Study On The Synthesis Of Novel Silyl-Bridged Non Metallocene Complexes Containing Salicylide-Type Ligand And The Perparation Of High-Tacticity Polypropylene

A series of [O, O, O, O]-type silyl-bridged non-metallocene bearing salicylide ligand were synthesized in different routes. The salicylide complexes with methylaluminoxane as cocatalyst were applied in polymerization of propylene and copolymerization of propylene and1-hexene. The optimum polymerization conditions were obtained. The microstructure and basic properties of the obtained polymers were fully characterized.Part I:The ligands were designed to be synthesized by three ways. Firstly, the salicylaldehyde was treated with dichlorodimethylsilane, dichlorodiethylsilane, triethylamine and reductive agent (i.e. sodium borohydride), getting the salicylide ligands. The resultant salicylide ligands named L1and L2were then treated with transition metal halide(TiCl4、ZrCl4、HfCl4). A novel type of silyl-bridged complexes bearing salicylide ligand were finally obtained. Elemental Analysis (EA) and Nuclear Magnetic Resonance (1H NMR) were used to characterize the elementary composition and structures of the ligands and complexes.Part II:Combinations of these novel [O, O, O, O] complexes and MAO formed catalysts for the synthesis of polypropylene, as well as copolymer of propylene and1-hexene. The influence of the structure of the ligands, center metal atoms of the catalysts as well as the reaction conditions including polymerization temperature, pressure, time, the concentration of catalysts, cocatalysts, Al/M (M=Ti, Zr, and Hf) in mol, comonomer concentration and dissolvant were investigated in detail. To confirm the microstructure and basic properties of the polymer, various analytical techniques such as solvent extraction, DSC, FT-IR, WAXD,13C NMR and GPC were employed.The resluts showed that, the bridged non-metallocene catalysts activated by MAO were high-performance catalyst system. And the tacticity, molecular weight of the obtained polymer were very high, while the molecular weight distribution was relatively narrow. The optimum polymerization was carried out at50℃, in toluene, for60min, the pressure by2atm, with the concentration of the complex being of1.0×10-4mol/L and [Al]/[M]=400(450for copolymerization). The highest activities were2.23×106gPP/molTi.h for propylene homopolymerization and2.31×106gPP/molTi.h for propylene/1-hexene copolymerization. The obtained polypropylene possessed high molecular weight (3.6×105g/mol), narrow MWD (2.6), with isotacticities [mmmm]up to96.9%and melting points as high as162.5℃. As for the copolymerization the optimum condition could also produce high molecular weight (Mn=3.4×103g/mol), isotactic ([mmmm]=95.3%) copolymer with narrow molecular weight distribution (MWD=2.7) and melting points of96.2℃. When1-hexene conentration was0.4mol/L the copolymer possessing abundant hexene units (up to4.7mol%) could be easily obtained under optimum condition. Then the isotacticity of the copolymer was93.1%with the melting points dropped to82.7℃.