Synthesis of hyperbranched polybenzimidazoles and their membrane formation

A series of amine-terminated hyperbranched polybenzimidazoles (HBPBIs) were successfully synthesized by condensation polymerization of aromatic dicarboxylic acids and an in situ synthesized aromatic hexamine intermediate product from 1,3,5-benzenetricarboxylic acid (BTA) and 3,3′-diaminobenzidine (DAB) in polyphosphoric acid (PPA) at 190 °C for 20 h. HBPBI membranes were fabricated by solution cast method in the presence of cross-linkers (ethylene glycol diglycidyl ether (EGDE) and terephthaldehyde (TPA)). The resulting HBPBI membranes displayed good mechanical properties and good thermal stability. High proton conductivity was obtained with the phosphoric acid-doped and TPA-cross-linked HBPBI membranes at 0% relative humidity.