Crosslinked copolymer, polymer membrane containing the same, and anion exchange membrane containing the polymer membrane.

Abstract

The present invention provides a new crosslinked copolymer that has excellent mechanical properties, excellent alkali stability, and high ionic conductivity and degree of hydration, and thus can be suitably used as a material for an anion exchange membrane (AEM) such as a fuel cell.

Description

[Technical Field]

[0001] [Cross-reference of related applications] This application claims priority rights based on Korean Patent Application No. 10-2022-0079130 dated June 28, 2022, and Korean Patent Application No. 10-2023-0040300 dated March 28, 2023, and all content disclosed in the documents of said Korean patent applications is incorporated herein by reference. The present invention relates to a crosslinked copolymer, a polymer membrane containing the same, and an anion exchange membrane containing the polymer membrane. [Background technology]

[0002] Hydrogen fuel cells are attracting attention as an environmentally friendly energy source because they produce only water (H2O) as a by-product during the process of generating electrical energy. Among these, anion exchange membrane fuel cells (AEMFCs) are attracting attention as a technology that can replace proton exchange membrane fuel cells (PEMFCs) due to their ability to use non-noble metal catalysts.

[0003] AEMFCs transmit hydroxide ions (OH) through a polymer electrolyte membrane. - It conducts ions and converts chemical energy into electrical energy. Therefore, in order to develop AEMFCs with superior performance, it is necessary to develop anion exchange polymer electrolyte membranes (AEMs) that have excellent ionic conductivity characteristics. However, AEMFCs are OH - Due to its property of conducting electricity and thereby producing a high pH, ​​i.e., an alkaline environment, is created when it is in operation.

[0004] Generally, AEMs consist of a polymer backbone and ionic conductors. However, the abundance of hydroxide ions in alkaline environments provides a high opportunity for nucleophilic attack on the polymer backbone and ionic conductors, which can induce a decrease in the ionic conductivity and mechanical properties of AEMs. Therefore, it is necessary to develop AEMs with excellent chemical stability to prevent performance degradation. In other words, developing AEMs with excellent ionic conductivity and chemical stability is essential for developing high-performance AEMFCs.

[0005] In the case of ion-conducting polymers (ionomers) such as AEMs, ionic conductivity is primarily influenced by the type of ion-conducting group and the ion exchange capacity (IEC). Furthermore, the morphology of the membrane also influences the formation of effective ion clusters and ion conducting channels.

[0006] The alkaline stability of AEMs is also influenced by a combination of factors, including the polymer backbone, ionic conductors, and hydration number. Therefore, improving the performance of AEMs (i.e., achieving high conductivity and alkaline stability) requires a comprehensive understanding of various AEM properties, including not only the ionic conductors and polymer backbone, but also the morphology of the film due to its molecular structure and the hydration number. For this reason, much research has been conducted on the ionic conductors and polymer backbone of AEMs over the past decade or so.

[0007] First, looking at the ion-conducting groups and polymer backbone from a structural perspective of AEM, research is actively being conducted on quaternary ammonium compounds such as benzyl ammonium and alkyl ammonium, and cyclic ammonium compounds such as imidazolium, piperidinium, and spiro ammonium as ion-conducting groups. Among these, piperidinium, in particular, is attracting attention due to its good moderate ion conductivity and excellent chemical stability. Next, regarding the polymer backbones that make up AEMs, poly(aryl ether sulfone) (PES), poly(aryl ether ketone) (PAEK), poly(phenylene oxide) (PPO), spirobisindane, polyphenylene (PP), and styrene-ethylene-butylene-styrene (SEBS) have been actively studied. In particular, polyphenylene polymer backbones with an aryl ether-free structure have recently been the subject of much research due to their excellent chemical stability and mechanical properties.

[0008] In addition to improving the performance of AEMs through the structure of ionic conductors and polymers, various approaches have been taken, including improving conductivity through the introduction of multications, controlling the morphology of the membrane through the introduction of block- or graft- and partially fluorinated polymer backbone or side chains, and maximizing the stability of the AEM through crosslinking.

[0009] By effectively controlling the structure of the conductive groups and polymers, as well as the morphology of the polymer membrane, AEM materials exhibiting extremely high cell performance close to that of PEMFCs (proton exchange membrane fuel cells), along with excellent chemical stability even under high temperature and high pH conditions, are being developed one after another. Examples include poly(aryl piperidinium) (PAP), poly(diphenylethane-co-terphenyl piperidinium) (PDTP), polycarbazole, and poly(aryl-co-terphenyl piperidinium).

[0010] These polyphenylene-based AEMs are characterized by a relatively low water uptake (WU) compared to high IECs, i.e., a low hydration number. Generally, water is involved in the ion conduction mechanism of AEMs through OH - In order to act as a conduction medium, AEMs must have a high water content (WU) for their high ionic conductivity. Furthermore, if the membrane has a high hydration number, OH -This also has the advantage of limiting nucleophilic attack on the conductive groups, ultimately increasing the chemical stability of AEMs. Furthermore, due to the strong π-π interaction between phenyl groups in the polymer backbone, polyphenylene-based AEMs exhibit high stress and relatively low strain properties. In addition, AEMs act as separators that prevent fuel supplied to the anode and cathode from moving to the opposite electrode, and therefore must not be damaged by gas flow or shock. Thus, it is clear that high mechanical stability, especially high stress properties, of the AEMs is essential to ensure the performance and durability of the AEMFC. However, in order to overcome mechanical failures that may occur at the edge of the MEA active area where mechanical stress is maximized during AEMFC operation, not only high stress but also high strain properties of the AEM are required.

[0011] On the other hand, SEBS-based (styrene-b-ethylene-co-butylene-b-styrene(SEBS)-based) AEMs have different physical properties from polyphenylene-based AEMs, namely high hydration number and high strain. This is due to the aliphatic chain structure of SEBS. In addition, SEBS has a well-developed morphology as a block copolymer structure of styrene and 1,4-butadiene, so in the case of this AEM, it has higher ionic conductivity and chemical stability compared to IEC. However, excessively high water content can cause AEMs to swell excessively, and the conductive ions, OH, can be a problem. - The so-called "dilution effect," which lowers the concentration of SEBS, can actually reduce the ionic conductivity of the membrane. Furthermore, SEBS's low tensile strength makes it vulnerable to membrane breakage and deformation, making it unsuitable for high-temperature and humid AEMFC operating environments. In addition, the limiting solubility of SEBS restricts its modification, making the development of superior SEBS-based AEMs difficult.

[0012] To overcome these limitations of SEBS, Korean Patent No. 10-2184530 proposes a copolymer (xTQA-PPO-SEBS) in which flexible SEBS and rigid PPO are crosslinked via triazole. This copolymer exhibits lower WU and higher deformability compared to existing SEBS-based films, and higher ionic conductivity and cell properties compared to IEC. However, this copolymer has the problem of low chemical stability to hydroxide ions due to its aryl-ether-containing structure. [Prior art documents] [Patent Documents]

[0013] [License 1] Korean Registration License No. 10-2184530 [Non-licensed literature]

[0014] [Non-licensed Document 1] Nat. Energy 4 (2019) 392-398 [Non-licensed Document 2] J. Power Sources 487 (2021), 229429 [Non-licensed Document 3] J. Mater. Chem. A. Mater. 9(2021) 327-337 [Non-licensed Document 4] Nat. Commun. 12 (2021) 2367 [Non-licensed Document 5] J. Membr. Sci. 621 (2021) [Non-licensed Document 6] J. Membr. Sci. 642 (2022), 119966 [Non-licensed Document 7] J. Polym. Sci. 58 (2020) 2181-2196 [Non-licensed Document 8] Int. J. Hydrogen Energy 46 (2021) 36301-36313 [Non-licensed Document 9] J. Membr. Sci. 599 (2020), 117829 [Non-licensed Document 10] Int. J. Hydrogen Energy 45 (2020) 15658-15671 [Non-licensed Document 11] J. Membr. Sci. (2022), 120029 [Non-licensed Document 12] J. Mater. Chem. A. 7 (2019) 6883-6893 [Non-Patent Document 13] J. Membr. Sci. 638 (2021), 119685 [Non-Patent Document 14] Energy Environ. Sci. 13 (2020) 3633-3645 [Non-Patent Document 15] Int. J. Hydrogen Energy 46 (2021) 18524-18533 [Non-Patent Document 16] J. Membr. Sci. 647 (2022), 120341 [Non-Patent Document 17] Angew. Chem. 133 (2021) 7789-7797 [Non-Patent Document 18] Membranes 10 (2020) 1-16 [Overview of the project] [Problems that the invention aims to solve]

[0015] The present invention aims to provide a novel crosslinked copolymer that can be suitably used as an anion exchange membrane (AEM) material for fuel cells and the like due to its excellent mechanical properties, excellent alkali stability, and high ionic conductivity and hydration. [Means for solving the problem]

[0016] According to one embodiment of the present invention, a crosslinked copolymer is provided comprising a first chain represented by the following chemical formula 1 and a second chain represented by the following chemical formula 2, wherein the first chain and the second chain are crosslinked with respect to each other:

[0017] [ka]

[0018] In the aforementioned chemical formula 1, * indicates the bonding position with chemical formula 2. The sum of q1, q2, q5, and q6 is an integer between 100 and 1,000. The sum of q3 and q4 is an integer between 150 and 2,000. a and b are each independent integers between 3 and 10. R1 to R4 are each independently hydrogen or -(CH2) p -CH3, where p is an integer from 0 to 5.

[0019] [ka]

[0020] In the aforementioned chemical formula 2, * indicates the bonding position with chemical formula 1. x and y are independent integers between 0 and 10. n is an integer between 10 and 1000. Furthermore, according to one embodiment of the present invention, a polymer film containing the crosslinked copolymer is provided. Furthermore, according to one embodiment of the present invention, (a) The step of producing a polymer represented by the following chemical formula 1-1; (b) The step of producing a polymer represented by the following chemical formula 2-1; and (c) A step of crosslinking a polymer represented by the following chemical formula 1-1 and a polymer represented by the following chemical formula 2-1 to produce a crosslinked copolymer; A method for producing a crosslinked copolymer containing the following is provided:

[0021] [ka]

[0022] In the aforementioned chemical formula 1-1, The sum of q1, q2, q5, and q6 is an integer between 100 and 1,000. The sum of q3 and q4 is an integer between 150 and 2,000. a and b are each independent integers between 3 and 10. R1 to R4 are each independently hydrogen or -(CH2) p -CH3, where p is an integer from 0 to 5. X1 and X2 are each an independent halogen group.

[0023] [ka]

[0024] In the aforementioned chemical formula 2-1, x and y are independent integers between 0 and 10. n is an integer between 10 and 1000. [Effects of the Invention]

[0025] The crosslinked copolymer of the present invention has a high water uptake (WU) while exhibiting excellent dimensional stability, high ionic conductivity, hydration, and alkali stability. Furthermore, the crosslinked copolymer has excellent mechanical properties such as tensile strength and elongation characteristics. As described above, the crosslinked copolymer of the present invention has excellent electrochemical and mechanical properties, and can therefore be suitably used as an anion exchange membrane material. [Brief explanation of the drawing]

[0026] [Figure 1] This graph shows the hydration number (λ) relative to IEC at room temperature for x-PBB-SEBS films of Examples 1-3, and for OH-form SEBS-based AEMs (open symbols) and poly(phenylene)-based AEMs (solid symbols) reported in the literature. [Figure 2] (a) TGA graph from 30°C to 250°C and (b) DSC graph from -20°C to 10°C for the x-PBB-SEBS films of Examples 1 to 3. [Figure 3] This graph shows (a) hydroxide ion conductivity (solid line) and normalized conductivity (dotted line) and (b) normalized conductivity and 95%RH conductivity of the x-PBB-SEBS films of Examples 1 to 3 at 60°C. [Figure 4](a) is an AFM image of 30x-PBB-SEBS, (b) is an AFM image of 40x-PBB-SEBS, (c) is an AFM image of 50x-PBB-SEBS, (d) is a TEM image of 30x-PBB-SEBS, (e) is a TEM image of 40x-PBB-SEBS, and (f) is a TEM image of 50x-PBB-SEBS. [Figure 5] (a) Hydroxide ion conductivity retention rate and (b) Residual IEC graph of the x-PBB-SEBS film after treatment with 2M KOH at 80°C. [Figure 6] This graph shows the single-cell performance of x-PBB-SEBS membranes under (a) 100% / 100%RH and (b) 70% / 100%RH conditions at 60℃ and H2 / O2 200 / 400mL min⁻¹. [Figure 7] This is the 1H NMR spectrum of poly(bibenzyl N-methylpiperidine)2. [Figure 8] (a) 1H NMR spectra of bromohexanoyl SEBS4 and (b) bromohexyl SEBS3. [Figure 9] These are photographs of cross-linked (bibenzyl N-methylpiperidinium)-SEBS films (x-PBB-SEBS) with different degrees of cross-linking. [Figure 10] These are the IR spectra of the X-PBB-SEBS film before (dotted line) and after (solid line) TMA treatment. [Figure 11] This graph shows the mechanical properties of the x-PBB-SEBS film under 50%RH conditions. [Figure 12] This graph compares the Young's modulus and fracture elongation between OH-morph x-PBB-SEBS films mentioned in the literature and representative AEMs (the fracture elongation is shown as ranging from 0% to 150% in the internal graph). [Figure 13] These are (a) thermogravimetric analysis (TGA) and (b) differential scanning calorimetry (DSC) graphs of the X-PBB-SEBS film. [Figure 14] This graph compares the normalized conductivity of x-PBB-SEBS films at room temperature with the normalized conductivity of representative films in the literature. [Figure 15]This is a TGA graph of 40x-PBB-SEBS films formed at 30°C to 800°C before and after oxidation stability testing. [Figure 16] This graph compares the maximum power density of x-PBB-SEBS membranes at 60°C and 200 / 400 mL min-1 under two conditions: 100% / 100% A / C RH (red) and 70% / 100% A / C RH (blue). [Modes for carrying out the invention]

[0027] The terms used herein are for illustrative purposes only and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0028] In this specification, terms such as “includes,” “equip,” or “have” are intended to indicate the existence of implemented features, stages, components, or combinations thereof, and should be understood not to preemptively exclude the existence or possibility of adding one or more other features, stages, components, or combinations thereof.

[0029] While the present invention can be modified in various ways and may take many forms, specific embodiments are illustrated and described in detail below. However, this should not be understood as limiting the present invention to any particular disclosure, but rather as including all modifications, equivalents, or substitutions that fall within the spirit and technical scope of the present invention.

[0030] The present invention will be described in detail below. According to one embodiment of the present invention, a crosslinked copolymer is provided which comprises a first chain represented by the following chemical formula 1 and a second chain represented by the following chemical formula 2, wherein the first chain and the second chain are crosslinked with respect to each other.

[0031] [ka] In the aforementioned chemical formula 1, * indicates the bonding position with chemical formula 2. The sum of q1, q2, q5, and q6 is an integer between 100 and 1,000. The sum of q3 and q4 is an integer between 150 and 2,000. a and b are each independent integers between 3 and 10. R1 to R4 are each independently hydrogen or -(CH2) p -CH3, where p is an integer from 0 to 5. [ka] In the aforementioned chemical formula 2, * indicates the bonding position with chemical formula 1. x and y are independent integers between 0 and 10. n is an integer between 10 and 1000.

[0032] The crosslinked copolymer of the present invention is formed by crosslinking a first chain of poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) with a second chain of poly(arylpiperidinium)

[0033] The first chain of the crosslinked copolymer has elastic properties, and the second chain has rigid properties, and both the first and second chains exhibit phase separation characteristics. By chemically crosslinking the first and second chains in this manner, the crosslinked copolymer of the present invention exhibits excellent mechanical properties, namely, appropriate tensile strength along with high elongation at break and Young's modulus.

[0034] Furthermore, the crosslinked copolymer exhibits excellent water retention capacity, high ionic conductivity, and excellent alkali stability due to its structural properties. Therefore, the crosslinked copolymer can be suitably used as an anion exchange membrane in fuel cells and the like.

[0035] The ratio of the first chain represented by chemical formula 1 and the second chain represented by chemical formula 2 can be adjusted according to the desired physical properties. For example, the crosslinked copolymer may contain 10 moles or more, or 20 moles or more, or 30 moles or more, or 40 moles or more of the second chain per 100 moles of the first chain, and 70 moles or less, or 60 moles or less, or 50 moles or less of the second chain. When the ratio of the first chain to the second chain of the crosslinked copolymer satisfies the above range, it can exhibit excellent mechanical and electrochemical properties.

[0036] Preferably, the sum of q1, q2, q5, and q6 is 100 or more, or 150 or more, or 200 or more, or 250 or more, or 300 or more, or 350 or more, or 400 or more, or 450 or more, or 500 or more, and may be an integer of 1,000 or less, or 950 or less, or 900 or less, or 850 or less, or 800 or less.

[0037] Preferably, the sum of q3 and q4 is 150 or more, or 200 or more, or 250 or more, or 300 or more, or 350 or more, or 400 or more, or 450 or more, or 500 or more, or 550 or more, or 600 or more, and may be an integer of 2,000 or less, or 1,800 or less, or 1,600 or less, or 1,500 or less, or 1,400 or less, or 1,200 or less, or 1,000 or less.

[0038] Preferably, q1 to q6 are each independently 10 or greater, or 20 or greater, or 25 or greater, or 30 or greater, and may be integers of 500 or less, or 450 or less, or 400 or less, or 350 or less, or 300 or less. Preferably, the ratio of the sum of q1, q2, q5, and q6 to the total sum of q1 to q6, that is, the total mole fraction of styrene-derived repeating units to the entire repeating unit of chemical formula 1, is 0.2 or more, or 0.25 or more, or 0.3 or more, and may be 0.5 or less, or 0.45 or less.

[0039] Preferably, the ratio of the sum of q1 and q6 to the total of q1, q2, q5, and q6, that is, the total molar fraction of unsubstituted styrene repeating units to the total styrene-derived repeating units of Chemical Formula 1, is 0.2 or more, or 0.25 or more, or 0.3 or more, or 0.35 or more, and can be 0.5 or less, or 0.45 or less, or 0.4 or less.

[0040] Preferably, a and b are each independently 3 or more, or 4 or more, and can be an integer of 10 or less, or 9 or less, or 8 or less, or 7 or less, or 6 or less. Preferably, R1 to R4 are each independently hydrogen or -(CH2) x -CH3, and x can be an integer from 0 to 3, or an integer from 0 to 2. Preferably, all of R1 to R4 can be hydrogen.

[0041] Preferably, n is 10 or more, or 100 or more, or 150 or more, and is an integer of 1000 or less, or 500 or less. Preferably, x is 1 or more, or 2 or more, and can be an integer of 9 or less, or 7 or less, or 5 or less, or 4 or less, or 3 or less. Preferably, y is 0 or more, and can be an integer of 7 or less, or 5 or less, or 3 or less, or 2 or less.

[0042] Specifically, the crosslinked copolymer can contain a repeating unit represented by the following Chemical Formula 3:

Chemical Formula

[0043] In Chemical Formula 3, q1 to q6, a, b, x, y, and n are as defined in Chemical Formula 1 and Chemical Formula Preferably, the crosslinked copolymer can contain a repeating unit represented by the following Chemical Formula 4:

Chemical Formula

[0044] The aforementioned crosslinked copolymer has positively charged quaternary ammonium groups, allowing only anions to pass through selectively. Therefore, the crosslinked copolymer can be used as an anion exchange membrane. The counterion (anion) group for the cation (quaternary ammonium group) of the crosslinked copolymer is OH - Cl - , Br - , or HCO3 - It may be, preferably OH - It is possible. Furthermore, the crosslinked copolymer exhibits excellent ion conduction efficiency and alkali stability due to its phase separation properties.

[0045] Therefore, according to one embodiment of the present invention, a polymer film containing the crosslinked copolymer is provided. The polymer film containing the crosslinked copolymer has a thickness of 20 μm or more, or 30 μm or more, or 45 μm or more, or 55 μm or more, and may be 70 μm or less, or 60 μm or less, or 55 μm or less. When the thickness of the polymer film satisfies the above range, it exhibits high mechanical properties and also has excellent electrochemical properties, making it suitable for use as an anion exchange membrane.

[0046] The aforementioned polymer membrane, by containing a crosslinked copolymer including the first and second chains, exhibits improved mechanical strength compared to existing polymers for AEMs, high ionic conductivity while showing appropriate IEC values, and excellent alkali stability. Therefore, a polymer membrane having the above-described properties can be suitably used as an anion exchange membrane contained in fuel cells and the like.

[0047] On the other hand, according to one embodiment of the present invention, a method for producing the crosslinked copolymer is provided. Specifically, the method for producing the crosslinked copolymer of the present invention includes the following steps. (a) The step of producing a polymer represented by the following chemical formula 1-1; (b) The step of producing a polymer represented by the following chemical formula 2-1; and (c) A step of crosslinking the polymer represented by the following chemical formula 1-1 and the polymer represented by the following chemical formula 2-1 to produce a crosslinked copolymer: [ka] In the aforementioned chemical formula 1-1, The sum of q1, q2, q5, and q6 is an integer between 100 and 1,000. The sum of q3 and q4 is an integer between 150 and 2,000. a and b are each independent integers between 3 and 10. R1 to R4 are each independently hydrogen or -(CH2) p -CH3, where p is an integer from 0 to 5. X1 and X2 are each an independent halogen group. [ka] In the aforementioned chemical formula 2-1, x and y are independent integers between 0 and 10. n is an integer between 10 and 1000.

[0048] The preferred ranges for q1 to q6, a, b, R1 to R4, x, y, and n in the aforementioned chemical formulas 1-1 and 2-1 are as described above for chemical formulas 1 and 2. X1 and X2 are each independently F, Cl, Br, or I, and are preferably Br.

[0049] Step (a) above is the step of introducing a halogen alkyl group into the styrene portion of the SEBS polymer. Specifically, the poly(styrene-b-ethylene-co-butylene-b-styrene) polymer represented by chemical formula 1-1 can be produced through the Friedel-Crafts acylation reaction and the reduction reaction of the carbonyl group of SEBS.

[0050] The acyl halide used in the acylation reaction is selected considering the desired number of a and b atoms. Specifically, the acyl halide is XR-COCl(where X is a halogen and R is C). 1-29 Alkanoyl chlorides having a halogen group at the alkyl chain terminus, represented as alkyl, can be used. If a and b are different from each other, or if X1 and X2 are different from each other, the acylation reaction can be carried out two or more times using different types of acyl halides. Aluminum chloride (AlCl3) can be used as a catalyst for the acylation reaction, and the reaction can be carried out at 20-30°C for 8-24 hours.

[0051] The reduction reaction of the carbonyl group can be carried out without limitation using methods known in the art. For example, the carbonyl group can be reduced by adding triethylsilane and trifluoroacetic acid and reacting them at 90-120°C for 20-30 hours. Through such a reaction, a poly(styrene-β-ethylene-CO-butylene-β-styrene) polymer represented by chemical formula 1-1 can be obtained.

[0052] The poly(styrene-b-ethylene-co-butylene-b-styrene) copolymer contains 30 moles or more, 40 moles or more, 50 moles or more, 55 moles or more, or 60 moles or more of halogen groups per 100 moles of styrene repeating units, and preferably contains 90 moles or less, 80 moles or less, 75 moles or less, 70 moles or less, or 65 moles or less. The number of moles of halogen groups per styrene repeating unit can be adjusted by adjusting the number of moles of acyl halide relative to the number of moles of styrene in the SEBS polymer during the acylation reaction.

[0053] Step (b) above is a step in which a poly(arylpiperidinium) polymer is produced. As an example, aryl [ka] A polymer represented by chemical formula 2-1 can be produced by reacting N-alkyl-4-piperidone (where x is as described in chemical formula 2) with trifluoroacetic acid and trifluoromethanesulfonic acid. This reaction can be carried out, for example, at -10 to 10°C for 12 to 60 hours.

[0054] Step (c) is a step of crosslinking the polymer represented by chemical formula 1-1 and the polymer represented by chemical formula 2-1 to produce a crosslinked copolymer. Since the polymer represented by chemical formula 1-1 contains a halogen group and the polymer represented by chemical formula 2-1 contains a tertiary amine group, the two polymers can be easily crosslinked through a nucleophilic substitution reaction without the need for a separate crosslinking agent.

[0055] In step (c) above, the polymer represented by chemical formula 2-1 is preferably used in an amount of 10 moles or more, or 20 moles or more, or 30 moles or more, or 40 moles or more, relative to 100 moles of halogen groups contained in the polymer represented by chemical formula 1-1, and is preferably 70 moles or less, or 60 moles or less, or 50 moles or less. When the above molar ratio is satisfied, the crosslinked polymer produced can have an appropriate first-chain and second-chain ratio, thereby exhibiting excellent hydroxide ion conductivity and mechanical properties.

[0056] The reaction in step (c) can be carried out at 40-60°C for 10-16 hours, preferably at 45-55°C for 11-13 hours. If the polymerization reaction temperature is below 40°C or the reaction time is less than 10 hours, the crosslinking reaction between polymers may not occur sufficiently, leading to a decrease in hydroxide ion conductivity and reduced alkali stability. Conversely, if the polymerization reaction temperature exceeds 60°C or the reaction time exceeds 16 hours, the crosslinking rate between polymers may increase excessively, causing the crosslinked polymer solution to gel.

[0057] On the other hand, after step (c), the step (d) may further include reacting the crosslinked copolymer with trimethylamine in order to convert all halogen groups remaining in the crosslinked copolymer into amine groups. Step (d) can be carried out, for example, at 40 to 60°C for 10 to 30 hours, preferably at 45 to 55°C for 20 to 30 hours. As described above, in the present invention, a halogen functional group is introduced into the SEBS main chain and reacted with a polymer represented by chemical formula 2-1 containing an amine group to produce a crosslinked copolymer. Therefore, the polymer can be quantitatively crosslinked without side reactions, and the degree of crosslinking can be easily controlled by adjusting the amount of each polymer.

[0058] Furthermore, the above method allows for the production of crosslinked copolymers more easily and with higher yields, thereby increasing process productivity and reducing costs. The present invention will be described in more detail below with reference to the following examples. However, the following examples are merely illustrative and the scope of the present invention is not limited to them.

[0059] [Examples] <Material> Vibenzyl (99%), aluminum chloride (99%), 6-bromohexanoyl chloride, N-methyl-4-piperidone (97%), and trimethylamine solution (45% by weight in water) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Trifluoromethanesulfonic acid (98%) was purchased from TCI (Tokyo, Japan). Triethylsilane (98%) was purchased from Alpha Acer (MA, USA). Trifluoroacetic acid was purchased from Daejung Chemical & Metal (Siheung, South Korea). Poly(styrene-β-ethylene-CO-butylene-β-styrene) (SEBS, A1535H) with a styrene content of 57% was purchased from Kraton Corporation (Houston, TX, USA). All other chemicals were obtained from commercial sources.

[0060] <Confirmation of the chemical structure of polymers> The chemical structures of the polymers obtained at each stage of the following examples are: 1 This was confirmed through 1H NMR spectroscopy and Fourier transform infrared (FTIR) spectroscopy. 1 The 1H NMR spectrum was obtained using CDCl as the solvent. 3 The spectra were obtained using a 400 MHz NMR instrument (Agilent 400 MR). The FTIR spectra were obtained using a PerkinElmer Spectrum Two ATR-FTIR spectrometer. The spectra were measured at 4000–400 cm⁻¹. -1 It was collected up to that point.

[0061] Example 1: Production of a 30x-PBB-SEBS (30% crosslinking degree) film (1) Synthesis of poly(vibenzyl N-methylpiperidine)2 [ka] (In the above reaction equation, n is 158.)

[0062] Bibenzyl (3.00 g, 16.46 mmol) and N-methyl-4-piperidone (2.23 g, 19.75 mmol) were poured into a completely dried 50 mL round-bottom flask under a nitrogen atmosphere, and then dissolved in dichloromethane (20 mL) using a magnetic stirrer. After the mixture was completely dissolved, the solution was cooled to 0°C using an ice bath. Next, trifluoroacetic acid (2.82 g, 24.69 mmol) and trifluoromethanesulfonic acid (24.70 g, 164.60 mmol) were gradually added to the solution with continuous stirring. The color of the solution changed from light brown to dark brown. After 48 hours, the viscous solution was poured into a large amount of KOH solution (500 mL), the precipitated polymer was filtered through filter paper, and the residual reaction products were removed by washing several times with deionized water (DI). The obtained polymer was dried in a vacuum oven at 80°C for 24 hours to obtain a yellow powder. 1 It was confirmed to be poly(vibenzyl N-methylpiperidine)2 via 1H-NMR analysis (4.51 g, 98.8%); δ H (400 MHz, CDCl3) 7.85-6.73 (8H, broad signal, H 1,2), 3.05-2.67 (4H, d, H 3,3’ ), 2.60-2.13 (8H, broadband signal, H 5,5’,6 ), 2.12-1.67 (4H, d, H 4,4’ (Figure 7)

[0063] (2) Synthesis of bromohexyl SEBS3 (2-1) Synthesis of bromohexanoyl SEBS4 [ka] (In the above reaction equation, the sum of q1, q2, q5, and q6 is 711, the sum of q3 and q4 is 996, and the ratio of the sum of q1 and q6 to the grand total of q1, q2, q5, and q6 is 0.3.)

[0064] SEBS (10.00 g, 54.73 mmol) was placed in a 1000 mL two-necked round-bottom flask under a nitrogen atmosphere and dissolved in dichloromethane (320 mL) using a magnetic stirrer. After the polymer was completely dissolved, 6-bromohexanoyl chloride of aluminum chloride (5.47 g, 41.05 mmol) and dichloromethane (8.76 g, 41.05 mmol) was gradually added using a dropping funnel. After 24 hours, the reaction mixture was poured into a large volume of ethanol (1500 mL), and the precipitated polymer was filtered through filter paper. The mixture was then washed several times with ethanol to remove residual reaction products. The obtained polymer was dried in a desiccator at room temperature for 24 hours to obtain bromohexanoyl SEBS4 in the form of white rubber (16.40 g, 97.7%). 1 Through H-NMR analysis, it was confirmed that bromohexanoyl side chains were bound to 70 mol% of the total styrene contained in SEBS;δ H (400 MHz, CDCl3) 7.92-7.37 (4H, broad signal, H 1,2 ), 7.26-6.28 (10H, broad signal, H 3,4 ), 3.50-3.38 (3H, broad signal, H 10), 3.03-2.80 (3H, broad signal, H6), 2.69-2.35 (2H, broad signal, H 12 ), 2.01-0.56 (46H, broad signal, H 7-9,11,13-18 (Figure 8a).

[0065] (2-2) Synthesis of bromohexyl SEBS3 [ka] (In the above reaction equation, the sum of q1, q2, q5, and q6 is 711, the sum of q3 and q4 is 996, and the ratio of the sum of q1 and q6 to the grand sum of q1, q2, q5, and q6 is 0.3.)

[0066] Bromohexanoyl SEBS4 (16.00 g, 38 mmol) was poured into a 1000 mL two-necked round-bottom flask connected to a reflux condenser, and after attaching a magnetic stirrer under a nitrogen atmosphere, it was dissolved in chloroform (320 mL). After the polymer was completely dissolved, triethylsilane (60.70 mL, 380 mmol) and trifluoroacetic acid (58.16 mL, 760 mmol) were added. The reaction mixture was gradually heated to 105 °C and left at this temperature for 24 hours. The reaction mixture was cooled to room temperature, and the solution was neutralized with 1 M KOH (400 mL). The organic layer was poured into methanol (1500 mL), and the precipitated polymer was filtered through filter paper and washed several times with methanol to remove residual reaction products. The obtained polymer was dried in a desiccator at room temperature for 24 hours, and bromohexyl SEBS3 appeared in the form of white rubber (15.28 g, 93.11%);δ H (400 MHz, CDCl3) 7.21-6.27 (12H, broad signal, H 1-4 ), 3.48-3.34 (3H, broad signal, H 10 ), 2.66-2.27 (5H, broad signal, H 6’,12 ), 1.99-0.59 (46H, broad signal, H 6-9,11,13-18 (Figure 8b).

[0067] (3) Production of cross-linked poly(bibenzyl N-methylpiperidinium)-SEBS1 film (30x-PBB-SEBS) [ka] (In the above reaction equation, n is 158, the sum of q1, q2, q5, and q6 is 711, the sum of q3 and q4 is 996, and the ratio of the sum of q1 and q6 to the grand sum of q1, q2, q5, and q6 is 0.3.)

[0068] Poly(vibenzyl N-methylpiperidine) 2, bromohexyl SEBS 3, and HPLC-grade chloroform (20 mL) were placed in a 20 mL vial and stirred until a homogeneous solution was obtained. At this time, poly(vibenzyl N-methylpiperidine) 2 was used in a ratio of 30 mol% to 100 mol% of bromohexyl SEBS 3 (total 0.5 g).

[0069] The polymer solution was heated overnight (12 hours) at 40°C to induce crosslinking. After the polymer solution was cooled to room temperature, it was poured into a glass petri dish with a cotton filter and dried at room temperature for 24 hours. After peeling the prepared film from the petri dish, it was immersed in deionized water (DI) to wash away any residual solvent. The film was then immersed in an aqueous trimethylamine (TMA) solution at 45°C for 24 hours, and then washed with deionized water to remove excess TMA. The film was then immersed in a 1M KOH solution at room temperature for at least 24 hours to allow for Br to develop. - and OH - 30x-PPB-SEBS membranes were fabricated by exchanging ions and washing several times with deionized water to remove excess KOH.

[0070] To confirm that the Br in the aforementioned cross-linked membrane was replaced with TMA, the IR change was observed before and after treatment with a trimethylamine (TMA) solution (Figure 10). After TMA treatment, approximately 642 cm⁻¹ -1 We confirmed that the C-Br peak had disappeared, which confirmed that the C-Br bond in x-PBB-SEBS had been replaced by TMA.

[0071] Example 2: Production of a 40x-PBB-SEBS (40% crosslinking degree) film (3) A 40x-PBB-SEBS film was prepared in the same manner as in Example 1, except that 40 mol% of poly(bibenzyl N-methylpiperidine) 2 was used relative to bromohexyl SEBS 3 in step (3).

[0072] Example 3: Production of a 50x-PBB-SEBS (50% crosslinking degree) film (3) A 50x-PBB-SEBS film was prepared in the same manner as in Example 1, except that 50 mol% of poly(vibenzyl N-methylpiperidine) 2 was used relative to bromohexyl SEBS 3 in step (3). Flexible films with a thickness of 30 to 35 μm were obtained through the above Examples 1 to 3 (Figure 9).

[0073] Experimental Example 1: Ion exchange capacity (IEC), water content (WU), and swelling rate (SR) (1) Ion exchange capacity (IEC) a. Experimental IEC The ion exchange capacity (IEC) of each membrane was measured using the back titration method. - The film was immersed in a 0.01 M HCl standard solution for 24 hours. The residual HCl was titrated again with a 0.01 M NaOH standard solution using a phenolphthalein indicator. The film was weighed (W dry The sample was dried to measure the IEC (meq g) values. The following formula was used to determine the experimental IEC (meq g) values. -1 ) was calculated using the moles of exchangeable hydroxide ions per gram: IEC (meq g -1 )=(C0V0-C0V x ) / W dry Here, V0 and V x These are the volume of NaOH before titration and the volume of NaOH consumed during the titration, respectively, C0 is the molar concentration of NaOH used in the back titration, and W dry This is the weight of the film after being dried in an oven for a minimum of 12 hours. b. Theoretical IEC The theoretical IEC value is,1 This was determined based on the number of Br atoms in bromohexyl SEBS3 calculated from the 1H NMR spectrum and the masses of the two polymers (2 and 3) used in the cross-linking process.

[0074] (2) Water content (WU) and swelling rate (SR) After immersing each of the circular membranes from Examples 1-3 in water at 20°C and 80°C, the water uptake (WU, %) and swelling ratio (SR, %) were calculated. - After immersing the morphological membrane in deionized water for a minimum of 24 hours, wipe the membrane surface and measure the weight of the sample (W). wet ), length (L wet ) and thickness (T wet The weight (W) of the dried film was measured rapidly. The film was dried in a vacuum atmosphere for 24 hours. dry ), length (L dry ), thickness (T dry ) was also measured. The moisture content (%) and swelling rate (%) were calculated using the following formula: WU(%)=(W wet -W dry ) / W dry ×100 SR(%)=(L wet -L dry ) / L dry ×100 or (T wet -T dry ) / T dry ×100 The hydration number (λ) of each membrane was calculated from WU and experimental IEC data for each membrane using the following formula: Hydration number (λ) = (Water uptake (WU) (%) × 1000) / (IEC × 18)

[0075] (3) Results The IEC, WU, and SR values ​​of the x-PBB-SEBS films of Examples 1 to 3 are shown in Table 1.

[0076] [Table 1] a 1Theoretical IEC calculated based on 1H NMR spectrum b Experimental IEC measured by back titration

[0077] IEC is defined as the milliequivalent of ion-conducting groups per unit mass of a polymer electrolyte membrane. Generally, a higher IEC of a polymer electrolyte membrane allows the membrane to contain more water (i.e., an increase in water content). Since water can act as a medium for hydroxide ion conduction in anion exchange membranes (AEMs), a higher IEC results in higher ionic conductivity. However, excessively high IEC sometimes leads to an increase in water content (WU), which decreases ionic conductivity through a mechanism called the "dilution effect." When this phenomenon occurs, the SR of the membrane also increases, reducing the membrane's mechanical properties and dimensional stability. Therefore, an appropriate IEC is necessary for an AEM to have high ionic conductivity and excellent mechanical properties.

[0078] The theoretical IEC values ​​for 30x-PBB-SEBS, 40x-PBB-SEBS, and 50x-PBB-SEBS are 1.96, 1.86, and 1.77 meq g, respectively. -1 The value showed a tendency to decrease with increasing crosslinking ratio. This is because the total amount of ion-conducting groups introduced decreased due to the decrease in the proportion of bromohexyl SEBS3. On the other hand, experimental IEC measurement results for the x-PBB-SEBS film were confirmed to be similar to the theoretical values. Thus, since the experimental and theoretical IEC values ​​are similar, it can be confirmed that each film has the intended degree of crosslinking.

[0079] The WU and SR measurements of x-PBB-SEBS confirmed that as the degree of crosslinking increased, both WU and SR decreased, indicating increased dimensional stability. This is attributed to the reduction in SEBS content, an elastic polymer, and the suppression of film expansion due to chemical bonding between polymer chains created through crosslinking.

[0080] Next, we calculated the hydration number (λ value) for each membrane and confirmed the expected trend of decreasing hydration number as the degree of crosslinking of x-PBB-SEBS increased (30x-PBB-SEBS=34.7, 40x-PBB-SEBS=31.1, 50x-PBB-SEBS=27.7).

[0081] The hydration numbers of the membranes in Examples 1-3 were compared with those of polyphenylene and SEBS-based membranes that have been previously reported (

[10] J. Mater. Chem. A. Mater. 9 (2021) 327-337;

[11] Nat. Commun. 12 (2021) 2367;

[32] Int. J. Hydrogen Energy 46 (2021) 36301-36313;

[33] J. Membr. Sci. 599 (2020), 117829;

[35] J. Membr. Sci. (2022), 120029;

[48] Korean Patent No. 10-2184530;

[53] J. Membr. Sci. 647 (2022), 120341) (Figure 1).

[0082] As a result, it can be confirmed that the x-PBB-SEBS membrane has a hydration number (λ value) that is somewhere between that of SEBS-based AEMs, which have a higher hydration number (λ value) than IEC, and that of poly(phenylene)-based AEMs, which have a relatively lower hydration number (λ value). As mentioned above, water plays the role of a medium for ion conduction, so in order for an AEM to obtain high ionic conductivity, it is necessary to have the highest possible hydration number. However, an excessively high value can actually hinder ionic conductivity, so it is necessary to have an appropriate value. From this perspective, it can be confirmed from the above results that in the case of x-PBB-SEBS, the hydration level can be easily adjusted by crosslinking polymers with different properties and adjusting the degree of crosslinking.

[0083] Experimental Example 2: Mechanical and Thermal Properties (1) Mechanical properties Using a benchtop tensile testing machine (Shimadzu EZ-TEST E2-L, Kyoto, Japan), a test was conducted at 25°C under 50% relative humidity for 10 mm min. -1 OH at crosshead speed - The mechanical properties of the morphological membranes were measured. The initial sample cross-sectional area was used to determine the engineering stress. The initial slope of the stress-deformation curve was used to calculate Young's modulus (E). For this test, each membrane sample was prepared in a dumbbell shape with a total area of ​​40 mm x 10 mm and a test area of ​​20 mm x 10 mm.

[0084] (2) Thermal stability The thermal stability of the film was investigated by thermogravimetric analysis (TGA) using a Scinco TGA N-1000 instrument (Seoul, South Korea). TGA was performed under a nitrogen atmosphere at 30-800°C for 10°C min. -1 It operated at this heating rate. The glass transition temperature (Tg) of each film was measured using a Differential Scanning Calorimeter (DSC) with a PerkinElmer DSC 4000 (Waltham, MA, USA). Samples were prepared in aluminum pans, and the heating and cooling rates were 10°C min. -1 Under these conditions, measurements were taken over two cycles at -40 to 200°C. Tg was measured from the second cycle onwards.

[0085] (3) Results In AEMFC, AEM is OH generated at the cathode. - The AEM acts as an electrolyte, conducting ions to the anode. Furthermore, it functions as a separator, preventing the H2 and O2 (or air) used as fuel from moving to opposite electrodes. Therefore, the AEM requires resistance to damage or deformation under battery operating conditions (gas flow, temperature, etc.), i.e., excellent mechanical properties and thermal stability.

[0086] The mechanical properties of x-PBB-SEBSs with different degrees of bridging were investigated using stress-strain curves (Figure 11). As a result, it was found that as the degree of bridging increased, the tensile strength and Young's modulus increased (30x-PBB-SEBS: 20.2 MPa and 360.3 MPa < 40x-PBB-SEBS: 25.1 MPa and 485.6 MPa < 50x-PBB-SEBS: 27.3 MPa and 650.4 MPa), while the elongation at break tended to decrease (30x-PBB-SEBS: 75.1% > 40x-PBB-SEBS: 70.3% > 50x-PBB-SEBS: 59.4%). This is because the increased degree of crosslinking reduces the content of SEBS, which is an elastic polymer, and increases the bonding between poly(bibenzyl N-methyl piperidine) and bromohexyl SEBS, resulting in stronger bonding between the polymer chains.

[0087] The mechanical properties of the x-PBB-SEBS film were studied using SEBS-based AEMs (

[31] J. Polym. Sci. 58 (2020) 2181-2196;

[33] J. Membr. Sci. 599 (2020), 117829;

[34] Int. J. Hydrogen Energy 45 (2020) 15658-15671;

[35] J. Membr. Sci. (2022), 120029) and polyphenylene-based AEMs ([9] J. Power Sources 487 (2021), 229429;

[10] J. Mater. Chem. A. Mater. 9 (2021) 327-337;

[11] Nat. Commun. 12 (2021) 2367;

[12] J. It was compared with xTQA-PPO-SEBS AEM obtained by crosslinking PPO and SEBS (

[48] Korean Registered Patent No. 10-2184530) (Table 2).

[0088] [Table 2]

[0089] As a result, it was confirmed that the x-PBB-SEBS film has tensile strength and elongation at break that are intermediate between SEBS and polyphenylene-based AEMs. This confirms that x-PBB-SEBS, which is made by crosslinking two polymers with different properties, has excellent tensile strength and mechanical stability in Young's modulus, while also having a high elongation at break, and that its mechanical properties can be adjusted by adjusting the degree of crosslinking.

[0090] The elongation at break and Young's modulus of x-PBB-SEBS were compared with those of previously reported AEMs (

[11] Nat. Commun. 12 (2021) 2367;

[12] J. Membr. Sci. 621 (2021);

[31] J. Polym. Sci. 58 (2020) 2181-2196;

[34] Int. J. Hydrogen Energy 45 (2020) 15658-15671;

[35] J. Membr. Sci. (2022), 120029;

[48] Korean Registered Patent No. 10-2184530) (Figure 12). As a result, it was confirmed that x-PBB-SEBS exhibits a similar Young's modulus to other AEMs, but has a higher elongation at break at a similar Young's modulus. In particular, it showed superior mechanical properties compared to the previous xTQA-PPO-SEBS film formed by crosslinking PPO and SEBS. This is attributed to the improved mechanical properties resulting from crosslinking the two polymers, poly(bibenzyl N-methyl piperidine) and SEBS, which exhibit excellent phase separation.

[0091] Next, the thermal stability of the x-PBB-SEBS membrane was investigated using TGA and DSC analysis (Figure 13). First, the TGA graph showed three stages of weight loss (Figure 13a): The first weight loss (30-150°C) occurred due to the evaporation of free water and bound water contained in the membrane. As the crosslinking ratio increased, the weight loss decreased, which is because the amount of water contained in the membrane, i.e., the water uptake (WU), decreased. The second weight loss (150-300°C) was due to the decomposition of conductive groups, and the final weight loss, which appeared after approximately 400°C, was due to the decomposition of the polymer backbone. Furthermore, the glass transition temperature (T) of polymers can be determined through DSC analysis. gWe attempted to confirm this. No special peaks were observed in any of the three types of x-PBB-SEBS films up to approximately 200°C, that is, the decomposition temperature of QA (Figure 13b). Generally, in the case of SEBS or functionalized SEBS, T is observed at approximately 50-70°C. g Although this may appear, in this invention, it can be confirmed that thermal stability is increased through crosslinking with a polymer having rigid properties.

[0092] From the TGA and DSC results mentioned above, it was confirmed that all three types of x-PBB-SEBS have suitable thermal stability for the typical AEMFC operating temperature range of approximately 60-80°C.

[0093] Experimental Example 3: Water Retention Capacity (1)Measurement method The freezing water and non-freezing water content of the membranes was measured by DSC using a PerkinElmer DSC 4000. Fully hydrated membrane samples were sealed in aluminum pans, and a sealed empty aluminum pan was also prepared for reference. The total weight of both pans was weighed and frozen to -40°C inside the DSC chamber. The temperature was then maintained constant while the system reached equilibrium. The DSC chamber was then cooled to 2°C min. -1 The membranes were heated to 20°C at the specified heating rate. This cycle was repeated twice, and values ​​were obtained during the second thermal cycle. The amount of frozen water in each membrane was measured for the melting heat resistance (ΔH). m The peak area of ​​the ) was integrated to calculate the total water content. The WU (%) of the membrane was used to measure the total water content. The frozen water and unfrozen water content were calculated using the following formula: Freezing water(%)=[melting enthalpy(J g -1 )] / [melting endothermic heat of funsion of pure water(334 J g -1 )] × 100 Non-freezing water(%)=total water(%)-freezing water(%)

[0094] (2) Results High water content (WU) in the membrane is essential for the high ionic conductivity and cell characteristics of AEMs. The water contained in the membrane is divided into free water, which has weak interactions with conducting groups and freezing and boiling points similar to those of ordinary water, and bound water, which has strong interactions with conducting groups and therefore has lower freezing and boiling points compared to free water. Previous studies have shown that under the conditions in which fuel cells operate, namely high temperature and RH 90-95%, the free water content in the membrane does not increase; therefore, a high bound water content in the membrane is important for obtaining high-performance fuel cells.

[0095] Bound water in x-PBB-SEBS membranes was analyzed using TGA and DSC (Figure 2). In TGA, mass loss occurring in the 30-100°C range was classified as free water, and mass loss occurring from 100°C until the decomposition of the conductive groups was classified as bound water (Figure 2a). It should be noted that, due to the different water content of the three types of x-PBB-SEBS membranes, this is a relative comparison rather than a quantitative comparison of bound water, and therefore has limitations.

[0096] The measurement results confirmed that the bound water content of the membrane increased with increasing degree of crosslinking (30x-PBB-SEBS: 19.71% < 40x-PBB-SEBS: 28.34% < 50x-PBB-SEBS: 33.42%). This was judged to be due to increased interaction between ion conductors and water as the degree of crosslinking increased, and to explain this, freezable water and non-freezable water were analyzed using DSC (Figure 2 and Table 3). As a result, all x-PBB-SEBS membranes in Examples 1-3 had a freezing point (T) lower than the typical freezing point of water, which is 0°C. FThis shows a dashed line. This allows us to conclude that there is an interaction between the ionic conductor and water. In addition, increasing the degree of crosslinking not only increases the content of non-freezing bound water, but also T F We confirmed that the freezing temperature of water shifted to lower temperatures (30x-PBB-SEBS: -2.7℃ > 40x-PBB-SEBS: -4.5℃ > 50x-PBB-SEBS: -6.8℃). This was determined to be because the interaction between water and conductive groups became stronger as the degree of crosslinking increased, showing a trend consistent with the bound water content confirmed by TGA analysis.

[0097] [Table 3]

[0098] Experimental Example 4: Morphology and Hydroxide Ion Conductivity (1) Morphology The morphology of each film was analyzed using field emission transmission electron microscopy (FE-TEM, Talos F200X, Thermo Fisher Scientific, MA, USA) imaging at an accelerating voltage of 200 kV. Samples were prepared as follows: Thin, homogeneous films were prepared by dropping 3-4 drops of a 1 wt% polymer solution of CHCl3 onto a copper grid. The grid was dried at 40°C for 12 hours, and then treated with TMA solution at 45°C for 12 hours. After TMA treatment, the grid was washed with DI water to remove excess TMA and dried in a 40°C oven. The fine phase separation of the membrane was observed using atomic force microscopy (AFM, Bruker, MUMMUMODE-8-AM, Billerica, MA, USA).

[0099] (2) Hydroxide ion conductivity The hydroxide ion conductivity (σ) of each film was measured by 2-probe impedance spectroscopy using an AC impedance analyzer (SP-200, Bio-Logic, SAS, Claix, France). The electrode system was coupled at a frequency of 2 MHz at 100 mHz. Rectangular samples were prepared in 1 x 4 cm size. Hydroxide ion conductivity was measured using resistance (R) in deionized water at 20°C to 80°C. Hydroxide ion conductivity was calculated using the following formula: σ = L / (R × A) Here, L is the distance between the reference electrodes, and A is the cross-sectional area of ​​the film.

[0100] (3) Results The ionic conductivity of AEM is a major factor that can directly affect battery performance. Therefore, the hydroxide ion conductivity of x-PBB-SEBS films with different crosslinking ratios was measured in water at a temperature range of 20°C to 80°C. From this, the normalized conductivity, obtained by dividing the hydroxide ion conductivity by the IEC ratio, was additionally calculated to evaluate the ionic conductivity of each film (Figure 3a and Table 4).

[0101] As a result, both the hydroxide ion conductivity and the normalized conductivity were 72.28–146.25 mS cm in 40x-PBB-SEBS. -1 and 38.45–77.79 mS cm -1 The highest measurement was obtained with AEMs. Since IEC is the number of ion-conducting groups in AEMs, films with a high IEC generally have high conductivity. Therefore, 30x-PBB-SEBS with a 30% crosslinking ratio (IEC: 1.97 meq g) -1 ) Compared to IEC, 40x-PBB-SEBS (1.88 meq g) has a lower IEC standard. -1The higher conductivity of the x-PBB-SEBS membrane is attributed to the increased interaction between conductive groups and water, and the resulting increase in bound water content, in the case of a membrane with a 40% crosslinking ratio. On the other hand, according to the aforementioned TGA and DSC measurement results, 50x-PBB-SEBS showed a higher bound water content than 40x-PBB-SEBS. Therefore, it was determined that additional factors other than water retention capacity are involved in explaining the conductivity trend of x-PBB-SEBS membranes.

[0102] Furthermore, the RH conductivity of the x-PBB-SEBS membrane was measured under fuel cell operating conditions, i.e., 60°C and 95% relative humidity (RH) (Figure 3b and Table 4). From the measurement results, it was confirmed that the behavior of ionic conductivity under fuel cell operating conditions is more normalized than the conductivity in water, i.e., more closely related to ionic conductivity efficiency.

[0103] [Table 4] a Measured at 60°C and 95% relative humidity (RH).

[0104] Next, we analyzed the morphology of xPBB-SEBS membranes with different crosslinking ratios. First, AFM imaging confirmed that hydrophilic-hydrophobic phase separation occurred well in all three membranes (Figure 4a-4c). In particular, the 40x-PBB-SEBS membrane showed the most pronounced phase separation.

[0105] Furthermore, the normalized conductivity of x-PBB-SEBS films at room temperature was compared with SEBS-based AEMs, polyphenylene-based AEMs (which have recently been reported to possess excellent ionic conductivity), and xTri-PPO-SEBS crosslinked films ([7]Nat. Energy 4 (2019) 392-398;

[10] J. Mater. Chem. A. Mater. 9(2021) 327-337;

[11] Nat. Commun. 12 (2021) 2367;

[31] J. Polym. Sci. 58 (2020) 2181-2196;

[32] Int. J. Hydrogen Energy 46 (2021) 36301-36313;

[35] J. Membr. Sci. (2022), 120029;

[41] J. Compared with Mater. Chem. A. 7 (2019) 6883-6893;

[53] J. Membr. Sci. 647 (2022), 120341;

[54] Angew. Chem. 133 (2021) 7789-7797) (Figure 14). All three types of x-PBB-SEBS membranes showed relatively low IEC (<2.0 meq g). -1 Despite this, we confirmed that it possesses a high level of normalized conductivity.

[0106] These results suggest that the x-PBB-SEBS membrane, while increasing its water content through the introduction of the SEBS polymer, simultaneously suppresses excessive water content through crosslinking, thereby maintaining an appropriate water content necessary for ion conduction and achieving high ion conduction efficiency. Furthermore, it is judged that the crosslinking of two polymers with excellent phase separation properties promotes the formation of ion channels, further maximizing ion conduction efficiency. In particular, 40x-PBB-SEBS exhibited the highest level of normalized conductivity (38.45 mS cm) compared to reported AEMs. -1 It was confirmed that the membrane possesses [specific properties]. This is judged to be a result of the membrane's high water retention capacity and excellent phase separation effect, as confirmed by the TGA and DSC analysis results.

[0107] Experimental Example 5: Alkaline Stability (1) Measurement Method OH - The chemical stability was evaluated by immersing the OH-form membranes in a 2 M KOH solution at 80 °C for 720 hours and measuring the changes in IEC and conductivity. Before measurement, the membranes were immersed in a freshly prepared 1 M KOH solution at 60 °C for at least 24 hours. After this period, the hydroxide ion conductivity of each membrane was measured in deionized water at 20 °C (at 120-hour intervals), and the IEC was measured by the back-titration method described above.

[0108] (2) Results Figure 5 shows the evaluation results of alkaline stability. Both x-PBB-SEBS membranes with different crosslinking ratios maintained more than 99% of the hydroxide ion conductivity even after 720 hours (Figure 5a), and the IEC values of the membranes after 720 hours also showed almost the same values as the initial IEC (Figure 5b).

[0109] Such excellent alkaline stability of the x-PBB-SEBS membranes is judged to be because the main chain does not contain aryl ether, the decomposition of the polymer chain is effectively suppressed, and such suppression contributes to improving the chemical stability of the polymer chain and ionic conductive groups together with the crosslinking effect. Also, the excellent phase separation characteristics of the polymer are considered to have improved the chemical stability of the membrane.

[0110] On the other hand, the alkali stability of the x-PBB-SEBS films of Examples 1-3 was compared with SEBS-based AEMs (

[34] Int. J. Hydrogen Energy 45 (2020) 15658-15671;

[35] J. Membr. Sci. (2022), 120029) and aryl-ether-free polyphenylene-based AEMs ([7] Nat. Energy 4 (2019) 392-398;

[10] J. Mater. Chem. A. Mater. 9 (2021) 327-337;

[11] Nat. Commun. 12 (2021) 2367;

[13] J. Membr. Sci. 642 (2022), 119966;

[41] J. Mater. Chem. A. 7 (2019)). The film was compared with the previously developed cross-linked xTQA-PPO-SEBS film (

[48] Korean Patent No. 10-2184530) (Table 5).

[0111] [Table 5] a QA=quaternary ammonium, Pip=piperidinium As a result, it was confirmed that the x-PBB-SEBS membrane possesses a high level of alkali stability similar to that of AEMs, which have been reported to have excellent alkali stability.

[0112] Experimental Example 6: Oxidation Stability (1) Fenton test The membrane was treated with Fenton's solution (4 ppm Fe) at 24-hour intervals for 120 hours at room temperature (25°C). 2+ The membranes were immersed in 3 wt% H2O2. Afterward, each membrane was washed several times with distilled water to remove the Fenton solution, and then dried in a 40°C oven for a minimum of 24 hours. The oxidative stability of the membranes was assessed from the changes in membrane weight and thermal stability. As a result, all three films—30x-PBB-SEBS, 40x-PBB-SEBS, and 50x-PBB-SEBS—showed excellent oxidative stability with a weight loss of <1% at room temperature, and it was confirmed that all films maintained their shape after testing.

[0113] (2)TGA analysis Structural changes in 40x-PBB-SEBS were observed through TGA graph analysis before and after oxidative stability measurement (Figure 15). Each film was dried in a 40°C oven for more than 12 hours before TGA analysis. As a result, in the case of 40x-PBB-SEBS, the TGA graph was almost the same before and after oxidative stability measurement, meaning that the polymer structure was maintained.

[0114] Experimental Example 7: Fabrication of Membrane Electrode Assemblies (MEAs) and Single-Cell Measurement (1)Measurement method For single-cell measurements, the membrane was pretreated with 1M KOH for 24 hours and washed with DI water. The catalyst ink was prepared using a Pt / C catalyst (Pt / C, 40 wt%, Alfa Aesar, Haverhill, MA, USA), 1-propanol, and an ionomer (FAA-3-SOLUT-10, Fumatech, Germany) and ultrasound. The amount of Pt loaded onto the negative and positive electrodes was 0.4 mg cm². -2 Subsequently, the surface of the manufactured film was coated with catalyst ink using an air spray gun. The catalyst-coated film was immersed in a 1M KOH solution for 12 hours, and then washed with DI. The active area of ​​the MEA (membrane electrode assembly) and unit cell sandwiched between the gas diffusion layer (SIGRACET 39BB) and the gasket was 5 cm². 2 The single-cell performance test involved using 200 / 400 mL of H2 / O2.-1 They were respectively supplied to the negative electrode and the positive electrode. The cell temperature was set to 60 °C at 100% and 70% RH, and before the single cell performance test, a load cycle (0.6, 0.4 V) was repeated for 2 hours to perform an activation process.

[0115] (2) Results A single cell test was performed at 60 °C and 100% RH using the obtained x-PBB-SEBS film (Fig. 6a). The single cell performance was 30x-PBB-SEBS (504 mW cm -2 and 657 mA cm -2 @0.6 V) < 50x-PBB-SEBS (529 mW cm -2 and 677 mA cm -2 @0.6 V) < 40x-PBB-SEBS (555 mW cm -2 and 665 mA cm -2 @0.6 V) in this order. This is the same trend as the RH conductivity rather than the conductivity in water, confirming that the cell performance of AEMs depends more on the conductivity under RH conditions than on the conductivity in water, which is also consistent with previous research results.

[0116] Next, the single-cell performance of the x-PBB-SEBS membrane was measured by changing the humidification conditions. Generally, AEMFCs consume water at the cathode and generate water at the anode during operation, so high RH conditions at the anode can induce flooding. Therefore, single-cell measurements were performed with the RH conditions of the anode and cathode set to 70% and 100%, respectively, and the single-cell performance of each was compared with the anode / cathode 100% / 100%RH conditions (Figures 6b and 16). All three types of x-PBB-SEBS membranes showed the same trend in single-cell performance as the anode / cathode = 100% / 100%RH conditions: 30x-PBB-SEBS (461mW cm²). -2 and 625mA cm -2 @0.6V)<50x-PBB_SEBS(503mW cm -2 and 665mA cm -2 @0.6V)<40x-PBB-SEBS(545mW cm -2 and 665mA cm -2 (@6V). Furthermore, the 30x, 40x, and 50x-PBB-SEBS maintained peak power densities of 91.5%, 98.2%, and 95.1%, respectively, depending on the RH conditions. This is judged to be a result of increased water retention capacity and morphological changes due to the increased crosslinking ratio.

[0117] conclusion In one embodiment of the present invention, the crosslinked copolymer exhibits excellent phase separation effects due to the crosslinking of the first and second chains, which have phase separation properties. This results in high strain properties (high elongation at break) and an excellent Young's modulus. Thus, it was confirmed that the crosslinked copolymer of the present invention possesses excellent mechanical properties by combining the high stress properties of PP-based polymer films with the high strain properties of SEBS-based polymer films.

[0118] The aforementioned crosslinked copolymer exhibited excellent water retention capacity, that is, strong interaction characteristics between conductive groups and water. Furthermore, AFM and TEM analysis confirmed that the crosslinked copolymer possessed excellent phase separation, i.e., optimal morphology, which demonstrated superior normalized conductivity, representing ion conduction efficiency.

[0119] Furthermore, the crosslinked copolymer exhibited excellent alkali stability (over 99% in 2M KOH, 80°C) and excellent phase separation characteristics due to its structure in which the first and second chains, which lack aryl ethers, are crosslinked, resulting in excellent oxidation stability. When the crosslinked copolymer was used as an anion exchange membrane in a fuel cell, it was confirmed to exhibit excellent power density.

[0120] From the above results, it can be confirmed that the crosslinked copolymer of the present invention exhibits excellent electrochemical properties and mechanical properties, and that its properties can be controlled by adjusting the degree of crosslinking. Therefore, it can be confirmed that the crosslinked copolymer can be suitably used as an anion exchange membrane material that can improve the performance and stability of fuel cells and the like.

Claims

1. A crosslinked copolymer comprising a first chain represented by the following chemical formula 1 and a second chain represented by the following chemical formula 2, wherein the amount of the second chain is 30 to 50 moles per 100 moles of the first chain, and the first and second chains are crosslinked with each other: 【Chemistry 1】 In the aforementioned chemical formula 1, * indicates the bonding position with chemical formula 2. q １ , q ２ , q ５ , and q ６ The sum is an integer between 100 and 1,000. q ３ and q ４ The sum is an integer between 150 and 2,000. a and b are each independent integers between 3 and 10. R １ ~R ４ each independently represents hydrogen or -(CH ２ ) ｐ -CH ３ where p is an integer from 0 to 5, 【Chemistry 2】 In the aforementioned chemical formula 2, * indicates the bonding position with chemical formula 1. x is an integer between 1 and 10, and y is an integer between 0 and 10. n is an integer between 10 and 1000.

2. q １ ~q ６ The crosslinked copolymer according to claim 1, wherein each of these is an integer from 10 to 500, independently.

3. q １ ~q ６ q for the total sum １ , q ２ , q ５ , and q ６ The crosslinked copolymer according to claim 1, wherein the total ratio of is 0.2 to 0.

5.

4. q １ , q ２ , q ５ , and q ６ q for the total sum １ and q ６ The crosslinked copolymer according to claim 1, wherein the total ratio of is 0.2 to 0.

5.

5. The crosslinked copolymer according to claim 1, wherein a and b are each independently integers from 4 to 6.

6. The aforementioned crosslinked copolymer is the crosslinked copolymer according to claim 1, represented by the following chemical formula 3: 【Transformation 3】 In the aforementioned chemical formula 3, q １ ~q ６ a, b, x, y, and n are defined as in Chemical Formula 1 and Chemical Formula 2.

7. A polymer film comprising the crosslinked copolymer according to any one of claims 1 to 6.

8. The polymer membrane according to claim 7, wherein the polymer membrane is an anion exchange membrane.

9. (a) The step of producing a polymer represented by the following chemical formula 1-1; (b) The step of producing a polymer represented by the following chemical formula 2-1; and (c) A step of producing a crosslinked copolymer by crosslinking the polymer represented by the following chemical formula 1-1 and the polymer represented by the following chemical formula 2-1; Includes, A method for producing a crosslinked copolymer, wherein in step (c) above, 30 to 50 moles of the polymer represented by chemical formula 2-1 are used relative to 100 moles of halogen groups contained in the polymer represented by chemical formula 1-1: 【Chemistry 4】 In the aforementioned chemical formula 1-1, q １ , q ２ , q ５ , and q ６ The sum is an integer between 100 and 1,000. q ３ and q ４ The sum is an integer between 150 and 2,000. a and b are each independent integers between 3 and 10. R １ ~R ４ Each is independently hydrogen or -(CH ２ ) ｐ -CH ３ And p is an integer from 0 to 5, X １ and X ２ Each of these is independently a halogen group, 【Transformation 5】 In the aforementioned chemical formula 2-1, x is an integer between 1 and 10, and y is an integer between 0 and 10. n is an integer between 10 and 1000.

10. (d) A method for producing a crosslinked copolymer according to claim 9, further comprising the step of reacting the crosslinked copolymer with trimethylamine.

11. The polymer represented by the chemical formula 1-1 contains 30 to 90 moles of halogen groups per 100 moles of styrene repeating units, according to the method for producing a crosslinked copolymer according to claim 9 or claim 10.

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