Ethene homopolymers and ethene copolymers with 1-hexene were prepared by Et[Ind]2ZrCl2/MAO and Et[IndH4]2ZrCl2/MAO catalyst systems in slurry polymerizations. The melt behavior of the polymers was studied with small amplitude dynamic rheological measurements. The low-frequency complex viscosity of the polymers was higher than expected on the basis of their GPC molecular weights. Furthermore, the polymers exhibited elevated activation energy for flow. The polymers catalyzed by Et[Ind]2ZrCl2/MAO had an Arrhenius-type flow activation energy of 50−60 kJ/mol, and those catalyzed by Et[IndH4]2ZrCl2/MAO a somewhat lower value of 40 kJ/mol. Branching could be detected by 13C NMR in homopolyethene samples polymerized by Et[Ind]2ZrCl2/MAO. We suggest that these properties are due to long-chain branching that occurs via in situ incorporation of vinyl-terminated polyethene macromonomers. With Et[Ind]2ZrCl2/MAO the polymerization parameters affecting the rheological behavior most were ethene partial pressure and comonomer concentration, whereas with Et[IndH4]2ZrCl2/MAO the major factor was the amount of hydrogen.

No abstract

No abstract

The influence of siloxy substitution of ethylene-bridged bis(indenyl)- and bis(tetrahydroindenyl)zirconium dichlorides on ethylene/α-olefin copolymerization and ethylene homopolymerization performance was investigated. Ethylene was copolymerized with 1-hexene and 1-hexadecene over rac-[ethylenebis(1-(tert-butyldimethylsiloxy)-3-indenyl)]zirconium dichloride (1), rac-[ethylenebis(1-(tert-butyldimethylsiloxy)-4,5,6,7-tetrahydro-3-indenyl)]zirconium dichloride (H1), rac-[ethylenebis(2-(tert-butyldimethylsiloxy)-1-indenyl)]zirconium dichloride (2), and rac-ethylenebis(1-indenyl)zirconium dichloride (EBI) using methylaluminoxane (MAO) as cocatalyst. 1-Siloxy substitution was found to remarkably improve the copolymerization ability and 2-siloxy substitution to enhance the polymerization activity of ethylenebis(indenyl)zirconium dichlorides. Optimum homo- and copolymerization performance was observed at a very low Al(MAO) concentration, which for 2 could be reduced to a level of 0.2 mmol/dm3 by using a small amount of triisobutylaluminum. The 1-siloxy-substituted metallocene catalysts 1 and H1 (hydrogenated 1) revealed decreasing comonomer incorporation and increasing induction times with increasing Al(MAO) concentration, which indicates the presence of unfavorable interactions between these metallocenes and MAO. Chain termination occurred mainly by chain transfer to the monomer and β-hydrogen transfer to the metal for catalysts with indenyl and tetrahydroindenyl ligands, respectively.

No abstract