New crosslinked composite membranes containing doped phosphoric acid (PA) were prepared by radiation induced grafting of 4-vinylpyridine (4-VP) and triallyl cyanurate (TAC) mixtures at various concentrations onto poly(ethylene-co-tetrafluoroethylene) (ETFE) films followed by acid doping. The effect of grafting parameters such as TAC concentration, absorbed dose and monomer concentration on the degree of grafting was investigated. The properties of the obtained membranes such as chemical composition, thermal stability and mechanical properties were evaluated using Fourier transform infrared (FTIR), thermal gravimetric analysis (TGA) and universal mechanical tester, respectively. The proton conductivity of the membranes was investigated in correlation with TAC content and temperature using the impedance spectroscopy. Of all samples, the crosslinked membrane obtained from grafting a mixture of 4-VP with 5 vol% TAC having a DG of 65% exhibited proton conductivity as high as 39 mS/cm under dry condition at 120 degrees C. The mechanical properties of the crosslinked membranes were significantly improved compared to the non-crosslinked counterpart. The presence of an interesting combination of properties in PA doped crosslinked membrane suggests a potential for application in medium temperature proton exchange membrane fuel cell. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.