Cocatalytic activities of methylaluminoxane prepared by direct water addition method in ethylene polymerization over Cp2ZrCl2

Abstract

The characterization of ethylene polymerization behaviors catalyzed over Cp2ZrCl2/MAO homogeneous system using methylaluminoxanes prepared by the direct hydrolysis of AlMe3 (Me=methyl) were reported. The MAO was prepared at the ratio of [H2O]/[Al]=1 and 0.5 and at three different temperatures, i.e., -40, -60 and -80 degrees C. The polymerization rate was not decreased with polymerization time when the MAO prepared at the ratio of [H2O]/[AlMe3]=1 at -60 degrees C was used as a cocatalyst regardless of the ratio of Al/Zr and the polymerization temperature. The polymerization rate drastically decreased with polymerization time above 60 degrees C in case of using MAO prepared at the ratio of [H2O]/[AlMe3]=1 at -80 degrees C. However, in case of the MAO prepared at the ratio of [H2O]/[AlMe3]=0.5 at -80 degrees C, the rate continuously increased with polymerization time at the polymerization temperature of 70 degrees C and 80 degrees C. The amount of MAO needed to activate Cp2ZrCl2 was larger than that of MAO prepared at the ratio of [H2O]/[Al]=1. The viscosity molecular weight of polyethylene (PE) cocatalyzed with MAO prepared at the ratio of [H2O]/[Al]=0.5 was lower than that of polyethylene obtained with MAO prepared at the ratio of [H2O]/[Al]=1.