Studies On The Preparation Of Late Transition Metal α-Diimine Nickel(Ⅱ) Complexes For Ethylene Polymerization

The thesis consists of six chapters as follows:Chapter 1: ReviewsThis chapter reviews recent development ofα-diimine nickel(â…¡),palladium(â…¡) and bis(imino)pyridyl Iron(â…¡),cobalt(â…¡) and their supported late transition metal complexes for olefin polymerization. The contributions of ligand and its corresponding complexes structure to the catalytic polymerization properties of late transition metal complexes are particularly emphasized in this review.Chapter 2: Synthesis and Characterization ofα-Diimine Nickel (â…¡) Catalyst Containing Br Groups for Ethylene PolymerizationA new Br-substitutedα-diimine compound and its corresponding Ni(â…¡) complex, {bis[N, N'-(3-bromo-2,4,6-trimethylphenyl)imino]acenaphthene}dibromonickel was successfully synthesized, and characterized by 1^H NMR, (13)^C NMR, elemental analysis, FTIR and XPS. The pre-catalyst 2 activated by methylaluminoxane (MAO) was tested in the polymerization of ethylene, showed to be highly active (5.50×10⁶g PE/(mol Ni.h.bar)). The catalyst system 2/MAO showed the highest activity with the 800 of Al/Ni molar ratio at 25℃. It was found that the catalyst containing electron-withdrawing groups Br showed better thermal stability and almost the same catalytic activity. At same time, branching degrees was increased in the presence of electron-withdrawing groups Br. The polymer were characterized by 1^H NMR, (13)^C NMR, GPC,TG,DSC.Chapter 3: Studies ofα-Diimine Nickel (â…¡)/DEAC Catalyst Containing Bromo Groups for Ethylene PolymerizationA new Br-substitutedα-diimine compound and its corresponding Ni(â…¡) complex, {bis[N, N'-(3-bromo-2,4,6-trimethylphenyl)imino]-2,3-butadiene}dibromonickel was successfully synthesized , and characterized by 1^H NMR, (13)^C NMR, elemental analysis, infrared spectroscopy (FTIR). The pre-catalyst 2 activated by aluminiumdiethylchloride (DEAC) showed slightly increasing activity (4.83×10⁶ g PE/ (mol Ni.h.bar)) in the presence of ligand electron-withdrawing groups Br. At the same time, it was found that the catalyst containing electron-withdrawing groups Br showed better thermal stability. The influence of Bromo substituent and the effects of the Al/Ni molar ratio,polymerization temperature were discussed on the catalyst activity of ethylene polymerization with DEAC as a co-catalyst. The catalyst system 2/DEAC showed the highest activity and lead to a branched Polyethylene(PE)(ca. 87branches/1000C) with the 850 of Al/Ni molar ratio at 25℃in 30 min. The polymer were characterized by (13)^C NMR, gel permeation chromatography(GPC),differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis.Chapter 4: Studies ofα-Diimine Nickel(â…¡)/DEAC Catalyst containing Naphthyl Moieties for Ethylene PolymerizationA new containing naphthyl moietiesα-diimine compound and its corresponding Ni(â…¡) complex, {bis [N, N'-(2-methyl-1-naphthyl) imino] acenaphthene} dibromonickel was successfully synthesized, characterized by 1^H NMR, (13)^C NMR, X-ray crystallography, elemental analysis, FTIR. The catalyst 2 activated by aluminiumdiethylchloride (DEAC) was tested in the polymerization of ethylene, showed to be highly active (87.6g PE/(mol Ni?h?Pa)). The influence of ligand structure and the effects of the Al/Ni molar ratio,polymerization temperature were discussed on the catalyst activity of ethylene polymerization with DEAC as a co-catalyst. The catalyst system 2/DEAC showed the highest activity with the 700 of Al/Ni molar ratio at 40℃in 30 min. The polymer obtained were characterized by (13)^C NMR, gel permeation chromatography (GPC),thermogravimetric (TG) analysis,differential scanning calorimetry (DSC).Chapter 5: Synthesis and Characterization of Branched Polyethylene by Homopolymerization withα-Diimine Nickel(â…¡) Bearing Naphthyl MoietiesA novel highly active catalyst {bis [N, N'-(2-methyl-1-naphthyl) imino]-2, 3-butadiene} dibromonickel(â…¡) was reported for ethylene polymerization. Its catalytic activity had been compared with that of {bis [N, N'-(1-naphthyl) imino]-2, 3-butadiene} dibromonickel(â…¡), activated by Diethylaluminium chloride (DEAC). It was found that catalytic system C1/DEAC showed a relatively high activity (6.39×10⁶ g PE (mol Ni. h. bar)^-1) even at a low Al/Ni molar ratio and reached the maximum activity at the molar ratio of Al/Ni 800 at 40℃. Branched polyethylene obtained with catalytic system C1/DEAC were confirmed by both 1^H NMR and (13)^C NMR spectra. Molecular weights (M_w) and molecular weight distributions (MWD) were determined by gel permeation chromatography (GPC). The thermal properties were evaluated by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The crystalline structure of polyethylene was measured using X-ray diffraction (XRD). The results indicated that the properties of the resulting polyethylene depended highly on the varying polymerization conditions. The M_w and melting temperature (Tm) values were observed to decrease obviously with increasing temperature, but the branching degrees increased. The polyethylene produced had a variety of branching distributions, high molecular weights, narrow and unimodal molecular weight distributions (MWD≈2.0), suggesting the single-site nature of the catalyst.Chapter 6:α-Diimine Nickel(â…¡) Catalysts Containing Chlorine Substituent for Ethylene Polymerization: Influence of the Ligand Structure on the Catalyst Activity and Properties of the Resulting PolymersThreeα-diimine nickel(â…¡) complexes containing chloro-substituted ligands, {bis[N, N′-(3-chloro-2-methylphenyl)imino]-2,3-butadiene} dibromonickel 2a, {bis[N, N′-(3-chloro-2,6-dimethylphenyl)imino]-2,3-butadiene} dibromonickel 2b and {bis[N, N′-(4-chloro-2,6-dimethylphenyl)imino]-2,3-butadiene} dibromonickel 2c, were synthesized and characterized. The molecular structure of complex 2a was determined by X-ray crystallography. In the solid state, complex 2a consists of twoα-diimine ligands and a nickel center, which has pseudo-octahedral geometry. These complexes activated by diethylaluminium chloride were tested in the polymerization of ethylene under mild conditions. NMR analysis shows that highly branched polyethylenes are obtained usingα-diimine nickel(â…¡) complexes containing electron-withdrawing Cl groups (84 branches/1000 C at 20℃). The catalytic activity, polymer molecular weight and polymer degree of branching were significantly affected by the position of chlorine substituents on the ligands of Ni(â…¡)α-diimine.