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

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-Ph 2 CH-C 6 H 2 -4-Me) 2 (THF) 2 ; Mg2 : Mg(O-2,6-Ph 2 CH-C 6 H 2 -4-OMe) 2 (THF) 2 ; Mg3 : Mg(O-2-Ph 2 CH-C 6 H 2 -4,6- t Bu 2 ) 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.