Catalysts for the ring-opening polymerization of ε-caprolactone and l-lactide and the mechanistic study

Two novel magnesium aryloxides have been prepared and their catalytic activities toward ring-opening polymerization (ROP) of ε-caprolactone and l-lactide have been investigated. The reaction of 2,2′-(2-methoxybenzylidene)-bis(4,6-di(1-methyl-1-phenylethyl)phenol) (MEMPEP-H2) (1) and 2,2′-methylene-bis(4,6-di(1-methyl-1-phenylethyl)phenol) (MMPEP-H2) with nBu2Mg yield dimeric magnesium complexes [Mg(μ-MEMPEP)(THF)]2 (2) and [Mg(μ-MMPEP)(THF)]2 (3), respectively. Catalytic studies of complexes 2 and 3 illustrate that both 2 and 3 are good catalysts in ε-caprolactone and l-lactide polymerization. Theoretical study of the ROP mechanism of ε-caprolactone catalyzed by 2 demonstrates that the initiator, benzyl alcohol, is activated by the formation of a hydrogen bond with the phenoxy oxygen of MEMPEP2− ligand.