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

Abstract

The present invention relates to a crosslinked copolymer that has excellent ion exchange capacity, exhibits high ionic conductivity and water content under various temperature conditions, has high density and low hydrogen permeability, and has excellent thermal stability and oxidative stability, and can be suitably used as an anion exchange membrane for water electrolysis to produce high-purity hydrogen and oxygen.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0150712 dated November 11, 2022, and all contents disclosed in the documents of said Korean patent application 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] Water electrolysis technology, which uses the electrolysis of water, has the advantages of not emitting greenhouse gases, having an unlimited supply of water as a raw material, and being able to store unused electricity in large quantities for a long period of time when combined with renewable energy.A water electrolysis device consists of electrodes that generate hydrogen and oxygen, and an ion exchange membrane that prevents the mixing of gases and transmits ions, with the ion exchange membrane being the core component that determines the efficiency and stability of the water electrolysis device.

[0004] Low-temperature water electrolysis technologies include alkaline water electrolysis, polymer electrolyte membrane water electrolysis, and anion exchange membrane water electrolysis. Anion exchange membrane water electrolysis is considered the ideal water electrolysis technology, combining the advantages of alkaline water electrolysis and polymer electrolyte membrane water electrolysis. Anion exchange membrane water electrolysis has a similar structure to polymer electrolyte membrane water electrolysis, allowing for easy high-pressure and differential pressure operation, high current density operation, and equipment miniaturization. Unlike polymer electrolyte membrane water electrolysis, it operates in an alkaline environment and can use non-precious metal catalysts rather than platinum-based catalysts, which offers advantages in ensuring the economic viability of green hydrogen production through lower material costs. Anion exchange membrane water electrolysis is still in the research and development stage, and commercialization requires overcoming issues such as the low ionic conductivity of anion exchange membranes and the performance and reliability of non-precious metal catalysts.

[0005] Meanwhile, poly(styrene-ethylene-co-butylene-styrene) (hereinafter referred to as SEBS), a type of triblock copolymer, has been widely used as an anion exchange membrane polymer material due to its high ionic conductivity resulting from the excellent morphology of block polymers, as well as its high alkaline stability resulting from its nonaryl-ether type polymer structure.

[0006] However, in the case of SEBS-based anion exchange membranes, when the ion exchange capacity (IEC) increases due to the elasticity of SEBS, the water content and swelling rate increase rapidly, resulting in a dilution effect that reduces conductivity. In addition, the low tensile strength and high water absorption and swelling rates reduce the mechanical and physical stability, making the membranes very inconvenient to handle.

[0007] To solve these problems, a polymer was proposed in which SEBS polymer and polyphenylene oxide polymer were cross-linked using N,N,N',N'-tetramethyl-1,6-hexamethylenediamine as a cross-linking agent (J.Membr.Sci.564(2018), 492-500). However, when producing this polymer, the reaction sites of the cross-linking agent and the two polymers were the same, making it impossible to control the 1:1 reaction between SEBS polymer and polyphenylene oxide polymer. This resulted in phase separation and the formation of an inhomogeneous membrane, which resulted in inconsistent hydroxyl ion conductivity.

[0008] To address these issues, a crosslinked polymer was developed by crosslinking an SEBS polymer with a polyphenylene oxide polymer containing triazole and amine groups without the addition of an additional crosslinking agent (Korean Patent Registration No. 10-2184530). However, the crosslinked polymer required complex manufacturing steps and its hydroxide ion conductivity and water content at high temperatures were insufficient for use in water electrolysis cells. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Korean Patent No. 10-2184530 [Non-patent literature]

[0010] [Non-Patent Document 1] Zhihua Wang, Ziming Li, Nanjun Chen, Chuanrui Lu, Fanghui Wang, Hong Zhu, Crosslinked poly (2,6-dimethyl-1,4-phenylene oxide) polyelectrolyte enhanced with poly (styrene-b-(ethylene-co-butylene)-b-styrene) for anion exchange membrane applications, J. Membr. Sci. 564 (2018), 492-500. Summary of the Invention [Problem to be solved by the invention]

[0011] An object of the present invention is to provide a new crosslinked copolymer that has excellent hydroxide ion conductivity and water content characteristics, as well as excellent thermal stability and oxidation stability, and that can be suitably used as an anion exchange membrane for water electrolysis. [Means for solving the problem]

[0012] In order to solve the above problems, according to one embodiment of the present invention, there is provided a crosslinked copolymer comprising a main chain represented by the following Chemical Formula 1 and a side chain represented by the following Chemical Formula 2: [ka] In the above 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 independently an integer of 3 to 10; R1 to R4 each independently represent 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, n and m each independently represent an integer of 10 to 50.

[0013] 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 polyphenylene oxide polymer represented by the following chemical formula 2-1; (c) crosslinking the poly(styrene-b-ethylene-co-butylene-b-styrene) polymer and the polyphenylene oxide 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 each independently represent hydrogen or -(CH2) p -CH3, and p is an integer of 0 to 5; X1 and X2 each independently represent a halogen group; [ka] In the above chemical formula 2-1, n and m each independently represent an integer of 10 to 50. [Effects of the Invention]

[0014] The crosslinked copolymer of the present invention has excellent ion exchange capacity, high ionic conductivity and water content under various temperature conditions, high density and low hydrogen permeability, and exhibits excellent thermal stability and oxidative stability under the operating conditions of a water electrolysis device, making it suitable for use as an anion exchange membrane for water electrolysis to produce high-purity hydrogen and oxygen. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a photograph of a polymer membrane produced from PPO-SEBS in Example 1. [Figure 2] 1 is a photograph of a polymer membrane prepared using DA-x30-PPO-SEBS in Comparative Example 1. [Figure 3A] 1 is a H-NMR spectrum of Br-PPO produced in Example 1 (1-1). [Figure 3B] 1 is an IR spectrum of Br-PPO produced in Example 1 (1-1). [Figure 4A] 1 is a H-NMR spectrum of DMA-PPO produced in Example 1 (1-2). [Figure 4B] 1 shows an IR spectrum of DMA-PPO produced in Example 1 (1-2). [Figure 5] FIG. 1 shows a comparison of the H-NMR spectrum and IR spectrum of Br-PPO produced in (1-1) and DMA-PPO produced in (1-2) of Example 1. [Figure 6A] 1 is a H-NMR spectrum of Ac-SEBS produced in Example 1 (2-1). [Figure 6B] 1 is an IR spectrum of Ac-SEBS produced in Example 1 (2-1). [Figure 7A] 1 is a 1H-NMR spectrum of Re-SEBS produced in Example 1 (2-2). [Figure 7B] 1 is an IR spectrum of Re-SEBS produced in Example 1 (2-2). [Figure 8]1 shows a comparison of the 1H-NMR spectrum and the IR spectrum of Ac-SEBS produced in (2-1) and Re-SEBS produced in (2-2) of Example 1. [Figure 9] 1 shows the results of thermogravimetric analysis of the PPO-SEBS of Example 1 and the TQA SEBS of Comparative Example 3. [Figure 10] 1 shows the results of oxidation stability tests of PPO-SEBS of Example 1 and TQA SEBS of Comparative Example 3. [Figure 11] 1 shows the measurement results of tensile strength and elongation of the PPO-SEBS of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0016] 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.

[0017] 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.

[0018] 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.

[0019] The present invention will be described in detail below.

[0020] 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 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 independently an integer of 3 to 10; R1 to R4 each independently represent 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, n and m each independently represent an integer of 10 to 50.

[0021] The crosslinked copolymer of the present invention has a structure in which a first chain containing poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) and a second chain containing polyphenylene oxide (PPO) are crosslinked via an alkylamine group.

[0022] Due to these structural characteristics, the cross-linked copolymer exhibits high ion exchange capacity, hydroxide ion conductivity, water content, and swelling ratio, and also exhibits higher density and lower hydrogen permeability than existing ion exchange membranes, making it suitable for use as an anion exchange membrane for water electrolysis to produce high-purity hydrogen and oxygen. Furthermore, since the cross-linked copolymer does not contain triazole, an aromatic functional group, in the polymer, it exhibits excellent oxidation stability and can be used stably even during long-term operation of a water electrolysis cell.

[0023] 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. If the number of second chains per 100 moles of the cross-linked copolymer is less than 10 moles, mechanical properties such as tensile strength may be reduced. If the number of second chains exceeds 70 moles, the mechanical properties may be excellent, but the hydroxide ion conductivity and alkaline stability may be reduced.

[0024] The above q1 to q6, a, b, n, and m are the numbers of each repeating unit.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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 repeating units derived from styrene to all repeating units 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.

[0029] 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 to all styrene-derived repeat units in Chemical Formula 1, is 0.2 or more, or 0.25 or more, or 0.3 or more, or 0.35 or more, and may be 0.5 or less, or 0.45 or less, or 0.4 or less.

[0030] Preferably, n is an integer of 10-50, and m is an integer of 25-45.

[0031] Preferably, the ratio of n to the sum of n and m may be 0.15 to 0.70, or 0.18 to 0.66.

[0032] 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.

[0033] 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.

[0034] Specifically, the cross-linked copolymer may include a structure represented by the following chemical formula 3: [ka] In Chemical Formula 3, q1 to q6, a, b, n, and m are as defined in Chemical Formula 1 and Chemical Formula 2.

[0035] Preferably, the cross-linked copolymer may include a structure represented by the following chemical formula 4: [ka] In Chemical Formula 4, q1 to q6, a, b, n, and m are as defined in Chemical Formula 1 and Chemical Formula 2.

[0036] 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 - or HCO3 - and preferably, OH - may be.

[0037] Therefore, according to one embodiment of the present invention, there is provided a polymer membrane comprising the cross-linked copolymer.

[0038] 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, or 70 μm or less, or 60 μm or less, or 55 μm or less. If the polymer membrane is less than 20 μm thick, the hydrogen permeability of the membrane may increase significantly, making it difficult to apply to the production of high-purity hydrogen. Conversely, if the thickness exceeds 70 μm, the membrane may have excellent mechanical properties, but the resistance may increase due to the large thickness, reducing hydroxide ion conductivity, resulting in reduced current density and power density.

[0039] The polymer membrane may have an ion exchange capacity (IEC) of 1.15 meq / g or more, 1.20 meq / g or more, or 1.30 meq / g or more, and 1.95 meq / g or less, 1.90 meq / g or less, or 1.80 meq / g or less, although the ion exchange capacity of the polymer membrane may vary depending on the molar ratio of the first chain to the second chain and is not limited to this range.

[0040] The polymer membrane described above includes a cross-linked copolymer having the first and second chains, which allows it to exhibit higher output characteristics when used in a water electrolyzer. In addition, the polymer membrane has high density and low hydrogen permeability, which is advantageous for producing high-purity hydrogen and oxygen.

[0041] Therefore, a polymer membrane having the above physical properties can be suitably used as an anion exchange membrane for water electrolysis.

[0042] The methods for measuring the ion exchange capacity, hydroxide ion conductivity, water content, swelling ratio, hydrogen permeability, and density will be specifically explained in the following examples.

[0043] Meanwhile, according to one embodiment of the present invention, there is provided a method for producing the crosslinked copolymer. Specifically, the method for producing the crosslinked copolymer of the present invention comprises the following steps: (a) preparing a poly(styrene-ethylene-butylene-styrene) polymer represented by the following chemical formula 1-1; (b) preparing a polyphenylene oxide polymer represented by the following chemical formula 2-1; (c) crosslinking the poly(styrene-ethylene-butylene-styrene) polymer and the polyphenylene oxide polymer to prepare a crosslinked copolymer.

[0044] [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 each independently represent hydrogen or -(CH2) p -CH3, and p is an integer of 0 to 5; X1 and X2 each independently represent a halogen group; [ka] In the above chemical formula 2-1, n and m each independently represent an integer of 10 to 50.

[0045] The preferred ranges of q1 to q6, a, b, R1 to R4, n, and m in Chemical Formula 1-1 and Chemical Formula 2-1 are as explained in Chemical Formulas 1 and 2 above.

[0046] The X1 and X2 are each independently F, Cl, Br, or I, and preferably Br.

[0047] 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.

[0048] 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, R is C 1-29 An alkanoyl chloride having a halogen group at the end of the alkyl chain, 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 types of acyl halides.

[0049] 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.

[0050] 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.

[0051] The poly(styrene-b-ethylene-co-butylene-b-styrene) copolymer preferably contains 30 moles or more, 40 moles or more, 50 moles or more, 55 moles or more, or 60 moles or more and 90 moles or less, 80 moles or less, 75 moles or less, 70 moles or less, or 65 moles or less of halogen groups per 100 moles of styrene repeating units. The number of moles of halogen groups per styrene repeating unit can be adjusted by adjusting the number of moles of acyl halide per mole of styrene in the SEBS polymer during the acylation reaction.

[0052] Step (b) is a step of preparing a polyphenylene oxide-based polymer having a tertiary amine group. For example, the polyphenylene oxide-based polymer represented by Formula 2-1 can be prepared by brominating the benzyl site of poly(2,6-dimethyl-1,4-phenylene oxide) to prepare a brominated polyphenylene oxide-based polymer, followed by an amination reaction.

[0053] Bromine (Br2) or N-bromosuccinimide can be used in the bromination reaction. The reaction temperature may be, for example, 120 to 140°C, and the reaction time may be 3 to 5 hours.

[0054] Next, the brominated polyphenylene oxide polymer produced by the bromination reaction is reacted with dimethylamine to produce a polyphenylene oxide polymer represented by Chemical Formula 2-1. The bromination reaction may be carried out at 50 to 100°C for 12 to 24 hours.

[0055] Step (c) is a step of reacting the poly(styrene-b-ethylene-co-butylene-b-styrene) polymer and the polyphenylene oxide polymer. Since the poly(styrene-b-ethylene-co-butylene-b-styrene) polymer contains a halogen group and the polyphenylene oxide polymer contains a tertiary amine group, the two polymers can be easily crosslinked by a nucleophilic substitution reaction without the need for a separate crosslinking agent.

[0056] In step (c), the polyphenylene oxide 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) 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.

[0057] 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.

[0058] 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.

[0059] As described above, in the present invention, a halogen functional group is introduced into the SEBS main chain and then reacted with an amine group-containing PPO main chain to produce a crosslinked copolymer, thereby preventing reactions between SEBS and PPO and quantitatively crosslinking SEBS and PPO. Therefore, the crosslinked copolymer does not undergo phase separation during membrane production, ensuring consistent quality.

[0060] Furthermore, the method allows for the easy production of crosslinked copolymers in high yields, thereby increasing process productivity and reducing costs.

[0061] 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.

[0062] [Example] Example 1: Preparation of PPO-SEBS (70% Funct.) (1) Production of Dimethylamine-functionalized-PPO (DMA-PPO) (1-1) Production of Brominated PPO (Br-PPO) [ka] (In the above reaction formula, n is 33 and m is 34.) 5 g (1 equivalent) of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO, Asahi Kasei) and 60 mL of chlorobenzene (12 mL per 1 g of PPO) were placed in a two-neck round bottom flask equipped with a reflux condenser, purged with nitrogen, and then stirred at 50 °C to dissolve the polymer.

[0063] After the polymer was completely dissolved, a mixture of 4.0736 g (0.55 equivalents) of n-bromosuccinimide (NBS, TCI Chemical) and 0.2050 g (0.03 equivalents) of azobisisobutyronitrile (2,2'-azobisisobutyronitrile, AIBN) was added to the polymer solution.

[0064] Thereafter, the flask was heated to 135°C, and after reaching this temperature, the mixture was stirred for 4 hours and 30 minutes to carry out the reaction.

[0065] After the reaction was completed, the reaction mixture was left to cool at room temperature and added to 500 mL of methanol to precipitate the polymer. The precipitated polymer was washed with methanol about four times until the filtrate became transparent. The polymer was then filtered under reduced pressure and dried in a vacuum oven at 80°C for more than 12 hours to obtain the polymer. 1 H-NMR and IR analyses (Figure 3) confirmed that the polymer was 32.9 wt% brominated PPO (Br-PPO).

[0066] 1 H NMR(400MHz, CDCl3)δ 6.76-6.42 (33H, t, H1), 6.58-6.44 (67H, d, H2), 4.41-4.30 (35H, s, H3), 2.16-2.04 (220H, s, H4)

[0067] (1-2) Preparation of Dimethylamine-functionalized-PPO (DMA-PPO) [ka] (In the above reaction formula, n is 33 and m is 34.) 3 g (1 equivalent) of the Br-PPO polymer produced in (1) above was added to 30 mL (10 mL per 1 g of polymer) of N-methyl-2-pyrrolidone (NMP) and dissolved at a temperature of 70°C.

[0068] After the polymer was completely dissolved, 9.14 mL (3 equivalents) of dimethylamine solution (2M in THF, TCI chemicals) was added to the polymer solution, and the temperature was maintained at 70°C for 24 hours.

[0069] After the reaction was completed, the reaction mixture was left to cool at room temperature and then added to 500 mL of a mixed solution of methanol and 1 M KOH (MeOH:1 M KOH = 3:1 volume ratio) to precipitate the polymer. The precipitated polymer was washed with methanol about four times until the filtrate became transparent. The polymer was then filtered under reduced pressure and dried in a vacuum oven at 80 °C for more than 12 hours to obtain the polymer.

[0070] The obtained polymer 1 H-NMR spectrum analysis confirmed that the CHBr peak (δ ~ 4.3 ppm) completely disappeared and a CHN(CH) peak (δ ~ 3.3 ppm) was generated (Figures 4A and 5A). This confirmed that all bromo groups in Br-PPO were replaced with amines to obtain DMA-PPO.

[0071] 1 H NMR(400MHz, CDCl3)δ 6.79-6.71 (1.3H, d, H4), 6.55-6.42 (4.2H, d, H5), 3.33-3.21 (2H, s, H2), 2.22-2.14 (6H, s, H1), 2.14-2.02 (13H, s, H3)

[0072] (2) Manufacturing of Reduced-SEBS (Re-SEBS) (2-1) Preparation of Acylated-SEBS (Ac-SEBS) [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 sum of q1, q2, q5, and q6 is 0.3.) A polymer solution was prepared by adding 5 g (1 equivalent of styrene) of poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS, Kraton A1535H) and 150 mL of dichloromethane (30 mL per 1 g of polymer) to a two-neck round-bottom flask equipped with a dropping funnel and dissolving the polymer completely.

[0073] Separately, a mixture of 2.74 g (0.75 equivalents) of aluminum chloride and 3.14 mL (0.75 equivalents) of 6-bromohexanoyl chloride in 50 mL of dichloromethane was prepared and added to the loading funnel. This mixture was slowly added dropwise (80 mL over 2 hours) to the stirred polymer solution. After the addition of the mixture was complete, the mixture was stirred at room temperature for 24 hours to react.

[0074] After the reaction was completed, 800 ml of ethanol was added to the reaction mixture to precipitate the polymer. The precipitated polymer was washed twice with ethanol and then dried in a vacuum oven at room temperature for 12 hours. 1 The H-NMR and IR analysis results (Figure 6) confirmed that Ac-SEBS was obtained, in which 69 mol% of the total 100 mol% of styrene contained in SEBS was acylated.

[0075] 1 H NMR(400MHz, CDCl3)δ 7.96-7.40 (1.98H, broad peak, H 6’,7’ ), 7.25-6.30 (4.75H, broad peak, H 6-10 ), 3.53-3.38 (2.00H, t, H1), 3.07-2.79 (1.99H, broad peak, H 5,12’ ), 2.73-2.32 (0.61H, broad peak, H 12 ), 2.05-0.48 (H 2-4,11,13-18 )

[0076] (2-2) Production of Reduced-SEBS (Re-SEBS) [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 sum of q1, q2, q5, and q6 is 0.3.) 5 g of Ac-SEBS (1 equivalent of Br functional group) prepared in (3) above and 125 mL of chloroform (HPLC grade) (25 mL per 1 g of polymer) were placed in a two-necked round-bottom flask to dissolve the polymer.

[0077] After the polymer was completely dissolved, 18.83 mL (10 equivalents) of triethylsilane was added, followed by 45.11 mL (50 equivalents) of trifluoroacetic acid (TFA). A reflux condenser was attached to the flask, and the temperature was raised to 105°C. The reaction was allowed to proceed with stirring for 48 hours.

[0078] After the reaction was completed, the reaction mixture was cooled to room temperature, 150 ml of 1 M KOH aqueous solution was added, and the mixture was stirred at 500 rpm for 30 minutes. The reaction mixture was then separated using a separating funnel to obtain a lower layer (chloroform layer), which was then precipitated in 800 ml of methanol. The precipitated polymer was washed four times with methanol, and the obtained polymer was dried at room temperature in a vacuum atmosphere for 24 hours. 1 H-NMR and IR analyses confirmed that all carbonyl groups had been reduced (Figures 7 and 8).

[0079] 1 H NMR(400MHz, DMSO-d6)δ 7.23-6.22 (6.71H, broad peak, H 6-10 ), 3.48-3.33 (2H, t, H1), 2.68-2.28 (2.61H, broad peak, H 5’ ), 2.00-0.60 (30.19H, broad peak, H 2-5,11,13-18 )

[0080] (3) Production of cross-linked polymer (PPO-SEBS) [ka] (In the above reaction formula, n is 33, m is 34, 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.) DMA-PPO (1) prepared in (1) and Re-SEBS (2) prepared in (2) were added to 20 mL of chloroform, and 50 moles of DMA-PPO (relative to 100 moles of Br contained in Re-SEBS) was added and stirred at 45°C for 12 hours. After 12 hours, the completely dissolved polymer solution was dried at room temperature for 24 hours, and the precipitate was washed with distilled water for 3 hours. The washed precipitate was then placed in a 30 wt% aqueous trimethylamine solution and reacted at 45°C for 24 hours to convert the remaining Br groups to quaternary ammonium groups, producing PPO-SEBS1 copolymer.

[0081] (4) Polymer membrane production PPO-SEBS copolymer was dissolved in chloroform, poured into a cleaned Petri dish, and dried at room temperature for 24 hours to form a PPO-SEBS polymer film. The polymer film was then peeled off from the Petri dish, washed 3-4 times with distilled water, and dried at room temperature to obtain a 50 μm-thick PPO-SEBS polymer film (Figure 1).

[0082] Example 2: Preparation of PPO-SEBS (50% Funct.) PPO-SEBS was prepared in the same manner as in Example 1, except that in the preparation of Ac-SEBS in step (2-1), 50 wt% acylated Ac-SEBS was prepared using 0.55 equivalents of aluminum chloride and 0.55 equivalents of 6-bromohexanoyl chloride relative to 1 equivalent of styrene in SEBS.

[0083] Comparative Example 1: Preparation of DA-x30-PPO-SEBS [ka] (In the above reaction formula, n is 33, m is 34, 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.) The Re-SEBS prepared in Example 1(2) and the Br-PPO prepared in Example 1(1-1) were added to 100 mL of N,N,N',N'-tetramethyl-1,6-hexanediamine (N,N,N',N'-tetramethyl-1,6-hexanediamine), a crosslinker. 30 moles of Br-PPO was added per 100 moles of Br in the Re-SEBS, and the mixture was stirred at 30°C for 12 hours. After 12 hours, the completely dissolved polymer solution was dried at room temperature for 24 hours, and the precipitate was washed with distilled water for 3 hours. The washed precipitate was then placed in a 30 wt% trimethylamine aqueous solution and reacted at 40°C for 24 hours to convert the remaining Br groups to quaternary ammonium groups, producing a DA-x30-PPO-SEBS1 copolymer.

[0084] Thereafter, the DA-x30-PPO-SEBS copolymer was used to obtain a 20 μm-thick DA-x30-PPO-SEBS1 polymer membrane (FIG. 2) in the same manner as in Example 1(4).

[0085] Comparative Example 2: Preparation of DA-x30-PPO-SEBS A DA-x30-PPO-SEBS2 polymer membrane was prepared in the same manner as in Comparative Example 1.

[0086] Comparative Example 3: Production of xTQA-SEBS (70% Functional) (1) Production of Cli-PPO [ka] (In the above reaction formula, n is 33 and m is 34.) (1-1) Production of Brominated PPO (Br-PPO) 3 g of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) polymer and 36 mL of chlorobenzene were placed in a two-neck round-bottom flask equipped with a reflux condenser and stirred until the polymer was completely dissolved. Then, 2.7 g of n-bromosuccinimide (NBS) and 123 mg of azobisisobutyronitrile (AIBN) were mixed into the polymer solution. The mixture was then stirred at 130°C for 4 hours to react. After the reaction was completed, the resulting reaction mixture was poured into methanol to precipitate the polymer, which was then washed with methanol four times. The washed polymer was filtered under reduced pressure and dried in a vacuum oven at 80°C to obtain the polymer. 1 H-NMR analysis confirmed that the polymer was 32.9 wt% brominated PPO (Br-PPO).

[0087] 1 H NMR(400MHz, CDCl3)δ 6.76-6.42 (33H, t, H1), 6.58-6.44 (67H, d, H2), 4.41-4.30 (35H, s, H3), 2.16-2.04 (220H, s, H4)

[0088] (1-2) Production of N3-PPO by azidation reaction To attach the azide group, a functional group for the click reaction, to PPO, 3.5 g (8 mmol) of the synthesized Br-PPO was placed in a single-neck round-bottom flask and completely dissolved in 30 mL of N-methyl-2-pyrrolidone (NMP). Then, 2.5 g (39 mmol) of sodium azide was added to the polymer solution and stirred at 60°C for 24 hours. After 24 hours, the reaction mixture was poured into methanol to precipitate the polymer, which was then washed 3-4 times with methanol. The washed polymer was filtered under reduced pressure and dried in a vacuum oven at 80°C. 1 H NMR and IR confirmed that all bromo groups of Br-PPO were converted to azide groups, and that N3-PPO was successfully synthesized.

[0089] 1 H NMR(400MHz, CDCl3)δ 6.68-6.63 (18H, broad peak, H 3’ ), 6.49 (36H, broad peak, H3), 4.22 (20H, s, H2), 2.10 (135H, broad peak, H1)

[0090] (1-3) Preparation of Cli-PPO by Click reaction To introduce triazole groups capable of hydrogen bonding with the tertiary amine functional groups of the PPO polymer for reaction with the SEBS polymer, 1 g (2.4 mmol) of dried N3-PPO was dissolved in 7 mL of NMP. The polymer solution, 0.381 mL (1.8 mmol) of N,N,N',N'',N''-pentamethyldiethylenetriamine (PMDTA), 131 mg (0.9 mmol) of copper(I) bromide, and 0.393 mL (3.65 mmol) of 3-dimethylamino-1-propyne were added to a Schlenk flask. The flask was then subjected to freezing and pump thawing three to four times to remove oxygen from the flask. The mixture was then stirred at 50°C for 24 hours to react. After 24 hours, the reaction mixture was poured into a 3:1 weight ratio mixture of water and methanol to precipitate the polymer, which was then washed 3-4 times with the mixture of water and methanol. The washed polymer was filtered under reduced pressure and dried in a vacuum oven at 80°C. 1 H NMR and IR confirmed that all the azide groups of N3-PPO had reacted, resulting in the successful synthesis of Cli-PPO bearing triazole and tertiary amine functional groups.

[0091] 1 H NMR(400MHz, CDCl3)δ 7.53-7.49 (10H, broad peak, H4), 6.64 (10H, broad peak, H 3’ ), 6.48 (36H, broad peak, H3), 5.37 (20H, broad peak, H2), 3.60 (20H, broad peak, H5), 2.27 (58H, broad peak, H6), 2.10 (114H, broad peak, H1)

[0092] (2) Manufacturing of Reduced-SEBS (Re-SEBS) Re-SEBS was produced in the same manner as in step (2) of Example 1.

[0093] (3) Synthesis of xTQA-PPO-SEBS copolymer [ka] (In Reaction Scheme 3, n is 33, m is 34, 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.) The Cl-PPO prepared in (1) and the Re-SEBS prepared in (2) were added to 15 mL of chloroform, and Cl-PPO was added in an amount of 50 moles relative to 100 moles of Br contained in the Re-SEBS. The mixture was stirred at 50°C for 12 hours. After 12 hours, the completely dissolved polymer solution was dried at room temperature for 24 hours, and the precipitate was washed with distilled water for 3 hours. The washed precipitate was then placed in a 30 wt% aqueous trimethylamine solution and reacted at 40°C for 24 hours to convert the remaining Br groups to quaternary ammonium groups, synthesizing the xTQA-PPO-SEBS copolymer.

[0094] (4) Polymer membrane production The xTQA-PPO-SEBS copolymer was dissolved in chloroform, poured into a cleaned Petri dish, and dried at room temperature for 24 hours to form an xTQA-PPO-SEBS polymer film. The polymer film was then peeled off from the Petri dish, washed four times with distilled water, and dried at room temperature to obtain a 40 μm-thick xTQA-PPO-SEBS polymer film.

[0095] Experimental Example 1: Evaluation of ion exchange capacity, hydroxide ion conductivity, water content, and swelling ratio (1) Measurement of ion exchange capacity (IEC) a. Experimental IEC Hydroxide ion (OH -For the exchange, a square polymer membrane (1 cm x 1 cm) was immersed in 1 M KOH solution at 20°C for 24 hours. The surface of the polymer membrane was then wiped and immersed in 10 ml of 0.01 M HCl solution for 24 hours. Three drops of 1 wt% phenolphthalein solution were added as an indicator, and the membrane was titrated with a 0.01 M NaOH standard solution.

[0096] The experimental IEC value was calculated using the following formula 1, and each sample was measured three times and the average value was calculated. [Formula 1] IEC(meq / g)=(V 0NaOH C NaOH -V xNaOH C NaOH / W dry where V 0NaOH and V xNaOH are the volume of NaOH before titration and the volume of NaOH consumed in titration, respectively, and C NaOH is the molar concentration of NaOH titrated by the oxalic acid standard solution, and W dry is the weight of the dry membrane.

[0097] b. Theoretical IEC The theoretical IEC was calculated as the product of the total molar mass of one block copolymer and the degree of functionalization.

[0098] (2) Hydroxide ion conductivity (OH - conductivity) measurement The hydroxide ion conductivity (σ) in the in-plane direction of the membrane was calculated using the following equation 2 while a square polymer membrane (1 cm × 4 cm) was immersed in water (20°C, 40°C, 60°C, or 80°C). The conductivity value was measured at least three times at the same time interval and the average value was calculated. [Formula 2] σ=L / RWd Here, L is the distance between the reference electrodes (1 cm), R is the resistance, W is the width of the polymer film (1 cm), and d is the thickness of the polymer film (cm).

[0099] Ohmic resistance (R) was measured by four-probe alternating current (ac) impedance spectroscopy using an electrode system coupled to an impedance / gain-phase analyzer (SI-1260) and an electrochemical interface (SI-1287) in the frequency range of 10–200 kHz. To minimize unwanted carbonate formation, the cells were fully immersed in degassed, demineralized water, and impedance spectra were collected rapidly.

[0100] (3) Measurement of water uptake (WU) and swelling ratio (SR) For hydroxide ion (OH-) exchange, two circular polymer membranes with a diameter of 2.23 cm were immersed in a 1 M KOH solution at 20°C for 24 h.

[0101] The polymer membrane samples were washed with distilled water to remove the KOH, and then one was immersed in distilled water at 20°C and the other in distilled water at 80°C for 1 hour. Then, each sample was taken out, the surface was wiped, and the thickness (t wet ), diameter (l wet ), and weight (W wet ) was measured. Each sample was dried in an oven at 40°C for 24 hours, and then the thickness (t dry ), diameter (l dry ), and weight (W dry ) was measured.

[0102] The water content (WU) was calculated from the change in weight using the following equation 3, and the swelling ratios (Δt and Δl) were calculated from the changes in thickness and diameter using the following equations 4 and 5. [Formula 3] WU(%)=[(W wet -W dry ) / W dry ] x 100 [Formula 4] △t(%)=[(t wet -t dry ) / t dry ] x 100 [Formula 5] △l(%)=[(l wet -ldry ) / l dry ×100

[0103] <Evaluation of the Theoretical Ion Exchange Capacity (IEC) and Hydroxide Ion Conductivity of DA-x30-PPO-SEBS Polymers> The theoretical ion exchange capacity (IEC) and hydroxide ion conductivity (OH - conductivity) of the DA-x30-PPO-SEBS polymer membranes produced in Comparative Example 1 and Comparative Example 2 were measured, and the results are shown in Table 1.

[0104] Figure 2 is a photograph of the DA-x30-PPO-SEBS polymer membrane produced in Comparative Example 1. Referring to Figure 2, it was confirmed that a phenomenon such as phase separation observable with the naked eye occurred on the surface of the formed membrane, and a polymer membrane with a very non-uniform surface was produced in part.

[0105]

Table 1

[0106] [[ID=2笑]] Referring to Table 1 above, it can be confirmed that Comparative Examples 1 and 2 were produced in the same manner but show non-reproducible results where the hydroxide ion conductivity varies beyond the error range by temperature. This is because when diamine or dihalide crosslinking agents crosslink different polymers, the reactivity of the reaction sites is not all the same, so chemical reactions occur randomly, and crosslinking can occur between SEBS polymers and SEBS polymers, or between PPO polymers and PPO polymers. As a result, phase separation is generated in the membrane, and it was found that non-reproducible data was obtained.

[0107] <Evaluation of the Ion Exchange Capacity, Hydroxide Ion Conductivity, Water Content, and Swelling Ratio of TQA-SEBS Polymers and PPO-SEBS Polymers> The ion exchange capacity, hydroxide ion conductivity, water content, and swelling ratio of the TQA-SEBS polymer prepared in Comparative Example 3 and the PPO-SEBS polymer prepared in Example 1 were measured, and the results are shown in Table 2 below.

[0108] [Table 2]

[0109] Referring to Table 2, it can be seen that the PPO-SEBS of Example 1 has excellent ion exchange capacity and significantly higher hydroxide ion conductivity and water content than those of Comparative Example 3. In the case of TQA-SEBS, the hydrogen bonds of the triazole are broken at high temperatures, but PPO-SEBS does not have this problem, which is thought to be why the conductivity of PPO-SEBS, which has a relatively high IEC despite having the same composition, is higher.

[0110] Therefore, it is expected that PPO-SEBS will exhibit higher output characteristics than TQA-SEBS under the same acylation rate and crosslinking degree conditions.

[0111] Experimental Example 2: Measurement of density and hydrogen permeability The density and hydrogen permeability of the TQA-SEBS polymer membrane prepared in Comparative Example 3 and the PPO-SEBS polymer membrane prepared in Example 1 were measured by the following methods, and the results are shown in Table 3 below.

[0112] (1) Density For density measurement, a square polymer film (2 cm × 2 cm) was dried in a vacuum oven at 40 °C for 24 hours. Then, the weight in air (W air ) and weight (W hep The density was calculated from the change in weight using the following equation 6. [Formula 6] Density (g / cm 3 )=[W air / (W air -W hep )]×D hep

[0113] (2) Hydrogen permeability The hydrogen permeability was measured using a bubble flow meter that was custom-made. 2 (A), 25 μm thick (l), was dried in a vacuum oven at 40°C for 24 hours. After that, the membrane was installed inside the cell of a custom-made bubble flow meter, the pressure inside the flow meter was fixed at 150 cmHg (P), hydrogen was injected at a rate of 200 sccm, and the hydrogen permeability was measured as the volume of bubbles moving per unit time (Vp / s) inside the bubble flow meter. The hydrogen permeability was calculated using the following equation 7. [Formula 7] Transparency (barrer)=10 -10 ×(V p(STP) ×l) / (A×s×P)

[0114] [Table 3]

[0115] Referring to Table 3, it can be seen that the PPO-SEBS of Example 1 exhibits a higher density and a lower hydrogen permeability than the TQA-SEBS of Comparative Example 3, and is therefore more suitable for producing high-purity hydrogen and oxygen when used in an ion exchange membrane for water electrolysis.

[0116] Experimental Example 3: Measurement of thermal stability The thermal stability of the TQA-SEBS polymer membrane prepared in Comparative Example 3 and the PPO-SEBS polymer membrane prepared in Example 1 was measured by thermogravimetric analysis (TGA), and the results are shown in FIG.

[0117] Thermal stability was measured using a Scinco TGA N-1000 instrument. Specifically, mass loss was measured in the temperature range of 30-800°C at a heating rate of 10°C / min under nitrogen gas.

[0118] Referring to FIG. 9, it can be seen that the PPO-SEBS polymer membrane of Example 1 exhibits thermal stability at a level equivalent to that of the existing TQA-SEBS and is thermally stable under the operating conditions of a water electrolysis device (80°C or lower), and is therefore suitable as an ion exchange membrane for water electrolysis.

[0119] Experimental Example 4: Measurement of oxidation stability The oxidation stability of the TQA-SEBS polymer membrane prepared in Comparative Example 3 and the PPO-SEBS polymer membrane prepared in Example 1 was measured by the following method, and the results are shown in FIG.

[0120] The oxidation stability was evaluated by drying the membrane in a vacuum oven at 40°C for 24 hours and measuring the weight (W Before ) and then Penton reagent (4 ppm Fe 2+ After immersing the membrane in 3 wt.% H2O2 at 60°C, the weight (W After ) was measured and the change in weight of both was measured. The mass loss was calculated using the following equation 8. [Formula 8] Oxidation stability (%) = [(W Before -W After ) / W Before ]×100(%)

[0121] 10, it can be seen that the PPO-SEBS polymer membrane of Example 1 has superior oxidation stability compared to the existing TQA-SEBS. This confirms that the polymer membrane of the present invention exhibits excellent durability even under conditions where radicals are formed, and is therefore suitable for use in water electrolysis devices.

[0122] Experimental Example 5: Measurement of mechanical properties The mechanical stability of the PPO-SEBS polymer membrane prepared in Example 1 was measured by the following method, and the results are shown in FIG.

[0123] The mechanical stability was measured using a benchtop tensile tester (Shimadzu EZ-TEST E2-L). The measurement was carried out by placing an array-shaped test piece with a total width of 1 cm × 4 cm and a test width of 1 cm × 2 cm on an OH plate. - The test was carried out at a speed of 10 mm / min under 50% RH conditions.

[0124] The measurement results showed that the tensile strength was 27.1 MPa, the elongation at break was 129.5%, and the Young's modulus was 275.5 MPa.

[0125] These results confirm that the PPO-SEBS polymer membrane of the present invention exhibits sufficient mechanical strength for use as an anion exchange membrane, and in particular, exhibits a significantly improved elongation ratio compared to existing anion exchange membranes.

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 The sum of 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, n and m are each independently an integer of 10 to 50.

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 The crosslinked copolymer according to claim 1 or claim 2, wherein each independently represents 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 any one of claims 1 to 3, wherein the total ratio of

5. q １ , q ２ , q ５ , and q ６ q for the sum of １ and q ６ The crosslinked copolymer according to any one of claims 1 to 4, wherein the total ratio of

6. The crosslinked copolymer according to any one of claims 1 to 5, wherein a and b are each independently an integer of 4 to 6.

7. 7. The crosslinked copolymer according to claim 1, wherein the ratio of n to the sum of n and m is 0.15 to 0.

70.

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

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

10. An anion exchange membrane for water electrolysis, comprising the polymer membrane according to claim 9.

11. (a) preparing a poly(styrene-b-ethylene-co-butylene-b-styrene)-based polymer represented by the following chemical formula 1-1; (b) preparing a polyphenylene oxide polymer represented by the following chemical formula 2-1; (c) crosslinking the poly(styrene-b-ethylene-co-butylene-b-styrene) polymer and the polyphenylene oxide 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 The sum of 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, n and m are each independently an integer of 10 to 50.

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

13. The method for producing a crosslinked copolymer according to claim 11 or 12, wherein the poly(styrene-b-ethylene-co-butylene-b-styrene) copolymer contains 30 to 90 moles of halogen groups per 100 moles of styrene repeating units.

14. 14. The method for producing a cross-linked copolymer according to claim 11, wherein in step (c), the polyphenylene oxide polymer is used in an amount of 10 to 70 moles per 100 moles of halogen groups contained in the poly(styrene-b-ethylene-co-butylene-b-styrene) copolymer.

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