Ring-opening polymerization of cyclic esters mediated by zinc complexes coordinated with benzotriazo-based imino-phenoxy ligands

A series of zinc complexes coordinated with benzotriazo-based imino-phenoxy ligands (ZnII(BTPIP)) has been developed for the mediation of ring-opening polymerization (ROP) of ε−caprolactone (ε−CL) and L−lactide (L−LA). In the presence of ZnII(BTPIP), the polymerization generated the PCL with the molecular weights in the range of 9600–17700 g mol−1 and narrow dispersity (Ð) around 1.08 to 1.33 as well as the PLA showing a molecular weight as 12300–14400 g mol−1 with narrow molecular weight distribution (Ð < 1.11). Furthermore, the living characters of the linearly increased molecular weight with monomer conversion and the synthesis of the tri-block copolymer of PEG-b-PCL-b-PLA were achieved. The substituent effect of ZnII(BTPIP) in the ROPs of ε−CL and L−LA was rationalized by the DFT calculations based on the coordination-insertion mechanism.