Thermodynamics of polymer solutions. Part 3.—Polyisobutylene and cyclohexane

Abstract

Activities and excess volumes for concentrated mixtures of polyisobutylene and cyclohexane have been determined at 25°C. The former yield χ 0.5; variations of χ with concentration, expressed as segment fractions, are small. The volume change on mixing is negative, amounting to ca. –0.14% of the total volume at φ₂= 0.5. These results in conjunction with the previously determined enthalpy of mixing are rationally interrelated by theory; arbitrary assignment of X₁₂ 1.4 cal cm^–3 suffices. This value of X₁₂ denotes a very small difference for the interactions between neighbour pairs. The dependence of χ on concentration is overestimated by theory, but the magnitude of the large entropic contribution to χ is correctly predicted.