Preparation of Ultra High MolecularWeight Polyethylene Using Bi-supported SiO2/MgCl2 (spherical)/TiCl4 Catalyst: A Morphological Study

Polyethylene with a viscosity average molecular weight (Mv) as high as 3.42×106 was synthesized. The Mv increased with monomer pressure, while higher polymerization temperature decreased the molecular weight of the resulting polymer. The method of polymerization involved slurry using morphologically improved bisupported catalyst of spherical SiO2/MgCl2/TiCl4. Triethylaluminium (TEA) was used as a cocatalyst, and hydrogen served as the chain transfer agent. The crystallinity of the obtained polymer was between 50% and 60%, indicating semicrystalline polyethylene. Morphological study reveals that the main damage suffered by the catalyst particles was due to chemical interactions with the cocatalyst at the early stages of the polymerization. The rate/time profile of the polymerization decayed with the highest activity at the beginning of the polymerization. The behaviour also affected the morphology of the polymer particles which could be due to the sudden fragmentation that resulted from fast-growing polymer particles. The optimal activity was obtained at [Al]:[Ti] = 770:1 molar ratio at 60ºC. The polymerization was first order with respect to the monomer concentration. Polymerization activity was stable between 55ºC and 70ºC.