Abstract
Hereunder is presented a report of studies made of the melt viscosities of the fractions of linear and ethyl-branched polyethylenes having very narrow molecular weight distributions. The Newtonian melt viscosities, ηo, of the linear fractions were related to their weight-average molecular weight Mw, by the following equation, at 190°C.ηo=2.39×10-15Mw3.42It was possible to reduce the relation between the viscosities and the shear rates of these fractions to a single master curve irrespective of their molecular weights, using the reduced variables, η/ηo and ηoMwγ for the ordinate and the abscissa, respectively. Meanwhile, this master curve was different from that of the polyethylenes having broader molecular weight distributions: the reduced viscosity of the former fell more sharply than the latter as the reduced hear rate increased.It was found that in the branched fractions having 10-25 ethyl-branches per 1000 chain atoms, the Newtonian viscosities were about half a decade greater than that of the linear fractions at the same molecular weight. It was found also that the critical shear rates, the shear rates of the onset of the non-Newtonian flow, were lower than the linear homologues.
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