This work describes the synthesis and characterization of two nonfluorinated proton-conducting polymer systems, one consisting of a hydrogenated styrene-butadiene rubber (HSBR) block copolymer and the other consisting of an HSBR blend with isobutylene isoprene rubber for the improved mechanical stability of the final product. The films obtained were crosslinked, sulfonated, and microstructurally and electrically characterized. In addition, water and methanol crossover was determined, the results being compared with those of Nafion 117. The properties measured in the different samples confirmed that these systems may constitute a valid alternative to commercial membranes, being low-cost and less polluting and having a lower methanol crossover. (C) 2003 Wiley Periodicals, Inc.