Thermodynamics of polystyrene solutions. Part 1.—Polystyrene and methyl ethyl ketone

Abstract

The excess volumes VE of mixtures of polystyrene with methyl ethyl ketone determined at 25°C are negative. At a segment fraction ϕ2= 0.5 of polymer, VE is ca. 0.9 % of the total volume. Osmotic pressures have been measured from ϕ2= 0.10 to 0.35 at 10° and at 50°C. The temperature coefficient of the reduced residual chemical potential χ indicates a very small positive heat of mixing in accord with vapour pressure measurements of Bawn, Freeman and Kamaliddin at higher concentrations. The recent statistical thermodynamic theory of solutions which relates their properties to characteristics of the pure liquids manifested in the equation-of-state parameters succeeds in accounting for the principal features of this system. This theory correctly predicts the sign of the excess volume, although it underestimates its magnitude. It also accounts for the observed increase of χ with concentration, and for the small negative entropy of dilution at low concentrations, with change of sign at ca.ϕ2= 0.05. Thermal expansivities and thermal pressure coefficients for methyl ethyl ketone have been measured from 20° to 60°C with an accuracy of ±1 % or better.