The sulfonated diamine, 4,4’-bis(3-aminophenoxy)biphenyl-3,3’-disulfonic acid (mBAPBDS), was successfully synthesized and characterized by FT-IR and 1H NMR spectra. A series of new sulfonated polyimides (NTDA-mBAPBDS/APBA) containing a benzoxazole structure were synthesized from mBAPBDS, [5-amine-2-(4-aminophenyl)benzo[d](1,3)oxazol] (APBA) and 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA) using a one-step high temperature polymerization method. The sulfonation degree of NTDA-mBAPBDS/APBA copolymers was controlled through varying the molar ratio of mBAPBDS to APBA. The results showed that the NTDA-mBAPBDS/APBA copolymers possessed good solubility and film processing property. TG analysis indicated that the SPI copolymers displayed good thermal stability with the decomposition temperature above 300 ℃. The SPI membranes were prepared by casting from the polymer solution, and their water uptake, swelling ratio and proton conductivity were also investigated, which displayed adequate water uptake and good dimensional stability. The proton conductivities of the SPI membranes were between 4.72×10－3～9.60×10－3 S/cm at room temperature, which was close to that of Nafion®117 membrane measured under the same condition (9.8×10－3 S/cm).

Key words: fuel cell, sulfonated polyimide, proton exchange membrane