Polystyrene frequency dependence, transitions

Temperature-Modulated Calorimetry of the Frequency Dependence of the Glass Transition of Poly(ethylene terephthalate) and Polystyrene... 

B. Wunderlich and 1. Okazaki, Temperature-Modulated Calorimetry of the Frequency Dependence of the Glass Transition of Poly(Ethylene Terephthalate) and Polystyrene. In M.R. Taut and A.l. Hhl, Eds. Structure and Properties of Glassy Polymers, ACS Symposium Series 710, Am. Chem. Soc., Washington, DC (1998) 103 116. 

An example of the moduli-frequency dependence for the case of a nine-arm star polystyrene is shown in Figure 16. For comparison coXoj has been multiplied by Si to realize identical values of [G"]r for linear and star polymers at low frequency. It can be seen that star polymers have relatively higher values of [GHj and [G jj than linear polymers at high frequency. Also, the transition from low to high frequency occurs over a narrower frequency range. The low value of [G ] of the star at low frequency compared to the linear polymer is to be noted. Unfortunately, in order to fit the 0-temperature data an unrealistically high hydrodynamic interaction parameter h — 0.40 had to be used. This problem does not occur in good solvents. 

Experimental phase diagrams for amorphous block copolymers were explored by Khandpur and co-workers (29). First, low-frequency isochronal shear modulus-temperature curves were developed on a series of polyiso-prene-h/ocA -polystyrene polymers to guide the selection of temperatures for the transmission electron microscopy and SAXS experiments to follow see Figure 13.14 (29). Both order-order (OOT) and ODT transitions were iden-tihed. The OOT are marked by open arrows, while the ODT are shown by hlled arrows. Since the ODT occurs as the temperature is raised, an upper critical solution temperature is indicated, much more frequent with block copolymers than with polymer blends. The regions marked A, B, C, and D denote lamellar, bi-continuous, cylindrical, and perforated layered microstructures, respectively. The changes in morphology are driven by the temperature dependence of Xn,... 

In the introduction of this communication we pointed out the similarities between the pressure dependence, the activation energy, and the annealing effects of the (Tp< Tg) and the (T/ > Tg) transitions, which strongly suggests that these transitions are the manifestation of the same relaxation process, probably issued from the complexity of the kinetic mechanism responsible for the glass transition temperature itself. In the second part of this communication we present and reanalyze DSC studies of atactic Rheomolded polystyrene specimens treated with various thermal-mechanical histories. The effect of frequency, amplitude of vibration, and annealing time... 

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