Sulfonated polyimides for polymer electrolyte membrane fuel cell

Two types of novel sulfonated diamines bearing sulfonic acid groups directly bonded to polyimide main chains (main-chain type) or in the side alkoxy chains (side-chain type), and the corresponding sulfonated polyimides were successfully synthesized. Water vapor sorption, proton conductivity sigma, methanol permeability P-M, membrane stability toward hot water, and size change with water uptake of the sulfonated polyimide membranes were investigated. The membranes of sulfonated polyimides prepared on the basis of the proper molecular design showed much better water stability and higher proton conductivity compared with the conventional polyimides based on 2,2'-benzidinedisulfonic acid. They also displayed the higher ratio of sigma over P-M than Nafion 117 membrane. They might have potential for polymer electrolyte fuel cell and methanol direct fuel cell applications.