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

Abstract

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

Description

Technical Field

[0001] [Cross - reference to related applications] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0079130 filed on June 28, 2022, and Korean Patent Application No. 10-2023-0040300 filed on March 28, 2023, and all the contents disclosed in the documents of the Korean patent applications are included as part of this specification. The present invention relates to a crosslinked copolymer, a polymer membrane containing the same, and an anion exchange membrane containing the polymer membrane.

Background Art

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

[0003] AEMFCs conduct hydroxide ions (OH - ) through a polymer electrolyte membrane and convert chemical energy into electrical energy. Therefore, in order to develop AEMFCs with excellent performance, it is necessary to develop an anion exchange polymer electrolyte membrane having excellent ion conductivity characteristics, that is, an anion exchange membrane (AEMs). However, because AEMFCs conduct OH - and thereby produce electricity, a high pH, that is, an alkaline environment is created during operation.

[0004] Generally, AEMs are composed of a polymer backbone and ion-conducting groups. However, the abundant hydroxide ions in an alkaline environment provide opportunities for high nucleophilic attacks on the polymer backbone and ion-conducting groups, which may induce a decrease in the ionic conductivity and mechanical properties of AEMs. Therefore, it is necessary to develop AEMs with excellent chemical stability to prevent the performance degradation of AEMs. In other words, to develop AEMFCs with excellent performance, it is essential to develop AEMs with excellent ionic conductivity and chemical stability.

[0005] In the case of ion-conducting polymers (ionomers) such as AEMs, the ionic conductivity is mainly affected by the type of ion-conducting groups and the ion exchange capacity (IEC). In addition, the formation of effective ion clusters and ion-conducting channels due to the morphology of the membrane also affects the ionic conductivity.

[0006] The alkaline stability of AEMs is also affected by complex factors such as the polymer backbone, ion-conducting groups, and hydration number. Therefore, to improve the performance of AEMs (i.e., to have high conductivity and alkaline stability), a comprehensive understanding of various properties of AEMs is required, including not only ion-conducting groups and polymer backbones but also the morphology of the membrane and hydration number determined by the molecular structure. For this reason, many studies on ion-conducting groups and polymer backbones of AEMs have been conducted over the past decade or so.

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

[0008] In addition to improving the performance of AEMs by the structure of the ionic conduction group and the polymer, various approaches have been taken, such as improving conductivity through the introduction of multication, controlling the morphology of the membrane through the introduction of block- or graft- and partially fluorinated-polymer main chains or side chains, and maximizing the stability of AEMs through crosslinking.

[0009] By thus well controlling the structure of the conduction group and the polymer and the morphology of the polymer membrane, AEM materials that exhibit very high cell performance approaching that of PEMFC (proton exchange membrane fuel cell) and have excellent chemical stability even under high-temperature and high-pH conditions have been successively developed. For example, poly(aryl piperidinium) (PAP), poly(diphenylethane-co-terphenyl piperidinium) (PDTP), polycarbazole, poly(aryl-co-terphenyl piperidinium), etc. correspond to this.

[0010] Such polyphenylene-based AEMs are characterized by having a relatively low water uptake (WU), that is, a low hydration number, compared to a high IEC. Generally, in the ion conduction mechanism of AEMs, water serves as a conduction mediator for OH - Therefore, for the high ionic conduction characteristics of AEMs, a high water uptake (WU) must be accompanied. Also, if the membrane has a high hydration number, OH -It also has the advantage that it can ultimately increase the chemical stability of AEMs by restricting the nucleophilic attack on the conduction group. In addition, due to the strong π-π interaction between the phenyl groups contained in the polymer backbone, polyphenylene-based AEMs exhibit properties of high stress and relatively low strain. Also, since AEMs serve as a separation membrane to block the fuel supplied to the anode and cathode from moving to the opposite electrode, they must not be damaged by gas flow or impact. Therefore, it is clear that high mechanical stability, especially high stress properties, of the AEM are essential to ensure the performance and durability of AEMFCs. However, in order to overcome the mechanical failure that may occur at the edge of the MEA active area where mechanical stress is maximized during the operation of AEMFCs, not only high stress but also high strain properties of the AEM are required.

[0011] On the one hand, styrene-b-ethylene-co-butylene-b-styrene (SEBS)-based AEMs have different physical properties from polyphenylene-based AEMs, namely, a high hydration number and high strain. This is due to the aliphatic chain structure of SEBS. Moreover, since SEBS has a well-developed morphology in the block copolymer structure of styrene and 1,4-butadiene, the AEMs in question have higher ionic conductivity and chemical stability compared to IEC. However, an overly high water content may instead cause the AEMs to swell excessively, and due to the so-called "dilution effect" that reduces the concentration of the conductive ion OH - , the ionic conductivity of the membrane may instead be reduced. In addition, the low tensile strength of SEBS is vulnerable to membrane breakage and deformation and is not suitable for the driving environment of AEMFCs at high temperatures and humidity. In addition, the problem of the limited solubility of SEBS limits the modification of SEBS, making it difficult to develop SEBS-based AEMs with better performance.

[0012] To overcome such limitations of SEBS, Korean Registered Patent No. 10-2184530 proposes a copolymer (xTQA-PPO-SEBS) obtained by crosslinking flexible SEBS and rigid PPO through triazole. The copolymer exhibits lower WU and higher deformability compared to existing SEBS-based membranes, and higher ionic conductivity and cell characteristics compared to IEC. However, the copolymer has a problem in that its chemical stability against hydroxide ions is low due to its structure containing aryl-ether.

Prior Art Documents

Patent Documents

[0013]

Patent Document 1

Non-Patent Documents

[0014]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Non-Patent Document 5

Non-Patent Document 6

Non-Patent Document 7

Non-Patent Document 8

Non-Patent Document 9

Non-Patent Document 10

Non-Patent Document 11

Non-Patent Document 12

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Non-Patent Document 15

Non-Patent Document 16

Non-Patent Document 17

Non-Patent Document 18

Summary of the Invention

Problems to be Solved by the Invention

[0015] An object of the present invention is to provide a new crosslinked copolymer that has excellent mechanical properties, excellent alkali stability, and high ionic conductivity and degree of hydration, and can be suitably used as a material for an anion exchange membrane (AEM) such as a fuel cell.

Means for Solving the Problems

[0016] According to one embodiment of the present invention, there is provided a crosslinked copolymer containing 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:

[0017]

Chem.

[0018] In the Chemical Formula 1, * is the bonding position with Chemical Formula 2, The sum of q1, q2, q5, and q6 is an integer of 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, and p is an integer from 0 to 5,

[0019]

Chemical formula

[0020] In the chemical formula 2, * is the bonding position with the chemical formula 1, x and y are each independently an integer from 0 to 10, n is an integer from 10 to 1,000. Also, according to an embodiment of the present invention, a polymer film containing the crosslinked copolymer is provided. Also, according to an embodiment of the present invention, (a) The step of producing a polymer represented by the following chemical formula 1-1; (b) The step of producing a polymer represented by the following chemical formula 2-1; and (c) The step of crosslinking the polymer represented by the following chemical formula 1-1 and the polymer represented by the following chemical formula 2-1 to produce a crosslinked copolymer; A method for producing a crosslinked copolymer is provided, including:

[0021]

Chemical formula

[0022] In the 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, and p is an integer from 0 to 5, X1 and X2 are each independently a halogen group,

[0023] [Chemical formula]

[0024] In the chemical formula 2-1, x and y are each independently an integer from 0 to 10, n is an integer from 10 to 1000. [Advantages of the Invention]

[0025] The crosslinked copolymer of the present invention has high water uptake (WU), excellent dimensional stability, high ionic conductivity, degree of hydration, and alkali stability. Further, the crosslinked copolymer is very excellent in mechanical properties such as tensile strength and elongation rate characteristics. Thus, since the crosslinked copolymer of the present invention has excellent electrochemical properties and mechanical properties, it can be suitably used as an anion exchange membrane material. [Brief Description of the Drawings]

[0026]

Figure 1

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Figure 7

Figure 8

Figure 9

Figure 10

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Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

DETAILED DESCRIPTION OF THE INVENTION

[0027] The terms used in this specification are used only to illustrate exemplary embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0028] In this specification, terms such as "comprising," "including," or "having" are intended to specify the presence of implemented features, steps, components, or combinations thereof, and should not be construed as precluding the presence or addition of one or more other features, steps, components, or combinations thereof.

[0029] The present invention can be modified in various ways and can have various forms. Specific embodiments are illustrated and described in detail below. However, this is not intended to limit the present invention to specific disclosed forms, and it should be understood to include all modifications, equivalents, or alternatives within the spirit and technical scope of the present invention.

[0030] Hereinafter, the present invention will be described in detail. According to an embodiment of the present invention, there is provided a crosslinked copolymer including 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 to each other.

[0031]

CHEM.

[0032] The crosslinked copolymer of the present invention is one in which a first chain of poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) and a second chain of poly(aryl piperidinum) are crosslinked.

[0033] The first chain of the crosslinked copolymer has elastic properties, the second chain has rigid properties, and both the first chain and the second chain exhibit phase separation characteristics. By chemically crosslinking such a first chain and a second chain, the crosslinked copolymer of the present invention exhibits excellent mechanical properties, that is, a high elongation at break and Young's modulus together with an appropriate tensile strength.

[0034] In addition, the crosslinked copolymer is excellent in water retention ability due to the above structural characteristics, exhibits high ionic conductivity, and is also excellent in alkali stability. Therefore, the crosslinked copolymer can be suitably used as an anion exchange membrane for fuel cells and the like.

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

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

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

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

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

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

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

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

Chem.

[0043] In Chemical Formula 3, q1 to q6, a, b, x, y, and n are as defined in Chemical Formula 1 and Chemical Formula 2. Preferably, the crosslinked copolymer can contain a repeating unit represented by the following Chemical Formula 4:

Chem.

[0044] The crosslinked copolymer described above has a positively charged quaternary ammonium group and can selectively allow only anions to pass through. Therefore, the crosslinked copolymer can be applied as an anion exchange membrane. The counterion (anion) group to the cation (quaternary ammonium group) of the crosslinked copolymer is OH - , Cl - , Br - , or HCO3 - and can preferably be OH - . In addition, the crosslinked copolymer exhibits excellent ion conduction efficiency and alkali stability due to its phase separation characteristics.

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

[0046] The polymer membrane described above contains a crosslinked copolymer including the first chain and the second chain, and thus has improved mechanical strength compared to existing polymers for AEMs, exhibits high ion conductivity while showing an appropriate IEC, and is excellent in alkali stability. Therefore, the polymer membrane having the above physical properties can be suitably used as an anion exchange membrane included in fuel cells and the like.

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

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

[0049] The step (a) is a step of introducing 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 produced through the Friedel-Crafts acylation reaction and the reduction reaction of the carbonyl group of SEBS.

[0050] The acyl halide used in the acylation reaction is selected in consideration of the target numbers of a and b. Specifically, as the acyl halide, alkanoyl chloride having a halogen group at the end of the alkyl chain, represented by X-R-COCl (where X is a halogen and R is C 1-29 alkyl), can be used. When a and b are different from each other, or 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. As a catalyst for the acylation reaction, aluminum chloride (AlCl3) can be used, and the reaction can be carried out at 20 to 30 °C for 8 to 24 hours.

[0051] For the reduction reaction of the carbonyl group, known methods in the art can be used without limitation. As an example, triethylsilane and trifluoroacetic acid are added and reacted at 90 to 120 °C for 20 to 30 hours to reduce the carbonyl group. Through such a reaction, the poly(styrene-b-ethylene-co-butylene-b-styrene) polymer represented by Chemical Formula 1-1 can be obtained.

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

[0053] The step (b) is a step of producing a poly(aryl piperidinum) polymer. As an example, aryl(

Chemical Formula

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

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

[0056] The reaction in the 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. At this time, if the polymerization reaction temperature is less than 40°C or the reaction time is less than 10 hours, the crosslinking reaction between the polymers may not occur sufficiently, resulting in a decrease in hydroxide ion conductivity and a reduction in alkali stability. Conversely, if the polymerization reaction temperature exceeds 60°C or the reaction time exceeds 16 hours, the crosslinking rate between the polymers may increase excessively, causing the crosslinked polymer solution to gel.

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

[0058] In addition, according to the above method, since the crosslinked copolymer can be produced more simply and in a high yield, the productivity of the process can be increased and the cost can be reduced. Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples are merely for illustrating the present invention, and the scope of the present invention is not limited thereto.

[0059] [Examples] [Materials] Divinylbenzene (99%), aluminum chloride (99%), 6-bromohexanoyl chloride, N-methyl-4-piperidone (97%), trimethylamine solution (45 wt% in water) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Trifluoromethanesulfonic acid (98%) was purchased from TCI (Tokyo, Japan). Triethylsilane (98%) was purchased from Alfa Aesar (MA, USA). Trifluoroacetic acid was purchased from Daejung Chemical & Metal (Siheung City, Korea). Poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS, A1535H) with a styrene content of 57% was purchased from Kraton Corporation (Houston, TX, USA). All other chemicals were received from commercial sources.

[0060] [Confirmation of Chemical Structure of Polymer] The chemical structures of the polymers obtained at each stage of the following examples were 1 confirmed through 1H NMR spectroscopy and Fourier transform infrared (FTIR) spectroscopy. 1 The 1H NMR spectra were obtained using a 400 MHz NMR instrument (400 MR from Agilent) with CDCl 3 as the solvent. The FTIR spectra were determined using a Spectrum Two ATR-FTIR spectrometer from PerkinElmer. The spectra were collected up to 4000 - 400 cm -1 .

[0061] Example 1: Preparation of 30x-PBB-SEBS (30% crosslinking degree) film (1) Synthesis of poly(divinylbenzyl N-methylpiperidine) 2

Chemical formula

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

[0063] (2) Synthesis of Bromohexyl SEBS3 (2 - 1) Synthesis of Bromohexanoyl SEBS4 [Chemical formula] (In the above reaction formula, the sum of q1, q2, q5, and q6 is 711, the sum of q3 and q4 is 996, and the ratio of the sum of q1 and q6 to the total sum of q1, q2, q5, and q6 is 0.3.)

[0064] SEBS (10.00 g, 54.73 mmol) was placed in a 1000 mL two - necked round - bottom flask under a nitrogen atmosphere and dissolved in dichloromethane (320 mL) with a magnetic stirrer. After the polymer was completely dissolved, 6 - bromohexanoyl chloride of aluminum chloride (5.47 g, 41.05 mmol) and dichloromethane (8.76 g, 41.05 mmol) was gradually added using a dropping funnel. After 24 hours, the reaction mixture was poured into a large amount of ethanol (1500 mL), and the precipitated polymer was filtered through filter paper and then washed several times with ethanol to remove the residual reactants. The obtained polymer was dried in a desiccator at room temperature for 24 hours to obtain bromohexanoyl SEBS4 in the form of a white rubber (16.40 g, 97.7%). 1 Through 1H - NMR analysis, it was confirmed that bromohexanoyl side chains were bonded to 70 mol% of the total 100 mol% of styrene contained in SEBS; δ H (400 MHz, CDCl3) 7.92 - 7.37 (4H, broad signal, H 1,2 ), 7.26 - 6.28 (10H, broad signal, H 3,4 ), 3.50 - 3.38 (3H, broad signal, H 10), 3.03 - 2.80 (3H, broad signal, H6), 2.69 - 2.35 (2H, broad signal, H 12 ), 2.01 - 0.56 (46H, broad signal, H 7-9,11,13-18 )(Figure 8a).

[0065] (Synthesis of (2 - 2) Bromohexyl SEBS3) [Chemical Formula] (In the above reaction formula, the sum of q1, q2, q5, and q6 is 711, the sum of q3 and q4 is 996, and the ratio of the sum of q1 and q6 to the total sum of q1, q2, q5, and q6 is 0.3.)

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

[0067] (3) Preparation of Crosslinked Poly(benzyl N - methylpiperidinium)-SEBS1 Membrane (30x - PBB - SEBS) [Chemical formula] (In the above reaction formula, n is 158, the sum of q1, q2, q5, and q6 is 711, the sum of q3 and q4 is 996, and the ratio of the sum of q1 and q6 to the total sum of q1, q2, q5, and q6 is 0.3.)

[0068] Poly(benzyl N - methylpiperidine)2, bromohexyl SEBS3, and HPLC - grade chloroform (20 mL) were placed in a 20 - mL vial and stirred until a homogeneous solution was obtained. At this time, poly(benzyl N - methylpiperidine)2 was used at a ratio of 30 mol% relative to 100 mol% of bromohexyl SEBS3 (total 0.5 g).

[0069] The polymer solution was heated at 40 °C for 12 hours to induce crosslinking. After cooling the polymer solution to room temperature, it was poured into a glass Petri dish with a cotton filter and dried at room temperature for 24 hours. After peeling the produced membrane from the Petri dish, it was immersed in deionized water (DI) to wash away the residual solvent. Then, the membrane was immersed in an aqueous solution of trimethylamine (TMA) at 45 °C for 24 hours and then washed with deionized water to remove the excess TMA. It was immersed in 1M KOH solution at room temperature for at least 24 hours to exchange Br - and OH - ions and washed several times with deionized water to remove the excess KOH to produce a 30x - PPB - SEBS membrane.

[0070] To confirm that Br in the crosslinked membrane was replaced by TMA, the IR changes before and after the trimethylamine (TMA) solution treatment were confirmed (Figure 10). After the TMA treatment, it was confirmed that the C - Br peak at about 642 cm -1 disappeared, thereby confirming that the C - Br bond in x - PBB - SEBS was replaced by TMA.

[0071] Example 2: Production of 40x-PBB-SEBS (crosslinking degree 40%) film (3) A 40x-PBB-SEBS film was produced in the same manner as in Example 1, except that poly(divinylbenzyl N-methylpiperidine) 2 was used at 40 mol% with respect to bromohexyl SEBS 3.

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

[0073] Experimental Example 1: Ion exchange capacity (IEC), water content (WU), and swelling ratio (SR) (1) Ion exchange capacity (IEC) a. Experimental IEC The ion exchange capacity (IEC) of each film was measured using a back-titration method. The film in the hydroxide (OH - ) form was immersed in a 0.01 M HCl standard solution for 24 hours. The residual HCl was titrated again with a 0.01 M NaOH standard solution using a phenolphthalein indicator. The film was dried to measure its weight (W dry , g). The experimental IEC (meq g -1 ) was calculated in moles of exchangeable hydroxide ions per gram using the following formula: IEC (meq g -1 ) = (C0V0 - C0V x ) / W dry Here, V0 and V x are the volume of NaOH before titration and the volume of NaOH consumed in the titration, respectively, C0 is the molar concentration of NaOH used in the back-titration, and W dry is the weight of the film dried in an oven for at least 12 hours. b. Theoretical IEC The theoretical IEC value is1 It was determined based on the number of Br atoms contained in bromohexyl SEBS3 calculated by 1H NMR spectrum and the masses of the two polymers (2 and 3) used in the cross-linking process.

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

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

[0076]

Table 1

[0077] IEC is defined as the milliequivalent of ion-conducting groups per unit mass of the polymer electrolyte membrane. Generally, the higher the IEC of the polymer electrolyte membrane, the more water can be contained in the membrane (i.e., the water content increases). Since water can act as a mediator for hydroxide ion conduction in an anion exchange membrane (AEM), the higher the IEC, the higher the ion conductivity. However, an overly high IEC sometimes leads to an increase in the water content (WU), and through a mechanism called the "dilution effect", it reduces the ion conductivity. When such a phenomenon occurs, the SR of the membrane also increases, reducing the mechanical properties and dimensional stability of the membrane. Therefore, for an AEM to have high ion conductivity and excellent mechanical properties, an appropriate IEC is necessary.

[0078] The theoretical IECs of 30x-PBB-SEBS, 40x-PBB-SEBS, and 50x-PBB-SEBS were 1.96, 1.86, and 1.77 meq g, respectively -1 and showed a tendency to decrease with the increase in the crosslinking ratio. This is because the total amount of ion-conductive groups introduced decreased due to the decrease in the ratio of bromohexyl SEBS3. On the other hand, it was confirmed that all the experimental IEC measurement results of the x-PBB-SEBS membranes were similar to the theoretical values. Thus, from the fact that the experimental and theoretical values of IEC showed similar numerical values, it can be confirmed that each membrane has the intended degree of crosslinking.

[0079] Regarding the WU and SR measurement results of x-PBB-SEBS, it was confirmed that as the degree of crosslinking increased, both WU and SR decreased, and the dimensional stability increased. This is judged to be because, along with the decrease in the content of SEBS, which is an elastic polymer, the expansion of the membrane was suppressed by the chemical bonds between the polymer chains formed through crosslinking.

[0080] Next, the hydration number (λ value) of each membrane was calculated. As a result, as expected, it was confirmed that the hydration number decreased (30x-PBB-SEBS = 34.7, 40x-PBB-SEBS = 31.1, 50x-PBB-SEBS = 27.7) as the crosslinking degree of x-PBB-SEBS increased.

[0081] The hydration numbers of the membranes of Examples 1 to 3 were compared with the numerical values of existing reported polyphenylene- and SEBS-based membranes (

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

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

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

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

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

[48] Korean Registered Patent No. 10 - 2184530;

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

[0082] As a result, it can be confirmed that the x-PBB-SEBS membrane has intermediate numerical values between SEBS-based AEMs with a relatively high hydration number (λ value) compared to IEC and poly(phenylene)-based AEMs with a relatively low hydration number (λ value). As described above, since water serves as a medium for ion conduction, in order for an AEM to obtain a high ionic conductivity, it is necessary to have the highest possible hydration number. However, an excessively high value may rather interfere with the ionic conductivity, so it is necessary to have an appropriate value. From such an aspect, in the case of the said x-PBB-SEBS, it can be confirmed from the above results that the degree of hydration can be easily adjusted by crosslinking polymers with different properties and adjusting the crosslinking degree.

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

[0084] (2) Thermal stability The thermal stability of the membranes was investigated by thermogravimetric analysis (TGA) using a Scinco TGA N-1000 instrument (Seoul, South Korea). The TGA was operated at a heating rate of 10 °C / min from 30 to 800 °C under a nitrogen atmosphere. -1 The glass transition temperature (Tg) of each membrane was measured by differential scanning calorimetry (DSC) using a PerkinElmer DSC 4000 (Waltham, MA, USA). The samples were prepared in aluminum pans and measured over two cycles from -40 to 200 °C at a heating and cooling rate of 10 °C / min. The Tg was measured from the second cycle. -1

[0085] (3) Results In AEMFCs, the AEM serves as an electrolyte that conducts OH - ions generated at the cathode to the anode. In addition, it serves as a separation membrane that blocks the movement of H2 and O2 (or air) used as fuels to different electrodes. Therefore, the AEM is required to have resistance to breakage or deformation under battery-operating conditions (such as gas flow and temperature), that is, excellent mechanical properties and thermal stability.

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

[0087] The mechanical properties of the x-PBB-SEBS membrane were compared with those of SEBS-based AEMs (

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

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

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

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

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

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

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

[47] J. Membr. Sci. 638 (2021), 119685;

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

[54] Angew. Chem. 133 (2021) 7789-7797), and the xTQA-PPO-SEBS AEM obtained by crosslinking PPO and SEBS (

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

[0088]

Table 2

[0089] As a result, it was confirmed that the x-PBB-SEBS membrane had intermediate tensile strength and elongation at break between those of SEBS and polyphenylene-based AEMs. Thus, it can be confirmed that x-PBB-SEBS, prepared by crosslinking two polymers with different properties, has high elongation at break while having excellent mechanical stability in terms of tensile strength and Young's modulus, and that the mechanical properties can be adjusted by controlling the degree of crosslinking.

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

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

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

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

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

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

[48] Korean Registered Patent No. 10-2184530) (Figure 12). As a result, it was confirmed that x-PBB-SEBS exhibits a similar Young's modulus compared to other AEMs, but has a high elongation at break at a similar Young's modulus. In particular, it showed better mechanical properties compared to the previously cross-linked xTQA-PPO-SEBS membrane of PPO and SEBS. This is presumably because the mechanical properties increased due to cross-linking of two polymers, poly(bibenzyl N-methyl piperidine) with excellent phase separation and SEBS.

[0091] Next, the thermal stability of the x-PBB-SEBS membrane was investigated using TGA and DSC analyses (Figure 13). First, three stages of weight loss appeared in the TGA graph (Figure 13a): The first weight loss (30-150 °C) occurred due to the evaporation of free water and bound water contained in the membrane. As the cross-linking rate increased, the weight loss decreased because the amount of water contained in the membrane, that is, the water uptake (WU), decreased. The second weight loss (150-300 °C) was due to the decomposition of the conductive groups, and the final weight loss that appeared after about 400 °C was due to the decomposition of the polymer backbone. Furthermore, through DSC analysis, the glass transition temperature (T g) was attempted to be confirmed. For all three types of x-PBB-SEBS membranes, no special peak was observed up to about 200 °C, that is, the decomposition temperature of QA (Figure 13b). Generally, in the case of SEBS or functionalized SEBS, T g appears at about 50 - 70 °C, but in the present invention, it can be confirmed that the thermal stability has been increased through crosslinking with a polymer having rigid properties.

[0092] From the above TGA and DSC results, it was confirmed that all three types of x-PBB-SEBS have thermal stability suitable for the temperature range of about 60 - 80 °C, which is the general driving condition of AEMFC.

[0093] Experimental Example 3: Water retention capacity (1) Measurement method The content of freezing water and non-freezing water in the membrane was measured by DSC using a DSC 4000 from PerkinElmer. A fully hydrated membrane sample was sealed in an aluminum pan, and a sealed empty aluminum pan was also prepared for reference. The weights of both pans were measured and frozen to -40 °C inside the DSC chamber. Then, the temperature was maintained constant while the system reached equilibrium. Then, the DSC chamber was heated to 20 °C at a heating rate of 2 °C min -1 . Such a cycle was repeated twice, and values were obtained in the second heat cycle. The amount of freezing water in each membrane was calculated by integrating the peak area of the melting heat (ΔH m ). The total water content was measured using the WU (%) of the membrane. The contents of freezing water and non-freezing water were calculated using the following formula: Freezing water (%) = [melting enthalpy (J g -1 )] / [melting endothermic heat of fusion of pure water (334 J g -1 )] × 100 Non-freezing water(%) = total water(%) - freezing water(%)

[0094] (2) Results Due to the high ionic conductivity and cell characteristics of AEM, a high water content (WU) in the membrane is essential. The water contained in the membrane is divided into free water, which has a weak interaction with the conducting group and has a freezing point and boiling point similar to those of ordinary water, and bound water, which has a strong interaction with the conducting group and thus has a lower freezing point and a higher boiling point compared to free water. According to previous studies, under the conditions under which the fuel cell operates, that is, at high temperature and RH90 - 95%, the content of free water in the membrane decreases. Therefore, it is important to have a high content of bound water in the membrane to obtain a high-performance fuel cell.

[0095] The bound water of the x-PBB-SEBS membrane was analyzed using TGA and DSC (Figure 2). The mass loss occurring in the range of 30 - 100 °C by TGA was classified as free water, and the mass loss occurring from 100 °C until before the decomposition of the conducting group was classified as bound water (Figure 2a). It should be noted that there is of course a limitation that it is a relative comparison rather than a quantitative comparison for the bound water because the water contents of the three types of x-PBB-SEBS membranes are different.

[0096] The measurement results confirmed that the bound water content of the membrane increased with the increase in the degree of crosslinking (30x-PBB-SEBS: 19.71% < 40x-PBB-SEBS: 28.34% < 50x-PBB-SEBS: 33.42%). This is judged to be because the interaction between the ionic conducting group and water increased with the increase in the degree of crosslinking. To explain this, DSC was used to analyze freezable water and non-freezable water (Figure 2 and Table 3). As a result, all of the x-PBB-SEBS membranes of Examples 1 - 3 had a freezing point (T F, (dashed line) was shown. From this, it can be determined that there is an interaction between the ion-conductive group and water. Also, not only does the content of non-freezing bound water increase due to the increase in the degree of crosslinking, but it was confirmed that T F (freezing temperature of water) shifts to a lower temperature (30x - PBB - SEBS: -2.7°C > 40x - PBB - SEBS: -4.5°C > 50x - PBB - SEBS: -6.8°C). This is judged to be because the interaction between water and the conductive group becomes stronger as the degree of crosslinking increases, showing a tendency consistent with the bound water content rate confirmed by TGA analysis.

[0097]

Table 3

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

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

[0100] (3) Results The ionic conductivity of AEMs is a major factor that can directly affect battery performance. Therefore, the hydroxide ion conductivity of x-PBB-SEBS membranes with different crosslinking ratios was measured in water in the temperature range from 20 °C to 80 °C, and the normalized conductivity, which is the value obtained by dividing the hydroxide ion conductivity by the IEC, was additionally calculated to evaluate the ionic conduction efficiency of each membrane (Figure 3a and Table 4).

[0101] As a result, both the hydroxide ion conductivity and the normalized conductivity were measured to be the highest at 40x-PBB-SEBS, at 72.28 - 146.25 mS cm -1 and 38.45 - 77.79 mS cm -1 In AEMs, the IEC is the number of ionic conduction groups. Therefore, generally, membranes with a high IEC tend to have a high conductivity. Thus, compared to 30x-PBB-SEBS with a 30% crosslinking ratio (IEC: 1.97 meq g -1 ), 40x-PBB-SEBS with a lower IEC (1.88 meq g -1) became to have a higher conductivity. In the case of the film with a 40% crosslinking rate, it is judged that this is due to the increase in the interaction between the conductive group and water and the resulting increase in the bound water content. On the other hand, according to the above-mentioned TGA and DSC measurement results, 50x-PBB-SEBS showed a higher bound water content than 40x-PBB-SEBS. Therefore, it was judged that additional factors other than the water retention ability are involved in explaining the conductivity tendency of the x-PBB-SEBS film.

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

[0103]

Table 4

[0104] Next, the morphology of xPBB-SEBS films with different crosslinking rates was analyzed. First, in the AFM images, it was confirmed that phase separation between hydrophilic and hydrophobic regions occurred well in all three films (Figs. 4a - 4c). In particular, in the case of 40x-PBB-SEBS, it was confirmed that phase separation occurred most prominently.

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

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

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

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

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

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

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

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

[54] Angew. Chem. 133 (2021) 7789-7797) (Figure 14). It was confirmed that all three types of x-PBB-SEBS membranes possess a high level of normalized conductivity despite having a relatively low IEC (<2.0 meq g -1 ).

[0106] Such results are judged to be due to the fact that the x-PBB-SEBS membrane has achieved a high ion conduction efficiency by increasing the water content while introducing SEBS polymers and at the same time suppressing excessive water content through crosslinking, so as to possess an appropriate water content necessary for ion conduction. Moreover, it is judged that the formation of ion channels has been promoted by crosslinking two polymers with excellent phase separation properties, maximizing the ion conduction efficiency. In particular, it was confirmed that 40x-PBB-SEBS possesses the highest level of normalized conductivity (38.45 mS cm -1 ) compared with the reported AEMs. This is judged to be the result of the high water retention capacity and excellent phase separation effect of the membrane, as confirmed from the TGA and DSC analysis results.

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

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

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

[0110] On the one hand, the alkali stability of the x-PBB-SEBS membranes of Examples 1 to 3 was compared with SEBS-based AEMs known to have excellent alkali stability (

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

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

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

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

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

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

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

[45] Int. J. Hydrogen Energy 46 (2021) 18524-18533;

[47] J. Membr. Sci. 638 (2021), 119685;

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

[54] Angew. Chem. 133 (2021) 7789-7797;

[58] Membranes 10 (2020) 1-16), and the previously developed crosslinked xTQA-PPO-SEBS membrane (

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

[0111]

Table 5

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

[0113] (2) TGA analysis The structural changes were observed through TGA graph analysis before and after the measurement of the oxidation stability of 40x-PBB-SEBS (Figure 15). TGA analysis was performed after each membrane was dried in an oven at 40 °C for 12 hours or more. As a result, in the case of 40x-PBB-SEBS, almost the same TGA graph, that is, the polymer structure was maintained, before and after the measurement of the oxidation stability.

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

[0115] (2) Results Using the obtained x-PBB-SEBS membrane, a single cell test was conducted at 60 °C and 100% RH (Figure 6a). The single cell performance was in the order of 30x-PBB-SEBS (504 mW cm -2 and 657 mA cm -2 @0.6 V) < 50x-PBB-SEBS (529 mW cm -2 and 677 mA cm -2 @0.6 V) < 40x-PBB-SEBS (555 mW cm -2 and 665 mA cm -2 @0.6 V). This is the same trend as the RH conductivity, not the conductivity in water, which confirms that the cell performance of AEMs depends more on the conductivity under RH conditions than on the conductivity in water, and this is also consistent with previous research results.

[0116] Next, the humidification conditions were changed for the x-PBB-SEBS membrane and the single cell performance was measured. Generally, in AEMFCs, water is consumed at the cathode and generated at the anode during operation. Therefore, a high RH condition at the anode may induce flooding. Thus, single cell measurements were performed with the RH conditions of the anode and cathode set at 70% and 100% respectively, and the single cell performance of each was compared with the anode / cathode 100% / 100%RH condition (Figs. 6b and 16). All three types of x-PBB-SEBS membranes showed single cell performance with the same tendency as the anode / cathode = 100% / 100%RH condition: 30x-PBB-SEBS (461 mW cm -2 and 625 mA cm -2 @0.6 V) < 50x-PBB_SEBS (503 mW cm -2 and 665 mA cm -2 @0.6 V) < 40x-PBB-SEBS (545 mW cm -2 and 665 mA cm -2 @6 V). Also, 30x, 40x, and 50x-PBB-SEBS showed maintenance of peak power density of 91.5%, 98.2%, and 95.1% respectively due to the change in RH conditions. This is judged to be the result of an increase in water retention capacity due to an increase in the crosslinking rate and a change in morphology.

[0117] Conclusion According to one embodiment of the present invention, the crosslinked copolymer has a first chain and a second chain with phase separation characteristics crosslinked to exhibit an excellent phase separation effect, thereby showing high strain characteristics (high elongation at break value) and at the same time an excellent Young's modulus value. As a result, it was confirmed that the crosslinked copolymer of the present invention has excellent mechanical properties by possessing all the high stress characteristics of the PP-based polymer film and the high strain characteristics of the SEBS-based polymer film.

[0118] The crosslinked copolymer exhibited excellent water retention capacity, that is, strong interaction characteristics between the conductive group and water. Also, from the AFM and TEM analysis results, it was confirmed that the crosslinked copolymer has excellent phase separation, that is, an optimal morphology, and thereby it was shown to be excellent in the normalized conductivity meaning ion conduction efficiency.

[0119] In addition, the crosslinked copolymer has excellent alkali stability (over 99% in 2M KOH, 80°C) due to the structure in which the first chain and the second chain without aryl ether are crosslinked, and shows excellent oxidation stability by showing excellent phase separation characteristics. As a result of using the crosslinked copolymer as the anion exchange membrane of the fuel cell, it was confirmed that it shows excellent power density.

[0120] From the above results, it can be confirmed that the crosslinked copolymer of the present invention shows excellent electrochemical characteristics and mechanical properties, and physical property control is possible by adjusting the degree of crosslinking. Therefore, it can be confirmed that the crosslinked copolymer can be suitably used as an anion exchange membrane material capable of improving the performance and stability of fuel cells and the like.

Claims

1. A crosslinked copolymer comprising a first chain represented by the following Chemical Formula 1 and a second chain represented by the following Chemical Formula 2, wherein the first chain and the second chain are crosslinked to each other: 【Chemical 1】 In the Chemical Formula 1, * is the bonding position with Chemical Formula 2, q １ , q ２ , q ５ , and q ６ The sum of which is an integer from 100 to 1,000, q ３ and q ４ The sum of which is an integer from 150 to 2,000, a and b are each independently an integer from 3 to 10, R １ ~R ４ each independently represents hydrogen or -(CH ２ ) ｐ -CH ３ and p is an integer from 0 to 5, 【Chemical Formula 2】 In the Chemical Formula 2, * is the bonding position with Chemical Formula 1, x and y are each independently an integer from 0 to 10, n is an integer from 10 to 1000.

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

3. q １ ~q ６ The crosslinked copolymer according to claim 1 or claim 2, wherein q and ~q are each independently an integer of 10 to 500.

4. q １ ~q ６ The ratio of q to the total of １ q ２ q ５ and q ６ is 0.2 to 0.5, the crosslinked copolymer according to any one of claims 1 to 3.

5. q １ 、q ２ 、q ５ 、and q ６ The ratio of q to the total of q １ and q ６ is 0.2 to 0.5, the crosslinked copolymer according to any one of claims 1 to 4.

6. The crosslinked copolymer according to any one of Claims 1 to 5, wherein 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, wherein the crosslinked copolymer is represented by the following Chemical Formula 3: 【Chemical Formula 3】 In the above Chemical Formula 3, q １ ~q ６ , a, b, x, y, and n are as defined in Chemical Formula 1 and Chemical Formula 2.

8. A polymer film comprising the crosslinked copolymer according to any one of Claims 1 to 7.

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

10. (a) a step of producing a polymer represented by the following Chemical Formula 1-1; (b) a step of producing a polymer represented by the following Chemical Formula 2-1; and (c) a step of crosslinking the polymer represented by the following Chemical Formula 1-1 and the polymer represented by the following Chemical Formula 2-1 to produce a crosslinked copolymer; A method for producing a crosslinked copolymer, comprising: 【Chemical Formula 4】 In the Chemical Formula 1-1, q １ , q ２ , q ５ , and q ６ The sum of which is an integer from 100 to 1,000, q ３ and q ４ The sum of which is an integer from 150 to 2,000, a and b are each independently an integer from 3 to 10, R １ to 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, 【Chemical Formula 5】 In the Chemical Formula 2-1, x and y are each independently an integer from 0 to 10, n is an integer from 10 to 1000.

11. The method for producing a crosslinked copolymer according to Claim 10, further comprising (d) a step of reacting the crosslinked copolymer with trimethylamine.

12. The method for producing a crosslinked copolymer according to Claim 10 or Claim 11, wherein the polymer represented by the Chemical Formula 1-1 contains 30 to 90 moles of a halogen group per 100 moles of a styrene repeating unit.

13. In the step (c), the polymer represented by the Chemical Formula 2-1 is used in an amount of 10 to 70 moles per 100 moles of the halogen group contained in the polymer represented by the Chemical Formula 1-1. The method for producing a crosslinked copolymer according to any one of Claims 10 to 12.

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