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Preparation of ultra-high-molecular-weight polyethylene and its morphological study with a heterogeneous Ziegler–Natta catalyst



Ultra-high-molecular-weight polyethylene (PE) with viscosity-average molecular weight (Mv) of 3.1 × 106 to 5.2 × 106 was prepared with a heterogeneous Ziegler–Natta MgCl2 (ethoxide type)/TiCl4/triethylaluminum catalyst system under controlled conditions. The optimum activity of the catalyst was obtained at a [Al]/[Ti] molar ratio of 61 : 1 and a polymerization temperature of 60°C, whereas the activity of the catalyst increased with monomer pressure and decreased with hydrogen concentration. The titanium content of the catalyst was 2.4 wt %. The rate/time profile of the catalyst was a decay type with a short acceleration period. Mv of the PE obtained decreased with increasing hydrogen concentration and polymerization temperature. The effect of stirrer speeds from 100 to 400 rpm did not so much affect the catalyst activity; however, dramatic effects were observed on the morphology of the polymer particles obtained. A stirrer speed of 200 rpm produced PE with a uniform globulelike morphological growth on the polymer particles. The particle size distributions of the polymer samples were determined and were between 14 and 67 μm. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010