Metallocenes for Ethene/Propene Copolymerizations with High Product of Reactivity Ratios

Abstract

Ethene/propene copolymerizations were performed with catalytic systems composed of a stereorigid racemic isospecific metallocene and polymethylalumoxane. A number of complexes were used as representatives of three different classes of metallocenes. r-Me2C(3-t-Bu-Cp)2ZrCl2, r-Me2C(3-t-Bu-Ind)2ZrCl2, r-EBDMIZrCl2, r-EBDMTHIZrCl2, and r-Me2Si(2-Me-4-Ph-Ind)2ZrCl2 were chosen as sterically hindered complexes. The parent metallocenes, r-Me2C(Ind)2ZrCl2, r-EBIZrCl2, and r-Me2Si(Ind)2ZrCl2 were also employed as well as other compounds bearing different substituents on the indenyl ligands such as r-Me2C(3-Me3Si-Ind)2ZrCl2, r/m-Me2C(3-Me-Ind)2ZrCl2, and r-Me2Si(2-Me-Ind)2ZrCl2. The reactivity ratios of copolymerization (r E and r P) were determined and examined in the light of the metallocene structure. The complexes that were particularly demanding from the steric point of view were identified as suitable candidates for promoting copolymerizations with a high product of reactivity ratios, giving r E r P in a range from 1.7 to 3.0. The other two classes of metallocenes gave rise to r E r P clearly lower than 1. A more complex situation was observed as far as the reactivity ratios r E and r P are concerned. The enhancement of the steric hindrance brought about in most cases an increase of r E but not a substantial decrease of r P. In some cases, r E was found to remain almost unchanged and r P dramatically increased. A correlation between the reactivity ratios and the metallocene structure is attempted.

Ethylene/1-hexene copolymerizations by syndioselective metallocenes: Direct comparison of Me2C(Cp)(Flu)ZrMe2 with Et(Cp)(Flu)ZrMe2

“…A clear trend was observed for the activity and molecular weight, i.e., both decreases as ␤ increases in the ethylene polymerizations by using various bridged metallocenes containing two indenyl ligands. 23 This is in good agreement with our results.…”

“…17 Because we can safely assume that structures of 1 and 2 are the same as those of the corresponding metallocene chlorides, the difference in the activity according to polymerization temperature is expected to be deeply related to these structural differences, especially in solution. Galimberti et al 23 have studied the influence of the -ligands of the metallocenes: (a) their symmetry, (b) the bridge between them, (c) substituents of the rings, on the activity, stereospecificity, regiospecificity, and molecular weight of final polymer. Based on the investigation of the role played by the bridge connecting the two indenyl ligands, they conclude that the dihedral angle (␤ in Chart I) is most affected, whereas minor changes are observed as far as the other angles and the bond distances are concerned.…”

C2-Symmetric Zirconocenes for High Molecular Weight Amorphous Poly(propylene)

“…[44] From the fitting parameter the reactivity ratio values r 1 = 5.73, r 2 = 0.038, r 1 6 r 2 = 0.22 were obtained, indicating a very good distribution of ethylene along the poly(propylene) chain.…”

Synthesis of branched polyethylene by ethylene homopolymerization with a novel (α‐diimine)nickel complex in the presence of methylaluminoxane

“…Constrained-geometry catalysts [21][22][23] and monotitanocene catalysts 30 offer the possibility of yielding long-chain-branched PE from only ethylene polymerization. The results have been discussed in terms of a mechanism in which ethylene is copolymerized with macromonomers of ␣-olefin, which can be obtained via ␤-hydride elimination or chain transfer to ethylene monomers.…”