Patent ID: 7875392

Claim:
A polymer electrolyte membrane comprising a uniform (b)-in-(a) microdispersion structure-containing polymer mixture of: (a) 90.000 to 99.990% by weight, based on the total weight of components (a) and (b), of a fluorinated polymer electrolyte having an ion exchange group, and (b) 0.010 to 10.000% by weight, based on the total weight of components (a) and (b), of a basic polymer, wherein, optionally, at least a part of component (a) and at least a part of component (b) are chemically bonded to each other, said polymer electrolyte membrane exhibiting a sea/islands structure when a cross-section of said membrane which is taken in a thicknesswise direction of the membrane is examined with respect to a 15 μm×15 μm area thereof by a transmission electron microscope, said sea/islands structure having its sea phase and island phase which are, respectively, composed mainly of said fluorinated polymer electrolyte (a) and said basic polymer (b).