A method for estimating both the solubility parameters and molar volumes of liquids

TLDR

The solubility parameters and molar volumes of substances are used to estimate thermodynamic properties of solutions, such as polymer–solvent interactions and liquid uptake by polymers, but for high‑molecular‑weight polymers the low volatility precludes direct measurement of ΔEv, requiring indirect estimation methods. For low‑molecular‑weight liquids, δ is calculated from ΔEv and molar volume derived from molecular weight and density, while for high‑molecular‑weight polymers a group‑additive approach based on Small’s molar‑attraction constants is commonly used, though it still needs experimental density. The proposed group‑additive method improves upon Small’s approach by incorporating a larger set of functional‑group contributions and requiring only the structural formula, eliminating the need for experimental density.

Abstract

Abstract The solubility parameters and molar volumes of substances can be used, in conjunction with suitable theory, to provide estimates of the thermodynamic properties of solutions; the solubility characteristics of polymer‐solvent systems and the estimation of the equilibrium uptake of liquids by polymers are examples of the type of practical problems that are amenable to treatment. For low molecular weight liquids, the solubility parameter, δ, is conveniently calculated using the expression δ = (Δ E v / V )½, where Δ E v is the energy of vaporization at a given temperature and V is the corresponding molar volume which is calculated from the known values of molecular weight and density. For high molecular weight polymers, the volatility is much too low for Δ E v to be obtained directly and hence recourse must be made to indirect methods for estimating δ for these materials. One such widely used method is based on Small's additive group “molar‐attraction constants” which when summed allow the estimation of δ from a knowledge of the structural formula of the material; however, the density must still be determined experimentally. The proposed method of estimating δ, also based on group additive constants is believed to be superior to Small's method for two reasons: (1) the contribution of a much larger number of functional groups have been evaluated, and (2) the method requires only a knowledge of the structural formula of the compound.