Ion-conducting polymers via acid-catalyzed polyhydroxyalkylation for electrochemical devices

Abstract

The dependency of modern-day human life on synthetic polymers is becoming increasingly evident. At present, polymers are used in a broad spectrum of applications, ranging from commodity polymers in everyday plastics, to functionalized polymers in highly specialized applications. This thesis focuses on one specific application, i.e., the use of ion conducting polymers as polymer electrolyte membranes in electrochemical energy conversion and storage systems, such as fuel cells. Among many polymerization techniques, the use of acid-catalyzed polyhydroxyalkylation reaction for the synthesis of polymers that are later functionalized into ion conducting polymers is highlighted herein. In the recent years, this reaction has gained significant popularity due to its synthetic convenience, capacity for scaled-up synthesis, and inexpensive raw materials. A major advantage of this polymerization method is the assortment of monomers that can be used to produce polymers with desired chemical structures. This thesis discusses three separate projects. The first two projects are aimed at exploring different monomers to create anion conducting polymers with unique structural diversities. In order to do so, variations were carried out at the polymer backbone structure, cation distribution and side chain length. The properties of these anion conducting polymers were studied in relation to their structure, and their suitability in respect of specific requirements of anion exchange membrane fuel cells are discussed. these studies reflect the ability of this reaction to create specialized ion conducting polymers by tailoring polymer properties depending on the desired function or purpose. In the third project, the potential of a selected series of under-exploited monomers in acid-catalyzed polyhydroxyalkylation reaction were investigated. The studies were aimed at broadening the scope of the reaction and discovering environmentally friendly fluorine-free polymers. By converting the polymers into proton conducting membranes, the application of these polymers in high-temperature proton exchange membrane fuel cells was demonstrated. This study serves as a steppingstone to discovering novel polymer structures synthesized by acid-catalyzed polyhydroxyalkylation and the diverse utility of its products.