The ethylene and ethylene/1-hexene polymerization activities of seven catalysts, consisting of (n-BUCP)(2)ZrCl2/MAO supported on five different types of spherical polymer beads, were determined for gas-phase polymerization at 1.4 MPa ethylene pressure and initial I-hexene concentrations of up to 40 Mol/M3. The catalytic activity for all the catalysts was highest at 80-90 degrees C. Copolymerization activities were higher than homopolymerization activities; the average rates for I h runs ranged from 0.1 to 4.1 and from 2.4 to 13 kg PE/(mol Zr s MPa C2H4) for homo- and copolymerization, respectively. Specific rates decreased with increasing Zr content for copolymerization (range of Zr concentration 0.21-0.39 mass%). The rates of 1-hexene incorporation decreased with increasing Al:Zr ratios (range of Al:Zr ratios 100370). Most of the catalysts produced spherical copolymer particles without the production of fines. Molar masses of copolymers were lower than those of homopolymers, but they did not change appreciably with changes in 1-hexene concentration. (c) 2005 Elsevier B.V. All rights reserved.