Proton conducting membranes based on blends of PBI with aromatic polyethers containing pyridine units

Abstract

New aromatic copolymers bearing polar pyridine units in the main chain have been synthesized. Depending on the content of the pyridine monomer, soluble, high molecular weight polymers were obtained. The studied copolymers showed high thermal and oxidative stability and high T g values but moderate ability to be doped with phosphoric acid. Blends with polybenzimidazole were prepared in order to further improve the acid uptake and subsequently reach the desired conductivity values. Depending on the copolymer and blend composition, phase separated or miscible pairs were obtained as was found based on the single glass transition criterion. The thermal and oxidative stability of these blends were also tested. Even the membranes with high PBI content retained their flexibility and good mechanical properties after the treatment with H 2O 2, indicating the high oxidative stability of the system. Doping with phosphoric acid at various conditions resulted in ionically conducting membranes, with conductivity in the range of 10 −2 S/cm, a prerequisite for use of these materials in fuel cells operating above 100 °C.