Temperature dependence of viscosity–shear rate behavior in undiluted polystyrene

The time—temperature superposition principle is well‐established for linear viscoelastic properties of polymer systems. It is generally supposed that the same principle carries over into nonlinear phenomena, such as the relationship between viscosity η and shear rate {article}{empty}{document}γ{document} . Guided by this principle and the forms of various molecular theories, one would expect that η—{article}{empty}{document}γ{document} data on the same polymer at different temperatures would superimpose when plotted as η/η0 versus {article}{empty}{document}γ{document} η0/ρT, η0 being the limiting viscosity at low shear rates, ρ the polymer density, and T the absolute temperature. Data on polystyrene melts, obtained in a plate‐cone viscometer, appear systematically to violate this principle in the range 140–190°. Such anomalies are absent in concentrated solutions of polystyrene. The trends are similar to those reported by Plazek in the steady‐state compliance of polystyrene melts near Tg, but they appear to persist to higher temperatures than the compliance anomaly.