Five titanium complexes having F(s) or CF3(S) Containing phenoxy-imine chelate ligands were prepared and investigated for their potential as ethylene polymerization catalysts using methylalumoxane (MAO) as a co-catalyst at 25 degreesC under atmospheric pressure. Polymerization results showed that the electrophilicity of the titanium center plays a dominant role in determining activity. These results clearly demonstrate, for the first time, the electron-withdrawing substituent effects on polymerization activity. The complexes possessing plural F(s) or CF3(S) in the phenoxy-imine ligand displayed very high activities exceeding those for Cp2TiCl2 and Cp2ZrCl2. The activity, 43,300 kg polyethylene (PE) mol-cat(-1) h(-1), exhibited by the complex having three fluorines in the ligand, represents the highest value reported to date for ethylene polymerization catalysts based on titanium complexes under atmospheric pressure at ambient temperatures. (C) 2002 Elsevier Science B.V. All rights reserved.