Highly proton-conductive polymer electrolyte membranes that excel in mechanical strength and a process for producing the same

Abstract

A vinyl monomer is graft polymerized on an aromatic hydrocarbon-based polymer film substrate to introduce graft chains into the substrate and thereafter a functional monomer represented by the following formula and having sulfonic acid groups or functional groups capable of conversion to sulfonic acid groups is graft polymerized to introduce the sulfonic acid groups or the functional groups capable of conversion to sulfonic acid groups: where R is an aromatic ring or an aliphatic chain; X is (1) —OH, (2) —OLi, —ONa or —OK, (3) —F or —Cl, or (4) —OCHwhere n is an integer of 1 to 7. Since the graft chains obtained by graft polymerization of the vinyl monomer can also be utilized as scaffold polymers, the graft polymerizability of the functional monomer to the aromatic hydrocarbon-based polymer film substrate is sufficiently improved to enable the preparation of a polymer electrolyte membrane that excels not only in proton conductivity and mechanical strength but also in dimensional stability.