Olefin Polymerization And Ring-Opening Polymerization Of External Stimulation

After two decades of research,late-transition metal catalysts based on Ni and Pd for olefin polymerization have attracted much attention owing to their low oxophilicity and the potential in copolymerization olefins with polar monomers.The pioneering work by Brookhart and co-workers on the discovery of cationic α-diimine-based Ni and Pd catalysts marked a new era in the field of olefin polymerization.This type of catalyst can produce branched polyolefins using only ethylene as a raw material.This is achieved through their characteristic chain walking process,which has been extensively studied both experimentally and theoretically.In addition to olefin polymerization,post-transition metal catalysts are also widely used in ring-opening polymerization,which are two interlinked fields about the skeleton modification for catalysts,the polymerization methods,and the modulation strategies of polymerization.Focused on the imine-type catalysts and combined with the two fields of olefin polymerization and ring-opening polymerization,here the properties of olefin polymerization catalysts and the strateges for modulating ring-opening polymerization were studied.1.An α-diimine nickel and palladium catalyst with the three characteristics of substituted large steric hindrance imine groups,asymmetric skeleton structure and good solubility in nonpolar solvents was synthesized,and a series of characterizations were performed.Few post-transition metal catalysts can dissolve in nonpolar solvents,so the good solubility of the catalysts in nonpolar solvents has been used to investigate the polymerization in toluene and n-hexane solvents.The melting point of polymers in nickel-catalyzed ethylene polymerization and the degree of branching of polymers in palladium-catalyzed ethylene and α-olefin polymerization are affected by the difference in solvents which shows a certain regularity.According to the characteristic chain walking and the effects of solvents,the inferred results are exactly the contrary of the regularity.In addition,it found that the change in the concentration of the co-catalyst has a certain regular influence on the polymer properties.Further analysing and testing to the polymer and designing controlled experiments need to be done to find out how the change of solvent affects the polymerization process.2.Two β-diimine zinc complexes were prepared and found to show high activity and well-controlled catalytic behavior in the ring-opening polymerization of rac-lactide.Coordination of the Lewis acid to the zinc complexes completely terminated the polymerization.The coordinated Lewis acid was easily cleaved by using a Lewis base,so that the polymerization could resume.Thus,switchable polymerization could be realized by the subsequent addition of a Lewis acid and a Lewis base.This work provides a new strategy to control the ring-opening polymerization of lactone.3.A serious of salicylaldimine zinc complexes with azophenyl group was synthesized and characterized.Isomerization of these catalysts between trans-and cis-can be achieved using light as an ideal external stimulus.These catalysts show good ring-opening polymerization activity.Moreover,the polymerization activity for the same monomer changed under light stimulation,and in copolymerization reaction,light-modulating isomerization will change the selectivity of the catalyst for different monomers.Using light as a ideal stimulation is a potential stratage to achieve controlling the polymerization process and polymer composition.