Effect of polymerization temperature on the polymerization of ethylene with dicyclopentadienylzirconiumdichloride/methylalumoxane catalyst

The effect of polymerization temperature on catalyst activity and polymer properties in the polymerization of ethylene was studied. The catalyst system was a homogeneous metallocene catalyst Cp₂ZrCl₂ with methylaluminoxane (MAO) as a cocatalyst. The polymerizations were carried out in n-heptane at temperatures from -20 to 90°C and the polymer properties determined were molecular weight, molecular weight distribution, melting point, crystallinity, and density. The catalyst activity increased 2.3-fold between 70°C and 80°C, evidently due to the improved solubility of polyethylene in n-heptane at elevated temperatures. Above 30°C the molecular weight began to decrease significantly, causing the crystallinity and density to increase and the melting point to decrease. The molecular weight distribution of the polyethylene was tailored by using stepwise polymerization procedure. The MWDs varied from 2.4 to 20.2 when the polymerization was performed at two different temperatures.