On-Demand Nonalternating Copolymerization Enables Upcycling of Mixed Polyethylene and Nylon Plastics

The increasing accumulation of plastic waste in the environment brings about a potential danger for ecosystems and human society; mechanical recycling remains one of the most economical strategies to deal with the growing crisis of plastic pollution; however, it suffers from substantial performance deterioration when processing immiscible blends of polyethylene and nylon plastics. Here, we report on-demand nonalternating copolymerization of ethylene with carbon monoxide (CO) via a facile tandem gas compensation strategy, which achieves a precision control over carbonyl incorporation with uniform distribution across a broad range (0-50%). Such a synthetic advance offers a unique multiblock structure having short polar segments ((CH₂-CH₂)_n-CO-) (n < 4) and extended nonpolar methylene sequences (n > 4). Remarkably, the resulting quasi-multiblock copolymer (q-MBCP) delivers a robust compatibilization for polyethylene and nylon blends, thus transforming brittle materials into mechanically tough composites. This work elucidates the mechanistic evolution between nonpolar polyethylene and polar alternating polyketone phases, while offering a practical and sustainable solution to advance closed-loop recycling of mixed plastic waste.