Sulfonated block-graft copolyimide for high proton conductive and low gas permeable polymer electrolyte membrane

► A series of sulfonated block and/or graft polyimides were synthesized. ► The S-bg-PI membrane showed higher proton conductivity than Nafion and other SPI membranes. ► Oxygen permeability of the S-bg-PI membrane was much lower than those of other membranes. ► The novel S-bg-PI membrane with excellent properties is expected for fuel cell applications.