Synthesis of proton-conductive sol–gel membranes from trimethoxysilylmethylstyrene and phenylvinylphosphonic acid

Novel proton-conductive inorganic–organic hybrid membranes were synthesized from (trimethoxysilylmethyl)styrene (TMSMS) and phenylvinylphosphonic acid (PhVPA) mixed at various ratios using radical copolymerization followed by the sol–gel process. Self-standing, homogeneous, highly transparent membranes were synthesized. TG-DTA analysis indicated that these membranes were thermally stable up to 180 °C. FT-IR and 13C NMR revealed that the functionalized alkoxysilane was copolymerized with phenylvinylphosphonic acid. The phosphonic acid groups of the TMSMS/PhVPA copolymer were chemically bound to the organosiloxane network formed via the hydrolysis and polycondensation reaction between the silanol groups of TMSMS. The proton conductivity of the hybrid membranes increased with the phosphonic acid content. The TMSMS/PhVPA membrane of a 1/4 ratio revealed conductivities of 3.7 × 10−2 S cm−1 under 100% R.H. at 130 °C and 9.5 × 10−4 S cm−1 under about 19.2% R.H. at 130 °C.