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

Abstract

The present invention provides a new crosslinked copolymer which has excellent mechanical properties, excellent stability against hydroxide ions, high ionic conductivity and degree of hydration, and can be preferably used as an anion exchange membrane (AEM) material for fuel cells and the like.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0014254, filed February 3, 2022, and Korean Patent Application No. 10-2023-0014346, filed February 2, 2023, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a cross-linked copolymer, a polymer membrane containing the same, and an anion exchange membrane containing the polymer membrane. [Background technology]

[0003] Anion exchange membrane fuel cells (AEMFCs) have continuously improved, particularly in terms of power density, and their price competitiveness has increased with the adoption of non-platinum group metal (PGM) catalysts. Because of these advantages, AEMFCs have attracted considerable interest as an alternative to proton exchange membrane fuel cells (PEMFCs), which use expensive PGM-based catalysts and perfluorinated polymers such as Nafion as proton exchange membranes (PEMs). However, for AEMFCs to be commercially viable, further improvements in cell durability and power density are required. Therefore, the performance of the anion exchange membrane (AEM), which has a significant impact on the overall performance of AEMFCs, must be improved to the desired level. To achieve this, a new AEM that is physicochemically stable under the actual operating conditions of AEMFCs (i.e., high pH, ​​temperature, and RH conditions) while also improving ionic conductivity is needed.

[0004] AEMs generally consist of a polymer backbone, i.e., a hydrophobic component that governs the overall membrane properties, and an ion-conducting head group, i.e., hydroxide ions (OH - ) and hydrophilic components involved in the transport of ions. Therefore, the conductive headgroup and polymer backbone must be investigated simultaneously to improve the overall performance of AEMs.

[0005] Among the ion-conducting head groups, piperidinium, pyrrolidinium, substituted imidazolium, and cyclic ammonium derivatives such as 6-azonia-spiro[5,5]undecane are frequently studied due to their high stability. Quaternary ammonium groups, especially hexyltrimethylammonium, are widely used due to their chemical stability similar to that of cyclic ammonium derivatives.

[0006] Meanwhile, various polymer backbones, such as poly(phenylene oxide) (PPO), poly(ether ketone) (PEK), poly(ether sulfone) (PES), polybenzimidazole (PBI), poly(phenylene) (PP), polyolefin, spirobisindene, and polynorbornene (NB), have been investigated. Furthermore, various attempts have been made to improve the performance of AEMs by employing various strategies based on multiblock copolymers, fluoropolymers, spacer-type polymers, multication systems, and crosslinked polymers. However, despite all these efforts, only a few of these AEMs exhibit performance similar to PEMs. These AEMs were characterized by piperidinium or hexyltrimethylammonium ion-conducting headgroups and aromatic polymer backbones such as polycarbazole, polybiphenyl, polyterphenyl, or polybibenzyl. Unlike PPO or PES, these polymers are based on a backbone without aryl ether linkages, ensuring excellent chemical stability against hydroxide ions. Not only that, the ion-conducting headgroups are incorporated within or grafted to the backbone structure, providing high ion exchange capacity (IEC), conductivity, and overall cell performance.

[0007] However, such rigid aromatic polymers generally have low water absorption rates. In ion-conducting polymers such as AEM and PEM, water tends to act as a medium for ionic conduction, and therefore high ionic conductivity can only be achieved at a certain level of water content (WU). In a previous study, AEM based on such rigid aromatic polymers exhibited a water absorption rate of 2.5 meq g -1 AEMs with a relatively high IEC (i.e., by introducing more ion-conducting groups) or higher provided the required level of WU and ionic conductivity. However, the positively charged ion-conducting headgroups are relatively less stable to hydroxide ions than the polymer backbone. This means that the introduction of more ion-conducting groups may have a negative impact on the stability of the AEM.

[0008] Furthermore, while such AEMs are mechanically strong, they have relatively poor elastic properties. The mechanical properties of AEMs can actually result in membrane damage during cell operation (e.g., pinhole formation or failure at the periphery of the membrane electrode assembly (MEA) active area). Therefore, achieving a certain level of elongation is preferred to ensure high performance of AEMFCS.

[0009] Poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) is a polymer that exhibits phase separation of styrene and butylene as a block structure, and also has excellent elastic properties and chemical stability. There have been various attempts to utilize SEBS as an AEM by introducing ion-conducting head groups, and some of these efforts have resulted in the development of AEMs with excellent phase separation and high ionic conductivity, despite their relatively low IEC values.

[0010] At the same time, such SEBS-based AEMs have very low tensile strength and high swelling ratios (SR). These mechanical properties make it more difficult to process SEBS into thin membranes and can cause excessive swelling under humid conditions, i.e., the actual operating conditions of fuel cells. Furthermore, such SEBS polymers have very limited solubility. Therefore, it is extremely difficult to adjust the degree of SEBS functionalization or to improve the conductivity or mechanical properties of the AEMs by blending or grafting with other molecules that have desired properties. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Korean Patent No. 10-1535062 [Non-patent literature]

[0012] [Non-Patent Document 1] Nat. Energy 4 (2019) 392-398 [Non-patent document 2] Nat. Commun. 12 (2021) 2367 [Non-patent document 3] Adv. Funct. Mater. 28 (2018) 1-10 [Non-patent document 4] Int. J. Hydrogen Energy 46 (2021) 18524-18533 [Non-patent document 5] J. Mater. Chem. A. 9 (2021) 327-337 [Non-patent document 6] J. Membr. Sci. 642 (2022), 119966 [Non-Patent Document 7] ACS Macro Lett. 6 (2017) 566-570 [Non-patent document 8] Energy Environ. Sci. 13 (2020) 3633-3645

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[0013] The present invention aims to provide a new crosslinked copolymer that has excellent mechanical properties, excellent stability against hydroxide ions, high ionic conductivity and degree of hydration, and can be suitably used as a material for anion exchange membranes (AEM) in fuel cells and the like. [Means for solving the problem]

[0014] Therefore, according to one embodiment of the present invention, there is provided a cross-linked 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 first chain and the second chain are cross-linked to each other:

[0015] [ka] In the above Chemical Formula 1, * indicates the bonding position to 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 independently an integer of 3 to 10; R1 to R4 are each independently hydrogen or -(CH2) p -CH3, and p is an integer of 0 to 5; [ka] In the above Chemical Formula 2, * indicates the bonding position to Chemical Formula 1, R5 is -(CH2) p’ -CH3, and p' is an integer of 0 to 5, n is an integer of 10 to 1000.

[0016] According to one embodiment of the present invention, there is provided a polymer membrane comprising the cross-linked copolymer.

[0017] Moreover, according to one embodiment of the present invention, (a) preparing a poly(styrene-b-ethylene-co-butylene-b-styrene)-based polymer represented by the following chemical formula 1-1; (b) preparing a poly(m-terphenyl N-alkylpiperidine) polymer represented by the following chemical formula 2-1; and (c) crosslinking the poly(styrene-b-ethylene-co-butylene-b-styrene) polymer with the poly(m-terphenyl-N-alkylpiperidine) polymer to prepare a crosslinked copolymer; A method for producing a crosslinked copolymer is provided, comprising: [ka] In the above 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 independently an integer of 3 to 10; R1 to R4 are each independently hydrogen or -(CH2) p -CH3, and p is an integer of 0 to 5; X1 and X2 are each independently a halogen group; [ka] In the above chemical formula 2-1, R5 is -(CH2) p’-CH3, and p' is an integer of 0 to 5, n is an integer of 10 to 1000. [Effects of the Invention]

[0018] The crosslinked copolymer of the present invention has excellent dimensional stability, ionic conductivity, degree of hydration, and alkali stability despite a high water uptake (WU), and also has excellent mechanical properties such as tensile strength and elongation.

[0019] As described above, the crosslinked copolymer of the present invention has excellent electrochemical and mechanical properties, and therefore can be suitably used as a material for anion exchange membranes. [Brief explanation of the drawings]

[0020] [Figure 1] 1 shows the structure of a poly(m-terphenyl-N-methylpiperidinium)-SEBS membrane 1 (x-PmTP-SEBS) according to one embodiment of the present invention. [Figure 2] Figure 1 shows the (a) hydration number (λ) vs. IEC and (b) mechanical properties of x-PmTP-SEBS (stars) compared with the OH-form SEBS-based AEMs (circles) and poly(phenylene)-based AEMs (squares) reported in the literature at room temperature. [Figure 3] (a and d) SEM surfaces and (d and f) AFM images of PmTP-SEBS membranes: (a and d) 30x-PmTP-SEBS, (b and e) 40xPmTP-SEBS, and (c and f) 50xPmTP-SEBS membranes. [Figure 4] 1 is a graph showing the SAXS profile of an x-PmTP-SEBS film. [Figure 5] 1 shows (a) a TGA graph of x-PmTP-SEBS membranes from 30° C. to 300° C. and (b) a graph showing the relative ratio of free water to bound water in x-PmTP-SEBS membranes. [Figure 6]Graph comparing (a) ionic conductivity (solid line) and normalized conductivity (dotted line) and (b) normalized conductivity of x-PmTP-SEBS membrane compared to representative membranes from the literature. [Figure 7] 1 is a graph showing (a) hydroxide ion conductivity and (b) residual IEC of x-PmTP-SEBS membranes in 2 M KOH at 80° C. [Figure 8] Graph showing single cell performance of x-PmTP-SEBS membrane with (a) no back pressure and (b) 0.1 MPa back pressure. [Figure 9] 1 is a graph showing the 1H NMR spectrum of poly(m-terphenyl-N-piperidine) 2. [Figure 10] 1 is a graph showing the 1H NMR spectra of (a) SEBS, (b) bromohexanoyl SEBS4, ​​and (c) bromohexyl SEBS3. [Figure 11] FTIR spectra of bromohexanoyl SEBS4 and its derivative, bromohexyl SEBS3. [Figure 12] 1 is a photograph of cross-linked (m-terphenyl-N-methylpiperidinium)-SEBS membranes (x-PmTP-SEBS) with different cross-linking degrees. [Figure 13] FTIR spectra of x-PmTP-SEBS membranes with different crosslinking degrees. [Figure 14] 1 is a graph showing the mechanical properties of x-PmTP-SEBS AEM under 50% RH conditions. [Figure 15] 1 shows (a) TGA and differential thermal analysis (DTG) graphs and (b) differential scanning calorimetry (DSC) graph of x-PmTP-SEBS membrane. [Figure 16] Graphs showing DSC plots of x-PmTP-SEBS membranes at (a) -40°C to 20°C and (b) -10°C to 0°C. [Figure 17] 1 is a graph comparing the maximum power density of PP-based and SEBS-based AEMFCs with x-PmTP-SEBS membranes. DETAILED DESCRIPTION OF THE INVENTION

[0021] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0022] It should be understood that in this specification, the terms "comprises," "comprises," or "having" are intended to specify the presence of embodied features, steps, components, or combinations thereof, but do not preclude the possible presence or addition of one or more other features, steps, components, or combinations thereof.

[0023] Although the present invention can be embodied in various forms through various modifications, specific embodiments are described in detail below by way of example, but it should be understood that this is not intended to limit the present invention to the specific disclosed embodiments, and that the present invention encompasses all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention.

[0024] The present invention will be described in detail below. According to one embodiment of the present invention, there is provided a cross-linked 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 first chain and the second chain are cross-linked to each other. [ka] In the above Chemical Formula 1, * indicates the bonding position to 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 independently an integer of 3 to 10; R1 to R4 are each independently hydrogen or -(CH2) p -CH3, and p is an integer of 0 to 5; [ka] In the above Chemical Formula 2, * indicates the bonding position to Chemical Formula 1, R5 is -(CH2) p’ -CH3, and p' is an integer of 0 to 5, n is an integer of 10 to 1000.

[0025] The crosslinked copolymer of the present invention is formed by crosslinking a first chain containing poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) with a second chain containing poly(m-terphenyl N-alkyl piperidine) (PmTP).

[0026] By satisfying this structure, the cross-linked copolymer exhibits higher tensile strength and Young's modulus than existing SEBS-based cross-linked copolymers and significantly improved elongation characteristics compared to PP-based polymers. Furthermore, the cross-linked copolymer exhibits high water retention capacity and a high hydration number due to the free volume induced by the twisted structure of m-terphenyl, thereby exhibiting high ionic conductivity. Furthermore, the cross-linked copolymer has excellent alkaline stability and exhibits a shielding effect due to its high hydration number. Therefore, the cross-linked copolymer is suitable for use as an anion exchange membrane in fuel cells and the like.

[0027] The ratio of the first chain represented by Chemical Formula 1 to the second chain represented by Chemical Formula 2 can be adjusted depending on the desired physical properties. For example, the cross-linked copolymer may contain 10 moles or more, or 20 moles or more, or 30 moles or more, or 40 moles or more, and 70 moles or less, or 60 moles or less, or 50 moles or less of the second chain per 100 moles of the first chain. When the ratio of the first chain to the second chain of the cross-linked copolymer satisfies the above range, the copolymer can exhibit excellent mechanical properties and electrochemical properties.

[0028] Preferably, the sum of q1, q2, q5, and q6 may be an integer of 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 1,000 or less, or 950 or less, or 900 or less, or 850 or less, or 800 or less.

[0029] Preferably, the sum of q3 and q4 may be an integer of 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 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.

[0030] Preferably, q1 to q6 may each independently be an integer of 10 or more, or 20 or more, or 25 or more, or 30 or more, and 500 or less, or 450 or less, or 400 or less, or 350 or less, or 300 or less.

[0031] Preferably, the ratio of the sum of q1, q2, q5, and q6 to the sum of q1 to q6, i.e., the total molar fraction of styrene-derived repeating units to all repeating units of Chemical Formula 1, may be 0.2 or more, or 0.25 or more, or 0.3 or more, and 0.5 or less, or 0.45 or less.

[0032] Preferably, the ratio of the sum of q1 and q6 to the sum of q1, q2, q5, and q6, i.e., the total molar fraction of unsubstituted styrene repeat units relative to all styrene-derived repeat units in Chemical Formula 1, may be 0.2 or more, or 0.25 or more, or 0.3 or more, or 0.35 or more, and 0.5 or less, or 0.45 or less, or 0.4 or less.

[0033] Preferably, n is an integer of 10 or more, or 100 or more, or 150 or more, and 1000 or less, or 500 or less.

[0034] Preferably, a and b may each independently be an integer of 3 or more, or 4 or more, and 10 or less, or 9 or less, or 8 or less, or 7 or less, or 6 or less.

[0035] Preferably, R1 to R4 are each independently hydrogen or -(CH2) x It may be —CH3, where x is an integer of 0 to 3, or an integer of 0 to 2. Preferably, R1 to R4 may all be hydrogen.

[0036] Specifically, the crosslinked copolymer may contain a repeating unit represented by the following chemical formula 3: [ka] In Chemical Formula 3, q1 to q6, a, b, and n are as defined in Chemical Formula 1 and Chemical Formula 2.

[0037] Preferably, the crosslinked copolymer may contain a repeating unit represented by the following chemical formula 4: [ka] In Chemical Formula 4, q1 to q6 and n are as defined in Chemical Formula 1 and Chemical Formula 2.

[0038] Figure 1 shows the crosslinked structure of compound (1) represented by formula 4 according to one embodiment of the present invention. As shown on the right side of Figure 1, the crosslinked copolymer of the present invention has a structure in which a poly(styrene-b-ethylene-co-butylene-b-styrene) polymer and a poly(m-terphenyl-N-alkylpiperidine) polymer are crosslinked to each other. Due to these structural characteristics, the crosslinked copolymer exhibits high tensile strength and elongation, and its water holding capacity and hydration number are high, resulting in excellent ionic conductivity and cell performance.

[0039] The cross-linked copolymer described above has a positively charged quaternary ammonium group, and can selectively pass only anions. Therefore, the cross-linked copolymer can be used as an anion exchange membrane. The counter ion (anion) group for the cation (quaternary ammonium group) of the cross-linked copolymer is OH. - , Cl - , Br - , or HCO3 - and preferably, OH - may be.

[0040] Therefore, according to one embodiment of the present invention, there is provided a polymer membrane comprising the cross-linked copolymer.

[0041] The polymer membrane containing the cross-linked copolymer may have a thickness of 20 μm or more, or 30 μm or more, or 45 μm or more, or 55 μm or more, and 70 μm or less, or 60 μm or less, or 55 μm or less. When the polymer membrane has a thickness within this range, it exhibits high mechanical properties and also has excellent electrochemical properties, making it suitable for use as an anion exchange membrane.

[0042] The polymer membrane described above contains a crosslinked copolymer including the first and second chains, and thus has improved mechanical strength compared to existing polymers for AEM, high ionic conductivity while exhibiting an appropriate IEC, and excellent alkaline stability. Therefore, a polymer membrane having such physical properties can be suitably used as an anion exchange membrane in a fuel cell or the like.

[0043] Meanwhile, according to one embodiment of the present invention, there is provided a method for preparing the crosslinked copolymer. Specifically, the method for preparing the crosslinked copolymer of the present invention includes the following steps: (a) preparing a poly(styrene-b-ethylene-co-butylene-b-styrene)-based polymer represented by the following chemical formula 1-1; (b) preparing a poly(m-terphenyl N-alkylpiperidine) polymer represented by the following chemical formula 2-1; and (c) crosslinking the poly(styrene-b-ethylene-co-butylene-b-styrene) polymer with the poly(m-terphenyl N-alkylpiperidine) polymer to prepare a crosslinked copolymer: [ka] In the above 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 independently an integer of 3 to 10; R1 to R4 are each independently hydrogen or -(CH2) p -CH3, and p is an integer of 0 to 5; X1 and X2 are each independently a halogen group; [ka] In the above chemical formula 2-1, R5 is -(CH2) p’ -CH3, and p' is an integer of 0 to 5, n is an integer of 10 to 100.

[0044] The preferred ranges of q1 to q6, a, b, R1 to R4, and n in Chemical Formula 1-1 and Chemical Formula 2-1 are as explained in Chemical Formulas 1 and 2 above.

[0045] The X1 and X2 are each independently F, Cl, Br, or I, and preferably Br.

[0046] Step (a) is a step of introducing a halogen alkyl group into the styrene moiety of the SEBS polymer. Specifically, the poly(styrene-b-ethylene-co-butylene-b-styrene) polymer represented by Chemical Formula 1-1 can be prepared by Friedel-Crafts acylation of SEBS and reduction of the carbonyl group.

[0047] The acyl halide used in the acylation reaction is selected taking into consideration the number of the desired a and b. Specifically, the acyl halide is XR-COCl (X is a halogen and R is C 1-29 An alkanoyl chloride having a halogen group at the alkyl chain end, represented by (alkyl), can be used. When a and b are different from each other, or when X1 and X2 are different from each other, the acylation reaction can be carried out two or more times using different acyl halides.

[0048] Aluminum chloride (AlCl3) can be used as a catalyst for the acylation reaction, and the reaction may be carried out at 20 to 30°C for 8 to 24 hours.

[0049] The carbonyl group reduction reaction can be carried out by any method known in the art without limitation. For example, triethylsilane and trifluoroacetic acid can be added and reacted at 90 to 120°C for 20 to 30 hours to reduce the carbonyl group. This reaction can produce a poly(styrene-b-ethylene-co-butylene-b-styrene)-based polymer represented by Chemical Formula 1-1.

[0050] The poly(styrene-b-ethylene-co-butylene-b-styrene) copolymer preferably contains 30 or more, 40 or more, 50 or more, 55 or more, or 60 or more and 90 or less, 80 or less, 75 or less, 70 or less, or 65 or less moles of halogen groups per 100 moles of styrene repeating units. The moles of halogen groups per styrene repeating unit can be adjusted by adjusting the moles of acyl halide per mole of styrene in the SEBS polymer during the acylation reaction.

[0051] The step (b) is a step of preparing a poly(m-terphenyl N-alkylpiperidine) polymer. For example, a poly(m-terphenyl N-alkylpiperidine) polymer can be prepared by reacting m-terphenyl with an N-alkyl-4-piperidone in the presence of trifluoroacetic acid and trifluoromethanesulfonic acid. For example, the reaction may be carried out at 0 to 10°C for 12 to 48 hours.

[0052] Step (c) is a step of crosslinking the poly(styrene-b-ethylene-co-butylene-b-styrene)-based polymer and the poly(m-terphenyl N-alkylpiperidine) polymer to prepare a crosslinked copolymer. Since the poly(styrene-b-ethylene-co-butylene-b-styrene)-based polymer contains a halogen group and the poly(m-terphenyl N-alkylpiperidine) polymer contains a tertiary amine group, the two polymers can be easily crosslinked by a nucleophilic substitution reaction without the use of a separate crosslinking agent.

[0053] In step (c), the poly(m-terphenyl N-alkylpiperidine) polymer 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 and 70 moles or less, or 60 moles or less, or 50 moles or less, relative to 100 moles of halogen groups contained in the poly(styrene-b-ethylene-co-butylene-b-styrene)-based polymer. When this molar ratio is satisfied, the crosslinked polymer produced can have an appropriate ratio of first chains and second chains, thereby exhibiting excellent hydroxide ion conductivity and mechanical properties.

[0054] The reaction in step (c) can be carried out at 40-60°C for 10-16 hours, preferably 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, resulting in a decrease in hydroxide ion conductivity and a decrease in alkaline stability. Conversely, if the polymerization reaction temperature is above 60°C or the reaction time is above 16 hours, the crosslinking rate between polymers may increase excessively, resulting in gelation of the crosslinked polymer solution.

[0055] Meanwhile, after step (c), the cross-linked copolymer may be further subjected to step (d) of reacting with trimethylamine to convert all remaining halogen groups in the cross-linked copolymer to amine groups. Step (d) may 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.

[0056] As described above, in the present invention, a halogen functional group is introduced into the SEBS main chain and then reacted with the PmTP main chain containing an amine group to produce a crosslinked copolymer. This allows quantitative crosslinking of SEBS and PmTP without side reactions, and the degree of crosslinking can be easily controlled by adjusting the amount of each main chain.

[0057] Furthermore, the method allows for the easy production of crosslinked copolymers in high yields, thereby increasing process productivity and reducing costs.

[0058] The present invention will be described in more detail with reference to the following examples, but the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention. [Example]

[0059] [Example] <Material> Poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS, A1535H) with a styrene content of 57% was obtained from Clayton (Houston, TX, USA). m-Terphenyl (99%) and triethylsilane (98%) were obtained from Alfa-Aesar (Haverhill, MA, USA). 6-Bromohexanoyl chloride (97%), aluminum chloride (99%), and N-methyl-4-piperidone (97%) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Trifluorometanesulfonic acid (98%) was obtained from TCI (Tokyo, Japan). Trifluoroacetic acid was purchased from Daejung Chemical Metals (Siheung, South Korea). All other chemicals were obtained from commercial sources.

[0060] <Confirmation of polymer chemical structure> The chemical structures of the polymers obtained at each stage in the following examples are as follows: 1 It was confirmed by 1 H NMR spectroscopy and Fourier transform infrared (FTIR) spectroscopy. 1 H NMR spectra were obtained using a 400 MHz NMR instrument (Agilent 400MR) with CDCl as the solvent. FTIR spectra were obtained using a PerkinElmer Spectrum Two ATR-FTIR spectrometer. The spectra were obtained from 4000 to 400 cm. -1 was collected up to.

[0061] Example 1: Preparation of 30x-PmTP-SEBS (30% cross-linking degree) membrane (1) Synthesis of poly(m-terphenyl N-methylpiperidine) 2 [ka] (In the above reaction formula, n is 158.)

[0062] In a completely dry 50 mL two-necked round-bottom flask equipped with a magnetic stirrer, m-terphenyl (3.00 g, 13.03 mmol) and N-methyl-4-piperidone (1.92 g, 16.93 mmol) were poured into a nitrogen atmosphere and then dissolved in dichloromethane (DCM, 15 mL). After complete dissolution, the solution was cooled to 0 °C using an ice bath. While continuously stirring the solution, trifluoroacetic acid (TFA, 2.23 g, 19.54 mmol) and trifluoromethanesulfonic acid (TFSA, 19.56 g, 130.30 mmol) were slowly added. The color of the solution changed from light brown to dark brown. After 48 h, the viscous solution was poured into KOH solution (500 mL). The precipitated polymer was filtered through filter paper and washed several times with deionized water to remove residual reactants. The resulting polymer was dried in a vacuum oven for 24 hours to give poly(m-terphenyl-N-methylpiperidine) as a white fibrous solid (4.13 g, 97.4%); δH (400 MHz, CDCl3), 7.79-7.27 (12H, broad signal, H 1-5 ), 7.75-7.38(8H, wide signal, H 6、7 ), 2.35-2.20 (3H, s, H8) (Figure 9).

[0063] (2) Synthesis of Bromohexyl-SEBS3 (2-1) Synthesis of Bromohexanoyl SEBS4 [ka] (In the above reaction formula, 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 total sum of q1, q2, q5, and q6 is 0.3.)

[0064] SEBS (5.00 g, 27.36 mmol) was dissolved in dichloromethane (150 mL) in a 500 mL two-necked round-bottom flask equipped with a magnetic stirrer under a nitrogen atmosphere. After the polymer was completely dissolved, aluminum chloride (2.01 g, 15.06 mmol) and 6-bromohexanoyl chloride (3.21 g, 15.06 mmol) were slowly added to dichloromethane (50 mL). After 24 h, the reaction mixture was poured into a large amount of ethanol (1000 mL). The precipitated polymer was filtered through filter paper and washed several times with ethanol to remove residual reactants. The resulting polymer was dried in a dryer at room temperature (25°C) for 24 hours to obtain white rubbery bromohexanoyl SEBS4 (8.20 g, 97.7%), in which 70 mol% of the total styrene contained in the SEBS (100 mol%) had bromohexanoyl functional groups. δH (400 MHz, CDCl3) 7.92-7.39 (4H, broad signal, H 6、7 ), 7.25-6.29 (10H, wide signal, H 8、9、10 ), 3.50-3.37 (3H, wide signal, H1), 3.04-2.80 (3H, wide signal, H5), 2.70-2.32 (2H, wide signal, H 12 ), 2.02-0.55(46H, wide signal, H 2-4、11、13-18 ) (Figure 10(b)); ATR-FTIR (cm -1 ) 3026 (aromatic C-H stretching), 2922-2852 (alkane C-H stretching), 1680 (C=O stretching) (Figure 11).

[0065] (2-2) Synthesis of Bromohexyl SEBS3 [ka] (In the above reaction formula, 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 total sum of q1, q2, q5, and q6 is 0.3.)

[0066] Bromohexanoyl SEBS4 (8.00 g, 14.74 mmol) was dissolved in chloroform (200 mL) in a 500 mL two-necked round-bottom flask equipped with a magnetic stirrer connected to a reverse condenser under a nitrogen atmosphere. After the bromohexanoyl SEBS4 was completely dissolved, triethylsilane (23.55 mL, 147.4 mmol) and trifluoroacetic acid (22.56 mL, 294.8 mmol) were added. The reaction mixture was slowly heated to 105 °C and maintained at this temperature for 48 h. After cooling to room temperature, the reaction mixture was neutralized with 1 M KOH (200 mL). The organic layer was poured into methanol (1000 mL), and the precipitated polymer was filtered through filter paper and washed several times with methanol to remove residual reactants. The resulting polymer was dried in an oven at room temperature for 24 hours to give white rubbery bromohexyl SEBS3 (7.66 g, 93.54%); δH (400 MHz, CDCl3) 7.23-6.19 (12H, broad signal, H 6-10 ), 3.51-3.38 (3H, wide signal, H1), 2.67-2.26 (5H, wide signal, H 5’、12 ), 2.11-0.55(47H, wide signal, H 2-5、11、13-18 ) (Figure 10(c)); ATR-FTIR (cm -1 ) 3024 (aromatic CH stretching), 2922-2852 (alkane CH stretching) (Figure 11).

[0067] (3) Preparation of crosslinked poly(m-terphenyl-N-methylpiperidinium)-SEBS (x-PmTP-SEBS) membrane [ka] (In the above reaction formula, 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 total sum of q1, q2, q5, and q6 is 0.3.)

[0068] Poly(m-terphenyl-N-methylpiperidine)2, bromohexyl SEBS3, and HPLC-grade chloroform (20 mL) were placed in a 20 mL bottle and the mixture was stirred until the polymer was completely dissolved. Poly(m-terphenyl-N-methylpiperidine)2 was used at a 30 mol% ratio relative to bromohexyl SEBS3. The polymer solution was heated overnight at 45 °C to induce cross-linking. After cooling to room temperature, the polymer solution was filtered, poured into a glass Petri dish, and dried at room temperature for 24 hours. The formed membrane was peeled from the Petri dish and immersed in deionized water to wash out any remaining solvent. The membrane was then immersed in a trimethylamine (TMA) aqueous solution at 40 °C for 24 hours, followed by rinsing with deionized water (DI) to remove the TMA. The membrane was then immersed in a 1 M KOH solution at room temperature for a minimum of 24 hours to induce cross-linking. - ions and OH - Finally, the membrane was washed several times with DI water before measurements were taken.

[0069] Example 2: Preparation of 40x-PmTP-SEBS (40% cross-linking degree) membrane A 40x-PBB-SEBS membrane was prepared in the same manner as in Example 1, except that in step (3), poly(m-terphenyl-N-methylpiperidine) 2 was used in an amount of 40 mol % relative to bromohexyl SEBS 3 .

[0070] Example 3: Preparation of 50x-PmTP-SEBS (50% cross-linking) membrane A 50x-PBB-SEBS membrane was prepared in the same manner as in Example 1, except that in step (3), poly(m-terphenyl-N-methylpiperidine) 2 was used in an amount of 50 mol % relative to bromohexyl SEBS 3 .

[0071] Flexible film-like membranes having thicknesses of 35 to 40 μm were obtained in Examples 1 to 3. Fig. 12 is a photograph of the membranes produced in Examples 1 to 3.

[0072] In addition, the FTIR spectra of 30x-PmTP-SEBS, 40x-PmTP-SEBS, and 50x-PmTP-SEBS in Examples 1 to 3 showed that the 3000-2800 cm band of bromohexyl SEBS3 increased with increasing degree of crosslinking. -1 (aliphatic CH) and 1600-1800 cm -1 The (aromatic C=C) peak was confirmed to decrease, suggesting that cross-linking was successful (Figure 13).

[0073] Experimental Example 1: Ion Exchange Capacity (IEC), Water Content (WU), Swelling Ratio (SR), Density, and Free Volume (1) Measurement of ion exchange capacity (IEC) a. Experimental IEC The ion exchange capacity (IEC) of each membrane was measured using the back titration method. - The membranes in the form of HCl were immersed in 0.01 M HCl standard solution for 24 hours. The residual HCl was again titrated with 0.01 M NaOH standard solution using a phenolphthalein indicator. The membranes were weighed (W dry , g) were dried for measurement. The experimental IEC (meq g) was calculated using the following formula: -1 ) was calculated in moles of exchangeable hydroxide ions per gram: IEC(meq g -1 )=(C0V0-C0V x ) / W dry where V0 and V x are the volume of NaOH before titration and the volume of NaOH consumed in titration, respectively, C0 is the molar concentration of NaOH used in the back titration, and W dry is the weight of the membrane after drying in the oven for a minimum of 12 hours.

[0074] b. Theoretical IEC The theoretical IEC value is: 1 The number of Br atoms contained in bromohexyl SEBS3 was determined based on the calculated H NMR spectrum and the masses of the two polymers (2 and 3) used in the cross-linking process.

[0075] (2) Water content (WU) and swelling ratio (SR) The water content (WU, %) and swelling ratio (SR, %) of each membrane were calculated by immersing the circular membrane in water at 20°C and 80°C. - The membrane was immersed in deionized water for a minimum of 24 hours, and then the membrane surface was wiped and weighed (W wet ) and thickness (T wet The membrane was dried under vacuum for 24 hours, and the weight of the dry membrane (W dry ) and thickness (T dry The moisture content (%) and swelling ratio (%) 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 the WU and experimental IEC of each membrane. The hydration number was calculated using the following equation: Hydration number(λ)=(Water uptake(%)×1000) / (IEC×18)

[0076] (3) Density In step (3) of each example, the Br obtained after crosslinking poly(m-terphenyl N-methylpiperidine) 2 and bromohexyl SEBS 3 and treating with trimethylamine - The density of the as-prepared membrane (i.e., the membrane before ion-exchange by KOH treatment) was measured by the following method. Before the measurements, the membranes were dried in an oven at 40 °C for a minimum of 24 h and then resuspended in n-heptane (density = 0.684 g cm) at room temperature. -3 The density of each film was measured using the buoyancy method (g cm). -3 ) was calculated: density (g cm -3 )=W air / (W air -W hep )×D hep where W air is the weight of the film in air, W hep is the weight of the membrane immersed in heptane, D hep is the density of n-heptane, 0.684 g cm -3 is.

[0077] (4) Fractional Free Volume (FFV) Fractional free volume (FFV) is a dimensionless parameter that characterizes the volume of a cell that is not occupied by the polymer and can be calculated using the Visualizer module of the Material studio package. The molecular surface can be calculated in three ways, but in this invention, the van der Waals (vdW) surface created by the surface intersecting the vdW radii of the atoms was obtained. The following equation was used to determine the fractional free volume: FFV=(V sp -1.3V vdW ) / V sp where V vdW is the vdW volume calculated by the group contribution method, and 1.3 is the universal packing factor. sp denotes the specific volume defined by the inverse density.

[0078] (5) Results The IEC, WU, SR, density, and FFV of the x-PmTP-SEBS membranes of Examples 1 to 3 are shown in Table 1.

[0079] [Table 1] a1 Theoretical IEC calculated based on H NMR spectra b Experimental IEC measured by back titration

[0080] The IEC is defined as the milliequivalent of ion-conducting groups per unit mass of a polymer electrolyte membrane. Generally, the higher the IEC of a polymer electrolyte membrane, the more water it can contain. Because water can act as a mediator for hydroxide ion conduction in anion exchange membranes (AEMs), the higher the IEC, the higher the ionic conductivity. However, an excessively high IEC can sometimes lead to an increase in water content (WU), which reduces ionic conductivity through a mechanism known as the "dilution effect." This phenomenon also increases the membrane's SR, reducing its mechanical properties. Therefore, for an AEM to have high ionic conductivity and excellent mechanical properties, the IEC must be well matched.

[0081] The theoretical IECs of 30x-PmTP-SEBS, 40x-PmTP-SEBS, and 50x-PmTP-SEBS were 1.90, 1.79, and 1.69 meq g, respectively. -1 The calculated IEC values ​​were calculated as: , which indicates that the IEC values ​​decreased with increasing crosslinking degree. This decrease is due to the decrease in the ratio of bromohexyl SEBS3 relative to the total mass of the polymer that serves as the backbone of the membrane. The experimental IEC values ​​of the x-PmTP-SEBS membranes were measured using the back-titration method. The results showed that the experimental IEC values ​​were similar to the theoretical values ​​for all three membranes.

[0082] Measurements of the WU and SR of the x-PmTP-SEBS membranes showed that for all three membranes, WU and SR decreased with increasing crosslinking degree. Due to the inherent properties of SEBS as an elastomeric polymer, WU and SR values ​​were higher when the crosslinking degree was low. As the crosslinking degree increased, the polymer chains formed an increasingly dense network, resulting in a decrease in WU and SR values. This phenomenon is commonly observed in general crosslinked membranes. However, the x-PmTP-SEBS membranes exhibited intermediate levels of SR and higher WU (over 127%) compared to other SEBS-based crosslinked membranes.

[0083] Next, the density and FFV of the x-PmTP-SEBS membrane were measured. Generally, as the degree of crosslinking increases, the polymer density increases while the FFV decreases. However, the x-PmTP-SEBS membrane developed in this invention showed the opposite trend (i.e., the polymer density decreased [30x-PmTP-SEBS (1.136) > 40x-PmTP-SEBS (1.131) > 50x-PmTP-SEBS (1.127)]), while the FFV increased with increasing degree of crosslinking. This behavior is due to the twisted structure of m-terphenyl introduced into the polymer backbone, which suppresses the packing of the polymer chains and contributes to an increase in FFV. This twisted structure is believed to be the cause of the high WU of the x-PmTP-SEBS membrane, as water can be effectively absorbed within the twisted structure despite the cross-linked structure.

[0084] The calculation of the relative hydration number (λ) of the x-PmTP-SEBS membrane to the IEC value showed that the x-PmTP-SEBS membrane is comparable to other SEBS-based crosslinked membranes (

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

[50] Eur. Polym. J. 154 (2021), 110528;

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

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

[53] Int. J.Hydrogen Energy 45 (2020) 15658-15671), PP-based membranes ([3] Nat. Energy 4 (2019) 392-398; [4] Nat. Commun. 12 (2021) 2367; [6] Int. J. Hydrogen Energy 46 (2021) 18524-18533; [8] J. Mater. Chem. A. 9 (2021) 327-337;

[36] Energy Environ.Sci. 13 (2020) 3633-3645), and previously reported crosslinked PPO-SEBS membranes (

[54] J. Mater. Chem. A. 9 (2021) 1062-107). These membranes exhibited higher hydration numbers (30xPmTP-SEBS: 45.2, 40xPmTP-SEBS: 42.2, and 50xPmTP-SEBS: 42.0) (Figure 2a).

[0085] Experimental Example 2: Mechanical and Thermal Properties (1) Mechanical properties A bench-top tensile tester (Shimadzu E-TEST E2-L, Kyoto, Japan) was used to measure the strength of the specimen at 10 mm min at 25°C with a relative humidity of 50%. -1 At a crosshead speed of - The mechanical properties of the membranes were measured. The initial cross-sectional area of ​​the sample was used to determine the engineering stress. The initial slope of the stress-deformation curve was used to calculate Young's modulus. 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.

[0086] (2) Thermal stability The thermal stability of the films was investigated by thermogravimetric analysis (TGA) using a Scinco TGA N-1000 instrument (Seoul, Korea). TGA was performed at 30–800 °C for 10 °C min under nitrogen atmosphere. -1 It operated at a heating rate of . The glass transition temperature (TG) of each film was measured by differential scanning calorimetry (DSC) using a PerkinElmer DSC4000 (Waltham, MA, USA). Samples were prepared in aluminum pans and heated and cooled at rates of 10 °C min. -1 The temperature was measured from -40 to 200 °C for two cycles. Tg was determined in the second heating cycle.

[0087] (3) Results When used in AEMFC, AEM not only acts as an electrolyte to conduct hydroxide ions, but also as a separator between the positive and negative electrodes to prevent H2 and O2 fuels from migrating from one electrode to the other. Therefore, the mechanical and thermal stability of the membrane are also important factors to consider for the commercialization of AEMFC.

[0088] The mechanical properties of the x-PmTP-SEBS membranes were investigated based on the stress-strain curves (Figure 14 and Table 2). As expected, the stress (tensile strength) and Young's modulus of the thin films increased with increasing crosslinking degree: 30xPmTP-SEBS (15.3 MPa and 91.4 MPa) < 40xPmTP-SEBS (18.9 MPa and 99.7 MPa) < 50xPmTP-SEBS (28.5 MPa and 170.3 MPa). These results confirmed that the crosslinking process contributed to improving the membrane's mechanical properties. This improvement was due to the fact that increasing the crosslinking degree decreased the proportion of SEBS as an elastomeric polymer while simultaneously increasing the relative proportion of poly(m-terphenyl-N-methylpiperidine) units as a rigid polymer.

[0089] [Table 2]

[0090] The mechanical properties of the x-PmTP-SEBS membrane were also compared with those of other SEBS-based AEMs and PP-based AEMs (

[54] J. Mater. Chem. A. 9 (2021) 1062-1079;

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

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

[47] J. Membr. Sci. 643 (2022), 120029;

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

[38] J. Power Sources 480 (2020), 228805; [3] Nat. Energy 4 (2019) 392-398;

[34] ACS Macro Lett. 6 (2017) 566-570; [8] J. Mater. Chem. A. 9 (2021) 327-337; [4] Nat. Commun. 12 (2021) 2367;

[61] Membranes 10 (2020) 1-16;

[62] J. Membr. Sci. 598 (2020) (Table 2 and Figure 2b). The results showed that membranes in which SEBS was crosslinked with a rigid polymer exhibited higher tensile strength and Young's modulus (i.e., improved mechanical properties) than membranes in which SEBS or the SEBS component alone was crosslinked. Furthermore, the x-PmTP-SEBS membrane crosslinked with SEBS exhibited significantly higher tensile properties (deformation values) than PP-based membranes containing poly(terphenyl) and poly(biphenyl). These results strongly suggest that the mechanical properties of a membrane can be controlled by crosslinking two polymers with different properties, as proposed in this invention. Furthermore, the x-PmTP-SEBS membrane exhibited a higher deformation rate than the previously developed crosslinked PPO-SEBS membrane, which is thought to be due to the plasticizer effect caused by the membrane absorbing more water in the free volume induced by the m-terphenyl structure.

[0091] Next, the thermal stability of the x-PmTP-SEBS membrane was determined using TGA and DSC. TGA results showed that the thermal decomposition process proceeded in three stages (Figure 15). The first weight loss observed in the temperature range below 100 °C was due to the evaporation of water contained in the membrane. The amount of water inside the membrane decreased with increasing crosslinking degree, which was consistent with the WU results. The second weight loss occurred around 200 °C and was due to the decomposition of the conductive headgroups, followed by the decomposition of the polymer backbone at around 400 °C.

[0092] Analysis of the DTG graph revealed two peaks at 190°C and 250°C, corresponding to the decomposition of the quaternary ammonium (QA) group and the cross-linked piperidinium, respectively (Figure 15a). Generally, QA groups exhibit higher thermal stability, i.e., higher degradation temperatures, when incorporated into cross-linked structures compared to non-cross-linked structures. The observed results of the present invention are consistent with this trend. Furthermore, the DTG graph showed a tendency for the peak intensity at 190°C, corresponding to the decomposition of the QA group, to decrease with increasing cross-linking degree, while the peak intensity at 250°C, corresponding to the decomposition of the cross-linked piperidinium, to increase with increasing cross-linking degree. These results confirmed that the amount of QA in the film decreased, and the amount of cross-linked piperidinium increased with increasing cross-linking degree. The third weight loss, which began at approximately 400°C, was due to the decomposition of the polymer backbone.

[0093] Next, we investigated the glass transition temperature (Tg) of each polymer. No peak was observed in the x-PmTP-SEBS film up to 200 °C, at which point the conductive headgroups began to decompose (Figure 15b). While the Tg of typical SEBS is approximately 46 °C, no Tg peak was observed in x-PmTP-SEBS from 180 °C until the decomposition temperature of ammonium was reached. This result indicates that the introduction of rigid poly(m-terphenyl-N-methylpiperidine) units combined with cross-linking structures effectively improves the alignment between polymer components and increases the thermal stability of SEBS as a rubbery polymer.

[0094] These TGA and DSC results indicated that the x-PmTP-SEBS membrane, which was crosslinked with poly(m-terphenyl N-methylpiperidine) 2 and bromohexyl SEBS 3, exhibited high thermal stability suitable for fuel cell operation.

[0095] Experimental Example 3: Morphological analysis (1)Measurement method The surface morphology of each membrane was analyzed using a Pt-coated scanning electron microscope (SEM, JSM-7800F, Tokyo, Japan) at an accelerating voltage of 15.0 kV. Microphase separation of the membranes was observed using an atomic force microscope (AFM, Bruker MUMTIMODE-8-AM, Billerica, MA, USA). A high-resolution X-ray diffractometer (HR-XRD, SmartLab, Rigaku, Japan) was used with Cu-Kα X-rays (λ = 1.54 Å) in the 2θ range from 0° to 5° at a rate of 0.2° min. -1 A scanning speed of 1000 s was used to collect small-angle X-ray diffraction scattering spectra of the membranes. The membranes were thoroughly dried at 40°C before the measurements.

[0096] (2) Results The phase separation present in each membrane was confirmed by SEM. Images showed that the phase separation was more pronounced in the 50-PmTP-SEBS membrane, where the crosslinking degree was higher than in the 30-PmTP-SEBS membrane (Figures 3a-3c). The reason for the more pronounced phase separation with increasing crosslinking degree is that the alignment of the polymer structure is affected by the crosslinking degree. More specifically, at low crosslinking degrees, SEBS remains randomly crosslinked with poly(m-terphenyl-N-methylpiperidine). This structure makes it difficult for the SEBS components, which are highly vulnerable to phase separation, to align well, leading to a limited level of phase separation. However, with increasing crosslinking degree, bromohexyl SEBS becomes increasingly crosslinked with poly(m-terphenyl-N-methylpiperidine), improving the alignment of the polymer chains.

[0097] AFM images of the x-PmTP-SEBS membrane further confirmed the phase separation by the coexistence of dark hydrophilic and light hydrophobic regions. Furthermore, the size of ion clusters increased with increasing cross-linking degree (Figures 3d-3f) due to the increased phase separation.

[0098] SAXS analysis further confirmed that the q value decreased (i.e., the d-spacing increased) with increasing crosslinking degree (Figure 4). This decrease occurred because increasing the crosslinking degree promoted the aggregation of conductive groups, which promoted phase separation between hydrophilic and hydrophobic units, increasing the size of ion clusters. This result was consistent with the SEM and AFM results.

[0099] Experimental Example 4: Moisture retention capacity (1)Measurement method The freezing and non-freezing water content of the membranes was measured by DSC in a fully hydrated state using a PerkinElmer DSC4000. A fully hydrated membrane sample was sealed in an aluminum pan, and an empty sealed aluminum pan was also prepared for reference. Both pans were weighed and frozen at -40°C inside the DSC chamber. The temperature was then held constant while the system equilibrated. The DSC chamber was then cooled for 2°C min -1 The film was heated to 20 °C at a heating rate of 1000 kJ / s. This cycle was repeated twice, and the value was calculated for the second heating cycle. The amount of frozen water in each film was calculated by the peak area of ​​the melting heat resistance (ΔH m ) was calculated by integrating the WU (%) of the membrane. The WU (%) of the membrane was used to determine the total water content. The frozen and unfrozen water contents were calculated using the following formula: Freezing water(%)=[melting enthalpy(J g -1 )] / [melting endothermic heat of funsion of pure water(334J g -1 )] × 100 Non-freezing water(%)=total water(%)-freezing water(%)

[0100] (2) Results In AEMFCs, water acts as a medium for conducting hydroxide ions formed at the positive electrode to the negative electrode. Therefore, the water capacity of AEMs is important for characterizing their ion conduction capability. Water in membranes is generally divided into free water and bound water. Free water does not actively interact with the ion-conducting head groups and has freezing and boiling temperatures similar to those of ordinary water. Conversely, bound water has a strong interaction with the ion-conducting head groups and exhibits a lower freezing point and higher boiling point than free water. Previous studies have shown that the content of bound water has a greater effect on the ionic conductivity of AEMs than free water. Considering that fuel cells generally operate at 90%-95% RH, i.e., 90%-95% hydrated H2 and O2, increasing the content of bound water should improve overall cell performance.

[0101] The water content of x-PmTP-SEBS membranes was measured using TGA and DSC. In the TGA results, the weight loss observed below 100 °C was assumed to correspond to the evaporation of free water, whereas the weight loss above 100 °C and 150 °C was assumed to be due to the evaporation of bound water (Figure 5a). This TGA-based water analysis method allows only qualitative analysis, not quantitative analysis, due to the variable WU for each test membrane. Therefore, the results obtained with this approach were only used to determine how the free and bound water contents differ from each other.

[0102] With increasing crosslinking degree, the overall WU of the x-PmTP-SEBS membranes decreased, but the bound water content increased (Figure 5b). This is because the content of poly(m-terphenyl-N-methylpiperidine) increased with increasing crosslinking degree. More specifically, the twisted structure of the m-terphenyl unit within poly(p-terphenyl-N-methylpiperidine) enhanced the interaction with water, increasing the FFV of each membrane. This result was consistent with the FFV analysis results (Table 1).

[0103] The state of water was further analyzed using DSC to examine the content of "unfrozen water" and "frozen water" (frozen-free water and frozen-bound water). The following peaks were observed in all three x-PmTP-SEBS membranes: T, which corresponds to the freezing temperature of free water; F1 and T, which corresponds to the freezing temperature of the frozen bound water. F2 (Dotted line in Figure 16). In the case of unfrozen water, no phase change was observed because this form of water strongly interacts with the ion-conducting headgroups. On the other hand, the peaks corresponding to free water and frozen-bound water partially overlapped, and these two types of water were treated as frozen water. Based on this result, the DSC enthalpy of fusion (ΔH m The change in the ρ (ρ = 0.01) of the water content of each membrane was calculated to determine the ratio of frozen water to non-frozen water relative to the total water content of each membrane (Table 3). As expected, the ratio of non-frozen water increased with increasing cross-linking degree. This is because the interaction between the ion-conducting headgroups and water was strengthened with increasing cross-linking degree.

[0104] [Table 3]

[0105] To confirm this interpretation, T F2 Further analysis was performed on T (Fig. 16b). F2 The temperature shifted to lower values ​​as the degree of crosslinking increased (i.e., the interaction between the ion-conducting headgroups and water became stronger). This was consistent with the TGA results, confirming that the introduction of crosslinking bonds increased the bound water content. These results confirmed that the introduction of poly(m-terphenyl N-methylpiperidine) units could successfully increase the bound water content by improving the free volume, as in the previously crosslinked PPO-SEBS containing triazole groups, without the need for triazole groups.

[0106] Experimental Example 5: Hydroxide ion conductivity (1)Measurement method The hydroxide ion conductivity (σ) of each membrane was measured by four-probe impedance spectroscopy using an AC impedance analyzer (SP-200, Bio-Logic SAS, Claix, France). The electrode system was coupled at frequencies ranging from 100 mHz to 2 MHz. Rectangular samples measuring 1 x 4 cm were prepared. Hydroxide ion conductivity was measured using resistance (R) in deionized water at temperatures between 20 °C and 80 °C. Hydroxide ion conductivity was calculated using the following equation: σ=L / (R×A) where L is the distance between the reference electrodes and A is the cross-sectional area of ​​the membrane.

[0107] (2) Results In AEMFCs, the AEM conducts hydroxide ions to generate energy. Therefore, the hydroxide ion conductivity of the AEM is one of the most important properties that determine the performance of a single cell. In this study, the hydroxide ion conductivity of x-PmTP-SEBS AEMs was measured at 20-80°C (Figure 6 and Table 4). The results showed that the ionic conductivity of each membrane increased with increasing crosslinking degree across the entire temperature range (Figure 6a).

[0108] To eliminate the influence of differences in IEC between each membrane on ionic conductivity, we measured and compared normalized conductivity. These results also showed that ionic conductivity increased with increasing crosslinking degree (Figure 6b). In particular, 50xPmTP-SEBS exhibited the highest ionic conductivity of the three membranes (56.31 mS / cm at 20 °C and 116.32 mS / cm at 80 °C) despite its high level of crosslinking and low IEC and WU. This is due to the increased crosslinking degree, which allowed the membrane to establish a well-defined phase-separated morphology while increasing the size of ionic clusters and the ratio of bound water, as confirmed by morphological analysis using AFM, SEM, and XRD, and water-holding capacity measurements using TGA and DSC.

[0109] The normalized conductivity of the x-PmTP-SEBS membrane was compared with that of various AEMs, including the previously developed and commercialized cross-linked PPO-SEBS AEM ([3] Nat. Energy 4 (2019) 392-398; [4] Nat. Commun. 12 (2021) 2367; [5] Adv. Funct. Mater. 28 (2018) 1-10; [6] Int. J. Hydrogen Energy 46 (2021) 18524-18533; [8] J. Mater. Chem. A. 9 (2021) 327-337; [9] J. Membr. Sci. 642 (2022), 119966;

[36] Energy Environ.Sci. 13 (2020) 3633-3645;

[37] J. Power Sources 487 (2021), 229429;

[49] J. Membr. Sci. 644 (2022), 120109;

[61] Membranes 10 (2020) 1-16) were additionally compared (Figure 6b). The x-PmTP-SEBS membrane exhibited high ionic conductivity despite its low IEC value. This confirmed that the cross-linking of poly(m-terphenyl-N-methylpiperidine) with bromohexyl SEBS provides such x-PmTP-SEBS membranes with very high ionic conductivity for two reasons. The first is the good phase separation effect initiated by the triple-block copolymer SEBS, as confirmed by morphological analysis. The second reason is that the twisted structure of poly(m-terphenyl-N-methylpiperidine) strengthens the interaction between the ion-conducting headgroup and water, as confirmed by bound water analysis using TGA and DSC.

[0110] The normalized conductivity of the crosslinked x-PmTP-SEBS membrane is much higher than that of the previously reported x-TQA-PPO-SEBS membrane prepared by crosslinking PPO and SEBS via triazole. This result suggests that increasing the bound water content by introducing the twisted poly(m-terphenyl-N-methylpiperidine) structure was more effective than introducing the hydrogen-bonding sites of triazole. Due to this combined effect, 50xPmTP-SEBS exhibited a normalized conductivity of 33.52 mS cm at 20 °C. -1 showed excellent normalized conductivity of .

[0111] The ionic conductivity of the crosslinked x-PmTP-SEBS membrane was additionally measured at 95% room humidity (RH) and 60°C, which are the operating conditions of fuel cells in practical applications. The ionic conductivity of water (50xPmTP-SEBS: 32.44 mS cm) -1 >40x-PmTP-SEBS:30.73mS cm -1 >30x-PmTP-SEBS:28.58mS cm -1 ), the RH conductivity increased with increasing crosslinking degree (Table 4). This is because the amount of twisted m-terphenyl units in the crosslinked x-PmTP-SEBS increased, as confirmed by the aqueous state analysis, resulting in higher conductivity even under RH conditions for the highly crosslinked membranes.

[0112] [Table 4] a Measured at 95% RH and 60°C

[0113] Experimental Example 6: Alkaline Stability (1)Measurement method OH -Chemical stability was evaluated by measuring the change in IEC and conductivity after immersion of the membranes in 2M KOH solution at 80°C for 600 hours. Prior to the measurements, each membrane was immersed in freshly prepared 1M KOH solution at room temperature for a minimum of 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 before and after each alkaline stability test using the back-titration method described above.

[0114] (2) Results The results of the alkaline stability test of the x-PmTP-SEBS membrane are shown in FIG. All three membranes with different crosslinking degrees exhibited excellent alkaline stability (conductivity and IEC retention rates of over 99% for 600 hours). Furthermore, it was found that this alkaline stability further improved with increasing crosslinking degree. The high alkaline stability of the x-PmTP-SEBS membrane was due to the fact that the two polymers that make up the x-PmTP-SEBS membrane (poly(m-terphenyl-N-methylpiperidine) and SEBS) lacked aryl ether bonds, which are highly resistant to backbone decomposition induced by hydroxide ions. The crosslinking of these two polymers also improved the chemical stability of the ion-conducting groups. As confirmed by the previous water-holding capacity measurements, the content of bound water increased with increasing crosslinking degree, and this bound water surrounded the ion conductor, creating a shielding effect and protecting it from hydroxide ion attack. The combination of all these factors improved the alkaline stability of this membrane.

[0115] In addition, the alkaline stability of the x-PmTP-SEBS membrane developed in this invention was compared with that of some representative AEMs reported in the literature, including the previously developed crosslinked PPO-SEBS (xTQA50-PPO-SEBS,

[54] J. Mater. Chem. A. 9 (2021) 1062-1079) (

[47] J. Membr. Sci. 643 (2022), 120029;

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

[66] Macromolecules 52 (2019) 2139-2147;

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

[48] J. Membr. Sci. 599), by comparing the percentage of conductivity remaining after the stability test. (2020), 117829;

[50] Eur. Polym. J. 154 (2021), 110528;

[55] J. Membr. Sci. 633 (2021), 119418; [6] Int. J. Hydrogen Energy 46 (2021) 18524-18533;

[61] Membranes 10 (2020) 1-16; [8] J. Mater. Chem. A. 9 (2021) 327-337; [4] Nat. Commun. 12 (2021) 2367;

[49] J. Membr. Sci. 644 (2022), 120109; [3] Nat. Energy 4 (2019) 392-398; [9] J. Membr. Sci. 642 (2022), 119966;

[37] J. Power Sources 487 (2021), 229429;

[46] Angew. Chem. Int. Ed. 61(2022) 1-8;

[62] J. Membr. Sci. 598 (2020)) were additionally compared (Table 5). All x-PmTP-SEBS membranes showed higher residual conductivity values ​​(i.e., greater stability) than PP- and SEBS-based AEMs.

[0116] [Table 5A] [Table 5B] a QA=quaternary ammonium, Pip=piperidinium

[0117] Experimental Example 7: Fabrication of membrane electrode assembly (MEA) and single cell measurement (1)Measurement method The single cell test was carried out as follows: First, the catalyst ink was added at 0.3 mg cm for the positive electrode. -2 For the negative electrode, Pt / C (46.2 wt%, Tanaka Kikinzoku Kogyo-TKK, Tokyo, Japan) and 0.4 mg cm of PtRu / C (HiSpec10000, Johnson Matthe, London) with deionized water, 2-propanol, and 10 wt% FAA-3 ionomer solution. -2 The catalyst ink was then coated onto the membrane surface using an air spray gun, and the membrane was then immersed in a 1M KOH solution for 3 hours to produce a catalyst-coated membrane (CCM). The CCM was then used to fabricate a 5cm membrane electrode assembly (MEA). 2 The electrode was sandwiched between a 39BB gas diffusion layer (GDL, Sigracet, SGL Carbon, Wiesbaden, Germany) with an effective electrode area of ​​0.6 L min and a Teflon gasket. H and O were supplied at 0.6 L min, respectively. -1 and 0.8L min -1 The fuel cell test was carried out at 60°C under RH 95%. The polarization curve was then measured at 50 mA s -1 The measurement was performed at a scan speed of .

[0118] (2) Results The x-PmTP-SEBS membrane developed in this study exhibited excellent physicochemical stability, well-established phase separation morphology, and high conductivity in water and under practical RH conditions. Single-cell tests were then conducted using the x-PmTP-SEBS membrane at 60°C and 95% RH.

[0119] The results showed that the maximum power density and current density (at 0.6 V) of such membranes increased with increasing crosslinking degree: 50xPmTP-SEBS (592 mW cm -2 and 1156mA cm -2 )>40x-PmTP-SEBS(496mW cm -2 and 926mA cm -2 )>30x-PmTP-SEBS(391mW cm -2 and 737mA cm -2 ) (Figure 8a). This result was consistent with the trends observed in the conductivity measurements (both in water and under actual RH conditions).

[0120] For the 50xPmTP-SEBS membrane with the best cell performance, additional tests were performed at a back pressure of 0.1 MPa. As a result, a slightly improved cell performance was achieved: 50xPmTP-SEBS (642 mW cm) -2 and 1315mA cm -2 ) (Fig. 8b). This suggests that cell performance can be further optimized.

[0121] The cell performance of 50xPmTP-SEBS membranes was reported in previous studies as being comparable to that of other SEBS-based AEMs (

[47] J. Membr. Sci. 643 (2022), 120029;

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

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

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

[66] Macromolecules 52 (2019) 2139-2147) or PP-based AEMs ([3] Nat. Energy 4 (2019) 392-398; [6] Int. J. Hydrogen Energy 46 (2021) 18524-18533; [8] J. Mater. Chem. A. 9 (2021) 327-337;

[34] ACS Macro Lett. 6 (2017) 566-570;

[67] J. Membr. Sci. 588 (2019), 117120;

[68] Int. J. Hydrogen Energy 44 (2019) 24954-24964) (Figure 17). Because single-cell operation involves a variety of factors, such as flow rate, backpressure, RH conditions, cell operating temperature, catalyst, and ionomer, it is difficult to directly compare cell performance measured at other conditions. However, the 50xPmTP-SEBS membrane, in which poly(m-terphenyl N-methylpiperidine) and bromohexyl SEBS were cross-linked, showed a relatively high peak power density, even though it was measured at a relatively low H2 / O2 flow rate (0.6 / 0.8 L / min, respectively) and a low temperature (60°C). These results indicate that the phase-separated morphology and high water-holding capacity of the x-PmTP-SEBS AEM enable such membranes to provide high hydroxide ion conductivity and excellent cell performance when actually used in fuel cells.

[0122] conclusion The poly(m-terphenyl-N-methylpiperidinium)-SEBS membrane (x-PmTP-SEBS) according to one embodiment of the present invention exhibited higher tensile strength (15 MPa or more) and Young's modulus (91 MPa or more) than existing crosslinked SEBS membranes. Furthermore, the x-PmTP-SEBS membrane exhibited significantly higher elongation properties (118% or more at break) than typical PP-based membranes.

[0123] The x-PmTP-SEBS membrane exhibited high dimensional stability at an SR of about 30%, despite its high WU (127% or more at 20°C).

[0124] Furthermore, the x-PmTP-SEBS membranes according to one embodiment of the present invention exhibited high water-holding capacity and high hydration number (λ>42) due to the well-segregated morphology resulting from the triple-block structure of SEBS and the free volume induced by the twisted structure of m-terphenyl. As a result, these membranes exhibited excellent normalized conductivity and excellent cell performance. In particular, the 50xPmTP-SEBS membrane with a crosslinking degree of 50% exhibited an IEC of 1.68 meq g -1 However, at 80°C in water, it was 116 mS cm -1 , 95%RH, 32mS cm at 60°C -1 It exhibits high conductivity of 642 mW cm of H2 / O2 gas flow at 60°C and 95% RH. -2 It showed a high peak power density.

[0125] Moreover, all cross-linked x-PmTP-SEBS membranes based on polymer backbones lacking aryl-ether bonds exhibited excellent alkaline stability (more than 99% of ionic conductivity and IEC were maintained even at 80 °C for 600 h in 2 M KOH), outperforming typical AEMs reported in the literature due to the shielding effect of their high hydration numbers.

[0126] From the above results, it was confirmed that the polymer film including the cross-linked copolymer according to one embodiment of the present invention has excellent mechanical properties and excellent physicochemical and electrical properties. Furthermore, it was confirmed that the physical properties of the polymer film including the cross-linked copolymer can be controlled by adjusting the degree of cross-linking of the cross-linked copolymer.

[0127] Furthermore, the polymer membrane was confirmed to have stable and excellent electrochemical properties, such as excellent ionic conductivity while maintaining a suitable IEC. These results demonstrate that the strategy used in the present invention, instead of a strategy to increase the IEC of polymers, can be used to develop an AEM with excellent performance.

Claims

1. A cross-linked 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 first chain and the second chain are cross-linked to each other: 【Chemistry 1】 In the above Chemical Formula 1, * indicates the bonding position with Chemical Formula 2, q １ , q ２ , q ５ , and q ６ is an integer between 100 and 1,000, q ３ and q ４ is an integer between 150 and 2,000, a and b are each independently an integer from 3 to 10; R １ ~R ４ are each independently hydrogen or -(CH ２ ) ｐ -CH ３ and p is an integer from 0 to 5. 【Chemistry 2】 In the above Chemical Formula 2, * indicates the bonding position with Chemical Formula 1, R ５ is -(CH ２ ) ｐ’ -CH ３ and p' is an integer from 0 to 5; n is an integer from 10 to 1000.

2. The crosslinked copolymer according to claim 1, comprising 10 to 70 moles of the second chains per 100 moles of the first chains.

3. q １ ~q ６ and each independently represent an integer of 10 to 500.

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

5.

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

5.

6. 2. The crosslinked copolymer according to claim 1, wherein a and b are each independently an integer of 4 to 6.

7. The cross-linked copolymer of claim 1 , which is represented by the following chemical formula 3: 【Transformation 3】 In the above Chemical Formula 3, q １ ~q ６ , a, b, and n are as defined in Chemical Formula 1 and Chemical Formula 2.

8. A polymer membrane comprising the crosslinked copolymer according to any one of claims 1 to 7.

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

10. (a) preparing a poly(styrene-b-ethylene-co-butylene-b-styrene)-based polymer represented by the following chemical formula 1-1: (b) preparing a poly(m-terphenyl N-alkylpiperidine) polymer represented by the following formula 2-1: (c) crosslinking the poly(styrene-b-ethylene-co-butylene-b-styrene) polymer with the poly(m-terphenyl-N-methylpiperidine) polymer to prepare a crosslinked copolymer; A method for producing a crosslinked copolymer comprising: 【Chemistry 4】 In the above chemical formula 1-1, q １ , q ２ , q ５ , and q ６ is an integer between 100 and 1,000, q ３ and q ４ is an integer between 150 and 2,000, a and b are each independently an integer from 3 to 10; R １ ~R ４ are each independently hydrogen or -(CH ２ ) ｐ -CH ３ and p is an integer from 0 to 5. X １ and X ２ are each independently a halogen group, 【Transformation 5】 In the above chemical formula 2-1, R ５ is -(CH ２ ) ｐ’ -CH ３ and p' is an integer from 0 to 5; n is an integer from 10 to 1000.

11. 11. The method of claim 10, further comprising the step of: (d) reacting the crosslinked copolymer with trimethylamine.

12. The method for producing a crosslinked copolymer according to claim 10, wherein the poly(styrene-b-ethylene-co-butylene-b-styrene) polymer contains 30 to 90 moles of halogen groups per 100 moles of styrene repeating units.

13. 11. The method for producing a crosslinked copolymer according to claim 10, wherein in step (c), 10 to 70 moles of the poly(m-terphenyl N-alkylpiperidine) polymer is used per 100 moles of halogen groups contained in the poly(styrene-b-ethylene-co-butylene-b-styrene)-based polymer.

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