A new method for the determination of the kinetics of Tg

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Abstract
Differential scanning calorimetry has been found useful in studying the kinetics of the Tg. The method commonly used involves annealing the polymer at temperatures below Tg for various periods of time and then measuring the enthalpy change in going from the glassy to the liquid state as a function of annealing time and temperature. However, annealing below Tg is a slow process, and therefore the quantity of research that can be done by this method is limited. Moreover, the above method measures primarily the kinetics of the annealing process. We are also interested in the kinetics of the transition from the glass to the liquid state. We have developed a DSC method to measure the kinetics of the transition of a polymer from the glassy to the liquid state. It involves quickly heating the polymer from below the glass transition to slightly above it and measuring the change in enthalpy with time as the polymer goes from the glass to the liquid. The method depends on subtracting out, by use of a computer, a DSC response that results from the need for the instrument to reach equilibrium. A relaxation time of 10.9 sec for polystyrene at 375°K was determined. These results are shown to be consistent with other theoretical and experimental volume relaxation studies.

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