Calorimetric study of 1,3-diphenyl-1,1,3,3-tetramethyldisiloxane: Emergence of alpha-, beta-, and crystalline-glass transitions

Heat-capacities of fragile liquid 1,3-diphenyl-1,1,3,3-tetramethyldisiloxane (PMS) were precisely measured in the temperature range between 13 K and 300 K with an adiabatic calorimeter, alpha- and beta-glass transitions were observed at around 167 K and 69 K, respectively, in the liquid state, and another glass transition at around 150 K in the stable crystalline state, PMS was thus found to be guile a rare substance to show glass transitions both in the liquid and crystalline states in one substance. The interrelation between the transition temperatures is discussed with respect to their modes of molecular motions.