Polyethylene with in-chain isolated ketones is an attractive target for achieving photodegradability while maintaining polyolefin material properties. This work reports a method to functionalize post-consumer polyethylene through radical C–H activation to install TEMPO functionalities and subsequent oxidation to obtain in-chain isolated ketones without compromising the polymer molecular weights. This process does not require metals, catalysts, or expensive reagents and allows tunable ketone incorporation up to 3 mol %. The thermal and mechanical properties were investigated to demonstrate that the ketone-containing polyethylene could potentially work as a photodegradable alternative of existing polyethylene. Photodegradation of the ketone-containing polyethylene reveals a clear decrease in molecular weights and suggests random installation of functionalities. This approach enables the conversion of post-consumer polyethylene into ketone functionalized materials through simple chemical transformations.