Viscoelastic Properties of Amorphous Polymers. 7. Changes of the Anomalous Behavior of Low Molecular Weight Polystyrene with the Addition of a Diluent

Abstract

Torsional shear measurements of the recoverable creep compliance of a 54.7% solution of a narrow molecular weight distribution polystyrene of low molecular weight, 4000, in tri- m -tolyl phosphate are reported as a function of temperature, near and above the glass temperature. Time−temperature superposition of the experimental data is found to be impossible. In fact the steady-state recoverable compliance, J s, decreases with decreasing temperature as in undiluted low molecular weight polystyrene and other polymers. However, compared with the recoverable compliance data obtained previously in an undiluted polystyrene sample with a comparable molecular weight of 3400, J s is a significantly weaker function of temperature. Furthermore, the large difference between the temperature dependences of the local segmental retardation time τ* α and η J s observed in the bulk polymer is significantly reduced when the polymer is diluted by TCP. As a consequence, the separation between log τ* α and log(η J s ), is drastically reduced. These changes of the viscoelastic anomalies of low molecular weight polystyrene when diluted by a lower T g solvent are shown to be consistent with the predictions of the coupling model.