Differential scanning calorimetry (DSC) experiments were conducted on a DSC Q1000 (TA Instruments, New Castle, United States) that was calibrated with indium. Approximately 2 -5 mg of sample was weighed and sealed in an aluminium hermetic pan. A similar empty pan was used as the reference. The glass transition temperature (Tg) of the sample was measured using a heat-cool-heat cycle between -60 °C and 210 °C under nitrogen atmosphere at heating/cooling rates of 10 °C/min. The midpoint Tg is reported from the second heating.