Polymer electrolyte membranes consisting of alkyl sulfonic acid for fuel cells, synthesized by radiation-induced graft polymerization and subsequent chemical transformation

Maekawa, Yasunari; Takahashi, Shuichi; Hanh, T. T.*; Okonogi, Hiroyuki*; Hagiwara, Tokio*

Polymer electrolyte membranes (PEMs) consisting of alkylsulfonic acid in grafting chains can be prepared by radiation-induced graft polymerization of methyl acrylate (MA) onto a poly(ethylene-co-tetrafluoroethylene) (ETFE) film, followed by the sulfonation of MA units in the grafting chains using an equimolar complex of chlorosulfonic acid and dioxane. The sulfonation reaction accompanied equimolar decarboxylation of the MA unit (substitution of carboxylic acid with sulfonic acid) to give the PEMs with conductivity of 0.01-0.11 S/cm. Furthermore, the replacement of the MA unit with methyl metacrylate (MMA) as a comonomer in grafting chains enhances the stability of the PEM at higher temperatures.