Patent ID: 7919537

Claim:
A method for producing a polymer electrolyte membrane for polymer electrolyte fuel cells, the method comprising: crosslinking a polytetrafluoroethylene substrate by irradiating the polytetrafluoroethylene substrate in a vessel using gamma-rays, cooling the vessel, and recovering a crosslinked polytetrafluoroethylene substrate from the vessel; charging a container with the crosslinked polytetrafluoroethylene substrate; irradiating the crosslinked polytetrafluoroethylene substrate using gamma-rays; charging the container with a liquid mixture comprising a styrenic monomer and a bis(vinylphenyl)ethane monomer; graft polymerizing the styrenic monomer and the bis(vinylphenyl)ethane monomer to the crosslinked polytetrafluoroethylene substrate; and introducing sulfonic acid groups into graft side chains formed by the graft polymerization.