For the past decade, much effort has been dedicated to non-fluorinated polymeric membranes as alternatives for commercial Nafion in the field of direct methanol fuel cells (DMFCs). However, most of researches have used solvents that are environmentally unfriendly during the membranes preparation. This work reported a novel solvent-free route to prepare non-fluorinated proton exchange membranes (PEMs) via the in situ reaction and grafting of sodium 4-styrene sulfonate (NaSS) to hydrogenated nitrile butadiene rubber (HNBR) during peroxide curing. Membrane morphology was characterized by TEM and SEM-EDX experiments. The effect of NaSS loading and unsaturation level of HNBR on the membrane properties were studied. The obtained membranes exhibited proton conductivity on the order of 0.01 S/cm and selectivity (the ratio of proton conductivity to methanol permeability) higher than that of Nafion, and could be potentially used for the application in DMFCs. (C) 2012 Elsevier Ltd. All rights reserved.