| A novel series of Ziegler-Natta catalysts containing aryloxy ligands were prepared via treating magnesium chloride support with trichloro monophenoxide titanium complexes, (ArO)TiCl3, with a purpose of investigating the effects of aryloxy ligands on olefin polymerization catalyzed with MgCl2-supported Ziegler-Natta catalysts.Five kinds of (ArO)TiCl3 complexes (ArO-= C6H5O-,2,6-Me2C6H3O-, 2,6-i-Pr2C6H3O-,2,6-t-Bu2C6H3O-,2,6-t-Bu2-4-MeC6H2O-) were synthesized from a series of phenols. The immobilization behaviors of (ArO)TiCl3 compounds on magnesium chloride support were systematically studied, and two series of MgCl2-supported catalysts based on each individual (ArO)TiCl3 as well as two MgCl2/TiCl4 type traditional Ziegler-Natta catalysts were prepared in two different procedures:(1) batch addition of the titanium compound to suspension of MgCl2 and their reaction at 120℃; (2) gradual addition of titanium compound to suspension of MgCl2 and their reaction at 80℃. During the process of supporting the aryloxy titanium compound on MgCl2, a part of the ArO ligand left the supported Ti species, therefore, the supported catalysts were in fact carrying both (ArO)TiCl3 and TiCl4. Comparing to TiCl4, ArO on the aryloxy titanium compound may hinder the tight arrangements of the titanium species on the support surface as TiCl4, thus caused a deduction of titanium content in catalyst. Yet the electron donating effect from ArO liand to titanium could not be neglected, since it would lower the Lewis acidity of the compound and promote its adsorption on the Lewis acidic magnesium chloride. Higher titanium compound concentration and reaction temperature during immobilization were beneficial to increase the titanium content in the catalyst, yet caused a negative effect on the amount of reserved ArO ligand on the support.Ethylene polymerizations and ethylene/1-hexene copolymerizations catalyzed by catalysts prepared in the batch addition procedure were studied. Factors that influenced the catalytic behavior were investigated, including kinds and concentrations of cocatalysts, temperature, and concentrations of comonomers. Distinct effects of the aryloxy ligands on catalytic characteristic such as activity, Mw, etc. were found. Polymers synthesized by catalysts containing aryloxy have more homogeneous chemical composition distribution than those synthesized by conventional Ziegler-Natta catalyst. The active center distributions of the catalysts containing aryloxy were greatly changed by addition of hydrogen in the polymerization system, and the polymers contained fewer 1-hexene units and had a broader chemical composition distribution.Accordingly, ethylene polymerizations and ethylene/1-hexene copolymerizations catalyzed by catalysts prepared in the gradual addition procedure were studied. Comparing to conventional Ziegler-Natta catalyst, the activity of both homo and copolymerization catalyzed by the catalysts containing aryloxy were higher due to the presence of aryloxy ligand. When hydrogen was introduced in the ethylene polymerization system, the activity of conventional Ziegler-Natta catalyst was suppressed, however, activity of the catalysts containing aryloxy was activated. Ethylene/1-hexene copolymers prepared by the catalysts containing aryloxy possessed higher 1-hexene unit content than those of conventional Ziegler-Natta catalyst, indicating positive effect of aryloxy in upgrading the copolymerization ability.Finally, based on the different behaviors of catalysts prepared by the batch addition and gradual addition procedures, and according to the different behaviors of immobilizing (ArO)TiCl3 and TiCl4 on surface of magnesium chloride support, a mechanism model was proposed to explain the structure of active centers as well as the catalysis processes of the Ziegler-Natta catalysts carrying aryloxy ligands.
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