Iron(III)-Catalyzed C─H Hydroxylation of Low-Density Polyethylene Coupled with Short Chain Branching Growth

Abstract

Low-density polyethylene (LDPE) is widely used in packaging applications, but after being discarded its environmental impact is a pressing concern due to a lack of effective chemical recycling strategies, especially owing to its chemical inertness and nonpolar nature. To address these challenges, we present a mild iron(III)-catalyzed oxidative upcycling of LDPE in which C─H hydroxylation of LDPE occurs coupled with the growth of methyl short chain branching (Me-SCB) and ethyl shortchain branching (Et-SCB). As a result, the resulting products achieve significant improvements in surface wettability, crystallinity, and mechanical properties despite a concomitant reduction in molecular weight. CH…F interactions and σ–π interactions are found between LDPE and the catalyst. Density functional theory (DFT) calculations elucidate the catalytic mechanism that fluorine on the ligand facilitates hydrogen peroxide activation and subsequent deprotonation, leading to the formation of high-valent ironoxo species. The growth of short-chain branching (SCB) involves the β-scission of CC bonds and a radical-mediated chain-walking mechanism. This work represents a transformative advancement in deep understanding of polyolefin upcycling and opens a new approach of polyolefin functionalization and architecture modulation.