Synthesis And Characterization Of α-diimine Nickel (Ⅱ) Complexe For Polymerization Of Ethylene And Styrene

Olefin polymerization catalyzed by late-transition-metal catalysts has attractedincreasing attention due to their high functional group tolerance and their ability toproduce polyethylenes with various types of branches. The activity of the catalysts andthe properties of the resulting polyolefin were greatly depended on the ligand structure.A variety of α-diimine ligands containing substituted N-aryl rings were employed tostudy their influence on the catalytic activity of the Ni(II) and Pd(II)[MX2(α-diimine)]precatalysts. In this work, we study the effect of methylphenyl substituents in theortho-aryl or/and para-aryl position of the ligand on the catalytic behavior and theproperties of the resulting polymers.The thesis consists of four chapters as follows:Chapter I: ReviewsPolyolefin is a very important kind of polymer for its wide use in various industries,and its production technology represents the development level of a country’spetrochemical industry to a large degree. Development of core polyolefin material is thedevelopment of new catalysts for olefin polymerization. The design and synthesis ofnovel olefin polymerization catalyst has always been a research focus of the polymerdisciplinary. In this thesis, on one hand, we reviewed the history of olefinpolymerization catalysts and the advantages and disadvantages of their development.On the other hand, we described the catalysts involved ethylene polymerization andstyrene polymerization and the mechanisms of olefin polymerization.Chapter II: Preparation of α-diimine nickel (II) catalysts for olefin polymerizationTwo new Ni(II) complexes containing methylphenyl groups,{bis[N,N’-(2,6-dimethyl-4-p-methylphenylphenyl)imino]acenaphthene}diromonicke4a and{bis[N,N’-(2-ethyl-4,6-di(p-methylphenyl)phenyl)imino]acenaphthene}diromonicke4b, were synthesized and characterized. The molecular structures of complexes4a and4b was determined by single-crystal X-ray diffraction. The structures of complexes4aand4b have pseudo-tetrahedral geometry about the nickel center, showing pseudo C2vand C2molecular symmetry, respectively.Chapter III: α-diimine nickel (II) olefin polymerizationThese complexes4a-c, activated by diethylaluminum chloride (DEAC) were tested in the polymerization of ethylene and styrene under mild conditions. The precatalyst4bbearing one ortho-ethyl group and two bulky p-methylphenyl groups in the ortho-andpara-aryl position of the ligand, displays highly catalytic activity for thepolymerization of ethylene [4.70×106g PE/(mol Ni·h·bar)] and produced branchedpolyethylene (76methyl,8ethyl,5propyl and22butyl or longer branches/1000C at60°C). Interestingly, complex4b also displays highly catalytic activity (5.46×105gpolystyrene/(mol Ni·h)) for styrene polymerization, and produces nearly atacticpolystyrene at30°C (stereo-triad distributions: rr,39.9%; mr,30.4%; mm,29.8%;stereo-diad distributions: r,55.1%; m,44.9%).