Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2000-12-22
2004-07-13
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S304000, C429S314000, C429S317000
Reexamination Certificate
active
06761989
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polymer electrolyte, particularly, a polymer electrolyte suitably used for a fuel cell and a method for producing the same.
2. Description of the Related Art
As a proton conductive polymer electrolyte used in a solid polymer-type fuel cell, perfluorosulfonic acid-based materials typically including Nafion (trade mark of Dupont) are mainly used conventionally because of their excellent property as a fuel cell.
However, this material is very expensive which is believed to be a serious problem in wide-spreading a powder generation system using a fuel cell in the future.
Under such circumstances, there are recently activating developments of cheap polymer electrolytes which can replace the perfluorosulfonic acid-based materials. Among others, materials obtained by introducing sulfonic acid groups into an aromatic polyether which is excellent in heat resistance and has high film strength are recognized as hopeful, and for example, JP-A (Kohyo publication) No. 11-502249 describes a sulfonated polyether ketone-based polymer electrolyte, and JP-A Nos. 10-45913 and 10-21943 describe a sulfonated polyether sulfone-based polymer electrolyte.
In these materials, when the amount of introduced sulfonic acid group is larger, proton conductivity increases generally, however, water absorption of a polymer tends to increase simultaneously. When a film produced from a polymer having high water absorption property is used in a fuel cell, water produced in using the cell causes large dimension change and reduction in strength.
On the other hand, JP-A (Kohyo publication) No. 10-503788 describes a polymer electrolyte obtained by introducing sulfonic acid groups into a styrene-(ethylene-butylene)-styrene triblock copolymer. There is a fear of low heat resistance of this block copolymer since the main chain of the copolymer is flexible.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a novel polymer electrolyte excellent in water resistance, having high heat resistance, and suitable for a proton conductive film of a cheap fuel cell, and a method for producing the same.
The present inventors have intensively studied for attaining the above-mentioned object, and resultantly, found that a polymer electrolyte containing a block copolymer having a specific combination of blocks has an excellent property as a proton conductive film for a fuel cell, and completed the present invention.
Namely, the present invention relates to (1) a polymer electrolyte containing a block copolymer comprising one or more blocks having sulfonic acid groups and one or more blocks having substantially no sulfonic acid group, and at least one block among all blocks is a block having aromatic rings in the main chain thereof. Also, the present invention relates to (2) a method for producing a polymer electrolyte of (1), comprising the steps of reacting a precursor of a block having a repeating unit represented by below described general formula [1], [2] or [3] with a precursor of a block having a repeating unit represented by the general formula [4] to produce a block copolymer, and then sulfonating the copolymer. Further, the present invention relates to (3) a fuel cell obtained by using a polymer electrolyte of (1).
DETAILED DESCRIPTION OF THE INVENTION
The polymer electrolyte of the present invention contains a block copolymer comprising one or more blocks having sulfonic acid groups and one or more blocks having substantially no sulfonic acid group, and in which at least one block among all the blocks is a block having aromatic rings in the main chain thereof.
In the present invention, the term block means a polymer in which two or more units of the same kind of repeating units are connected. The term block copolymer means a polymer in which two or more blocks are directly bonded or bonded via a connecting group, namely, a polymer comprising a plurality of blocks composed of two kinds or more repeating units.
In the present invention, the term block containing sulfonic acid groups means a block in which 0.5 or more in average of sulfonic acid groups (represented by —SO
3
H) are bonded to one repeating unit constituting a block, at any portion of the repeating unit.
Bonding form of the sulfonic acid groups to repeating units constituting a block is not particularly restricted, and a structure in which sulfonic acid groups are directly bonded to aromatic rings is preferable since synthesis thereof is relatively easy.
On the other hand, in the present invention, the term block containing substantially no sulfonic acid group means a block in which the introduced amount of sulfonic acid group is 0.1 or less in average per one repeating unit constituting a block.
In the present invention, the block having aromatic rings in the main chain thereof may be a block containing sulfonic acid groups, a block containing substantially no sulfonic acid group, or both of them.
In the present invention, examples of the block containing sulfonic acid groups include blocks obtained by introducing sulfonic acid groups into blocks composed of polystyrene, poly(&agr;-methylstyrene), poly(allyl phenyl ether), poly(phenyl glycidyl ether), poly(phenylene ether), polyphenylene sulfide, polyether ether ketone, polyether ether sulfone, polysulfone, poly(phenylmethylsiloxane), poly(diphenylsiloxane), poly(phenylmethylphosphazene), poly(diphenylphosphazene), epoxy resins and the like.
Among them, blocks obtained by introducing sulfonic acid groups into a block having a repeating unit represented by the general formula [1], a block having a repeating unit represented by the general formula [2], or a block composed of an epoxy resin, are preferably used.
In the formula [1], X represents —O—, —S—, —NH— or direct bond, R
1
represents an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms or a phenyl group, and a is an integer from 0 to 3. When a plurality of R
1
s are present, these may be the same or different.
Examples of the block having a repeating unit represented by the general formula [1] include poly(phenylene), poly(aniline), poly(phenylene ether), poly(phenylene sulfide) and the like.
Among them, poly(phenylene ether) represented by the general formula [1] wherein X is —O— is preferable, and specific examples thereof include poly(1,4-phenylene ether), poly(2-methyl-1,4-phenylene ether), poly(2,6-dimethyl-1,4-phenylene ether), poly(2-phenyl-1,4-phenylene ether), poly(2,6-diphenyl-1,4-phenylene ether), poly(2-methyl-1,3-phenylene ether), poly(2,6-dimethyl-1,3-phenylene ether), poly(2-phenyl-1,3-phenylene ether), poly(2-6-diphenyl-1,3-phenylene ether) and the like, and among them, poly(1,4-phenylene ether), poly(2-phenyl-1,4-phenylene ether), poly(2,6-diphenyl-1,4-phenylene ether) are more preferable, and poly(2-phenyl-1,4-phenylene ether) is further preferable.
The precursor of a block having a repeating unit represented by the general formula [1] can be produced by a known method. For example, in the case of poly(phenylene ether), it can be produced by an oxidation polymerization method in which phenol is oxidized in the presence of a catalyst, or a method (called Ullmann reaction) in which a halogenated phenol is condensed in the presence of a catalyst and alkali.
Here, the term precursor of a block means a homopolymer having a reaction site which becomes a block by a copolymerization reaction.
In the formula [2], Ar
1
represents a group selected from the following structures,
in the above formulae, R
2
represents an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a phenyl group or a phenoxy group, b is an integer from 0 to 4, and c is an integer from 0 to 6. When a plurality of R
2
s are present, these may be the same or different.
The precursor of a block having a repeating unit represented by the general formula [2] is obtained, for example, by rin
Ikeda Takashi
Iwasaki Katsuhiko
Terahara Atsushi
Birch & Stewart Kolasch & Birch, LLP
Mercado Julian
Ryan Patrick
Sumitomo Chemical Company Limited
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