Temperature-modulated calorimetry polystyrene

Temperature-Modulated Calorimetry of the Frequency Dependence of the Glass Transition of Poly(ethylene terephthalate) and Polystyrene... [Pg.103]

Glass transitions involve mainly the onset or freezing of cooperative, large-amplitude motion and can be studied using thermal analysis. Temperature-modulated calorimetry, TMC, is a new technique that permits to measure the apparent, fiequency-dependent heat capacity. The method is described and a quasi-isodiermal measurement method is used to derive kinetic parameters of the glass transitions of poly(ethylene terephthalate) and polystyrene. A first-order kinetics expression can describe the approach to equilibrium and points to the limits caused by asymmetry and cooperativity of the kinetics. Activation energies vary from 75 to 350 kJ/mol, dependent on thermal pretreatment. The preexponential factor is, however, correlated with the activation energy. [Pg.103]

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. [Pg.318]