Ring-opening polymerization of cyclic esters with lithium amine-bis(phenolate) complexes

摘要

Lithium compounds of tetradentate amino-bis(phenolato)-tetrahydrofuranyl ligands, Li_2L1 (1) and Li_2L2 (2) (where L1 = 2-tetrahydrofuranyl-N,N-bis(2-methylene-4-methyl-6-tert-butylphenolate), and L2 = 2-tetrahydrofuranyl-N,N-bis(2-methylene-4,6-tert-butylphenolate)) were characterized by multinuclear solution NMR and solid-state ~6Li and ~7Li NMR spectroscopy. The proligands, n-propylamino-N,N-bis(2- methylene-4-methyl-6-tert-butylphenol), (H_2L3) and benzylamino-N,N-bis(2-methylene-4,6-di-tert-amylphenol), H_2L4 were reacted with n-butyllithium in THF to give the related dilithium compounds Li_2L3 (4) and Li_2L4 (5), respectively. The pyridine adduct of 1, (py)_2Li_2L1 (3) and complexes 4 and 5 have been structurally characterized by single-crystal X-ray diffraction and NMR spectroscopy. The reactivity of these complexes for the ring-opening polymerization of rac-lactide, as well as the influences of monomer concentration, monomer/Li molar ratio, polymerization temperature and time, were studied.