Mn(III)/Alkali-Metal(I) III )/Alkali-Metal( I ) Heterodinuclear Catalysts for the Ring-opening Polymerization of Lactide and ε-Caprolactone

A series of large-ring metal coordination catalysts with manganese(III) as the axial ligand and alkali metal(I) as the core were synthesized in this experiment, and their structures were characterized in detail by matrix assisted laser desorption time-of-flight mass spectrometer (MALDI-TOF-MS) and elemental analysis. These catalysts can catalyze the polymerization of propylene glycolide (LA) and epsilon-caprolactone (epsilon-CL) in the presence of cyclohexane oxide (CHO). We screened and optimized different alkali metal ions to ensure the best polymerization performance. The experimental results show that the introduction of alkali metal centers significantly improves the performance of the catalysts, far exceeding that of mononuclear Schiff base manganese catalysts. The steric hindrance effect of the amine bridge moiety of the catalyst on the reaction activity is also significant. We investigated the stereo-selectivity of the catalysts for monomers and conducted copolymerization studies using different LA isomers, finding that this catalyst is more prone to obtaining polymers with isotactic tendencies. The polymerization mechanism was further analyzed by using MALDI-TOF-MS spectrometer to analyze the end groups of the obtained PLA and assist in the study of the polymerization mechanism. Experimental studies show that the stereo-selectivity of the polymerization is achieved through a chain-end control mechanism.