Immortal Ring Opening Polymerization of ε-caprolactone and rac-lactide by magnesium precatalysts bearing sterically congested phenoxide ligands

Abstract

This report describes the synthesis of a series of magnesium complexes bearing sterically congested phenoxide ligands and their catalytic performances in initiating immortal Ring Opening Polymerization of ε-caprolactone and rac-lactide. The magnesium complexes Mg1-Mg3 were obtained in high yields, by treating bulky phenoxide ligands with half equivalents of Mg(n-Bu)2 in THF (Mg1: Mg(O-2,6-Ph2CH-C6H2-4-Me)2(THF)2; Mg2: Mg(O-2,6-Ph2CH-C6H2-4-OMe)2(THF)2; Mg3: Mg(O-2-Ph2CH-C6H2-4,6-tBu2)2(THF)2), and well-characterized by NMR spectrum analysis. The molecular structures of Mg2, Mg3 were further determined by single crystal X-ray diffractions. In combination with excess of benzhydrol, these complexes could catalyze immortal Ring Opening Polymerization (ROP) of ε-caprolactone and rac-lactide, and benzhydrol served as co-initiator and chain transfer agents simultaneously, which afforded polymer esters with well-controlled molecular weights and narrow molecular weight distributions. End-functionalized polyester could be also accessed if functionalized benzhydrols were employed as chain transfer agents.