Mono- and dimeric zinc() complexes for PLA production and degradation into methyl lactate - a chemical recycling method

• Published in: Polymer chemistry 2020-04, Vol.11 (13), p.2381-2389
• Main Authors: Payne, Jack, McKeown, Paul, Mahon, Mary F, Emanuelsson, Emma A. C, Jones, Matthew D
• Format: Article
• Language: English
• Subjects: Biocompatibility; Crystallography; Degradation; Dimers; NMR spectroscopy; Polymer chemistry; Spectrum analysis; Zinc compounds
• ISSN: 1759-9954; 1759-9962
• DOI: 10.1039/d0py00192a

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. A series of well-defined mono- and dimeric Zn( ii )-complexes were prepared and fully characterised by X-ray crystallography and NMR spectroscopy.