Hydroxy polybenzimidazoles for high temperature fuel cells and the solution polymerization of polybenzimidazole.

摘要

In this dissertation, two different hompolymers of polybenzimidazole (PBI) containing hydroxyl functional units were synthesized via the PPA Process to produce gel membranes. These polymers and their phosphoric acid doped membranes were characterized to further explore structure-property relationships in functionalized PBI's. Fuel cell performance of the doped membranes was evaluated and compared to previously reported PBI membrane chemistries. Copolymers of p-OH PBI and para-PBI were prepared at five different copolymer compositions to examine the effects of hydroxy content on membrane properties and compared to the respective homopolymers. The reactivity of the hydroxy groups and the formation of phosphate bridges were important in the final properties of the doped membranes.;A new method for producing high inherent viscosity (IV) PBI directly in organic solution was studied. Initially, small molecule studies were performed in order to find appropriate chemical functionalities that allow for the formation of benzimidazole in dimethyl acetamide (DMAc). Once appropriate chemical functionalities were identified, polymerization studies were conducted to determine the critical variables for the synthesis of high molecular weight polymers. Insights on the mechanism of polymerization and complete benzimidazole ring closure were important for developing a method to produce PBI at high molecular weight and at high polymer concentrations that are relevant for the processing of films, coatings and fibers. Finally the synthesis of PBI analogs containing an ether linkage was explored. These polymers were synthesized via the new solution polymerization method to demonstrate the utility of the method for different monomer and polymer structures. Thermal studies were performed on the ether-PBI analogs to understand the effect of the ether linkage on the potential processability of polymers.