Synthesis, Characterization Of Tetra (Phenolate)sodium, Potassium, Magnesium, Zinc Complexes And Their Applications In The Ring-Opening Polymerization Of Lactide

Polylactic acid has excellent biodegradability,permeability,biocompatibility,and similar physical and mechanical properties as traditional petroleum-based polymers.It has attracted widespread industrial attention and been widely used in many fields due to its raw-materials availability,renewable and environmental-friendly properties.Because the resulting polymers have controlled molecular weights and narrow molecular weight distributions,using metal complexes as catalysts to catalyze?initiate?the ring-opening polymerization of lactide is the most effective method for the synthesis of polylactic acid.Sodium,potassium,magnesium,and zinc are essential components of living organisms,and notoxic?low toxic?to the human body as well as easily accessible.In this paper,a series of bulky tetraphenol ligands and their corresponding multi-nuclear sodium,potassium,magnesium and zinc complexes have been designed,synthesized and fully characterized.The catalytic performances of these multinuclear metal complexes in the ring-opening polymerization of lactide have also been systematically studied.This paper includes the following main sections:The first chapter briefly describes the application of polyester?mainly polylactic acid?,the mechanism for the ring-opening polymerization of lactide catalyzed by metal complexes,the application of sodium,potassium,magnesium,and zinc metal complexes in the ring-opening polymerization of lactide.In the second chapter,a series of bulky tetraphenolate ligands L^1-4-H₄ and their corresponding multi-nuclear sodium and potassium complexes 1-8 have been designed,synthesized and fully characterized by ¹H NMR,¹³C NMR,elemental analysis and X-ray single crystal diffraction analysis.Single crystal diffraction results show that these sodium and potassium complexes form tetranuclear stable structures.In the presence of BnOH,these complexes 1-8 efficiently catalyze the ring-opening polymerization of lactide in a controlled manner to give polymers with the theoretical molecular weight and relatively narrow molecular weight distributions.In the third chapter,a series of trinuclear magnesium and zinc complexes 9-14 based on bulky tetraphenolate ligands L^1-3-H₄ have been synthesized and fully characterized by ¹H NMR,¹³C NMR,elemental analysis and X-ray single crystal diffraction analysis.Single crystal diffraction results show that the complexes 9,13 and 14 form similar trinuclear structures and each metal centre are tetra-coordinated.One metal center is connected to two oxygen atoms ether of groups and two oxygen atoms of phenolate groups,and the other two metal centers are coordinated to three oxygen atoms of phenolate groups and the carbon atom of the alkyl group?ⁿBu/Et?.In the presence of BnOH,these complexes 9-14 exhibit good catalytic activity and controllable characteristics for the ring-opening polymerization of lactide.The obtained polymers,which molecular weights agree with the theoretical molecular weights,have narrow molecular weight distribution.