Thermal analysis was carried out on a Differential Scanning Calorimeter (TA instrument). The powder samples, approximately 20 mg in weight, were heated from 40 °C to 600 °C in a hermetically sealed aluminum pan under N2 atmosphere. The glass transition temperature (Tg) was obtained by drawing tangents to the exothermic peak and the onset of crystallization (Tx) was taken as the temperature at which the heat flow starts to increase positively from its constant value.