Polylactide (PLA) is a bio-derived aliphatic polyester targeted for applications spanning commodity plastics to biomedical materials. It is best prepared by the ring-opening polymerization of lactide, a process that is initiated by various metal complexes. Stereoselective initiators are of particular interest as the tacticity of the resulting PLA controls its chemical-physical properties, such as its melting temperature or degradation rate. Aluminium salen initiators are widely reported as highly iso-selective initiators for the ring-opening polymerisation (ROP) of rac-lactide. Recently, the potential for phosphasalen complexes of Group 3 or lanthanide metals was demonstrated as a means to combine both high activity and moderate/high iso-selectivity. This presentation will describe the synthesis and characterisation of novel mixed phosphasalen/salen hybrid ligands and their coordination chemistry with Al(III) and In(III) metal centres. The analogous metal salen and phosphasalen complexes were also synthesised and characterised. The series of complexes are compared as initiators in the ring-opening polymerisation (ROP) of rac-lactide. They all show well-controlled polymerizations, with predictable polymer molecular weights and narrow dispersities. The hybrid initiators show higher polymerisation rates and iso-selectivity values than the salen or phosphasalen metal counterparts. Multinuclear NMR studies and single crystal X-ray diffraction data are used to characterize the complexes and allow insights into the basis for the stereoselectivity.

Asymmetric hybrid salen/phosphasalen initiators for the iso-selective ring-opening polymerisation of rac-lactide

253rd National Meeting (2017)

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