The thermodynamic parameters of polymethylphenylsiloxane in the temperature range 0-340 K

The temperature dependence of the heat capacity of polymethylphenylsiloxane was studied in the temperature range 5-340 K in an adiabatic vacuum calori meter. Measurements were made with an error of 0.2%. The thermodynamic para meters of compound vitrification and of the vitreous state were determined. The experimental data were used to calculate the C(p)degrees (T), H degree s(T)- H degrees(0), S degrees(T), and G degrees(T)-H degrees(0) thermodynam ic functions in the temperature range 0-340 K. From the results of this wor k and the literature data, the Delta(f)H degrees, Delta(f)S degrees, Delta( f)G degrees, and InKf parameters of the formation of the polymer at T = 298 .15 K were determined; the enthalpies, entropies, and Gibbs functions were also calculated for bulk polymerization with ring opening of cis- and trans -1,3,5-trimethyl-1,3,5-triphenylcyclotrisiloxanes and cis-1,3,5,7-tetrameth yl-1,3,5,7-tetraphenylcyclotetrasiloxane to polymethylphenylsiloxane at 0-3 40 K. It was shown that the polymerization of these cyclosiloxanes had the lower temperature limits and that the cis and trans isomers of 1,3,5-trimet hyl-1,3,5-triphenylcyclotrisiloxane also had the upper temperature limits o f polymerization.