Polymer/solvent interactions in dilute solution

Apparent specific volumes of two, previously well‐characterized, polystyrene fractions were determined at 25° in solvents offering an interesting display of polymer/solvent interactions. Adaptations of differential pycnometry techniques permitted a sensitive detection of the small density differences between solvents and solutions, allowing four significant figures in the apparent specific volumes at concentrations as low as 0.20%. The measurements unambiguously confirm the solvent and concentration dependencies. The solvent dependency at high dilutions also confirms the anomaly that the extremes in polymer/solvent interactions causing very good and very poor polymer solubility yield higher values for the partial specific volumes of polystyrene than obtained for the intermediate range of interactions. The concentration dependency permits indirect approximations of the functions, Δ H̄ 1 and Δ H̄ 2 vs. poIymer concentration. The deviations from athermal mixing are greater and more irregular than anticipated, and are shown frequently to complicate both experimental and theoretical studies of the properties of dilute solutions. The thermodynamic behavior of dilute solutions of polystyrene in butanone appears to be particularly complex.