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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.

This paper explores shear and extensional rheological behavior of unimodal, metallocenecatalyzed polyethylenes with low contents of long-chain branching (LCB). The polymers were produced in semibatch slurry polymerizations with methylaluminoxane (MAO) activated metallocene catalysts bis-(n-butylcyclopentadienyl)hafnium dichloride (1), rac- [ethylenebis(2-tert-butyldimethylsiloxy) 3), and rac-[ethylenebis(1-triisopropylsiloxy)indenyl)]zirconium dichloride (4). Melt properties in low oscillatory shear, in contrast to molecular weight and molecular weight distribution data from gel permeation chromatography, suggested that the polymers prepared with the ethylene-bridged complexes 2, 3, and 4 contain small but different amounts of LCB. In the melt uniaxial elongation experiments, the long-chain branched polymers exhibited strain hardening at all extension rates (rate range was from 1.0 to 0.01 s -1 ) with continual increase in strain hardening toward low strain rates. Unexpectedly, the behavior in LVE regime low shear and uniaxial elongation in the nonlinear range arranged the polymers in dissimilar order of apparently increasing LCB. Even though both these rheological techniques are sensitive to the molecular structure, they evidently reveal different features of it. Variation in the distribution (topology) of the long-chain branching due to differences in catalyst systems offers a plausible explanation of the differences in uniaxial elongation.

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