Synthesis of polyhedral oligomeric silsesquioxane (POSS) copolymers for proton conducting polymers

Althogh hydrocarbon polymer electrolytes having phosphoric acid groups, polyphosphoxyetyl-methacrylate (PPHM), showed excellent radical stability and water adsorption properties, their mechanical properties were insufficient for fuel cell applications. It has been reported that the mechanical and thermal properties of polymer materials were improved by introducing polyhedral oligomeric silsesquioxane (POSS) containing an inorganic Si8O 12 core surrounded by organic substitutes. In this study, copolymers consisting of PHM and POSS (poly(PHM-co-POSS)) were synthesized in order to improve the mechanical properties and control the water adsorption of PPHM and their electrical properties. The X-ray diffraction profiles of poly(PHM-co-POSS) showed that the crystalline structures formed in the copolymers due to the aggregation of POSS. The conductivity of poly(PHM-co-POSS) under low relative humidity (40-70 %) at 80°C was higher than that of PPHM homopolymers. The high conductivities of poly(PHM-co-POSS) under low humidity were attributed to the formation of the efficient proton conducting pathway caused by the aggregation of POSS.