Proton-conductive inorganic-organic hybrid membranes synthesized from a trimethoxysilylmethylstyrene-fluorophenylvinyl acid copolymer

Inorganic-organic hybrid membranes composed of Si-O networks and an aliphatic main-chain polymer backbone were synthesized from an alkoxysilane derivative and an F-substituted phenylvinylphosphonic acid via copolymerization and sol-gel reaction. Thus, (trimethoxysilylmethyl)styrene (TMSMS) was copolymerized with 3-fluorophenyl- vinylphosphonic acid (FC₆H₄VPA), and the product was hydrolyzed to afford an inorganic-organic hybrid composite. Spectroscopic analysis revealed that the inorganic-organic hybrid structure was constructed via the polymerization of TMSMS and FC₆H₄VPA and the condensation of methoxy-Si bonds. The membranes showed good thermal stability up to 180°C, and it was found that the aliphatic chains bound to the F-substituted aromatic rings and the Si-O linkages in the hybrid membranes improved their mechanical properties. In addition, the proton conductivity of the membranes depended on the P/Si ratio of the product and increased as the P content increased. Notably, the conductivity at 130°C for the hybrid membrane synthesized with a TMSMS/FC₆H₄VPA ratio of 1/6 was 1.6×10^-3Scm^-1 and 6.4×10^-2Scm^-1 at low and 100% relative humidity (RH), respectively, while its power density at 140°C and 30% RH was 3.0mW/cm².