Selective, Oxygen-Tunable, and Metal-Free Functionalization of Polyethylene Through Dual-Mode Nitrosation and Carbonylation.

Polyethylene (PE), the world's most produced synthetic polymer, is highly durable but resistant to chemical modification due to its inert carboncarbon backbone. This work presents a metal-free, nitrosation process for direct CH functionalization of PE, enabling selective formation of oxime- or carbonyl-functionalized polymers. The method operates under mild visible-light conditions in solution and through thermally driven reactive extrusion, making it suitable for both laboratory and industrial applications. The key reagent, tert-butyl nitrite (t-BuONO), produces an alkoxy radical (t-BuONO•) for CH activation and a persistent nitrosyl radical (NO•) that installs ketoxime functionalities. Mechanistic studies using quantum yield determination and time-resolved transient absorption spectroscopy confirm the energy-transfer activation of t-BuONO and hydrogen atom transfer pathways. Unlike previous strategies, this approach yields pure oxime or keto-functionalized PE's without metals or pre-functionalization. Moreover, oxime groups serve as intermediates convertible into esters, ethers, or urethanes, allowing control over polymer polarity and thermomechanical properties. Together, this strategy transforms a venerable small-molecule transformation into a scalable, selective, and tunable route for the upcycling of PE, and enables a selective and sustainable route to valorize one of the world's most ubiquitous, but most recalcitrant plastics.