Synthesis And Catalytic Activities Of ?-Ketoiminate Zinc Complexes

Polylactide,also known as polylactic acid and abbreviated as PLA,is a biocompatible and biodegradable new material.At present,the preparation of PLA is mainly based on the ring-opening polymerization of lactide initiated by metal complex.It has been known that the polymers contain some metal residues resulting from the metal catalyst.Aluminum,tin and some other metal complexes are toxic,which limits the use of PLA in the food,medicine and other fields.Therefore,it is of great significance to develop metal catalysts with low toxicity.Zinc element is a common metal element that has a low toxicity,and PLA initiated by zinc complexes has much more application including in the medicine field,so the investigation of zinc complexes as the catalysts for the ring-opening polymerization has gained more and more attention.We have synthesized a series of ketoiminate zinc complexes by modulatingthe steric hindrance,electronic effect and chirality of the ligands,and examine their catalytic activities for the ring-opening polymerization of lactide.In this thesis,11 new mono-zinc complexes are reported,which were prepared by the reaction of N-alkyl-?-ketoiminate ligands and ZnEt2.The zinc complexes are characterized by1 H NMR,EI-HRMS and X-ray analysis.All these 11 zinc complexes show catalytic activities for the ring-opening polymerization of lactide,and the polymers are analyzed by 1H NMR and GPC.The investigation shows that complexes 2b-2f have higher activities for the ring-opening polymerization of lactide among the examined catalysts,and the monomer conversions achieve more than 90% within 1 h.The number-average molecular weight of the polylactide catalyzed by complexes 2b and 2c are over 13000 g/mol.Furthermore,the polymer catylzed by complex 2b has a narrow molecular distribution(PDI = 1.17).Complex2 c has a higher catalytic activity than that of complex 2k,and the monomer conversion is96% and 49%.