Synthesis and characterization of sulfonated polyimides derived from 2,2′-bis(4-sulfophenyl)-4,4′-oxydianiline as polymer electrolyte membranes for fuel cell applications

A novel sulfonated diamine bearing aromatic sulfophenyl pendant groups, named as, 2,2′-bis(4-sulfophenyl)-4,4′-oxydianiline (SPhODA) was synthesized. Sulfonated (co)polyimides (SPIs) with flexible ether linkage in the main chain and sulfophenyl groups in the side chain were synthesized from SPhODA, 1,4,5,8-naphthalene tetracarboxylic dianhydride and nonsulfonated diamines. The SPI membranes showed good solubility in common aprotic solvents and high desulfonation temperature of 320 °C. The SPIs with ion exchange capacities of 1.57-2.50 meq g−1 displayed reasonably high proton conductivities of 0.09-0.21 S cm−1 at 60 °C in water and 0.02-0.05 S cm−1 at 70% relative humidity. They also displayed high mechanical properties, but their water stability was not enough high at high temperatures. They showed high potential for DMFC application at low and/or mediate temperatures.