Closed Loop Recycling of High T_c Biodegradable Polymers by Reactive Distillation

A closed loop cycle for polymer production and disposal is needed to handle the estimated half a billion metric tons a year of polymer that will be used by 2050. Current methods for polymer recycling are insufficient to meet this need. Herein, we disclose a simple and inexpensive catalyst system that can readily and selectively depolymerize polyesters and polycarbonates with high ceiling temperatures (T_c > 200 °C) back to their constituent monomers. Quantitative recovery of the depolymerized monomer was demonstrated for a variety of aliphatic polyesters and polycarbonates, including the stereo-retentive depolymerization of poly(lactic acid) and the depolymerization of polyethylene-like poly(pentadecalactone). The catalyst was readily recyclable for multiple depolymerization batches using the same distillation apparatus, making the method readily adaptable to continuous feed distillations. The catalyst is also capable of carrying out selective depolymerization from a mixture of post-consumer polymers. Finally, monomer recovered from the reactive distillation reactions can be used without further purification to reform the polymer, closing the loop for polymer recycling.