Patent ID: 7482388

Claim:
A polymer electrolyte membrane for a polymer electrolyte fuel cell comprising a fluorine polymer substrate having grafted thereon vinyl monomers having sulfone groups as a cation-exchange group, wherein a main chain of the graft chain comprises a hydrocarbon or a partially fluorinated hydrocarbon, and sulfone groups or substituents having sulfone groups are bonded to the main chain through a C—C single bond as a side chain, and wherein the monomer is represented by formula (1) wherein X represents H, hydrocarbon or F; when X is H, R 1 represents —O—C n H 2n+1 , —C(═O)—C n H 2n+1 , —C(═O)—O—C n H 2n+1 , —C(═O)—OH wherein R 2 represents —H, —CH 3 , —CH 2 Cl, —CH 2 OH, —C(CH 3 ) 3 , —CH 2 SO 3 Na, —Cl, —Br or —F; when X is CH 3 , R 1 represents —C 6 H 5 or —C(═O)—OH; and when X is F, R 1 represents —C(═O)—OH or —C(═O)—C n H 2n+1 wherein n is 1-10; wherein in element compositional ratio by X-ray photoeletron spectroscopy (“ESCA”), at least one surface of the polymer eletrolyte membrane has O/S value of 5.0 or higher, and a surface element proportion of S is 0.4-5.0%.