Homogeneous Ziegler–Natta catalysis. II. Ethylene polymerization by IVB transition metal complexes/methyl aluminoxane catalyst systems

Abstract

Abstract Homogeneous Ziegler‐Natta systems for the ethylene polymerization, deriving from R 2 R 2′ M complexes (R = cyclopentadienyl; R′ = alkyl, aryl; M = Ti, Zr, Hf) and oligomeric oxoalane compounds, were studied. Further results concerning the methyl aluminoxane synthesis and the related chemistry are reported. On the basis of spectroscopic data a delocalized electronic structure could be inferred for these compounds. Results from polymerization experiments showed that the highest productivities are obtained only by oxoalane cocatalysts having a high degree of oligomerization. The catalytic activity of the systems under investigation was strongly affected also by changing both the σ‐alkyl and the π‐cyclo‐pentadienyl ligands. Furthermore, it was found that in the presence of methyl aluminoxane, the homoleptic σ‐alkyl derivatives of IVB transition metals, such as Zr(CH 2 C 6 H 5 ) 4 , are also able to polymerize ethylene with a fairly high productivity. Active species containing ZrOAl bonds have been postulated.