Date of Award

Spring 2023

Document Type

Open Access Dissertation

Department

Chemistry and Biochemistry

First Advisor

Brian C. Benicewicz

Abstract

Polybenzimidazoles (PBI) are heterocyclic polymers that possess high thermal and oxidative stability. The inherent strength and chemical and thermal stability of PBI make it ideal for use in extreme environments; however, the current processing of PBI molded parts makes the process practically and economically unfavorable. These intrinsic properties make PBIs of particular interest for many industrial applications, varying from fabrics to membrane materials to molded parts. Processing these molded parts is extremely difficult, as the high glass transition temperature and extremely high melting point (>500°C) of PBI result in poor flow properties of PBI resins even at high temperatures. One approach to improve the processability of PBI resins would be to lower the Tg of the polymers by preparing lower molecular weight oligomers. However, the enhanced mechanical, chemical, and thermal properties of PBIs are directly related to higher molecular weights. Thus, to increase processability and maintain good mechanical properties, lower molecular weight oligomers with reactive end-groups were prepared that showed improved processability and then subsequently crosslinked to increase mechanical strength. Easily processable PBI resins with reactive oligomers were synthesized, characterized, and tested in molding studies.

As renewable energy sources such as wind and solar power become more prevalent and in demand, large scale energy storage is a key technology needed to compete with traditional power sources like coal and natural gas. Vanadium redox flow batteries

(VRFBs) are long lasting and scalable, which makes them suitable for large-scale utility applications. VRFBs harness chemical energy by utilizing the many oxidation states of vanadium and converts it to electrical energy. A crucial element in VRBs is the ion exchange membrane (IEM) which is responsible for transferring ions from the anode to cathode, as well as for preventing cross mixing of the positive and negative electrolytes. Polybenzimidazoles are currently being investigated for IEMs because of their high conductivity and chemical stability; however, improvements in vanadium permeability are critical for real world applications. A membrane with high proton conductivity and chemical and thermal stability, combined with low vanadium ion permeability, could lead to broad applications in energy storage devices. The synthesis and application of reactive end group oligomers, crosslinking chemistry, and post modifications to enhance PBI membranes will be described.

Rights

© 2023, Caroline Marie Rohlfing

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