Synthesis of fluorinated polymer electrolyte membranes by radiation grafting and atom transfer radical polymerization techniques

Zhai, M.; Chen, J.; Hasegawa, Shin; Maekawa, Yasunari

A novel polymer electrolyte membrane was synthesized by radiation-induced grafting and consequent atom transfer radical polymerization (ATRP) using a fluorinated substrate polymer. First, bromine-containing perfluorinated grafts were prepared by radiation grafting. By adjusting the molar ratio of bromine-initiator/CuBr/bpy and the reaction temperature, branched poly(styrene) with a grafting yield of above 100% on the perfluorinated grafts was constructed in the films. Thermal analysis revealed that the perfluorinated grafts were miscible to the fluorinated substrate polymer, whereas the hydrocarbon poly(styrene) branches were phase-separated from the fluorinated film. The sulfonation of the poly(styrene) grafts gave the membrane exhibiting higher proton conductivity than commercial Nafion 117 membrane. Likewise, it had better chemical stability than graft-type membranes prepared by conventional radiation-induced grafting.