Highly active Mg(ii) and Zn(ii) complexes for the ring opening polymerisation of lactide

Abstract

A range of simple ethylenediamine based Zn(II) and Mg(II) complexes have been prepared and their structures determined via NMR spectroscopy and X-ray crystallography. Preparation of these complexes was also demonstrated to be scalable, with 25 g of Zn(1)₂ being readily produced. These complexes were trialed for the ring opening polymerisation (ROP) of lactide under industrially relevant conditions. Their reactivity has been related to their structure in solution. Incredibly high activity is achieved in the majority of cases including low catalytic loading and high temperatures, under industrially relevant conditions (180 °C 10 000 : 1 : 100 [LA] : [Zn] : [BnOH]), with high conversion achieved within 10 minutes and TOFs in excess of 100 000 h⁻¹ achieved. The performance of these initiators for polymer production is supported by GPC, DSC and IR spectroscopy which all highlight the excellent control achieved.