Salen complexes based on 1,4-diaminocyclohexane and their exploitation for the polymerisation of rac-lactide

In this paper we have prepared a series salen derived ligands based on a trans-1,4-diaminocyclohexane backbone. The ligands could be easily complexed to either Ti(iv) or Al(iii) metal centres generating complexes with formulae Ti2(OiPr)6(L) and Al2(Me)4(L) respectively. The complexes were shown to be efficient initiators for the ring opening polymerisation of rac-lactide. The Al(iii) complexes were more controlled than their Ti(iv) analogues, producing PLA with a moderate isotactic bias and narrow molecular weight distribution. The molecular weight of the resultant polymer, for the Al(iii) system, could be controlled by the amount of benzyl alcohol added initiator indicating that these systems show immortal behaviour.