Second-Coordination-Sphere Strategy To Modulate Ring-Opening Polymerization And Polyolefin

Polymers such as plastics,fibersc and rubber are increasingly common in our daily life.Polyolefins,as an important part of them,have received extensive attention in recent years.Polyolefins are derived from petroleum and are favored by consumers at a low price.At present,extensive research has been conducted on the conversion of simple polyolefin materials into functionalized polyolefin materials by copolymerizing with polar monomers.With the increase in the demand for functionalized polyolefin materials in the industry,the development and research of new functionalized polyolefin catalysts need to be expanded.Polylactic acid-based degradable polyester materials have been widely studied in recent years,because their properties are widely sourced,biocompatible,and can be rapidly degraded.More and more research has been devoted to the study of ring-opening polymerization catalysts,of which salon,β-diimine,and salicylaldimine systems have excellent polymerization properties,and considerable catalysts can effectively control the stereoregularity of polylactic acid,For catalyst combining the poroperty of high activity,stereoregularity is still quite lacking.We hope to introduce the second-coordination-sphere effect in the above two types of catalytic systems to improve the catalytic performance of the existing catalyst systems and provide a new way to improve the catalyst performance.1.A series of nitrogen-containing α-diimine ligands with a second-coordination-sphere effect was synthesized and characterized.The ligands were then coordinatied with palladium and nickel compounds to form the catalysts.The polymerization and copolymerization of ethylene was studied.The results show that this type of nickel catalysts can significantly reduce the branching degree of polyethylene in the polymerization of ethylene.In addition,such nickel catalysts have successfully achieved the copolymerization of olefins with polar monomers.This kind of palladium catalyst can realize the copolymerization of ethylene with a series of polar monomers.Control experiments and computer simulations show that the nitrogen atoms in the ligand play a key role in achieving this polymerization performance.2.Secondly,a series of salicylaldimine zinc and aluminum catalysts were synthesized and characterized.The nitrogen atoms were introduced into the ligands.The effect of nitrogen atoms to metal centers is regulated by electrons and stericeffects.The ring-opening polymerization of lactide is efficiently achieved,and polylactic acid having a high stereoregularity and a narrow molecular weight distribution is obtained.In addition,a series of monomers such as caprolactone and carbonate are also polymerized.Catalyst aluminum can achieve ring-opening polymerization at high temperatures.3.A series of salicylaldimine zinc and magnesium catalysts were synthesized and characterized.In the salicylaldimine ligands,azo groups were introduced.Under the regulation of UV-visible light,this type of catalyst can successfully achieve cis-trans isomerism.Under the action of this type of catalyst,a series of monomers such as lactide,caprolactone,and carbonic acid esters were successfully obtained by ring-opening polymerization.Studies have shown that under UV or visible light,this type of catalyst has a change in the catalytic activity of the same kind of monomer.Further studies have found that when the two monomers are copolymerized,the cis-or trans-structured catalyst changes the copolymerization ratio of the monomer.Using this feature,under light mediation,we successfully obtained a one-pot process for the preparation of multi-block polymers.4.In addition,a series of cyclopentapene structural aluminum catalysts were synthesized and characterized by introducing oxygen atoms and sulfur atoms containing different steric hindrance and electronic effects in the ligands.With benzyl alcohol as the initiator,this type of catalyst can efficiently catalyze the ring-opening polymerization of lactide.The high activity of such catalysts may result from the formation of smaller chelate rings with aluminum and greater ring tension.The activity of the catalyst containing the second-layer coordination steric effect was significantly higher than that of the catalyst without the fast catalytic rate,and the monomer ratio was 100:1.At a temperature of 80℃,almost all of the lactide can be polymerized.At the same time,the second-order collocation space effect also affects the tacticity of the polylactic acid.5.Finally,we have successfully explored and characterized a series of nitrogen-heterocyclic carbene palladium catalysts by exploring the direction of alkyne hydrocarbon polymerization.The monodentate azacyclic carbene palladium is reacted with tetrakis(3,5-trifluoromethyl)phenyl boronic acid sodium salt(NaBAF)to form a weak anion coordinated cationic palladium,which can highly catalytically catalyze the polymerization of disubstituted benzene acetylenes..Carbene ligands and weakly coordinated borate anions are key to high activity.Compared with the conventional molybdenum catalyst catalyzed by the disubstituted benzene acetylene,the palladium catalyst catalyzes the production of higher molecular weight polymers with better thermal stability but poorer solubility.When alpha-olefin is added as a chain transfer agent,the molecular weight of the polymer is clearly controlled.