JP2006210326A - Polymer electrolyte film for solid polymer fuel cells, membrane-electrode assembly, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polymer electrolyte film for a solid polymer fuel cell, a membrane/electrode assembly using the same, and a solid polymer fuel cell, economical, environmentally friendly, and excellent in moldability and anti-radical properties. <P>SOLUTION: The polymer electrolyte film for the solid polymer fuel cell, the membrane/electrode assembly and the solid polymer fuel cell contain a polymer block (A) with an aromatic vinyl system compound unit with α-carbon in quaternary carbon, and a flexible polymer block (B) as constituent components and that, the polymer block (A) contains a block copolymer having an ion-conductive group. <P>COPYRIGHT: (C)2006,JPO&NCIPI

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 that use both electric power and heat, as well as power sources for electric vehicles and portable devices, 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 (Membrane 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, Nafion (registered trademark of Nafion, DuPont), which is a perfluorosulfonic acid polymer, is generally used because it is chemically stable. It has been. However, since Nafion is a fluorine-based polymer, it is very expensive. Further, Nafion has a problem that when methanol is used as a fuel, a phenomenon (methanol crossover) in which methanol permeates the electrolyte membrane from one electrode side to the other electrode side occurs. In addition, the fluorine-containing polymer contains fluorine, and environmental considerations are required during synthesis and disposal. From such a background, development of a novel polymer electrolyte membrane is desired.

  Several efforts have already been made for the development of ion conductive polymers based on non-fluorine polymers. For example, there is an example in which a polystyrene sulfonic acid polymer electrolyte membrane is used in a solid polymer fuel cell developed by General Electric in the United States in the 1950s. However, since there was not sufficient stability, sufficient battery life could not be obtained.

  Further, polyether ether ketone (PEEK) (Patent Document 1), which is a heat-resistant aromatic polymer, has been developed. However, in general, the sulfonated aromatic polymer has insufficient ion conductivity, so that the performance as a fuel cell is not sufficient. It is also known that increasing the amount of sulfonation to increase ionic conductivity makes the membrane brittle, making it very difficult to use.

  On the other hand, a structure in which a polystyrene block is made into an ion conductive channel by sulfonated a polystyrene block of a block copolymer composed of styrene and a rubber component has been proposed. For example, in Patent Document 2, an inexpensive, mechanically and chemically stable polymer electrolyte membrane is composed of a sulfonated product of SEBS (polystyrene-poly (ethylene-butylene) -polystyrene triblock copolymer). Ion conductive membranes have been proposed. However, as a result of our actual tests, it was found that chemical stability, particularly radical resistance, is not sufficient. This indicates that when this membrane is used in a fuel cell, the operable time is limited.

  Patent Document 3 proposes an ion conductive membrane made of a sulfonated body of SiBuS (polystyrene-polyisobutylene-polystyrene triblock copolymer) having an isobutylene skeleton having excellent chemical stability as a rubber component. Yes. In fact, Patent Document 3 shows that radical resistance is higher in sulfonated SiBuS than in sulfonated SEBS proposed in Patent Document 3, which is an index of radical resistance. The amount of ion exchange after the Fenton reaction has been reduced to about 1/2, and the chemical stability is not necessarily sufficient.

Thus, the fact is that no improved polymer electrolyte membrane for a polymer electrolyte fuel cell that is economical and highly durable has been proposed.
JP-A-6-93114 Japanese National Patent Publication No. 10-503788 Japanese Patent Laid-Open No. 2001-210336

  The object of the present invention is a polymer electrolyte membrane for a polymer electrolyte fuel cell that is economical, environmentally friendly, excellent in moldability, and excellent in radical resistance and consequently durability, and a membrane using the electrolyte membrane- An electrode assembly and a polymer electrolyte fuel cell are provided.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a polymer block and a flexible polymer block (B) having an aromatic vinyl compound unit in which the α-carbon is a quaternary carbon as a repeating unit. ) And a block copolymer having an ion conductive group in the polymer block (A) meets the above object as a polymer electrolyte membrane for a polymer electrolyte fuel cell, and the present invention is completed. did.

  That is, the present invention comprises a polymer block (A) having a main repeating unit of an aromatic vinyl compound whose α-carbon is a quaternary carbon and a flexible polymer block (B) as constituent components, and The present invention relates to a polymer electrolyte membrane for a polymer electrolyte fuel cell, wherein the combined block (A) contains a block copolymer having an ion conductive group.

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 presence of the polymer block (B) makes the block copolymer elastic and flexible as a whole, and formability (assembly property, bonding property) in the production of membrane-electrode assemblies and polymer electrolyte fuel cells. Performance, tightenability, etc.). The flexible polymer block (B) is composed of an alkene unit or a conjugated diene unit. The aromatic vinyl compound unit in which the α-carbon is a quaternary carbon includes an aromatic vinyl compound unit in which the hydrogen atom bonded to the α-position carbon atom is substituted with an alkyl group, a halogenated alkyl group or a phenyl group. To do. The ion conductive group is bonded to the polymer block (A), which is necessary for improving radical resistance. Ion conductive groups include sulfonic acid groups and phosphonic acid groups and salts thereof.
The present invention also relates to a membrane-electrode assembly and a fuel cell using the above electrolyte membrane.

  The polymer electrolyte membrane, membrane-electrode assembly and polymer electrolyte fuel cell of the present invention are economical, environmentally friendly, have excellent radical resistance and durability, and sufficiently function even under high temperature conditions. . The polymer electrolyte membrane of the present invention is also excellent in moldability.

  Hereinafter, the present invention will be described in detail. The block copolymer constituting the polymer electrolyte membrane of the present invention is a polymer having an aromatic vinyl compound unit in which α-carbon is a quaternary carbon as a main repeating unit and having at least one ion-conducting group. The block (A) is a component.

  The aromatic vinyl compound in which the α-carbon is a quaternary carbon has an alkyl group (a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-containing hydrogen atom bonded to the α-carbon atom). -Butyl group, isobutyl group or tert-butyl group), a C1-C4 halogenated alkyl group (chloromethyl group, 2-chloroethyl group, 3-chloroethyl group, etc.) or an aromatic vinyl group substituted with a phenyl group A compound is preferred. Examples of the aromatic vinyl compound serving as a skeleton include styrene, vinyl naphthalene, vinyl anthracene, vinyl pyrene, and vinyl pyridine. The hydrogen atom bonded to the aromatic ring of these aromatic vinyl compounds may be substituted with 1 to 3 substituents, and each independently represents an alkyl group having 1 to 4 carbon atoms (methyl group, Ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group or tert-butyl group), C1-C4 halogenated alkyl group (chloromethyl group, 2-chloroethyl group, 3-chloroethyl group, etc.) ) And the like. Specific examples of the aromatic vinyl compound in which the α-carbon is a quaternary carbon include α-methylstyrene. Aromatic vinyl compounds in which the α-carbon is a quaternary carbon may be used alone or in combination of two or more. The form in the case of polymerizing (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 aromatic vinyl compounds [styrene, alkyl groups having 1 to 3 hydrogen atoms bonded to the benzene ring (methyl group, ethyl group, n-propyl group, isopropyl group, n- Styrene, vinylnaphthalene, vinylanthracene, vinylpyrene, etc.) substituted with a butyl group, an isobutyl group or a tert-butyl group], a conjugated diene having 4 to 8 carbon atoms (specific examples are described in the description of the polymer block (B) described later) The same as in the description of the polymer block (B) described later), (meth) acrylate (methyl (meth) acrylate, ethyl (meth) acrylate) Butyl (meth) acrylate), vinyl esters (vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, etc.), vinyl ester Ether (methyl vinyl ether, isobutyl vinyl ether, etc.), and the like. The copolymerization form of the aromatic vinyl compound in which the α-carbon is a quaternary carbon and the other monomer needs to be random copolymerization.

  The aromatic vinyl compound unit in which the α-carbon in the polymer block (A) is a quaternary carbon is used in order to impart sufficient radical resistance to the finally obtained polymer electrolyte membrane. It is preferable to occupy 50% by mass or more of A), more preferably 70% by mass or more, and even more preferably 90% by mass or more.

  The molecular weight of the polymer block (A) is appropriately selected depending on the properties of the polymer electrolyte membrane, the required performance, other polymer components, and the like. When the molecular weight is large, the mechanical properties such as the tensile strength of the polymer electrolyte membrane tend to be high, and when the molecular weight is small, the electric resistance of the polymer electrolyte membrane tends to be small, and the molecular weight is appropriately adjusted according to the required performance. It is important to choose. The number average molecular weight in terms of polystyrene is usually preferably selected from 100 to 1,000,000, more preferably from 1,000 to 100,000.

  The block copolymer used in the polymer electrolyte membrane of the present invention has a flexible polymer block (B) in addition to the polymer block (A). The polymer block (A) and the polymer block (B) undergo a microphase separation, and the polymer block (A) and the polymer block (B) have a property of gathering together, and the polymer block (A ) Has an ion conductive group, so that an ion channel is formed by the assembly of the polymer blocks (A) and becomes a passage for protons. By having such a polymer block (B), the block copolymer becomes elastic and flexible as a whole, and formability (assembly property, bondability) in the production of membrane-electrode assemblies and polymer electrolyte fuel cells. , Tightenability, etc.). 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 types 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, the carbon-carbon double bond is preferably hydrogenated at 30 mol% or more, and 50 mol%. The above is more preferably hydrogenated, and more preferably 80 mol% or more is hydrogenated. The hydrogenation rate of the carbon-carbon double bond can be calculated by a commonly used method, for example, iodine value measurement method, ¹ H-NMR measurement or the like.

  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. Unit, cycloalkene unit having 5 to 8 carbon atoms, vinylcycloalkene unit having 7 to 10 carbon atoms, conjugated diene unit having 4 to 8 carbon atoms, conjugated cycloalkadiene unit having 5 to 8 carbon atoms, carbon-carbon double 7 to 10 carbon cycloalkene units having some or all of the hydrogenated hydrogen atoms, 4 to 8 carbon conjugated diene units having some or all of the carbon-carbon double bonds hydrogenated, and carbon -A polymer block comprising at least one repeating unit selected from conjugated cycloalkadiene units having 5 to 8 carbon atoms in which some or all of the carbon double bonds are hydrogenated. Preferably, the alkene unit having 2 to 8 carbon atoms, the conjugated diene unit having 4 to 8 carbon atoms, and the conjugated diene unit having 4 to 8 carbon atoms in which some or all of the carbon-carbon double bonds are hydrogenated are selected. More preferably, the polymer block is composed of at least one repeating unit, and the alkene unit having 2 to 6 carbon atoms, the conjugated diene unit having 4 to 8 carbon atoms, and a part or all of the carbon-carbon double bonds are included. It is even more preferable that the polymer block comprises at least one repeating unit selected from hydrogenated conjugated diene units having 4 to 8 carbon atoms. 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.

  As the alkene having 2 to 8 carbon atoms, ethylene, propylene, 1-butene, 2-butene, isobutene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, 1-heptene, 2-heptene, 1 -Octene, 2-octene, and the like. Examples of the cycloalkene having 5 to 8 carbon atoms include cyclopentene, cyclohexene, cycloheptene, and cyclooctene. Examples of the vinylcycloalkene having 7 to 10 carbon atoms include vinylcyclopentene, vinylcyclohexene, Examples thereof include vinylcycloheptene and vinylcyclooctene. Examples of the conjugated diene having 4 to 8 carbon atoms include 1,3-butadiene, 1,3-pentadiene, isoprene, 1,3-hexadiene, 2,4-hexadiene, 2 , 3-Dimethyl-1,3-butadiene, 2-ethyl-1,3-butyl Diene, 1,3-heptadiene, 1,4-heptadiene, 3,5-heptadiene and the like, cyclopentadiene, 1,3-cyclohexadiene, and the like as a conjugated cycloalkadiene having 5 to 8 carbon atoms.

  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. Aromatic vinyl compounds such as naphthalene; halogen-containing vinyl compounds 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%.

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,
A-B-A-B type tetrablock copolymer, A-B-A-B-A type pentablock copolymer, B-A-B-A-B type pentablock copolymer, (A-B ) NX type star copolymer (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.

  The mass ratio of the polymer block (A) and the polymer block (B) is preferably 95: 5 to 5:95, more preferably 90:10 to 10:90, and 50:50 to 10 : 90 is even more preferable. When this mass ratio is 95: 5 to 5:95, it is advantageous for the ion channel formed by the polymer block (A) to become a cylindrical or continuous phase by microphase separation, which is practically sufficient. Excellent ionic conductivity is exhibited, and the ratio of the polymer block (B) that is hydrophobic is appropriate, and excellent water resistance is exhibited.

The block copolymer constituting the polymer electrolyte membrane of the present invention may contain another polymer block (C) different from the polymer block (A) and the polymer block (B).
The polymer block (C) is not particularly limited as long as it is a component that undergoes microphase separation from the polymer block (A) and the polymer block (B). Examples of the monomer constituting the polymer block (C) include aromatic vinyl compounds [styrene, alkyl groups having 1 to 3 hydrogen atoms bonded to the benzene ring (methyl group, ethyl group, n-propyl group). , Styrene, vinylnaphthalene, vinylanthracene, vinylpyrene, etc., substituted with isopropyl group, n-butyl group, isobutyl group or tert-butyl group), conjugated dienes having 4 to 8 carbon atoms (specific examples are polymer blocks described later) (As in the description of (B)), alkenes having 2 to 8 carbon atoms (specific examples are the same as in the description of the polymer block (B) described above), (meth) acrylate (methyl (meth) acrylate) , Ethyl (meth) acrylate, butyl (meth) acrylate, etc.), vinyl esters (vinyl acetate, vinyl propionate, vinyl butyrate, pivalic acid) Sulfonyl, etc.), vinyl ethers (methyl vinyl ether, isobutyl vinyl ether, etc.), and the like.

When the polymer block (C) is microphase-separated from the polymer block (A) and the polymer block (B) and does not substantially contain an ionic group and has a function of acting as a constrained phase, this is required. The polymer electrolyte membrane of the present invention having a polymer block (C) tends to have excellent shape stability, durability, and mechanical properties under wet conditions. Preferable examples of the monomer constituting the polymer block (C) in this case include the aromatic vinyl compounds described above. Moreover, the above-mentioned function can be imparted by making the polymer block (C) crystalline.

  When the above-mentioned function depends on the aromatic vinyl compound unit, the aromatic vinyl compound unit in the polymer block (C) preferably occupies 50% by mass or more of the polymer block (C), and 70% by mass. %, More preferably 90% by mass or more. From the same viewpoint as described above, it is desirable that units other than the aromatic vinyl compound unit that can be included in the polymer block (C) are randomly polymerized.

  As a particularly preferable example from the viewpoint of causing the polymer block (C) to microphase-separate from the polymer block (A) and the polymer block (B) and to function as a constrained phase, a polystyrene block; a poly p-methylstyrene block, a poly Polystyrene block such as p- (t-butyl) styrene block; copolymer block composed of two or more kinds of styrene, p-methylstyrene and p- (t-butyl) styrene of any mutual ratio; crystalline water Examples include 1,4-polybutadiene block; crystalline polyethylene block; crystalline polypropylene block and the like.

  As a form in case the block copolymer used by this invention contains a polymer block (C), an ABC type triblock copolymer, an ABCA type tetrablock copolymer, A -B-A-C type tetrablock copolymer, B-A-B-C type tetrablock copolymer, A-B-C-B type tetrablock copolymer, C-A-B-A-C Type pentablock copolymer, CBACBBC type pentablock copolymer, ACCBCA type pentablock copolymer, ACCBAA type pentablock copolymer Block copolymer, A-B-C-A-B type pentablock copolymer, A-B-C-A-C type pentablock copolymer, A-B-C-B-C type pentablock copolymer Polymer, ABACBBC type pentablock copolymer, ABBACB type pentablock copolymer B-A-B-A-C type pentablock copolymer, B-A-B-C-A type pentablock copolymer, B-A-B-C-B type pentablock copolymer, etc. are mentioned. It is done.

  When the block copolymer 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 is preferably 40% by mass or less, It is more preferably 35% by mass or less, and further preferably 30% by mass or less.

  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 2,000,000. Preferably, 15,000 to 1,000,000 is more preferable, and 20,000 to 500,000 is even more preferable.

The block copolymer constituting the polymer electrolyte membrane of the present invention needs to have an ion conductive group 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. 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) because it is particularly effective for improving the radical resistance of the entire block copolymer.

  There are no particular restrictions on the position at which the ion conductive group is introduced into the polymer block (A). Even if it is introduced into the aromatic vinyl compound unit in which the α-carbon is a quaternary carbon, the other units described above Although it may be introduced into the body unit, it is most preferably introduced into the aromatic ring of the aromatic vinyl compound unit in which the α-carbon is a quaternary carbon in view of the improvement of radical resistance.

  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.

  In addition, the polymer block (A) into which an ion conductive group is introduced is an aromatic vinyl compound in which a hydrogen atom bonded to an α-carbon atom is substituted with an alkyl group having 1 to 4 carbon atoms, such as α-methyl. When composed of styrene, the solubility parameter of the polymer block (A) is smaller than when composed of aromatic vinyl compound units in which the α-carbon is tertiary carbon, and due to microphase separation. The hydrophobicity in the ion channel formed by the polymer block (A) is improved. For this reason, in a fuel cell using methanol as a fuel, the phenomenon (methanol crossover) in which methanol permeates the electrolyte membrane from one electrode side to the other electrode side tends to be suppressed. When other monomer units having a solubility parameter smaller than that of α-methylstyrene are (co) polymerized, methanol crossover tends to be further suppressed.

  Moreover, the polymer blocks (A) of ion conductive groups may be cross-linked by a known method within a range not impairing the effects of the present invention. By introducing cross-linking, the form stability of the film increases, and methanol crossover tends to be suppressed.

  The production method of the block copolymer used in the present invention is roughly classified into the following two methods. That is, (1) First, a method of producing a block copolymer having no ion conductive group and then binding the ion conductive group, (2) block copolymerization using a monomer having an ion conductive group This is a method for producing a coalescence.

First, the first manufacturing method will be described.
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 preferred from the viewpoint of molecular weight, molecular weight distribution, polymer structure, ease of bonding with the polymer block (B) or (A) comprising a flexible component, and specifically, a living radical polymerization method. Living anionic polymerization and living cationic polymerization are preferred.

  Specific examples of the production method include a production method of a block copolymer comprising a polymer block (A) made of poly (α-methylstyrene) and a polymer block (B) made of conjugated diene, and poly (α- A method for producing a block copolymer comprising a polymer block (A) composed of methylstyrene and a polymer block (B) composed of isobutene will be described. In this case, it is preferable to produce by a living anionic polymerization method or a living cationic 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), etc. The following specific synthesis examples are 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 mold 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) 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. Α-methylstyrene is polymerized, the resulting living polymer is polymerized with a conjugated diene, and the resulting α-methylstyrene polymer block and the block copolymer living polymer of the block copolymer consisting of a conjugated diene polymer block are polymer blocks (C ) To obtain an ABC type block copolymer.
(5) Cationic polymerization of isobutene in the presence of Lewis acid using a bifunctional organic halogen compound in a mixed solvent of halogenated hydrocarbon and hydrocarbon at −78 ° C. in the presence of Lewis acid, followed by addition of diphenylethylene, Further, after the addition of Lewis acid, α-methylstyrene is polymerized to obtain an ABA type block copolymer (Macromolecules, (1995), 28, 4893-4898), and (6) halogenated carbonization. In a mixed solvent of hydrogen and hydrocarbon at −78 ° C., using a monofunctional organic halogen compound, α-methylstyrene is polymerized in the presence of Lewis acid, and then Lewis acid is further added to polymerize isobutene. Then, a coupling reaction is carried out with a coupling agent such as 2,2-bis- [4- (1-phenylethenyl) phenyl] propane, and the ABA block Method for obtaining a polymer (Polym. Bull.,
(2000), 45, 121-128)

When producing a block copolymer comprising as a component a polymer block (A) comprising poly (α-methylstyrene) and a polymer block (B) comprising a conjugated diene compound, a specific method for producing the block copolymer Among these, the methods (3) and (4) are preferable, and the method (3) is particularly preferable.
When producing a block copolymer comprising a polymer block (A) composed of poly (α-methylstyrene) and a polymer block (B) composed of isobutene, the method shown in (5) or (6) is adopted. Is done.

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.

  A method for introducing phosphonic acid groups 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, a method may be exemplified 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 be sulfonated or phosphonated 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 α-methylstyrene block in the block copolymer is determined by acid titration, infrared spectroscopy, nuclear It can be calculated using an analytical means such as magnetic resonance spectrum ( ¹ H-NMR spectrum) measurement.

The second production method of the block copolymer used in the present invention is a method for producing a block copolymer using at least one monomer having an ion conductive group.
As the monomer having an ion conductive group, a monomer in which an ion conductive group is bonded to an aromatic vinyl compound is preferable. Specifically, styrene sulfonic acid, α-alkyl-styrene sulfonic acid, vinyl naphthalene sulfonic acid, α-alkyl-vinyl naphthalene sulfonic acid, vinyl anthracene sulfonic acid, α-alkyl-vinyl anthracene sulfonic acid, vinyl pyrene sulfonic acid, α-alkyl-vinylpyrenesulfonic acid, styrenephosphonic acid, α-alkyl-styrenephosphonic acid, vinylnaphthalenephosphonic acid, α-alkyl-vinylnaphthalenephosphonic acid, vinylanthracenephosphonic acid, α-alkyl-vinylanthracenephosphonic acid, vinyl Examples include pyrenephosphonic acid and α-alkyl-vinylpyrenephosphonic acid. Among these, o-, m- or p-styrene sulfonic acid, α-alkyl-o-, m- or p-styrene sulfonic acid is particularly preferable from the viewpoint of industrial versatility and ease of polymerization.

  As the monomer containing an ion conductive group, a monomer in which an ion conductive group is bonded to a conjugated diene compound can also be used. Specifically, 1,3-butadiene-1-sulfonic acid, 1,3-butadiene-2-sulfonic acid, isoprene-1-sulfonic acid, isoprene-2-sulfonic acid, 1,3-butadiene-1-phosphonic acid, Examples include 1,3-butadiene-2-phosphonic acid, isoprene-1-phosphonic acid, isoprene-2-phosphonic acid, and the like.

Examples of the monomer containing an ion conductive group include vinyl sulfonic acid, α-alkyl-vinyl sulfonic acid, vinyl alkyl sulfonic acid, α-alkyl-vinyl alkyl sulfonic acid, vinyl phosphonic acid, α-alkyl-vinyl phosphone. Acid, vinyl alkyl phosphonic acid, α-alkyl-vinyl alkyl phosphonic acid and the like can also be used. Among these, vinyl sulfonic acid and vinyl phosphonic acid are preferable.
As the monomer containing ion conductivity, a (meth) acrylic monomer to which an ion conductive group is bonded can also be used. Specific examples include methacrylic acid, acrylic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid, and the like.

  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-conducting group is introduced by producing a polymer using sodium o-, m- or p-styrene sulfonate, or sodium α-methyl-o-, m- or p-styrene sulfonate. it can. 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 may contain a softening agent as long as the effects of the present invention are not impaired. Softeners include petroleum-based softeners such as paraffinic, naphthenic or aroma-based process oils, paraffin, vegetable oil-based softeners, plasticizers, etc., and these may be used alone or in combination of two or more. it can. Although there is no restriction | limiting in particular in the usage-amount of a softening agent, It is preferable that it is 0-1,000 mass parts with respect to 100 mass parts of block copolymers, and it is more preferable that it is 0-500 mass parts, It is still more preferable that it is 0-300 mass parts.

  The polymer electrolyte membrane of the present invention further includes various additives as required, for example, phenol stabilizers, sulfur stabilizers, phosphorus stabilizers, light stabilizers, antistatic agents, mold release agents, flame retardants. , Foaming agents, pigments, dyes, brighteners, carbon fibers and the like may be contained singly or in combination of two or more. Specific examples of the stabilizer include 2,6-di-t-butyl-p-cresol, pentaerystyryl-tetrakis [3- (3,5-di-t-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-hydroxy) Phenyl) propionate, triethylene glycol-bis [3- (3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy- 3,5-di-t-butylanilino) -1,3,5-triazine, 2,2, -thio-diethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propi Onate], 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-hydroxy-5-methylphenyl) propionyloxy ] -1,1-dimethylethyl} -2,4,8,10-tetraoxaspiro [5,5] undecane and other phenolic stabilizers; pentaerythrityltetrakis (3-laurylthiopropionate), distearyl Sulfur such as 3,3′-thiodipropionate, dilauryl 3,3′-thiodipropionate, dimyristyl 3,3′-thiodipropionate Stabilizers: trisnonylphenyl phosphite, tris (2,4-di-t-butylphenyl) phosphite, diasteryl pentaerythritol diphosphite, bis (2,6-di-t-butyl-4-methylphenyl) ) Phosphorus stabilizers such as pentaerythritol diphosphite. These stabilizers may be used alone or in combination of two or more.

  The polymer electrolyte membrane of the present invention can be further added with an inorganic filler as required, as long as the effects of the present invention are not impaired. Specific examples of such inorganic fillers include talc, calcium carbonate, silica, glass fiber, mica, kaolin, titanium oxide, montmorillonite, and alumina.

  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 contrary, when the film thickness is thicker than 500 μm, the membrane resistance increases and sufficient proton conductivity does not appear, so that the power generation characteristics of the battery tend to be lowered. The film thickness is more preferably 10 to 300 μm.

As the 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, the block copolymer constituting the polymer electrolyte membrane of the present invention or the block can be used. The block copolymer is dissolved or suspended by mixing the copolymer and additives as described above with an appropriate solvent, and cast into a plate-like material such as glass, or coated using a coater or applicator. In addition, a method of obtaining an electrolyte membrane having a desired thickness by removing the solvent under appropriate conditions, a method of forming a film using a known method such as hot press molding, roll molding, extrusion molding, or the like may be used. it can.
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 being cast or coated 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 configuration of the block copolymer, the molecular weight, the ion exchange capacity, etc., one or a combination of two or more can be appropriately selected from the solvents exemplified above and used.

  The solvent removal conditions can be arbitrarily selected as long as the solvent can be completely removed at a temperature 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. . 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, after preliminary drying for several hours under vacuum conditions of room temperature to 60 ° C., the solvent is removed under vacuum conditions of 100 ° C. or higher, preferably 100 to 120 ° C. for about 12 hours. However, the present invention is not limited to these examples.

  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 two pairs 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 two pairs of base films on the base film are 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 of 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 such as carbon / catalyst support, the amount of catalyst used is small and it is 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 polyetheretherketone.

  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 chemical stability, has little deterioration in power generation characteristics over time, and can be used stably for a long time.

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

Reference example 1
Production of block copolymer comprising poly α-methylstyrene (polymer block (A)) and hydrogenated polybutadiene (polymer block (B)) In the same manner as the previously reported method (WO 02/40611), A poly α-methylstyrene-b-polybutadiene-b-polyα-methylstyrene type triblock copolymer (hereinafter abbreviated as mSEBmS) was synthesized. The number average molecular weight (GPC measurement, polystyrene conversion) of the obtained mSEBmS is 76000, the 1,4-bond amount determined from ¹ H-NMR measurement is 55%, and the content of α-methylstyrene unit is 30.0. 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.
Prepare a cyclohexane solution of synthesized mSEBmS, charge it in a pressure-resistant vessel with sufficient nitrogen substitution, and then use a Ni / Al Ziegler hydrogenation catalyst for 5 hours at 80 ° C. in a hydrogen atmosphere. To obtain a poly α-methylstyrene-b-hydrogenated polybutadiene-b-polyα-methylstyrene type triblock copolymer (hereinafter abbreviated as HmSEBmS). The hydrogenation proportion of the resulting HmSEBmS was calculated by ¹ H-NMR spectrum measurement, it was 99.6%.

Reference example 2
Production of block copolymer (HmSEBmS) comprising poly α-methylstyrene (polymer block (A)) and hydrogenated polybutadiene (polymer block (B)) In the same manner as in Reference Example 1, number average molecular weight 51300 Then, mSEBmS having a 1,4-bond content of 59.2% and an α-methylstyrene unit content of 31.3% by mass was synthesized. In this polybutadiene block, α-methylstyrene was not substantially copolymerized. Subsequently, HmSEBmS having a hydrogenation rate of 99.4% was obtained in the same manner as in Reference Example 1 except that this mSEBmS was used.

Reference example 3
Production of block copolymer (HmSEBmS) comprising poly α-methylstyrene (polymer block (A)) and hydrogenated polybutadiene (polymer block (B)) In the same manner as in Reference Example 1, number average molecular weight 74700 Then, mSEBmS having a 1,4-bond content of 39.5% and an α-methylstyrene unit content of 42.0% by mass was synthesized. In this polybutadiene block, α-methylstyrene was not substantially copolymerized. Subsequently, HmSEBmS having a hydrogenation rate of 99.4% was obtained in the same manner as in Reference Example 1 except that the hydrogenation reaction was carried out at 50 ° C. for 7 hours using this mSEBmS.

Reference example 4
Production of block copolymer consisting of polystyrene (polymer block (A)) and polyisobutylene (polymer block (B))
A polystyrene-b-polyisobutylene-b-polystyrene triblock copolymer (hereinafter abbreviated as SiBuS) was produced according to a previously reported method (WO 98/14518). The number average molecular weight (GPC measurement, polystyrene conversion) of the obtained triblock copolymer was 69000, and the styrene content was 28.4%.

Example 1
(1) Synthesis of sulfonated HmSEBmS 100 g of the block copolymer (HmSEBmS) obtained in Reference Example 1 was vacuum-dried in a glass reaction vessel equipped with a stirrer for 1 hour and then purged with nitrogen, and then 1000 ml of methylene chloride. And dissolved by stirring at 35 ° C. for 2 hours. After dissolution, a sulfating reagent obtained by reacting 21.0 ml of acetic anhydride and 9.34 ml of sulfuric acid at 0 ° C. in 41.8 ml of methylene chloride was gradually added dropwise over 20 minutes. After stirring at 35 ° C. for 0.5 hour, the polymer solution was poured into 2 L of distilled water while stirring to coagulate and precipitate the polymer. The precipitated solid was washed with distilled water at 90 ° C. for 30 minutes and then filtered. 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 HmSEBmS. The sulfonation rate of the benzene ring of the α-methylstyrene unit of the obtained sulfonated HmSEBmS was 20.6 mol% from ¹ H-NMR analysis, and the ion exchange capacity was 0.48 meq / g.
(2) Preparation of electrolyte membrane for fuel cell A 5% by mass THF / MeOH (mass ratio 8/2) solution of the sulfonated HmSEBmS obtained in (1) was prepared, and about 1000 μm of polytetrafluoroethylene sheet was prepared. A film having a thickness of 50 μm was obtained by casting at a thickness and sufficiently drying at room temperature.

Example 2
(1) Synthesis of sulfonated HmSEBmS A sulfonated HmSEBmS was obtained in the same manner as in Example 1 except that the reaction time for sulfonation was set to 1 hour in Example 1 (1). The sulfonation rate of the benzene ring of the α-methylstyrene unit of the obtained sulfonated HmSEBmS was 30.1 mol% from ¹ H-NMR analysis, and the ion exchange capacity was 0.69 meq / g.
(2) Production of Fuel Cell Electrolyte Membrane A membrane having a thickness of 50 μm was obtained in the same manner as in Example 1 (2) except that the sulfonated HmSEBmS was used.

(3) Production of single cell for polymer electrolyte fuel cell An electrode for a polymer electrolyte fuel cell was produced by the following procedure. A 5% by mass methanol solution of Nafion was added to and mixed with the Pt—Ru alloy catalyst-supporting carbon so that the mass ratio of the Pt—Ru alloy to Nafion was 2: 1 to prepare a uniformly dispersed paste. This paste was applied to a transfer sheet and dried for 24 hours to prepare an anode side catalyst sheet. Also, a 5% by mass solution of Nafion in a mixed solvent of lower alcohol and water was added to and mixed with Pt catalyst-supported carbon so that the mass ratio of Pt catalyst to Nafion was 2: 1, and dispersed uniformly. The prepared paste was prepared, and a cathode side catalyst sheet was prepared in the same manner as the anode side. The fuel membrane electrolyte membrane produced in (2) is sandwiched between the two types of catalyst sheets so that the membrane and the catalyst surface face each other, and the outside is sandwiched between two heat resistant films and two stainless steel plates in order. The membrane and the catalyst sheet were joined by hot pressing (150 ° C., 100 kg / cm ² , 10 min). Finally, the transfer sheet was peeled off, and the heat-resistant film and the stainless steel plate were removed to prepare a membrane-electrode assembly. Next, the membrane-electrode assembly produced was sandwiched between two sheets of carbon paper, the outside was sandwiched between two conductive separators that also function as gas supply channels, and the outside of the two collector plates And an evaluation cell for a polymer electrolyte fuel cell was produced by sandwiching the two clamp plates.

Example 3
(2) Fabrication of Fuel Cell Electrolyte Membrane An 18% by mass toluene / isobutyl alcohol (mass ratio 8/2) solution of the sulfonated HmSEBmS obtained in Example 1 (1) was prepared, and the release-treated PET film [Toyobo Co., Ltd. “Toyobo Ester Film K1504”] was coated with a thickness of about 550 μm and sufficiently dried at room temperature to obtain a film with a thickness of 50 μm.

Example 4
(2) Production of Fuel Cell Electrolyte Membrane An 18% by mass cyclohexane / isopropyl alcohol (mass ratio 7/3) solution of the sulfonated HmSEBmS obtained in Example 2 was prepared, and the release-treated PET film [(stock ) "Toyobo Ester Film K1504" manufactured by Toyobo] with a thickness of about 550 µm and sufficiently dried at room temperature to obtain a membrane with a thickness of 50 µm.

Example 5
(1) Synthesis of Sulfonated HmSEBmS Sulfonated HmSEBmS was obtained in the same manner as in Example 1 (1) except that the reaction time after dropping the sulfating reagent was 8 hours in Example 1 (1). The sulfonation rate of the benzene ring of the α-methylstyrene unit in the obtained sulfonated HmSEBmS was 51.0 mol% from ¹ H-NMR analysis, and the ion exchange capacity was 1.12 meq / g.
(2) Preparation of Fuel Cell Electrolyte Membrane A 14% by mass toluene / isobutyl alcohol (mass ratio 8/2) solution of the sulfonated HmSEBmS obtained in (1) was prepared, and the release-treated PET film [(stock ) "Toyobo Ester Film K1504" manufactured by Toyobo] with a thickness of about 650 µm and sufficiently dried at room temperature to obtain a membrane with a thickness of 50 µm.

Example 6
(1) Synthesis of sulfonated HmSEBmS 90 g of the block copolymer (HmSEBmS) obtained in Reference Example 2 was vacuum-dried in a glass reaction vessel equipped with a stirrer for 1 hour and then purged with nitrogen, followed by 816 ml of methylene chloride. And dissolved by stirring at 35 ° C. for 2 hours. After dissolution, a sulfating reagent obtained by reacting 18.3 ml of acetic anhydride and 8.17 ml of sulfuric acid at 0 ° C. in 36.5 ml of methylene chloride was gradually added dropwise over 20 minutes. After stirring at 35 ° C. for 4 hours, the polymer solution was poured into 3 L of distilled water while stirring to coagulate and precipitate the polymer. The precipitated solid was washed with distilled water at 90 ° C. for 30 minutes and then filtered. 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 HmSEBmS. The sulfonation rate of the benzene ring of the α-methylstyrene unit of the sulfonated HmSEBmS obtained was 30.8 mol% from ¹ H-NMR analysis, and the ion exchange capacity was 0.74 meq / g.
(2) Preparation of Fuel Cell Electrolyte Membrane A 22% by weight toluene / isobutyl alcohol (mass ratio 8/2) solution of the sulfonated HmSEBmS obtained in (1) was prepared, and the release-treated PET film [(stock ) “Toyobo Ester Film K1504” manufactured by Toyobo] A film with a thickness of about 50 μm was obtained by coating the film with a thickness of about 450 μm and sufficiently drying at room temperature.

Example 7
(1) Synthesis of sulfonated HmSEBmS 106 g of the block copolymer (HmSEBmS) obtained in Reference Example 2 was vacuum-dried in a glass reaction vessel equipped with a stirrer for 1 hour and then purged with nitrogen, followed by 900 ml of methylene chloride. And dissolved by stirring at 35 ° C. for 2 hours. After dissolution, a sulfating reagent obtained by reacting 29.3 ml of acetic anhydride and 13.1 ml of sulfuric acid at 0 ° C. in 58.6 ml of methylene chloride was gradually added dropwise over 20 minutes. After stirring for 9 hours at 35 ° C., the polymer solution was poured into 3 L of distilled water while stirring to coagulate and precipitate the polymer. The precipitated solid was washed with distilled water at 90 ° C. for 30 minutes and then filtered. 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 HmSEBmS. The sulfonation rate of the benzene ring of the α-methylstyrene unit of the obtained sulfonated HmSEBmS was 52.7 mol% from ¹ H-NMR analysis, and the ion exchange capacity was 1.21 meq / g.
(2) Preparation of electrolyte membrane for fuel cell The sulfonated HmSEBmS obtained in (1) was treated in the same manner as in Example 6 (2) to obtain a membrane having a thickness of 50 μm.

Example 8
(1) Synthesis of sulfonated HmSEBmS 30 g of the block copolymer (HmSEBmS) obtained in Reference Example 3 was vacuum-dried in a glass reaction vessel equipped with a stirrer for 1 hour and then purged with nitrogen, followed by 381 ml of methylene chloride. And dissolved by stirring at 35 ° C. for 2 hours. After dissolution, a sulfating reagent obtained by reacting 6.55 ml of acetic anhydride and 2.93 ml of sulfuric acid at 0 ° C. in 13.1 ml of methylene chloride was gradually added dropwise over 20 minutes. After stirring at 35 ° C. for 4 hours, the polymer solution was poured into 1 L of distilled water while stirring to coagulate and precipitate the polymer. The precipitated solid was washed with distilled water at 90 ° C. for 30 minutes and then filtered. 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 HmSEBmS. The sulfonation rate of the benzene ring of the α-methylstyrene unit of the sulfonated HmSEBmS obtained was 28.5 mol% from ¹ H-NMR analysis, and the ion exchange capacity was 0.95 meq / g.
(2) Preparation of electrolyte membrane for fuel cell The sulfonated HmSEBmS obtained in (1) was treated in the same manner as in Example 6 (2) to obtain a membrane having a thickness of 50 μm.

Comparative Example 1
(1) Synthesis of Sulfonated SEBS A sulfated reagent was prepared by reacting 17.1 ml of acetic anhydride and 7.64 ml of sulfuric acid at 0 ° C. in 34.2 ml of methylene chloride. On the other hand, 100 g of SEBS (styrene- (ethylene-butylene) -styrene) block copolymer [“Septon 8007” manufactured by Kuraray Co., Ltd.] was vacuum-dried in a glass reaction vessel equipped with a stirrer for 1 hour, and then nitrogen. After the replacement, 1000 ml of methylene chloride was added and dissolved by stirring at 35 ° C. for 4 hours. After dissolution, the sulfating reagent was gradually added dropwise over 20 minutes. After stirring at 35 ° C. for 5 hours, the polymer solution was poured into 2 L of distilled water while stirring to coagulate and precipitate the polymer. The precipitated solid was washed with distilled water at 90 ° C. for 30 minutes and then filtered. 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 SEBS. The sulfonation rate of the benzene ring of the styrene unit in the obtained sulfonated SEBS was 19.3 mol% from ¹ H-NMR analysis, and the ion exchange capacity was 0.51 meq / g. (2) Preparation of electrolyte membrane for fuel cell A membrane having a thickness of 50 μm was obtained in the same manner as in Example 1 (2) except that the sulfonated SEBS was used.

Comparative Example 2
(1) Synthesis of sulfonated SEBS A sulfonated HmSEBmS was obtained in the same manner as in Comparative Example 1 (1) except that the reaction time for sulfonation was 12 hours in Comparative Example 1 (1). The sulfonation rate of the benzene ring of the styrene unit of the obtained sulfonated SEBS was 29.0 mol% from ¹ H-NMR analysis, and the ion exchange capacity was 0.75 meq / g.
(2) Production of Fuel Cell Electrolyte Membrane A membrane having a thickness of 50 μm was obtained in the same manner as in Example 1 (2) except that the sulfonated SEBS was used.
(3) Production of single cell for polymer electrolyte fuel cell A single cell was produced in the same manner as in Example 2 (3) except that the membrane was used.

Comparative Example 3
(2) Preparation of fuel cell electrolyte membrane An 18% by weight toluene / isobutyl alcohol (mass ratio 8/2) solution of the sulfonated SEBS obtained in Comparative Example 2 (1) was prepared, and the release-treated PET film [Toyobo Co., Ltd. “Toyobo Ester Film K1504”] A film with a thickness of about 550 μm was coated on the film and dried sufficiently at room temperature to obtain a film with a thickness of 50 μm.

Comparative Example 4
(1) Synthesis of sulfonated SiBuS A sulfating reagent was prepared by reacting 11.6 ml of acetic anhydride and 5.17 ml of sulfuric acid at 18.degree. C. in 18.2 ml of methylene chloride. On the other hand, 100 g of the block copolymer (SiBuS) obtained in Reference Example 2 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 sulfating reagent was gradually added dropwise over 20 minutes. After stirring at 35 ° C. for 2 hours, the polymer solution was poured into 2 L of distilled water while stirring to coagulate and precipitate the polymer. The precipitated solid was washed with distilled water at 90 ° C. for 30 minutes and then filtered. 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 obtained sulfonated SiBuS was 19.1 mol% from ¹ H-NMR analysis, and the ion exchange capacity was 0.50 meq / g.
(2) Film formation A film having a thickness of 80 μm was obtained in the same manner as in Example 1 (2) except that the sulfonated SiBuS was used.

Comparative Example 5
(1) Synthesis of sulfonated SiBuS A sulfonated SiBuS was obtained in the same manner as in Comparative Example 4 (1) except that the reaction time for sulfonation was changed to 10.5 hours in Comparative Example 4 (1). The sulfonation rate of the benzene ring of the styrene unit of the sulfonated SiBuS obtained was 28.1 mol% from ¹ H-NMR analysis, and the ion exchange capacity was 0.72 meq / g.
(2) Production of Fuel Cell Electrolyte Membrane A membrane having a thickness of 50 μm was obtained in the same manner as in Example 1 (2) except that the sulfonated SiBuS was used.
(3) Production of single cell for polymer electrolyte fuel cell A single cell was produced in the same manner as in Example 2 (3) except that the membrane was used.

Comparative Example 6
A DuPont Nafion film (Nafion 112) was selected as the perfluorocarbon sulfonic acid polymer electrolyte. The film had a thickness of about 50 μm and an ion exchange capacity of 0.91 meq / g.
A single cell for a polymer electrolyte fuel cell was produced in the same manner as in Example 2 (3) except that the above film was used instead of the fuel cell electrolyte membrane.

Performance Tests of Polymer Membranes of Examples and Comparative Examples as Electrolyte Membranes for Solid Polymer Type Fuel Cells In the following tests 1) to 4), the sulfonated block obtained in each Example or Comparative Example was used as a sample. A membrane or Nafion film prepared from the polymer was used.
1) Measurement of ion exchange capacity A sample was weighed (a (g)) in a glass container capable of being sealed, and an excess amount of a saturated aqueous sodium chloride solution was 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

2) Measurement of proton conductivity A sample of 1 cm × 4 cm was sandwiched between a pair of platinum electrodes and attached to an open cell. The measurement cell was installed in a constant temperature and humidity chamber adjusted to a temperature of 60 ° C. and a relative humidity of 90%, and proton conductivity was measured by an AC impedance method.

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.

4) Radical stability test D-glucose and iron (II) chloride tetrahydrate were dissolved in a 3% by mass aqueous hydrogen peroxide solution to prepare a radical reaction reagent. After confirming that the temperature of the radical reaction reagent became constant at 60 ° C., a sample was added and reacted for 4 hours and 8 hours. The sample was then washed thoroughly with distilled water.

5) Evaluation of output performance of single cell for fuel cell The output performance of the single cell for polymer electrolyte fuel cell prepared in Example 2 and Comparative Examples 2, 5 and 6 was evaluated. 1M for fuel
A MeOH aqueous solution was used, and air was used as the oxidizing agent. The test was conducted at a cell temperature of 80 ° C. under the conditions of MeOH: 5 cc / min and air: 500 cc / min.

Table 1 shows the measurement results of proton conductivity of the membranes produced in Examples 1 to 8 and Comparative Examples 2, 5 and 6 as a result of the performance test as a polymer electrolyte membrane . Comparison between Example 1 and Example 2 and comparisons of Examples 3 to 5 in Table 1 revealed that proton conductivity was improved as the sulfonation rate increased. Moreover, it became clear from the comparison with Example 2, the comparative example 2, and the comparative example 5 that the proton conductivity of the same level expresses even if a polymer frame | skeleton differs.

Table 1 shows the results of the film strength of the films prepared in Examples 1 to 8 and Comparative Examples 2, 5 and 6.
The membranes produced in Examples 1, 2, 3, 4 and 6 having a relatively low sulfonation rate showed a membrane strength of Nafion 112 or higher. On the other hand, in the film | membrane which increased ion conductive group amount, the tendency for film | membrane strength to fall was seen like Example 5 with respect to Example 3 and Example 4 and Example 7 with respect to Example 6. FIG. This is presumably because water molecules adsorbed on the ion conductive group act like a plasticizer.
Further, in the comparison with the polymer skeletons of Example 2, Comparative Example 2 and Comparative Example 5 (the amount of ion conductive groups was almost constant), it was found that sulfonated HmSEBmS had the most excellent membrane strength.

The radical stability test of the films produced in Examples 1 and 2 and Comparative Examples 1, 2, 4, 5 and 6 was performed. Table 2 shows the measurement results of the mass retention rate and ion exchange capacity retention rate after the reaction for 4 hours and 8 hours.
In Table 2, the film produced in Comparative Examples 1 and 2 swelled about 1.3 times on each side after 4 hours test, and the cloudiness and wrinkle were severe. The film after the 8-hour test swelled 1.5 times or more on each side, and white turbidity and severe wrinkles were observed. The films produced in Comparative Examples 4 and 5 retained the shape after the 4 hour test, but they were severely wrinkled and partly clouded. After the reaction for 8 hours, the film produced in Comparative Example 4 retained the shape, but the entire film was severely whitened and whitened, and the film produced in Comparative Example 5 could not retain the shape, and the reaction solution had a minute amount. Dispersed as powder.
In addition, in the films prepared in Comparative Examples 1, 2, and 4, the mass retention rate is considerably lowered after the 8-hour test, and the ion exchange capacity is greatly reduced after the 4-hour test, and further reduced after the 8-hour test. did.

On the other hand, the films produced in Examples 1 and 2 showed no radical change even after 8 hours test, and showed excellent radical stability with a mass of 98% or more and an ion exchange capacity of 92% or more. It was.
From the results in Table 2, the fuel cell electrolyte membrane comprising the α-methylstyrene block copolymer of the present invention has a significantly higher ion exchange capacity retention in the radical stability test than the SEBS and SiBuS sulfonated products. It was revealed that the ion channel portion has radical resistance.
On the other hand, as for Nafion 112 of Comparative Example 6, no change in the appearance of the membrane was observed as in the case of sulfonated HmSEBmS, but the ion exchange capacity changed with time, and decreased to 79.0% after 8 hours of reaction. Since almost no mass change was observed, it is considered that deterioration due to elimination of the sulfonic acid group progressed rather than deterioration due to the main chain decomposition reaction.

As the power generation characteristics of the single cells for polymer electrolyte fuel cells obtained in Example 2 and Comparative Examples 2, 5, and 6, changes in voltage with respect to current density were measured. The results are shown in FIGS. The single cell fabricated in Example 2 has an open circuit voltage of 0.62 V and a maximum output density of 58.2 mW / cm ² , and the open voltage of Nafion 112 of Comparative Example 6 is 0.61 V and the maximum output density is 57.0 mW / cm ^{2. It} was the same level as ^2, and was sufficiently usable as a single cell for a fuel cell. On the other hand, the unit cell produced in Comparative Example 2 and Comparative Example 5, respectively open voltage is 0.34 V, 0.37 V, the maximum power density, respectively 15.0 mW ^/ cm 2, a 21.1mW / cm ² low It was a characteristic. About this, since the film | membrane obtained in Comparative Example 2 (2) and Comparative Example 5 (2) has low film | membrane intensity | strength, a pinhole etc. are carried out to a film | membrane by the hot press at the time of producing a membrane-electrode assembly These defects are likely to have occurred, and it is considered that only low performance was obtained by these defects.
From the results of the power generation characteristics of the single fuel cell, it was revealed that the single cell for a polymer electrolyte fuel cell produced in Example 2 (3) of the present invention exhibited high power generation characteristics.

It is a figure which shows the current density-output voltage of the single cell for polymer electrolyte fuel cells (Example 2 (3)). It is a figure which shows the current density-output voltage of the single cell for polymer electrolyte fuel cells (comparative example 2 (3)). It is a figure which shows the current density-output voltage of the single cell for polymer electrolyte fuel cells (Comparative Example 5 (3)). It is a figure which shows the current density-output voltage of the single cell for polymer electrolyte fuel cells (comparative example 6).

Claims (11)

The polymer block (A) and the flexible polymer block (B) having an aromatic vinyl compound unit in which the α-carbon is a quaternary carbon as a main repeating unit are constituents, and the polymer block (A) A polymer electrolyte membrane for a polymer electrolyte fuel cell, comprising a block copolymer having an ion conductive group. The electrolyte membrane according to claim 1, wherein the proportion of the aromatic vinyl compound unit in which the α-carbon in the polymer block (A) is quaternary carbon is 50% by mass or more. The electrolyte membrane according to claim 1 or 2, wherein the mass ratio of the polymer block (A) to the polymer block (B) is 95: 5 to 5:95. In the aromatic vinyl compound unit in which the α-carbon is a quaternary carbon, the hydrogen atom bonded to the α-carbon atom is an alkyl group having 1 to 4 carbon atoms, a halogenated alkyl group having 1 to 4 carbon atoms, or a phenyl group. The electrolyte membrane according to claim 1, which is a substituted aromatic vinyl compound unit. The flexible 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 carbon. A conjugated cycloalkadiene unit having 5 to 8 carbon atoms, a vinylcycloalkene unit having 7 to 10 carbon atoms in which part or all of the carbon-carbon double bond has been hydrogenated, a conjugated diene unit having 4 to 8 carbon atoms and carbon The electrolyte membrane according to any one of claims 1 to 4, which is a polymer block composed of at least one repeating unit selected from the group consisting of conjugated cycloalkadiene units of formula 5-8. The flexible polymer block (B) is an alkene unit having 2 to 8 carbon atoms, a conjugated diene unit having 4 to 8 carbon atoms, and 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 4, which is a polymer block comprising at least one repeating unit selected from conjugated diene units. The aromatic vinyl compound unit in which the α-carbon is a quaternary carbon is an α-methylstyrene unit, and the flexible polymer block (B) is a conjugated diene unit having 4 to 8 carbon atoms and one carbon-carbon double bond. 5. The electrolyte membrane according to claim 1, which is at least one repeating unit selected from conjugated diene units having 4 to 8 carbon atoms, all or part of which are hydrogenated. (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 any one of claims 1 to 8, 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 electrolyte membrane according to claim 1.

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