Fluorene-based ionomer containing long alkyl side chains, method for preparing the same, and use thereof in anion exchange membranes

Abstract

A fluorene-based ionomer containing long alkyl side chains, its preparation method, and its application in anion exchange membranes. This invention belongs to the field of fluorene-based ionomers and their preparation. The purpose of this invention is to solve the technical problem that existing anion exchange membranes based on polymers constructed from ether-free polyfluorene backbones and quaternary ammonium salt cations cannot achieve an optimal balance between mechanical and ion conductivity. This invention introduces long alkyl side chains of a specific length onto a highly rigid fluorene-based polymer backbone, constructing a molecular structure that combines rigidity and flexibility, thereby significantly improving the overall performance of the anion exchange membrane. The resulting fluorene-based ionomer containing long alkyl side chains is applied as an anion exchange membrane component in the field of fuel cell alkaline batteries.

Description

Technical Field

[0001] This invention belongs to the field of fluorenyl ionomers and their preparation, specifically relating to a fluorenyl ionomer containing a long alkyl side chain, its preparation method, and its application in anion exchange membranes. Background Technology

[0002] Anion exchange membranes (AEMs) are a core component of alkaline fuel cells, and their performance directly determines the cell's energy conversion efficiency and long-term operational stability. Currently, developing AEM materials that combine high ionic conductivity, excellent alkaline stability, and good mechanical properties is crucial for the commercialization of alkaline fuel cells.

[0003] Traditional anion exchange membranes are mostly constructed based on polyarylene ether backbones and quaternary ammonium salt cations. These materials have significant drawbacks in high-temperature, high-concentration alkaline environments: on the one hand, the ether bonds in the polyarylene ether backbone are susceptible to OH groups. - Nucleophilic attacks cause hydrolytic breakage; on the other hand, quaternary ammonium cations are prone to degradation by Hoffmann elimination or SN2 substitution reactions, leading to membrane performance degradation.

[0004] To improve the mechanical properties of membranes, researchers replaced polyarylene ethers with ether-free polyfluorene backbones and introduced quaternary phosphine salt cations to enhance alkali resistance. However, existing technologies still have limitations in molecular chain structure design: the interactions between molecular chains and cationic substituents have a crucial impact on the mechanical properties, phase separation structure, and ion transport channel formation of the membrane, but the underlying mechanisms have not been fully studied. Therefore, it is urgent to conduct research to achieve synergistic optimization of the mechanical properties and ion conduction properties of membrane materials. Summary of the Invention

[0005] The purpose of this invention is to solve the technical problem that existing anion exchange membranes based on polymers constructed from ether-free polyfluorene backbones and quaternary ammonium salt cations cannot achieve an optimal balance between mechanical properties and ion conductivity. The invention provides a fluorene-based ionomer containing long alkyl side chains, its preparation method, and its application in anion exchange membranes.

[0006] One objective of this invention is to provide a method for preparing fluorene ionomers containing long alkyl side chains, the method comprising the following steps: Step (1): Mix fluorene, NaOH aqueous solution and tetrabutylammonium iodide, then add a dibromosubstituted alkane with more than 6 carbon atoms under gas protection, heat to react, extract, dry, evaporate the organic phase and pass it through a silica gel column to obtain alkylfluorene; wherein the dibromosubstituted alkane with more than 6 carbon atoms is 1-8 dibromooctane or 1-10 dibromodecane; Step (2): First, dissolve alkyl fluorene, biphenyl and 1,1,1-trifluoroacetone in dichloromethane to obtain a copolymer solution. Then, cool the solution system to 0°C, add trifluoromethanesulfonic acid dropwise and react at room temperature. Finally, precipitate, wash and dry in ethanol to obtain ether-free alkyl polyfluorene. Step (3): Dissolve the ether-free alkyl polyfluorene and trimethylamine ethanol solution completely in N-methylpyrrolidone, react at room temperature, then precipitate and wash, and dry to obtain fluorene ionomer containing long alkyl side chains.

[0007] Further specifying, the concentration of the NaOH aqueous solution in step (1) is 46-60 wt%.

[0008] Further specifying, the mass ratio of fluorene to NaOH aqueous solution in step (1) is 1:(15-25).

[0009] Further specifying, the molar ratio of fluorene to tetrabutylammonium iodide in step (1) is (4-6):1.

[0010] Further specifying, the molar ratio of fluorene to dibromosubstituted alkanes in step (1) is 1:(4-6).

[0011] Further, the heating reaction temperature in step (1) is 60-80℃ and the time is 10-14h.

[0012] Further specified, the amount of alkylfluorene used in step (2) is 35-40% of the sum of the molar contents of alkylfluorene and biphenyl.

[0013] Further specifying, in step (2), the molar ratio of biphenyl to 1,1,1-trifluoroacetone is 1:(1.5-2.5).

[0014] Further specifying, the concentration of the copolymerization solution in step (2) is 0.3-0.5 g / mL.

[0015] Further specifying, in step (2), the molar ratio of trifluoromethanesulfonic acid to alkylfluorene is (2-3) mL: 1 mmol.

[0016] Further specifying, the reaction time in step (2) is 0.5-1h at room temperature.

[0017] Further specifying, in step (3), the ratio of the mass of the ether-free alkyl polyfluorene to the volume of the trimethylamine ethanol solution is 1 g: (2-3) mL.

[0018] Further specifying, the trimethylamine concentration in the trimethylamine ethanol solution in step (3) is 20-40 wt%.

[0019] Further specifying, in step (3), the ratio of the mass of the ether-free alkyl polyfluorene to the volume of N-methylpyrrolidone is 1 g: (10-20) mL.

[0020] Further specifying, the reaction in step (3) is to be carried out at room temperature for 20-24 hours.

[0021] The second objective of this invention is to provide a fluorenyl ionomer containing long alkyl side chains obtained by the above preparation method.

[0022] A third objective of this invention is to provide an application of the fluorene ionomer containing long alkyl side chains obtained by the above preparation method in anion exchange membranes.

[0023] The significant advantages of this invention compared to existing technologies are: Excessively short connecting chains restrict cation aggregation, hindering ion channel construction; excessively long connecting chains may reduce the membrane's mechanical strength, affecting its dimensional stability and lifespan. This invention, by introducing long alkyl side chains of a specific length onto a highly rigid fluorene polymer backbone, constructs a molecular structure that combines rigidity and flexibility, thereby significantly improving the overall performance of the anion exchange membrane. Specific advantages are as follows: 1) Significantly improved mechanical strength, resolving the membrane damage problem caused by high swelling. The introduced long alkyl side chains not only act as flexible spacer groups to regulate the stacking of molecular chains, but more importantly, they generate strong hydrophobic interactions between the long chains. This interaction forms a reinforcing network similar to "physical cross-linking points" at the microscopic level, greatly enhancing the binding force between molecular chains. Experimental data show that the modified membrane material has significantly enhanced tensile strength and a substantial increase in maximum stress value. This superior mechanical strength ensures that the membrane is not prone to fracture or damage under battery assembly and high-voltage operating conditions, significantly improving the reliability of the device.

[0024] 2) Effectively suppresses excessive swelling and improves dimensional stability. The hydrophobic properties of the long alkyl side chains synergistically work with the rigid main chain to construct a robust hydrophobic framework network. When the membrane absorbs water, this network effectively limits the unlimited expansion of hydrophilic regions, thereby ensuring unobstructed ion transport channels while suppressing excessive swelling of the membrane. This solves the problem of dimensional deformation caused by excessive water absorption in traditional high ion exchange capacity membranes, ensuring the stability of the membrane electrode assembly interface.

[0025] 3) This invention breaks the constraint between high electrical conductivity and high mechanical strength. In existing technologies, improving electrical conductivity often requires sacrificing mechanical strength. This invention, through the dual effects of "internal plasticization" and "reinforcement" of the long alkyl chain, introduces necessary flexibility and interaction forces while maintaining the rigidity of the polymer backbone. This allows the membrane material to achieve a good ion transport environment without significantly increasing water absorption, thus realizing the synergistic optimization of high mechanical strength and excellent ion transport performance, providing a reliable material basis for high-performance water electrolysis hydrogen production or fuel cells. Attached Figure Description

[0026] Figure 1 The stress-strain curve of the fluorenyl ionomer containing a long alkyl side chain with 8 carbons prepared in Example 1 of the present invention; Figure 2 The stress-strain curve of the fluorenyl ionomer containing a long alkyl side chain with 10 carbon atoms prepared in Example 2 of the present invention; Figure 3 The stress-strain curves of the fluorene ionomer containing a long alkyl side chain with 6 carbon atoms prepared in Comparative Example 1 of this invention are shown. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0028] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0029] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used in the following embodiments, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such a composition, step, method, article, or apparatus.

[0030] In this invention, "an embodiment" or "embodiment" refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that excludes other embodiments.

[0031] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0032] Example 1: The preparation method of the fluorene ionomer containing long alkyl side chains in this example is carried out according to the following steps: Step (1): Fluorene (4.00 g, 24.1 mmol), 50 wt% NaOH aqueous solution (80.0 g), and tetrabutylammonium iodide (1.70 g, 4.60 mmol) were mixed, and then 1,8-dibromooctane (32.62 g, 120 mmol) was added under gas protection. The reaction was carried out at 70 °C for 12 h. The reaction solution was then poured into water and extracted with petroleum ether. The solution was dried, the organic phase was evaporated to dryness, and the solution was passed through a silica gel column (hexane as eluent). 9,9-Di(8-bromooctyl)fluorene was finally obtained. Step (2): First, dissolve 9,9-bis(8-bromooctyl)fluorene (1.76 g, 3.25 mmol), biphenyl (0.852 g, 5.53 mmol), and 1,1,1-trifluoroacetone (1.18 g, 10.54 mmol) obtained in step (1) in 10 mL of dichloromethane. Then, cool the solution system to 0℃, add 8 mL of trifluoromethanesulfonic acid dropwise, and react at room temperature for 50 min. Then, pour the viscous reaction solution into ethanol to precipitate the crude product, wash with water and ethanol, and dry to obtain ether-free alkyl polyfluorene; Step (3): First, completely dissolve 2g of the ether-free alkyl polyfluorene obtained in step (2) and 5mL of 30wt% trimethylamine ethanol solution in 30mL of N-methylpyrrolidone and react at room temperature for 24h. Then, pour the reaction solution into diethyl ether to precipitate, collect the precipitate and wash it with diethyl ether, and then dry it to obtain a fluorene ionomer containing a long alkyl side chain with 8 carbons.

[0033] Example 2: The difference between this example and Example 1 is that the 1,8-dibromooctane mentioned in step (1) is replaced with 1,10-dibromodecane. The other steps and parameters are the same as in Example 1.

[0034] Comparative Example 1: The preparation method of the fluorene ionomer containing alkyl side chains in this comparative example is carried out according to the following steps: Step (1): Fluorene (4.00 g, 24.1 mmol), 50 wt% NaOH aqueous solution (80.0 g), and tetrabutylammonium iodide (1.70 g, 4.60 mmol) were mixed, and 1,6-dibromohexane (29.25 g, 120 mmol) was added under gas protection. The reaction was carried out at 70 °C for 12 hours. The reaction solution was then poured into water, extracted with CHCI, dried, and the organic phase was evaporated to dryness and passed through a silica gel column (with n-hexane as the eluent). Finally, 9,9-di(6-bromohexyl)fluorene was obtained. Step (2): First, dissolve 9,9-bis(6-bromohexyl)fluorene (1.58 g, 3.25 mmol), biphenyl (0.85 g, 5.53 mmol), and 1,1,1-trifluoroacetone (1.18 g, 10.54 mmol) in 10 mL of dichloromethane. Then, cool the solution to 0 °C, add 8 mL of trifluoromethanesulfonic acid dropwise, and react at room temperature for 50 minutes. The viscous reaction solution is then poured into ethanol to precipitate the crude product. After washing with water and ethanol, the product is dried to obtain ether-free alkyl polyfluorene PFBr.

[0035] Step (3): First, completely dissolve 2g of the ether-free alkyl polyfluorene PFBr obtained in step (2) and 5mL of 30wt% trimethylamine ethanol solution in 30mL of N-methylpyrrolidone and react at room temperature for 24 hours. Then, pour the reaction solution into diethyl ether to precipitate, collect the precipitate and wash it with diethyl ether, and then dry it to obtain the fluorene ionomer PFQA containing alkyl side chains.

[0036] Example of results: Sample preparation: The fluorenyl ionomer with 8 carbon long alkyl side chains prepared in Example 1, the fluorenyl ionomer with 10 carbon long alkyl side chains prepared in Example 2, and the fluorenyl ionomer with 6 carbon alkyl side chains prepared in Comparative Example 1 (PFQA) were dissolved in DMSO to prepare 5wt% casting solutions. The casting solutions were then uniformly coated onto a glass plate and heated at 60°C for 24 hours to allow the solvent to evaporate completely. The glass was then immersed in deionized water, and the film was peeled off the glass plate to obtain a test sample with a thickness of 0.02 mm and a width of 10 mm.

[0037] Mechanical testing: The specimen was subjected to a tensile test at a speed of 1 mm / min, and the results are as follows. Figure 1 , Figure 2 and Figure 3 As shown, from Figure 1 and Figure 3 The comparison shows that the fluorene ionomer with alkyl side chains containing 8 carbons prepared in this invention has a tensile strength of 54.1057 N / mm² and an elongation at break of 22.94%, while the fluorene ionomer with alkyl side chains containing 6 carbons prepared in the comparative example has a tensile strength of 20.7828 MPa and an elongation at break of 12.0185%. Figure 2 and Figure 3 The comparison shows that the tensile strength of the fluorenyl ionomer with 10 carbon alkyl side chains prepared by this invention is 46.4446 N / mm², and the elongation at break is 19.14%. This fully demonstrates that the comprehensive mechanical properties of the fluorenyl ionomer with 8 carbon alkyl side chains and the fluorenyl ionomer with 10 carbon alkyl side chains of this invention are superior to those of the fluorenyl ionomer with 6 carbon alkyl side chains.

[0038] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a fluorene ionomer containing a long alkyl side chain, characterized in that, The method described: Step (1): Mix fluorene, NaOH aqueous solution and tetrabutylammonium iodide, then add a dibromosubstituted alkane with more than 6 carbon atoms under gas protection, heat to react, extract, dry, evaporate the organic phase and pass it through a silica gel column to obtain alkylfluorene; wherein the dibromosubstituted alkane with more than 6 carbon atoms is 1-8 dibromooctane or 1-10 dibromodecane; Step (2): First, dissolve alkyl fluorene, biphenyl and 1,1,1-trifluoroacetone in dichloromethane to obtain a copolymer solution. Then, cool the solution system to 0°C, add trifluoromethanesulfonic acid dropwise and react at room temperature. Finally, precipitate, wash and dry in ethanol to obtain ether-free alkyl polyfluorene. Step (3): Dissolve the ether-free alkyl polyfluorene and trimethylamine ethanol solution completely in N-methylpyrrolidone, react at room temperature, then precipitate and wash, and dry to obtain fluorene ionomer containing long alkyl side chains.

2. The method according to claim 1, characterized in that, In step (1), the concentration of NaOH aqueous solution is 46-60wt%, and the mass ratio of fluorene to NaOH aqueous solution is 1:(15-25).

3. The method according to claim 1, characterized in that, In step (1), the molar ratio of fluorene to tetrabutylammonium iodide is (4-6):1, and the molar ratio of fluorene to dibromosubstituted alkanes is 1:(4-6).

4. The method according to claim 1, characterized in that, In step (1), the heating reaction temperature is 60-80℃ and the time is 10-14h.

5. The method according to claim 1, characterized in that, In step (2), the amount of alkylfluorene used is 35-40% of the sum of the molar contents of alkylfluorene and biphenyl, and the molar ratio of biphenyl to 1,1,1-trifluoroacetone is 1:(1.5-2.5).

6. The method according to claim 1, characterized in that, In step (2), the concentration of the copolymerization solution is 0.3-0.5 g / mL, the volume of trifluoromethanesulfonic acid and the molar ratio of alkylfluorene are (2-3) mL: 1 mmol, and the reaction is carried out at room temperature for 0.5-1 h.

7. The method according to claim 1, characterized in that, In step (3), the mass ratio of the ether-free alkyl polyfluorene to the volume of the trimethylamine ethanol solution is 1 g: (2-3) mL, the trimethylamine concentration in the trimethylamine ethanol solution is 20-40 wt%, and the mass ratio of the ether-free alkyl polyfluorene to the volume of N-methylpyrrolidone is 1 g: (10-20) mL.

8. The method according to claim 1, characterized in that, In step (3), the reaction is carried out at room temperature for 20-24 hours.

9. The fluorenyl ionomer containing long alkyl side chains obtained by the method of any one of claims 1-8.

10. The application of the fluorenyl ionomer containing long alkyl side chains as described in claim 9 in anion exchange membranes.

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