Aluminium salalen complexes based on 1,2-diaminocyclohexane and their exploitation for the polymerisation of rac-lactide

In this paper nine various salalen ligands have been prepared and characterised. The steric and electronic effects of both the salen and salan fragments have been varied in a systematic fashion to ascertain how this affects the selectivity for the ROP of rac-lactide. These were complexed to AlMe3 to generate pseudo trigonal bypyramidal metal centred complexes. Upon addition of benzyl alcohol the active initiator can be easily prepared. The complexes were screened for the ROP of rac-lactide in solution and melt conditions. PLA with narrow molecular weight distributions (PDIs range from 1.07-1.67) could be isolated with moderate degrees of tacticity. Significantly it was found that chloro groups on the imine fragment increased the degree of heterotactic enchainment in the polymer. The kinetics for one series of salalen-Al complexes was also investigated.