Macromolecules, Vol.31, No.24, 8448-8454, 1998
Long-chain branched polyethene polymerized by metallocene catalysts Et[Ind](2)ZrCl2/MAO and Et[IndH(4)](2)ZrCl2/MAO
Ethene homopolymers and ethene copolymers with I-hexene were prepared by Et[Ind](2)ZrCl2/ MAO and Et[IndH(4)](2)ZrCl2/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](2)ZrCl2/MAO had an Arrhenius-type flow activation energy of 50-60 kJ/mol, and those catalyzed by Et[IndH(4)](2)ZrCl2/MAO a somewhat lower value of 40 kJ/mol. Branching could be detected by C-13 NMR in homopolyethene samples polymerized by Et[Ind](2)ZrCl2/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](2)ZrCl2/MAO the polymerization parameters affecting the rheological behavior most were ethene partial pressure and comonomer concentration, whereas with Et[IndH(4)](2)ZrCl2/MAO the major factor was the amount of hydrogen.
Keywords:MOLECULAR-WEIGHT DISTRIBUTION;TWIN-SCREW EXTRUDER;HIGH-DENSITY POLYETHYLENES;OLEFIN POLYMERIZATION;RHEOLOGICALPROPERTIES;PEROXIDE TREATMENT;ETHYLENE;LLDPES;MICROSTRUCTURE;BEHAVIOR