Modulated differential scanning calorimetry in the glass transition region .3. Evaluation of polystyrene and poly(ethylene tetrephthalate)

Modulated differential scanning calorimetry (MDSC)) presents a new method to evaluate the kinetics underlying the glass transition. Equations that were derived earlier to describe the various time effects in the glass transition, based on irreversible thermodynamics and the theory of liquids, are applied to quasi-isothermal MDSC experiments on amorphous polystyrene and poly(ethylene terephthalate). The analysis involves the computation of a phase angle for the change in the apparent heat capacity at the glass transition that becomes 60 degrees at the point of half-vitrification, followed by a determination of the activation energy as a function of modulation amplitude. Activation energies of 346 and 328 kJ mol(-1) were found for the respective polymers.