Versatile catalytic systems based on complexes of zinc, magnesium and calcium supported by a bulky bis(morpholinomethyl)phenoxy ligand for the large-scale immortal ring-opening polymerisation of cyclic esters

A new heteroleptic ethyl-zinc complex stabilized by a chelating bis(morpholinomethyl) phenoxy ligand has been synthesised and shown to be a highly potent initiator for the immortal ring-opening polymerisation (ROP) of lactide and beta-butyrolactone, being able to convert up to 50 000 equiv. of monomer in the presence of up to 1000 equiv. of an alcohol as transfer agent. Two related heteroleptic complexes of magnesium and calcium have also been prepared. These complexes are stable in solution, even in the presence of large amounts of alcohol, and constitute effective catalysts for the immortal ROP of lactide under mild conditions.