Highly active tridentate amino-phenol zinc complexes for the catalytic ring-opening polymerization of ε-caprolactone

Tridentate 2,6-bis(imino)phenol ( L1 − L4 ) and 2,6-bis(amino)phenol ( L5 − L8 ) ligands and their corresponding zinc chloride complexes ( 1 – 8 ) have been synthesized and well characterized by FT-IR, 1 H and 13 C NMR , elemental analysis and single-crystal X-ray diffraction analysis. It was found that zinc complexes ( 1 – 4 ) with 2,6-bis(imino)phenol ligands were inactive for the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) even if they were activated by methyllithium . Zinc complexes ( 5 – 8 ) with 2,6-bis(amino)phenol ligands were proved to be highly efficient initiators for the ROP of ε-CL in combination with 4 equiv. of methyllithium. The ROP of ε-CL in the absence or presence of benzyl alcohol , including the influence of monomer ratio, reaction temperature and the substituents in the ligands, were investigated. The structure and thermal properties of obtained polymers were analyzed by NMR and MALDI-TOF mass spectra, DSC and TGA , respectively.