Study On The Preparation Of Metal Complexes And Their Catalytic Activity On Cyclic Ester Ring-Opening Polymerization

In recent years,biodegradable environmentally friendly materials have received increasing attention.Polylactic acid(PLA)is considered to be the most promising degradable aliphatic polyester material,and its material properties such as melting point,crystallinity,and degree of degradability are affected by the structure of the polymer segment.The influence of polymer segment structure can be dissociated by chemical and biological methods,and has wide application value in many fields such as creating materials,medicine,etc.Part of the material of polycaprolactone is derived from petroleum,but it is also a multi-application polymer due to its excellent degradability.A large number of studies have shown that ring-opening polymerization is the most effective method for preparing polylactic acid and polycaprolactone,which can avoid the influence of by-products on the polymerization.The metal complex catalyzes the ring-opening polymerization of cyclic ester monomers.Research the most in-depth methods for the synthesis of degradable polymers.At present,metal catalysts have been greatly developed,but there are still gaps in the new and cross-cutting fields for traditional catalysts.In this work,we have made new developments and explorations based on the advantages of traditional catalysts for the polymerization activity,high stereoselectivity and preparation of high melting point solid composites.1.A series of new type Schiff bases,Salen ferric chloride(III)complexes,which have the advantages of simple structure,water and oxygen stability,and no toxicity to the central metal,are synthesized.The catalytic properties of this series of complexes for the ring-opening polymerization of lactide were investigated in detail.The relationship between the structure of the complex and the substituent and its catalytic performance was investigated in detail by polymerization kinetics.At the same time,this series of Schiff base iron complexes were applied to the stereoselective polymerization of racemic lactide(rac-LA).The results show that the series of complexes have certain isotactic selectivity.Furthmore,the catalytic ring-opening polymerization mechanism was studied.It was explained that the cyclization reaction of propylene oxide in the complex catalysis was carried out,and the Schiff base iron complex with alkoxy substitution was prepared in-situ to further catalyze the ring opening of cyclic ester monomer via catalytic mechanism of coordination insertion polymerization.2.The application of biodegradable materials in the medical field has very strict requirements on metal residues in polymers.Magnesium metal has been applied to medical metal nails in recent years due to its almost non-toxic advantages.Therefore,we chose magnesium as the metal center to synthesize a series of semi-?-dikelimine silazane magnesium metal catalysts with simple structure and easy synthesis.The series of ligands have a NNO tridentate coordination structure with a semi-Schiff base framework,and a catalyst having in-situ initiation ability can be obtained by coordination with magnesium silazane.This series of catalysts has moderate catalytic activity in the polymerization of lactide and caprolactone.The polymerization kinetics of the complexes are investigated by in-situ infrared polymerization of the polymerization reaction.The structure of the ligands and the substituents are complexes.The catalytic activity has a very large effect,the benzene ring substitution on the ligand can improve the catalytic activity,the complex with the longer amine bridge can increase the activity in the polymerization of caprolactone,and the activity in the lactide polymerization will decrease.Thus,the structural design of the complex can provide an idea for the controlled polymerization of lactide and caprolactone.3.Stannous octanoate,as a mature catalyst,has been widely used in the field of industrial production of cyclic ester polymers.Its advantages of high polymerization activity and low relative toxicity make it widely recognized.PLA plays an important role in the field of biomedical materials for bioengineering.It is of great significance to study the catalysts with lower toxicity and higher catalytic efficiency for the preparation of biomedical materials by ring opening polymerization of cyclic esters.Natural amino acids have attracted more and more attention because of their advantages such as simple material,low cost and good biocompatibility.Inspired by the biological origin of natural amino acids and the high-efficiency catalytic activity of tin metal,we prepared a series of complexes of amino acid stannous metal complexes through neutralization reaction as the catalyst for ring opening polymerization of cyclic ester monomers,which have good ring opening polymerization activity for lactide,carbonate and caprolactone,and l-phenylalanine complex of stannous has high polymerization activity and The polymer has certain structure selectivity,low cytotoxicity and good biocompatibility,so it has a good prospect in the field of medical material preparation.4.Compared with the method for preparing stereocomplex by stereoselective polymerization of racemic lactide,the stereocomposite prepared by the mixture of Land D-polylactic acid directly has the advantages of controllable segment length and higher melting point.We used two different catalytic systems to obtain a polylactic acid stereocomplex by optically pure left-handed or right-handed polylactic acid.The first one uses a highly active oxazoline ring-coordinated silazane magnesium as a catalyst to catalyze polymerization in a short time at room temperature to avoid side reactions caused by high temperature and long-term reaction.The prepared polylactic acid has a broad molecular weight distribution,and the prepared three-dimensional composite has a single crystal melting peak of polylactic acid of about 170 ° C and a solid composite melting peak of about 220 ° C.This result indicates that an excessively broad molecular weight distribution is detrimental to the formation of a polylactic acid stereocomplex.The other method uses a highly stereoselective catalyst to inhibit the racemization side reaction in the polymerization process,thereby obtaining a polylactic acid material with high stereoregularity,and the molecular weight of the obtained polymer is well controlled,has a very narrow molecular weight distribution,and has a total solution.The stereocomposite prepared by the mixed method has a high melting point(about 250 ° C).DSC studies have shown that a suitable heat treatment can change the order of crystals in a tacticity composite,thereby affecting its melting behavior.In summary,the formation of the stereocomplex of the high-melting polylactic acid is restricted by the molecular weight distribution of the optically pure left-handed and right-handed polylactic acid materials used,the regularity of the microscopic chain structure,and the molecular weight.