Explorations into the Synthesis and Reactivity of Polynorbornene Frameworks

Thesis (Ph.D.)--University of Washington, 2019Polynorbornenes are a highly versatile polymer that allows for much modification of the side chains and multiple methods for polymerization. Chapter 1 introduces our unique photoredox mediated ring-opening metathesis polymerization (photo-ROMP) technique for ring-opening metathesis polymerizations (ROMP) that utilizes an organic redox mediator and a vinyl ether initiator, in contrast to metal-based initiators traditionally used in ROMP. The reversibility of the redox-mediated initiation and propagation steps enable spatiotemporal control over the polymerization. In Chapter 2, we explore control over polynorbornene molecular weights using alpha olefins as chain transfer agents, allowing the initiator to be recycled to reduce costs and access low molecular weight oligomers. Molecular weights between 30 kDa and 1 kDa can be targeted simply through altering the stoichiometry of the reaction. Chapter 3 details our work on the development of a continuous flow reactor for large scale synthesis of photo-ROMP polymers. In Chapter 4, we report the discovery of a mechanochemical method to produce ROMP polynorbornene (ROMP-PNB) from vinyl-addition polynorbornene (VA-PNB). VA-PNBs with three different side chains were found to undergo ring-opening olefination upon sonication in dilute solutions. The sonicated polymers exhibited spectroscopic signatures consistent with conversion of the bicyclic norbornane repeat units into ROMP-PNB. In Chapter 5, we investigated the reversible hetero-Diels–Alder reaction of 1,2-oxazines derived from a peralkylcyclopentadiene and a series of nitrosocarbonyl dienophiles. The nature of the dienophile was found to impart broad tunability to the dynamic character of the oxazine adducts. The reversibility was also observed in polymeric systems of a ROMP-PNB framework. The fidelity of the reaction and tunable sensitivity toward elevated temperature and water signify potential applications in the development of dynamic covalent materials or delivery systems for small molecule payloads