Predicting the linear viscoelastic properties of monodisperse and polydisperse polystyrenes and polyethylenes |
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Authors: | Cattaleeya Pattamaprom Ronald G Larson |
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Institution: | (1) Department of Chemical Engineering Thammasat University, Pratumthani 12121 Thailand, TH;(2) Department of Chemical Engineering University of Michigan Ann Arbor, MI 48109, USA e-mail: rlarson@engin.umich.edu, US |
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Abstract: | For linear homopolymers the linear viscoelastic predictions of the double reptation model are compared to those of a recent,
more detailed model, the “dual constraint model” and to experimental data for monodisperse, bidisperse, and polydisperse polystyrene
melts from several laboratories. A mapping procedure is developed that links the empirical parameter K of the double reptation
model to the molecular parameter τe of the dual constraint model, thereby allowing the parameter K to be related to molecular characteristics such as the monomeric
friction coefficient ζ. Once K (or τe) are determined from data for monodisperse polymers, the double reptation model predicts that for fixed weight-average molecular
weight Mw, the zero-shear viscosity η0 increases slightly with increasing polydispersity Mw/Mn for log normal distributions, while for the dual constraint model η0 is almost independent of Mw/Mn. Experimental data for polystyrenes show no increase (or even a slight decrease) in η0 with increasing Mw/Mn at fixed Mw, indicating a deficiency in the double reptation model. The dual constraint theory is also applied to hydrogenated polybutadienes
and commercial high-density polyethylenes, where we believe it can be used to indicate the presence of long side branches,
which are difficult to detect by other analytic methods.
Received: 11 October 2000 Accepted: 17 May 2001 |
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Keywords: | Dual constraint model Double reptation model Polydispersity Polystyrene Polyethylene Hydrogenated polybutadiene |
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