Guanidine Carboxy Zinc Complexes for the Chemical Recycling of Renewable Polyesters

Our previously published non-toxic guanidine carboxy Zn catalysts, suitable for lactide ring opening polymerisation (ROP) under industrially preferred melt conditions, have been tested towards the alcoholysis of renewable polyesters. A structure-reactivity relationship has been found for the methanolysis of PLA in anhydrous THF, dependent on the substituents introduced at the ligand backbone. Using the unsubstituted "TMGasme" catalyst C2, a polyester conversion of 41 % was reached after 5 h at 60 °C. Introducing an electron density donating -NMe₂ group at the ligand (C3) caused and increase in catalyst activity, resulting in a PLA conversion of 72 %. Hence, C3 was further tested, stressing the industrial applicability of PLA chemical recycling. Catalyst recycling, process scale up as well as solvent free alcoholysis, with full degradation in the PLA melt after 1 h, were demonstrated, allowing for the implementation of a circular (bio)plastics economy promoted by these catalysts.