WO2023081083A1

WO2023081083A1 - Poly(phenylene) compound intergrated with functionalized fluorene portion for anion exchange ionomer and anion exchange ionomer

Info

Publication number: WO2023081083A1
Application number: PCT/US2022/048352
Authority: WO
Inventors: Qiuying ZHANG; Bamdad Bahar
Original assignee: Ffi Ionix Ip, Inc.
Priority date: 2021-11-02
Filing date: 2022-10-31
Publication date: 2023-05-11

Abstract

An anion exchange polymer has an ionomer structure containing poly(phenylene) compound integrated with functionalized poly(fluorene). The anion conducting co-polymer includes a poly(fluorene) compound and a poly(phenylene) compound covalently bonded together. The poly(fluorene) compound has a 9H-fluorene structure that is a polycyclic aromatic hydrocarbon having a center ring with five carbon atoms, and a benzene ring on each of opposing sides of said center ring. The poly(phenylene) compound is covalently bonded to each of the pair of benzene rings of the poly(fluorene) compound. A pair of sidechains extends from the center ring of the poly(fluorene) compound to a respective terminal group. The terminal groups are configured on sidechains of the poly(fluorene) compound and can be converted into functional groups such as quaternary ammonium or n-methyl piperidine functional groups. The anion exchange polymer may include a porous scaffold support.

Description

POLY(PHENYLENE) COMPOUND INTERGRATED WITH FUNCTIONALIZED FLUORENE PORTION FOR ANION EXCHANGE IONOMER AND ANION EXCHANGE IONOMER

Cross Reference To Related Applications

[0001] This application claims the benefit of priority to U.S. provisional patent application No. 63/274,621, filed on November 2, 2021 ; the entirety of which is hereby incorporated by reference herein.

FIELD OF THE INVENTION

[0002] This application is directed to a functionalized anion exchange co-polymer structure with poly(phenylene) and poly(fluorene) compounds.

BACKGROUND OF THE INVENTION

[0003] In the recent years, proton exchange membrane fuel cells including solid polymer membrane as the electrolyte has been widely studied due to their high efficiency and density as well as low start temperature. However, the use of noble metal catalysts such as platinum has been an obstacle of viable commercialization of proton exchange membrane fuel cells. Also, high pH condition is a significant requirement for alkaline membrane fuel cells, which limits the utilization of proton exchange membrane. Therefore, the interest of developing anion exchange membranes (AEM) for alkaline fuel cells has prominently grown due to the low overpotentials caused by electrochemical reactions at alkaline environment and the dispensation of noble metal catalysts. A good anion exchange membrane for alkaline fuel cells should be with necessary conductivity, chemical and mechanical stability. Moreover, low cost is another significant requirement of developing new anion exchange membranes. For example, a well-known cation exchange membrane (Nation) developed by DuPont contributes up to 40% of the total cost of some redox flow batteries. Hence, the high cost rendered people to seek more cheaper alternatives, primarily anion exchange membranes. Up to now, most commercially available anion exchange membranes are based on cross- linked polystyrene, which are not chemically stable in alkaline environments. Some other aryl ether-containing polymer backbones of anion exchange membranes tend to be attacked by hydroxide ions, which causes the degradation of the polymers. As a result, developing aryl ether-free polyphenylene-based ionomers employing stable cationic groups is a promising direction for anion exchange membrane (AEM) fuel cell. Poly(phenylene)s and their derivatives have received many attentions because of their good performance on thermal, mechanical, and electrochemical properties. However, the lower solubility of the growing rigid rod chains in the process of polymerization of poly(phenylene)s causes the low molecular weight. In order to overcome the issue, researchers tried to introduce pendent sidechains to the phenyl rings and successfully improved the solubility of poly(phenylene)s. It should be noted that poly(phenylene)s is a kind of conjugated polymer which is promising in the application of biosensors research. To use those kind of polymer materials in biological applications, introducing appropriate sidechains to poly(phenylene) compounds and render them soluble in water and other polar solvents is critically necessary.

[0004] AEMs are generally made up of ionomers with pendant cationic groups such as benzyl trimethylammonium (BTMA) which is most commonly used, sulfonate and carboxylate etc. Hibbs et.al have applied BTMA cations for attaching to polymer backbones. Many BTMA-containing AEMs developed by them showed excellent properties and chemical stability. For example, the ion exchange capacity of a perfluorinated AEM with BTMA decreased less than 5% after 233-hour test at 50 °C. Moreover, some BTMA-containing membranes can bear high temperature over 60 °C and keep chemical stability without thermal-degradation. Hence, the investigation and development of more chemically stable sidechains are becoming a considerable direction of enhancing anion exchange membrane (AEM) fuel cell.

SUMMARY OF THE INVENTION

[0002] The present invention provides an anion conducting co-polymer and a composite anion conducting membrane that may include a porous scaffold support. The anion conducting co-polymer includes a poly(fluorene) compound and an poly(phenylene) compound covalently bonded together. The poly(fluorene) compound has a 9H-fluorene structure that is a polycyclic aromatic hydrocarbon having a center ring with five carbon atoms, and a benzene ring on each of opposing sides of said center ring. The poly(phenylene) compound is covalently bonded to each of the pair of benzene rings of the poly(fluorene) compound. A pair of sidechains extends from the center ring of the poly(fluorene) compound to a respective terminal group. The terminal groups are configured on sidechains of the poly(fluorene) compound and can be converted into functional groups such as quaternary ammonium or n-methyl piperidine functional groups.

[0003] A porous scaffold support, such as a porous membrane may be incorporated into a composite anion conducting membrane for reinforcement. Typically, the anion exchange membrane is prepared by imbibing the porous scaffold support with an anion exchange polymer solution of a non-ionic precursor polymer followed by conversion of a functional moiety on the polymer to form quaternary ammonium or n-methyl piperidine cation. Such a conversion can be accomplished by treatment of the precursor anion exchange membrane with basic trimethylamine or aqueous solution or N-Methylpiperidine DMSO solution. The thickness of an anion conducing membrane may be preferably very thin, such about 100 micrometers or less 50 micrometers or less, about 25 micrometers or less, about 10 micrometers or less, and in some embodiments about 5 micrometers or less.

[0004] Exemplary poly(phenylene)-poly(fluorene) anion exchange co-polymer may have functional groups selected from the group of quaternary ammoniums, n-methyl piperidine, tertiary diamines, phosphonium, benz(imidazolium), sulphonium, guanidinium, metal cations, pyridinium. Preferably the functional group is quaternary ammonium or n-methyl piperidine.

[0005] An exemplary porous scaffold support is made from polymer group consisting of polyolefins, polyamides, polycarbonates, cellulosics, polyacrylates, copolyether esters, polyamides, polyarylether ketones, polysulfones, polybenzimidazoles, fluoropolymers, and chlorinated polymers.

[0006] Exemplary polyphenylene-poly(fluorene) anion exchange co-polymer may have additive selected from a group consisting of radical scavengers, plasticizers, fillers, anion conducting material, crosslinking agent.

[0007] The present invention provides a mechanically reinforced anion exchange membrane comprising a functional polymer based on a poly(phenylene)-poly(fluorene) co- structure with quaternary ammonium functional groups and an inert porous scaffold support for reinforcement. Typically, the anion exchange membrane is prepared by imbibing the porous scaffold support with a polymer solution of a non-ionic precursor polymer followed by conversion of a functional moiety on the polymer to form a trimethyl ammonium cation. Such a conversion can be accomplished by treatment of the precursor polymer membrane with trimethylamine. In addition, an optional chemical crosslinking reaction can also be used to toughen the polymer by converting it from a thermoplastic to a thermoset material. Such a conversion can be accomplished by treatment of the precursor polymer membrane by a diamine, which is typically performed before the amination reaction. Typically, the thickness of the functionalized membrane is 25 micrometers or less, more typically 10 micrometers or less, and in some embodiments 5 micrometers or less.

[0008] The polyphenylene-poly(fluorene) co-polymers integrated with functionalized fluorene molecules are presented in this embodiment. Carbon-carbon coupling polymerizations such as has been successfully used to synthesize poly(phenylene)s, is costly and strict to the environment of storing palladium-containing catalysts. In the present invention a catalyst-free Diels-Alder polycondensation reaction for the synthesis of the co- polymer mixtures is used comprising: an aromatic arone monomer having the structure (1):

a 9,9-Bis(6-bromohexyl)-2,7-diethynyl-9H-fluorene monomer having the structure (2)

Wherein: n is in the range of 1-6

The anion exchange co-polymers having the formula (1):

Wherein:

R is selected from

[0009] The hydroxide exchange co-polymers are synthesized which comprises ether free functionalized polyphenylene compounds integrated with functionalized poly(fluorene). The water uptake, I EC and conductivity.

[0010] A method of synthesizing the hydroxide exchange co-polymers shown in Formula (1 ) is described below, which comprises that reacting monomers shown in structures (1) & (2) in organic solvent to form neutral intermediate polymers; quaternization of the neutral intermediate polymer in organic solvent to form ionic polymer; dissolvent the ionic polymer in organic solvent for solution-casting membranes; the membrane is immersed in base solution for ion exchange to form hydroxide exchange membrane.

[0011] The poly(fluorene) compound is a polycyclic aromatic with a center with five carbons and two benzene rings on either side of said center ring. The compound has a pair of sidechains that each extend to a respective terminal group, such as bromine, which can be functionalized with a functional group (Fn), such as quaternary ammonium or n-methyl piperidine.

[0012] The sidechains may be hydrocarbon and may have four or more carbons, six or more carbons, eight or more carbons and any range between and including the number carbons listed. A longer sidechain may provide high anion conductivity as the functional groups responsible for anion conduction may be more mobile.

[0013] The porous scaffold may be a microporous scaffold having an average or mean flow pore size of less than 1 micron as determined by a Capillary Flow Porometer, available from Porous Materials, Inc. Ithaca, NY, and the mean flow pore size may be about 0.5 microns or less, or even about 0.25microns or less. A porous scaffold may be a porous fluoropolymer, such as expanded polytetrafluoroethylene or a porous olefin, such as a porous polyethylene and the like.

[0014] The summary of the invention is provided as a general introduction to some of the embodiments of the invention and is not intended to be limiting. Additional example embodiments including variations and alternative configurations of the invention are provided herein.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

[0015] The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and together with the description serve to explain the principles of the invention. [0016] Figure 1 shows an embodiment of anion conducting co-polymer with poly(phenylene) compound covalently bonded to a poly(fluorene) compound and with functionalized terminal groups on the side chains of the poly(fluorene) compound.

[0017] Figure 2 shows an embodiment of a reaction sequence for synthesizing the anion conducting co-polymer.

[0018] Determination of the polymer structure is preferably conducted through NMR analysis and the molecular weight of the polymer is preferably conducted through Gel Permeation Chromatography.

[0019] Corresponding reference characters indicate corresponding parts throughout the several views of the figures. The figures represent an illustration of some of the embodiments of the present invention and are not to be construed as limiting the scope of the invention in any manner. Some of the figures may not show all of the features and components of the invention for ease of illustration, but it is to be understood that where possible, features and components from one figure may be an included in the other figures. Further, the figures are not necessarily to scale, some features may be exaggerated to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0020] As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having" or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Also, use of "a" or "an" are employed to describe elements and components described herein. This is done merely for convenience and to give a general sense of the scope of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.

[0021] Certain exemplary embodiments of the present invention are described herein and are illustrated in the accompanying figures. The embodiments described are only for purposes of illustrating the present invention and should not be interpreted as limiting the scope of the invention. Other embodiments of the invention, and certain modifications, combinations, and improvements of the described embodiments, will occur to those skilled in the art and all such alternate embodiments, combinations, modifications, improvements are within the scope of the present invention.

[0022] According to one embodiment, a synthetic route and a composition are disclosed. The composition shown in Formula I includes the co-polymer structures with poly(phenylene) compounds integrated with functionalized poly(fluorene) compound. Where n is selected from 1-6 and R is selected from trimethylamine or N-methylpiperidine.

[0023] As shown in Figures, an anion conducing co-polymer 500 includes a poly(fluorene) and poly(phenylene) structures deriving from the compound 502 and the compound 508, wherein the fluorene-based compound 502 has sidechains 504, 504’ that extend to a respective terminal group 505, 505' that can be reacted to produce a functional group 503, 503’. FIG. 1 shows a polymer diagram of an anion conducting co-polymer 500 having a poly(fluorene) deriving from fluorene-based compound 502 and a poly(phenylene) deriving from the aromatic compound 508 covalently bonded to the poly(fluorene) compound. The fluorene-based compound is a polycyclic aromatic with a center with five carbons and two benzene rings on either side of said center ring. The compound has a pair of sidechains 504, 504’ that each extend to a respective terminal group 505, 505’, such as bromine, which can be functionalized with a functional group (R), 503, 503’ such as quaternary ammonium or n-methyl piperidine

[0024] The aromatic monomer 508 shown in the FIG. 2 was synthesized according to previous literature. 1 ,4-bisbenzil (7.10 g) and 1 ,3-(diphenyl)propan-2-one (9.15 g) were combined in ethanol/toluene (10:1) mixture solvent and stirred at 70 °C until the solution is clear. Then, KOH (1.45 g) dissolved in methanol was added dropwise to the reaction solution and refluxed at 130 °C for 45 minutes. The reaction mixture was stored at 0 °C for 2 hours and resulting black-purple solids were filtrated and washed with ethanol and water for three times. The crude samples were purified through recrystallization in dichloromethane and dried at 80 °C under vacuum for overnight.

[0025] The fluorene-based compound 502 shown in the FIG. 2 was synthesized according to previous literatures. A general method is shown below, 2,7-dibromofluorene (1.62 g), trimethylsilylacetylene (4.9 g), Pd(PPh₃)₄ (0.58 g) and Cui (0.10 g) were mixed in the mixture solvent containing 30 ml THF and 10 m diisopropylamine under Argon. The reaction was stirred at 75 °C for 24 hours and the filtrate was concentrated under vacuum to give crude product, which was purified by flash column chromatography. The pure solids obtained was added in to THF/methanol (1:1) solvent containing potassium carbonate and stirred at room temperature overnight. The suspension was filtered and concentrated by rotary evaporation, which gives yellow solids of the product. The yellow solids was then mixed with tetrabutylammonium iodide, 1 ,6-dibromohexane in 50% KOH aqueous solution at 75 °C for 15 minutes. The mixture was extracted with dichloromethane and purified by flash column chromatography to give pure intermediate 502.

[0026] Details of a process for synthesizing the target precursor copolymer 501 shown in Figure 2 are presented in Example 1.

[0027] Example 1: Synthesis of the target precursor co-polymer 501 shown in Figure 2. For the synthesis, a 100 ml three-neck flask was added with a mixture of the intermediate 508 bis (10.0 g) and intermediate 502 (7.82 g) in a 100 mL three-neck round bottom flask, diphenyl ether(50 mL) was added and the mixture was degassed three times. Then the mixture was heated at 180°C for 24 h. The reaction vessel is then cooled to room temperature and its contents were precipitated in 10-fold methanol to give the precursor co- polymer 501.

[0028] The solution of precursor co-copolymer 501 in toluene was applied for casting a membrane on glass plate, the resulting film was then immersed in trimethylamine or N- methylpiperidine aqueous solution for 48 hours to functionalize the terminal groups of the sidechains to produce the anion conducting co-polymer

[0029] It will be apparent to those skilled in the art that various modifications, combinations, and variations can be made in the present invention without departing from the scope of the invention. Specific embodiments, features and elements described herein may be modified, and/or combined in any suitable manner. Thus, it is intended that the present invention cover the modifications, combinations and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims

What is claimed is:

1 . An anion conducting co-polymer comprising: a. a polymeric backbone comprising repeat units of a poly(phenylene) compound bonded to an poly(fluorene) compound; wherein said poly(fluorene) compound has a 9H-fluorene structure that is a polycyclic aromatic hydrocarbon having a center ring with five carbon atoms, and a benzene ring on each of opposing sides of said center ring; and a pair of sidechains extending from the center ring to a respective terminal group; and wherein said poly(phenylene) compound is covalently bonded to each of said benzene rings of the poly(fluorene) compound.

2. The anion conducting co-polymer of claim 1 , wherein the ratio of the poly(fluorene) compound concentration to the poly(phenelyne) structure concentration is 1:1.

3. The anion conducting polymer of claim 1 , wherein each of the pair of sidechains includes at least four carbons.

4. The anion conducting polymer of claim 1 , wherein each of the pair of sidechains includes at least six carbons.

5. The anion conducting polymer of claim 1 , wherein each of the pair of sidechains is a hydrocarbon.

6. The anion conducting polymer of claim 5, wherein each of the pair of sidechains includes at least six carbons.

7. The anion conducting polymer of claim 1 , wherein each of the pair of sidechains comprises alkyl halides.

8. The anion conducting co-polymer of claim 7, wherein the terminal group is bromine.

9. The anion conducting co-polymer of claim 7, wherein the terminal group is a functional group.

10. The anion conducting co-polymer of claim 9, wherein the functional group includes quaternary ammonium.

11 . The anion conducting co-polymer of claim 9, wherein the functional group includes n-methyl piperidine. The anion conducting co-polymer of claim 1 , wherein the terminal group is bromine. The anion conducting co-polymer of claim 1 , wherein the terminal group is a functional group. The anion conducting co-polymer of claim 13, wherein the functional group includes quaternary ammonium. The anion conducting co-polymer of claim 13, wherein the functional group includes n-methyl piperidine. An anion exchange membrane comprising: a) a porous support scaffold; b) the anion conducting co-polymer of any of claims 1 or 2 or 3. The anion exchange membrane of claim 16, wherein the porous scaffold comprises a porous polymer. The anion exchange membrane of claim 17, wherein the porous polymer is selected from the group consisting of polyolefins, polyamides, polycarbonates, cellulosics, polyacrylates, copolyether esters, polyamides, polyarylether ketones, polysulfones, polybenzimidazoles, fluoropolymers, and chlorinated polymers. The anion exchange membrane of claim 18, further comprising an additive selected from the group consisting of radical scavengers, plasticizers, fillers, anion conducting material, crosslinking agent. The anion exchange membrane of claim 19, wherein the additive is coupled to the porous support scaffold. The anion exchange membrane of claim 16, further comprising a radical scavenger that is an antioxidant selected from the group consisting of Cerium (Ce), Manganese (Mn), phenolic compounds, nitrogen-containing heterocyclic compounds, quinones, amine, phosphites, phosphonites, and thioesters. The anion exchange membrane of claim 21 , wherein the radical scavenger is coupled to the porous support scaffold. The anion exchange membrane of claim 16, further comprising a plasticizer selected from the group consisting of nylon 6,6, Glycerol, ionic liquids. The anion exchange membrane of claim 23, wherein the plasticizer is coupled to the porous support scaffold. The anion exchange membrane of claim 16, further comprising a filler, wherein the filler is a hygroscopic inorganic filler. The anion exchange membrane of claim 25, wherein the filler is a carbon-based materials selected from the group consisting of oxides of aluminum, silicon, titanium, zirconium and zirconium phosphate, cesium phosphate, zeolites, clays and carbon black, multiwall carbon nanotubes, reduced graphene oxide The anion exchange membrane of claim 25, wherein the filler is coupled to the porous support scaffold. The anion exchange membrane of claim 27, wherein the filler is a carbon-based materials selected from the group consisting of oxides of aluminum, silicon, titanium, zirconium and zirconium phosphate, cesium phosphate, zeolites, clays and carbon black, multiwall carbon nanotubes, reduced graphene oxide The anion exchange membrane of claim 16, further comprising a crosslinking agent. The anion exchange membrane of claim 29, wherein the crosslinking agent includes a tertiary diamine head groups which include DABCO (1 ,4- diazabicyclo[2,2,2]octane) and TMHDA (N,N,N,N -tetramethylhexane diammonium), 1 ,4-diiodobutane. The anion exchange membrane of claim 16, wherein the thickness is no more than 100pm. The anion exchange membrane of claim 16, wherein the thickness is no more than 50pm. The anion exchange membrane of claim 16, wherein the thickness is no more than 25pm. The anion exchange membrane of claim 16, wherein the anion exchange membrane is configured into a tube.