Low-Temperature Thermal Depolymerization of Polymethacrylates

Abstract

The chemical recycling of poly(methyl methacrylate) (PMMA) typically requires energy-intensive pyrolysis (>450 °C) or specialized photochemical setups restricted by light penetration depth. Herein, we report a purely thermal, low-temperature strategy that drives the efficient depolymerization of native, unaltered PMMA at 170 °C using commercially accessible peroxides. By maintaining a low steady-state radical concentration, oligomer formation can be fully eliminated, resulting in >95% of regenerated monomer under judiciously optimized conditions. Mechanistic studies and vapor-trapping experiments implicate a dual-activation pathway, where alkoxy radicals work alongside highly reactive chlorine radicals that undergo efficient hydrogen atom transfer with the polymer backbone, resulting in chain scission and subsequent depropagation to monomer. The full omission of chlorinated solvents could also be achieved, albeit at slightly higher temperatures. Notably, the real-world utility of this system is demonstrated by the direct depolymerization of commercial Plexiglas, despite the presence of comonomers, pigments, and additives.