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

A novel polymer electrolyte membrane was synthesized by radiation-induced grafting and consequent atom transfer radical polymerization (ATRP). First, bromine-containing perfluorinated grafts were prepared by radiation grafting of 2-brotnotetrafluoroethyl trifluorovinyl ether (BrTFF) into a poly(ethylene co-tetrafluoroethylene) (ETFE) film. Then, the bromine atoms in the ETPE-g-PBrTFF grafted films were acted as initiators, and the films were treated with Cu(1)-based catalytic system of a CuBr and 2,2'-bipyridyl (bpy) for the ATRP. By adjusting the molar ratio of initiator/CuBr/bpy and the reaction temperature, branched poly(styrene) with a grafting yield of above 1001 on the poly(BrTFF) main chains was constructed in ETFE-g-PBrTFF films. Thermal analysis revealed that the perfluorinated poly(BrTFF) main chains were miscible to ETFE, whereas the hydrocarbon poly(styrene) branches were phase-separated froth the ETFE-g-PBrTFF film. Sulfonic groups could be further introduced into the polystyrene) grafts of ETFE-g-PBrTFF-g-PS films with homogeneous distribution in a perpendicular direction to the membrane surface. The resulting membrane with a styrene grafting yield of 1595 exhibited higher proton conductivity than commercial Nafion 117 membrane. Likewise, it had better chemical stability than ETFE-g-PSSA membrane prepared by conventional radiation-induced grafting. (c) 2009 Elsevier Ltd. All rights reserved.