Thermodynamic Properties of Tetraphenyltetrahydroxycyclotetrasiloxane,Octaphenyltetrahydroxytricyclooctasiloxane, Octaphenylpentacyclosilsesquioxane,and Polyphenylsilsesquioxane in the Range 0-300 K

The temperature dependences of the heat capacities of crystalline tetraphenyltetrahydroxycyclotetrasiloxane, octaphenyltetrahydroxytricyclooctasiloxane, and octaphenylpentacyclosilsesquioxane and of glassy polyphenylsilsesquioxane were measured in the range 6-300 K with an adiabatic vacuum calorimeter, with an accuracy of 0.3%. From these data, the thermodynamic functions C⁰_p(T), H⁰(T) - H⁰(0), S⁰(T) - S⁰(0), and G⁰(T) - H⁰(0) of these substances were calculated for the range 0-300 K. The standard entropies of their formation from elements at 298.15 K, _fS⁰, and the entropies of mutual transformations of these substances in the range 0-298.15 K were calculated.