Effects of ethylene polymerization conditions on the activity of SiO2-supported zirconocene and on polymer properties

The effects of polymerization conditions were evaluated on the production o f polyethylene by silica-supported (n-BuCp)(2)ZrCl2 grafted under optimized conditions and cocatalyzed by methylaluminoxane (MAO). The Al : Zr molar r atio, reaction temperature, monomer pressure, and the age and concentration of the catalyst were systematically varied. Most reactions were performed in toluene. Hexane, with the addition of triisobutilaluminum (TIBA) to MAO, was also tested as a polymerization solvent for both homogeneous and heter ogeneous catalyst systems. Polymerization reactions in hexane showed their highest activities with MAO : TIBA ratios of 3:1 and 1:1 for the homogeneou s and supported systems, respectively. Catalyst activity increased continuo usly as Al : Zr molar ratios increased from 0 to 2000, and remained constan t up to 5000. The highest activity was observed at 333 It. High monomer pre ssures (approximate to 4 atm) appeared to stabilize active species during p olymerization, producing polyethylenes with high molecular weight (approxim ate to 3 x 10(5) g mol(-1)). Catalyst concentration had no significant effe ct on polymerization activity or polymer properties. Catalyst aging under i nert atmosphere was evaluated over 6 months; a pronounced reduction in cata lyst activity [from 20 to 13 x 10(5) g PE (mol Zr h)(-1)] was observed only after the first two days following preparation. (C) 1999 John Wiley & Sons , Inc.