Toward the bimodality of polyethylene, initiated with a mixture of a Ziegler-Natta and a metallocene/MAO catalyst system

Polymerization of ethylene catalyzed by a mixture of a Ziegler-Natta (Z-N) and a metallocene system cocatalyzed with methylaluminoxane (MAO) were carr ied out in a single reactor. The Z-N catalyst can be activated in the prese nce of MAO, without any addition of a conventional Z-N activator. The activ ities of the mixture Z-N with Cp2MCl2 (M = Ti,Zr,Hf) (1,2,3) or CpZrCl3 (4) were lower than the obtained with the mixture Z-N and en(Ind)(2)ZrCl2 (5). The weight-average molecular weight (Mw) of the polyethylene (PE) obtained with the mixture Z-N with Cp2MCl2 (M = Ti,Zr,Hf) or en(Ind)(2)ZrCl2 was lo wer than the PE obtained with Z-N and CpZrCl3. For the binary mixture of Z- N with CpZrCl3 (4), the PE obtained showed a bimodal molecular weight distr ibution (MWD) for an appropriate composition of the mixed catalyst in the a bsence of hydrogen in the reaction medium. (C) 2000 Elsevier Science: B.V. All rights reserved.