Macromolecules, Vol.30, No.18, 5450-5456, 1997
Viscoelastic Properties of Amorphous Polymers .7. Changes of the Anomalous Behavior of Low-Molecular-Weight Polystyrene with the Addition of a Diluent
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 tau(alpha)*, and eta J(s) observed in the bulk polymer is significantly reduced when the polymer is diluted by TCP. As a consequence, the separation between log tau(alpha)* and log(nJ(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.
Keywords:GLASS TRANSFORMATION TEMPERATURE;ELASTIC NEUTRON-SCATTERING;SEGMENTAL CHAIN DYNAMICS;TIME-SCALE SHIFTS;TERMINAL DISPERSIONS;CONDUCTIVITY SPECTRA;ALPHA-RELAXATION;FORMING SYSTEMS;ION DYNAMICS;DEPENDENCE