Investigation Of Novel Transition Metal Catalysts For Olefin Coordination Polymerization

Polyolefins are a class of thermoplastic elastomers which are produced by the(co)polymerization of ethylene,propylene,α-olefins and some kinds of cyclenes.Owing to the abundant raw materials,processing easily and excellent performance,the capacity of polyolefins are very huge and related products are widely used in a lot of areas,among them polyethylene and polypropylene are the most important materials.On account of the variety in molecular weight,distribution of molecular weight,density of branch,branch structure and block sequence,polyethylene can exhibit quite different and fantastical characters.In recent years,the latest research and progress has given rise to a lot of attention in both academic and industry fields.In the process of olefin polymerization accessing new materials,the mode of olefin coordination polymerization has been investigated emphatically due to the properties of tuning polymer microstructures and molecular weight exactly.The system of transition-metal complexes equipped with cocatalysts or other assistants have played a significant role when it comes to the coordination polymerization.So far,the researches and developments of new catalyst systems are taking the centre stage in the coordination polymerization field.In the thesis,the olefin coordination polymerizations are as the main line and a series of Co,Ni,Ti and Zr complexes have been designed and synthesized.Further investigations were focused on the catalyst behaviors of olefins polymerization and copolymerization to seek high-quality polyolefin materials.The main research contents are as follows:1.A series of steric hindrance acenaphthene-based α-diimine nickel complexes were synthesized and all the complexes were fully characterized by IR spectra and mass spectra.Some catalysts were further determined by single-crystal X-ray diffraction analysis.The analysis of single-crystal X-ray data indicated that the Ni center displays slightly distorted tetrahedral geometry.The dihedral angles of substituted aromatic ring and naphthalenyl can be adjusted by varying the substituents.Para-tert-butyl substituted benzyl ring in Ni4 and naphthalenyl ring in Ni5 were almost parallel with the electron-deficient acenaphthene ring,what’s more,the plane distance was very short.Such a ligand structure clearly indicates the presence of π-πstacking between them.These structure features will exert a significant influence on the catalytic olefin polymerization behaviours:the stronger the π-π stacking interaction is,the better thermal stability of the catalysts is due to the stability of catalyst skeleton structure,furthermore,opening coordination space will improve polymerization activities and the varieties of branch structures.2.A series of mono-and bis-benzimidazolin-2-iminato titanium complexes were synthesized herein and fully characterized by NMR spectra and mass spectra.Some catalysts were further determined by single-crystal X-ray diffraction analysis.The analysis of single-crystal X-ray data indicated that the titanium complexes revealed distorted tetrahedral geometries.Incorporation of the benzene ring to the backbone of the imidazolin-2-iminato ligand enhances the electron donor properties,which is a benefit to the stability of the highly-charged metal center.What’s more,introducing the nonsymmetric R-N substituents of the present benzimidazolin-2-iminato ligand enlarged the coordination space of metal space in both mono-and bis-ligated titanium complexes,which can improve the olefin polymerization activity of catalysts.For bis-ligated complexes,the interligand angle is also well-related to their capacity in the copolymerization of ethylene and α-olefins,so the smaller interligand angle caused by asymmetry is more profitable.3.A series of benzene-bridged dinuclear phenolic complexes Ti2-Ti5 were synthesized and characterized by the NMR spectra.Til is a mononuclear catalyst which was used as a comparison.Ti3 was para-benzene-bridged while Ti2,Ti4 and Ti5 were meta-benzene-bridged(Ti2,Ti4 and Ti5 have difference in the electronic and steric effect of the substituent groups).Firstly,we performed the ethylene polymerization with Til and Ti2 to investigate the influence.Then Ti2 and Ti3 were used for ethylene polymerization to study the influence of the spatial distance of two metal centers.Next,Ti2,Ti4 and Ti5 were studied on the difference in polymerization properties associated with substituents in ortho-and para-position.Compared with mononuclear catalysts,the thermal stability of dinuclear catalysts has been improved a lot.What’s more,the difference of catalytic behavior can be also observed in dinuclear phenoxide titanium complexes due to the synergistic effect of two metal centers and the diversities in substituent groups.4.A series of benzene-bridged dinuclear steric hindrance phenoxyiminato titanium complexes were synthesized and characterized by NMR spectra.Five kinds of catalysts wered synthesized.Til is a mononuclear catalyst which was used as a comparison.Ti2-1 is a bidentate[ON]complex while Ti2-2,Ti2-3 and Ti2-4 are with[ONZ]ligand(Z=O)by introducing the third coordination site on the ortho-position of the benzene linked with imine.At the temperature of 30-90℃,ethylene polymerization used Ti2-4 resulted in oligomers due to the intense chain transfer and chain termination reaction.Varying the pressure of ethylene has no influence of the molecular weight.To our real surprise,further increasing the polymerization temperature,the molecular weight of the obtained polymer was improved a lot and the optimal polymerization temperature is 150℃,what’s more,even at the temperature of 190℃,the catalyst Th-4 can exhibit considerable activity for ethylene polymerization,indicating excellent thermal stability.Compared with mononuclear catalyst,the copolymerization activity of the ethylene and α-olefins was also improved a lot for for dinuclear titanium complexes due to the synergistic effect of two metal centers.5.A series of new-type constrained geometry zirconium catalysts equipped with the second auxiliary coordination substituents had been synthesized.We had explored a new efficient synthesis route for the tridentate ligand structure.Compared with the traditional constrained geometry catalysts,the new-type tridentate ligand structures can be tuned and motified easily not only on the cyclopentadiene but also the thrid coordination substituent groups.What’s more,the introduction of the newly substituent groups can reduce the Lewis acidity and eletrophilicity of the center metal according to the electron donor,which is of great importance for the improvement of catalyst activity and the suppress of chain-transfer reaction in the polymerization process.