PROTON-CONDUCTIVE POLYMER ELECTROLYTE FILM HAVING EXCELLENT OXIDATION RESISTANCE, AND PROCESS FOR PRODUCTION THEREOF

The process for producing a proton conductive polymer electrolyte membrane of the present invention includes the steps of: irradiating resin fine particles with radiation; graft-polymerizing a vinyl monomer having a sulfonic acid group precursor and a vinyl monomer having a carbonyl group equivalent with the resin fine particles in a solid-liquid two-phase system to obtain a finely particulate graft polymer; preparing a casting solution of a polymer having a phosphoric acid group or a phosphonic acid group and the graft polymer, and forming a cast membrane from this solution; drying the cast membrane to obtain a film; converting the sulfonic acid group precursor into a sulfonic acid group; and forming a crosslinked structure between the carbonyl group equivalents. In the solid-liquid two-phase system, a liquid phase includes the vinyl monomers and a solvent for the monomers, and a solid phase includes the resin fine particles. By this process, a proton conductive polymer electrolyte membrane having high oxidation resistance, and a process capable of producing this membrane industrially are provided.