The Catalytic Performances Of Quinolinyl Zinc Complexes And Organic Derivatives For ?-Caprolactone And Rac-Lactide

Today,human life without plastics and synthetic organic polymers,seems unimaginable.In fact,polymers are used extensively in almost all industries,such as medical and construction sectors.However,these products bring great convenience to human beings,and also cause environmental pollution due to their non-degradable problems.Therefore,development of environmentally-friendly biodegradable polymer materials to replace petroleum-based polymers is a major issue nowadays.Biodegradable materials are widely used in medical,biological and architectural fields due to their degradability and reproducibility.It has been found that metal-catalyzed ring-opening polymerization(ROP)is the most effective method for the synthesis of biodegradable materials,especially polycaprolactone(PCL)and polylactide(PLA).Although many metal-based catalyst systems have been developed for the ROP of cyclic esters,zinc complexes have been widely preferable due to their low toxicity,highstability,bio-compatibility,and easy of synthesis.A number of effective zinc based complexes containing a variety of ligands with different steric and electronic properties have been established in the ROP of cyclic esters.The ligand structure and its coordination mode to the metal play a very crucial role in the polymerization,such as affecting the molecular weight and molecular weight distribution in the polymerization process.In addition,the use of an external stimulus such as light,redox processes,or mechanical force to control polymerisations is a very promising area of research.Light has many advantages over other external triggers,such as its non-invasive nature,easy handling,and its ability to exert a high level of control by tuning the wavelength or intensity of the light source.The use of light to control molecular weight and gain sequence control is therefore highly attractive in the area of polymer chemistry.Azobenzene is one of the most widely used photochromic units for this purpose.Herein,we report the successful synthesis of enamine organic catalysts containing azobenzene units.The main summary contents of this article are as follows:Chapter 1,we summarize the development of biodegradable materials and the ROP mechanism of cyclic esters,and then briefly summarizes the metal atom coordinated with different ligands.The activity of the compounds has been tested in the application of ROP of rac-LA and?-CL.Chapter 2,we reported the synthesis and characterization of bis(?-quinolylenolate)zinc complexes with[L₂Zn]-type structure as catalysts for the ROP of?-CL and LA,to investigate the substituents effects of the complexes on the propagation rate of the ROP.In the ROP of?-CL,complex2.3 having an ortho-methyl group in aryl ring(Ar)of enamino framework exhibited the higher activity than other analogue.This work elucidates the influence of substituents on the catalytic properties based on kinetic studies and insights into the mechanism for the ROP of?-CL.However,those Zn complexes are almost inactive to LA.Chapter 3,a series of organic catalysts with azobenzene units were synthesized and characterized.Under the light irradiation of?=365 nm,the organic catalysts can undergo a transformation from trans to cis structure.The photostationary state(PSS)is reached after 20 mins,and the proportion of cis structure can reach 35%.If there is no light source,the cis structure will gradually return to the trans structure,because the cis structure is relatively unstable.According to this characteristic of these organic complexes,the polymerization reaction is completed at a ratio of rac-LA:enamino:Me ONa=100:1:1 in DCM at 35°C.The experimental results show that these organic catalysts can effectively catalyze the ROP of cyclic esters.However,if the polymerization is carried out under the light irradiation of?=365 nm,the reaction conversion rate is accelerated,and the polymer PDI becomes narrower,which shows that light will affect the activity of the catalyst.