Synthesis and characterization of a phosphonated graft copolyimide for direct methanol fuel cells application

The synthesis method and characterization of novel phosphonate graft copolyimides series via 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA) were proposed. A branched polyimide structure was achieved by coupling the hydrophilic phosphonated polymide and hydrophobic polyimide with 3, 3'-diaminobenzidine. A phosphonated branched copolyimide exhibited high thermal stability, with a starting decomposition temperature in nitrogen of similar to 450 degrees C. The proton conductivity and the methanol permeability of phosphonate graft copolyimide membrane were studied. At room temperature and hydrated condition, the phosphonated membrane with highest IEC similar to 1.43 meq/g showed slightly lower proton conductivity than Nafion (R) 117, however its methanol permeability is 5 times lower than Nafion (R) 117. The decrease in methanol permeability with desirable proton conductivity could increase the feasibility of polymer electrolyte membranes for DMFC application.