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 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 τ e 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 τ e ) are determined from data for monodisperse polymers, the double reptation model predicts that for fixed weight-average molecular weight M w , the zero-shear viscosity η 0 increases slightly with increasing polydispersity M w /M n for log normal distributions, while for the dual constraint model η 0 is almost independent of M w /M n . Experimental data for polystyrenes show no increase (or even a slight decrease) in η 0 with increasing M w /M n at fixed M w , 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

Predicting the linear viscoelastic properties of monodisperse and polydisperse polystyrenes and polyethylenes