A Highly Efficient Catalyst for the “Living” and “Immortal” Polymerization of ε-Caprolactone and l-Lactide

A novel ligand, 2,2‘-methylenebis(4,6-di(1-methyl-1-phenylethyl)phenol) (MMPEP-H2) (1), has been prepared by the reaction of 2,4-bis(α,α-dimethylbenzyl)phenol with formaldehyde in the presence of a catalytic amount of benzenesulfonic acid. Further reaction of compound 1 with Me3Al in diethyl ether produces a four-coordinated monomeric aluminum complex [(MMPEP)AlMe(OEt2)] (2). [(MMPEP)Al(μ-OBn)]2 (3) can then be synthesized from the reaction of 2 with 1 molar equiv of benzyl alcohol at ambient temperature. 3 has demonstrated highly efficient catalytic activities in the ROP of e-caprolactone and the ROP of l-lactide. The “living” character of complex 3 enable us to prepare PCL-b-PLA copolymer, and the “immortal” character of 3 has paved a way to synthesize as much as 160-fold polymer chains of poly(caprolactone) with very narrow PDI in the presence of a small amount of initiator.