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

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.