Probing the catalytic degradation of unsaturated polyolefin materials via Fe‐based Lewis acids‐initiated carbonyl‐olefin metathesis

Abstract

Degradation and recyclability of polymeric materials including extensively used polyolefins is becoming increasingly necessary. Chemically stable saturated polyolefin backbones make their degradation frustratedly challenging. The current effective strategy is to create cleavable defects e.g. C=C double bonds along the backbone, subsequently depolymerize them via cross‐metathesis reaction with olefins. High‐value chemicals or reusable polymeric segments are obtained. This two‐step protocol provides operable means for alleviating plastics problems. There are several approaches to introduce unsaturation into polymer backbone like dehydrogenation or copolymerization of olefins and conjugated dienes. However, for the second step to conduct cross‐metathesis reaction, only noble metal catalysts can be used in most time. Regardless of their limited availability, that these organometallics are unfavorably sensitive to impurities would raise barriers in industrial practices. Herein we employed earth‐abundant and inexpensive iron‐based Lewis acids to initiate carbonyl‐olefin metathesis reaction between ketone/aldehyde reagents and unsaturated polyolefins. After explorations in poly(diene)s and industrial thermoplastic elastomers, we extended this protocol to degrade low‐density polyethylene (LDPE). Low‐molecular weight PE wax‐like products were obtained as useful chemicals. This catalytic degradation system is expected to enable the development of more efficient metathesis strategies to promote degradation of polyolefins and pave sustainable ways for reuse of polymeric materials.