Covalently cross-linked nonfluorinated hydrocarbon ionomers are synthesized by introducing sulfonate groups and a siloxane cross-linker through thermally and chemically stable imide bonding on poly(styrene-co-maleic anhydride). The three-dimensional polysiloxane framework, which does not only act as a robust scaffold but also provide sites for the hydrogen bonding with water, contribute to the increase in bound water degree, higher proton conductivity at lower ion exchange capacity, and greatly decreased methanol permeability. The spherical-shaped ionic clusters produce a comparable proton conductivity (10(-1) S cm(-1) above 60 degrees C) to Nafion-117. The conductivity of the hybrid ionomer does not decrease to gain its selectivity, but instead increased. Methanol permeability is similar to 70% lower than that of Nafion-117. but has a higher water uptake and IEC. The membrane with IEC values of 1.1 mequiv.g(-1) exhibits a constant conductivity for 200 h in hydrolytic stability test, and produce a power density 20% higher than Nafion-117 in single DMFC operation. (C) 2010 Elsevier B.V. All rights reserved.