The activities of two (n-BuCp)(2)ZrCl2 catalysts supported on methylaluminoxane (MAO)-treated polymer particles were evaluated. The supports were spherical polymeric particles, containing macropores and prepared by suspension polymerization of 2-hydroxyethyl methacrylate, divinyl benzene, ethyl styrene, and styrene. Both catalysts had a Zr content of 0.31 mass % and an Al/Zr ratio of 185; the supports for one of the catalysts contained 59 mass % 2-hydroxyethyl methacrylate, whereas the support for the other catalyst had a 2-hydroxyethyl methacrylate content of 10 mass %. Ethylene homo- and ethylene/1-hexene copolymerization activities were determined for gas-phase operation at temperatures of 50 to 90degreesC and ethylene pressures of approximate to1.4 MPa. Polymerization activities were strong functions of temperature and 1-hexene concentration; copolymerization activities of up to 23,200 kg PE/(mol Zr h(-1)) were obtained for I-h polymerization runs. The product particle morphology was excellent, mostly spherical particles essentially without fines. Scanning electron microscopy showed that the spherical copolymer particles, for all copolymerization conditions, consisted of well-defined concentric spherical shells. (C) 2003 Wiley Periodicals, Inc.