Synthesis Of Novel Zinc Complexes And Their Catalysis In The Ring-opening Polymerization Of ?-caprolactone

As an important biodegradable polymer,polycaprolactone(PCL)is widely used in packaging,medicine and other fields.The efficient route to synthesize PCL is the metal-catalyzed ring-opening polymerization(ROP)of?-caprolactone(?-CL),which follows the coordination-insertion mechanism.Due to its low toxicity,environmental friendliness and excellent biocompatibility,zinc complexes have been becoming more and more attractive as catalysts in the ring-opening polymerization(ROP)of cyclic esters.In this dissertation,we aim to design and synthesize stable and efficient zinc complex catalysts for ROP of?-caprolactone.Firstly,based on the framework of Schiff base(half-salphen),by adjusting the electronic effect of substituents on salicylaldehyde part and the relative amount of zinc salt to substituted salicylaldehyde in the synthesis of zinc complex,we obtained one type of single-site zinc complexes L₂Zn and two types of bimetallic zinc complexes(LZnCl)₂ and LZn₂(OAc)₃.All zinc compounds were characterized by single crystal X-ray diffraction,¹H NMR,¹³C NMR,FT-IR and elementary analysis.The results of characterization showed that zinc centers in these complexes take penta-coordination.For bimetallic zinc complexes,two zinc centers are bridged by phenoxide.Specifically,for LZn₂(OAc)₃,the acetate anion takes bidental coordination mode.Then,the activity of all three types of zinc complexes were tested in catalyzing the ring-opening polymerization of?-CL under two different initiator systems.The single initiator system uses Bn OH as the initiator,while Li Me/Bn OH are used as the initiator in the co-initiator system.The results showed that in the presence of Bn OH,only LZn₂(OAc)₃ complexes showed low activity.In the presence of co-initiator Bn OH/Li Me,all zinc complexes showed high catalytic activity.(LZnCl)₂ and LZn₂(OAc)₃ can catalyze the ROP of?-CL within 2 mins at room temperature.The molecular weight can reach up to M_n,GPC=14182 g/mol and the PDI=1.41.The polymer produced by LZn₂(OAc)₃/Li Me/Bn OH system has relatively higher molecular weight.We think LZn₂(OAc)₃can act as an appropriate system to search for more active zinc catalyst.The synthesis route of zinc complexes in this dissertation avoids the use of air-sensitive zinc reagents like Et₂Zn and expensive Zn(N(Si Me₃)₂)_2,so it is mild,simple and highly efficient.The obtained zinc complexes show good catalytic activity towards ROP of?-CL in a relatively mild condition.