Slow molecular mobility in the amorphous thermoplastic polysulfone

Abstract

The thermally stimulated depolarization current (TSDC) technique has been used to study the slow molecular mobility of polysulfone in the glassy state and in the glass transformation region, i.e., in the temperature ranging from −155 to 183 °C. Since the polysulfone is a rigid polymer without polar side-groups, a broad and low-intensity secondary relaxation was detected in the temperature region from −120 °C up to the glass transition; the activation energy of the motional modes of this secondary relaxation is in the range between 35 and 100 kJ mol⁻¹. The glass transition temperature of polysulfone provided by the TSDC technique is T _M = T _g = 176 °C (at 4 °C min⁻¹). The relaxation time at this temperature is τ(T _g) = 33 s and the fragility index was found to be m = 91. Our results are compared with literature values obtained by dynamic mechanical analysis and by dielectric relaxation spectroscopy. The amorphous polysulfone was also characterized by DSC; a glass transition signal with an onset at T _on = 185.5 ± 0.3 °C (heating rate 10 °C min⁻¹) was detected, with ΔC _p = 0.21 ± 0.01 J g⁻¹ °C⁻¹.