UC Berkeley

The following dissertation discusses the development of reactions that transform polyolefins, selectively cleave polyolefins, and furnish materials with circular economies to address the limitations of commodity plastics. These reactions include the synthesis of circular polymers from renewable natural sources that undergo reversible cleavage of siloxane linkages, derivatization of oxyfunctionalized polyethylenes to furnish materials of higher value with greater reuse, and incorporation of functional groups into the backbone of polyethylene to imbue new properties to the polymer and incorporate cleavable linkages for selective degradation of polyethylene. The development of transition metal-catalyzed C–H acyloxylation reactions of polyolefins will also be discussed.

Chapter 1 is an overview on the synthesis, application, and limitations of polyolefins. Strategies that could potentially overcome the limitations of polyolefins and examples of them in the literature are discussed in detail.

Chapter 2 discusses the synthesis of monomers from the hydrosilylation of plant oils to furnish polyesters, polycarbonates, polyamides, and polyurethanes with in-chain siloxane linkages that enable programmed depolymerization. Acid-catalyzed siloxane metathesis enables the depolymerization and repolymerization of select polymers at the siloxane linkages. Studies on the microbial digestion of isotopically labelled fragments after enzymatic hydrolysis of these polymers suggest that the main chain of the polymer is metabolized to carbon dioxide in soil.

Chapter 3 discusses methods to derivatize pendent ketones and alcohols of oxyfunctionalized polyethylene to incorporate esters and oximes to the backbone to generate monofunctional polyethylenes that can be accessed from waste polymers. Judiciously selected conditions highlight the challenges of performing reactions on polymers. The esters and oximes imbue the monofunctional polyethylenes with enhanced properties when compared to unmodified polyethylene. In addition, these functional groups enable recovery through removal of the functional group or selective dissolution to recover the starting polymers for reuse.

Chapter 4 discusses incorporation of in-chain amide linkages in polyethylene through Beckmann rearrangement. The resulting long-chain polyamides possess similar bulk properties as unmodified polyethylene yet have improved surface properties over unmodified polyethylene. These polyamides cannot be synthesized through step-growth or ring-opening polymerization. Hydrogenolysis of the amide linkages furnish telechelic alcohols and amines demonstrating a method to selectively cleave materials derived from polyethylene. These amine- and alcoholterminated fragments were reacted with diisocyanate linkers to furnish polyurea-urethane elastomers with valuable properties.

Chapter 5 discusses the development of nickel-catalyzed C–H acyloxylation of polymers to furnish pendent esters in one chemical step. These ester-containing polymers have enhanced properties from unmodified polyethylene and can be accessed readily from abundant base metals and peroxides.