Glass transition in the stable crystalline state of 2,5-dichlorothiophene

Heat capacities of 2,5-dichlorothiophene were measured between 13 and 300 K using an adiabatic calorimeter. Fusion temperature at the triple point was found to be 232.72 K and the enthalpy and entropy of fusion were determined to be 11.87 kJ mol−1 and 51.0 J K−1 mol−1, respectively. The glass transition temperature and the associated heat capacity jump in the stable crystalline phase were determined to be 138 K and 0.53 J K−1 mol−1, respectively. The activation energy was estimated to be 45 kJ mol−1, and a linear relation between the activation energy and the glass transition temperature was confirmed to hold.