[(Salen*)Co(OAc)] as a robust initiator for the immortal bulk ring-opening (co)polymerization of l-lactide and ε-caprolactone

Abstract

The easily accessible and robust [(Salen*)Co^III(OAc)] complex (1) was applied as a unimolecular initiator and moderator for the bulk ring-opening polymerization (ROP) of ε-caprolactone (CL) and bio-based L-lactide (LLA), producing the corresponding biodegradable polyesters, polycaprolactone (PCL) and poly(L-lactide) (PLLA), with relatively good control. The high tolerance of the cobalt(III) complex 1 towards protic additives, such as alcohols, allowed performing the polymerization reactions under immortal conditions, using methanol or benzyl alcohol as transfer agents. Such an approach allows using catalytic amounts of metal (vs. polymer chains) and fine tuning both the polyester chain length (monomer/alcohol ratio) and the nature of the chain end (alcohol). Taking advantage of the living character of the ROP process mediated by complex 1, a well-defined PCL-b-PLLA copolymer could be synthesized in bulk under immortal conditions.