JP5188025B2 - POLYMER ELECTROLYTE MEMBRANE FOR SOLID POLYMER FUEL CELL, MEMBRANE-ELECTRODE ASSEMBLY AND FUEL CELL - Google Patents

Description

  The present invention relates to a polymer electrolyte membrane used in a polymer electrolyte fuel cell, preferably a solid polymer direct methanol fuel cell, a membrane-electrode assembly using the polymer electrolyte membrane, and a fuel cell.

  A polymer electrolyte fuel cell is generally configured as follows. First, catalyst layers containing carbon powder carrying a white metal catalyst and an ion conductive binder made of a polymer electrolyte are formed on both sides of the polymer electrolyte membrane having ion 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.

  In a solid polymer fuel cell, particularly a direct methanol fuel cell that directly supplies methanol to the anode of the fuel cell without reforming, Nafion 117 (DuPont's) having a thickness of about 175 μm has been used for the electrolyte membrane. Perfluorocarbon sulfonic acid polymer electrolyte membranes typified by registered trademarks (the same applies hereinafter) are generally used and are being developed as power sources for portable devices such as mobile phones and laptop computers. These electrolyte membranes have a feature that the ionic conductivity of the membrane is high, but the phenomenon that methanol as a fuel permeates the electrolyte membrane from one electrode side to the other electrode side (methanol crossover) easily occurs. Therefore, it has been pointed out that the power generation efficiency is lowered.

Therefore, non-perfluorocarbon sulfonic acid polymer electrolyte membranes having low methanol permeability have been studied (Patent Document 1, Patent Document 2, and Non-Patent Document 1).
Unlike the perfluorocarbon sulfonic acid polymer electrolyte membrane, the engineering plastic polymer electrolyte membrane described in Patent Literature 1 and Patent Literature 2 is unlikely to form an ion channel, so that methanol permeability can be reduced. Is possible. However, there is a drawback that the electric resistance of the film tends to be high, and when the amount of ion group introduction is increased to reduce the electric resistance of the film, the film tends to swell. There is also a known defect that bonding failure with an electrode is likely to occur. Therefore, the present situation is that engineering plastic polymer electrolyte membranes do not exhibit sufficient performance as electrolyte membranes used in direct methanol fuel cells.

The sulfonated polystyrene-b-polyisobutylene-b-polystyrene triblock copolymer (sulfonated SiBuS) described in Non-Patent Document 1 also has a higher methanol barrier property than the perfluorocarbon sulfonic acid polymer electrolyte membrane. However, an electrolyte membrane having satisfactory performance for a direct methanol fuel cell has not yet been obtained.
JP 2003-288916 A JP 2003-331868 A J. Membrane Science 217 (2003) 227

  An object of the present invention is to provide a polymer electrolyte membrane having high ionic conductivity, excellent methanol barrier property and good bonding property with an electrode, and a membrane-electrode assembly and a solid polymer fuel using the electrolyte membrane. To provide a battery.

As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention can solve the above-described problems by an electrolyte film that is an electrolyte film made of a specific block copolymer or containing this as a main component. As a result, the present invention was completed.
That is, in the present invention, the hydrogen atom bonded to the α-carbon atom is unsubstituted or substituted with an alkyl group having 1 to 4 carbon atoms, and at least one of the hydrogen atoms directly bonded to the aromatic ring is 1 to 1 carbon atom. The polymer block (A) having a vinyl aromatic compound unit substituted with 8 alkyl groups as a repeating unit and the flexible polymer block (B) are constituents, and the polymer block (A) has an ion conductive group. The present invention relates to a polymer electrolyte membrane for a polymer electrolyte fuel cell, comprising a block copolymer having

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 ion conductive group includes a sulfonic acid group and a phosphonic acid group and salts thereof, and is bonded to the polymer block (A).
The present invention also relates to a membrane-electrode assembly and a fuel cell using the above electrolyte membrane.

  The polymer electrolyte membrane of the present invention is economical, environmentally friendly, combines high ionic conductivity and excellent methanol barrier properties, and exhibits excellent performance in solid polymer fuel cells, particularly direct methanol fuel cells. To do. The polymer electrolyte membrane of the present invention is also excellent in bondability and moldability.

Hereinafter, the present invention will be described in detail.
In the block copolymer constituting the polymer electrolyte membrane of the present invention, the hydrogen atom bonded to the α-carbon atom is unsubstituted or substituted with an alkyl group having 1 to 4 carbon atoms, and is directly bonded to the aromatic ring. An aromatic vinyl compound unit in which at least one hydrogen atom is substituted with an alkyl group having 1 to 8 carbon atoms (hereinafter, the aromatic vinyl compound is referred to as an aromatic vinyl compound (a), the aromatic vinyl compound). A polymer block (A) having a unit as a repeating unit (sometimes referred to as an aromatic vinyl compound (a) unit) and having at least one ion-conducting group is a constituent component.

  In the above, examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, and a tert-butyl group, and examples of the alkyl group having 1 to 8 carbon atoms include methyl Group, ethyl group, propyl group, isopropyl group, butyl group, tert-butyl group, neopentyl group, hexyl group, heptyl group, 2-ethylhexyl group and the like. The alkyl group bonded to the α-carbon atom is preferably a methyl group or an ethyl group, and more preferably a methyl group. The alkyl group directly bonded to the aromatic ring is preferably an alkyl group having 1 to 6 carbon atoms, and more preferably an alkyl group having 1 to 4 carbon atoms. The aromatic ring is preferably a carbocyclic aromatic ring, and examples thereof include a benzene ring, a naphthalene ring, an anthracene ring, and a pyrene ring. The number of alkyl groups substituted above is preferably 1 to 3. Preferable specific examples of the aromatic vinyl compound (a) include p-methylstyrene, 4-tert-butylstyrene, α, p-dimethylstyrene, o, p-dimethylstyrene and the like.

The aromatic vinyl compound (a) may be used alone or in combination of two or more.
The polymer block (A) may contain another aromatic vinyl compound unit in addition to the aromatic vinyl compound unit (a). Examples of other aromatic vinyl compounds include styrene, α-methylstyrene, vinylnaphthalene, α-methylvinylnaphthalene, vinylanthracene, and vinylpyrene.
When copolymerizing two or more kinds of aromatic vinyl compounds (a) or when copolymerizing aromatic vinyl compounds (a) with other aromatic vinyl compounds, random copolymer or block copolymer may be used. However, it may be graft copolymerization or tapered copolymerization.

  The polymer block (A) may contain one or more monomer units other than 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 form of copolymerization of the aromatic vinyl compound and other monomers other than the aromatic vinyl compound needs to be random copolymerization in order to cause microphase separation.

  The aromatic vinyl compound (a) unit in the polymer block (A) may occupy 10% by mass or more of the polymer block (A) in order to form an ion channel and suppress methanol crossover. Preferably, it occupies 15% by mass or more, and more preferably occupies 20% by mass or more. Further, the content of other monomer units other than the aromatic vinyl compound unit in the polymer block (A) is preferably 50% by mass or less, more preferably 30% by mass or less. It is still more preferable that it is below mass%.

  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.) are 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 vinylcycloalkene having 7 to 10 carbon atoms in which one of the carbon-carbon double bonds is hydrogenated, and a carbon-carbon double bond A hydrogenated conjugated diene having 4 to 8 carbon atoms, a hydrogenated conjugated cycloalkadiene having one hydrogenated carbon-carbon double bond, (meth) acrylic acid ester ((meth)) Methyl acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, etc.), vinyl esters (vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, etc.), vinyl Ethers (methyl vinyl ether, isobutyl vinyl ether, etc.), and the like. These may be used alone or in combination. 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 a vinylcycloalkene unit, a conjugated diene unit, or a conjugated cycloalkadiene unit, the present invention From the standpoints of improving the power generation performance of the membrane-electrode assembly using the polymer electrolyte membrane, improvement in heat deterioration resistance, etc., it is preferable that 30 mol% or more of such carbon-carbon double bonds are hydrogenated, More preferably, 50 mol% or more is 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, and cyclopentene having 5 to 8 carbon atoms include cyclopentene, cyclohexene, cycloheptene and cyclooctene, and vinylcycloalkene having 7 to 10 carbon atoms as 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, 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.

  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 used in 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). As the monomer unit constituting the polymer block (C), for example, an aromatic vinyl compound [1 to 3 alkyl groups having 1 to 3 hydrogen atoms bonded to an aromatic ring (methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, etc.)) unit, carbon number 4 -8 conjugated dienes (specific examples are the same as in the description of the polymer block (B) described above) units, alkenes having 2 to 8 carbon atoms (specific examples are in the description of the polymer block (B) described above) Similarly) units, (meth) acrylic acid esters (methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, etc.) units, vinyl esters (acetic acid Alkenyl, vinyl propionate, vinyl butyrate, vinyl pivalate, etc.) units, vinyl ether (methyl vinyl ether, isobutyl vinyl ether) units, and the like. The monomer block constituting the polymer block (C) may be one kind or plural.

When the polymer block (C) is microphase-separated from the polymer block (A) and the polymer block (B), does not substantially contain an ion conductive group, and has a function of acting as a constrained phase. The electrolyte membrane of the present invention having such a polymer block (C) tends to be excellent in form stability, durability and mechanical properties under wet conditions. Preferable examples of the monomer unit constituting the polymer block (C) in this case include the aromatic vinyl compound unit 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. Further, from the same viewpoint as described above, units other than the aromatic vinyl compound unit that can be included in the polymer block (C) are preferably randomly copolymerized.

  Examples of the polymer block (C) that is particularly suitable 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 constraining phase include poly p -A polystyrene block such as a methyl styrene block or a poly p- (tert-butyl) styrene block; a co-polymer comprising two or more of styrene, p-methyl styrene and poly p- (tert-butyl) styrene in any mutual proportion. Polymer block; crystalline hydrogenated 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 constituting the polymer electrolyte membrane of 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 is preferable, 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 set to the polymer block (A) because the introduction of the ion conductive group is easy and the formation of the ion channel is facilitated.

  The introduction position of the ion conductive group into the polymer block (A) is not particularly limited, and even if it is introduced into the aromatic vinyl compound unit (a), it may be introduced into other aromatic vinyl compound units. Alternatively, it may be introduced into other monomer units other than the aromatic vinyl compound unit. However, from the viewpoint of facilitating ion channel formation and suppression of methanol crossover, the aromatic ring of the aromatic vinyl compound unit (a), other aromatic vinyl compound units such as styrene units, α-methyl, etc. It is preferable to introduce into an aromatic ring of a styrene unit, a vinyl naphthalene unit or an α-methyl vinyl naphthalene unit.

  The amount of ion-conducting group introduced is important in determining the performance of a polymer electrolyte membrane having both high ionic conductivity and excellent methanol barrier properties. In order to exhibit sufficient ionic conductivity for use as a polymer electrolyte membrane for a solid polymer fuel cell, particularly a direct methanol fuel cell, the ion exchange capacity of the polymer electrolyte membrane of the present invention is 0. The amount is preferably 30 meq / g or more, more preferably 0.40 meq / g or more. The upper limit of the ion exchange capacity is preferably 2.0 meq / g or less, because if the ion exchange capacity becomes too large, the hydrophilicity increases and methanol as a fuel tends to permeate with water.

  Further, the polymer block (A) having an ion conductive group which is a constituent component of the block copolymer constituting the polymer electrolyte membrane of the present invention may be crosslinked within a range not impairing the effects of the present invention. Good. By introducing cross-linking, the form stability of the membrane increases, and methanol crossover tends to be suppressed. Examples of means for crosslinking include a thermal crosslinking method. As the thermal crosslinking method, thermal crosslinking is possible by copolymerizing a monomer having a thermal crosslinking site in the polymer block (A). Examples of suitable monomers include p-methylstyrene.

  The method for producing the block copolymer constituting the polymer electrolyte membrane of 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, anion polymerization method or cation polymerization method are preferably selected from 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. Or a living anionic polymerization method and a living cation polymerization method are preferable.

  As specific examples of the production method, polymer block (A) having an aromatic vinyl compound unit (a) in which α-carbon is tertiary carbon such as p-methylstyrene unit and conjugated diene such as butadiene unit. A process for producing a block copolymer comprising as a component a polymer block (B) comprising a unit; an aromatic vinyl compound unit (a) in which α-carbon such as p-methylstyrene unit is tertiary carbon; Of block copolymer comprising polymer block (A) and polymer block (B) consisting of alkene unit such as isobutene unit; α-carbon such as α, p-dimethylstyrene unit is quaternary carbon A block comprising as a component a polymer block (A) having an aromatic vinyl compound unit (a) as a repeating unit and a polymer block (B) comprising a conjugated diene unit such as a butadiene unit A method for producing a polymer; and a polymer block (A) in which an α-carbon such as an α, p-dimethylstyrene unit is a quaternary carbon (a) and a polymer block (A) and an isobutene unit. A method for producing a block copolymer comprising a polymer block (B) comprising an alkene unit as a component will be described. In this case, it is preferable to produce by a living anionic polymerization method and 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.

When the block copolymer constituting the polymer electrolyte membrane of the present invention is produced by anionic polymerization, the aromatic vinyl compound unit (a) in which α-carbon such as p-methylstyrene is tertiary carbon is polymer block. When the repeating unit (A) is used,
(1) Polymerizing an aromatic vinyl compound in which α-carbon is tertiary carbon such as p-methylstyrene under a temperature condition of 20 to 100 ° C. using an anionic polymerization initiator in a cyclohexane solvent; A method of polymerizing a conjugated diene and then sequentially polymerizing an aromatic vinyl compound in which the α-carbon is a tertiary carbon such as p-methylstyrene to obtain an ABA type block copolymer;
(2) An anionic polymerization initiator is used in a cyclohexane solvent to polymerize an aromatic vinyl compound in which α-carbon such as p-methylstyrene is a tertiary carbon under a temperature condition of 20 to 100 ° C., and then conjugated. A method of obtaining an ABA type block copolymer by polymerizing a diene and then adding a coupling agent such as phenyl benzoate,
It is possible to adopt / apply known methods such as

When the block copolymer constituting the polymer electrolyte membrane of the present invention is produced by anionic polymerization, an aromatic vinyl compound unit (a) in which α-carbon such as α, p-dimethylstyrene unit is quaternary carbon is used. When it is a repeating unit of the polymer block (A),
(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 of the above, a conjugated diene is polymerized to the resulting living polymer, and then a coupling agent such as phenyl benzoate is added to obtain an ABA type 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 is polymerized, the resulting living polymer is polymerized with a conjugated diene, and the resulting α-methylstyrene polymer block and conjugated diene polymer block are formed into a polymer block (C ) To obtain an ABC type block copolymer,
It can manufacture according to well-known methods, such as. Among the specific methods for producing the block copolymer, the method (3) is more preferable.

When the block copolymer constituting the polymer electrolyte membrane of the present invention is produced by cationic polymerization, an aromatic vinyl compound unit (a) in which α-carbon such as p-methylstyrene is tertiary carbon is polymer block. When the repeating unit (A) is used,
(5) Isobutene was cationically polymerized in the presence of Lewis acid in a halogen / hydrocarbon mixed solvent at −78 ° C. in the presence of Lewis acid, and then styrene was polymerized. It can be produced according to a known method using styrene such as a method for obtaining a B-A type block copolymer (Macromol. Chem., Macromol. Symp. 32, 119 (1990)).

When the block copolymer constituting the polymer electrolyte membrane of the present invention is produced by cationic polymerization, the aromatic vinyl compound unit (a) in which α-carbon such as α, p-dimethylstyrene is quaternary carbon is overlapped. When the repeating unit of the combined block (A) is used,
(6) Cationic polymerization of isobutene in the presence of Lewis acid using a bifunctional halogenation initiator at −78 ° C. in a halogen / hydrocarbon mixed solvent, followed by addition of diphenylethylene; A method in which α-methylstyrene is polymerized after post-addition of a Lewis acid to obtain an ABA type block copolymer (Macromolecules, (1995), 28, 4893-4898)
It can manufacture according to well-known methods, such as.

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 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, 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.

As described above, the degree of sulfonation or phosphonation is such that the ion exchange capacity of the polymer electrolyte membrane of the present invention is 0.30 meq / g or more, particularly 0.40 meq / g or more. It is desirable to sulfonate or phosphonate so that it is 0 meq / g or less. Thereby, practical ion conduction performance is obtained. The ion exchange capacity of the finally obtained polymer electrolyte membrane, the ion exchange capacity of the sulfonated or phosphonated block copolymer, or the sulfonation rate or phosphonation in the polymer block (A) in the block copolymer The rate can be calculated by using an analytical means such as acid value titration method, infrared spectrum measurement, nuclear 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, o, m or p-alkyl styrene sulfonic acid, α-alkyl-o, m or p-alkyl-styrene sulfonic acid, styrene sulfonic acid, α-alkyl-styrene sulfonic acid, o, m or p- Examples thereof include alkylstyrene phosphonic acid, α-alkyl-o, m or p-alkyl-styrene phosphonic acid, styrene phosphonic acid, α-alkyl-styrene phosphonic acid and the like.

  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.
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 can be introduced by producing a polymer using sodium o, m, or p-alkylstyrene sulfonate, or sodium α-methyl-o, m, or p-alkylstyrene 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.

  In addition to the block copolymer used in the present invention, the polymer electrolyte membrane of the present invention may contain a softening agent as necessary within a range not impairing the effects of the present invention. 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.

  The polymer electrolyte membrane of the present invention is further provided with various additives, for example, a phenol-based stabilizer, a sulfur-based stabilizer, a phosphorus-based stabilizer, and a light stabilizer, as long as the effects of the present invention are not impaired. , Antistatic agents, mold release agents, flame retardants, foaming agents, pigments, dyes, whitening agents, carbon fibers and the like may be used alone 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.

  From the viewpoint of ion conductivity, the content of the block copolymer in the polymer 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. Is even more preferred.

  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 electric resistance of the film 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 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, the block copolymer constituting the polymer electrolyte membrane of the present invention or the block copolymer and the above-mentioned additive are mixed with an appropriate solvent to dissolve or suspend the block copolymer, and PET A method of obtaining an electrolyte membrane having a desired thickness by casting on a plate-like body such as glass or applying using a coater or applicator and removing the solvent under appropriate conditions, hot press molding, roll A film forming method using a known method such as molding or extrusion molding can be 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 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 are arbitrary as long as the solvent can be completely removed at a temperature below the temperature at which ion-conductive groups such as sulfone groups of the block copolymer constituting the polymer electrolyte membrane of the present invention drop off. It is possible to select. 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, an ion conductive group may be in a salt state with a metal such as Na, and a treatment for returning to a proton type by acid treatment after bonding may be performed.

  Examples of the ion conductive binder constituting the membrane-electrode assembly include existing perfluorocarbon sulfones 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 polymer electrolyte membrane and the gas diffusion electrode, it is preferable to use an ion conductive binder formed from the same or similar material as the polymer electrolyte.

  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 economical, environmentally friendly, has high ionic conductivity and excellent methanol barrier properties, and is a solid polymer fuel cell, particularly a direct methanol fuel cell. Excellent power generation performance can be exhibited.

  The present invention is shown below with reference examples, examples and comparative examples, and performance tests (ion exchange capacity, electrical resistance of the membrane, methanol permeation rate) and results as proton conducting electrolyte membranes for polymer electrolyte fuel cells. However, the present invention is not limited to these.

Reference example 1
Production of block copolymer composed of poly (p-methylstyrene) (polymer block (A)) and hydrogenated polybutadiene (polymer block (B)) When the polymer block (A) is synthesized, aromatic Polyvinylstyrene (p) is used as the vinyl compound (a), and butadiene is used when synthesizing the polymer block (B). Polyvinyl styrene is synthesized in the same manner as the previously reported method (JP-A-2005-281373). (P-methylstyrene) -b-polybutadiene-b-poly (p-methylstyrene) (hereinafter abbreviated as pmSBpmS) was synthesized. The number average molecular weight of the obtained pmSBpmS was 78000, the amount of 1,4-bond determined from ¹ H-NMR measurement was 58.5%, and the content of p-methylstyrene units was 30% by mass.

A cyclohexane solution of synthesized pmSBpmS was prepared and charged into a pressure-resistant vessel that had been sufficiently purged with nitrogen. Then, a hydrogenation reaction was performed at 50 ° C. for 7 hours in a hydrogen atmosphere using a Ni / Al Ziegler hydrogenation catalyst. Then, poly (p-methylstyrene) -b-hydrogenated polybutadiene-b-poly (p-methylstyrene) triblock copolymer (hereinafter abbreviated as pmSEBpmS) was obtained. It was 99.7% when the hydrogenation rate of obtained pmSEBpmS was computed by ¹ H-NMR spectrum measurement.

Reference example 2
Production of block copolymer comprising poly (styrene / 4-tert-butylstyrene) (polymer block (A)) and hydrogenated polyisoprene (polymer block (B)) Synthesize polymer block (A) In this case, 4-tert-butylstyrene as the aromatic vinyl compound (a) and styrene as the other aromatic vinyl compound are mixed at a mass ratio of 50/50, and the polymer block (B) is used. Poly (styrene / 4-tert-butylstyrene) -b-polyisoprene-b-poly (styrene) was synthesized in the same manner as the previously reported method (Japanese Patent Laid-Open No. 2005-281373) using isoprene. / 4-tert-butylstyrene) (hereinafter abbreviated as (S / tBS) I (S / tBS)). The number average molecular weight of the obtained (S / tBS) I (S / tBS) is 51800, the 1,4-bond content determined from ¹ H-NMR measurement is 94.0%, and the content of styrene units is 15 The content of 0.6 mass% and 4-tert-butylstyrene unit was 15.6 mass%.
Using the synthesized (S / tBS) I (S / tBS), poly (styrene / 4) having a hydrogenation rate of 99.9% was obtained in the same manner as in Reference Example 1 except that the hydrogenation reaction was performed for 9 hours. -Tert-butylstyrene) -b-hydrogenated polyisoprene-b-poly (styrene / 4-tert-butylstyrene) triblock copolymer (hereinafter abbreviated as (S / tBS) EP (S / tBS)) Obtained.

Example 1
(1) Synthesis of sulfonated pmSEBpmS 51 g of the block copolymer (pmSEBpmS) 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, followed by 658 ml of methylene chloride. And dissolved by stirring at 35 ° C. for 2 hours. After dissolution, a sulfonation reagent obtained by reacting 9.40 ml of acetic anhydride and 4.20 ml of sulfuric acid at 0 ° C. in 18.9 ml of methylene chloride was gradually added dropwise over 5 minutes. After stirring at 35 ° C. for 6 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 the polymer collected at the end was vacuum dried to obtain sulfonated pmSEBpmS. The sulfonation rate of the benzene ring of the p-methylstyrene unit of the obtained sulfonated pmSEBpmS was 29 mol% from ¹ H-NMR analysis.
(2) Preparation of electrolyte membrane for fuel cell A 5% by mass THF solution of the sulfonated pmSEBpmS obtained in (1) is prepared, cast on a polytetrafluoroethylene sheet at a thickness of about 1000 μm, and dried sufficiently at room temperature. Then, the film was sufficiently vacuum-dried to obtain a film having a thickness of 52 μm.

Example 2
(1) Synthesis of Sulfonated (S / tBS) EP (S / tBS) 30 g of the block copolymer ((S / tBS) EP (S / tBS)) obtained in Reference Example 2 was made of glass with a stirrer. After vacuum-drying in a reaction vessel for 1 hour and then purging with nitrogen, 30 ml of methylene chloride was added and stirred at 35 ° C. for 2 hours to dissolve. After dissolution, a sulfonation reagent obtained by reacting 5.53 ml of acetic anhydride and 2.47 ml of sulfuric acid at 0 ° C. in 11.1 ml of methylene chloride was gradually added dropwise over 5 minutes. After stirring at 35 ° C. for 6 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 the polymer collected at the end was vacuum dried to obtain a sulfonated (S / tBS) EP (S / tBS). The sulfonation rate of the benzene ring of the obtained sulfonated (S / tBS) EP (S / tBS) was 31.0 mol% from ¹ H-NMR analysis.
(2) Preparation of electrolyte membrane for fuel cell A 23 mass% toluene / isobutyl alcohol (mass ratio 8/2) solution of the sulfonated (S / tBS) EP (S / tBS) obtained in (1) was prepared. A film having a thickness of 49 μm is coated on a PET film [Toyobo Co., Ltd. “Toyobo Ester Film K1504”] having a thickness of about 450 μm, sufficiently dried at room temperature, and then sufficiently vacuum dried. Got.

Comparative Example 1
(1) Synthesis of Sulfonated SEBS A sulfonating 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 sulfonation reagent was gradually added dropwise over 5 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 29.0 mol% from ¹ H-NMR analysis.
(2) Preparation of fuel membrane electrolyte membrane Prepare a 5% by mass THF solution of the sulfonated SEBS obtained in (1), cast it on a polytetrafluoroethylene sheet at a thickness of about 1000 μm, and dry it sufficiently at room temperature. Then, the film was sufficiently vacuum-dried to obtain a film having a thickness of 52 μm.

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

Comparative Example 3
Perfluorocarbon sulfonic acid polymer electrolyte membrane A DuPont Nafion film (Nafion 117) was selected as the perfluorocarbon sulfonic acid polymer electrolyte membrane.

Examples 1 and 2 and performance tests of polymer membranes of Comparative Examples 1 to 3 as electrolyte membranes for polymer electrolyte fuel cells In the following tests 1) to 3), samples were obtained in each Example or Comparative Example. A membrane or Nafion membrane prepared from the sulfonated block copolymer obtained 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 electrical resistance of film A sample of 1 cm × 4 cm was sandwiched between a pair of platinum electrodes and mounted in 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 the electrical resistance of the film was measured by an AC impedance method.

3) Methanol Permeation Rate Methanol permeation rate was determined by inserting an electrolyte membrane between H-type cells, injecting 55 ml of 10M (mol / liter) aqueous methanol solution on one side of the cell, and 55 ml of pure water in the other cell, The amount of methanol diffusing into the pure water through the electrolyte membrane was measured by using gas chromatography while stirring (the area of the electrolyte membrane was 4.5 cm ² ).

As a result of the performance test as a polymer electrolyte membrane, the electrical resistance of the membranes produced in Examples 1 and 2 and Comparative Examples 1 and 2 and the Nafion membrane of Comparative Example 3 and the methanol permeation rate of 10M-MeOH aqueous solution were measured. The results are shown in Table 1.

From the comparison between Examples 1 and 2 and Comparative Examples 1 and 2, when the hydrogen atom directly bonded to the benzene ring is substituted with an alkyl group, the electrical resistance of the film is not greatly changed as compared with the case where it is not substituted. However, it was revealed that methanol permeability was greatly suppressed. In the case of a styrene derivative substituted with an alkyl group, it is considered that the hydrophobicity in the ion channel formed by the polymer block (A) is increased and the methanol permeation rate is reduced because the hydrophobicity is higher than that of styrene. .
In addition, from the comparison between Examples 1 and 2 and Comparative Example 3, the polymer electrolyte membrane of the present invention has both membrane electrical resistance and methanol permeability compared to Nafion membrane, which is a typical example of an electrolyte membrane for fuel cells. It became clear that it was decreasing significantly.
Therefore, it can be said that the polymer electrolyte membrane of the present invention is very useful as a molecular electrolyte membrane for a solid polymer fuel cell, particularly as a polymer electrolyte membrane for a direct methanol fuel cell.

Claims (7)

The hydrogen atom bonded to the α-carbon atom is unsubstituted or substituted with an alkyl group having 1 to 4 carbon atoms, and at least one of the hydrogen atoms directly bonded to the aromatic ring is an alkyl group having 1 to 8 carbon atoms. The polymer block (A) having a substituted aromatic vinyl compound unit as a repeating unit and the conjugated diene unit having 4 to 8 carbon atoms in which a part or all of the carbon-carbon double bond is hydrogenated as a repeating unit The polymer block (B) has a constituent component, the proportion of the aromatic vinyl compound unit in the polymer block (A) is 20% by mass or more, and the polymer block (A) has an ion conductive group. A polymer electrolyte membrane for a polymer electrolyte fuel cell containing a block copolymer, wherein the content of the block copolymer in the membrane is 90% by mass or more. The mass ratio of polymer block (A) and polymer block (B) is 95: 5 to 5:95 in which claim 1 Symbol placement of the electrolyte membrane. The electrolyte membrane according to claim 1 or 2 , wherein the aromatic vinyl compound unit is a p-methylstyrene unit or a 4-tert-butylstyrene unit. (Wherein, M represents a hydrogen atom, an ammonium ion or an alkali metal ion) ion-conducting group is -SO ₃ M group or a -PO ₃ HM group claim 1-3 is a group represented by 1 The electrolyte membrane according to item. The electrolyte membrane according to any one of claims 1 to 4 , wherein the ion exchange capacity is 0.30 meq / g or more. A membrane-electrode assembly using the electrolyte membrane according to any one of claims 1 to 5 . A polymer electrolyte fuel cell using the electrolyte membrane according to any one of claims 1 to 5 .