Thermodynamics of chain-molecule mixtures : heats of mixing of linear methylsiloxanes

Abstract

Heats of mixing have been obtained at 25° for the following mixtures of linear methylsiloxanes : hexamethyldisiloxane (dimer)-octamethyltrisiloxane (trimer); dimer-tetramer; dimer-pentamer; trimer-pentamer and dimer-polymer. The heats are consistent with the Prigogine cell theory for the thermodynamics of chain-molecule mixtures and with Brϕnsted's principle of congruence. Two assumptions concerning the volume dependence of the configurational energy of a liquid were tested : that of a van der Waals liquid which gave good results and a 6-12 model which gave poor results. Two excess volume results were also in accord with the former model. The relation between the Prigogine cell theory and the recent theory of Flory, Orwoll and Vrij is examined.