SUMMARY
A new synthesis route of phosphonated multiblock, branched copolyimide is proposed in this research. The synthesis and characterization of the series of new phosphonated graft copolyimides were prepared by combination of one-step high temperature polymerization and phosphonation method by lithiation and reaction with excess diethylchlorophosphate. The phosphonate ester product was converted to the phosphonic acid by hydrolysis. A branched polyimide structure was achieved by coupling the two polyimides with 3, 3'-diaminobenzidine. A phosphonated branched copolyimide with 32% mol phosphonation exhibited high thermal stability, with a decomposition temperature in nitrogen of ~475°C. Proton exchange membranes prepared from these copolyimides had proton conductivity of 0.02 - 0.03 S/cm at 100% humidity over a temperature range of 40 - 100°C.