EFFECT OF ALUMINOXANE ON SEMIBATCH POLYMERIZATION OF ETHYLENE USING ZIRCONOCENE DICHLORIDE

Several types of commercial and developmental aluminoxanes were studie d in the semi-batch polymerization of ethylene using bis(cyclopentadie nyl) zirconium dichloride (Cp2ZrCl2). High temperature gel permeation chromatography (GPC) measurements of polyethylene (PE) formed using va rious types of aluminoxanes approximated Flory's most probable distrib ution from a single site-type with PE M-w/M(n)s approaching 2.0 for po lymerization temperatures ranging from 50 to 90 degrees C. The structu re and type of aluminoxane co-catalyst were found not to influence the molecular weight distribution (MWD) of PE although to influence the a ctivity of the Cp2ZrCl2 catalyst. In general, modified methylaluminoxa nes (MMAOs) and methylaluminoxanes (MAOs) were found to have similar a ctivities, whereas isobutylaluminoxane (IBAO) gave a very low activity in the polymerization of ethylene. Increasing isobutyl content in the aluminoxane co-catalyst led to a continual decrease in catalyst activ ity. Increasing aluminium/zirconium (Al/Zr) molar ratio, by increasing the MAO concentration, led to increasing catalyst activity up to a ma ximum activity at an Al/Zr molar ratio of 2400. Like the structure and type of the aluminoxane co-catalyst, the Al/Zr molar ratio was found not to influence the PE MWD. Mixing in additional trimethylaluminium ( TMA) with MAO was found not to alter the MWD but gave lower activity a t similar Al/Zr molar ratios than that from MAO itself. (C) 1998 Elsev ier Science Ltd. All rights reserved.