Analytical and rheological characterization of long-chain branched metallocene-catalyzed ethylene homopolymers

The aim of this paper is to compare the results of analytical and rheological characterization techniques with respect to the analysis of long-chain branches (LCB) in polyethylenes. The materials investigated are metallocene-catalyzed ethylene homopolymers into which LCB were introduced by the selection of appropriate polymerization conditions. The samples were characterized analytically by C-13 NMR, IR-spectroscopy, and size exclusion chromatography coupled with a multi-angle laser light scattering detector. The rheological characterization was performed using dynamic-mechanical measurements and creep and creep recovery experiments in shear. It was found that the analytical methods were in good qualitative agreement for the most highly branched sample whose LCB content was 0.12 LCB/1000 C as determined by C-13 NMR spectroscopy. However, even a 10-times lower LCB content, which is almost beyond the detection limit Of C-13 NMR measurements, had a significant impact on the rheological behavior. Rheological experiments clearly indicated the presence of LCB by changes in the frequency dependence of dynamic-mechanical material functions and the molecular mass dependence of the zero shear-rate viscosity in comparison to linear polyethylenes. (C) 2002 Published by Elsevier Science Ltd.