Crosslinked copolymer, polymer membrane comprising same, and anion exchange membrane comprising polymer membrane

Abstract

The present invention relates to a cross-linked copolymer having excellent ion exchange capacity, exhibiting high ionic conductivity and water content under different temperature conditions, and having high density, low hydrogen permeability, and excellent thermal stability and oxidation stability, the anion exchange membrane can be used for producing high-purity hydrogen and oxygen through water electrolysis.

Description

Technical Field

[0001] Cross - Reference to Related Applications

[0002] This application claims priority to Korean Patent Application No. 10-2022-0150712, filed on November 11, 2022, the entire disclosure of which is incorporated herein by reference.

[0003] The present disclosure relates to a crosslinked copolymer, a polymer film including the crosslinked copolymer, and an anion exchange membrane including the polymer film. Background Art

[0004] Hydroelectrolysis technology using water electrolysis does not generate greenhouse gases, uses water as an almost unlimited raw material, and can achieve large-capacity and long-term surplus power storage when combined with renewable energy. A water electrolysis device consists of electrodes that generate hydrogen and oxygen and an ion exchange membrane that prevents gas mixing and allows ion migration. Among these components, the ion exchange membrane is a key component that determines the efficiency and stability of the water electrolysis device.

[0005] Low-temperature water electrolysis technologies include alkaline water electrolysis, polymer electrolyte membrane water electrolysis, and anion exchange membrane water electrolysis. Among them, anion exchange membrane water electrolysis is considered an ideal water electrolysis technology that combines the advantages of alkaline water electrolysis and polymer electrolyte membrane water electrolysis. The structure of anion exchange membrane water electrolysis is similar to that of polymer electrolyte membrane water electrolysis, allowing high-pressure and pressure-difference operations, capable of operating at high current densities, and enabling a compact system design. Different from polymer electrolyte membrane water electrolysis, anion exchange membrane water electrolysis operates in an alkaline environment, so non-noble metal catalysts can be used, thereby reducing material costs and facilitating economically competitive green hydrogen production. Anion exchange membrane water electrolysis is still in the research and development stage. To achieve commercialization, problems related to low ionic conductivity of the anion exchange membrane and the performance and reliability of non-noble metal catalysts must be overcome.

[0006] Meanwhile, poly(styrene-ethylene-co-butene-styrene) (hereinafter referred to as "SEBS") is a triblock copolymer that has been widely used as a polymer material for anion exchange membranes because of its excellent morphological structure as a block copolymer, which gives it high ionic conductivity, and its high alkaline stability due to its non-aromatic ether polymer structure.

[0007] However, for SEBS-based anion exchange membranes, when the ion exchange capacity (IEC) increases, due to the elasticity of SEBS, the water content and swelling ratio increase sharply, and the resulting dilution effect actually reduces the conductivity. In addition, the high water absorption rate, swelling ratio, and low tensile strength greatly reduce the mechanical and physical stability of the membrane, making the membrane very difficult to handle.

[0008] One attempt to solve these problems was to use N,N,N',N'-tetramethyl-1,6-hexanediamine as a crosslinking agent to crosslink SEBS polymer and polyphenylene ether polymer, thereby obtaining a polymer (J. Membr. Sci. 564 (2018), 492 - 500). However, since the reaction sites in the crosslinking agent and the two polymers are exactly the same, it is impossible to adjust the 1:1 reaction between the SEBS polymer and the polyphenylene ether polymer, resulting in phase separation and the formation of an uneven membrane with non-reproducible hydroxide ion conductivity.

[0009] To solve this problem, a crosslinked polymer was developed, which is formed by crosslinking SEBS polymer with a polyphenylene ether polymer containing triazole groups and amine groups without introducing an additional crosslinking agent (Korean Patent No. 10 - 2184530). However, the synthesis process of this crosslinked polymer is complex, and it lacks sufficient high-temperature hydroxide ion conductivity and water content required for water electrolysis cells.

[0010] [Prior Art Documents]

[0011] (Patent Document 1) Korean Patent No. 10 - 2184530

[0012] (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

[0013] Technical Problem

[0014] The present disclosure relates to a novel crosslinked copolymer having excellent hydroxide ion conductivity and water content, as well as outstanding thermal stability and oxidation stability, and being suitable for use as an anion exchange membrane for water electrolysis.

[0015] Technical Solution

[0016] According to an embodiment of the present disclosure, 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:

[0017] [Chemical Formula 1]

[0018]

[0019] In Chemical Formula 1,

[0020] * represents the bonding position with Chemical Formula 2,

[0021] The sum of q1, q2, q5, and q6 is an integer from 100 to 1,000,

[0022] The sum of q3 and q4 is an integer from 150 to 2,000,

[0023] a and b are each independently an integer from 3 to 10,

[0024] R1 to R4 are each independently hydrogen or –(CH2) p –CH3, where p is an integer from 0 to 5;

[0025] [Chemical Formula 2]

[0026]

[0027] In Chemical Formula 2,

[0028] * represents the bonding position with Chemical Formula 1,

[0029] n and m are each independently an integer from 10 to 50.

[0030] Furthermore, according to an embodiment of the present disclosure, a method for preparing a crosslinked copolymer is provided, including:

[0031] (a) preparing a poly(styrene-b-ethylene-co-butene-b-styrene) polymer represented by the following Chemical Formula 1-1;

[0032] (b) preparing a polyphenylene ether-based polymer represented by the following Chemical Formula 2-1; and

[0033] (c) crosslinking the poly(styrene-b-ethylene-co-butene-b-styrene) polymer with the polyphenylene ether-based polymer to obtain the crosslinked copolymer:

[0034] [Chemical Formula 1-1]

[0035]

[0036] In Chemical Formula 1-1,

[0037] The sum of q1, q2, q5, and q6 is an integer from 100 to 1,000,

[0038] The sum of q3 and q4 is an integer from 150 to 2,000,

[0039] a and b are each independently an integer from 3 to 10,

[0040] R1 to R4 are each independently hydrogen or -(CH2) p –CH3, p is an integer from 0 to 5,

[0041] X1 and X2 are each independently a halogen group;

[0042] [Chemical formula 2-1]

[0043]

[0044] In chemical formula 2-1,

[0045] n and m are each independently an integer of 10 to 50.

[0046] Beneficial Effects

[0047] The cross-linked copolymer disclosed in the present invention has excellent ion exchange capacity, exhibits high ion conductivity and water content in a wide temperature range, and has high density and low hydrogen permeability. In addition, the cross-linked copolymer exhibits excellent thermal stability and oxidative stability under the operating conditions of the water electrolysis device, and can therefore be suitable for use as an anion exchange membrane for producing high-purity hydrogen and oxygen. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 is a photograph of the polymer film prepared from PPO-SEBS in Example 1.

[0049] Figure 2 This is a photograph of the polymer film prepared from DA-x30-PPO-SEBS in Comparative Example 1.

[0050] FIG. 3 shows the Br-PPO prepared in step (1-1) of Example 1. 1 H-NMR spectrum (a) and IR spectrum (b).

[0051] Figure 4 shows the DMA-PPO prepared in step (1-2) of Example 1. 1 H-NMR spectrum (a) and IR spectrum (b).

[0052] Figure 5 The Br-PPO prepared in step (1-1) and the DMA-PPO prepared in step (1-2) in Example 1 were compared. 1 H-NMR and IR spectra.

[0053] Figure 6 shows the Ac-SEBS prepared in step (2-1) of Example 1.1 1H-NMR spectrum (a) and IR spectrum (b).

[0054] Figure 7 shows the 1 1H-NMR spectrum (a) and IR spectrum (b) of the Re-SEBS prepared in step (2-2) of Example 1.

[0055] Figure 8 The 1H-NMR and IR spectra of the Ac-SEBS prepared in step (2-1) and the Re-SEBS prepared in step (2-2) of Example 1 were compared. 1 1H-NMR and IR spectra.

[0056] Figure 9 Shows the thermogravimetric analysis results of the PPO-SEBS of Example 1 and the TQA SEBS of Comparative Example 3.

[0057] Figure 10 Shows the oxidation stability test results of the PPO-SEBS of Example 1 and the TQA SEBS of Comparative Example 3.

[0058] Figure 11 Shows the tensile strength and elongation measurement results of the PPO-SEBS of Example 1. Detailed Description of the Invention

[0059] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. Unless otherwise clearly specified in the context, the singular forms also include the plural forms.

[0060] It should also be understood that when the terms "comprising", "including" or "having" are used in this disclosure, it means the presence of the described features, steps, components or combinations thereof, but does not exclude the presence or addition of one or more other features, steps, components or combinations thereof.

[0061] Since the present invention can be modified in various ways and has various forms, specific embodiments thereof are shown by way of example only and are described in detail. However, this does not mean that the present invention is limited to the specific forms disclosed, and it should be understood that the present invention includes all modifications, equivalents and alternatives within its concept and technical scope.

[0062] The present invention will be described in detail below.

[0063] According to an embodiment of the present disclosure, a crosslinked copolymer is provided, which comprises a first chain represented by the following Chemical Formula 1 and a second chain represented by the following Chemical Formula 2, wherein the first chain and the second chain are crosslinked with each other:

[0064] [Chemical Formula 1]

[0065]

[0066] In Chemical Formula 1,

[0067] * represents the bonding position with Chemical Formula 2,

[0068] The sum of q1, q2, q5, and q6 is an integer from 100 to 1,000,

[0069] The sum of q3 and q4 is an integer from 150 to 2,000,

[0070] a and b are each independently an integer from 3 to 10,

[0071] R1 to R4 are each independently hydrogen or –(CH2) p –CH3, where p is an integer from 0 to 5;

[0072] [Chemical Formula 2]

[0073]

[0074] In Chemical Formula 2,

[0075] * represents the bonding position with Chemical Formula 1,

[0076] n and m are each independently integers between 10 and 50.

[0077] The crosslinked copolymer of the present disclosure has the following structure: the first chain contains poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS), the second chain contains polyphenylene oxide (PPO), and the two are crosslinked through an alkylamine group.

[0078] Due to this structural feature, the crosslinked copolymer exhibits high ion exchange capacity, hydroxide ion conductivity, water content, and swelling ratio. Compared with traditional ion exchange membranes, the crosslinked copolymer has a higher density and a lower hydrogen gas permeability, making it suitable for use as an anion exchange membrane for water electrolysis designed to produce high-purity hydrogen and oxygen. In addition, the polymer chain of the crosslinked copolymer does not contain triazole aromatic functional groups, giving it excellent oxidation stability and enabling long-term stable use in a water electrolysis cell.

[0079] The ratio of the first chain shown in Chemical Formula 1 to the second chain shown in Chemical Formula 2 can be adjusted according to the desired physical properties. For example, based on 100 moles of the first chain, the crosslinked copolymer may contain more than 10 moles, more than 20 moles, more than 30 moles, more than 40 moles, and less than 70 moles, less than 60 moles, less than 50 moles of the second chain. If, based on 100 moles of the first chain, the second chain is less than 10 moles, mechanical properties such as tensile strength may decrease; if, based on 100 moles of the first chain, the second chain exceeds 70 moles, the mechanical properties remain excellent, but the hydroxide ion conductivity and alkaline stability may decrease.

[0080] In this specification, q1 to q6, a, b, n, and m represent the number of repeating units.

[0081] Preferably, the sum of q1, q2, q5, and q6 can be 100 or more, 150 or more, 200 or more, 250 or more, 300 or more, 350 or more, 400 or more, 450 or more, or 500 or more, and is an integer of 1000 or less, 950 or less, 900 or less, 850 or less, or 800 or less.

[0082] Preferably, the sum of q3 and q4 can be 150 or more, 200 or more, 250 or more, 300 or more, 350 or more, 400 or more, 450 or more, 500 or more, 550 or more, or 600 or more, and is an integer of 2,000 or less, 1,800 or less, 1,600 or less, 1,500 or less, 1,400 or less, 1,200 or less, or 1,000 or less.

[0083] Preferably, q1 to q6 can each independently be 10 or more, 20 or more, 25 or more, or 30 or more, and is an integer of 500 or less, 450 or less, 400 or less, 350 or less, or 300 or less.

[0084] Preferably, the ratio of the sum of q1, q2, q5, and q6 to the sum of q1 to q6 in Chemical Formula 1, that is, the total mole fraction of styrene-derived repeating units relative to all repeating units, can be 0.2 or more, 0.25 or more, or 0.3 or more, and is 0.5 or less, or 0.45 or less.

[0085] Preferably, the ratio of the sum of q1 and q6 to the sum of q1, q2, q5, and q6 in Chemical Formula 1, that is, the total mole fraction of unsubstituted styrene repeating units relative to all styrene-derived repeating units, can be 0.2 or more, 0.25 or more, 0.3 or more, or 0.35 or more, and is 0.5 or less, 0.45 or less, or 0.4 or less.

[0086] Preferably, n is an integer from 10 to 50, and m is an integer from 25 to 45.

[0087] Preferably, the ratio of n to (n + m) is between 0.15 and 0.70, or between 0.18 and 0.66.

[0088] Preferably, a and b are each independently an integer of at least 3 or 4 and at most 10, 9, 8, 7, or 6.

[0089] Preferably, R1 to R4 are each independently hydrogen or –(CH2) x –CH3, where x is from 0 to 3 or from 0 to 2. Preferably, R1 to R4 are all hydrogen.

[0090] Specifically, the crosslinked copolymer may comprise the structure shown in Chemical Formula 3 below:

[0091] [Chemical Formula 3]

[0092]

[0093] In Chemical Formula 3, q1 to q6, a, b, n, and m are defined as in Chemical Formulas 1 and 2 above.

[0094] More preferably, the crosslinked copolymer may comprise the structure shown in Chemical Formula 4 below:

[0095] [Chemical Formula 4]

[0096]

[0097] In Chemical Formula 4, q1 to q6, a, b, n, and m are defined as in Chemical Formulas 1 and 2 above.

[0098] The above crosslinked copolymer has a positively charged quaternary ammonium group and can selectively allow only anions to pass through. Therefore, the crosslinked copolymer can be used as an anion exchange membrane. The counterion (anion) group of the cation (quaternary ammonium group) of the crosslinked copolymer can be OH - , Cl - , Br - or HCO3 - , preferably OH - .

[0099] Therefore, in one embodiment of the present disclosure, a polymer membrane comprising the above crosslinked copolymer is provided.

[0100] The thickness of the polymer membrane comprising the crosslinked copolymer can be 20 μm or more, 30 μm or more, 45 μm or more, or 55 μm or more, and 70 μm or less, 60 μm or less, or 55 μm or less. If the membrane thickness is less than 20 μm, the hydrogen permeability may increase sharply, making it difficult to apply to the production of high-purity hydrogen. Conversely, if the thickness exceeds 70 μm, the mechanical properties may still be excellent, but the increase in thickness will lead to an increase in resistance, thereby reducing the hydroxide ion conductivity and resulting in a decrease in current density and power density.

[0101] The ion exchange capacity (IEC) of the polymer membrane can be 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. However, the ion exchange capacity of the polymer membrane is not limited to the above range because it depends on the molar ratio of the first chain to the second chain.

[0102] A polymer membrane containing the above crosslinked copolymer containing a first chain and a second chain can provide higher output characteristics when used in a water electrolysis cell. In addition, the polymer membrane has a high density and a low hydrogen gas permeability, which is beneficial for the preparation of high-purity hydrogen and oxygen.

[0103] Therefore, a polymer membrane exhibiting such characteristics can be suitably used as an anion exchange membrane for water electrolysis.

[0104] The measurement methods of ion exchange capacity, hydroxide ion conductivity, water content, swelling ratio, hydrogen gas permeability, and density will be described in detail in the following examples.

[0105] Meanwhile, according to an embodiment of the present disclosure, a method for preparing the above crosslinked copolymer is provided. Specifically, the method includes:

[0106] (a) preparing a poly(styrene-b-ethylene-co-butylene-b-styrene) polymer represented by the following Chemical Formula 1-1;

[0107] (b) preparing a polyphenylene ether-based polymer represented by the following Chemical Formula 2-1; and

[0108] (c) crosslinking the poly(styrene-b-ethylene-co-butylene-b-styrene) polymer with the polyphenylene ether-based polymer to form the crosslinked copolymer.

[0109] [Chemical Formula 1-1]

[0110]

[0111] In Chemical Formula 1-1,

[0112] the sum of q1, q2, q5, and q6 is an integer from 100 to 1,000,

[0113] the sum of q3 and q4 is an integer from 150 to 2,000,

[0114] a and b are each independently an integer from 3 to 10,

[0115] R1 to R4 are each independently hydrogen or –(CH2) p –CH3, and p is an integer from 0 to 5,

[0116] X1 and X2 are each independently a halogen group;

[0117] [Chemical Formula 2-1]

[0118]

[0119] In Chemical Formula 2-1,

[0120] n and m are each independently an integer from 10 to 50.

[0121] The preferred ranges of q1 to q6, a, b, R1 to R4, n and m in Chemical Formulas 1-1 and 2-1 are the same as those described in Chemical Formulas 1 and 2 above.

[0122] X1 and X2 are each independently F, Cl, Br or I, preferably Br.

[0123] Step (a): Introduce a haloalkyl 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 the Friedel-Crafts acylation reaction of SEBS, followed by reduction of the resulting carbonyl group.

[0124] The selection of the acyl halide used in the acylation reaction needs to consider the numbers of a and b. Specifically, an alkanoyl chloride with a halogen group at the end of the alkyl chain represented by X-R-COCl (where X is a halogen and R is an alkyl group) can be used as the acyl halide. When a and b are different or X1 and X2 are different, the acylation reaction can be carried out more than twice using different types of acyl halides. 1-29 When a and b are different or X1 and X2 are different, the acylation reaction can be carried out more than twice using different types of acyl halides.

[0125] The acylation reaction can use aluminum chloride (AlCl3) as a catalyst, and the reaction can be carried out at 20 to 30 °C for 8 to 24 hours.

[0126] The reduction reaction of the carbonyl group can be carried out using methods known in the art, but is not limited thereto. For example, the carbonyl group can be reduced by adding triethylsilane and trifluoroacetic acid, and then reacting at 90 to 120 °C for 20 to 30 hours. Through this reaction, the polymer based on poly(styrene-b-ethylene-co-butylene-b-styrene) represented by Chemical Formula 1-1 can be obtained.

[0127] Preferably, based on every 100 moles of styrene repeating units, the copolymer based on poly(styrene-b-ethylene-co-butylene-b-styrene) contains more than 30 moles, more than 40 moles, more than 50 moles, more than 55 moles, or more than 60 moles, 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. The molar number of the halogen groups relative to the styrene repeating units can be adjusted by adjusting the molar number of the acyl halide relative to the molar number of styrene in the SEBS polymer during the acylation reaction.

[0128] Step (b): Prepare a polyphenylene ether-based polymer having a tertiary amino group. For example, the benzyl site of poly(2,6-dimethyl-1,4-phenylene ether) can be brominated to obtain a brominated polyphenylene ether polymer, and then an amination reaction can be carried out.

[0129] Bromination can be carried out using bromine (Br2) or N-bromosuccinimide (NBS). The reaction temperature can be, for example, 120 to 140 °C, and the reaction time can be 3 to 5 hours.

[0130] Next, the polymer based on brominated polyphenylene ether thus obtained is reacted with dimethylamine to obtain a polymer based on polyphenylene ether represented by Chemical Formula 2-1. The amination reaction can be carried out at 50 to 100 °C for 12 to 24 hours.

[0131] Step (c) includes reacting a poly(styrene-b-ethylene-co-butene-b-styrene) polymer with a polymer based on polyphenylene ether. Since the poly(styrene-b-ethylene-co-butene-b-styrene) polymer contains halogen atoms and the polymer based on polyphenylene ether contains tertiary amine groups, they can be easily crosslinked by a nucleophilic substitution reaction without a separate crosslinking agent.

[0132] In step (c), based on 100 moles of the halogen groups contained in the poly(styrene-b-ethylene-co-butene-b-styrene) polymer, the amount of the polymer based on polyphenylene ether is preferably 10 moles or more, 20 moles or more, 30 moles or more, or 40 moles or more, and 70 moles or less, 60 moles or less, or 50 moles or less. The crosslinked polymer prepared in this molar ratio can have a suitable ratio of the first chain to the second chain, thereby exhibiting excellent hydroxide ion conductivity and mechanical properties.

[0133] The reaction in step (c) can be carried out at 40 to 60 °C for 10 to 16 hours, preferably at 45 to 55 °C for 11 to 13 hours. If the reaction temperature is lower than 40 °C or the reaction time is shorter than 10 hours, insufficient crosslinking may reduce the hydroxide ion conductivity and alkaline stability. On the contrary, if the reaction temperature exceeds 60 °C or the reaction time exceeds 16 hours, excessive crosslinking may cause gelation of the crosslinked polymer solution.

[0134] Optionally, after step (c), step (d) can be further carried out, which is to react the crosslinked copolymer with trimethylamine to convert all remaining halogen atoms into amino groups. For example, step (d) can be carried out at 40 to 60 °C for 10 to 30 hours, preferably at 45 to 55 °C for 20 to 30 hours.

[0135] In the present disclosure, SEBS is functionalized to contain a halogen moiety, which reacts with an amino group-containing PPO chain to form a crosslinked copolymer. This prevents the reaction between SEBS chains themselves or between PPO chains themselves and allows quantitative crosslinking between SEBS and PPO. Therefore, phase separation does not occur during the membrane preparation process, thereby achieving consistent and reproducible quality.

[0136] In addition, this method can produce cross-linked copolymers more simply and with high yields, thereby improving production efficiency and reducing costs.

[0137] The present invention will be described in more detail below through examples. However, the following examples are only used to illustrate the present invention, and the scope of the present invention is not limited thereto.

[0138] [Examples]

[0139] Example 1: Preparation of PPO-SEBS (70% functionalized)

[0140] (1) Preparation of dimethylamine-functionalized PPO (DMA-PPO)

[0141] (1-1) Preparation of brominated PPO (Br-PPO)

[0142]

[0143] (In the above reaction formula, n is 33 and m is 34.)

[0144] 5 g (1 equivalent) of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO, Asahi Kasei) and 60 mL of chlorobenzene (12 mL of chlorobenzene is added per 1 g of PPO) were added to a two-necked round-bottom flask equipped with a reflux condenser. Nitrogen was introduced into the flask, and the mixture was stirred at 50 °C until the polymer was completely dissolved.

[0145] After confirming that the polymer was completely dissolved, a mixture of 4.0736 g (0.55 equivalent) of N-bromosuccinimide (NBS, TCI Chemical) and 0.2050 g (0.03 equivalent) of 2,2'-azobisisobutyronitrile (AIBN) was added to the polymer solution.

[0146] Next, the flask was heated to 135 °C and the reaction was stirred at this temperature for 4.5 hours.

[0147] After the reaction was completed, the reaction mixture was cooled to room temperature, and 500 mL of methanol was added to precipitate the polymer. The precipitated polymer was washed with methanol about four times until the filtrate became transparent. Then the polymer was recovered by vacuum filtration and dried in a vacuum oven at 80 °C for at least 12 hours to obtain the polymer. Through 1 1H-NMR and IR analysis (Figure 3) confirmed that the polymer was PPO brominated to 32.9 wt% (Br-PPO).

[0148] 11H NMR (400 MHz, 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)

[0149] Preparation of (1 - 2) dimethylamine - functionalized PPO (DMA - PPO)

[0150]

[0151] (In the above reaction formula, n is 33 and m is 34.)

[0152] Dissolve 3 g (1 equivalent) of the Br - PPO polymer obtained in the above step (1) in 30 mL of N - methyl - 2 - pyrrolidone (NMP, 10 mL of NMP is added per 1 g of the polymer) at 70 °C.

[0153] After confirming complete dissolution, add 9.14 mL (3 equivalents) of dimethylamine solution (2 M THF solution, TCI chemicals), and stir the mixture at 70 °C for 24 hours.

[0154] After the reaction is completed, cool the mixture to room temperature, and then precipitate it in a 500 mL methanol / 1 M KOH mixed solution (MeOH:1 M KOH = 3:1, volume ratio). The precipitated polymer is washed with methanol about 4 times until the filtrate is clear. Then, the polymer is recovered by vacuum filtration and dried in a vacuum oven at 80 °C for at least 12 hours.

[0155] Perform 1 1H - NMR analysis on the obtained polymer. The results show that the CH2Br peak (δ ∼ 4.3 ppm) completely disappears, and a CH2N(CH3)2 peak (δ ∼ 3.3 ppm) is formed (Figure 4(a) and Figure 5 (a) of ), indicating that the bromine in Br - PPO is completely replaced by amine to form DMA - PPO.

[0156] 1 1H NMR (400 MHz, 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)

[0157] Preparation of (2) reduced SEBS (Re - SEBS)

[0158] Preparation of (2 - 1) acylated SEBS (Ac - SEBS)

[0159]

[0160] (In the reaction formula, the sum of q1, q2, q5, and q6 is 711, the sum of q3 and q4 is 996, and the ratio of (q1 + q6) to the sum of q1, q2, q5, and q6 is 0.3.)

[0161] 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 of dichloromethane per 1 g of polymer) were added to a two-necked round-bottom flask equipped with a dropping funnel. The polymer was completely dissolved to obtain a polymer solution.

[0162] Separately, 2.74 g (0.75 equivalent) of aluminum chloride and 3.14 mL (0.75 equivalent) of 6-bromohexanoyl chloride were dissolved in 50 mL of dichloromethane to form a mixed solution, which was placed in the dropping funnel. The mixed solution was added dropwise to the stirred polymer solution (80 mL in total) over at least two hours. After the addition was completed, the reaction was stirred at room temperature for 24 hours.

[0163] At the end of the reaction, 800 mL of ethanol was added to precipitate the polymer. The precipitated polymer was washed twice with ethanol and then dried in a vacuum drying oven at room temperature for 12 hours. 1 1H-NMR and IR analyses (Figure 6) confirmed that 69 mol% of the styrene units in SEBS were acylated to form Ac-SEBS.

[0164] 1 1H NMR (400 MHz, 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 )

[0165] (2-2) Preparation of Reduced SEBS (Re-SEBS)

[0166]

[0167] (In the reaction formula, the sum of q1, q2, q5, and q6 is 711, the sum of q3 and q4 is 996, and the ratio of (q1 + q6) to the total of q1, q2, q5, and q6 is 0.3.)

[0168] Add 5 g (1 equivalent of Br group) of the Ac-SEBS prepared in step (3) and 125 mL of chloroform (25 mL of chloroform is added per 1 g of polymer) to a two-necked round-bottom flask to dissolve the polymer.

[0169] After confirming complete dissolution, add 18.83 mL (10 equivalents) of triethylsilane, and then add 45.11 mL (50 equivalents) of trifluoroacetic acid (TFA). Connect a reflux condenser to the flask, heat to 105 °C and stir for 48 hours.

[0170] After the reaction is completed, cool the mixture to room temperature, add 150 mL of 1 M KOH, and stir at 500 rpm for 30 minutes. Then, separate the reaction mixture in a separatory funnel. Collect the lower layer (chloroform layer) and precipitate it in 800 mL of methanol. Wash the precipitated polymer 4 times with methanol, and vacuum dry the washed polymer at room temperature for 24 hours. 1 1H-NMR and IR analyses confirmed that the carbonyl group had been completely reduced (Figure 7 and Figure 8 ).

[0171] 1 1H NMR (400 MHz, 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 )

[0172] (3) Preparation of crosslinked polymer (PPO-SEBS)

[0173]

[0174] (In the reaction formula, the sum of q1, q2, q5 and q6 is 711, the sum of q3 and q4 is 996, and the ratio of (q1 + q6) to the total of q1, q2, q5, q6 is 0.3.)

[0175] Add the DMA-PPO(1) prepared in step (1) and the Re-SEBS(2) prepared in step (2) to 20 mL of chloroform, and add 50 moles of DMA-PPO per mole of Br in 100 moles of Re-SEBS. Stir the mixture at 45 °C for 12 hours. After 12 hours, dry the completely dissolved polymer solution at room temperature for 24 hours, and wash the obtained precipitate in distilled water for 3 hours. Place the washed precipitate in a 30 wt% aqueous solution of trimethylamine at 45 °C for 24 hours to replace the remaining bromine groups with quaternary ammonium groups, thereby obtaining the PPO-SEBS1 copolymer.

[0176] (4) Preparation of the polymer film

[0177] Dissolve the PPO-SEBS copolymer in chloroform to obtain a PPO-SEBS copolymer solution, and then pour it into a clean petri dish and dry it at room temperature for 24 hours to form a PPO-SEBS polymer film. Peel the film from the petri dish, wash it three to four times with distilled water, and then dry it at room temperature to obtain a PPO-SEBS polymer film with a thickness of 50 μm( Figure 1 ).

[0178] Example 2: Preparation of PPO-SEBS (50% functionality)

[0179] The preparation method of PPO-SEBS is the same as that of Example 1, except that in step (2-1), 0.55 equivalents of aluminum chloride and 0.55 equivalents of 6-bromohexanoyl chloride are used for each equivalent of styrene in SEBS, so that 50 wt% of the styrene moiety is acylated.

[0180] Comparative Example 1: Preparation of DA-x30-PPO-SEBS

[0181]

[0182] (In the 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 (q1+q6) to the total sum of q1, q2, q5, q6 is 0.3.)

[0183] Add the Re-SEBS obtained in step (2) of Example 1 and the Br-PPO obtained in step (1-1) of Example 1 to 100 mL of the crosslinking agent N,N,N',N'-tetramethyl-1,6-hexanediamine. Add 30 moles of Br-PPO for every mole of Br in 100 moles of Re-SEBS, and stir the mixture at 30 °C for 12 hours. After 12 hours, dry the completely dissolved polymer solution at room temperature for 24 hours, and wash the obtained precipitate in distilled water for 3 hours. Then place the washed precipitate in a 30 wt% aqueous solution of trimethylamine at 40 °C and let it stand for 24 hours to convert the remaining Br groups into quaternary ammonium groups, thereby preparing the DA-x30-PPO-SEBS1 copolymer.

[0184] Using this DA-x30-PPO-SEBS1 copolymer, prepare a DA-x30-PPO-SEBS1 polymer film with a thickness of 20 μm in the same manner as in step (4) of Example 1( Figure 2 ).

[0185] Comparative Example 2: Preparation of DA-x30-PPO-SEBS

[0186] The DA-x30-PPO-SEBS2 polymer film was prepared in the same manner as in Comparative Example 1.

[0187] Comparative Example 3: Preparation of xTQA-SEBS (70% functionality)

[0188] (1) Preparation of Cli-PPO

[0189]

[0190] (In the reaction formula, n is 33 and m is 34.)

[0191] (1-1) Preparation of brominated PPO (Br-PPO)3

[0192] 3 g of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and 36 mL of chlorobenzene were added to a two-necked round-bottom flask equipped with a reflux condenser. The mixture was stirred until the polymer was completely dissolved. Next, 2.7 g of N-bromosuccinimide (NBS) and 123 mg of azobisisobutyronitrile (AIBN) were added to the polymer solution. The mixture was stirred at 130 °C for 4 hours. After the reaction was completed, the mixture was precipitated in methanol. The precipitated polymer was washed with methanol about 4 times, recovered by vacuum filtration, and dried in a vacuum drying oven at 80 °C. It was confirmed by 1 1H-NMR that 32.9 wt% of PPO had been brominated to form Br-PPO.

[0193] 1 1H NMR (400 MHz, 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)

[0194] (1-2) Preparation of N3-PPO by azidation

[0195] To introduce an azide group (a functional group for click reaction) into PPO, 3.5 g (8 mmol) of the above-prepared Br-PPO was completely dissolved in 30 mL of N-methyl-2-pyrrolidone (NMP) in a single-necked round-bottom flask. Then, 2.5 g (39 mmol) of sodium azide was added at 60 °C, and the mixture was stirred for 24 hours. After 24 hours, the reaction mixture was precipitated in methanol; the precipitated polymer was washed with methanol about three to four times. The polymer was separated by vacuum filtration and dried in a vacuum oven at 80 °C. It was confirmed by 1 1H-NMR and IR analyses that the bromine in Br-PPO had been completely converted to azide groups, thus forming N3-PPO.

[0196] 1 1H NMR (400 MHz, 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)

[0197] (1 - 3) Preparation of Cli - PPO by click reaction

[0198] To introduce tertiary amine groups and hydrogen - bond - forming triazole groups into the PPO polymer to react with SEBS, in a Schlenk flask, 1 g (2.4 mmol) of dry N3 - PPO was dissolved in 7 mL of NMP. Then, 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. Oxygen was removed from the flask by three to four freeze–pump–thaw cycles. The mixture was stirred at 50 °C for 24 h. After completion, the reaction mixture was precipitated in a 3:1 mixture of water and methanol, and the precipitated polymer was washed three to four times with the same water - methanol mixture. The washed polymer was separated by vacuum filtration and dried in a vacuum oven at 80 °C. 1 1H - NMR and IR analyses confirmed that the azide groups in N3 - PPO had fully reacted to form triazole groups and tertiary amine groups, thus obtaining Cli - PPO.

[0199] 1 1H NMR (400 MHz, 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)

[0200] (2) Preparation of reduced SEBS (Re - SEBS)

[0201] The preparation method of Re - SEBS was the same as that of step (2) in Example 1.

[0202] (3) Synthesis of xTQA - PPO - SEBS copolymer

[0203]

[0204] (In Reaction Formula 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 (q1 + q6) to the total sum of q1, q2, q5, and q6 is 0.3.)

[0205] Dissolve the Cli-PPO prepared in step (1) and the Re-SEBS prepared in step (2) in 15 mL of chloroform, add 50 moles of Cli-PPO for every 100 moles of Br groups in Re-SEBS, and stir at 50 °C for 12 hours. After 12 hours, dry the completely dissolved polymer solution at room temperature for 24 hours, and wash the precipitate with distilled water for 3 hours. Then place the washed precipitate in a 30 wt% aqueous solution of trimethylamine at 40 °C and let it stand for 24 hours to convert the remaining Br groups into quaternary ammonium salt groups, thereby obtaining the xTQA-PPO-SEBS copolymer.)

[0206] (4) Preparation of Polymer Membrane

[0207] Pour the chloroform solution of the xTQA-PPO-SEBS copolymer into a clean petri dish and dry it at room temperature for 24 hours to form the xTQA-PPO-SEBS polymer membrane. Peel the membrane from the petri dish, wash it 4 times with distilled water, and dry it at room temperature to obtain the xTQA-PPO-SEBS polymer membrane with a thickness of 40 μm.)

[0208] Experimental Example 1: Evaluation of Ion Exchange Capacity, Hydroxide Ion Conductivity, Water Content, and Swelling Ratio

[0209] (1) Measurement of Ion Exchange Capacity (IEC)

[0210] a. Experimental IEC

[0211] For hydroxide ion (OH - ) exchange, immerse a square polymer membrane sample (1 cm × 1 cm) in a 1 M KOH solution at 20 °C for 24 hours. Blot the surface of the polymer membrane dry, place the membrane in 10 mL of 0.01 M HCl solution and let it stand for 24 hours. Then, add 3 drops of 1 wt% phenolphthalein indicator solution and titrate the sample with 0.01 M NaOH standard solution.)

[0212] Calculate the experimental IEC value using the following formula (1). Each sample is measured three times and the average value is calculated.)

[0213] [Formula 1]

[0214] IEC (meq / g) = (V 0NaOH C NaOH - V xNaOH C NaOH ) / W dry

[0215] Among them, V 0NaOH is the volume of NaOH before titration, and V xNaOH is the volume of NaOH consumed during titration. C NaOH is the molar concentration of NaOH determined by titration with a standard oxalic acid solution, and W dry is the weight of the dry film.

[0216] b. Theoretical IEC

[0217] The theoretical IEC is calculated by multiplying the total molecular weight of the entire block copolymer by the degree of functionalization.

[0218] (2) Hydroxide ion conductivity (OH - conductivity) measurement

[0219] Immerse a rectangular membrane sample (1 cm × 4 cm) in water at 20 °C, 40 °C, 60 °C, or 80 °C, and determine the in-plane hydroxide ion conductivity (σ) according to the following formula (2). Measure the conductivity at least three times at constant time intervals and take the average value.

[0220] [Formula 2]

[0221] σ = L / RWd

[0222] Among them, L is the distance between the reference electrodes (1 cm), R is the resistance, W is the membrane width (1 cm), and d is the membrane thickness (cm).

[0223] Use a frequency / gain phase analyzer (SI-1260) and an electrochemical interface analyzer (SI-1287) to measure the ohmic resistance (R) in the frequency range of 10 - 200 kHz using the four-probe alternating current impedance spectroscopy method. To minimize unnecessary carbonate formation, immerse the cell completely in degassed deionized water and quickly acquire the impedance spectrum.

[0224] (3) Water content (water absorption rate, WU) and swelling ratio (SR) measurement

[0225] To exchange the membrane to the OH - type, immerse two circular membrane samples with a diameter of 2.23 cm in 1 M KOH solution at 20 °C for 24 hours.

[0226] Then rinse each polymer membrane sample with deionized water to remove KOH. Immerse one sample in deionized water at 20 °C and the other in deionized water at 80 °C for 1 hour each. Then take out each sample, gently wipe the surface, and immediately measure the thickness (t wet ), diameter (l wet ), and weight (W wet ).

[0227] Next, each sample was dried in an oven at 40 °C for 24 hours, and its thickness (t dry ), diameter (l dry ), and weight (W dry ) were measured.

[0228] Based on the change in weight, the water content (WU) was calculated according to Equation (3) below. Based on the changes in thickness and diameter, the swelling ratios (Δt and Δl) were calculated according to Equations (4) and (5):

[0229] [Equation 3]

[0230] WU (%) = [(W wet - W dry ) / W dry × 100

[0231] [Equation 4]

[0232] Δt (%) = [(t wet - t dry ) / t dry × 100

[0233] [Equation 5]

[0234] Δl (%) = [(l wet - l dry ) / l dry × 100

[0235] <Evaluation of the Theoretical Ion Exchange Capacity (IEC) and Hydroxide Ion Conductivity of DA-x30-PPO-SEBS Copolymers>

[0236] The theoretical IEC and hydroxide ion conductivity of the DA-x30-PPO-SEBS polymer membranes prepared in Comparative Examples 1 and 2 were measured, as shown in Table 1.

[0237] Figure 2 is a photograph of the DA-x30-PPO-SEBS polymer membrane prepared in Comparative Example 1. Phase separation can be observed from Figure 2 , and the surface of part of the polymer membrane is clearly uneven.

[0238] [Table 1]

[0239]

[0240] As can be seen from Table 1, although Comparative Example 1 and Comparative Example 2 were prepared using the same method, the differences in the hydroxide ion conductivity at each temperature exceeded the error range, indicating a lack of reproducibility. This is because when a diamine or a dihalide crosslinking agent crosslinks two different polymers, the reactivity of each reaction site is the same, so the reaction occurs randomly, and crosslinking may occur between SEBS polymers themselves or between PPO polymers themselves. As a result, phase separation occurs in the membrane, and the data obtained lacks reproducibility.

[0241] <Evaluation of Ion Exchange Capacity, Hydroxide Ion Conductivity, Water Content and Swelling Ratio of TQA-SEBS and PPO-SEBS>

[0242] 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. The results are listed in Table 2 below.

[0243] [Table 2]

[0244]

[0245] Referring to Table 2, the PPO-SEBS of Example 1 has an excellent ion exchange capacity, and the hydroxide ion conductivity and water content are significantly higher than those of the TQA-SEBS of Comparative Example 3. In TQA-SEBS, the hydrogen bonds of the triazole groups will break at high temperatures, while this problem does not exist in PPO-SEBS. Therefore, under the same composition conditions, PPO-SEBS exhibits higher conductivity due to its relatively high IEC.

[0246] Therefore, under the same degree of acylation and crosslinking density, PPO-SEBS is expected to have higher output performance than TQA-SEBS.

[0247] Experimental Example 2: Measurement of Density and Hydrogen Permeability

[0248] The density and hydrogen permeability of the TQA-SEBS polymer membrane in Comparative Example 3 and the PPO-SEBS polymer membrane in Example 1 were measured by the following method, and the results are listed in Table 3.

[0249] (1) Density

[0250] To measure the density, rectangular membrane samples (2 cm × 2 cm) were dried in a vacuum oven at 40 °C for 24 hours. Then, a buoyancy-based density measurement method was used to measure their weight (W air ) in air and their weight (W hep ) in n-heptane (density = 0.684 g). The density was calculated by Equation (6):

[0251] [Equation 6]

[0252] Density (g / cm 3 ) = [W air / (W air - W hep )] × D hep

[0253] (2) Hydrogen Permeability

[0254] The hydrogen permeability was measured using a customized bubble flowmeter. A circular membrane (area 19.6 cm 2 (A), thickness 25 μm (l)) was dried in a vacuum oven at 40 °C for 24 hours and then installed in the measurement cell of the bubble flowmeter. The internal pressure of the flowmeter was fixed at 150 cmHg (P), and the hydrogen flow rate was 200 sccm. By monitoring the volume displacement of the bubbles per unit time (Vp / s) inside the bubble flowmeter, the hydrogen permeability could be determined. The hydrogen permeability was calculated by formula (7):

[0255] [Formula 7]

[0256] Permeability (barrer) = 10 -10 × (V p(STP) × l) / (A × s × P)

[0257] [Table 3]

[0258]

[0259] As can be seen from Table 3, the PPO-SEBS in Example 1 has a higher density and a lower hydrogen permeability than the TQA-SEBS in Comparative Example 3, indicating that it is more suitable for use as an ion exchange membrane for the preparation of high-purity hydrogen and oxygen by water electrolysis.

[0260] Experimental Example 3: Measurement of Thermal Stability

[0261] The thermal stabilities of the TQA-SEBS polymer membrane in Comparative Example 3 and the PPO-SEBS polymer membrane in Example 1 were measured by thermogravimetric analysis (TGA), and the results are as Figure 9 shown.

[0262] The thermal stability was measured using a Scinco TGAN-1000 device. Specifically, under nitrogen protection, the mass loss was measured in the temperature range of 30 °C to 800 °C at a heating rate of 10 °C / minute.

[0263] From Figure 9It can be seen that the PPO-SEBS in Example 1 exhibits thermal stability comparable to that of TQA-SEBS and still maintains thermal stability under the operating conditions (below 80 °C) of the water electrolysis device, demonstrating its suitability as an ion exchange membrane for water electrolysis.

[0264] Experimental Example 4: Measurement of Oxidation Stability

[0265] The oxidation stabilities of the TQA-SEBS polymer membrane in Comparative Example 3 and the PPO-SEBS polymer membrane in Example 1 were measured by the following method, and the results are as Figure 10 shown.

[0266] To measure the oxidation stability, each membrane was dried in a vacuum oven at 40 °C for 24 hours, and its initial weight (W Before ) was measured. Then, each membrane was immersed in Fenton's reagent (4 ppm Fe 2+ dissolved in 3 wt% H2O2) at 60 °C, and its weight (W After ) was measured every 24 hours. The weight loss was calculated by Equation (8):

[0267] [Equation 8]

[0268] Oxidation stability (%) = [(W Before - W After ) / W Before × 100 (%)

[0269] As Figure 10 shown, the PPO-SEBS in Example 1 exhibits more excellent oxidation stability than TQA-SEBS. Therefore, even under the conditions of free radical formation, the polymer membrane of the present disclosure exhibits excellent durability, demonstrating its suitability for water electrolysis devices.

[0270] Experimental Example 5: Measurement of Mechanical Properties

[0271] The mechanical stability of the PPO-SEBS polymer membrane prepared in Example 1 was measured by the following method, and the results are as Figure 11 shown.

[0272] The mechanical stability was measured using a Shimadzu EZ-TEST E2-L bench-top tensile testing machine. Dog-bone shaped specimens were prepared in the OH - type under 50% RH conditions, with an overall size of 1 cm × 4 cm and a test section size of 1 cm × 2 cm. The tensile test was carried out at a speed of 10 mm / min.

[0273] The results showed that the measured tensile strength was 27.1 MPa, the elongation at break was 129.5%, and the Young's modulus was 275.5 MPa.

[0274] These results confirm that the PPO-SEBS polymer membranes of the present disclosure have sufficient mechanical strength and can be used as anion exchange membranes, especially showing a significantly improved elongation rate compared to conventional anion exchange membranes.

Claims

1. A crosslinked copolymer comprising a first chain represented by the following Chemical Formula 1 and a second chain represented by the following Chemical Formula 2, wherein, The first chain and the second chain are crosslinked with each other: [Chemical Formula 1] In Chemical Formula 1, * represents the bonding position with Chemical Formula 2, The sum of q1, q2, q5 and q6 is an integer from 100 to 1,000, The sum of q3 and q4 is an integer from 150 to 2,000, a and b are each independently an integer from 3 to 10, Each of R1 to R4 is independently hydrogen or –(CH2) p –CH3, where p is an integer from 0 to 5; [Chemical Formula 2] In Chemical Formula 2, * represents the bonding position with Chemical Formula 1, n and m are each independently an integer from 10 to 50.

2. The crosslinked copolymer according to claim 1, Among them, Based on 100 moles of the first chain, it contains 10 to 70 moles of the second chain.

3. The crosslinked copolymer according to claim 1 or 2, Among them, q1 to q6 are each independently an integer from 10 to 500.

4. The crosslinked copolymer according to any one of claims 1 to 3, Among them, The ratio of the sum of q1, q2, q5, q6 to the total sum of q1 to q6 is 0.2 to 0.

5.

5. The crosslinked copolymer according to any one of claims 1 to 4, Among them, The ratio of the sum of q1 and q6 to the total sum of q1, q2, q5, q6 is 0.2 to 0.

5.

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

7. The crosslinked copolymer according to any one of claims 1 to 6, Among them, The ratio of n to (n + m) is 0.15 to 0.

70.

8. The crosslinked copolymer according to any one of claims 1 to 7, Among them, The crosslinked copolymer is represented by the following Chemical Formula 3: [Chemical Formula 3] In Chemical Formula 3, q1 to q6, a, b, n and m are as defined in Chemical Formulas 1 and 2.

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

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

11. A method for preparing a crosslinked copolymer, comprising: (a) Preparing a poly(styrene-b-ethylene-co-butene-b-styrene) polymer represented by the following Chemical Formula 1-1; (b) Preparing a polyphenylene ether-based polymer represented by the following Chemical Formula 2-1; and (c) Crosslinking the poly(styrene-b-ethylene-co-butene-b-styrene) polymer with the polyphenylene ether-based polymer to produce the crosslinked copolymer: [Chemical Formula 1-1] In Chemical Formula 1-1, The sum of q1, q2, q5 and q6 is an integer from 100 to 1,000, The sum of q3 and q4 is an integer from 150 to 2,000, a and b are each independently an integer from 3 to 10, R1 to R4 are each independently hydrogen or –(CH2) p –CH3, p is an integer from 0 to 5, and X1 and X2 are each independently a halogen group; [Chemical Formula 2-1] In Chemical Formula 2-1, n and m are each independently an integer from 10 to 50.

12. The method for preparing a crosslinked copolymer according to claim 11, Further comprising (d) reacting the crosslinked copolymer with trimethylamine.

13. The method for preparing a crosslinked copolymer according to claim 11 or 12, Among them, Based on 100 moles of styrene repeating units, the poly(styrene-b-ethylene-co-butene-b-styrene) polymer contains 30 to 90 moles of halogen atoms.

14. A method for preparing a crosslinked copolymer according to any one of claims 11 to 13, Among them, in step (c), based on 100 moles of the halogen groups contained in the poly(styrene-b-ethylene-co-butylene-b-styrene) polymer, the amount of the polyphenylene ether-based polymer used is 10 to 70 moles.

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