Abstract
The heat capacity, C° p, of polydimethylsiloxane (PDS) between 8 and 332°K was measured in a vacuum adiabatic calorimeter to within 0·2%. The values of T g, T° melt and ΔH° melt were determined. The functions of H( T)− H°(0), S°( T) and G°( T)− H°(0) of amorphous and crystalline PDS were calculated for the range 0–350°K. The values of S°(0) and S° melt for a glassy polymer were estimated as well as those of H°(0)− H° c(0). The enthalpies of bulk polymerization of hexamethylcyclotrisiloxane (D 3) and octamethylcyclotetrasiloxane (D 4) to high molecular PDS at 298° were determined. The values of ΔH° p, ΔG° p and ΔG p of the polimerization processes of D 3 and D 4 in the range 0–350°K were calculated. The thermodynamic allowedness of polymerization of D 4 is due to an entropy rise in this process.
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