Kota Kitamura

Preparation and Properties of Sulfonated or Phosphonated Polybenzimidazoles and Polybenzoxazoles

Five series of copolybenzazoles, polybenzimidazoles and polybenzoxazoles, containing sulfonic acid or phosphonic acid were prepared and their basic properties were compared, although the backbone structures were not exactly corresponding each other. The sulfonic acid-containing polybenzimidazoles showed higher thermal stability and hydrolysis resistance than the sulfonic acid-containing polybenzoxazoles. However, Proton conductivity of the sulfonic acid-containing polybenzoxazoles was superior to that of the sulfonic acid-containing polybenzimidazoles. The phosphonic acid-containing polybenzimidazoles showed similar or higher thermal stability and lower proton conductivity than the sulfonic acid-containing correspondents. The characteristics of the polybenzimidazole systems seem to be explained by the salt formation between ionic functional groups and imidazole rings.