Molecular weight and molecular weight distribution of polyethene obtained with rac-Me₂Si(Ind)₂ZrCl₂/methylaluminoxane

Ethene and propene polymerizations were carried out with the rac-Me₂Si(Ind)₂ZrCl₂ (Me = CH₃, Ind = indenyl)/methylaluminoxane (MAO) catalyst in toluene. The molecular mass distribution index (MMD = M̄_w/M̄_n) of polypropenes was almost 2,0, while a bimodal MMD was observed for polyethene. The MMD of polyethene was independent of the [Al]/[Zr] ratio and the [Zr] concentration. However, the high molecular weight fraction disappeared when the polymerization was performed either at a low temperature or by using dry MAO. Addition of AlMe₃ to the MAO caused an increase of the low molecular weight fraction at the initial stage of polymerization. The low molecular weight fraction was also increased when the polymerization was conducted in a mixture of toluene and CH₂Cl₂ as the solvent. From these results, the active species formed in the catalyst system are discussed.