Preparation of novel six-member sulfonated polyimide proton exchange membranes

A series of new six-member sulfonated polyimides(SPI-X) containing benzoxazole moieties were prepared by one-step high temperature polymerization method. The sulfonated degree of the SPI copolymers was controlled through adjusting the molar ratio of sulfonated diamines to the non-sulfonated diamines. The structures of monomer and polymer of SPI were characterized by FT-IR, ¹HNMR and TG-DSC. The stability, water absorption, swelling ratio and proton conductibility of SPI membranes were investigated and compared with those of the Nafion® 117 membranes. The results show that the sulfonic group decomposition temperature of SPI membranes is up to 270°C, and its swelling ratio presents obvious anisotropy. The proton conductivity of SPI-25 membrane at room temperature can reach 6.0 × 10^-3 S/cm, which is close to proton conductivity (9.8 × 10^-3 S/cm) of Nafion® 117 membrane under the same condition.