Time‐temperature superposition and dynamic mechanical behavior of atactic polystyrene

Abstract

SynopsisT h e dynamic mechanical behavior of monodisperse atactic polystyrene (mol. wt. 98,OOO) has been measured in the frequency range, 10 ' to 10 Hz arid 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 pronounccd in the tan Q (C;"/G') plots. The tan $I 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 OIL heating near Tg so that the time-temperature superposition is vitiated.

Mechanical Behavior of Polystyrene Microgels

“…These characteristics are very similar to those observed for linear PS. 16 Figure 3 shows dynamic mechanical master curves for the storage and loss moduli of a PS microgel. The detailed shape is only approximate, given the aforementioned breakdown of time-temperature superpositioning in the transition zone.…”

Mechanical relaxation spectroscopy of three triepoxide-based polymers

“…For example, the mechanical loss tangent, tan, of polycarbonate of molecular weight 28,600 is 10 Ϫ2 in the range 290 to 350 K, 30 and for other molecular weight polycarbonates, the value remains nearly the same. 23,31,32 For the three new polymers prepared in this study, tan in this temperature range is 2.0 ϫ 10 Ϫ2 to 2.6 ϫ 10 Ϫ2 , as seen in Figure 5, which is greater than that of polycarbonate. We therefore conclude that the new polymers studied here absorb more mechanical energy at 1 Hz than polycarbonates, and their fracture toughness, we suggest, will be found to be comparable to that of polycarbonate.…”

“…4,5,23 It contributes to both the thermodynamics and kinetics of supercooled liquids and polymers. 28,29 Accordingly, an isothermal relaxation spectrum represents the sum of contributions from the ␣ and ␤ relaxations.…”

“…A widely used procedure for obtaining information of practical interest from the mechanical relaxation and creep data of amorphous polymers is the construction of "master" plots from time-temperature superposition 1,3,13,23 of the GЈ and GЉ data. In this procedure, GЈ and GЉ measured at different temperatures over a narrow frequency (or time) range are superposed by shifting each point of the spectra at a given T by the same amount horizontally along the frequency (or time) axis.…”

Structure Evolution in a Polyurea Segmented Block Copolymer Because of Mechanical Deformation

“…Figure 12 shows the mechanical loss tangent measured at various temperatures, each shifted on the frequency axis to superpose the data. Comparing loss tangent curves is a sterner test of superpositioning, [58][59][60] since unlike monotonic stress relaxation data, there is a peak in the loss tangent spectra and there is no vertical shifting (since any temperature or density effects on the storage and loss modulus cancel 27 ). It is evident that the loss tangents for PU do not superpose in the transition zone.…”