CAS: Development of a General System for Upcycling Polyolefins through C-H Diversification

With the support of the Macromolecular, Supramolecular and Nanochemistry program in the Division of Chemistry, Professor Erik J. Alexanian of the University of North Carolina at Chapel Hill is developing chemical reagents for upcycling polyolefins through C-H bond diversification. Polyolefins are a family of polyethylene and polypropylene thermoplastics that are non-toxic, durable, heat resistant, and capable of withstanding most kinds of chemical corrosion. They are produced mainly from oil and natural gas by polymerization of ethylene and propylene, respectively. They are the most widely utilized plastics in the world, with variations of each used in numerous products, ranging from drinking straws to sophisticated laboratory instruments. By chemical structure, they are long chain hydrocarbon macromolecules consisting exclusively of C-C and C-H bonds. This project will address sustainability and recyclability of polyolefins by developing reagents that enable the selective C–H diversification of polyolefin mixtures. Essentially, through such diversification, C-H groups along the main polymer backbone will be replaced with other valuable and diverse chemical functional groups. In the long run, the approaches associated with this research have the potential to provide valuable methods for polyolefin upcycling, where post-consumer plastic waste will serve as an abundant feedstock for the synthesis of plastics with a greater economic value and a smaller environmental footprint. The UNC Chemical Education Outreach group, established by Prof. Alexanian, will involve graduate students teaching at a range of local schools, especially those with high ethnic and socioeconomic diversity. The topics will aim to draw important connections between chemistry and its impact on our lives. Additionally, “Polymer Upcycling” outreach activities through the UNC Morehead Planetarium and Science Center’s Launch Lab Makerspace will engage local K-12 learners and the public on the challenges and opportunities for building more sustainable polymer lifecycles.This project will focus on the development of novel classes of N-functionalized amides and radical traps that enable the selective C–H diversification of polyolefin mixtures and impart a range of new polymer properties. In the first objective, new classes of O-alkenylhydroxamate and N-dithiocarbonyl reagents will be developed to increase the practicality of the platform and enable scalable, site-selective polyolefin C–H diversification. The second objective will focus on utilizing these structurally optimized reagents for the selective functionalization of polyethylene/polypropylene mixtures, and mixtures with other polymers commonly found in plastic waste streams. Finally, the last objective will identify a diverse set of thiosulfonates as radical trapping reagents to introduce a range of functionality onto polyolefins in a selective manner. Direct polyolefin C–H heteroarylation will also be pursued. The tools developed with this research have the potential to enable the upcycling of polyolefins to a range of new polymers under conditions relevant to the processing of mixed plastic waste.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.