Sulfonated block polyimide copolymers as a proton‐conductive membrane

Abstract

A series of sulfonated block copolyimide (SPI-B) ionomers were synthesized, and the effect of the block length was investigated. The new block SPI-B ionomer membranes showed chemical stability comparable to that of the random sulfonated polyimide equivalent. Among the SPI-B copolymers examined, the block/block copolymer SPI-B150/150 membrane, containing long block segments in both the hydrophilic and hydrophobic components, showed the highest proton conductivity of 2 × 10−2 S cm−1 at 48% relative humidity, which was comparable to that of a conventional perfluorinated ionomer membrane. Widespread and well-connected hydrophilic domains were confirmed by scanning transmission electron microscopy, proving the high proton-transporting properties of the SPI- B150/150 membrane. These results proved its potential availability as an electrolyte for high-temperature polymer electrolyte fuel cells.