Waste polystyrene upcycling via the Birch reduction with ball-mill grinding.

Commodity polymer upcycling methods that transform plastic waste into new functional polymers represent an important approach to reducing the burden of plastic on the environment. Here, we report the Birch reduction of polystyrene, polystyrene derivatives, and several types of waste polystyrene using a ball-mill grinding method. In most cases, high conversions were achieved with a 1 min reaction time, yielding primarily the dearomatized skipped diene repeat unit, with minimal cross-linking and chain scission. The reaction was compatible with several polystyrene derivatives, and reductive defunctionalization was also observed for halogenated- and sulfonated-polystyrene derivatives. Importantly, high reaction performance was maintained when the reaction was applied to waste polystyrene samples on a gram scale. The reduced products could also be cross-linked via thiol-ene reactions, giving network materials with distinct properties from polystyrene. These findings highlight a promising upcycling strategy that paves the way for new functional polymeric materials from polystyrene waste.