Proton conductive inorganic-organic hybrid membranes were synthesized from styrene derivatives of alkoxysilane and ethyl 2-[3-(dihydroxyphosphonyl)-2-oxopropyl] acrylate (EPA) through copolymerization followed by sol-gel reaction. Self-standing, homogeneous and transparent hybrid membranes with chemically bound phosphonic acid groups were synthesized. FT-IR analysis exhibited the hybrid membranes included phosphonic acid groups. C-13 and Si-29 NMR studies indicated that alkoxysilyl functionalized styrene derivatives were not only copolymerized with EPA but also condensed yielding Si-O-Si linkages by sol-gel reaction. TG-DTA analysis revealed that these membranes were thermally stable LIP to 200 degrees C in dry O-2. The proton conductivities of the hybrid membranes increased with phosphonic acid content and temperature. The P/Si ratio of the membrane was dependent on the number of alkoxy group in the starting alkoxysilane. The hybrid membrane from (dimethylmethoxysilylmethyl)styrene (DMMSMS(M))/EPA= 1/6 revealed proton conductivities of 6.3 x 10(-3) and 2.4 x 10(-4) S cm(-1) at 68.0% relative humidity and 18.8% relative humidity, respectively, at 140 degrees C. (C) 2009 Elsevier Ltd. All rights reserved.