Study On Olefin Polymerization By Ansa Metallocenes And FI-Titanium Complexes

Polyolefins, such as polyethylene (PE) and polypropylene (PP), are the most widely used polymers in our life. Because of their cost effectiveness as well as low density, high strength, and good resistance to chemical attack, these polyolefins can be applied for the manufacture of all kinds of packaging film and containers.Although commercial multi-site Ziegler-Natta catalysts exist very high activity for ethylene and propylene polymerization and high isospecificity in propylene polymerization ,single-site catalysts represented by metallocene catalysts and constrained-geometry catalysts (CGC) are gaining an increasing presence in the worldwide polyolefin market, especially for PE and PP. Duo to the well-defined active sites of these single-site catalysts in contrast to multi-site Ziegler-Natta catalysts and the advantage of control over polymer molecular weight and molecular weight distribution, uniform comonomer incorporation, and precise control of polymer stereoregularity, single-site catalysts have had a significant impact on contemporary polyolefin science and technology and have been in the forefront of these developments.The key step for these researches and developments (R&D) is to design ligands with suitable electronic and steric effects.Among the recently-developed single-site catalysts, phenoxy-based catalysts,which was firstly discovered and named with FI catalysts by the research group of Terunori Fujita of Mitsui Chemicals Inc., constitute an important class of olefin polymerization catalysts. Because of their super-high activities for olefins polymerization and the polymers' distinctive microstructures and related material properties, R&D for FI catalyst have become another forefront of developments of single-site catalysts. Phenoxy-based ligands can be commercially available in generally good to high yields and low cost, so FI catalysts have the advantageous properties of diversity as well as tunability. The most interesting is that the ligands are readily tailored synthetically from both an electronic and steric point of view and thus a wide range of FI catalyst can be designed for the synthesis of polymers with molecular weight ranging from thousands to several millions. By copolymerization between ethylene anda-olefin, MMA or AN ,various new type polymers can be obtained.Traditional researches for single-site catalysts for olefin polymerization focus on central metals. Basing on the new concept of "ligand-oriented catalyst design" and aiming at the relationship between high performance of single-site catalysts and the structure of their ligands, this dissertation study on the synthesis of early transition metal catalysts including the ansa metallocences and FI type titanium complexes and their catalytic performance in olefins polymerization.Firstly, the properties of ethylene polymerization under the same polymerization conditions with three of cycloalkylidene-bridged cyclopentadienyl titanium catalysts in the presence of MAO are investigated. It is firstly discovered by us that both ofcyclohexenebridged cyclopentadienyl titanocene A₂ and the cycloheptenebridged cyclopentadienyl titanocene A₃, in our polymerization conditions, the activity increase with temperature to a maximum activity at 60℃. This indicates that A₂ and A₃ are very thermally stable and do not deactivate even at higher temperatures. While the cyclopentene-bridged cyclopentadienyl titanocene A₁ has the highest activity at lower temperature (50℃)oSecondly, ansa-Cyclohexyl-bis(4,5,6,7-tertrahydro-l-indenyl) zirconium dichloride (B₁) was used as catalyst for propylene and ethylene polymerization together with methyl aluminoxane (MAO) as the cocatalyst. Isotactic polypropylene (PP) was obtained with the highest activity of 6.37×10⁷g-PP (mol-Zr)^-1h^-1. The meso-meso (mmmm) pentads sequence content of PP was determined by ¹³C NMR spectroscopy. The dependence of the microstructure on the reaction temperature and the Al/Zr molar ratio was examined and the catalytic activity of complex B₁ was compared with that of the similar ansa-zirconocene: trans-1,2-cycloalkylene-bridged bis(tetrahydro-indenyle)ZrCl₂. The high activity of the new zirconocene B₁ for propylene isospectic polymerization at high temperature (60 ℃) is the result of its unique bridged-group structure. Complex B₁/MAO displays also high catalytic activity of 0.46×10⁶ to 9.87×10⁶g-PE(mol-Zr)^-1h^-1 in the homopolymerization of ethylene. The visometric molecular weight of PE ranges from 0.97×10⁴ gmol^-1 to 11.16×10⁴ g·mol^-1 under the given conditions. ¹³C NMR spectroscopy analysis proves the PE to be linear polyethylene (LPE).Thirdly, two carbon bridged cyclopentadienylchromium complexes [(C₅H₄) C (C₅H₁₀) CH₂ (C₅H₄N) ]CrCl₂(C₁)and[ (C₅H₄) C (CH₃) 2CH₂ (C₅H₄N) ]CrCl₂ (C₂) were synthesized and characterized byh mass spectra and elemental analyses. The structure of C₁ and C₂ were determined by X-ray diffraction analysis. Activated by MAO,the complexes C₁ and C₂ were efficient for ethylene polymerization yielding linear polyethylene (LPE) with high molecular weight and narrow molecular weight distribution. For chromium complex C₁, polyethylene was produced with high catalytic activity of 7.96×10⁶g /mol·h and viscometric average molecular weight (M_v) of 2.969×10⁴ and the molecular weight distribution of 3.14 at 60℃ .High melting point and low branching degree of the obtained PE was confirmed by DSC and ¹³C NMR. Activated by Al(i-Bu)₃ ,Complex C₂ displayed a higher activity than Kaminsky catalyst-Cp₂TiCl₂ for methyl methacrylate (MMA) polymerization under the same reaction conditions. After 18 hours, 77.55% MMA was converted to poly(methyl-methacrylate) (PMMA) with a viscosity average molecular (M_v) of 261300 at 40℃ at MMA/ Al(i-Bu)₃ /titanium complex of 2000:20:1 in MMA bulk. High activities of polymerization are related to the unique electronic and steric structure of complexes C₁ and C₂.Finally, in order to study the relationship between ligands structure of FI catalystsand their catalytic performances for ethylene polymerization , thirteen kinds of mono-Schiff bases (ligands: L₁～L₁₃ ) and eight kinds of bis-Schiff bases(ligands: L₁₄～L₂₁)were synthesized and characterized by ¹H NMR , ¹³C NMR, IR ,GC/MS (or LC/MS) and elemental analyses ,then seven kinds of novel FI-catalysts with mono-titanium centre (D₁～D₇) and a novel binuclear titanium complex (D₈) were prepared and characterized by ¹H NMR ,¹³C NMR, MS, XRD and elemental analyses. In the presence of methylaluminoxane (MAO), the complexes D₁～D₃ in toluene are able to efficiently catalyze ethylene polymerization. Under the conditions of T= 60℃ ,P=0.2 MPa and n(MAO)/n(cat)=1500,the activities of (D₁～D₃) reach (4.55～8.80×10⁷ gPE /mol-Ti·h·MPa) which is much higher than that of bis[N-salicylidene-2,6-diisopropyl anilinato] titanium(IV) dichloride (D₉) .The viscometric average molecular weight of polyethylene rangs from 24.8×10⁴ to 44.9×10⁴ for D₁～D₃ and the molecular weight distribution M_w /M_n is 1.85 to 2.34. The effects of reaction conditions on polymerization were examined in detail. Increase in ethylene pressure and rise in polymerization temperature are favourable for D₁～D₃/MAO to raise catalytic activity and molecule weight of polyethylene. The results of ethylene polymerization under the temperature of 25～55℃ with binuclear titanium complex (D₈) as catalyst displays its moderate catalytic activity which is very lower than that of the similar structural mono-titanium catalyst (D₁₀). So no strong synergism of two metal centre exists within the binuclear FI catalyst.