Preparation of highly stable ion exchange membranes by radiation-induced graft copolymerization of styrene and Bis(vinyl phenyl)ethane into crosslinked polytetrafluoroethylene films

Yamaki, Tetsuya; Tsukada, Junichi; Asano, Masaharu; Katakai, Ryoichi*; Yoshida, Masaru

PEFC applications will require that the ion exchange membranes have a high ion exchange capacity and reasonable chemical stability. We prepared novel ion exchange membranes by the radiation-induced graft copolymerization of styrene and bis(vinyl phenyl)ethane (BVPE) into crosslinked polytetrafluoroethylene (cPTFE) films and subsequent sulfonation and then investigated their stability in an oxidizing environment and water uptake. In contrast to divinylbenzene (DVB), the degree of grafting of styrene/BVPE increased in spite of high crosslinker concentrations in the reacting solution (up to 70 mol%). Complete sulfonation of the crosslinked graft chains resulted in the preparation of the membranes with a large ion exchange capacity reaching 2.5 meq/g, which exceeded the performance of Nafion. The BVPE-crosslinked membranes exhibited higher durability in a 3% aqueous solution of HO at 60 C and decreased water uptake compared to the non-crosslinked one. These undoubtedly mean a profound effect of BVPE on PEFC performances of the membranes.