Modified Heterogeneous Ziegler-Natta Catalysts For Preparation Of Broad/Multi-Modal Molecular Weight Distribution Polyethylene

Three kinds of different structure of silanes, such as 4-R-PhOSi(Me)3 [R=CH3 (ED1); R=H (ED2); R=C1 (ED3)], were synthesized and characterized by 1H NMR and Elemental Analysis (EA). These silanes were uesd as the internal electron donor for the preparation of Ziegler-Natta catalysts to form a serious of modified heterogeneous Ziegler-Natta catalysts. These catalysts were used to promote polymerization of ethylene and copolymerization of ethylene with 1-hexene in the presence of Al(Et)3. The influence of catalytic preparation conditions, such as TiCl4 dropping temperature, the molar ratio of TiCl4/MgCl2, the structure of ED, the molar ratio of ED/MgCl2, the molar ratio of (CH3)2CHOH/MgCl2 was investigated in detail. The effect of polymerization conditions, including the polymerization temperature, polymerization time, the molar ratio of Al/Ti, the concentration of 1-hexene was also discussed. The morphology and the crystal property of these catalysts were characterized by SEM and X-ray power diffraction. The properties and structures of the obtained polymers were also characterized by 13C NMR, GPC, DSC, X-ray power diffraction and TG.These results indicated that the catalysts for polymerization of ethylene and copolymerization of ethylene/1-hexene had highly activity. The SEM results indicated the catalyst particles were showed spherical shape with surface defects. The X-ray power diffraction analysis revealed that MgCl2α-crystalline form was destructured and changed into amorphous state after added ED. The GPC results showed that the obtained polymers featured high molecular weight and broad molecular weight distribution ranged at 30 to 45. The SEM results exhibited that the polymer particle was spherical shape with well distribution in size. The DSC and the X-ray power diffraction results showed that the crystallinity of copolymer decreased as increasing of the comonomer (1-hexene) incorporation content within the polymeric chain. The TG results showed that the polymers, including polyethylene and copolymer of ethylene with 1-hexene, had good thermal stability and low ash contents. The 13C NMR result showed that the polyethylene was featured with linear structure.