Synthesis and Upcycling of All-Carbon-Backbone Degradable Polyethylene with Dispersed On-Chain Ketones

The challenges of photodegradable polyolefins, which have attracted much attention, persist in achieving controlled synthesis, efficient degradation, and chemical upcycling. Here, we report an all-carbon-backbone photodegradable polyethylene (PE) incorporating on-chain ketones through coordination-insertion copolymerization of ethylene and the optimal phenyl vinyl ketone (PVK). This strategy enables precise control over the chain structure, including PVK dispersed distribution (0.3-8.3 mol%), saturated C^sp3-C^sp3 backbone, and enhanced surface properties while retaining thermomechanical properties. Crucially, this is the first report that achieves the quantitative conversion (100%) of ketone units in photodegradable PE under ambient UVA light (λ = 390-395 nm) with high efficiency. Mechanistic studies on photodegradation reveal two competitive pathways: Norrish Type II scission and Norrish-Yang cyclization (∼50% for each), yielding well-defined telechelic PE oligomers. These insights allow predictable control over molecular weight of degraded product, enabling tailored polymer design. Photodegradation coupled with in situ thiol-ene click chemistry generates hydroxyl-terminated telechelic PE oligomers, which are upcycled into PLA-PE-PLA triblock copolymers, exhibiting excellent compatibility in HDPE/PLA blends. This work bridges the gap between PE degradation and upcycling, unifying customizable synthesis, controlled degradation, and value-added upcycling into a single platform for sustainable polyolefins.