JP2015122183A - Polymer electrolyte film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polymer electrolyte film made of a non-fluorine-based material, flexible and hard to crack and superior in resistance to hot water.SOLUTION: A polymer electrolyte film comprises a composition including: a block copolymer(Z) including a polymer block (A) made up of a structural unit originating an aromatic vinyl compound and having an ion-conductive group, and an amorphous polymer block (B) made up of a structural unit originating unsaturated aliphatic hydrocarbon and having no ion-conductive group; and a crosslinker (X) having, in its molecule, two or more oxetane rings. The crosslinking is performed after molding of the composition.

Description

  The present invention relates to a polymer electrolyte membrane useful for a polymer electrolyte fuel cell.

  In recent years, fuel cells have attracted attention as highly efficient power generation systems. Fuel cells are classified into molten carbonate type, solid oxide type, phosphoric acid type, solid polymer type, etc., depending on the type of electrolyte. Of these, a polymer electrolyte membrane is sandwiched between electrodes (anode and cathode), a fuel made of a reducing agent (usually hydrogen or methanol) at the anode, and an oxidant (usually air) at the cathode. Since the polymer electrolyte fuel cell to be supplied and generate electric power is excellent in low temperature operability, small size and light weight, etc., application to automobile power sources, portable device power sources, household cogeneration systems, etc. is being studied.

  Perfluorocarbon sulfonic acid polymers are often used as the material for polymer electrolyte membranes used in polymer electrolyte fuel cells because of their chemical stability. Environmental load becomes a problem.

  Under these circumstances, a polymer electrolyte membrane made of a material that does not contain fluorine (non-fluorine-based material) has recently been demanded. For example, a polymer electrolyte membrane made of polyether ether ketone (PEEK) into which a sulfonic acid group is introduced is known (see Patent Document 1). Although such a polymer electrolyte membrane is excellent in heat resistance, it is hard and brittle, so it is easily broken and lacks practical utility.

  On the other hand, there is known a polymer electrolyte membrane comprising a block unit comprising a polymer block having an ion conductive group and a flexible polymer block, which comprises a structural unit derived from an aromatic vinyl compound (Patent Document 2). reference). Such a polymer electrolyte membrane is flexible and difficult to break. Moreover, since the polymer block having the ion conductive group forms an ion conductive channel by microphase separation from the flexible polymer block, it has excellent ion conductivity.

  On the other hand, in a fuel cell using hydrogen as a fuel, it is required to increase the operating temperature for higher output. In order to meet such a demand, durability of the polymer electrolyte membrane against hot water (for example, 90 ° C.) ( Improvement of hot water resistance), specifically, suppression of elution of the polymer electrolyte membrane by hot water has been studied.

  For example, a polymer electrolyte membrane comprising, as a main component, a block copolymer in which the flexible polymer block is a structural unit derived from a vinyl compound and the flexible polymer block is crosslinked with 1,2-polybutadiene or the like. It is known that the hot water resistance of water increases (see Patent Document 3).

JP-A-6-93114 International Publication No. 2006/070929 International Publication No. 2012/043400

  However, there is still room for improvement in hot water resistance toward higher output of the polymer electrolyte fuel cell.

  Accordingly, an object of the present invention is to provide a polymer electrolyte membrane which is made of a non-fluorine material, is flexible and hardly cracked, and has excellent hot water resistance.

According to the invention, the object is
A polymer block (A) composed of a structural unit derived from an aromatic vinyl compound and having an ion conductive group (hereinafter simply referred to as “polymer block (A)”) and an unsaturated aliphatic hydrocarbon A block copolymer (Z) (hereinafter, referred to as “polymer block (B)”) comprising an amorphous polymer block (B) (hereinafter simply referred to as “polymer block (B)”) comprising a structural unit and having no ion conductive group. , Simply referred to as “block copolymer (Z)”), and a crosslinking agent (X) having two or more oxetane rings in the molecule (hereinafter simply referred to as “crosslinking agent (X)”) This is achieved by providing a polymer electrolyte membrane characterized in that crosslinking is performed after molding.

  According to the present invention, it is possible to provide a polymer electrolyte membrane which is made of a non-fluorine material, is flexible and hardly cracked, and has excellent hot water resistance.

(Block copolymer (Z))
The block copolymer (Z) is composed of a structural unit derived from an aromatic vinyl compound and does not have an ion conductive group (hereinafter referred to as “polymer block (A ₀ )”) and a polymer. It is obtained by introducing an ion conductive group into a polymer block (A ₀ ) of a block copolymer containing the block (B) (hereinafter referred to as “block copolymer (Z ₀ )”). In the following, description will be given in order.

<Polymer block (A)>
The polymer block (A) can be formed by introducing an ion conductive group into the polymer block (A ₀ ). The ion conductive group is usually introduced into the aromatic ring of the polymer block (A ₀ ).

The polymer block (A ₀ ) is composed of a structural unit derived from an aromatic vinyl compound, and the aromatic ring of the aromatic vinyl compound is a carbocyclic aromatic ring such as a benzene ring, a naphthalene ring, an anthracene ring, or a pyrene ring. Preferably, there is a benzene ring.

Examples of the aromatic vinyl compound that can form the polymer block (A ₀ ) include styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-ethylstyrene, 2,3-dimethylstyrene, 2, 4-dimethylstyrene, 2,5-dimethylstyrene, 3,5-dimethylstyrene, 2-methoxystyrene, 3-methoxystyrene, 4-methoxystyrene, vinylbiphenyl, vinylterphenyl, vinylnaphthalene, vinylanthracene, vinylpyrene, 4 -Phenoxystyrene etc. are mentioned.

  Of the hydrogen atoms on the vinyl group of the aromatic vinyl compound, the hydrogen atom bonded to the α-position carbon (α-carbon) of the aromatic ring may be substituted with another substituent. Such a substituent is preferably an alkyl group having 1 to 4 carbon atoms such as methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, and tert-butyl group; A chloromethyl group, a 2-chloroethyl group, a 3-chloroethyl group and the like, preferably a halogenated alkyl group having 1 to 4 carbon atoms; or a phenyl group. Examples of the aromatic vinyl compound in which a hydrogen atom bonded to the α-carbon is substituted with these substituents include α-methylstyrene, α-methyl-4-methylstyrene, α-methyl-2-methylstyrene, α-methyl. Examples include -4-ethylstyrene, 1,1-diphenylethylene, and the like.

Among the aromatic vinyl compounds that can form the above polymer block (A ₀ ), styrene, α-methylstyrene, 4-methylstyrene, 4-ethylstyrene, α-methyl-4-methylstyrene, α-methyl-2 -Methyl styrene, vinyl biphenyl and 1,1-diphenylethylene are preferable, styrene, α-methylstyrene, 4-methylstyrene and 1,1-diphenylethylene are more preferable, and styrene is more preferable.

A polymer block (A ₀ ) can be formed by polymerizing these aromatic vinyl compounds as monomers, one kind alone, or two or more kinds mixed.

In the present invention, the polymer block (A ₀ ) may contain other structural units not derived from one or more aromatic vinyl compounds within a range not impairing the effects of the present invention. Examples of monomers that can form such other structural units include butadiene, 1,3-pentadiene, isoprene, 1,3-hexadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1, Preferably conjugated dienes having 4 to 8 carbon atoms such as 3-butadiene and 1,3-heptadiene; ethylene, propylene, 1-butene, isobutene, 1-pentene, 1-hexene, 1-heptene, 1-octene and the like Is an alkene having 2 to 8 carbon atoms; (meth) acrylic acid ester such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate; vinyl acetate, vinyl propionate, vinyl butyrate, pivalic acid Vinyl esters such as vinyl; vinyl ethers such as methyl vinyl ether and isobutyl vinyl ether; In this case, the copolymerization form of these other monomers and the above-described aromatic vinyl compound is preferably random copolymerization. The amount of these other monomers used is preferably 5 mol% or less of the monomer used for forming the polymer block (A ₀ ).

The number average molecular weight (Mn) per polymer block (A ₀ ) is usually preferably in the range of 1,000 to 100,000, more preferably in the range of 2,000 to 70,000 as a standard polystyrene equivalent value. The range of 3,000 to 40,000 is more preferable. If the Mn is 1,000 or more, the ion conductivity is good, and if it is 100,000 or less, the film-forming property of the block copolymer (Z) is good. Thus, the production of the polymer electrolyte membrane of the present invention is possible. This is advantageous.

The ion conductive group possessed by the polymer block (A ₀ ) is preferably a proton conductive group, and —SO ₃ M or PO ₃ HM (wherein M represents a hydrogen atom, an ammonium ion or an alkali metal ion). One or more selected from sulfonic acid groups, phosphonic acid groups and salts thereof shown are more preferable, one or more selected from sulfonic acid groups and salts thereof are more preferable, and sulfonic acid groups are particularly preferable.

<Polymer block (B)>
The polymer block (B) is an amorphous polymer block composed of a structural unit derived from an unsaturated aliphatic hydrocarbon and having no ion conductive group. In addition, the amorphous property of a polymer block (B) can be confirmed by measuring the dynamic viscoelasticity of a block copolymer (Z), and not having the change of the storage elastic modulus derived from a crystalline olefin polymer.

  Examples of the unsaturated aliphatic hydrocarbon capable of forming the polymer block (B) include 2 carbon atoms such as ethylene, propylene, 1-butene, isobutene, 1-pentene, 1-hexene, 1-heptene, and 1-octene. -8 alkenes; preferably vinylcycloalkanes having 7 to 10 carbon atoms such as vinylcyclopentane, vinylcyclohexane, vinylcycloheptane, vinylcyclooctane; preferred such as vinylcyclopentene, vinylcyclohexene, vinylcycloheptene, vinylcyclooctene Is a vinylcycloalkene having 7 to 10 carbon atoms; butadiene, 1,3-pentadiene, isoprene, 1,3-hexadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1 , 3-heptadiene, etc., preferably 4-8 carbon conjugates Ethylene, propylene, 1-butene, isobutene, 1-pentene, 1-hexene, 1-hexene, cyclopentadiene, 1,3-cyclohexadiene and the like. Alkenes having 2 to 8 carbon atoms such as heptene and 1-octene; butadiene, 1,3-pentadiene, isoprene, 1,3-hexadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3 An unsaturated aliphatic hydrocarbon selected from conjugated diene having 4 to 8 carbon atoms such as butadiene and 1,3-heptadiene, more preferably a conjugated diene having 4 to 8 carbon atoms, selected from isobutene, butadiene and isoprene. More preferred is an unsaturated aliphatic hydrocarbon selected from butadiene and isoprene. Preferred. Using these unsaturated aliphatic hydrocarbons as a monomer, one kind is used alone, or two or more kinds are mixed and polymerized to form a polymer block (B).

  Further, the polymer block (B) is not derived from an unsaturated aliphatic hydrocarbon as long as the effect of the polymer block (B) that gives the block copolymer (Z) flexibility in the use temperature range is not impaired. Other structural units may be included. Examples of monomers that can form such other structural units include aromatic vinyl compounds such as styrene and vinyl naphthalene; halogen-containing vinyl compounds such as vinyl chloride; vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl pivalate. Vinyl esters; vinyl ethers such as methyl vinyl ether and isobutyl vinyl ether; and the like. In this case, the copolymerization form of these other monomers with the unsaturated aliphatic hydrocarbon described above is preferably random copolymerization. It is preferable that the usage-amount of these other monomers is 5 mol% or less of the monomer used for formation of a polymer block (B).

When the unsaturated aliphatic hydrocarbon has a plurality of carbon-carbon double bonds, any of them may be used for polymerization. For example, in the case of a conjugated diene, a 1,2-bond unit or a 1,4-bond unit Any of these bond units may be used. A polymer block formed by polymerizing a conjugated diene usually retains a carbon-carbon double bond, but from the viewpoint of improving heat deterioration resistance, etc., after the block copolymer (Z ₀ ) is polymerized, a hydrogenation reaction It is preferable to carry out (hereinafter referred to as “hydrogenation reaction”) and to hydrogenate the carbon-carbon double bond (hereinafter referred to as “hydrogenation”). The hydrogenation rate of such a carbon-carbon double bond (hereinafter referred to as “hydrogenation rate”) is preferably 30 mol% or more, more preferably 50 mol% or more, and further preferably 95 mol% or more. Thus, the deterioration of a polymer electrolyte membrane can be suppressed by reducing the carbon-carbon double bond in a polymer block (B).

Further, when an ion conductive group is introduced after polymerizing the block copolymer (Z ₀ ) to form the block copolymer (Z), if the polymer block (B) is a saturated hydrocarbon structure, It is preferable because introduction of an ion conductive group into the combined block (B) hardly occurs. Therefore, when the hydrogenation reaction of the carbon-carbon double bond remaining in the polymer block (B) after polymerizing the block copolymer (Z ₀ ) is performed before introducing the ion conductive group. desirable.
The hydrogenation rate of the carbon-carbon double bond can be calculated by ¹ H-NMR measurement.

  The Mn per polymer block (B) is usually preferably in the range of 5,000 to 250,000, more preferably in the range of 7,000 to 200,000 as a standard polystyrene equivalent value. The range of 10,000 to 100,000 is more preferable, and the range of 30,000 to 70,000 is particularly preferable. If the Mn is 5,000 or more, the mechanical strength is good, and if it is 250,000 or less, the film-forming property of the block copolymer (Z) is good. Therefore, in the production of the polymer electrolyte membrane of the present invention. It will be advantageous.

<Other polymer block (C)>
The block copolymer (Z) may further include a polymer block (C) that is composed of a structural unit derived from an aromatic vinyl compound and does not have an ion conductive group. In the polymer electrolyte membrane of the present invention, the polymer block (C) forms a microphase separation structure with the polymer block (A) and the polymer block (B).

  The polymer block (C) has the following general formula (1) because of its manufacturing advantages.

(In the formula, R ¹ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R ² represents an alkyl group having 3 to 8 carbon atoms, and R ³ and R ⁴ each independently represent a hydrogen atom or a carbon number. Represents an alkyl group of 3 to 8)
It is preferable that it consists of the structural unit derived from the aromatic vinyl compound shown by these.
When the polymer block (C) is a structural unit derived from an aromatic vinyl compound having at least one alkyl group having 3 to 8 carbon atoms on the aromatic ring, the polymer block (A ₀ ) as described later, When producing a polymer block (Z) by introducing an ion conductive group after producing a polymer block (B) and a block copolymer (Z ₀ ) containing the polymer block (C) An ion conductive group can be selectively introduced into the block (A ₀ ).

  Examples of the aromatic vinyl compound for forming the structural unit represented by the general formula (1) include 4-propylstyrene, 4-isopropylstyrene, 4-butylstyrene, 4-isobutylstyrene, 4-tert-butylstyrene, 4-octyl styrene, α-methyl-4-tert-butyl styrene, α-methyl-4-isopropyl styrene and the like can be mentioned. 4-tert-butyl styrene, 4-isopropyl styrene, α-methyl-4-tert-butyl Styrene and α-methyl-4-isopropylstyrene are more preferable, and 4-tert-butylstyrene is more preferable. Using these aromatic vinyl compounds as monomers, one type is polymerized alone, or two or more types are mixed to form a polymer block (C).

  The polymer block (C) may contain other structural units not derived from one or more aromatic vinyl compounds within a range not impairing the effects of the present invention. Examples of the monomer capable of forming such other structural units include butadiene, 1,3-pentadiene, isoprene, 1,3-hexadiene, 2,4-hexadiene, 2,3-dimethyl-1,3-butadiene, 2 -Preferably a conjugated diene having 4 to 8 carbon atoms such as ethyl-1,3-butadiene, 1,3-heptadiene; ethylene, propylene, 1-butene, isobutene, 1-pentene, 1-hexene, 1-heptene, 1 -Alkenes preferably having 2 to 8 carbon atoms such as octene; (meth) acrylate esters such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate; vinyl acetate, vinyl propionate, Vinyl esters such as vinyl butyrate and vinyl pivalate; vinyl ethers such as methyl vinyl ether and isobutyl vinyl ether; It is below. In this case, the copolymerization form of these other monomers and the above-described aromatic vinyl compound is preferably random copolymerization. It is preferable that the usage-amount of these other monomers is 5 mol% or less of the monomer used for formation of a polymer block (C).

  Mn per polymer block (C) is preferably in the range of 1,000 to 50,000, more preferably in the range of 1,500 to 30,000, as a standard polystyrene equivalent value. More preferably, it is in the range of 2,000 to 20,000. If Mn is 1,000 or more, the mechanical properties of the polymer electrolyte membrane tend to be excellent, and if it is 50,000 or less, the moldability and film forming property of the polymer electrolyte are good.

  When the block copolymer (Z) constituting the polymer electrolyte membrane of the present invention contains a polymer block (C), the proportion of the polymer block (C) in the block copolymer (Z) is 40% by mass or less. It is preferable that it is 35 mass% or less, and it is more preferable that it is 30 mass% or less.

<Production of block copolymer (Z ₀ )>
The block copolymer (Z) constituting the polymer electrolyte membrane of the present invention is a block copolymer comprising a polymer block (A ₀ ) and a polymer block (B) by polymerizing each of the aforementioned monomers. After producing the coalescence (Z ₀ ), it can be produced by a method of introducing an ion conductive group into the polymer block (A ₀ ).

The production method of the block copolymer (Z ₀ ) can be selected as appropriate, but a method of polymerizing each monomer described above by a polymerization method selected from a living radical polymerization method, a living anion polymerization method and a living cation polymerization method is preferable. .

As a method for producing a block copolymer (Z ₀ ) comprising as a component a polymer block (B) comprising a polymer block (A ₀ ) and a conjugated diene, for example, (1) an anionic polymerization initiator is used in a cyclohexane solvent. A method of obtaining an ABA type block copolymer by sequentially anionic polymerization of an aromatic vinyl compound, a conjugated diene and an aromatic vinyl compound under a temperature condition of 20 to 100 ° C .;
(2) An anionic polymerization initiator is used in a cyclohexane solvent, and an aromatic vinyl compound and a conjugated diene are successively subjected to anionic polymerization under a temperature condition of 20 to 100 ° C., and then a coupling agent such as phenyl benzoate is added. To obtain an ABA type block copolymer;
(3) In a nonpolar solvent, an organolithium compound is used as an initiator, and in the presence of a polar compound having a concentration of 0.1 to 10% by mass, a fragrance having a concentration of 5 to 50% by mass at a temperature of -30 to 30 ° C A method of obtaining an ABA type block copolymer by anionic polymerization of an aromatic vinyl compound and anionic polymerization of a conjugated diene to the resulting living polymer, and then adding a coupling agent such as phenyl benzoate;
Etc.
Further, as a method for producing a block copolymer (Z ₀ ) comprising a polymer block (A ₀ ) and a polymer block (B) composed of isobutene as components, for example, (4) a halogen / hydrocarbon mixed solvent At -78 ° C, isobutene was cationically polymerized in the presence of Lewis acid using a bifunctional halogenated initiator, and then an aromatic vinyl compound was cationically polymerized to form an ABA block copolymer. A method of obtaining coalescence;
Etc.
In addition, a polymer block (C) can be added as a component of a block copolymer by changing or adding the component made to react in the said anionic polymerization or cationic polymerization as needed.

The Mn of the block copolymer (Z ₀ ) is not particularly limited, but the standard polystyrene conversion value measured by gel permeation chromatography (GPC) method is usually preferably in the range of 10,000 to 300,000. The range of 20,000 to 250,000 is more preferable, and the range of 40,000 to 100,000 is more preferable.

In the block copolymer (Z ₀ ), from the viewpoint of ion conductivity and mechanical strength, (total amount of polymer block (A ₀ )) :( total amount of polymer block (B)) is a mass ratio. The range is preferably from 95: 5 to 5:95, more preferably from 65:35 to 15:85, and even more preferably from 55:45 to 20:80.

<Production of block copolymer (Z)>
A method for producing a block copolymer (Z) by introducing an ion conductive group into the block copolymer (Z ₀ ) will be described below.

First, a method for introducing a sulfonic acid group into the block copolymer (Z ₀ ) will be described. Introduction of a sulfonic acid group (sulfonation) can be performed by a known method. For example, the block copolymer (Z ₀₎ the organic solvent solution or suspension is prepared and such solutions and a method of mixing by adding a sulfonating agent to be described later to the suspension, the block copolymer (Z ₀₎ And a method of directly adding a gaseous sulfonating agent.

  Sulfonating agents include: sulfuric acid; a mixture of sulfuric acid and acid anhydride; chlorosulfonic acid; a mixture of chlorosulfonic acid and trimethylsilyl chloride; sulfur trioxide; a mixture of sulfur trioxide and triethyl phosphate; -Aromatic organic sulfonic acid represented by trimethylbenzenesulfonic acid and the like are exemplified. Of these, a mixture of sulfuric acid and acid anhydride is preferred. Examples of the organic solvent to be used include halogenated hydrocarbons such as methylene chloride, linear aliphatic hydrocarbons such as hexane, cyclic aliphatic hydrocarbons such as cyclohexane, aromatic compounds having an electron withdrawing group such as nitrobenzene, etc. Can be illustrated.

Next, a method for introducing a phosphonic acid group into the block copolymer (Z ₀ ) will be described. Introduction (phosphonation) of a phosphonic acid group can be performed by a known method. For example, the aromatic ring of the polymer block (A ₀ ) is reacted with halomethyl ether in the presence of aluminum chloride to introduce a halomethyl group, and then reacted with phosphorus trichloride and aluminum chloride to be substituted with a phosphorus derivative. A method of converting to a phosphonic acid group by decomposition; a method of converting a phosphinic acid group introduced by reacting phosphorus trichloride and anhydrous aluminum chloride into an aromatic ring of the aromatic vinyl compound into nitric acid to convert it to a phosphonic acid group Can be mentioned.

In the block copolymer (Z), the introduction rate (sulfonation rate, phosphonation rate, etc.) of the ion conductive group with respect to the structural unit derived from the aromatic vinyl compound of the polymer block (A) is ¹ H-NMR. Can be used to calculate.

  The ion exchange capacity of the block copolymer (Z) is preferably in the range of 0.40 to 4.50 meq / g, more preferably in the range of 1.00 to 3.50 meq / g, and 1.50 to 3.00 meq / g. The range of is more preferable. When the ion exchange capacity is 0.40 meq / g or more, the ionic conductivity is good, and when it is 4.50 meq / g or less, it is difficult to swell. The ion exchange capacity of the block copolymer (Z) can be calculated using an acid value titration method.

  Further, the block copolymer (Z) may have one or more polymer blocks (A) and / or polymer blocks (B). When there are a plurality of polymer blocks (A), their structures (kind of structural unit, degree of polymerization, kind of ion conductive group, introduction ratio, etc.) may be the same or different. Moreover, when it has two or more polymer blocks (B), those structures (kind of a structural unit, a polymerization degree, etc.) may mutually be the same, and may differ.

There is no restriction | limiting in particular in the coupling | bonding arrangement | sequence of the polymer block (A) and polymer block (B) in a block copolymer (Z). Each polymer block may be linearly bonded or branched and bonded. That is, the block copolymer (Z) used in the present invention includes a graft copolymer.
In the block copolymer (Z), as an example of the bond arrangement of the polymer block (A) and the polymer block (B), an AB type diblock copolymer (A and B are each a polymer block ( A) represents a polymer block (B), the same applies hereinafter), an ABA type triblock copolymer, a BAB type triblock copolymer, an ABAB type tetrablock. Copolymer, A-B-A-B-A type pentablock copolymer, B-A-B-A-B type pentablock copolymer, (A-B) _n D-type star copolymer ( D represents a coupling agent residue, n represents an integer equal to or greater than 2. Hereinafter, the same applies to (B-A) _n D-type star copolymer, and the like, from the viewpoint of mechanical strength and ion conductivity. A-B-A type triblock copolymer, A-B-A-B-A type pentablock copolymer, (A-B ) _N D type star copolymer is preferable, and ABA type triblock copolymer is more preferable. In the polymer electrolyte membrane of the present invention, these block copolymers may be used alone or in combination of two or more.

  As an example of the arrangement when the block copolymer (Z) used in the present invention contains a polymer block (C), an ABC type triblock copolymer (A, B, and C are polymer blocks, respectively). (A) represents a polymer block (B) and a polymer block (C), the same shall apply hereinafter), an A-B-C-A type tetrablock copolymer, an A-B-A-C type tetrablock copolymer. Polymer, B-A-B-C type tetrablock copolymer, A-B-C-B type tetrablock copolymer, A-C-B-C type tetrablock copolymer, C-A-B- A-C type pentablock copolymer, C-B-A-B-C type pentablock copolymer, A-C-B-C-A type pentablock copolymer, A-C-B-A- C-type pentablock copolymer, A-C-B-C-A-C type hexablock copolymer, C-A-B-C-- -C-type hexablock copolymer, A-C-A-C-B-C-type hexablock copolymer, A-C-A-C-B-C-A type heptablock copolymer, A-C -B-C-B-C-A type heptablock copolymer, C-A-C-B-C-A-C type heptablock copolymer, A-C-A-C-B-C-A -C-type octablock copolymer, A-C-B-C-B-C-A-C-type octablock copolymer, A-C-B-C-A-C-B-C-type octablock copolymer A polymer etc. are mentioned. From the viewpoints of mechanical strength and ionic conductivity, ABC type triblock copolymer, ABCA type tetrablock copolymer, ABCA type tetrablock copolymer Polymer, A-C-B-C type tetrablock copolymer, C-A-B-A-C type pentablock copolymer, C-B-A-B-C type pentablock copolymer, A- C—B—C—A type pentablock copolymer, A—C—B—A—C type pentablock copolymer, A—C—B—C—A—C type hexablock copolymer, C— A-B-C-A-C type hexablock copolymer, A-C-A-C-B-C type hexablock copolymer, A-C-A-C-B-C-A type heptablock Copolymer, A-C-B-C-B-C-A type heptablock copolymer, C-A-C-B-C-A-C type heptablock copolymer A-C-A-C-B-C-A-C type octablock copolymer, A-C-B-C-B-C-A-C type octablock copolymer, A-C-B-- C-A-C-B-C type octablock copolymer is preferable, A-B-C-type triblock copolymer, A-B-C-A type tetrablock copolymer, A-B-A- C-type tetrablock copolymer, A-C-B-C-type tetrablock copolymer, A-C-B-C-A type pentablock copolymer, A-C-B-A-C type pentablock Copolymer, A-C-B-C-A-C type hexablock copolymer, A-C-A-C-B-C type hexablock copolymer, A-C-A-C-B- C-A type heptablock copolymer, A-C-B-C-B-C-A type heptablock copolymer, A-C-A-C-B-C-A-C type octablock A copolymer, an A-C-B-C-B-C-A-C-type octablock copolymer, and an A-C-B-C-A-C-B-C-type octablock copolymer are more preferable. A-C-B-C-type tetrablock copolymer, A-C-B-C-A type pentablock copolymer, A-C-B-C-A-C type hexablock copolymer, A —C—A—C—B—C—A—C type octablock copolymer is more preferable, and A—C—B—C—A type pentablock copolymer, A—C—A—C—B—B— A C-A-C type octablock copolymer is particularly preferable, and an A-C-B-C-A type pentablock copolymer is most preferable. In the polymer electrolyte membrane of the present invention, these block copolymers (Z) may be used alone or in combination of two or more.

<Crosslinking agent (X)>
The crosslinking agent (X) is a compound having two or more oxetane rings in the molecule. In the present specification, the “oxetane ring” means a four-membered ring composed of three carbon atoms and one oxygen atom, and at least one hydrogen atom on the carbon atom of oxetane is substituted with a substituent, thereby forming a bridge. A partial structure of the agent (X) is formed. When the crosslinking agent (X) has two or more oxetane rings in the molecule, the hydrophilic polymer block (A) can be crosslinked, and the hot water resistance of the polymer electrolyte membrane of the present invention can be increased. Estimated.

The crosslinking agent (X) can be used without particular limitation as long as it is a compound having two or more oxetane rings in the molecule. Specific examples include compounds represented by the following general formulas (I) to (VIII) (hereinafter referred to as oxetane compounds (I) to (VIII)).
Among these, from the viewpoint of the mechanical properties of the polymer electrolyte membrane of the present invention, oxetane compounds (I) to (IV) are preferable, oxetane compounds (I) to (III) are more preferable, and oxetane compound (I) is further preferable.

（式中ｎは、１〜３の自然数を表す）

(Where n represents a natural number of 1 to 3)

（式中ｎは、０以上の整数を表す）

(Where n represents an integer of 0 or more)

  Crosslinking agent (X) may be used individually by 1 type, or may use 2 or more types together. The amount of the crosslinking agent (X) used is preferably in the range of 1 to 25 parts by weight, more preferably in the range of 3 to 15 parts by weight, with respect to 100 parts by weight of the block copolymer (Z). A range is further preferred. By making the usage-amount of the crosslinking agent (X) with respect to 100 mass parts of block copolymers (Z) 1 mass part or more, the hot water resistance of a polymer electrolyte membrane becomes high, On the other hand, being 25 mass parts or less, The ion conductivity of the polymer electrolyte membrane is increased.

  The crosslinking agent (X) described above may be a commercially available product or may be synthesized by a known method (for example, the method described in JP-A-2001-31665).

<Production of polymer electrolyte membrane>
The polymer electrolyte membrane of the present invention is generally prepared by preparing a composition containing a block copolymer (Z), which is a polymer electrolyte, a crosslinking agent (X), and a solvent, and forming the composition on a substrate. After molding, it is obtained by crosslinking.
The above composition is prepared by dissolving or dispersing the block copolymer (Z) and the crosslinking agent (X) in a solvent. If necessary, various stabilizers such as a softening agent, a phenol-based stabilizer, a sulfur-based stabilizer, a phosphorus-based stabilizer, an inorganic filler, a light stabilizer, an antistatic agent, as long as the effects of the present invention are not impaired. Various additives such as a release agent, a flame retardant, a foaming agent, a pigment, a dye, a bleaching agent, and carbon fiber may be dissolved or dispersed together. The content of the block copolymer (Z) in the component (solid content) other than the solvent in the composition is preferably 50% by mass or more from the viewpoint of ion conductivity of the obtained polymer electrolyte membrane, More preferably, it is 70 mass% or more, and it is still more preferable that it is 85 mass% or more.

  Examples of the softener that can be used in the composition include petroleum softeners such as paraffinic, naphthenic, and aromatic process oils, paraffin, vegetable oil softeners, plasticizers, and the like. These may be used alone or in combination of two or more.

  Stabilizers that can be used in the composition include 2,6-di-tert-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl). ) Propionate], 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene, octadecyl-3- (3,5-di-tert- Butyl-4-hydroxyphenyl) propionate, triethylene glycol-bis [3- (3-tert-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy -3,5-di-tert-butylanilino) -1,3,5-triazine, 2,2-thio-diethylenebis [3- (3,5- -Tert-butyl-4-hydroxyphenyl) propionate], N, N'-hexamethylenebis (3,5-di-tert-butyl-4-hydroxy-hydrodinamamide), 3,5-di-tert-butyl-4 -Hydroxy-benzylphosphonate-diethyl ester, tris- (3,5-di-tert-butyl-4-hydroxybenzyl) -isocyanurate, 3,9-bis [2- [3- (3-tert-butyl-4 Phenol-based stabilizers such as -hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane; pentaerythrityltetrakis (3 -Laurylthiopropionate), distearyl 3,3'-thiodipropionate, dilauryl 3,3 -Sulfur stabilizers such as thiodipropionate, dimyristyl 3,3'-thiodipropionate; tris (nonylphenyl) phosphite, tris (2,4-di-tert-butylphenyl) phosphite, distearylpenta Examples thereof include phosphorus stabilizers such as erythritol diphosphite. These may be used alone or in combination of two or more.

  Examples of the inorganic filler that can be used in the composition include talc, calcium carbonate, silica, glass fiber, mica, kaolin, titanium oxide, montmorillonite, and alumina. These may be used alone or in combination of two or more.

  The solvent that can be used in the composition is not particularly limited as long as it does not destroy the structure of the block copolymer (Z). Specifically, halogenated hydrocarbons such as methylene chloride; toluene, xylene, benzene, and the like. Aromatic hydrocarbons such as: hexane, heptane, octane, etc., linear aliphatic hydrocarbons; cyclohexane, etc., cyclic aliphatic hydrocarbons; tetrahydrofuran, etc. ethers; methanol, ethanol, propanol, isopropyl alcohol, butanol, isobutyl alcohol, etc. Alcohol. These may be used alone or in combination of two or more, but from the viewpoint of the solubility or dispersibility of the polymer block contained in each block copolymer (Z), a mixed solvent should be used. Is preferred. Preferred mixed solvents include a mixed solvent of toluene and isobutyl alcohol, a mixed solvent of xylene and isobutyl alcohol, a mixed solvent of toluene and isopropyl alcohol, a mixed solvent of cyclohexane and isopropyl alcohol, a mixed solvent of cyclohexane and isobutyl alcohol, and a tetrahydrofuran solvent. , Mixed solvent of tetrahydrofuran and methanol, mixed solvent of toluene, isobutyl alcohol and octane, mixed solvent of toluene, isopropyl alcohol and octane, mixed solvent of toluene and isobutyl alcohol, mixed solvent of xylene and isobutyl alcohol, toluene and isopropyl Mixed solvent of alcohol, mixed solvent of toluene, isobutyl alcohol and octane, toluene, isopropyl alcohol and octane Mixed solvent is more preferred.

  The composition is usually formed on a smooth substrate made of polyethylene terephthalate (PET), glass or the like. Examples of the molding method include a coating method using a coater, an applicator, or the like.

The substrate for molding the composition may be porous (porous substrate). In this case, the porous substrate is usually impregnated with at least a part of the composition. The porous substrate impregnated with at least a part of the composition functions as a reinforcing material by constituting a part of the polymer electrolyte membrane after crosslinking. As the porous substrate, a fibrous base material such as a woven fabric or a non-woven fabric, a film-like base material having fine through holes, or the like can be used. Examples of the film-like substrate include a fuel cell pore filling membrane. A fibrous base material is preferable from the viewpoint of strength. Examples of the fibers constituting the fibrous base material include aramid fibers, glass fibers, cellulose fibers, nylon fibers, vinylon fibers, polyester fibers, polyolefin fibers, rayon fibers, and the like. Polyester fibers and aramid fibers are preferred.
Examples of the method for forming the composition on the porous substrate include a dip nip method, a method of laminating and applying to a substrate using a coater, an applicator, and the like.

After the composition is formed on the substrate as described above, the solvent is removed. The temperature at which the solvent is removed can be arbitrarily selected as long as the block copolymer (Z) is not decomposed, and a plurality of temperatures may be arbitrarily combined. Solvent removal can be performed under ventilation conditions, vacuum conditions, etc., and these may be combined arbitrarily. Solvent removal method is a method of removing the solvent by drying at 60 to 120 ° C. for 4 minutes or longer in a hot air dryer; removing the solvent by drying at 120 to 140 ° C. for 2 to 4 minutes in a hot air dryer. Method of pre-drying at 25 ° C. for 1 to 3 hours and then drying in a hot air dryer at 80 to 120 ° C. for 5 to 10 minutes; pre-dried at 25 ° C. for 1 to 3 hours Thereafter, a method of drying under an atmosphere of 25 to 40 ° C. under reduced pressure for 1 to 12 hours may be mentioned.
From the viewpoint of easily preparing a polymer electrolyte membrane having good toughness, the solvent removal method is a method of drying at 60 to 120 ° C. for 4 minutes or more in a hot air dryer; A method of pre-drying and then drying in a hot air dryer at 80 to 120 ° C. for 5 to 10 minutes; after pre-drying at 25 ° C. for 1 to 3 hours, in an atmosphere of 25 to 40 ° C., 1 A method of drying for 1 to 12 hours under a reduced pressure condition of 3 kPa or less is preferably used.

  When the polymer electrolyte membrane is a multilayer film, for example, after forming the above composition on a substrate, after removing the solvent to form the first layer, the above composition containing another polymer electrolyte is formed. The second layer is formed by removing the solvent. Similarly, the third and subsequent layers may be formed. Alternatively, the produced polymer electrolyte membranes may be bonded to form a multilayer film.

The polymer electrolyte membrane of the present invention can be formed by forming a composition on a substrate and then performing crosslinking.
Crosslinking can be performed simultaneously with solvent removal. After removing the solvent, crosslinking may be carried out by irradiating active energy rays such as heating or electron beam, or after crosslinking at the same time as removing the solvent, an active energy ray such as heating or electron beam is further applied. You may carry out by adding bridge | crosslinking by irradiating.
When crosslinking is performed simultaneously with solvent removal, the above-mentioned solvent removal method can be employed. However, from the viewpoint of easily forming a uniform and uniform polymer electrolyte membrane, it can be carried out at 60 to 120 ° C. in a hot air dryer. Method of removing solvent over 40 minutes; Method of removing solvent at 25 ° C. for 1 to 3 hours and then removing the solvent at 80 to 120 ° C. for 5 to 10 minutes in a hot air dryer; 25 ° C. Is preferably preliminarily dried for 1 to 3 hours at 25 to 40 ° C. under a reduced pressure of 1.3 kPa or less, and the solvent is removed for 1 to 3 hours. A method of removing the solvent at ˜120 ° C. for 2 to 40 minutes is more preferred, and a method of removing the solvent at 90 to 110 ° C. for 4 to 8 minutes in a hot air dryer is further preferred.
When performing crosslinking by heating after removing the solvent, the heating temperature is preferably 40 to 250 ° C, more preferably 50 to 200 ° C, and even more preferably 60 to 150 ° C. The heating time can be arbitrarily selected as long as the polymer electrolyte membrane does not decompose, but is preferably 24 hours or shorter, more preferably 5 hours or shorter, and even more preferably 1 hour or shorter.
When crosslinking is performed with an electron beam, the acceleration voltage is preferably in the range of 50 to 250 kV, and the dose is preferably in the range of 100 to 800 kGy.
In addition, it can confirm that the block copolymer (Z) is bridge | crosslinked by the crosslinking agent (X) by the improvement of the below-mentioned hot water resistance, the raise of a gel fraction, etc.

  When the polymer electrolyte membrane is formed on a smooth substrate made of polyethylene terephthalate (PET), glass or the like, the polymer electrolyte membrane of the present invention can be usually obtained by peeling from the substrate. In the case where the polymer electrolyte membrane is formed on the porous substrate and the porous substrate is used as a part of the polymer electrolyte membrane, peeling is not necessary.

In the polymer electrolyte membrane of the present invention, the polymer block (A) and the polymer block (B) form a microphase separation structure. As a result, since the phase containing the polymer block (A) forms an ion conductive channel, it exhibits good ion conductivity.
Here, “microphase separation” means phase separation in a microscopic sense, and more specifically, means phase separation in which the formed domain size is less than or equal to the wavelength of visible light (3800 to 7800 mm). It shall be.

  The film thickness of the polymer electrolyte membrane of the present invention is preferably in the range of 1 to 500 μm, more preferably in the range of 7 to 300 μm, still more preferably in the range of 10 to 50 μm, from the viewpoint of mechanical strength, handling properties, and the like. A range of ˜25 μm is particularly preferred. When the film thickness is 1 μm or more, the polymer electrolyte membrane has good mechanical strength and fuel blocking properties, and when the film thickness is 500 μm or less, the polymer electrolyte membrane has good ion conductivity.

  The polymer electrolyte membrane of the present invention comprises a block copolymer (Z) containing a polymer block (A) and a polymer block (B), and a crosslinking agent (X), and at least one crosslinked after molding. It may be a multilayer film including a polymer electrolyte layer.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further more concretely, this invention is not restrict | limited to these Examples.

(Measurement of ion exchange capacity of block copolymer (Z))
A block copolymer (Z) is weighed (weighed value a (g)) in a glass container that can seal the sample, and an excess amount of a saturated sodium chloride aqueous solution ((300 to 500) × a (ml)) is added. Stir for 12 hours. Using phenolphthalein as an indicator, hydrogen chloride generated in water was titrated (a titration b (ml)) with a 0.01 N NaOH standard aqueous solution (titer f).
The ion exchange capacity was determined by the following formula.
Ion exchange capacity (meq / g) = (0.01 × b × f) / a

(Measurement of Mn of block copolymer (Z ₀ ))
Mn was measured by gel permeation chromatography (GPC) under the following conditions and calculated in terms of standard polystyrene.
Device: manufactured by Tosoh Corporation, trade name: HLC-8220GPC
Eluent: Tetrahydrofuran Column: manufactured by Tosoh Corporation, trade name: TSK-GEL (TSKgel G3000HxL (76 ml.D. × 30 cm), one TSKgel Super Multipore HZ-M (46 ml.D. × 15 cm) 3 in total)
Column temperature: 40 ° C
Detector: RI
Feed rate: 0.35 ml / min

(Measurement conditions for ¹ H-NMR)
The content of each structural unit of the block copolymer in the production example described later, and the 1,4-bonding rate and the hydrogenation rate in the polymer block (B) are based on the results of ¹ H-NMR measurement under the following conditions. Calculated.
Solvent: deuterated chloroform Measurement temperature: room temperature Integration count: 32 times The sulfonation rate was calculated from the result of ¹ H-NMR measurement under the following conditions.
Solvent: deuterated tetrahydrofuran / deuterated methanol (mass ratio 80/20) mixed solvent Measurement temperature: 50 ° C
Integration count: 32 times

(Measurement of storage modulus)
The polymer electrolyte membranes obtained in the examples and comparative examples were elevated in a tensile mode (frequency: 11 Hz) using a wide-range dynamic viscoelasticity measuring device (“DVE-V4FT Rheospectr” manufactured by Rheology). The temperature rate was raised from 3 ° C./min from −80 ° C. to 250 ° C., and the storage elastic modulus (E ′), loss elastic modulus (E ″) and loss tangent (tan δ) were measured. Based on the fact that there was no change in the storage elastic modulus at 80 to 100 ° C. derived from the crystallized olefin polymer, the amorphous nature of the polymer block (B) was judged. As a result, the polymer block (B) was amorphous for all the block copolymers obtained in the examples and comparative examples.

[Production Example 1]
(Production of block copolymer (Z ₀ -1))
After drying, 461 ml of dehydrated cyclohexane and 2.18 ml of sec-butyllithium (1.0 mol / L cyclohexane solution) were added to an autoclave with an internal volume of 1.4 L substituted with nitrogen, and then stirred at 60 ° C. 19.8 ml, 123 ml of isoprene, and 19.8 ml of styrene were sequentially added and polymerized to synthesize polystyrene-b-polyisoprene-b-polystyrene. The resulting block copolymer had an Mn of 66,000, a 1,4-bond content of the polyisoprene block of 94.0%, and a content of structural units derived from styrene of 30.0% by mass.

Prepare cyclohexane solution of the above block copolymer, put in nitrogen-substituted pressure vessel, and hydrogenate using Ni / Al Ziegler catalyst at 0.5-1.0 MPa under hydrogen pressure at 70 ° C. for 15 hours A block copolymer (Z ₀ ) [polystyrene-b-hydrogenated, comprising a polystyrene polymer block (polymer block (A ₀ )) and a hydrogenated polyisoprene polymer block (polymer block (B)), after the reaction. Polyisoprene-b-polystyrene (hereinafter referred to as “block copolymer (Z ₀ -1)”) was obtained.
The hydrogenation rate of the hydrogenated polybutadiene block of the obtained block copolymer (Z ₀ -1) was 99% or more.

(Production of block copolymer (Z-1))
In 242 ml of methylene chloride, 121 ml of acetic anhydride and 54 ml of sulfuric acid were mixed at 0 ° C. to prepare a sulfonating agent. On the other hand, 78 g of the block copolymer (Z ₀ -1) was put in a glass reaction vessel equipped with a 3 L stirrer, and the operation of introducing nitrogen into the system under vacuum was repeated three times. Then, methylene chloride was introduced with nitrogen introduced. After 846 ml was added and dissolved by stirring at room temperature for 4 hours, 417 ml of the sulfonating agent was added dropwise over 5 minutes. After completion of the dropping, the mixture was stirred at room temperature for 48 hours, and then 500 ml of distilled water was added dropwise with stirring to stop the reaction and solidify and precipitate the solid content.
The methylene chloride was removed by distillation at normal pressure, followed by filtration. The obtained solid content was transferred to a beaker, 1 L of distilled water was added and washing was performed with stirring, and then the solid content was collected by filtration. After repeating such washing and filtration until there is no change in the pH of the washing water, the recovered solid content is dried at 1.3 kPa, 30 ° C. for 24 hours, and used for the polymer electrolyte membrane of the present invention. (Z) was obtained (hereinafter referred to as “block copolymer (Z-1)”). The ratio of the sulfonic acid group to the structural unit derived from styrene (sulfonation rate) of the obtained block copolymer (Z-1) was 100 mol%, and the ion exchange capacity was 2.34 meq / g.

[Production Example 2]
(Production of block copolymer (Z ₀ -2))
After drying, 461 ml of dehydrated cyclohexane and 2.60 ml of sec-butyllithium (1.0 mol / L cyclohexane solution) were added to an autoclave with an internal volume of 1.4 L replaced with nitrogen, and then stirred at 60 ° C. 19.8 ml, 135 ml of butadiene, and 19.8 ml of styrene were sequentially added and polymerized to synthesize polystyrene-b-polybutadiene-b-polystyrene. Mn of the obtained block copolymer was 76,000, the 1,4-bond content of the polybutadiene block was 59.9%, and the content of the structural unit derived from styrene was 30.0% by mass.

Prepare cyclohexane solution of the above block copolymer, put in nitrogen-substituted pressure vessel, and hydrogenate using Ni / Al Ziegler catalyst at 0.5-1.0 MPa under hydrogen pressure at 70 ° C. for 15 hours A block copolymer (Z ₀ ) [polystyrene-b-hydrogenated polybutadiene comprising a polystyrene polymer block (polymer block (A ₀ )) and a hydrogenated polybutadiene polymer block (polymer block (B)) is reacted. -B-polystyrene (hereinafter referred to as “block copolymer (Z ₀ -2)”) was obtained.
The hydrogenation rate of the hydrogenated polybutadiene block of the obtained block copolymer (Z ₀ -2) was 99% or more.

(Production of block copolymer (Z-2))
In 389 ml of methylene chloride, 195 ml of acetic anhydride and 87.0 ml of sulfuric acid were mixed at 0 ° C. to prepare a sulfonating agent. On the other hand, 100 g of block copolymer (Z ₀ -2) was placed in a glass reaction vessel equipped with a 5 L stirrer, and the operation of introducing nitrogen into the system under vacuum was repeated three times. Then, methylene chloride was introduced with nitrogen introduced. After adding 1000 ml and stirring at room temperature for 4 hours to dissolve, 610 ml of the sulfonating agent was added dropwise over 5 minutes. After completion of the dropping, the mixture was stirred at room temperature for 48 hours, and then 720 ml of distilled water was added dropwise with stirring to stop the reaction and solidify and precipitate the solid content.
The methylene chloride was removed by distillation at normal pressure, followed by filtration. The obtained solid content was transferred to a beaker, 1 L of distilled water was added and washing was performed with stirring, and then the solid content was collected by filtration. After repeating such washing and filtration until there is no change in the pH of the washing water, the recovered solid content is dried at 1.3 kPa, 30 ° C. for 24 hours, and used for the polymer electrolyte membrane of the present invention. (Z) was obtained (hereinafter referred to as “block copolymer (Z-2)”). In the obtained block copolymer (Z-2), the ratio of the sulfonic acid group to the structural unit derived from styrene (sulfonation rate) was 100 mol%, and the ion exchange capacity was 2.34 meq / g.

[Production Example 3]
(Production of block copolymer (Z ₀ -3))
After drying, 710 ml of dehydrated cyclohexane, 1.95 ml of tetrahydrofuran and 1.99 ml of sec-butyllithium (0.7 mol / L cyclohexane solution) were added to an autoclave with an internal volume of 1.4 L purged with nitrogen, and then at 40 ° C. While stirring, 21.6 ml of 4-methylstyrene, 140 ml of butadiene, and 21.6 ml of 4-methylstyrene were sequentially added and polymerized to obtain poly (4-methylstyrene) -b-polybutadiene-b-poly (4-methyl). Styrene) was obtained. The Mn of the obtained block copolymer is 78,000, the 1,4-bond amount of the polybutadiene block determined from ¹ H-NMR (400 MHz) is 58.5%, and a structural unit derived from 4-methylstyrene The content of was 30.0% by mass.
Prepare a cyclohexane solution of the above block copolymer, put it in a pressure vessel which is purged with nitrogen, and hydrogenate using a Ni / Al Ziegler catalyst at a hydrogen pressure of 0.5 to 1.0 MPa and 70 ° C. for 18 hours. A block copolymer (Z ₀ ) [poly (4-methylstyrene) polymer block (polymer block (A ₀ )) and hydrogenated polybutadiene polymer block (polymer block (B)) is reacted. (4-Methylstyrene) -b-hydrogenated polybutadiene-b-poly (4-methylstyrene) (hereinafter referred to as “block copolymer (Z ₀ -3)”) was obtained. The hydrogenation rate of the hydrogenated polybutadiene block of the obtained block copolymer (Z ₀ -3) was 99% or more.

(Production of block copolymer (Z-3))
A sulfonating agent was prepared by mixing 23.4 ml of acetic anhydride and 10.5 ml of sulfuric acid at 0 ° C. in 35.1 ml of methylene chloride. On the other hand, 50 g of the block copolymer (Z ₀ -3) was placed in a glass reaction vessel equipped with a 3 L stirrer, and the operation of evacuating the system and introducing nitrogen was repeated three times, followed by chlorination with nitrogen introduced. After adding 612 ml of methylene and stirring for 4 hours at room temperature to dissolve, 69.1 ml of the sulfonating agent was added dropwise over 5 minutes. After stirring for 7 hours at room temperature, 500 ml of distilled water was added dropwise with stirring to stop the reaction and precipitate a solid. The methylene chloride was removed by distillation at atmospheric pressure, followed by filtration. The collected solid content was transferred to a beaker, 1 L of distilled water was added and washed with stirring, and then the solid content was collected again by filtration. After repeating this washing and filtration until there is no change in the pH of the washing water, the recovered solid content is dried at 1.3 kPa and 30 ° C. for 24 hours to obtain the block copolymer (Z) (hereinafter “block copolymer”). The ratio (sulfonated rate) of the sulfonic acid group to the structural unit derived from 4-methylstyrene of the obtained block copolymer (Z-3) was 65. The ion exchange capacity was 2 mol% and 1.47 meq / g.

[Production Example 4]
(Production of Oxetane Compound (I))
In a 1000 ml three-necked round bottom flask equipped with a thermometer, a condenser, a stirrer and a dropping funnel, 100.9 g (0.54 mol) of 4,4′-biphenol, 3-chloromethyl-3-ethyloxetane 191. 9 g (1.42 mol) and 9.8 g of tetrabutylphosphonium bromide were added as a catalyst, and the mixture was heated and stirred at 80 ° C. To this, 168.4 g (1.44 mol) of a 48 wt% potassium hydroxide aqueous solution was dropped from a dropping funnel over 30 minutes. After completion of dropping, the temperature was raised until reflux (about 110 ° C.), and the reaction was continued for 8 hours under reflux. After completion of the reaction, the reaction mixture was cooled to room temperature, 500 ml of pure water was added, and after stirring well, the precipitate was separated. The precipitate was washed 3 times with 200 ml of water and subsequently 3 times with 100 ml of methanol. Subsequently, it dried at 1.3 kPa and 30 degreeC with the vacuum dryer for 16 hours, and obtained 169.3 g of oxetane compound (I) of the white crystal | crystallization.

[Example 1]
(Production of polymer electrolyte membrane)
After preparing a 12% by weight toluene / isobutyl alcohol (mass ratio 65/35) solution of the block copolymer (Z-1) obtained in Production Example 1, the oxetane obtained in Production Example 4 was used as a crosslinking agent. Compound (I) was added so that the mass ratio of block copolymer (Z-1) / oxetane compound (I) was 100/9 to prepare a composition. Next, the composition is coated on a release-treated PET film (trade name: K1504, manufactured by Toyobo Co., Ltd.) with a thickness of about 350 μm, and dried at 100 ° C. for 6 minutes in a hot air dryer. Thus, a polymer electrolyte membrane having a thickness of 20 μm was obtained.

[Comparative Example 1]
(Production of polymer electrolyte membrane)
After preparing a 16% by weight toluene / isobutyl alcohol (mass ratio 70/30) solution of the block copolymer (Z-2) obtained in Production Example 2, 1,2-polybutadiene (Nippon Soda ( Co., Ltd., trade name: PB-1000; Mn = 1,000, polymerization degree = 19), 40 mass% toluene solution, block copolymer (Z-2) / 1,2-polybutadiene mass ratio is 100 / 5 was added to prepare a composition. Next, the composition is coated on a release-treated PET film (trade name: K1504, manufactured by Toyobo Co., Ltd.) with a thickness of about 350 μm, and dried at 100 ° C. for 4 minutes in a hot air dryer. Thus, a polymer electrolyte membrane having a thickness of 30 μm was obtained. The obtained polymer electrolyte membrane was subjected to an accelerating voltage of 150 kV, a beam current of 8.6 mA, and a dose of 300 kGy using an electrocurtain type electron beam irradiation apparatus (manufactured by Iwasaki Electric Co., Ltd., trade name: CB250 / 30/20 mA). The polymer electrolyte membrane of Comparative Example 1 was produced by crosslinking by applying electron beam irradiation.

[Comparative Example 2]
As a crosslinking agent, a 40% by mass toluene solution of 1,2-polybutadiene (manufactured by Nippon Soda Co., Ltd., trade name: PB-1000; Mn = 1,000, polymerization degree = 19) was used as a block copolymer (Z-2). ) / 1,2-polybutadiene was added in a mass ratio of 100/9 in the same manner as in Comparative Example 1 to obtain a polymer electrolyte membrane having a thickness of 30 μm. The obtained polymer electrolyte membrane was crosslinked by irradiating with an electron beam under the same conditions as in Comparative Example 1 to produce a polymer electrolyte membrane of Comparative Example 2.

[Comparative Example 3]
(Production of polymer electrolyte membrane)
A 16% by mass toluene / isobutyl alcohol (mass ratio 70/30) solution of the block copolymer (Z-3) obtained in Production Example 3 was prepared. Next, the composition is coated on a release-treated PET film (trade name: K1504, manufactured by Toyobo Co., Ltd.) with a thickness of about 350 μm, sufficiently dried at room temperature, and then sufficiently dried in vacuum. Thus, a film having a thickness of 30 μm was obtained. The obtained membrane was hot-pressed at 130 ° C. under a pressure of 1 MPa for 5 minutes to produce a polymer electrolyte membrane.

(Evaluation of polymer electrolyte membrane)
The polymer electrolyte membrane used in each example and comparative example was evaluated by the following measurement / evaluation method. The results are shown in Table 1.

(Hot water resistance test 1: Residual ratio of insoluble matter)
A polymer electrolyte membrane test piece (mass m ₁ ) cut out to 2 cm × 4 cm and stored for 4 hours or more at 25 ° C. and 50% RH relative humidity is placed in a 30 mL screw tube, and 25 mL of distilled water is added. It was added, screwed, and stored in a metal container made of SUS. After storing in a 90 ° C. thermostat, the contents in the screw tube were dried at 1.3 kPa, 30 ° C. for 12 hours. The contents were then stored for 4 hours at 25 ° C. and 50% RH relative humidity, and the mass (referred to as mass m ₂ ) was measured. The storage time in the thermostatic chamber was set to 270 hours in Examples and Comparative Examples 1 and 2, and 72 hours in Comparative Example 3.
The insoluble matter residual ratio (1) was determined by the following formula.
Insoluble matter residual ratio (1) (%) = m ₂ / m ₁ × 100
Moreover, the same test was implemented using another test piece obtained from the same polymer electrolyte membrane, and insoluble matter residual ratio (2) was calculated | required.
The insoluble matter residual rate (1) and the insoluble matter residual rate (2) thus obtained were arithmetically averaged to obtain the insoluble matter residual rate. It was judged that the higher the insoluble matter residual ratio, the higher the hot water resistance.

(Heat resistance test 2: Visual test)
The state of the surface of the polymer electrolyte membrane after the test piece of the polymer electrolyte membrane cut out to 2 cm × 4 cm was immersed in hot water at 90 ° C. for 270 hours was visually confirmed.

(Measurement of gel fraction)
As a relative comparison of the degree of crosslinking, the gel fraction of the polymer electrolyte membrane was measured.
The weight of the polymer electrolyte membrane test piece cut out to 4 cm × 8 cm was weighed with a precision balance. The weight of this case and M _1. Using a Soxhlet extractor, the test piece set on the cylindrical filter paper was refluxed with 100 ml of tetrahydrofuran for 8 hours. Thereafter, the test piece was taken out, and the tetrahydrofuran solution was evaporated with an evaporator under conditions of 11 kPa and 40 ° C. Then, the residue was further dried at 1.3 kPa and 80 ° C. for 12 hours. The weight of only the solid residue after drying was weighed with a precision balance. The weight of this case and M _2. The gel fraction was ((M ₁ −M ₂ ) / M ₁ ) × 100 (%).
The higher the gel fraction, the higher the degree of crosslinking.

As shown in Table 1, the polymer electrolyte membrane of the present invention exhibits high hot water resistance. Since the polymer electrolyte membranes of Comparative Examples 1 and 2 are polymer electrolyte membranes crosslinked with a crosslinking agent other than the crosslinking agent (X), the hot water resistance is lower than that of the polymer electrolyte membrane of the present invention.
Since the polymer electrolyte membrane of Comparative Example 3 does not use the crosslinking agent (X), the hot water resistance is low although the ion exchange capacity is low as compared with Example 1.

  The polymer electrolyte membrane of the present invention is made of a non-fluorine material, has a low environmental impact during production and disposal, is flexible and hardly cracked, and has excellent hot water resistance. Therefore, the polymer electrolyte membrane for a solid polymer fuel cell It can be suitably used as a film.

Claims (5)

  Amorphous vinyl compound comprising a structural unit derived from a polymer block (A) having an ion conductive group and a structural unit derived from an unsaturated aliphatic hydrocarbon and having no ion conductive group A block copolymer (Z) containing a functional polymer block (B) and a composition containing a crosslinking agent (X) having two or more oxetane rings in the molecule, and crosslinking after molding A polymer electrolyte membrane that is characterized.   The polymer electrolyte membrane according to claim 1, wherein crosslinking is performed by active energy rays or heat.   The polymer electrolyte membrane according to claim 1 or 2, wherein the unsaturated aliphatic hydrocarbon is a conjugated diene having 4 to 8 carbon atoms. The ion-conducting group is a -SO 3 M _(wherein, M represents a hydrogen atom, an ammonium ion or an alkali metal ion) at least one selected from a sulfonic acid group and salts thereof represented, claim 1 The polymer electrolyte membrane according to any one of -3.   The polymer electrolyte membrane according to any one of claims 1 to 4, wherein the amount of the crosslinking agent (X) used is in the range of 7 to 11 parts by mass with respect to 100 parts by mass of the block copolymer (Z).