Mechanochemical Chloromethylation–Substitution Strategy for Functional Upcycling of Waste Polystyrene

Abstract Developing new strategies for upcycling polystyrene (PS) waste into functional materials is an important avenue for mitigating plastic pollution. Here, we report a ball-milling-based post-polymerization modification strategy that converts waste PS into PS derivatives with tunable functionality, molecular weight distributions, and material properties. Waste PS foam is first converted to chloromethylated PS with a tunable degree of chloromethylation, which undergoes subsequent nucleophilic substitution with thiols or amines to afford thioether- or ammonium-functionalized PS derivatives, respectively. By varying the degree of chloromethylation and the identity of the nucleophile, polymers with significantly different thermal properties and solubilities were obtained. Importantly, mechanochemical chain scission could be intentionally promoted under modified milling conditions to tune the molecular weight distribution of the products. This ball-milling strategy therefore provides a versatile approach for converting waste PS into functional polymers with properties that can be tailored through both chemical modification and chain scission.