The miscibility of polymers: II. Miscibility and heat of mixing of liquid polyisobutenes and silicones

Abstract

Heats of mixing of low molecular weight polyisobutene and poly(dimethyl siloxane) fluids have been measured at 50°C and 100°C over the composition range in which they were miscible. Partial molar heats and entropies of transfer across the phase boundary have also been computed. The heats of mixing are comparable in magnitude with the values predicted by the van Laar-Hildebrand equation, suggesting that random mixing occurs. In sharp contrast to this, the entropies of transfer are much lower than the values calculated on the random mixing approximation, and the Flory-Huggins equation fails to predict the form of the coexistence curve.