Patent ID: 8664282

Claim:
A process to prepare a crosslinked membrane, comprising the steps: a. providing a copolymer comprising repeat units of Formulae (V) and (VI) wherein Rf and Rf′ are independently a linear or branched perfluoroalkylene group, optionally containing oxygen or chlorine; X is Br or Cl; and Q is F, Br, or Cl; b. forming a membrane from the copolymer; c. hydrolyzing the —SO 2 Q moiety to form a —SO 3 H moiety or salt thereof; and d. exposing the copolymer to radiation to form a crosslinked polymer, either before or after formation into a membrane; wherein the monomer of Formula VI can enable copolymerization, crosslinking and oxidation to a stable polymer electrolyte membrane that is conductive at low relative humidity, having through-plane conductivity, at 25% relative humidity and 80° C., of at least 13 mS/cm, and transverse direction swelling of not more than 78%.