The effects of aluminum alkyls on the gasphase ethylene homopolymerization and ethylene/1-hexene copolymerization over polymer-supported metallocene/ methylaluminoxane [(n-BUCP)(2)ZrCl2/MAO] catalysts were investigated. Results with triisobutyl aluminum (TIBA), triethyl aluminum (TEA), and tri-n-octyl aluminum (TNOA) showed that both the type and the amount of aluminum alkyl influenced the polymerization activity profiles and to a lesser extent the polymer molar masses. The response to aluminum alkyls depended on the morphology and the Al : Zr ratio of the catalyst. Addition of TIBA and TEA to supported catalysts with Al : Zr >200 reduced the initial activity but at times resulted in higher average activities due to broadening of the kinetic profiles, i.e., alkyls can be used to control the shape of the activity profiles. A catalyst with Al : Zr = 110 exhibited relatively low activity when the amount of TIBA added was <0.4 mmol, but the activity increased fivefold by increasing the TIBA amount to 0.6 mmol. The effectiveness of the aluminum alkyls in inhibiting the initial polymerization activity is in the following order: TEA > TIBA much greater than TNOA. A 2-L semibatch reactor, typically run at 80degreesC and 1.4 MPa ethylene pressure for 1 to 5 h was used for the gas-phase polymerization. (C) 2004 Wiley Periodicals, Inc.