Copolymerizations of ethylene with alpha-olefins (i.e., 1-hexene, I-octene, allylbenzene, and 4-phenyl-1-butene) using the bis(beta-enaminoketonato) titanium complexes [(Ph)NC(R-2)CHC)R-1)O](2)TiCl2 (1a: R-1 = CF3, R-2 = CH3; 1b: R-1 = Ph, R-2 = CF3; and 1c: R-1 = t-Bu, R-2 = CF3), activated with modified methylaluminoxane as a cocatalyst, have been investigated. The catalyst activity, comonomer incorporation, and molecular weight, and molecular weight distribution of the polymers produced can be controlled over a wide range by the variation of the catalyst structure, alpha-olefin, and reaction parameters such as the comonomer feed concentration. The substituents R-1 and R-2 of the ligands affect considerably both the catalyst activity and comonomer incorporation. Precatalyst la exhibits high catalytic activity and produces high-molecular-weight copolymers with high alpha-olefin insertion. (c) 2005 Wiley Periodicals, Inc.