Mono- and Dimeric Zinc(II) Complexes for PLA Production and Degradation into Methyl Lactate – A Chemical Recycling Method

A series of well-defined mono-and dimeric Zn(ii)-complexes were prepared and fully characterised by X-ray crystallography and NMR spectroscopy. Their application to the ROP of rac-LA to produce biocompatible atactic PLA was demonstrated in both solution and under industrially preferred melt conditions at 180 °C with a [rac-LA]:[Init]:[BnOH] of 3000:1:10. Exceptional activity was observed in all instances, albeit with generally poor molecular weight control (M _n) and broad dispersities (), with dimers outperforming their monomeric counterparts. The propensity of all Zn(ii)-complexes to facilitate PLA degradation into methyl lactate (Me-LA) under mild conditions is also demonstrated. Zn(2-3) ₂ were identified as the outstanding candidates, achieving full conversion to Me-LA within 8 h at 80 °C in THF. Further degradation kinetic analysis revealed Zn(2-3) ₂ to have k _app values of 0.63 ± 0.051 and 0.44 ± 0.029 h ^-1 for the rate of consumption of PLA respectively.