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A surface tension theory is developed for application to systems containing polydisperse polymers and using the Bronsted congruence principle for quantitative description of the thermodynamic functions of mixtures of homologues on the basis of the quasi-solution principle as applied to an homologuous polymer series. The alternative equilibrium conditions as between the homogeneous phase and a surface layer of finite thickness are described for concentrated polymer solutions. One of these conditions assumes that the chemical potentials of the macromolecules are equivalent, and another that the chemical potentials of the components of the quasi-solution (units and end groups) are equivalent. On realization of the second absorption mechanism the segregation of micromolecules by MM in the surface layer is eliminated. The feasibility of experimental checking of the conclusions from the theory is discussed.

Concentration dependences of the excess volume of mixing have been derived for mixtures of liquid homologues belonging to the same polymer-homologous series and also for homolog mixtures containing members of homomorphous series. The obtained functions have been analysed quantitatively using experimental data on the volume of mixing of higher linear alkanes, alkanols, and 1-chloroalkanes. The theory agrees with experiment for sufficiently long molecules. The lowest chain length limiting the range of applicability of the quasi-solution concept depends on the character of end groups.

It is proposed that an infinite sequence of linear polymer homologues be described as an open thermodynamic system whose equilibrium state is characterized by an additional parameter, i.e. by the length of macromolecules. This idea has led to the derivation of basic equations for the energy of a system: the repeat-units of chain molecules and the endgroups figure as independent components, like other substances present in the system. An analysis of the phase equilibria led to the derivation of an analogue of the known generalized differential van der Waals equation.