High temperature proton exchange membranes were synthesized via electron beam treatment of commercial poly(ethylene-alt-tetraflouroethylene) (ETFE) films and subsequent graft radical copolymerizations with 2-hydroxyethyl methacrylate (HEMA) and 2-hydroxyethyl acrylate (HEA). The maximum degree of grafting achieved was 193%. Both grafted monomers are hydrophilic and lead to high membrane affinity to phosphoric acid. Doping with phosphoric acid resulted in a maximum doping level of 310%. The grafted membranes combine stable ETFE backbone polymer with hydrophilic side chains. As indicated by stress-strain curves the graft copolymer membranes show good mechanical stability. In addition, the polymer-acid-composites are thermally stable up to around 210 degrees C. The polymer-acidcomposite materials were tested in H-2/O-2 fuel cells at 120 degrees C. Power densities of up to 108 mW cm(-2) were obtained at a current density of 200 mA cm(-2). It is shown that the alternate concept of polymeracid composites without any basic units is also suitable for the application in high temperature fuel cells. (C) 2015 Elsevier B.V. All rights reserved.