Time‐temperature superposition and dynamic mechanical behavior of atactic polystyrene

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Abstract
The dynamic mechanical behavior of monodisperse atactic polystyrene (mol. wt. 98,000) has been measured in the frequency range, 10−5 to 10 Hz and temperature range 359–374K. The time‐temperature superposition of the entire data in the frequency range of overlap seems less satisfactory in both the real and imaginary components of the complex shear modulus, G′ and G″, respectively. The lack of adequate superposition becomes pronounced in the tan ϕ (G″/G′) plots. The tan ϕ plots provide a more discerning criteria for the superposition than the G′ or G″ spectra.An analysis based on an earlier model for anelastic deformation shows that of the several changes that may occur in the dynamic mechanical behavior on heating of polystyrene, the predominant ones are both an increase in the size of the microshear domains and the correlations of movement of segments near entanglements. These decrease the contribution to the modulus on heating near Tg so that the time‐temperature superposition is vitiated.