Thermodynamics of Non-Dilute Polymer Solutions

An excellent new text, “Macromolecules in Solution,” by A. Morawetz emphasizes advances in polymer solution thermodynamics since publication of standard texts such as those of Tompa and Flory. Detailed development of the subject from 1950 may be followed in articles on polymers in Annual Reviews of Physical Chemistry, and particularly in the articles appearing every three years specially devoted to solution properties: Flory and Krigbaum (1951), Wall and Hiller (1954), Hermans (1957), Casassa (1960) and Hughes and von Frankenberg (1963). The articles on solutions of non-electrolytes are, of course, always of general interest and often deal directly with polymer solutions or mixtures of chain molecules. Because of this very satisfactory situation, the author has decided that the best thing is to review in more detail the single topic which is most interesting to him. This is the thermodynamics of non-dilute solutions where it is usually supposed that the quasi-lattice theories of the 40's are quite adequate at concentrations greater than about 10 per cent. For fifteen years or so, interest has centered on very dilute polymer solutions and the dimensions of isolated polymer molecules, particularly at temperatures near the θ point. Increasingly difficult mathematical problems have followed the McMillan-Mayer comparison of solutions and imperfect gases first applied to polymer solutions by Zimm and Stockmayer. Polymer solution thermodynamics seems to have moved far beyond the intuitive questions of Meyer as to why a polymer solution differs from an ideal solution or from a mixture of a monomeric solute and solvent. However, certain results, apparently not very widely known, make one feel that such qualitative questions are not out of date and that the thermodynamics of concentrated polymer solutions may be open to much further development.