Metallocene‐methylaluminoxane catalysts for olefin polymerization. V. Comparison of Cp₂ZrCl₂ and CpZrCl₃

Abstract

The ethylene polymerization by Cp2ZrCl2/MAO (Cp = η5: cyclopentadienyl; MAO = methyl aluminoxane) and CpZrCl3/MAO have been studied. The MW and PD (= Mw/Mw) of polymers obtained after 2.5‐60 min are the same, which indicate short chain lifetime. The values of rate constants for Cp2ZrCl2 at 70°C are: kp = 168−1670 (M s)−1 and ktrA1 = 0.012‐0.81 s−1 depending upon [Zr] and [MAO,] ktrβ = 0.28 s−1, and ktrH = 0.2 M−1 torr−1/2 s−1. These chain transfer rate constant values are two to three orders of magnitude greater than the corresponding values found for MgCl2 supported titanium catalysts. One significant difference between the heterogeneous and homogeneous catalysts is that the former decays according to an apparent second order kinetics, whereas the latter decay is simple first order at 0°C and biphasic first order at higher temperatures. The productivity of the catalysts depends weekly on temperature while the MW decreases strongly with increase of temperature above 30°C. All the active species were formed upon mixing Cp2ZrCl2 with MAO while it took up to 20 min for the CpZnCl3/MAO system. The productivity of the former increase more strongly with the decrease of [Zr] than the latter. Otherwise, the two catalyst systems have all their kinetic parameters differing less than a factor of two.

Effect of experimental conditions on ethylene polymerization within-situ-supported metallocene catalyst

“…Above 80°C, severe deactivation occurs. Chien et al 16 have speculated on the possible mechanism for deactivation. One possibility is a slow dissociation of stable active species to form inactive forms.…”

Activation of iPr(CpFluo)ZrCl2 by methylaluminoxane, 3. Kinetic investigation of the syndiospecific hex-1-ene polymerization in hydrocarbon and chlorinated media

“…They do not depend on the initial monomer concentration as well as on the MAO/Zr ratio. This suggests that the polymer chain length is mainly controlled by a unimolecular transfer process, likely a b-H abstraction reaction 18,19) .…”

Synthesis and reactivity of new silyl substituted monocyclopentadienyl zirconium complexes. X-ray molecular structure of [Zrη5-C5H4 (SiMe2CH2Ph)(CH2Ph)3]

“…Of these processes, Ziegler-Natta a-olefin polymerization is probably the most important [1][2][3][4][5]. However, the formal 12-electron monocyclopentadienyl group 4 metal complexes also play a role as catalysts in both organic synthesis and olefin polymerization [6][7][8][9][10][11][12]. Their reactivity profile differs considerably from those shown by their metallocene counterparts for both steric and electronic reasons.…”