The glass transition temperature of amorphous poly(ethylene terephthalate) by thermally stimulated currents

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Abstract
The relation between the temperature Tα of the dipolar relaxation, obtained by the technique of thermally stimulated currents (TSC) and the glass transition temperature Tg has been studied in amorphous poly(ethylene terephthalate) samples. The temperature Tα depends fundamentally on the polarization temperature Tp, the polarization time tp, and the heating rate v. For each heating rate a maximum Tα, TM, was obtained for an optimum polarization temperature Tpo. The value of Tpo is 70°C, independent of the heating rate, and very close to the glass transition temperature obtained by differential scanning calorimetry (69°C). The resulting value for TM coincides with Tpo in the limits of null heating rate and null isothermal polarization time, and, consequently, TM gives the value of the glass transition temperature for each heating rate as a function of the isothermal dipolar contribution on polarizing at the temperature Tpo.