ABSTRACT
To distinguish between the molecules of the polymer and the solvent, a new factor was introduced, namely, the difference in their free volumes and temperature dependence of the free volume. The concept of the role of free volume in the polymer solution theory was introduced by I. Prigogine. The theory by Prigogine was later developed by D. Patterson and became the theoretical basis for the description of liquid mixtures. It is known that the theory of regular solutions models considers them as dispersions of spherical molecules. The effect of the polar groups on thermodynamic functions in the new statistical theories has also been considered. I. Sanchez and R. H. Lacombe have proposed new equations of state for the liquid systems and polymer solutions. Their theory, called the theory of the lattice liquid, needs estimation of three parameters of the equation of state for pure components.
