Comparison of the Rheological Properties of Metallocene-Catalyzed and Conventional High-Density Polyethylenes

Dynamic measurements in a plate−plate system and steady state flow experiments in a capillary die are presented for conventional high-density polyethylenes (HDPEs) and a new type of polyolefin. The latter, the so-called metallocene-catalyzed HDPEs, are characterized by their low polydispersity and the total absence of branching. The metallocene-catalyzed materials show a different rheological behavior than commercial polyethylenes, which can be summarized as follows:  (a) Higher viscosities than conventional HDPEs of the same molecular weight. The dependence of the viscosity on the molecular weight follows a power law equation with an exponent of 4.2 for metallocene catalyzed and 3.6 for conventionals. (b) For high molecular weight materials, the storage modulus overcomes the loss modulus (G‘ > G‘‘) at 190 °C in all frequency ranges. However, for conventional HDPEs, G‘‘ > G‘ at the same temperature and frequency range. (c) At long relaxation times, the values of H(τ) spectra of metallocene-catalyzed sampl...