Accelerated Mechanochemical Depolymerization of Poly(styrene) Due To Formation of a Cohesive State.

Mechanochemical depolymerization in a ball mill can be used to convert poly(styrene) (PS) into monomeric styrene under milder conditions than thermal depolymerization. Continuous sampling of product flows shows that the rate of styrene formation increases significantly when PS powder is converted into a cohesive state, a viscous, continuous material phase that tends to coat the grinding spheres, once the temperature of the grinding surfaces approaches the PS glass transition temperature (~100°C). This enhancement is attributed to intensified mechanical shear stresses that generate favorable reaction environments for depropagation of chain-end radicals in the bulk of the cohesive state. The faster depropagation steps also increase the selectivity of styrene relative to byproducts, such as methane, benzene, toluene, and ethylbenzene.