JP2010135130A - Polymer electrolyte membrane for solid polymer electrolyte fuel cell, membrane-electrode assembly, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polymer electrolyte membrane for a solid polymer fuel cell which is economical, eco-friendly, and excellent in moldability, strength, flexibility and radical resistance, and to provide a membrane electrode assembly and a solid polymer fuel cell in which the electrolyte membrane is used. <P>SOLUTION: The polymer electrolyte membrane for a solid polymer fuel cell contains a polymer electrolyte (P) composed of a block copolymer having a structural composition of a polymer block (A) with an aromatic vinyl system compound unit as a main repeating unit and a flexible polymer block (B) with a mass ratio between the polymer block (A) and the polymer block (B) 65:35 to 5:95 and an ion conductive group substantially existing in the polymer block (A) only, and at least one kind of an antioxidant (Q) selected from a phosphorous acid system antioxidant and a thioether system antioxidant. As for the electrolyte membrane, a 100% modulus in a tension test under a condition that a temperature is 25°C, and a tension speed 500 mm/min. is 15 MPa, and fracture strength is 15 MPa or larger, and moreover, fracture elongation is 300% or larger. The membrane electrode assembly and the solid polymer fuel cell include the membrane. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polymer electrolyte membrane for a polymer electrolyte fuel cell, a membrane-electrode assembly using the electrolyte membrane, and a polymer electrolyte fuel cell.

  In recent years, fuel cell technology has been counted as one of the pillars of these new energy technologies as a fundamental solution to energy and environmental problems, and as a central energy conversion system in the future hydrogen energy era. In particular, polymer electrolyte fuel cells (PEFCs) are used for stationary power sources for electric vehicles, portable power devices, and households that use electricity and heat simultaneously from the viewpoint of miniaturization and weight reduction. Application to other power supply devices is under consideration.

  A polymer electrolyte fuel cell is generally configured as follows. First, a catalyst layer containing carbon powder carrying a white metal catalyst and an ion conductive binder made of a polymer electrolyte is formed on both sides of a polymer electrolyte membrane having proton conductivity. A gas diffusion layer, which is a porous material through which fuel gas and oxidant gas are passed, is formed outside each catalyst layer. Carbon paper, carbon cloth, or the like is used as the gas diffusion layer. A structure in which the catalyst layer and the gas diffusion layer are integrated is called a gas diffusion electrode, and a structure in which a pair of gas diffusion electrodes is bonded to the electrolyte membrane so that the catalyst layer faces the electrolyte membrane is a membrane-electrode assembly ( MEA (Mebrane Electrode Assembly). On both sides of this membrane-electrode assembly, separators having electrical conductivity and airtightness are disposed. A gas flow path for supplying a fuel gas or an oxidant gas (for example, air) to the electrode surface is formed in a contact portion of the membrane-electrode assembly and the separator or in the separator. Electric power is generated by supplying a fuel gas such as hydrogen or methanol to one electrode (fuel electrode) and an oxidant gas containing oxygen such as air to the other electrode (oxygen electrode). That is, at the fuel electrode, the fuel is ionized to produce protons and electrons, the protons pass through the electrolyte membrane, the electrons travel through an external electric circuit formed by connecting both electrodes, and are sent to the oxygen electrode, Water is produced by the reaction. In this way, the chemical energy of the fuel can be directly converted into electric energy and taken out.

  As a polymer electrolyte membrane for a polymer electrolyte fuel cell, a proton conductive ion exchange membrane having a thickness of 20 to 200 μm is usually used. Several efforts have already been made for the development of ion conductive polymers based on non-fluorine polymers. For example, polyether ether ketone (PEEK) (Patent Document 1), which is a heat-resistant aromatic polymer, has been developed and is being actively studied. As a problem of such non-fluorine polymer, it is mentioned that long-term stability is low as compared with a membrane made of a fluorine polymer electrolyte (for example, NAFION manufactured by DuPont, etc.) which has been mainly used conventionally. Yes. Various factors have been estimated as factors that hinder this long-term stability. Degradation of the polymer electrolyte membrane due to peroxide (eg, hydrogen peroxide) generated during battery operation, peeling between the membrane and the electrode It is known that the performance is reduced due to the above.

  As for the peroxide generated during battery operation, peroxide is generated in the catalyst layer formed at the interface between the polymer electrolyte membrane and the electrode. For example, in the fuel electrode, hydrogen peroxide is generated due to oxidation of hydrogen. It is presumed that the peroxide thus generated becomes hydroxy radicals while diffusing in the polymer electrolyte membrane and degrades the polymer electrolyte membrane. Therefore, improving the durability of the polymer electrolyte membrane against radicals (hereinafter referred to as “radical resistance”) is considered as one measure that leads to the long-term stability of the polymer electrolyte fuel cell. The stability of the polymer electrolyte membrane in an oxidizing atmosphere using the Fenton reagent can be seen as an index.

As a technique for imparting radical resistance to a polymer electrolyte membrane, Patent Document 2 discloses hindered phenols generally used as radical scavengers and organophosphorus compounds used as peroxide decomposers. Alternatively, a polymer electrolyte membrane for a fuel cell having improved durability by a composition in which an organic sulfur compound or the like is mixed with a polymer electrolyte is disclosed. Patent Document 3 discloses a polymer electrolyte membrane for a fuel cell having improved durability by a composition in which an organic phosphorus compound having a pentavalent phosphorus atom is mixed with a polymer electrolyte.
JP-A-6-93114 JP 2003-201403 A JP 2007-217675 A

  However, the radical resistance of the polymer electrolyte membrane for fuel cells of Patent Document 2 is not always satisfactory in an environment with a strong oxidizing atmosphere. Regarding the polymer electrolyte membrane for fuel cells of Patent Document 3, the membrane exhibits excellent radical resistance, but there is no description regarding durability during an actual power generation test.

  The object of the present invention is a polymer electrolyte membrane for a polymer electrolyte fuel cell, which is economical, environmentally friendly, excellent in moldability, has both strength and flexibility, and is excellent in radical resistance and durability. Another object of the present invention is to provide a membrane-electrode assembly and a polymer electrolyte fuel cell using the electrolyte membrane.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have a polymer block (A) and a flexible polymer block (B) having an aromatic vinyl compound unit as a main repeating unit as constituent components. An electrolyte membrane containing a polymer electrolyte (P) contained at a specific ratio and at least one antioxidant (Q) selected from a phosphorous acid antioxidant and a thioether antioxidant, Was found to satisfy the above-mentioned purpose as a polymer electrolyte membrane for a polymer electrolyte fuel cell, in which a tensile property in a tensile test under a condition of 25 ° C. and a tensile speed of 500 mm / min shows a specific value. completed.

  That is, the present invention comprises a polymer block (A) and a flexible polymer block (B) having an aromatic vinyl compound unit as a main repeating unit as constituent components, and the polymer block (A) and the polymer block (B ) And a phosphite-based polymer electrolyte (P) composed of a block copolymer that is substantially present only in the polymer block (A). A polymer electrolyte membrane for a polymer electrolyte fuel cell comprising at least one antioxidant (Q) selected from an antioxidant and a thioether-based antioxidant, having a temperature of 25 ° C. and a tensile speed of 500 mm And 100% modulus is 15 MPa or less, tensile strength is 15 MPa or more, and elongation at break is 300% or more

In the block copolymer, the polymer block (A) and the polymer block (B) undergo microphase separation, and the polymer block (A) and the polymer block (B) are aggregated. In addition, since the polymer block (A) has an ion conductive group, an ion channel is formed by the assembly of the polymer blocks (A) and becomes a passage for protons. Further, the polymer block (B) is present, and the mass ratio of the polymer block (A) and the polymer block (B) is limited to 65:35 to 10:90, so that the block copolymer as a whole can be obtained. As a result, the electrolyte membrane of the present invention has a 100% modulus of 15 MPa or less in a tensile test under the conditions of a temperature of 25 ° C. and a tensile speed of 500 mm / min. When the thickness is 15 MPa or more and the elongation at break is 300% or more, the moldability (assembling property, joining property, tightening property, etc.) in producing the membrane-electrode assembly and the polymer electrolyte fuel cell is improved. It is improved and durability is also improved. The flexible polymer block (B) is composed of an alkene unit or a conjugated diene unit. The polymer block (A) is composed of an aromatic vinyl compound unit or the like, and has an ion conductive group bonded thereto. Ion conductive groups include sulfonic acid groups and phosphonic acid groups and salts thereof. In addition, radical resistance is improved by adding at least one antioxidant (Q) selected from phosphorous acid antioxidants and thioether antioxidants. The present invention also relates to a membrane-electrode assembly and a fuel cell using the above electrolyte membrane.
In the present invention, “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 polymer electrolyte membrane of the present invention is economical, friendly to the environment, excellent in moldability, has both strength and flexibility, and is excellent in radical resistance, and therefore excellent in durability.

Hereinafter, the present invention will be described in detail.
The block copolymer constituting the polymer electrolyte membrane of the present invention comprises an aromatic vinyl compound unit as a main repeating unit and a polymer block (A) having at least one ion conductive group as a constituent component. .

The aromatic ring in the aromatic vinyl compound is preferably a carbocyclic aromatic ring, and examples thereof include a benzene ring, a naphthalene ring, an anthracene ring, and a pyrene ring. The α-carbon in the aromatic vinyl compound may be tertiary carbon or quaternary carbon. As specific examples of the aromatic vinyl compound, when α-carbon is tertiary carbon, styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-ethylstyrene, 4-isopropylstyrene 4-n-propylstyrene, 4-isopropylstyrene, 4-n-butylstyrene, 4-isobutylstyrene, 4-t-butylstyrene, 4-n-octylstyrene, 2,4-dimethylstyrene, 2,5- Examples include dimethylstyrene, 3,5-dimethylstyrene, 2,4,6-trimethylstyrene, 2-methoxystyrene, 3-methoxystyrene, 4-methoxystyrene, 1,1-diphenylethylene, vinylnaphthalene, and vinylanthracene. .
Further, when the α-carbon is a quaternary carbon, a hydrogen atom bonded to the α-carbon atom is an alkyl group having 1 to 4 carbon atoms (methyl group, ethyl group, n-propyl group, isopropyl group, n- An aromatic vinyl compound substituted with a butyl group, isobutyl group or tert-butyl group), a halogenated alkyl group having 1 to 4 carbon atoms (chloromethyl group, 2-chloroethyl group, 3-chloroethyl group, etc.) or a phenyl group. It is preferable that Specifically, α-methylstyrene, α-methyl-4-methylstyrene, α-methyl-4-ethylstyrene, and α-methyl-4-t-butylstyrene are preferable.
The above aromatic vinyl compounds can be used alone or in combination of two or more. Among them, styrene, α-methylstyrene, 4-methylstyrene, 4-ethylstyrene, α-methyl-4-methylstyrene, α-methyl -2-Methylstyrene is preferable, and α-methylstyrene, α-methyl-4-methylstyrene, and α-methyl-2-methylstyrene are particularly preferable from the viewpoint of improving radical resistance. The form in the case of copolymerizing two or more types may be random copolymerization, block copolymerization, graft copolymerization, or tapered copolymerization.

The polymer block (A) may contain one or more other monomer units as long as the effects of the present invention are not impaired. Examples of such other monomers include conjugated dienes having 4 to 8 carbon atoms (specific examples are the same as those in the description of the polymer block (B) described later), alkenes having 2 to 8 carbon atoms (specific examples are described later). (Same as in the description of the polymer block (B)), (meth) acrylate (methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate), vinyl ester (vinyl acetate, propion) Vinyl acid, vinyl butyrate, vinyl pivalate, etc.), vinyl ether (methyl vinyl ether, isobutyl vinyl ether, etc.) and the like. The copolymerization form of the aromatic vinyl compound and the other monomer needs to be random copolymerization.

  The aromatic vinyl compound unit in the polymer block (A) occupies 50% by mass or more of the polymer block (A) in order to impart sufficient ion conductivity to the finally obtained polymer electrolyte membrane. Preferably, it occupies 70% by mass or more, more preferably 90% by mass or more.

  The molecular weight of the polymer block (A) in the state where the ion conductive group is not introduced is appropriately selected depending on the properties of the polymer electrolyte, required performance, other polymer components, etc., but the number average molecular weight in terms of polystyrene In general, it is preferably selected from 1,000 to 500,000, and more preferably selected from 2,000 to 100,000.

  The polymer block (A) may be crosslinked by a known method within a range not impairing the effects of the present invention. By introducing cross-linking, the ion channel phase formed by the polymer block (A) is less likely to swell, and the change in mechanical properties (such as tensile properties) between drying and wetting tends to be further reduced.

  The polymer block (A) has substantially no ion-conducting group and has a constrained block (A1) that functions as a constrained phase (a phase that functions to maintain the microphase separation structure of the block copolymer). You may consist of the ion conductive block (A2) which has an ion conductive group. The restraint phase is described in detail in Japanese Patent Application Laid-Open No. 2007-258162. When the polymer block (A) is composed of a constraining block (A1) and an ion conductive block (A2), the polymer block (B), the constraining block (A1) and the ion conductive block (A2) are each microscopic. Phase separate. The restraint block (A1) has the following general formula (I)

(Wherein R ¹ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ^{2 to} R ⁴ each independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, at least one of which is carbon It represents a polymer block having an aromatic vinyl compound unit represented by the formula (1 to 8) as a main repeating unit.
The alkyl group having 1 to 4 carbon atoms represented by R ¹ in the general formula (I) may be linear or branched, and is a methyl group, ethyl group, propyl group, isopropyl group, butyl group, sec-butyl group. , Isobutyl group, and tert-butyl group. The alkyl group having 1 to 8 carbon atoms represented by R ^{2 to} R ⁴ in the general formula (I) may be linear or branched, and is methyl, ethyl, propyl, isopropyl, butyl, sec Examples include -butyl group, isobutyl group, tert-butyl group, pentyl group, isopentyl group, neopentyl group, tert-pentyl group, hexyl group, 1-methylpentyl group, heptyl group, octyl group and the like. Preferable specific examples of the aromatic vinyl compound unit represented by the general formula (I) include p-methylstyrene unit, 4-tert-butylstyrene unit, p-methyl-α-methylstyrene unit, 4-tert. -Alpha-methyl styrene unit etc. are mentioned, These may be used independently or may be used in combination of 2 or more type. The form in the case of copolymerizing two or more types may be random copolymerization, block copolymerization, graft copolymerization, or tapered copolymerization.

The constraining block (A1) may contain one or more other monomer units in addition to the aromatic vinyl compound unit within a range that does not hinder the function as the constraining phase. Examples of the monomer that gives such other monomer units include conjugated dienes having 4 to 8 carbon atoms (specific examples are the same as those in the description of the polymer block (B) described later), and alkenes having 2 to 8 carbon atoms. (Specific examples are the same as in the description of the polymer block (B) described later), (meth) acrylate esters (methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, etc.), vinyl Examples include esters (vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, etc.), vinyl ethers (methyl vinyl ether, isobutyl vinyl ether, etc.), and the like.
From the viewpoint of fulfilling the function as a constrained phase, the above-mentioned aromatic vinyl compound unit preferably occupies 50% by mass or more of the constrained block (A1), more preferably 70% by mass or more, and 90% by mass. It is even more preferable to occupy the above.

  The molecular weight of the constraining block (A1) is appropriately selected depending on the properties of the polymer electrolyte, the required performance, other polymer components, and the like. When the molecular weight is large, the mechanical properties of the polymer electrolyte tend to be high, but when it is too large, it becomes difficult to mold the block copolymer, and when the molecular weight is small, the mechanical properties tend to be low, and the required performance is reduced. It is important to select the molecular weight accordingly. The number average molecular weight in terms of polystyrene is usually preferably selected from 1000 to 300,000, more preferably from 2000 to 100,000.

  The ion conductive block (A2) having an ion conductive group has the following general formula (II):

(In the formula, Ar ¹ represents an aryl group having 6 to 14 carbon atoms which may have ¹ to 3 substituents, and R ⁵ represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or 1 to 3). An aromatic vinyl-based compound unit represented by a C6-C14 aryl group which may have one substituent as a main repeating unit.

Examples of the aryl group having 6 to 14 carbon atoms represented by Ar ¹ in the general formula (II) include a phenyl group, a naphthyl group, a phenanthryl group, an anthryl group, an indenyl group, a biphenylyl group, and a pyrenyl group. And a naphthyl group is preferable, and a phenyl group is more preferable. The optional 1 to 3 substituents that can be directly bonded to the aromatic ring of the aryl group are each independently a linear or branched alkyl group having 1 to 4 carbon atoms (methyl group, ethyl group, propyl group). Group, isopropyl group, butyl group, sec-butyl group, isobutyl group or tert-butyl group). R ⁵ in the general formula (II) has the same meaning as R ¹ in the general formula (I), and examples of the group and preferred examples thereof are also the same.
Specific examples of the aromatic vinyl compound that gives the aromatic vinyl compound unit represented by the general formula (II) include styrene, vinyl naphthalene, vinyl anthracene, vinyl phenanthrene, vinyl biphenyl, α-methyl styrene, 1-methyl. Examples include -1-naphthylethylene and 1-methyl-1-biphenylylethylene, and styrene and α-methylstyrene are particularly preferable.
The aromatic vinyl compound that gives the aromatic vinyl compound unit represented by the general formula (II) may be used alone or in combination of two or more. The form in the case of copolymerizing two or more types may be random copolymerization, block copolymerization, graft copolymerization, or tapered copolymerization.

  The ion conductive block (A2) may contain one or more other monomer units in addition to the aromatic vinyl compound unit within a range not impairing the effects of the present invention. Examples of the monomer that gives such other monomer units include conjugated dienes having 4 to 8 carbon atoms (specific examples are the same as those in the description of the polymer block (B) described later), and alkenes having 2 to 8 carbon atoms. (Specific examples are the same as in the description of the polymer block (B) described later), (meth) acrylate esters (methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, etc.), vinyl Examples include esters (vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, etc.), vinyl ethers (methyl vinyl ether, isobutyl vinyl ether, etc.), and the like.

  The proportion of the aromatic vinyl compound unit contained in the ion conductive block (A2) is preferably 50 mol% or more, more preferably 60 mol% or more from the viewpoint of imparting sufficient ion conductivity. 80 mol% or more is even more preferable.

The molecular weight of the ion conductive block (A2) in the state where the ion conductive group is not introduced is appropriately selected depending on the properties of the polymer electrolyte, required performance, other polymer components, etc., but the number average in terms of polystyrene The molecular weight is usually preferably selected from 500 to 300,000, more preferably from 1,000 to 100,000.
The ion conductive block (A2) may be crosslinked by a known method within a range not impairing the effects of the present invention. By introducing cross-linking, changes in dimensions and mechanical properties (tensile properties) between drying and wetting tend to be further reduced.

  When the polymer block (A) constituting the polymer electrolyte membrane of the present invention is composed of the constraining block (A1) and the ion conductive block (A2), if the proportion of the constraining block (A1) is large, the dimensional change and mechanical properties are increased. Although the change in properties (breaking strength, etc.) tends to be small, the ionic conductivity tends to be low, and when the proportion of the ionic conductive block (A2) is large, the ionic conductivity tends to be high, Changes in dimensions and mechanical properties (breaking strength, etc.) tend to increase, and it is important to select the ratio of both appropriately according to the required performance. The mass ratio of the constraining block (A1) to the ion conductive block (A2) in the polymer block (A) is preferably 95: 5 to 20:80, and preferably 93: 7 to 25:75. More preferably, it is more preferably 90:10 to 30:70.

In addition to the polymer block (A), the block copolymer used in the polymer electrolyte membrane of the present invention has a flexible polymer block (B) that has substantially no ion conductive group. When the polymer block (B) is present and the mass ratio of the polymer block (A) and the polymer block (B), which is the component ratio, is limited to 65:35 to 5:95, The polymer as a whole is easy to have both good strength and flexibility, and the 100% modulus is 15 MPa or less and the breaking strength is 15 MPa in a tensile test at a temperature of 25 ° C. and a tensile speed of 500 mm / min. By forming an electrolyte membrane having the above characteristics with an elongation at break of 300% or more, formability (assembleability, bondability, tightening property) in manufacturing a membrane-electrode assembly or a polymer electrolyte fuel cell Etc.) and the durability is also improved. The flexible polymer block (B) here is a so-called rubber-like polymer block having a glass transition point or softening point of 50 ° C. or lower, preferably 20 ° C. or lower, more preferably 10 ° C. or lower.

  Monomers that can constitute the repeating unit constituting the flexible polymer block (B) include alkenes having 2 to 8 carbon atoms, cycloalkenes having 5 to 8 carbon atoms, and vinylcycloalkenes having 7 to 10 carbon atoms. , A conjugated diene having 4 to 8 carbon atoms and a conjugated cycloalkadiene having 5 to 8 carbon atoms, a vinyl cycloalkene having 7 to 10 carbon atoms in which part or all of the carbon-carbon double bond is hydrogenated, and carbon-carbon. A conjugated diene having 4 to 8 carbon atoms in which some or all of the double bonds are hydrogenated, a conjugated cycloalkadiene having 5 to 8 carbon atoms in which some or all of the carbon-carbon double bonds are hydrogenated, ( Examples include (meth) acrylic acid esters, vinyl esters, vinyl ethers, and the like. These may be used alone or in combination of two or more. The form in the case of polymerizing (copolymerizing) two or more kinds may be random copolymerization, block copolymerization, graft copolymerization, or tapered copolymerization. Further, when the monomer to be used for (co) polymerization has two carbon-carbon double bonds, any of them may be used for the polymerization, and in the case of a conjugated diene, it is a 1,2-bond. 1,4-bonds may be used, and the ratio of 1,2-bonds to 1,4-bonds is not particularly limited as long as the glass transition point or softening point is 50 ° C. or lower.

When the repeating unit constituting the polymer block (B) has a carbon-carbon double bond as in the case of vinylcycloalkene, conjugated diene or conjugated cycloalkadiene, the polymer of the present invention From the viewpoint of improving the power generation performance of the membrane-electrode assembly using the electrolyte membrane and improving the heat deterioration resistance, it is preferable that 80 mol% or more of such carbon-carbon double bonds are hydrogenated, and 90 mol%. The above is more preferably hydrogenated, and more preferably 95 mol% or more is hydrogenated. The hydrogenation rate of the carbon-carbon double bond can be calculated by a commonly used method such as ¹ H-NMR measurement.

The polymer block (B) is an alkene having 2 to 8 carbon atoms from the viewpoint of giving the resulting block copolymer elasticity and, in turn, good moldability in the production of a membrane-electrode assembly and a polymer electrolyte fuel cell. (Ethylene, propylene, 1-butene, 2-butene, isobutene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, 1-heptene, 2-heptene, 1-octene, 2-octene, etc.) unit, C5-C8 cycloalkene (cyclopentene, cyclohexene, cycloheptene, cyclooctene, etc.) unit, C7-10 vinylcycloalkene (vinylcyclopentene, vinylcyclohexene, vinylcycloheptene, vinylcyclooctene, etc.) unit, carbon Conjugated dienes having a number of 4 to 8 (1,3-butadiene, 1,3-pentadiene, isoprene 1,3-hexadiene, 2,4-hexadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-heptadiene, 1,4-heptadiene, 3,5- Heptadiene etc.) unit, C5-C8 conjugated cycloalkadiene (cyclopentadiene, 1,3-cyclohexadiene etc.) unit, carbon number 7 to 10 in which some or all of carbon-carbon double bonds are hydrogenated A vinylcycloalkene unit, a conjugated diene unit having 4 to 8 carbon atoms in which some or all of the carbon-carbon double bonds are hydrogenated, and carbon in which some or all of the carbon-carbon double bonds are hydrogenated. It is preferably a polymer block comprising at least one repeating unit selected from conjugated cycloalkadiene units having 5 to 8 carbon atoms, alkene units having 2 to 8 carbon atoms, A polymer block comprising at least one repeating unit selected from a conjugated diene unit having 4 to 8 prime atoms and a conjugated diene unit having 4 to 8 carbon atoms in which part or all of carbon-carbon double bonds have been hydrogenated. More preferably, the alkene unit having 2 to 6 carbon atoms, the conjugated diene unit having 4 to 8 carbon atoms, and the conjugated diene having 4 to 8 carbon atoms in which some or all of the carbon-carbon double bonds are hydrogenated. It is even more preferable that the polymer block is composed of at least one repeating unit selected from the units.
In the above, the most preferable alkene unit is an isobutene unit, and the most preferable conjugated diene unit is a 1,3-butadiene unit and / or an isoprene unit.

  In addition to the above monomers, the polymer block (B) may contain other monomers such as styrene and vinyl as long as the purpose of the polymer block (B) that gives elasticity to the block copolymer is not impaired. An aromatic vinyl compound such as naphthalene; a halogen-containing vinyl compound such as vinyl chloride may be included. In this case, the copolymerization form of the monomer and other monomer needs to be random copolymerization. The amount of such other monomer used is preferably less than 50% by weight, more preferably less than 30% by weight, based on the total of the above monomers and other monomers. It is still more preferable that it is less than mass%.

  When the electrolyte membrane of the present invention has only the ion conductive block (A2) as the polymer block (A) but not the constraining block (A1), the polymer block (A) and the polymer block The mass ratio of (B) needs to be 65:35 to 10:90, preferably 50:50 to 10:90, and more preferably 45:55 to 15:85. When this mass ratio is 65:35 to 10:90, it becomes easy to combine good strength and flexibility, and it becomes easy to improve the bondability between the membrane and the electrode, so that the durability tends to be excellent. is there.

  Although the structure of the block copolymer which has a polymer block (A) and a polymer block (B) as a structural component is not specifically limited, ABA type | mold triblock copolymer, BAB, as an example Type triblock copolymer, ABA type triblock copolymer or a mixture of BAB type triblock copolymer and AB type diblock copolymer, ABA type B-type tetrablock copolymer, A-B-A-B-A type pentablock copolymer, B-A-B-A-B type pentablock copolymer, (AB) nX-type star copolymer Examples thereof include a polymer (X represents a coupling agent residue), (BA) nX type star copolymer (X represents a coupling agent residue), and the like. These block copolymers may be used alone or in combination of two or more.

  When the electrolyte membrane of the present invention has a constraining block (A1) and an ion conductive block (A2) as the polymer block (A), the mass ratio of the polymer block (A) to the polymer block (B) Is required to be 65:35 to 10:90, preferably 65:35 to 15:85, and more preferably 60:40 to 15:85. When this mass ratio is 65:35 to 10:90, it becomes easy to combine good strength and flexibility, and it becomes easy to improve the bondability between the membrane and the electrode, so that the durability tends to be excellent. is there.

  The structure of the block copolymer in the case where the block copolymer used in the present invention is composed of the constrained block (A1), the ion conductive block (A2) and the polymer block (B) is not particularly limited, A1-B-A2-type triblock copolymer, A2-B-A1-A2 tetrablock copolymer, B-A2-B-A1 tetrablock copolymer, A2-B-A1-B tetrablock copolymer A1-B-A1-A2 tetrablock copolymer, A2-B-A2-A1 tetrablock copolymer, A2-A1-B-A1-A2 pentablock copolymer, A1-A2-B-A2- A1 pentablock copolymer, A2-A1-B-A2-A1 pentablock copolymer, A1-B-A2-B-A1 pentablock copolymer, A2-B-A1-A2-B pen Block copolymer, A2-B-A1-A2-A1 pentablock copolymer, A2-B-A1-B-A1 pentablock copolymer, A2-B-A2-B-A1 pentablock copolymer, A2-B-A2-A1-B pentablock copolymer, B-A2-B-A2-A1 pentablock copolymer, B-A2-B-A1-A2 pentablock copolymer, B-A2-B -A1-B pentablock copolymer, A1-A2-A1-B-A1 pentablock copolymer, etc. are mentioned.

  The block copolymer used in the present invention includes those partially containing graft bonds. Examples of the block copolymer partially containing a graft bond include those in which a part of the constituting polymer block is grafted to the main part (for example, main chain) of the block copolymer.

  The number average molecular weight of the block copolymer used in the present invention in a state where the ion conductive group is not introduced is not particularly limited, but the number average molecular weight in terms of polystyrene is usually 10,000 to 1,000,000. Preferably, 15,000-700,000 are more preferable, and 20,000-500,000 are still more preferable.

The block copolymer constituting the polymer electrolyte membrane of the present invention needs to have an ion conductive group substantially only in the polymer block (A). Examples of ions in the present invention when referring to ionic conductivity include protons. The ion conductive group is not particularly limited as long as the membrane-electrode assembly produced using the polymer electrolyte membrane can express sufficient ionic conductivity. Among them, -SO ₃ M or- A sulfonic acid group, a phosphonic acid group or a salt thereof represented by PO ₃ HM (wherein M represents a hydrogen atom, an ammonium ion or an alkali metal ion) is preferably used. Examples of the alkali metal include sodium, potassium, and lithium. As the ion conductive group, a carboxyl group or a salt thereof can also be used. The introduction position of the ion conductive group is the polymer block (A) (if the polymer block (A) is composed of the constraining block (A1) and the ion conductive block (A2), the ion conductive block (A2)). ) Is particularly effective for improving the radical resistance of the entire block copolymer.

In the block copolymer, the ion conductive group exists substantially only in the polymer block (A). This is partly for facilitating the formation of ion channels, and partly for limiting the components that form the ion channels to the polymer block (A). By forming an ion channel with a single component, ion conductive groups exist at a high density, and high-efficiency ion conduction is possible.
In the present invention, the fact that the ion conductive group is substantially present only in the polymer block (A) is 70 mol% or more, preferably 80 mol% or more, more preferably, of the ion conductive group present in the block copolymer. Means 90 mol% or more, more preferably 95 mol% or more is present in the polymer block (A).

  The introduction position of the ion conductive group into the polymer block (A) is not particularly limited and may be introduced into the aromatic vinyl compound unit or other monomer units described above. From the viewpoint of facilitating ion channel formation, it is preferably introduced into the aromatic ring of the aromatic vinyl compound unit.

  The amount of ion-conducting group introduced is appropriately selected depending on the required performance of the resulting block copolymer, etc., but exhibits sufficient ion conductivity for use as a polymer electrolyte membrane for a polymer electrolyte fuel cell. In general, the amount is preferably such that the ion exchange capacity of the block copolymer is 0.30 meq / g or more, and more preferably 0.40 meq / g or more. . The upper limit of the ion exchange capacity of the block copolymer is preferably 3.0 meq / g or less because if the ion exchange capacity is too large, the hydrophilicity tends to increase and the water resistance becomes insufficient.

  The production method of the block copolymer used in the present invention is not particularly limited, and a known method can be used, but after producing the block copolymer having no ion conductive group, the ion conductivity is improved. A method of bonding groups is preferred.

  Depending on the type, molecular weight, etc. of the monomer constituting the polymer block (A) or (B), the production method of the polymer block (A) or (B) can be a radical polymerization method, an anionic polymerization method, a cationic polymerization method, Although it is appropriately selected from coordination polymerization method and the like, radical polymerization method, anionic polymerization method and cationic polymerization method are preferably selected from the viewpoint of industrial ease. In particular, the so-called living polymerization method is preferable from the viewpoint of molecular weight, molecular weight distribution, polymer structure, ease of bonding between the polymer block (B) and the polymer block (A) made of flexible components, and specifically living Manufacture of producing a block copolymer by radical polymerization, living anion polymerization or living cation polymerization and then subjecting it to a hydrogenation reaction by a known method if desired when the polymer block (B) has a conjugated diene unit. The method is preferred.

As a specific example of the production method, a production method of a block copolymer comprising as a component a polymer block (A) made of poly (α-methylstyrene) and a polymer block (B) made of a conjugated diene will be described. In this case, it is preferable to produce by a living anionic polymerization method from the viewpoint of industrial ease, molecular weight, molecular weight distribution, ease of bonding between the polymer block (A) and the polymer block (B), and the following specific examples A typical synthesis example is shown.
(1) A method of obtaining an ABA type block copolymer by sequentially polymerizing α-methylstyrene under a temperature condition of −78 ° C. after conjugated diene polymerization using a dianionic initiator in a tetrahydrofuran solvent (Macromolecules , (1969), 2 (5), 453-458),
(2) After bulk polymerization of α-methylstyrene using an anionic initiator, conjugated dienes are sequentially polymerized, and then a coupling reaction is performed with a coupling agent such as tetrachlorosilane. (AB) nX Method for obtaining a type block copolymer (Kautsch. Gummi, ... Kunstst., (1984), 37 (5), 377-379; Polym ... Bull., ... (1984), 12, 71-77) ,
(3) An organic lithium compound in a nonpolar solvent is used as an initiator, and a concentration of 5 to 50% by mass at a temperature of −30 ° C. to 30 ° C. in the presence of a polar compound having a concentration of 0.1 to 10% by mass. A polymer obtained by polymerizing α-methylstyrene, a conjugated diene is polymerized to the resulting living polymer, and then a coupling agent is added to obtain an ABA block copolymer.
(4) A concentration of 5 to 50% by mass at a temperature of −30 ° C. to 30 ° C. in the presence of a polar compound having a concentration of 0.1 to 10% by mass using an organolithium compound in a nonpolar solvent as an initiator. Α-methylstyrene (a monomer constituting the ion conductive block (A2)) is polymerized, and the resulting living polymer is polymerized with conjugated diene, and the resulting α-methylstyrene polymer block and conjugated diene polymer block are obtained. A method of obtaining a block copolymer A2-B-A1 by polymerizing a monomer constituting the constrained block (A1) to a living polymer of a block copolymer comprising:
Can be adopted / applied.

Specific examples of the production method include a constrained block (A1) having an aromatic vinyl compound such as 4-tert-butylstyrene as a main repeating unit, an ion conductive block (A2) comprising styrene or α-methylstyrene, and a conjugated diene. A method for producing a block copolymer comprising a polymer block (B) comprising: In this case, the living anion polymerization method is preferable from the viewpoint of industrial ease, molecular weight, molecular weight distribution, binding block (A1), polymer block (B), and ion-conductive block (A2), and the like. A specific synthesis example is shown.
(5) An anionic polymerization initiator is used in a cyclohexane solvent, and an aromatic vinyl compound such as 4-tert-butylstyrene is polymerized at a temperature of 10 to 100 ° C., and then a conjugated diene and styrene are sequentially polymerized. A method of obtaining an A1-B-A2 type block copolymer,
(6) An anionic polymerization initiator is used in a cyclohexane solvent, and an aromatic vinyl compound such as 4-tert-butylstyrene is polymerized at a temperature of 10 to 100 ° C., and then styrene and a conjugated diene are sequentially polymerized. And then adding a coupling agent such as phenyl benzoate to obtain an A1-A2-B-A2-A1 type block copolymer,
(7) Using an anionic polymerization initiator in a cyclohexane solvent, under a temperature condition of 10 to 100 ° C., an aromatic vinyl compound such as 4-tert-butylstyrene, a conjugated diene, 4-tert-butylstyrene, etc. A1-B-A1 type block copolymer is prepared by sequential polymerization of aromatic vinyl compounds and an anionic polymerization initiator system (anionic polymerization initiator / N, N, N ′, N′-tetramethylethylenediamine) is added. And then lithiating the conjugated diene unit and then polymerizing styrene to obtain an A1-B (-g-A2) -A1 type block / graft copolymer,
(8) A concentration of 5 to 50% by mass at a temperature of −30 ° C. to 30 ° C. in the presence of a polar compound having a concentration of 0.1 to 10% by mass using an organolithium compound in a nonpolar solvent as an initiator. Α-methylstyrene is polymerized, and the resulting living polymer is sequentially polymerized with an aromatic vinyl compound such as conjugated diene and 4-tert-butylstyrene to produce an A2-B-A1 type block copolymer, and α-methyl A method of sequentially polymerizing styrene, 4-tert-butylstyrene, conjugated diene and 4-tert-butylstyrene to obtain an A2-A1-B-A1 type block copolymer;
Can be adopted / applied.

  Next, a method for bonding an ion conductive group to the obtained block copolymer will be described. First, a method for introducing a sulfonic acid group into the obtained block copolymer will be described. Sulfonation can be performed by a known sulfonation method. As such a method, an organic solvent solution or suspension of a block copolymer is prepared, a sulfonating agent is added and mixed, a method of adding a gaseous sulfonating agent directly to the block copolymer, etc. Is exemplified.

  Sulfonating agents used include sulfuric acid, a mixture of sulfuric acid and aliphatic acid anhydride, chlorosulfonic acid, a mixture of chlorosulfonic acid and trimethylsilyl chloride, sulfur trioxide, a mixture of sulfur trioxide and triethyl phosphate. Examples thereof include aromatic organic sulfonic acids represented by 2,4,6-trimethylbenzenesulfonic acid. 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, and the like. You may use it, selecting suitably from several combinations.

  The method for isolating the sulfonated product from the reaction solution containing the sulfonated product of the block copolymer includes a method of pouring the reaction solution into water and precipitating the sulfonated product, and then distilling off the solvent at normal pressure. There is a method in which the stopper is gradually added and suspended, and then the sulfonated product is precipitated, and then the solvent is distilled off at atmospheric pressure. From the viewpoint of increasing the washing efficiency, a method of gradually adding a suspending agent water to the reaction solution and suspending it, and then precipitating a sulfonated product is preferably used.

  A method for introducing a phosphonic acid group into the obtained block copolymer will be described. Phosphonation can be performed by a known phosphonation method. Specifically, for example, an organic solvent solution or suspension of a block copolymer is prepared, and the copolymer is reacted with chloromethyl ether or the like in the presence of anhydrous aluminum chloride to introduce a halomethyl group into the aromatic ring. Thereafter, there may be mentioned a method in which phosphorus trichloride and anhydrous aluminum chloride are added and reacted, followed by a hydrolysis reaction to introduce a phosphonic acid group. Alternatively, there can be exemplified a method in which phosphorus trichloride and anhydrous aluminum chloride are added to the copolymer and reacted to introduce a phosphinic acid group into the aromatic ring, and then the phosphinic acid group is oxidized with nitric acid to form a phosphonic acid group.

The degree of sulfonation or phosphonation is as described above until the ion exchange capacity of the block copolymer is 0.30 meq / g or more, particularly 0.40 meq / g or more, but 3.0 meq / g or less. It is desirable to sulfonate or phosphonate so that Thereby, practical ion conduction performance is obtained. The ion exchange capacity of the sulfonated or phosphonated block copolymer, or the sulfonation rate or phosphonation rate in the aromatic vinyl compound in the block copolymer is determined by acid value titration, infrared spectroscopic measurement, nuclear It can be calculated using an analytical means such as magnetic resonance spectrum ( ¹ H-NMR spectrum) measurement.

  The ion conductive group may be introduced in the form of a salt neutralized with a suitable metal ion (for example, alkali metal ion) or counter ion (for example, ammonium ion). For example, a desired ion conductive group can be introduced by producing a polymer using sodium o-, m- or p-styrene sulfonate, or α-methyl-o-, m or p-sodium styrene sulfonate. . Or the block copolymer which made the sulfonic acid group into the salt form can be obtained by ion-exchange by a suitable method.

  The polymer electrolyte membrane of the present invention contains, in addition to the polymer electrolyte (P), at least one antioxidant (Q) selected from a phosphite antioxidant and a thioether antioxidant. It is a feature. Among the antioxidants (Q), phosphorous acid antioxidants are particularly preferable for sufficiently exhibiting radical resistance. Antioxidants (Q) may be used alone or in combination of two or more.

  Known phosphorous acid antioxidants can be used. Specific examples thereof include tris (2,4-di-t-butylphenyl) phosphite, tris (nonylphenyl) phosphite, hydrogenated bisphenol. A. Pentaerythritol phosphite polymer, distearyl pentaerythritol diphosphite, tris (mono, dinonylphenyl) phosphite, trioleyl phosphite, tristearyl phosphite, bis (2,4-di-t-butylphenyl) ) [1,1-biphenyl] -4,4′-diylbisphosphite, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, triethyl phosphite, tri-n-butyl phosphite (Triphenyl phosphite, phenyl didecyl phosphite, Ridecyl phosphite, tetraphenyldipropylene glycol diphosphite, bis (2,4-di-t-butylphenyl) pentaerythritol diphosphite, tris (tridecyl) phosphite, bis (nonylphenyl) pentaerythritol diphosphite Bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite, bis [2,4-di (1-phenylisopropyl) phenyl] pentaerythritol diphosphite, trilauryl trithiophosphite 4,4′-butylidenebis (3-methyl-6-tert-butylphenylditridecyl) phosphite, tetrakis (2,4-di-tert-butyl-5-methylphenyloxy) 4,4′-biphenylene-di -Phosphine, 2-[[2,4,8,10 Tetrakis (1,1-dimethylethyl) dibenzo [d, f] [1,3,2] dioxaphosphepin6-yl] oxy] -N, N-bis [2-[[2,4,8, 10-tetrakis (1,1-dimethylethyl) dibenzo [d, f] [1,3,2,] dioxaphosphin-6-yl] oxy] -ethyl] ethanamine, tetra (C12-C15 mixed alkyl) -4,4'-isopropylidene diphenyl diphosphite, tetra (tridecyl) -4,4'-butylidenebis (3-methyl-6-tert-butylphenol) diphosphite, diphenylmonooctyl phosphite, tri (p-cresyl) phos Phyto, diphenyl monodecyl phosphite, diphenyl mono (tridecyl) phosphite, tris (2-ethylhexyl) phosphite, Oxa (tridecyl) -1,1,3-tris (2-methyl-5-tert-butyl-4-hydroxyphenyl) butane-triphosphite, hydrogenated bisphenol A phosphite polymer, tetrakis (2,4-di- (t-butylphenyloxy) 4,4′-biphenylene-di-phosphine, 2,2′-methylenebis (4,6-di-t-butylphenyl) octyl phosphite, and the like. Among these compounds, in this application, those having high heat resistance are preferable from the viewpoint of bleeding out from the electrolyte membrane and the effect of improving the durability of the electrolyte membrane. Tris (2,4-di-t-butylphenyl) Phosphite or the like is preferably used.

  As the thioether-based antioxidant, any known compound can be used. Specific examples thereof include 4,6-bis (dodecylthiomethyl) -o-cresol and dilauryl-3,3′-thiodipropio. , Pentaerythritol tetrakis (3-laurylthiopropionate), dilauryl-3,3′-thiodipropionate, 3,3′-thiobispropionic acid didodecyl ester, 2-mercaptobenzimidazole, dimyristyl-3, 3'-thiodipropionate, distearyl-3,3'-thiodipropionate, ditridecyl-3,3'-thiodipropionate, ditridecyl-3,3'-thiodipropionate, 3,3'- Thiobispropionic acid diocdecyl ester, 1,3,5-tris-β-stearylthiopropioni Examples include ruoxyethyl isocyanurate. Among these compounds, it is particularly preferable to use a compound having a high molecular weight and high heat resistance from the viewpoint of bleeding out from the electrolyte membrane and the effect of improving the durability of the electrolyte membrane.

The amount of the antioxidant (Q) used relative to 100 parts by mass of the polymer electrolyte (P) is preferably 0.01 to 20 parts by mass, more preferably 0.03 to 10 parts by mass, and It is still more preferable that it is 05-10 mass parts. When the amount of the antioxidant (Q) used is less than 0.01 parts by mass, it is difficult to obtain radical resistance due to the antioxidant (Q). Conversely, when the amount exceeds 20 parts by mass, it is used for the polymer electrolyte (P). An excessive amount tends to adversely affect the strength, proton conductivity, etc. of the electrolyte membrane.

The polymer electrolyte membrane of the present invention can be added to various additives such as a softening agent, a stabilizer, a light stabilizer, an antistatic agent, a release agent, a flame retardant, a foaming agent, and a pigment as long as the effects of the present invention are not impaired. , Dyes, brighteners, carbon fibers, inorganic fillers and the like may be used alone or in combination of two or more.
Examples of the softener include petroleum softeners such as paraffinic, naphthenic or aromatic process oils, paraffin, vegetable oil softeners, plasticizers, and the like.
Specific examples of the inorganic filler include talc, calcium carbonate, silica, glass fiber, mica, kaolin, titanium oxide, montmorillonite, and alumina.

  From the viewpoint of ion conductivity, the content of the polymer electrolyte (P) in the electrolyte membrane of the present invention is preferably 50% by mass or more, more preferably 70% by mass or more, and 90% by mass or more. Even more preferably.

  In a fuel cell, when power is generated for a long time, the electrolyte membrane swells and peeling between the electrolyte membrane and the electrode tends to occur, and stable power generation may not be possible. In particular, when the tensile modulus is large when the electrolyte membrane swells and the membrane is stretched, peeling between the membrane and the electrode tends to occur. From the above viewpoint, the 100% modulus, which is the stress at 100% elongation at break, in a tensile test under the conditions of a temperature of 25 ° C. and a tensile speed of 500 mm / min of the polymer electrolyte membrane of the present invention is 15 MPa or less. And is preferably 0.3 MPa or more and 13 MPa or less, and more preferably 0.5 MPa or more and 12 MPa or less. The 100% modulus can be reduced by increasing the mass ratio of the polymer block (B) in the block copolymer to be used.

  Moreover, when the strength of the electrolyte membrane is weak and lacks flexibility, not only the durability of the electrolyte membrane is inferior, but also the bondability between the membrane and the electrode is deteriorated, and as a result, power is generated for a long time in the fuel cell. In such a case, peeling between the electrolyte membrane and the electrode tends to occur, and stable power generation tends to be impossible. From the above viewpoint, the breaking strength of the polymer electrolyte membrane of the present invention in a tensile test under the conditions of a temperature of 25 ° C. and a tensile speed of 500 mm / min is required to be 15 MPa or more, and 16 MPa or more. The elongation at break needs to be 300% or more, preferably 320% or more and 1000% or less, more preferably 330% or more and 800% or less. . The breaking strength can be increased by increasing the number average molecular weight of the block copolymer used and increasing the mass ratio of the polymer block (A). The elongation at break can be increased by increasing the mass ratio of the polymer block (B) of the block copolymer used.

  The content of the block copolymer in the polymer electrolyte membrane of the present invention is preferably 50% by mass or more, and 70% by mass or more from the viewpoints of the above properties and ion conductivity in the tensile test of the polymer electrolyte membrane. It is more preferable that it is 90 mass% or more.

  The polymer electrolyte membrane of the present invention preferably has a thickness of about 5 to 500 μm from the viewpoints of performance required as an electrolyte membrane for fuel cells, membrane strength, handling properties, and the like. When the film thickness is less than 5 μm, the mechanical strength of the film and the gas barrier property tend to be insufficient. On the other hand, when the film thickness exceeds 500 μm, the membrane resistance (electrical resistance of the membrane) increases, and sufficient proton conductivity does not appear, so the power generation characteristics of the battery tend to be low. The film thickness is more preferably 10 to 300 μm.

As a method for preparing the polymer electrolyte membrane of the present invention, any method can be adopted as long as it is a normal method for such preparation. For example, a block copolymer (that is, a polymer constituting the polymer electrolyte membrane of the present invention (that is, Polymer electrolyte (P)) and antioxidant (Q), or the block copolymer, antioxidant (Q) and additives as described above are mixed with an appropriate solvent, and the solid content is 8% by mass or more. An electrolyte membrane having a desired thickness is prepared by applying a solution or suspension of the above to a PET film or the like that has been subjected to a release treatment using a coater or applicator, and then removing the solvent under appropriate conditions. After casting a solution or suspension of 5% by mass or less on a solution coating method or polytetrafluoroethylene sheet or the like to obtain a desired thickness by gradually removing the solvent over 1 to several days Yes An electrolyte membrane having good strength and flexibility can be prepared by using a casting method for obtaining an electrolyte membrane, a method for forming a film using a known method such as hot press molding, roll molding, and extrusion molding. From the viewpoint of facilitating, a solution coating method is preferably used.
Further, the same or different block copolymer solution may be newly applied on the obtained electrolyte membrane layer and dried to be laminated. Further, the same or different electrolyte membranes obtained as described above may be laminated by being pressure-bonded by hot roll molding or the like.

  The solvent used at this time is not particularly limited as long as it can prepare a solution having a viscosity capable of solution coating without destroying the structure of the block copolymer. Specifically, halogenated hydrocarbons such as methylene chloride, aromatic hydrocarbons such as toluene, xylene, and benzene, linear aliphatic hydrocarbons such as hexane and heptane, and cyclic aliphatic carbonization such as cyclohexane. Examples thereof include ethers such as hydrogen and tetrahydrofuran, alcohols such as methanol, ethanol, propanol, isopropanol, butanol and isobutyl alcohol, or mixed solvents thereof. Depending on the composition of the block copolymer, the molecular weight, the ion exchange capacity, etc., one or two or more combinations can be appropriately selected and used from the solvents exemplified above. From the viewpoint of easy preparation of a flexible electrolyte membrane, a mixed solvent of toluene 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, tetrahydrofuran solvent, tetrahydrofuran and A mixed solvent of methanol is preferable, and a mixed solvent of toluene and isobutyl alcohol and a mixed solvent of toluene and isopropyl alcohol are particularly preferable.

  In addition, the solvent removal conditions in the solution coating method are arbitrarily selected as long as the conditions allow the solvent to be completely removed at a temperature equal to or lower than the temperature at which the ion conductive group such as the sulfone group of the block copolymer of the present invention is removed. It is possible. In order to express desired physical properties, a plurality of temperatures may be arbitrarily combined, or a combination of ventilation and vacuum may be arbitrarily combined. Specifically, a method of removing the solvent by hot air drying at about 60 to 100 ° C. over 4 minutes, a method of removing the solvent in 2 to 4 minutes by hot air drying at about 100 to 140 ° C., After pre-drying at about 25 ° C. for about 1 to 3 hours and then drying with hot air drying at about 100 ° C. for several minutes, or after pre-drying at about 25 ° C. for about 1 to 3 hours, 25 Examples include a method of drying for about 1 to 12 hours by vacuum drying in an atmosphere of about 40 ° C. From the viewpoint of easy adjustment of an electrolyte membrane having good strength and flexibility, a method of removing the solvent over 4 minutes or more by hot air drying at about 60 to 100 ° C., or about 1 to 3 hours at about 25 ° C. After drying, it is dried by hot air drying at about 100 ° C. over several minutes, or after preliminary drying at about 25 ° C. for about 1 to 3 hours, and then vacuum drying in an atmosphere of about 25-40 ° C. For example, a method of drying for about 1 to 12 hours is preferably used.

  Next, a membrane-electrode assembly using the polymer electrolyte membrane of the present invention will be described. The production of the membrane-electrode assembly is not particularly limited, and a known method can be applied. For example, a catalyst paste containing an ion conductive binder is applied on the gas diffusion layer by a printing method or a spray method and dried. To form a joined body of the catalyst layer and the gas diffusion layer, and then to join the two pairs of joined bodies with the catalyst layer on the inside and by hot pressing or the like on both sides of the polymer electrolyte membrane, There is a method in which a catalyst paste is applied to both sides of a polymer electrolyte membrane by a printing method or a spray method, dried to form a catalyst layer, and a gas diffusion layer is pressure-bonded to each catalyst layer by hot pressing or the like. As another production method, a solution or suspension containing an ion conductive binder is applied to both surfaces of the polymer electrolyte membrane and / or the catalyst layer surface of a pair of gas diffusion electrodes, and the electrolyte membrane and the catalyst layer surface are bonded together. There is a method of joining by thermocompression bonding. In this case, the solution or suspension may be applied to either the electrolyte membrane or the catalyst layer surface, or may be applied to both. As another manufacturing method, first, the catalyst paste is applied to a base film made of polytetrafluoroethylene (PTFE) and dried to form a catalyst layer, and then a pair of base films on the base film is formed. The catalyst layer is transferred to both sides of the polymer electrolyte membrane by thermocompression bonding, the base film is peeled off to obtain a joined body of the electrolyte membrane and the catalyst layer, and the gas diffusion layer is crimped to each catalyst layer by hot pressing. There is a way. In these methods, these methods may be performed in a state where the ion conductive group is made into a salt with a metal such as Na, and a treatment for returning to a proton type by an acid treatment after bonding may be performed.

  Examples of the ion conductive binder constituting the membrane-electrode assembly include existing perfluorosulfones such as “Nafion” (registered trademark, manufactured by DuPont) and “Gore-select” (registered trademark, manufactured by Gore). An ion conductive binder made of an acid polymer, an ion conductive binder made of sulfonated polyethersulfone or sulfonated polyetherketone, an ion conductive binder made of polybenzimidazole impregnated with phosphoric acid or sulfuric acid can be used. . Moreover, you may produce an ion conductive binder from the block copolymer which comprises the polymer electrolyte membrane of this invention. In order to further enhance the adhesion between the electrolyte membrane and the gas diffusion electrode, it is preferable to use an ion conductive binder formed from the same material as the polymer electrolyte membrane.

  The constituent material of the catalyst layer of the membrane-electrode assembly is not particularly limited as the conductive material / catalyst support, and examples thereof include carbon materials. Examples of the carbon material include carbon black such as furnace black, channel black, and acetylene black, activated carbon, graphite, and the like. These may be used alone or in combination of two or more. The catalyst metal may be any metal that promotes the oxidation reaction of fuel such as hydrogen and methanol and the reduction reaction of oxygen, such as platinum, gold, silver, palladium, iridium, rhodium, ruthenium, iron, Cobalt, nickel, chromium, tungsten, manganese, palladium, etc., or alloys thereof, for example, platinum-ruthenium alloys are mentioned. Of these, platinum and platinum alloys are often used. The particle size of the metal serving as a catalyst is usually 10 to 300 angstroms. When these catalysts are supported on a conductive material / catalyst carrier such as carbon, the amount of catalyst used is small and advantageous in terms of cost. The catalyst layer may contain a water repellent as necessary. Examples of the water repellent include various thermoplastic resins such as polytetrafluoroethylene, polyvinylidene fluoride, styrene butadiene copolymer, and polyether ether ketone.

  The gas diffusion layer of the membrane-electrode assembly is made of a material having conductivity and gas permeability, and examples of such a material include porous materials made of carbon fibers such as carbon paper and carbon cloth. Moreover, in order to improve water repellency, this material may be subjected to water repellency treatment.

A polymer electrolyte fuel obtained by inserting the membrane-electrode assembly obtained by the above-described method between a conductive separator material that also serves as a gas supply flow path to the electrode and the electrode chamber separation. A battery is obtained. The membrane-electrode assembly of the present invention uses a pure hydrogen type using hydrogen as a fuel gas, a methanol reforming type using hydrogen obtained by reforming methanol, and hydrogen obtained by reforming natural gas. Natural gas reforming type, gasoline reforming type using hydrogen obtained by reforming gasoline, direct methanol type using methanol directly, etc. can be used as a membrane-electrode assembly for polymer electrolyte fuel cells. is there.
The fuel cell using the polymer electrolyte membrane of the present invention is excellent in radical resistance and membrane-electrode bonding.

  Hereinafter, performance examples (ion exchange capacity measurement, proton conductivity measurement, radical stability test, and membrane strength measurement) as reference examples, examples and comparative examples, and proton conductive electrolyte membranes for polymer electrolyte fuel cells and their The present invention will be described more specifically by showing the results. However, the present invention is not limited to these.

Reference example 1
Manufacture of a sulfonated block copolymer composed of polystyrene (polymer block (A)) and polyisobutylene (polymer block (B)) (1) Manufacture of the above block copolymer (WO 98/14518) No.), a polystyrene-b-polyisobutylene-b-polystyrene triblock copolymer (hereinafter abbreviated as SiBuS) was produced. The number average molecular weight of the obtained SiBuS was 65300, and the content of styrene units was 29.0% by mass.
(2) Synthesis of sulfonated SiBuS A sulfonating reagent was prepared by reacting 20.5 ml of acetic anhydride and 9.18 ml of sulfuric acid at 0 ° C in 41.1 ml of methylene chloride. On the other hand, 60 g of the block copolymer (SiBuS) obtained in (1) was vacuum-dried in a glass reaction vessel equipped with a stirrer for 1 hour and then purged with nitrogen. And stirred for 2 hours to dissolve. After dissolution, the sulfonation reagent was gradually added dropwise over 20 minutes. After stirring for 4 hours at 35 ° C., 10 ml of distilled water as a stopper was added. Thereafter, 1.3 L of distilled water was slowly poured into the polymer solution to solidify and precipitate the polymer. The methylene chloride was removed by distillation at atmospheric pressure, followed by filtration. The solid content obtained by filtration was transferred to a beaker, 1.3 L of distilled water was added, and washing was performed with stirring, followed by filtration and recovery. This washing and filtration operation was repeated until there was no change in the pH of the washing water, and finally the polymer collected by filtration was vacuum dried to obtain sulfonated SiBuS. The sulfonation rate of the benzene ring of the styrene unit of the sulfonated SiBuS obtained was 40.0 mol% from ¹ H-NMR analysis, and the ion exchange capacity was 1.00 meq / g.

Reference example 2
Manufacture of a sulfonated body of a block copolymer composed of poly α-methylstyrene (polymer block (A)) and hydrogenated polybutadiene (polymer block (B)) (1) Manufacture of the above block copolymer A poly α-methylstyrene b-polybutadiene-b-poly α-methylstyrene type triblock copolymer (hereinafter abbreviated as mSEBmS) was synthesized in the same manner as in (WO 02/40611). The number average molecular weight (GPC measurement, polystyrene conversion) of the obtained mSEBmS is 78000, the 1,4-bond amount determined from ¹ H-NMR measurement is 55%, and the content of α-methylstyrene unit is 28.0. It was mass%. Further, it was found by composition analysis by ¹ H-NMR spectrum measurement that α-methylstyrene was not substantially copolymerized in the polybutadiene block.
A cyclohexane solution of synthesized mSEBmS was prepared and charged into a pressure-resistant vessel that had been sufficiently purged with nitrogen. Then, a hydrogenation reaction was performed at 80 ° C. for 5 hours in a hydrogen atmosphere using a Ni / Al Ziegler hydrogenation catalyst. To obtain a poly α-methylstyrene-b-hydrogenated polybutadiene-b-polyα-methylstyrene type triblock copolymer (hereinafter abbreviated as mSEBmS). The hydrogenation proportion of the resulting mSEBmS was calculated by ¹ H-NMR spectrum measurement, it was 99.3%.
(2) Synthesis of sulfonated mSEBmS 70 g of the block copolymer (mSEBmS) obtained in (1) was vacuum-dried in a glass reaction vessel equipped with a stirrer for 1 hour and then purged with nitrogen, and then 563 ml of methylene chloride. And dissolved by stirring at 35 ° C. for 2 hours. After dissolution, a sulfonation reagent obtained by reacting 20.0 ml of acetic anhydride and 8.84 ml of sulfuric acid at 0 ° C. in 38.7 ml of methylene chloride was gradually added dropwise over 20 minutes. After stirring at 35 ° C. for 5 hours, 10 ml of distilled water as a stopper was added. Thereafter, 1.2 L of distilled water was slowly poured into the polymer solution with stirring to solidify and precipitate the polymer. The methylene chloride was removed by distillation at atmospheric pressure, followed by filtration. The solid content obtained by filtration was transferred to a beaker, 1.2 L of distilled water was added, and washing was performed with stirring, followed by filtration and recovery. This washing and filtration operation was repeated until there was no change in the pH of the washing water, and the polymer collected at the end was vacuum-dried to obtain sulfonated mSEBmS. The sulfonation rate of the benzene ring of the α-methylstyrene unit of the obtained sulfonated mSEBmS was 51.5 mol% from ¹ H-NMR analysis, and the ion exchange capacity was 1.06 meq / g.

Reference example 3
Sulfonated block copolymer consisting of polystyrene (ion conductive block (A2)), hydrogenated polyisoprene (polymer block (B)) and poly (4-tert-butylstyrene) (restraint block (A1)). (1) Manufacture of the above block copolymer A 1400 mL autoclave was charged with 512 ml of dehydrated cyclohexane and 2.9 ml of sec-butyllithium (0.8 M-cyclohexane solution), and then 39.1 ml of 4-tert-butylstyrene. By sequentially adding 12.1 ml of styrene and 57.1 ml of isoprene, polymerizing sequentially at 30 ° C., and then coupling by adding 10.4 ml of 3% by weight cyclohexane solution of phenyl benzoate, poly (4-tert- Butylstyrene) -b-polystyrene-b-polyisopre N-b-polystyrene-b-poly (4-tert-butylstyrene) (hereinafter abbreviated as tBSSIStBS) was synthesized. The number average molecular weight (GPC measurement, polystyrene conversion) of the obtained tBSSIStBS is 120,000, the 1,4-bond content determined from ¹ H-NMR measurement is 94.0%, and the content of styrene units is 12.3 mass. %, 4-tert-butylstyrene unit content was 40.5% by mass.
After preparing a cyclohexane solution of synthesized tBSSIStBS and charging it in a pressure vessel sufficiently purged with nitrogen, a hydrogenation reaction was performed at 80 ° C. for 20 hours in a hydrogen atmosphere using a Ni / Al Ziegler hydrogenation catalyst. To obtain poly (4-tert-butylstyrene) -b-polystyrene-b-hydrogenated polyisoprene-b-polystyrene-b-poly (4-tert-butylstyrene) (hereinafter abbreviated as tBSSEPStBS). When the hydrogenation rate of the obtained tBSSEPStBS was calculated by ¹ H-NMR spectrum measurement, the hydrogenation rate was 99.9%.
(2) Synthesis of sulfonated tBSSEPStBS A sulfonating reagent was prepared by reacting 10.7 ml of acetic anhydride and 4.77 ml of sulfuric acid at 2 ° C. in 21.3 ml of methylene chloride. On the other hand, 20 g of the block copolymer (tBSSEPStBS) obtained in the above (1) was vacuum-dried for 1 hour in a glass reaction vessel equipped with a stirrer, and then purged with nitrogen. The mixture was stirred at 2 ° C. for 2 hours for dissolution. After dissolution, the sulfonation reagent was gradually added dropwise over 20 minutes. After stirring for 72 hours at a room temperature of 25 ° C., 5 ml of distilled water as a stopper was added. Thereafter, 0.6 L of distilled water was slowly poured into the polymer solution to solidify and precipitate the polymer. The methylene chloride was removed by distillation at atmospheric pressure, followed by filtration. The solid content obtained by filtration was transferred to a beaker, 0.6 L of distilled water was added, and washing was performed with stirring, followed by filtration and recovery. This washing and filtration operation was repeated until there was no change in the pH of the washing water, and finally the polymer collected by filtration was vacuum dried to obtain sulfonated tBSSEPStBS. The sulfonation rate of the benzene ring of the styrene unit in the obtained sulfonated tBSSEPStBS was 100 mol% from ¹ H-NMR analysis, and the ion exchange capacity was 1.00 meq / g.

Example 1
Production of Electrolyte Membrane Containing Components of Sulfonated SiBuS and Phosphite Antioxidant A 26% by mass toluene / isobutyl alcohol (mass ratio 7/3) solution of sulfonated SiBuS obtained in Reference Example 1 was prepared. Thereafter, tris (2,4-di-t-butylphenyl) phosphite (IRGAFOS 168, manufactured by Ciba Specialty Chemicals Co., Ltd.) as a phosphite-based antioxidant with respect to 100 parts by mass of sulfonated SiBuS. 1 part by mass was added, and the solution was prepared by stirring for 4 hours and dissolving. This solution is coated on a PET film [Toyobo Co., Ltd. “Toyobo Ester Film K1504”] with a thickness of about 200 μm and dried at 100 ° C. for 4 minutes to obtain a film with a thickness of 30 μm. It was.

Example 2
Production of Electrolyte Membrane Containing Sulfonated SiBuS and Thioether Antioxidant In place of the phosphorous acid antioxidant of Example 1, the thioether antioxidant 4,6-bis (dodecylthiomethyl)- A film having a thickness of 30 μm was obtained in the same manner as in Example 1 except that o-cresol (IRGANOX 1726, manufactured by Ciba Specialty Chemicals Co., Ltd.) was used.

Example 3
Production of Electrolyte Membrane Containing Components of Sulfonated mSEBmS and Phosphite Antioxidant A 16.5% by mass toluene / isobutyl alcohol (mass ratio 8/2) solution of sulfonated mSEBmS obtained in Reference Example 2 After the preparation, phosphite antioxidant tris (2,4-di-t-butylphenyl) phosphite (IRGAFOS 168, manufactured by Ciba Specialty Chemicals Co., Ltd.) with respect to 100 parts by mass of sulfonated mSEBmS. ) 1 part by mass was added, and the solution was prepared by stirring and dissolving for 4 hours. This solution was coated on a PET film [Toyobo Co., Ltd. “Toyobo Ester Film K1504”] with a thickness of about 300 μm and dried at 100 ° C. for 4 minutes to obtain a 30 μm thick film. It was.

Example 4
Production of electrolyte membrane containing sulfonated tBSSEPStBS and phosphorous acid antioxidant as constituents A 20% by mass toluene / isobutyl alcohol (mass ratio 8/2) solution of sulfonated tBSSEPStBS obtained in Reference Example 3 was prepared. Thereafter, tris (2,4-di-t-butylphenyl) phosphite (IRGAFOS 168, manufactured by Ciba Specialty Chemicals Co., Ltd.), a phosphite-based antioxidant, with respect to 100 parts by mass of sulfonated tBSSEPStBS 1 A solution was prepared by adding part by mass and stirring for 4 hours to dissolve. This solution is coated on a PET film [Toyobo Co., Ltd. “Toyobo Ester Film K1504”] with a thickness of about 250 μm and dried at 100 ° C. for 4 minutes to obtain a film with a thickness of 30 μm. It was.

Example 5
Production of Electrolyte Membrane Containing Sulfonated tBSSEPStBS and Thioether Antioxidant In place of the phosphorous acid antioxidant of Example 4, the thioether antioxidant 4,6-bis (dodecylthiomethyl)- A film having a thickness of 30 μm was obtained in the same manner as in Example 4 except that o-cresol (IRGANOX 1726, manufactured by Ciba Specialty Chemicals Co., Ltd.) was used.

Comparative Example 1
Production of electrolyte membrane comprising sulfonated SiBuS A membrane having a thickness of 30 μm was obtained in the same manner as in Example 1 except that the phosphorous acid antioxidant in Example 1 was not used.

Comparative Example 2
Production of electrolyte membrane comprising sulfonated SiBuS and hindered phenolic antioxidant as constituent components Instead of the phosphorous acid antioxidant of Example 1, pentaerythrityl-tetrakis as hindered phenolic antioxidant [ Thickness in the same manner as in Example 1 except that 3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] (IRGANOX 1010, manufactured by Ciba Specialty Chemicals Co., Ltd.) was used. A film having a thickness of 30 μm was obtained.

Comparative Example 3
Production of Electrolyte Membrane Containing Sulfonated mSEBmS A membrane having a thickness of 30 μm was obtained in the same manner as in Example 3 except that the phosphorous acid antioxidant in Example 3 was not used.

Comparative Example 4
Production of Electrolyte Membrane Containing Sulfonated mSEBmS and Hindered Phenol Antioxidant Instead of the phosphorous acid antioxidant of Example 3, the hindered phenol antioxidant pentaerythrityl-tetrakis [3 -(3,5-di-t-butyl-4-hydroxyphenyl) propionate] (IRGANOX 1010, manufactured by Ciba Specialty Chemicals) was used in the same manner as in Example 1 to obtain the thickness. A 30 μm membrane was obtained.

Comparative Example 5
Production of electrolyte membrane comprising sulfonated tBSSEPStBS A membrane having a thickness of 30 μm was obtained in the same manner as in Example 4 except that the phosphorous acid antioxidant in Example 4 was not used.

Comparative Example 6
Perfluorocarbon sulfonic acid polymer electrolyte membrane A DuPont Nafion film (Nafion 211) was selected as the perfluorocarbon sulfonic acid polymer electrolyte membrane. The thickness of the film was about 25 μm.

The block copolymer of Reference Examples 1 to 3 and the measurement sample of the ion exchange capacity of Nafion 211 of Comparative Example 6 are weighed (a (g)) in a glass container that can be sealed, and an excess amount of a saturated aqueous sodium chloride solution is added thereto. And stirred overnight. Hydrogen chloride generated in the system was titrated (b (ml)) with a 0.01N NaOH standard aqueous solution (titer f) using a phenolphthalein solution as an indicator. The ion exchange capacity was determined by the following formula.
Ion exchange capacity = (0.01 × b × f) / a

Performance test of electrolyte membranes of Examples 1 to 5 and Comparative Examples 1 to 6 as electrolyte membranes for polymer electrolyte fuel cells Samples obtained in the following Examples 1 and 3) were obtained in each Example or Comparative Example. An electrolyte membrane was used.

1) Ionic conductivity measurement A sample of 1 cm × 4 cm was sandwiched between a pair of gold electrodes and attached to an open cell. The measurement cell was installed in water at a temperature of 40 ° C., and the ionic conductivity was measured by the AC impedance method.

2) In radical stability test method 1, a radical reaction reagent was prepared by dissolving iron (II) sulfate heptahydrate at a concentration of 20 ppm in a 3% by mass aqueous hydrogen peroxide solution. Subsequently, after measuring the mass (A) of the dried sample, it added to the radical reaction reagent, and was made to react in 25 degreeC atmosphere for 8 hours. The sample was thoroughly washed with distilled water, the mass (B) after drying was measured, and the mass reduction rate as an index of radical stability was calculated by the following formula.
Mass reduction rate (%) = (A−B) / A × 100
In Method 2, the test was conducted in the same manner as in Method 1 except that a radical reaction reagent prepared by dissolving iron sulfate (II) heptahydrate at 30 ppm in a 10% by mass aqueous hydrogen peroxide solution was used. Carried out.

3) Film strength measurement A sample was molded into a dumbbell shape, and the breaking strength was measured under the condition of a tensile speed of 500 mm / min.

Results of performance test as electrolyte membrane for polymer electrolyte fuel cell Table 1 shows the results of performance test as electrolyte membrane for polymer electrolyte fuel cell of the electrolyte membranes of Examples 1-5 and Comparative Examples 1-5. .

As can be seen from Examples 1-2 and Comparative Examples 1-2, Example 3, Comparative Examples 3-4, and Examples 4-5 and Comparative Example 5, phosphorous acid antioxidants or thioether antioxidants The radical stability was improved while maintaining ionic conductivity and tensile properties (100% modulus, tensile strength, tensile elongation). Further, when the Nafion film 211 of Comparative Example 6 is used, although the radical stability is excellent, there is a problem in mechanical durability because the tensile properties (100% modulus, tensile elongation) are poor.
From this, the electrolyte membrane of the present invention has both strength and flexibility, and is excellent in radical resistance, so it has excellent durability, and the durability of a membrane-electrode assembly and a polymer electrolyte fuel cell using the same It can be said that it is excellent.

Claims (11)

  The polymer block (A) and the flexible polymer block (B) having an aromatic vinyl compound unit as a main repeating unit are constituent components, and the mass ratio of the polymer block (A) to the polymer block (B) is 65:35 to 5:95, and a polymer electrolyte (P), a phosphite-based antioxidant, and a thioether-based polymer, each of which has a block copolymer that is present only in the polymer block (A). A polymer electrolyte membrane for a polymer electrolyte fuel cell, comprising at least one antioxidant (Q) selected from antioxidants, at a temperature of 25 ° C. and a tensile speed of 500 mm / min. The electrolyte membrane having a 100% modulus of 15 MPa or less, a breaking strength of 15 MPa or more, and a breaking elongation of 300% or more in a tensile test.   The electrolyte membrane according to claim 1, wherein the amount of the antioxidant (Q) used is 0.1 to 20 parts by mass with respect to 100 parts by mass of the polymer electrolyte (P).   The polymer block (A) is composed of a constraining block (A1) that substantially does not have an ion conductive group and functions as a constrained phase, and an ion conductive block (A2) having an ion conductive group. The electrolyte membrane described. In the polymer block (A), the constraining block (A1) is represented by the following general formula (I):

(In the formula, R ¹ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ^{2 to} R ⁴ each independently represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, but at least one of them is carbon. A polymer block having an aromatic vinyl compound unit represented by the formula (II) as a main repeating unit, and the ion conductive block (A2) is represented by the following general formula (II):

(In the formula, Ar ¹ represents an aryl group having 6 to 14 carbon atoms which may have ¹ to 3 substituents, and R ⁵ represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or 1 to 3). 4. The electrolyte membrane according to claim 3, which is a polymer block having a main repeating unit of an aromatic vinyl compound unit represented by (C 6-14 aryl group optionally having substituents).   The electrolyte membrane according to claim 3 or 4, wherein the mass ratio of the constrained block (A1) and the ion conductive block (A2) of the block copolymer is 95: 5 to 20:80.   The polymer block (B) is an alkene unit having 2 to 8 carbon atoms, a cycloalkene unit having 5 to 8 carbon atoms, a vinylcycloalkene unit having 7 to 10 carbon atoms, a conjugated diene unit having 4 to 8 carbon atoms, and 5 carbon atoms. A conjugated cycloalkadiene unit having 8 to 8 carbon atoms, a vinylcycloalkene unit having 7 to 10 carbon atoms in which some or all of the carbon-carbon double bonds are hydrogenated, a conjugated diene unit having 4 to 8 carbon atoms and a carbon number of 5 The electrolyte membrane according to any one of claims 1 to 5, which is a polymer block comprising at least one repeating unit selected from the group consisting of -8 conjugated cycloalkadiene units.   The polymer block (B) is an alkene unit having 2 to 8 carbon atoms, a conjugated diene unit having 4 to 8 carbon atoms, and a conjugate having 4 to 8 carbon atoms in which some or all of the carbon-carbon double bonds are hydrogenated. The electrolyte membrane according to any one of claims 1 to 6, which is a polymer block comprising at least one repeating unit selected from diene units. (Wherein, M represents a hydrogen atom, an ammonium ion or an alkali metal ion) ion-conducting group is -SO ₃ M or _-PO 3 HM in claim 1 is a group represented by The electrolyte membrane described.   The electrolyte membrane according to claim 1, wherein the block copolymer has an ion exchange capacity of 0.30 meq / g or more.   The membrane-electrode assembly using the electrolyte membrane of any one of Claims 1-9. A polymer electrolyte fuel cell using the membrane-electrode assembly according to claim 10.