Calorimetric study of 1,1,3,3,5,5-hexaethylcyclotrisiloxane and polydiethylsiloxane and the process of polymerization of 1,1,3,3,5,5-hexaethylcyclotrisiloxane in the range 13–330 K

Abstract

An adiabatic vacuum calorimeter has been used to study the thermal capacity C p ° of 1,1,3,3,5,5-hexaethylcyclotrisiloxane and polydiethylsiloxane in the region 13–330 K with an error of 0·2% with determination of the temperatures and enthalpies of the physical transitions. It was found that the first exists in three crystalline and liquid states and the second in the partially crystalline and liquid states, the polymer crystals existing in two modifications. The functions H 0( T)− H 0(0), S°( T) and G°( T)− H°(0) of the monomer and polymer have been calculated. The zero entropy S g°(0) of glassy polydiethylsiloxane and the difference in the zero enthalpies of the polymer in the glassy and crystalline states H g°(0)− H c °(0) have been evaluated. The calorimeter was used to measure the enthalpy of polymerization of hexaethylcyclotrisiloxane in bulk at 433 K and p = 101·325 kPa. From the results the authors calculate the values ΔH p ° ΔS p ° and ΔG p ° of the process hexaethylcyclotrisiloxane→polydiethylsiloxane for the region 0–330 K. The upper limiting temperature of polymerization of hexaethylcyclotrisiloxane has been evaluated.