From Polyethylene to Conjugated Polyenes: a Mechanochemical One‐Pot Upcycling Strategy for Selective Functionalization

Abstract Upcycling strategies for polyolefins remain a significant challenge due to their chemical inertness and complex degradation pathways. A solvent‐free, mechanochemical approach is reported to introduce conjugated polyene sequences into polyethylene (PE) via a twin‐screw extrusion process. The controlled iodination/elimination strategy enables the stereoselective formation of cis‐transoid polyenes, a configuration typically achieved under cryogenic conditions but here accessible at high temperatures (106 °C) in a melt‐processing environment. This novel approach is confirmed through spectroscopic characterization, including ATR‐FTIR, Raman, and CP‐MAS ¹³C NMR, and a Diels–Alder reaction that verified the stereochemistry of the resulting polyene. The polymer shows remarkable oxidative stability, with no degradation observed even after six months under ambient conditions. The unsaturated fragments within the polymer exhibit distinct reactivity, allowing selective post‐functionalization via epoxidation under reactive extrusion conditions. Mechanochemical epoxidation with m‐chloroperoxybenzoic acid (mCPBA) improves solubility and processability without chain fragmentation, as evidenced by SEC analysis. This work presents a scalable route for the selective functionalization of polyolefins, opening new avenues for their valorization into advanced materials and demonstrating the feasibility of high‐temperature processing for the formation of conjugated polyenes.