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 (Tc>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. Polyesters and polycarbonates are depolymerized using the combination of zinc dichloride and polyethylene glycol as a catalyst under reactive distillation conditions carried out at temperatures significantly below the ceiling temperature of the polymers evaluated. Selective polyester depolymerization occurred in the presence of other polymer classes, thereby demonstrating the promise for using the chemistry for the chemical recycling of plastics.