JP7599705B2 - Composition, cured product, method for producing the cured product, solid electrolyte membrane, fuel cell, water electrolysis device, redox flow battery, and actuator - Google Patents

Description

The present invention relates to a composition, a cured product, a method for producing the cured product, a solid electrolyte membrane, a fuel cell, a water electrolysis device, a redox flow battery, and an actuator.

Hydrocarbon-based proton-conductive solid electrolytes are known. Patent Document 1 describes a proton-conductive polymer electrolyte made of a sulfonated polyphenyl compound having multiple repeating units, in which an average of two or more sulfone groups are introduced into each repeating unit.

International Publication No. 2017/029967

The proton-conductive polymer electrolyte described in Patent Document 1 has room for improvement in terms of ion conductivity.
Therefore, an object of the present invention is to provide a composition which, when cured, gives a cured product having excellent ion (proton) conductivity. Another object of the present invention is to provide a cured product, a method for producing the cured product, a solid electrolyte membrane, a fuel cell, a water electrolysis device, a redox flow battery, and an actuator.

As a result of extensive research into achieving the above object, the inventors have discovered that the above object can be achieved by the following configuration.

[1] A composition comprising a polymer compound having a repeating unit represented by the following formula 1 described below, and a radical polymerization initiator.
[2] The composition according to [1], wherein the ratio of the content of the radical polymerization initiator to the content of the polymer compound on a mass basis is 0.05 to 0.30.
[3] The composition according to [1] or [2], wherein the repeating unit represented by formula 1 described later is a repeating unit represented by formula 2 described later.
[4] The composition according to [3], wherein the repeating unit represented by the above formula 2 is a repeating unit represented by the below-mentioned formula 3.
[5] The composition according to [4], wherein the repeating unit represented by the above formula 3 is a repeating unit represented by the below-mentioned formula 4.
[6] The composition according to any one of [1] to [5], wherein the radical polymerization initiator is an azo compound.
[7] The composition according to any one of [1] to [3], wherein the polymer compound has 2 to 6 groups having a sulfonic acid group or a salt thereof in total per one of the repeating units.
[8] A cured product obtained by curing the composition according to any one of [1] to [7].
[9] The cured product according to [8], wherein the polymer compound is crosslinked via -S(=O) ₂ -.
[10] The cured product according to [8] or [9], which does not contain the radical polymerization initiator.
[11] A method for producing a cured product, comprising heating the composition according to any one of [1] to [7] to obtain a cured product.
[12] A method for producing the cured product according to [11], comprising immersing the cured product in an acidic solution.
[13] A solid electrolyte membrane comprising the cured product according to any one of [8] to [10].
[14] A fuel cell comprising the solid electrolyte membrane according to [13].
[15] A water electrolysis device comprising the solid electrolyte membrane according to [13].
[16] A redox flow battery comprising the solid electrolyte membrane according to [13].
[17] An actuator comprising the solid electrolyte membrane according to [13].

The present invention provides a composition that, when cured, gives a cured product having excellent ionic conductivity. The present invention also provides a cured product, a method for producing the cured product, a solid electrolyte membrane, a fuel cell, a water electrolysis device, a redox flow battery, and an actuator.

FIG. 1 is an exploded perspective view of an example of an embodiment of a fuel cell according to the present invention. 2 is a cross-sectional view of a stack included in the fuel cell of FIG. 1. 1 is an example of an embodiment of a water electrolysis device of the present invention. 1 is an example of an embodiment of a redox flow battery of the present invention. FIG. 1 is a schematic cross-sectional view of an example of an embodiment of an actuator of the present invention. The results show the results of evaluating the presence or absence of a radical polymerization initiator in a cured product using Fourier Transform Infrared Spectroscopy (FTIR). 1 shows the results of measuring the mechanical properties of the cured product.

The present invention will be described in detail below.
The following description of the components may be based on a representative embodiment of the present invention, but the present invention is not limited to such an embodiment.
In this specification, a numerical range expressed using "to" means a range that includes the numerical values before and after "to" as the lower and upper limits.

[Composition]
The composition according to an embodiment of the present invention (hereinafter also referred to as "the composition") contains a polymer compound represented by the below-mentioned formula 1 and a radical polymerization initiator. Although the mechanism by which the problem is solved by the composition is not necessarily clear, the present inventors speculate as follows.

The hydrocarbon-based polymer electrolyte described in Patent Document 1 achieves both water resistance and proton conductivity by dehydrating and condensing some of the sulfonic acid groups responsible for proton conduction to form intermolecular crosslinks via -S(=O) ₂ -. This cured material was prone to forming a dense and strong crosslinked structure.

This composition contains a radical polymerization initiator. Therefore, when heated, it is assumed that the radical species generated by the radical polymerization initiator first promotes bonding between the ends of the polymer compound, causing a reaction that extends the molecular chain of the polymer compound.

When the composition is further heated, -S(=O) ₂ - crosslinks are formed by dehydration condensation, but it is presumed that the influence of the earlier extension of part of the molecular chain of the polymer compound causes changes such as an increase in the molecular weight between crosslinking points in the cured product, resulting in a crosslinked structure that differs from that of conventional hydrocarbon-based polymer electrolytes. It is presumed that this change in crosslinked structure surprisingly leads to an improvement in ionic conductivity. Each component contained in this composition will be described in detail below.

<Polymer Compound>
(Unit 1)
The polymer compound contains a repeating unit represented by the following formula 1 (hereinafter also referred to as "unit 1"), and each repeating unit has at least one group having a sulfonic acid group or a salt thereof at a predetermined position.

In formula 1, Ar ¹¹ represents an arylene group or a heteroarylene group. The number of carbon atoms contained in Ar ¹¹ is preferably 6 to 20, more preferably 6 to 15, and still more preferably 6 to 12. Ar ¹¹ may be a group represented by the following AR1.
In terms of obtaining a composition having better effects of the present invention, Ar ¹¹ is preferably a p-phenylene group.

In formula 1, L ¹¹ represents a single bond or a divalent group. Examples of the divalent group include -C(=O)-, -C(=O)O-, -OC(=O)-, -O-, -S-, -S(=O) ₂ -, -NR ^A - (R ^A represents a hydrogen atom or a monovalent organic group), a hydrocarbon group (preferably having 1 to 10 carbon atoms) in which a hydrogen atom may be substituted with a halogen atom, and combinations thereof.

Among these, from the viewpoint of obtaining a composition having more excellent effects of the present invention, the divalent group for L ¹¹ is preferably at least one group selected from the group consisting of -O-, -S-, -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -C(═O)-, and -S(═O) ₂ -.

In formula 1, m represents an integer from 2 to 40, preferably an integer from 2 to 20, and more preferably an integer from 2 to 10.

The unit 1 contains a plurality of groups represented by Ar ¹¹ and a plurality of groups represented by L ^11. The plurality of Ar ¹¹ and L ¹¹ may be the same or different. That is, the unit 1 may contain a plurality of types of Ar ¹¹ and/or L ¹¹ .
From the viewpoint of obtaining a composition having a more excellent effect of the present invention, it is preferred that unit 1 contains a plurality of types of Ar ¹¹ and a plurality of types of L ¹¹ .

Sulfonic acid group-containing group The polymer compound has a group (hereinafter also referred to as a "sulfonic acid group-containing group") having one or more sulfonic acid groups or salts thereof (hereinafter also referred to as a "sulfonic acid group-containing group") per unit 1. This sulfonic acid group-containing group is bonded by replacing a hydrogen atom of any one of the groups represented by Ar ¹¹ contained in the unit 1. This replacing hydrogen atom is preferably a hydrogen atom directly bonded to a carbon atom constituting a ring of Ar ¹¹ .

Here, among the groups containing a sulfonic acid group, the structure of the group having a sulfonic acid group is not particularly limited, but the group represented by the following S1 is preferred.

In the above formula S1, L ^S1 is a single bond or an m+n+1 valent group, m and n are each independently an integer of 0 or more, and when L ^S1 is a single bond, m is 0 and n is 1, and when L ^S1 is an m+n+1 valent group, n is an integer of 1 or more and m is an integer of 0 or more, and * represents a bonding position.
In formula S1, R ¹ represents a hydrogen atom or a monovalent substituent, and is preferably a hydrogen atom.
In addition, it is preferable that m is 0 and n is 1, since this will provide a more excellent effect of the present invention.

The m+n+1 valent group of L ^S1 is not particularly limited, but examples of the divalent group include the same groups as the divalent group represented by L ¹¹ in formula 1.

The trivalent or higher valent group of L ^S1 is not particularly limited, and examples thereof include groups represented by the following formulae (1a) to (1d).

In formula (1a), _L3 represents a trivalent group. _T3 represents a single bond or a divalent group, and three _T3 may be the same or different.
_L3 includes a nitrogen atom, a trivalent hydrocarbon group (preferably having 1 to 10 carbon atoms. The hydrocarbon group may be an aromatic hydrocarbon group or an aliphatic hydrocarbon group), or a trivalent heterocyclic group (preferably a 5- to 7-membered heterocyclic group), and the hydrocarbon group may contain a heteroatom (for example, -O-). Specific examples of _L3 include a nitrogen atom, a glycerin residue, a trimethylolpropane residue, a phloroglucinol residue, and a cyclohexanetriol residue.

In formula (1b), _L4 represents a tetravalent group. _T4 represents a single bond or a divalent group, and the four _T4s may be the same or different from each other.
Suitable forms of _L4 include a tetravalent hydrocarbon group (preferably having 1 to 10 carbon atoms. The hydrocarbon group may be either an aromatic hydrocarbon group or an aliphatic hydrocarbon group) and a tetravalent heterocyclic group (preferably a 5- to 7-membered heterocyclic group), and the hydrocarbon group may contain a heteroatom (for example, -O-). Specific examples of _L4 include a pentaerythritol residue and a ditrimethylolpropane residue.

In formula (1c), _L5 represents a pentavalent group. _T5 represents a single bond or a divalent group, and the five _T5 may be the same or different from each other.
Suitable examples of _L5 include a pentavalent hydrocarbon group (preferably having 2 to 10 carbon atoms. The hydrocarbon group may be an aromatic hydrocarbon group or an aliphatic hydrocarbon group) or a pentavalent heterocyclic group (preferably a 5- to 7-membered heterocyclic group), and the hydrocarbon group may contain a heteroatom (for example, -O-). Specific examples of _L5 include an arabinitol residue, a phloroglucidol residue, and a cyclohexanepentanol residue.

In formula (1d), _L6 represents a hexavalent group. _T6 represents a single bond or a divalent group, and the six _T6 may be the same or different.
Suitable forms of _L6 include a hexavalent hydrocarbon group (preferably having 2 to 10 carbon atoms. The hydrocarbon group may be an aromatic hydrocarbon group or an aliphatic hydrocarbon group) or a hexavalent heterocyclic group (preferably a 6- to 7-membered heterocyclic group), and the hydrocarbon group may contain a heteroatom (e.g., -O-). Specific examples of _L6 include a mannitol residue, a sorbitol residue, a dipentaerythritol residue, a hexahydroxybenzene residue, and a hexahydroxycyclohexane residue.

In formula (1a) to formula (1d), specific examples and preferred forms of the divalent groups represented by T ₃ to T ₆ may be the same as the divalent group of L ^S1 already explained.

Among these, the group having a sulfonic acid group is preferably a group represented by formula S2.

In formula S2, L ^S2 represents a single bond or a divalent group, and the divalent group of L ^S2 may have the same form as that shown for the divalent group of L ^S1 , and preferred forms are also the same as those mentioned above.

The group having a salt of sulfonic acid is preferably a salt of the above-mentioned sulfonic acid group, and the counter ion is preferably a metal cation, such as Li, Na, K, Mg, Ca, Sr, Ti, Al, Fe, Rh, Pt, Ru, Ir, and Pd, with Li, Na, or K being preferred.

The content of unit 1 in the polymer compound is not particularly limited, but from the viewpoint of obtaining a composition having a better effect of the present invention, when the total repeating units of the polymer compound are taken as 100 mol %, the content is preferably 90 mol % or more, and more preferably 95 mol % or more. The polymer compound is preferably composed of unit 1.

(Unit 2)
The unit 1 is preferably a repeating unit represented by the following formula 2 (hereinafter also referred to as "unit 2"), in that a composition having better effects of the present invention can be obtained.

In formula 2, Ar ²¹ , Ar ²² and Ar ²³ each independently represent an arylene group or a heteroarylene group, and examples thereof include the same groups as those represented by Ar ¹¹ in formula 1, and preferred embodiments are also the same.

In formula 2, L ²¹ and L ²² each independently represent a single bond or a divalent group selected from the group consisting of -O-, -S-, -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -C(═O)-, and -S(═O) ₂ -.

In formula 2, p represents an integer of 1 to 5, preferably 1 or 2, and q represents an integer of 0 to 30, preferably 1 to 20, and more preferably 2 to 10.

The unit 2 may contain a plurality of groups represented by Ar ²¹ , Ar ²² , Ar ²³ , L ²¹ , and L ^22. These groups may be the same or different.

One or more sulfonic acid or similar group-containing groups are contained per unit 2. The sulfonic acid or similar group-containing group is bonded by replacing a hydrogen atom possessed by at least one group selected from the group consisting of groups represented by Ar ²¹ , Ar ²² , and Ar ²³ contained in the unit 2. The hydrogen atom to be replaced is preferably a hydrogen atom directly bonded to a carbon atom constituting a ring possessed by the groups represented by Ar ²¹ , Ar ²² , and Ar ²³ .

The content of unit 2 in the polymer compound is not particularly limited, but is the same as the content of unit 1 already described, and the preferred form is also the same.

(Unit 3)
In terms of obtaining a composition having better effects of the present invention, unit 2 is preferably a repeating unit represented by the following formula 3 (hereinafter also referred to as "unit 3").

In formula 3, L ³¹ and L ³² each independently represent a single bond, an oxygen atom, a sulfur atom, or —SO ₂ —, and preferably an oxygen atom.
X ³¹ , X ³² and X ³³ each independently represent a hydrogen atom, a lithium atom, a sodium atom or a potassium atom, preferably a hydrogen atom or a sodium atom, m represents an integer of 1 to 5, preferably 1 or 2, r represents an integer of 1 to 3, preferably 2, and n represents an integer of 0 to 10, preferably 1.

In addition, _y1 , _y2 , and _y3 each independently represent an integer of 0 to 4, and at least one of them is 1 or more. That is, the sum of _y1 to _y3 is 1 or more, preferably 2 or more, and is preferably 8 or less, more preferably 6 or less, and even more preferably 4 or less.
In particular, y ₁ and y ₂ are preferably 0 to 2, and y ₃ is preferably 0 to 2, in that a composition having more excellent effects of the present invention can be obtained.

The content of unit 3 in the polymer compound is not particularly limited, but is the same as the content of unit 1 already described, and the preferred form is also the same.

(Unit 4)
In terms of obtaining a composition having better effects of the present invention, the unit 3 is preferably a repeating unit represented by the following formula 4 (hereinafter also referred to as "unit 4").

In formula 4, X ⁴¹ , X ⁴² , X ⁴³ and X ⁴⁴ each independently represent a hydrogen atom, a lithium atom, a sodium atom or a potassium atom, and are preferably a hydrogen atom or a sodium atom.
z ₁ , z ₂ , z ₃ , and z ₄ each independently represent an integer of 0 to 4, and at least one selected from the group consisting of z ₁ , z ₂ , z ₃ , and z ₄ is 1 or more. That is, the sum of z ₁ to z ₄ is 1 or more, preferably 2 or more, preferably 8 or less, more preferably 6 or less, and even more preferably 4 or less.
In particular, z ₁ and z ₂ are preferably 0 to 2, and z ₃ and z ₄ are preferably 0 to 2, in that a composition having more excellent effects of the present invention can be obtained.

The content of unit 4 in the polymer compound is not particularly limited, but is the same as the content of unit 1 already described, and the preferred form is also the same.

The polymer compound may have other repeating units in addition to the above-mentioned units 1, 2, and 3. The content of the other repeating units is preferably 10 mol % or less when the total repeating units of the polymer compound are taken as 100 mol %.

The molecular weight of the polymer compound is not particularly limited, but is generally preferably 20,000 to 1,000,000, and more preferably 50,000 to 500,000.

The method for producing the polymer compound is not particularly limited, and a known method can be used. For example, the method for producing the polymer compound is described in paragraphs 0007 to 0029 of WO 2016/072350, which is incorporated herein by reference.
More specifically, the polymer compound can be produced by a method in which an aromatic dihalogen compound and an aromatic dihydroxy compound are subjected to desalting polycondensation in an aprotic polar solvent in the presence of potassium carbonate, an example of which is shown in Scheme 1 below.

In the above scheme 1, the sulfonation and recrystallization of bis(4-fluorophenyl)sulfone can be carried out, for example, by the following method. First, a mixture of bis(4-fluorophenyl)sulfone and 30% by mass fuming sulfuric acid is heated (for example, at 120°C for 12 hours), and the heated mixture is poured into saline solution to precipitate the product. The precipitate is filtered and then redissolved in water and neutralized with an aqueous NaOH solution. Next, table salt is added to obtain a precipitate of a crude product, which is then recrystallized from a water-ethanol mixture. In this way, sulfone diphenyl sulfone (referred to as "SFPS" in the above scheme) is obtained.

Next, the SFPS and 4,4'-biphenol (referred to as "BP" in the above scheme) are subjected to desalting polycondensation to obtain 2S-PPSU ("disulfonated polyphenylsulfone" in which two sulfonic acid groups (forming a salt with the counter ion Na ⁺ in the above scheme 1) are introduced per repeating unit). In the formula, n represents an integer of 2 or more.

As a method for desalting polycondensation, for example, a method of mixing SFPS, BP, _K2CO3 , DMSO (dimethyl _sulfoxide ), and toluene and heating the mixture under a nitrogen gas atmosphere (for example, at 140°C for 24 hours) can be used. After polymerization, the polymer is precipitated in sulfuric acid, filtered to obtain a crude product, which may then be redissolved in water, dialyzed, dehydrated, and dried. The polymer obtained may further be washed with sulfuric acid to activate the sulfonic acid group ( _-SO3Na to _-SO3H ).

As a method for producing a polymer compound, for example, the method shown in Scheme 2 below can also be used.

2S-PPSU and concentrated sulfuric acid are mixed, the mixture is heated at 60°C for two days, and the heated mixture is poured into ice water, dialyzed, dehydrated, and dried in a vacuum oven at 80°C for two days to obtain 4S-PPSU ("tetrasulfonated polyphenylsulfone" in which four sulfonic acid groups are introduced per repeat unit) as described in the above scheme. Note that n1 and n2 in Scheme 2 represent integers of 2 or more.

Similarly, PPSU (polyphenylsulfone) and 30 wt% fuming sulfuric acid are mixed and the mixture is heated at about 50°C for three days or more to sulfonate, resulting in D6S-PPSU (a "hexasulfonated polyphenylsulfone" in which six sulfonic acid groups are introduced per repeat unit). This reaction is shown in Scheme 3. In Scheme 3, n1 and n2 represent integers of 2 or more.

As will be described in detail later, the polymer compound has a group containing a sulfonic acid group or the like, and can form a crosslinked structure by causing a dehydration reaction between the group and an active hydrogen atom bonded to a carbon atom having high electron density. An example of the carbon atom having high electron density is hydrogen bonded to an aromatic ring.
An example of such a crosslinking reaction of a polymer compound is shown in the following scheme 4. In scheme 4, n represents an integer of 2 or more. As shown in the following scheme, the polymer compound is crosslinked via -SO ₂ -.

The crosslinking reaction can be carried out by heating the specific polymer, typically in the presence of a dehydrating agent as necessary.
When a dehydrating agent is used, a known dehydrating agent can be used, and is not particularly limited, and examples thereof include phosphorus pentoxide and polyphosphoric acid, which may be dissolved in a solvent to be used as a liquid dehydrating agent. Examples of the solvent include alkylsulfonic acids such as methanesulfonic acid and trifluoromethanesulfonic acid, and aromatic sulfonic acids such as chlorobenzenesulfonic acid.

<Radical Polymerization Initiator>
The radical polymerization initiator may be a photoradical polymerization initiator that initiates radical polymerization by light, or a thermal radical polymerization initiator that initiates radical polymerization by heat, or these may be used in combination. It is preferable that the present composition generates a cured product by sequentially inducing radical generation and dehydration condensation, and from the viewpoint that both of the above reactions proceed by heating, the radical polymerization initiator is preferably a thermal radical polymerization initiator.

A known radical polymerization initiator can be used, for example, the one described in International Publication No. WO 2018/016614.

Examples of the thermal radical polymerization initiator include azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(methyl isobutyrate), 2,2'-azobis-2,4-dimethylvaleronitrile, and 1,1'-azobis(1-acetoxy-1-phenylethane); peroxides such as benzoyl peroxide, di-t-butylbenzoyl peroxide, t-butyl peroxypivalate, and di(4-t-butylcyclohexyl)peroxydicarbonate; and persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate. Among these, azo compounds or peroxides are preferred, and azo compounds are more preferred, in that a composition having the effects of the present invention can be obtained.
When the composition contains an azo compound, the resulting cured product has better flexibility.

Examples of photoradical polymerization initiators include acetophenone-based compounds, benzyl-based compounds, benzophenone-based compounds, thioxanthone-based compounds, bisimidazole-based compounds, acridine-based compounds, acylphosphine-based compounds, and oxime ester compounds.

The content of the radical polymerization initiator in the composition is not particularly limited, but in order to obtain a composition having a more excellent effect of the present invention, the mass ratio of the content of the radical polymerization initiator to the content of the polymer compound in the composition (content of radical polymerization initiator/content of polymer compound) is preferably 0.01 or more, more preferably 0.03 or more, preferably 0.05 or more, preferably more than 0.05, preferably 0.30 or less, more preferably 0.20 or less, even more preferably 0.15 or less, and particularly preferably less than 0.15.

When the ratio exceeds 0.05, the resulting cured product has better ionic conductivity in a high-temperature, low-humidity environment. In this case, the ratio is preferably 0.30 or less, more preferably 0.20 or less, and even more preferably 0.15 or less.

Furthermore, when the above ratio is greater than 0.05 and less than 0.15, the resulting cured product has better ionic conductivity at low temperatures (low and high humidity) and at high temperatures and high humidity.

The composition may contain one type of radical polymerization initiator alone, or may contain two or more types. When the composition contains two or more types of radical polymerization initiators, it is preferable that the total content is within the above numerical range.

<Other ingredients>
The composition may contain other components other than the above components. Examples of other components include solvents. The solvent is not particularly limited, but from the viewpoint that the cured product obtained by curing the composition is likely to have better ion conductivity, a solvent that can dissolve (or dissolve and diffuse monomolecularly) both the polymer compound and the radical polymerization initiator is preferable. From the above viewpoint, the solvent is preferably an aprotic polar solvent such as dichloromethane, tetrahydrofuran, acetone, dimethylformamide, acetonitrile, and dimethylsulfoxide.

The amount of the solvent in the composition is not particularly limited, but is preferably 10 to 100 mL, and more preferably 20 to 80 mL, per 1 g of the total amount of the polymer compound and the radical polymerization initiator.

<Production method of composition>
The method for producing the composition is not particularly limited, and the above-mentioned components may be mixed. The order of mixing is not particularly limited, but the composition can be produced, for example, by dissolving a polymer compound in a solvent to prepare a polymer compound solution, dissolving a radical polymerization initiator in a solvent to prepare a radical polymerization initiator solution, and mixing the two solutions.

[Uses of the composition]
According to the above composition, a cured product having excellent ion conductivity can be formed. In addition, the obtained cured product has excellent proton conductivity. Therefore, the cured product can be used as a solid electrolyte membrane in a polymer electrolyte fuel cell (PEFC). The above composition can be used for producing a solid polymer electrolyte (membrane).

The cured material can also be used as an ion (cation) exchange membrane, and an ion exchange membrane containing the cured material can be used, for example, as a cation exchange membrane having a water-permeable support and a layer of the cured material disposed on the support. The cation exchange membrane can be used, for example, in combination with an anion exchange membrane, in electrochemical measurement devices, water electrolysis devices, wastewater treatment devices, and the like.

[Cured product]
The cured product according to the embodiment of the present invention is a cured product obtained by curing the composition already described.
As already explained, since the present composition contains a radical polymerization initiator, it is presumed that the radical species generated from the radical polymerization initiator acts on the terminal portion of the polymer compound, causing the molecular chain to be extended and crosslinking between molecules to occur through a dehydration condensation reaction. The order in which these two reactions occur may be either first or in parallel, but from the viewpoint of being more likely to produce a cured product with superior ion conductivity, it is preferable that the radical species is generated first and then the dehydration condensation reaction occurs.

From the above viewpoint, in the method for producing a cured product, when the radical polymerization initiator is a thermal radical polymerization initiator, it is preferable to hold the mixture at a temperature of 30 to 120° C. for 6 to 72 hours, and then hold the mixture at a temperature of 160 to 200° C. for 6 to 72 hours.
In this way, the generation of radical species by the thermal radical polymerization initiator is likely to precede the initiation of the dehydration condensation reaction.

In addition, since water molecules are generated in the dehydration condensation reaction, a dehydrating agent may be used. In this case, a known dehydrating agent can be used, and examples of the agent include, but are not limited to, phosphorus pentoxide and polyphosphoric acid.

The obtained cured product may be washed. By washing the cured product, the radical polymerization initiator and the like can be removed from the cured product. The washing method is not particularly limited, but may be a method in which the cured product is immersed in a washing liquid and the substances to be removed are dissolved in the washing liquid.
Among them, washing with an alkaline washing solution and an acid washing solution in sequence is preferable in that a cured product having a more excellent effect of the present invention can be obtained. If the cured product is finally immersed in an acidic solution (such as sulfuric acid) to dissociate the salt of the sulfonic acid group and convert it to a sulfonic acid group (activation treatment), the obtained cured product is likely to exhibit more excellent ion conductivity.

The alkaline cleaning solution is not particularly limited, but examples include aqueous solutions of alkali metal hydroxides such as an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, an aqueous lithium hydroxide solution, and an aqueous calcium hydroxide solution.

The acid cleaning solution is not particularly limited, but examples include sulfuric acid. By cleaning with sulfuric acid, the sulfonic acid groups in the salt state can be dissociated, making it easier to obtain a cured product with better proton conductivity. Hereinafter, the cleaning process including acid cleaning may be referred to as an activation treatment.

In addition to the acid cleaning solution and alkaline cleaning solution, it is also preferable to use water to clean the cured product. For example, it is preferable to clean the product by changing the cleaning solution in the following order: alkaline cleaning, water cleaning, acid cleaning, and water cleaning.

There are no particular limitations on the temperature of the cleaning solution during cleaning, but in general, 10 to 150°C is preferred, and 30 to 100°C is more preferred.

The cured product preferably does not contain a radical polymerization initiator. The washing step removes unreacted radical polymerization initiator from the cured product. The cured product does not contain a radical polymerization initiator means that the free radical polymerization initiator contained in the composition has been removed from the cured product.
A structure derived from a radical polymerization initiator incorporated into the molecular structure of a polymer compound (e.g., bonded by a covalent bond or the like) is not included in the “radical polymerization initiator” referred to here. In other words, even if the cured product does not contain a radical polymerization initiator, the polymer compound may have a structure derived from the radical polymerization initiator in the molecule.

(Drying process)
The drying step is a step of drying the cured product after washing to obtain a dried cured product. The drying method is not particularly limited, but includes a method of holding the cured product with or without heating. When heating, the temperature is not particularly limited, but generally, 30 to 80°C is preferred.

[Application]
The cured product has excellent proton conductivity even under high temperature and low humidity conditions. Furthermore, when the cured product is crosslinked, the crosslinked structure provides the cured product with superior mechanical properties.
Since the present cured product has the above-mentioned properties, it can be used as a solid electrolyte in polymer electrolyte fuel cells (PEFCs) and the like.

[Fuel Cell]
1 is an exploded perspective view of an example of an embodiment of a fuel cell according to the present invention, which is a polymer electrolyte fuel cell having a laminate including an electrolyte layer including a solid electrolyte membrane including the cured product, a pair of catalyst layers sandwiching the electrolyte layer from both sides, and gas diffusion layers respectively disposed on the surfaces of the catalyst layers opposite to the cured product.

As shown in FIG. 1, the fuel cell 10 comprises a laminate 11, gas diffusion layers 12 and 13 sandwiching the laminate 11 from both sides, and separators 14 and 15 arranged on the surface of each gas diffusion layer opposite the fuel cell 10.
2 is a cross-sectional view of the laminate 11. The laminate 11 has an electrolyte layer 21 having a cured material, and catalyst layers 22 and 23 sandwiching the electrolyte layer from both sides.

Here, the separators 14 and 15 are each made of a material that is electrically conductive and has low gas permeability. Such materials are not particularly limited, but examples include metal plates that have been treated to be corrosion-resistant, and carbon-based materials such as baked carbon.

The separator 14 is disposed facing the gas diffusion layer 12, and is provided with a flow path 16 having a comb-shaped structure on the side facing the gas diffusion layer 12, so that the reactant gas can flow through the flow path 16. A similar flow path 17 is also provided in the separator 15.
A cooling water flow passage 18 is formed on the surface of the separator 14 opposite to the flow passage 16 , and a cooling water flow passage 19 is formed on the surface of the separator 15 opposite to the flow passage 17 .

The fuel gas first passes through the flow passage 16 of the separator 14 , and the oxidant gas first passes through the flow passage 17 of the separator 15 .
A fuel gas (e.g., hydrogen, methane, etc.) is supplied to the stack 11 via the gas diffusion layer 12 while passing through the flow passage 16 of the separator 14. On the other hand, an oxidant gas (oxygen, air, etc.) is supplied to the stack 11 via the gas diffusion layer 13 while passing through the flow passage 17 of the separator 15.
Both the gas diffusion layers 12 and 13 are made of a material that has high electrical conductivity and high gas diffusivity. Although there is no particular limitation on the material, a porous material is preferable.
The thickness of the gas diffusion layers 12 and 13 is not particularly limited, but is generally preferably 50 to 1000 μm each.

The laminate 11 has an electrolyte layer 21, a catalyst layer 22 arranged on one side of the electrolyte layer 21, and a catalyst layer 23 arranged on the other side.

The laminate 11 has an electrolyte layer 21 formed in a layer shape. The form of the cured material of the electrolyte layer 21 has already been described, and the preferred form is also the same, so description thereof will be omitted.
The thickness of the electrolyte layer 21 is not particularly limited, but is generally preferably 1 to 500 μm. A thickness of 1 μm or more is preferable in terms of ease of production and handling. On the other hand, a thickness of 500 μm or less is preferable in terms of smaller membrane resistance.

The catalyst layers 22 and 23 each contain catalyst particles and an electrolyte. There is no particular restriction on the shape when viewed from above, but a roughly rectangular shape makes it easy to form.

The catalyst particles are not particularly limited, and platinum group elements such as platinum, palladium, ruthenium, iridium, rhodium, and osmium can be used. In addition, metals such as iron, lead, copper, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum, as well as alloys, oxides, and double oxides thereof can also be used.
The electrolyte used in the catalyst layers 22 and 23 may be any electrolyte that has ion conductivity.
According to the fuel cell, the cured material has excellent proton conductivity, and as a result, electric current can be generated more efficiently.

[Ion exchange membrane]
The ion exchange membrane according to an embodiment of the present invention is the ion exchange membrane having the cured material already described.
Since the cured product can be used as a cation exchange membrane, the ion exchange membrane may be formed only from the cured product. However, in terms of having better durability, the ion exchange membrane is preferably a laminate having a substrate and a layer (cured product layer) containing the cured product formed on the substrate.

The substrate is not particularly limited, but a substrate having water permeability is preferred. A typical example of a substrate having water permeability is a porous member, and an example of the porous member is a continuous inorganic oxide porous film containing a chemically stable inorganic oxide. The inorganic oxide is not particularly limited, but examples thereof include titanium oxide, silicon oxide, aluminum oxide, niobium oxide, tantalum oxide, and nickel oxide. In addition, a porous polymer having a halogenated polymer can also be used as the porous member.

The ion exchange membrane as a laminate may further have an anion exchange membrane on the surface of the substrate opposite to the surface on which the cured material layer is disposed. The anion exchange membrane is not particularly limited, and any known anion exchange membrane may be used.
Since the present cured product has excellent ion conductivity, the ion exchange membrane has excellent ion conductivity.

[Water electrolysis device]
FIG. 3 shows an embodiment of a water electrolysis device according to the present invention.
The water electrolysis device 30 has a pair of electrodes (electrode 31 and electrode 32), which are isolated from each other by an ion exchange membrane 33. The electrodes 31, 32 and the ion exchange membrane 33 are arranged in a container 34 so as to be in contact with an electrolytic solution 35. The electrodes 31 and 32 are each electrically connected to a potential/current control device (not shown) so as to be able to control and measure the current and potential, respectively.

When raw water is supplied to the water electrolysis device 30, a current is passed between the pair of electrodes to electrolyze the raw water, thereby producing hydrogen and oxygen.
In the above water electrolysis method, known electrolysis conditions (raw water, current density, etc.) can be applied, such as those described in JP-A-57-131376.

[Redox flow battery]
FIG. 4 shows an example of an embodiment of the redox flow battery of the present invention.
The redox flow battery 40 is divided into a positive electrode cell 42 and a negative electrode cell 43 by a separator 41 made of the solid electrolyte membrane. The positive electrode cell 42 and the negative electrode cell 43 each include a positive electrode and a negative electrode. The positive electrode cell 42 is connected to a positive electrode tank 46 for supplying and discharging a positive electrode electrolyte 44 through a pipe. The negative electrode cell 43 is also connected to a negative electrode tank 47 for supplying and discharging a negative electrode electrolyte 45 through a pipe. The electrolyte is circulated through pumps 48 and 49, and an oxidation-reduction reaction (i.e., a redox reaction) occurs in which ions of oxidized water are converted, thereby causing charging and discharging at the positive electrode and the negative electrode.

[Actuator]
5 is a schematic cross-sectional view of an example of an embodiment of the actuator of the present invention. The actuator element 50 has a pair of flexible electrodes 51 and 52 and an electrolyte layer 53 disposed between the flexible electrodes, the electrolyte layer 53 being made of a solid electrolyte membrane containing the cured material. The cured material has excellent flexibility in addition to excellent proton conductivity, and therefore does not interfere with the operation of the actuator.

In addition to the actuators mentioned above, the present cured product can also be used for the actuators described in, for example, paragraphs 0054 to 0075 of JP 2018-189452 A and paragraphs 0006 to 0024 of JP 2019-511259 A.

The present invention will be described in more detail below with reference to examples. The materials, amounts used, ratios, processing contents, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the examples shown below.

[Synthesis of polymer compound (SPPSU)]
First, PPSU (polyphenylsulfone) beads were mixed with sulfuric acid and kept at 60° C. for 2 days to be sulfonated. The sulfonated PPSU was then cooled to precipitate, washed with a dialysis membrane until the pH reached 7, and water was removed to obtain SPPSU. The content of sulfonic acid groups in the obtained SPPSU was determined by titration, and the number of sulfonic acid groups per repeating unit was 2.3.
The synthesized SPPSU (IEC = 3.68 meq/g) was dissolved in DMSO (dimethyl sulfoxide) to obtain an SPPSU solution.

[Preparation of Composition 1 (SPPSU/BPO)]
A DMSO solution of SPPSU (SPPSU/DMSO) and a DMSO solution of BPO (benzoyl peroxide) (BPO/DMSO) were prepared, and BPO/DMSO was added to SPPSU/DMSO and stirred for about 1 hour. The resulting mixture was placed in a petri dish and heat-treated at 80°C, 120°C, 160°C, and 180°C for 24 hours each to obtain a cured product.

The resulting cured product was treated overnight in 0.5 M NaOH at 80° C., then in boiling water for 2 hours, in 1 M H ₂ SO ₄ at 80° C. for 2 hours, and then in boiling water for 2 hours, and then dried. Table 1 shows the formulations of each of the compositions prepared.

[Preparation of Composition 2 (SPPSU/AIBN)]
Except for using AIBN (azobisisobutyronitrile) instead of BPO, compositions were prepared in the same manner as in "Composition Preparation 1" to obtain cured products. Table 2 shows the formulation of each of the compositions prepared.

[Example 9: Preparation of cured product]
A composition (hereinafter, the sample name is referred to as "CSPPSU") was prepared in the same manner as in "Composition Preparation 1" except that BPO was not used, and a cured product was obtained.

The mechanical properties, FTIR properties, ion exchange capacity, and proton conductivity of the obtained cured products of Examples 1 to 8 and the cured product of Example 9 were measured using the following methods.

(FTIR characteristics)
The presence or absence of the radical polymerization initiator in the cured product was evaluated using FTIR (Thermoscitific, Nicolet 6700), and the results are shown in FIG.

6, (a) represents the spectrum of AIBN, (b) represents the spectrum of SPPSU, (c) represents the spectrum of the cured product obtained using the composition of Example 7 before cleaning (activation treatment), and (d) represents the spectrum of the cured film obtained using the composition of Example 7 after cleaning (activation treatment). From these results, it was revealed that AIBN was not contained in the cured product after cleaning (activation treatment), since 2998 cm ^-1 , 2948 cm ^-1 (ν _as CH ₃ ), and 2870 cm ^-1 , (ν _s CH ₃ ) derived from the CH ₃ vibration of AIBN in (a) were not observed.

(Mechanical properties)
As mechanical properties of the cured product, tensile strength (MPa) and breaking elongation (%) were measured using a tensile tester (Shimadzu, EZ-S). Samples were prepared using a super dumbbell cutter (model: SDMP-1000 special, conforming to JIS K6251-7). The test was carried out at room temperature, with a strain rate of 1 mm/min. The results are shown in Figure 7.

In Figure 7, (A) shows the results for the Nafion (registered trademark)-212 membrane (thickness = 0.050 mm), which had a breaking stress of 16.9 MPa and a breaking elongation of over 150%.

(B) indicates the results for the cured product of Example 9 (CSPPSU) (thickness = 0.061 mm), which had a breaking stress of 55.6 MPa and a breaking elongation of 69.6%.
(C) shows the results for the cured product (after activation treatment) (thickness = 0.052 mm) obtained using the composition of Example 3 (10% BPO), which had a breaking stress of 51.3 MPa and a breaking elongation of 59.2%.
(D) indicates the result of the cured product (after activation treatment) (thickness = 0.057 mm) obtained using the composition of Example 7 (10% AIBN), which had a breaking stress of 41.2 MPa and a breaking elongation of 134.7%.

The above results show that the cured product obtained using the composition of Example 7, which contains an azo-based compound as a radical polymerization initiator, has a greater breaking elongation than the cured product obtained using the composition of Example 3.

(Ion exchange capacity)
The ion exchange capacity (IEC) of the cured product was evaluated by a titration method. After drying at 80° C., the cured product was immersed in 2 M NaCl and titrated with 0.01 M NaOH.
IEC (meq./g) = M ₁ V ₁ /W _dry
( _M1 is the molar concentration of NaOH, _V1 is the amount (ml) adjusted to pH 7, and _Wdry is the mass of the dried cured product.)

(Proton Conductivity)
The proton conductivity of the cured product was measured by a four-probe method using a membrane resistance measurement system MTS740 (Scribner Associates) equipped with a PSM1735 analyzer (Newtons4th). The measurements were performed at temperatures of 40 and 80° C. and humidity of 0 to 90% RH. The impedance measurements were performed at an applied voltage of 10 mV (peak to peak) and a frequency of 1 Hz to 1 MHz.
Table 3 shows the measurement results of the ion exchange capacity and the proton conductivity.

In Table 3, "-" indicates that there is no data. Also, the sample name "nafion" 212 refers to the Nafion (registered trademark)-212 membrane.

From the results in Table 3, the cured products obtained using the compositions of Examples 2 to 4 and Examples 6 to 8 had better proton conductivity at both low temperature (40°C) and high temperature (80°C) than the cured film obtained using the composition of Example 9, which did not contain a radical polymerization initiator. In particular, they had better proton conductivity even at high temperature and low humidity (40% RH).

The results in Table 3 also reveal that the cured product obtained using the composition of Example 6, which contains an azo compound as a radical polymerization initiator, has superior proton conductivity compared to the composition of Example 2.

The results in Table 3 also reveal that the cured product obtained using the composition of Example 7, in which the content of radical polymerization initiator relative to the content of SPPSU (polymer compound) in the composition is greater than 0.05 and less than 0.15, has better ionic conductivity at low temperatures and at high temperatures (80°C) and high humidity (90% RH) compared to the cured products obtained using the compositions of Examples 6 and 8.

The results in Table 3 also reveal that the cured product obtained using the composition of Example 7, in which the content of radical polymerization initiator relative to the content of SPPSU (polymer compound) in the composition exceeds 0.05, has better proton conductivity at high temperature (80°C) and low humidity (40% RH) than the cured product obtained using the composition of Example 6.

10: fuel cell 11: laminate 12, 13: gas diffusion layer 14, 15: separator 16, 17: flow path 18, 19: cooling water flow path 21: electrolyte layer 22, 23: catalyst layer 30: water electrolysis device 31, 32: electrode 33: ion exchange membrane 34: container 35: electrolyte 40: redox flow battery 41: separation membrane 42: positive electrode cell 43: negative electrode cell 44: positive electrode electrolyte 45: negative electrode electrolyte 46: positive electrode tank 47: negative electrode tank 48, 49: pump 50: actuator element 51: flexible electrode 53: electrolyte layer

Claims (16)

A polymer compound having a repeating unit represented by the following formula 2 :
A thermal radical polymerization initiator;
A composition comprising :
(In formula 2, Ar ²¹ , Ar ²² , and Ar ²³ each independently represent an arylene group or a heteroarylene group; L ²¹ and L ²² each independently represent a single bond or a divalent group selected from the group consisting of -O-, -S-, -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -C(═O)-, and -S(═O) ₂ -; a plurality of Ar ²¹ , Ar ²² , Ar ²³ , L ²¹ , and L ²² may be the same or different; p represents an integer of 1 to 5; q represents an integer of 0 to 30; and the group represented by Ar ²¹ , the group represented by Ar ²² , and Ar At least one hydrogen atom of at least one group selected from the group consisting of groups represented by ^{formula (I)} and (II) is substituted with a group having a sulfonic acid group or a salt thereof. The composition according to claim 1, wherein a ratio of the content of the thermal radical polymerization initiator to the content of the polymer compound on a mass basis is 0.05 to 0.30. The composition according to claim 1 or 2 , wherein the repeating unit represented by formula 2 is a repeating unit represented by formula 3 below.
(In formula 3, L ³¹ and L ³² each independently represent a single bond, an oxygen atom, a sulfur atom, or -SO ₂ -; a plurality of L ³¹ and L ³² may be the same or different; X ³¹ , X ³² , and X ³³ each independently represent a hydrogen atom, a lithium atom, a sodium atom, or a potassium atom; m represents an integer of 1 to 5; r represents an integer of 1 to 3; n represents an integer of 0 to 10; y ₁ , y ₂ , and y ₃ each independently represent an integer of 0 to 4; and at least one selected from the group consisting of y ₁ , y ₂ , and y ₃ is 1 or greater.) The composition according to claim 3 , wherein the repeating unit represented by formula 3 is a repeating unit represented by formula 4 below.
(In formula 4, X ⁴¹ , X ⁴² , X ⁴³ , and X ⁴⁴ each independently represent a hydrogen atom, a lithium atom, a sodium atom, or a potassium atom; z ₁ , z ₂ , z ₃ , and z ₄ each independently represent an integer of 0 to 4, and at least one selected from the group consisting of z ₁ , z ₂ , z ₃ , and z ₄ is 1 or greater.) The composition according to any one of claims 1 to 4 , wherein the thermal radical polymerization initiator is an azo compound. The composition according to any one of claims 1 to 5 , wherein the polymer compound has 2 to 6 groups having a sulfonic acid group or a salt thereof in total per one of the repeating units. A cured product obtained by curing the composition according to any one of claims 1 to 6 . The cured product according to claim 7 , wherein the polymer compound is crosslinked via -S(=O) ₂ -. The cured product according to claim 7 or 8 , which does not contain the thermal radical polymerization initiator. A method for producing a cured product, comprising heating the composition according to any one of claims 1 to 6 to obtain a cured product. The method for producing the cured product according to claim 10 , comprising immersing the cured product in an acidic solution. A solid electrolyte membrane comprising the cured product according to any one of claims 7 to 9 . A fuel cell comprising the solid electrolyte membrane of claim 12 . A water electrolysis device comprising the solid electrolyte membrane according to claim 12 . A redox flow battery comprising the solid electrolyte membrane according to claim 12 . An actuator comprising the solid electrolyte membrane according to claim 12 .