Thermodynamics of polymer solutions. Part 1.—Natural rubber and benzene

Abstract

Activities of rubber-benzene solutions have been determined at 10, 25 and 40°C over the range of concentration, expressed as the segment fraction φ₂ of polymer, from 0.05 to 0.945, using high pressure osmometry and an improved vapour sorption method. Results are in general agreement with earlier work of Gee and co-workers, except that they yield lower values for the reduced partial molar excess enthalpy : χ= text-decoration:overlineH ^E ₁/RTφ² ₂ 0.1 ± 0.1. Excess volumes, also determined at 25°C, are small and positive, amounting to ca. 0.09 % at φ₂= 0.5. These results, including the excess volumes, are compared with calculations according to recent theory which takes account of the equation-of-state characteristics of the pure components. Good agreement is established. The small experimental entropy of dilution compared with that calculated from the combinatorial contribution alone is well explained by equation-of-state contributions. The observed increase of the conventional free-energy parameter χ with concentration arises from the latter contribution and is unambiguously predicted by theory.