Intrinsically proton conducting polymers and copolymers containing benzimidazole moieties: Glass transition effects

Proton conducting polymers and copolymers containing tethered benzimidazole moieties spanning a wide range of glass transition temperatures (2–113 °C) have been prepared. Conductivity versus temperature plots of the homopolymers display the competing effects of mobility and charge carrier density. Consistent with literature reports, T g values of benzimidazole-containing polymers increased over the parent polymer, however, successful reduction of T g was accomplished by copolymerizing a benzimidazole functional acrylate monomer (B5A) with poly(ethylene glycol) methyl ether acrylate (PEGMEA). The reduction in T g is thought to occur through disruption of intermolecular forces between benzimidazole units. Evaluation of conductivity as a function of temperature by ac impedance methods indicate that decreasing T g through copolymerization results in conductivity increases over the low and intermediate temperature range (40–160 °C). Copolymer T g decreases with increasing PEGMEA content, and conductivity at 40 °C can be increased by nearly 2.5 orders of magnitude over B5A homopolymer. However, conductivity at high temperatures (> 160 °C) decreases due to charge carrier dilution by the addition of PEGMEA.