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

Abstract

Homogeneous Ziegler‐Natta systems for the ethylene polymerization, deriving from R2R2′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(CH2C6H5)4, are also able to polymerize ethylene with a fairly high productivity. Active species containing ZrOAl bonds have been postulated.

In situ1H- and27AL-NMR studies on metallocene catalyst systems?Catalysts for olefin polymerization

“…27 Al-NMR investigations show that the in situ hydrolyzed products of TMA with H 2 O are tetra-coordinated, and their molecular weights are low. High polymerization activity could also be achieved with MAO with low molecular weight as the cocatalyst, which is different from the result reported by Giannetti et al 3 5. Cp 2 ZrCl 2 can be partially monoalkylated by TMA, MAO, and the in situ partially hydrolyzed products of TMA with water.…”

“…It may be concluded that at relatively lower concentration, the spectrum mainly displays the resonance of the residual TMA and MAO with low molecular weight (2), and at higher concentration it displays that of MAO with relatively high molecular weight (3). It can also be concluded that the hydrolysis concentration of TMA is important for the molecular weight of MAO after the same reaction time.…”

“…In the literature, MAO has been characterized by 1 H-NMR, 2 13 C-NMR, 3 27 Al-NMR, 4 -6 IR, 4 UVVis, 3 and GPC, 7 but all those characterizations were conducted with finished products, and therefore, can reflect neither the actual changes during the reaction nor the influence of hydrolysis conditions on structure or composition.…”

AlOx Coating of Ultrastable Zeolite Y: A Possible Method for Vanadium Passivation of FCC Catalysts

“…The UV region of the coated samples presents several absorption bands assigned to the solvent (toluene) and a broad, less intense, band around 300 nm due to an oxygen to aluminum p π -d π dative bond, typical for the oxygen-bridged organoaluminum compounds. 17,18 In the near-IR region (see the insert, Figure 3), the samples are characterized by several absorption bands: the band at 1410 nm could be assigned to the overtone of the stretching mode of the silanol groups, while the band at 1458 nm could be assigned to the overtone of the OH stretching in water molecules. Both of them are decreasing during triisobutylaluminum hydrolysis.…”

Effects of residual and external alkylaluminum on the synthesis of syndiotactic polystyrene with cyclopentadienyltitanium tribenzyloxide-methylaluminoxane catalyst

“…6 Reddy et al 7 reported that addition of TMA to the Cp 2 ZrCl 2 -MAO system for ethylene polymerization leads to a dramatic increase in catalyst productivity and catalyst lifetime. However, as reported by Giannetti et al 8 and Chien and Wang, 9 catalytic activities decrease with increasing an [TMA]/[MAO] ratio when Cp 2 Zr(CH 2 C 6 H 5 ) 2 and (Ind) 2 ZrMe 2 , and Cp 2 ZrCl 2 were used in ethylene polymerizations.…”