High Proton Conductive Sulfonated Graph Copolyimide Membranes Containing Chemically Stable Naphthalene Moieties

Abstract

Syntheses, proton conductivity, gas permeability properties, and membrane stabilities of novel sulfonated graft copolyimides were investigated. The sulfonated graft copolyimide membrane showed significantly high proton conductivity (0.96 S/cm at 90°C and 98%RH, more than 6 times that of Nafion), suggesting that the protons in the sulfonated graft copolyimide membranes were efficiently transported. The oxidative stability of the novel sulfonated graft copolyimide was higher than that of the conventional graft copolyimide because of their polymer structures containing chemically stable naphthalene moieties and non–sulfonated polymer main–chain. Furthermore, the oxygen permeability of the membrane was approximately one–fourth the value of Nafion and had a very excellent gas barrier property. We demonstrated that the graft copolymer membrane could realize high proton conductivity and low gas permeability to have potential applications for use in fuel cells.