Proton exchange type polymer electrolyte membranes (PEM) consisting of ion conducting alkylsulfonic acid and hydrophilic groups such as a hydroxyl group were successfully synthesized by radiation-induced graft polymerization of vinyl acetate (VAc) into a poly(ethylene-co-tetrafluoroethylene) (ETFE) film, followed by saponification and alkylsulfonation with 1,3-propanesulfone. In contrast to the typical S(N)2 reactions in a solution, the base-catalyzed nucleophilic ring-opening reactions of hydroxyl groups of poly(vinylalcohol) grafts with 1,3-propanesultone in solid state ETFE films hardly proceeds in the hydrophilic solvents, but it does proceed in hydrophobic toluene with a weak base (triethylamine) to yield ETFE-grafted poly(vinylalcohol-co-vinylsulfopropyl ether) (PEM-OH) with various values of ion-exchange capacity (IEC) and molar ratio of hydroxyl to sulfo groups in the grafts. The relative-humidity (RH) dependence of the proton conductivity of the sulfonated membrane was compared with that of poly(styrenesulfonic acid)-grafted ETFE (PEM-PSSA) with a similar IEC (similar to 1.3 mmol g(-1)) at 80 degrees C. The PEM-OH showed a conductivity of 1.0 x 10(-3) S cm(-1) under 30% RH, which is higher than those of PEM-PSSA. Further, the PEM-OH with higher IEC (1.9 mmol g(-1)) prepared with a grafting degree of 82% and a sulfonation degree of 41% showed 3.8 x 10(-3) S cm(-1) under 30% RH at 80 degrees C. The conductivity is higher than that of PEMs based on sulfonated polyimide and poly(ether sulfone) with a similar IEC. Furthermore, the tensile strength of PEM-OH was 48 MPa with the elongation at break of 422%, which are better than those of Nafion. These results strongly indicate that the radiation-grafted PEM with hydroxyl groups is a promising material with excellent mechanical and electrochemical properties, which are important characteristics for a fuel cell operating at a high temperature and low humidity. (c) 2012 Elsevier B.V. All rights reserved.