more organic photovoltaic fields, and there are few reports of applications in the fuel cell field.

In conclusion, in order to further promote the commercial use of anion exchange membranes, an anion exchange membrane with good ion conductivity, excellent alkali resistance and excellent dimensional stability is yet to be developed.

Disclosure of Invention

In order to prepare an anion exchange membrane with high ionic conductivity and high alkali-resistant stability, the invention selects piperidine cations with excellent alkali-resistant stability and designs and synthesizes 9-position methylene side chain substituted fluorenyl monomers with different sizes. The fluorenyl polymer without ether bonds is prepared by acid-catalyzed Friedel-Crafts polymerization to improve the chemical stability of the anionic membrane. The whole preparation process is simple and efficient. A methylene side chain is introduced into a hydrophobic section of a polymer main chain, so that the formation of micro-phase separation inside the membrane is promoted, and a high-speed channel is provided for the transmission of ions, thereby further improving the conductivity of the membrane.

In order to achieve the purpose, the invention adopts the technical scheme that: 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 1-12; r is methyl or H.

The technical scheme adopted by the invention is as follows: a preparation method of a main chain type alkaline anion exchange membrane based on ether bond-free polyfluorene specifically comprises the following steps:

step (1) synthesis of 9, 9-dialkyl-2, 7-diphenylfluorene monomer:

the 9, 9-dialkyl-2, 7-dibromo-fluorene and the excess phenylboronic acid are stirred and dissolved in toluene with 1M Na₂CO₃Adding Pd (pph) as an alkali source under the protection of nitrogen₃)₄And stirring and reacting for 36-48 hours at 80-100 ℃. Extracting the obtained solution with dichloromethaneAnd taking and drying an organic layer, and then separating and purifying a crude product by column chromatography to obtain a target product 9, 9-dialkyl-2, 7-diphenylfluorene monomer.

Wherein, Na₂CO₃The dosage is 10 to 15 times of the molar weight of the 9, 9-dialkyl-2, 7-dibromofluorene; the dosage of the palladium catalyst is 0.1 to 1 percent of the molar weight of the 9, 9-dialkyl-2, 7-dibromofluorene; the stationary phase used in the column chromatography separation is silica gel, and the eluent is mixed liquid with volume gradient change of n-hexane and dichloromethane.

Step (2) preparation of ether bond-free fluorenyl polymer:

stirring and dissolving 9, 9-dialkyl-2, 7-diphenylfluorene and N-methyl-4-piperidone in dichloromethane, and sequentially adding trifluoroacetic acid and trifluoromethanesulfonic acid in an ice water bath to ensure that the mass fraction of 9, 9-dialkyl-2, 7-diphenylfluorene and N-methyl-4-piperidone is 10-30 wt%. The mixture is mechanically stirred at 0-20 ℃ for 24-48 hours, and the solution becomes highly viscous. The crude product was treated with Na sequentially₂CO₃And deionized water is used for ultrasonic cleaning until the polymer is washed to be neutral, filtered and dried in vacuum.

And (3) preparing an ether bond-free polyfluorenyl anion exchange membrane:

stirring and dissolving the ether bond-free fluorenyl polymer prepared in the step (2) in an organic solvent to form a 5 wt% solution, then adding alkyl halide, and reacting at the temperature of 20-60 ℃ for 12-24 hours for quaternization. Pouring the reaction solution into a clean tetrafluoroethylene mold, and drying in a vacuum drying oven to form a film to obtain the halogen type polymer film. And soaking the halogen type polymer membrane in 1M alkali solution for ion exchange to finally obtain the OH-type anion exchange membrane.

Wherein the molar ratio of the alkyl halide to the polymer is 1: 1; the organic solvent is common polar solvent such as DMSO, DMF, NMP, etc., and the base is KOH or NaOH.

The ether bond-free fluorenyl anion-exchange membrane prepared by the invention can be applied to fuel cells, flow batteries, electrolysis, electrodialysis or separation membranes.

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

fluorene has a highly conjugated structure and has excellent chemical stability. A polymer skeleton without ether bonds is designed and synthesized based on fluorene, and piperidine cations with excellent chemical stability are selected as conductive cations, so that an anion exchange membrane with excellent alkali resistance stability can be prepared.

The methylene group at the 9 th position of the fluorene has extremely high reaction activity, and modification is facilitated. The methylene is carried out on the 9 th site of the fluorene, so that the molecular weight of the polymer can be increased, and the solubility of the polymer can be improved; in addition, the introduction of the hydrophobic side chain facilitates the construction of a microphase separation structure in the polymer, provides a high-speed channel for the transmission of ions, and further improves the ionic conductivity of the membrane.

The ether bond-free fluorenyl polymer prepared by the invention is an aromatic polymer and has excellent dimensional stability, thermal stability and mechanical property.

Description of the drawings:

FIG. 1 is a diagram of ether bond-free fluorenyl polymer prepared in example 1¹H NMR spectrum.

Detailed Description

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

Example 1

(1)9, 9-dihexyl-2, 7-dibromofluorene (1.72g, 3.5mmol) was dissolved in 35ml of toluene, and 35ml of 1M Na was added₂CO₃An aqueous solution. The mixture was heated to 100 ℃ and phenylboronic acid (1.28 g, 10.5mmol) and Pd (pph) were added under nitrogen protection₃)₄(4.2mg, 0.1mmol), the reaction was stirred for 36 hours. The reaction solution was extracted with dichloromethane and water, and the dried organic layer was collected. And (3) carrying out column chromatography separation and purification on the crude product by using a mixed solution with volume gradient change of n-hexane and dichloromethane to obtain 9, 9-dihexyl-2, 7-diphenylfluorene with the yield of 95%.

(2) 9, 9-dihexyl-2, 7-diphenylfluorene (2.2g,4.5mmol) and N-methyl-4-piperidone (0.56g,4.95mmol) were dissolved in 9ml of dichloromethane. 0.5ml of trifluoroacetic acid and 6ml of trifluoromethanesulfonic acid are added successively under an ice-water bath. The mixture was mechanically stirred at room temperature for 48 hours, and the mixture became highly viscous. Mixing the mixed solution withNa₂CO₃And respectively cleaning the polymer with aqueous solution and deionized water until the polymer becomes neutral to obtain the ether bond-free fluorenyl polymer.

(3) The prepared fluorenyl polymer is dissolved in dimethyl sulfoxide at 60 ℃, and excessive methyl iodide is added for quaternization reaction. Pouring the reaction solution into a clean tetrafluoroethylene mold, and drying in vacuum to obtain the halogen type fluorenyl polymer electrolyte membrane, wherein the chemical structure of the halogen type fluorenyl polymer electrolyte membrane is shown in figure 1. The halogen polymer electrolyte membrane is soaked in 1M KOH for ion replacement for 24 hours to obtain OH^-Type anion exchange membranes.

The prepared anion exchange membrane has the ionic conductivity of 77.86mS cm at the temperature of 80 DEG C^-1The degree of swelling at 80 ℃ is only 6.6%. The tensile strength was 25.6 MPa. The membrane was soaked in a 2M KOH solution at 80 ℃ for 30 days with only a 10.13% loss in conductivity.

Example 2

This example is similar to example 1, except that n-butane, the chemical structure of which is shown in the figure, is modified at position 9 of fluorene:

the prepared anion exchange membrane has the ionic conductivity of 70.11mS cm at the temperature of 80 DEG C^-1The degree of swelling at 80 ℃ is only 6.1%. The tensile strength was 21.2 MPa. The membrane was soaked in a 2M KOH solution at 80 ℃ for 30 days with only a 12.42% loss in conductivity.

Example 3

This example is similar to example 1, except that the fluorene modification at position 9 is methane, which has the chemical formula shown in the figure:

the prepared anion exchange membrane has the ionic conductivity of 66.68mS cm at the temperature of 80 DEG C^-1The swelling degree at 80 ℃ is only 5.7%. The tensile strength was 20.2 MPa. The membrane was soaked in a 2M KOH solution at 80 ℃ for 30 days with only a 14.48% loss in conductivity.

Example 4

This example is similar to example 1, except that n-butyl bromide was used instead of methyl iodide in the final quaternization, and the resulting fluorenyl anion exchange membrane has the structure shown in the figure:

the prepared anion exchange membrane has the ionic conductivity of 76.68mS cm at the temperature of 80 DEG C^-1The degree of swelling at 80 ℃ is only 6.8%. The tensile strength was 24.1 MPa. The membrane was soaked in a 2M KOH solution at 80 ℃ for 30 days with only an 11.48% loss in conductivity.

Example 5

This example is similar to the two examples, except that octane bromide is used to replace methyl iodide in the final quaternization process, and the structure of the prepared fluorenyl anion exchange membrane is shown in the following figure:

the prepared anion exchange membrane has the ionic conductivity of 64.38mS cm at the temperature of 80 DEG C^-1The swelling degree at 80 ℃ is only 5.9%. The tensile strength was 21.3 MPa. The membrane was soaked in a 2M KOH solution at 80 ℃ for 30 days with only a 13.52% loss in conductivity.

Comparative example 1

This comparative example is similar to example 1 except that the 9-position of fluorene is not modified and has the chemical structureWhen the operation of step (3) is performed, the substance obtained in step (2) is not dissolved in DMSO, and a polymer film cannot be obtained.

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.