Patent ID: 7803846

Claim:
A polymer electrolyte membrane for fuel cells that is produced by subjecting a polymer film substrate to multi-graft polymerization with monomers comprising at least one monofunctional vinyl monomer of the following group A as combined with at least one polyfunctional vinyl monomer of the following group B, crosslinking the film substrate containing the grafted molecular chains by irradiation, and then introducing sulfonic acid groups into the grafted molecular chains or the aromatic rings in the grafted molecular chains, the monofunctional vinyl monomer of group A being a monomer selected from the group consisting of styrene; alkylstyrenes such as methylstyrenes (e.g., α-methylstyrene and vinyltoluene), ethylstyrenes, dimethylstyrenes, trimethylstyrenes, pentamethylstyrenes, diethylstyrenes, isopropylstyrenes, and butylstyrenes (e.g., 3-tert-butylstyrene and 4-tert-butylstyrene); halogenated styrenes such as chlorostyrenes, dichlorostyrenes, trichlorostyrenes, bromostyrenes (e.g., 2-bromostyrene, 3-bromostyrene and 4-bromostyrene), and fluorostyrenes (e.g., 2-fluorostyrene, 3-fluorostyrene and 4-fluorostyrene); alkoxystyrenes such as methoxystyrenes, methoxymethylstyrenes, dimethoxystyrenes, ethoxystyrenes, and vinylphenyl allyl ethers; hydroxystyrene derivatives such as hydroxystyrenes, methoxyhydroxystyrenes, acetoxystyrenes, and vinylbenzyl alkyl ethers; vinylbenzoic acids; carboxystyrene derivatives such as formylstyrenes; nitrostyrene derivatives such as nitrostyrenes; aminostyrene derivatives such as aminostyrenes and dimethlaminostyrenes; vinyl benzylsulfonic acids; and ion-containing styrene derivatives such as styrene sulfonyl fluorides; and the polyfunctional vinyl monomer of group B being a crosslinking agent selected from the group consisting of bis(vinylphenyl)ethane, divinylbenzene, 2,4,6-triallyloxy-1,3,5-triazine (triallylcyanurate), triallyl-1,2,4-benzenetricarboxylate (triallyltrimellitate), diallyl ether, triallyl-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione, 2,3-diphenylbutadiene, 1,4-diphenyl-1,3-butadiene, 1,4-divinyloctafluorobutane, bis(vinylphenyl)methane, divinylacetylene, divinyl sulfide, divinyl sulfone, divinyl ether, divinyl sulfoxide, isoprene, 1,5-hexadiene, butadiene, and 1,4-divinyl-2,3,5,6-tetrachlorobenzene.