A Simple, Selective, and General Catalyst for Ring Closing Depolymerization of Polyesters and Polycarbonates for Chemical Recycling

The ability to efficiently and selectively process mixed polymer waste is important to address the growing plastic waste problem. Herein, we report that the combination of ZnCl₂ and an additive amount of poly(ethylene glycol) under vacuum can readily and selectively depolymerize polyesters and polycarbonates with high ceiling temperatures (T_c>200 °C) back to their constitute monomers. Mechanistic experiments implicate a random chain scission mechanism and a catalyst structure containing one equivalent of ZnCl₂ per ethylene glycol repeat unit in the poly(ethylene glycol). In addition to being general for a wide variety of polyesters and polycarbonates, the catalyst system could selectively depolymerize a polyester in the presence of other commodity plastics, demonstrating how reactive distillation using the ZnCl₂/PEG600 catalyst system can be used to separate mixed plastic waste.