Editing of Polyester and Polyurethane Backbones via [3,3]-Sigmatropic Rearrangements

Modern technological progress and increasing environmental pollution have simultaneously been driven by the discovery and use of polymers. Polymer backbones—the core of a polymer which dictates both lifecycle and functionality—have played a major role in both aforementioned areas. The ability to edit polymer backbone chemical composition through post-polymerization modification is a fundamental scientific challenge with the potential to transform polymer function and further sustainability efforts. Yet, most existing post-polymerization modification techniques for upcycling and chemical modification have focused on the polymer periphery, leaving the polymer backbone untouched. Even amidst efforts to edit polymer backbones, the use of sigmatropic rearrangements—concerted processes that involve migration of a σ-bond—have barely been studied via computational methods and have not been experimentally realized. Herein, the use of [3,3]-sigmatropic rearrangements has been demonstrated as a scission-free method of transforming polyester and polyurethane backbones. In Chapter 1, the existing scope of work in polymer backbone editing is examined. First, polymer backbone and polymer backbone editing are defined, followed by discussion of all elementary polymer backbone edits—insertion/deletion, cyclization/de-cyclization, and rearrangement. Existing precedents for application of sigmatropic rearrangements for post-polymerization modification is also discussed. In Chapter 2, polyesters containing pendant vinyl groups were found to undergo nearly quantitative, scission-free modification to vinyl polymers resembling commodity materials via the Ireland-Claisen rearrangement. Dramatic changes in thermal stability and glass transition temperature are observed post-transformation. In Chapter 3, branched polyesters and polyurethanes containing pendant vinyl groups were found to undergo transformation to their linear counterparts via palladium(II)-catalyzed [3,3]-sigmatropic oxo-rearrangements. The effects on material properties were subtle for polyesters, however more dramatic changes were observed for polyurethanes. Incorporation of alkenes into the polymer backbone through this [3,3]-sigmatropic oxo-rearrangement enables deconstruction via ethenolysis. Ultimately, the utility of [3,3]-sigmatropic rearrangements for polymer backbone editing in both polyesters and polyurethanes was demonstrated to afford previously inaccessible materials by non-traditional methods with tunable physical and chemical properties.