A Theory of the Thermodynamic Properties of Large Molecules

Abstract

The nature of the viscosity of linear polymers led Kauzmann and Eyring, in an earlier paper, to interpret flow as occurring by means of the more or less random motion of segments. In this paper it is shown that this theory of motion of segments provides an explanation for a variety of thermodynamic properties. These are: (a) the change of melting temperature with chain length; (b) the abnormally large increase in the osmotic pressure of large linear polymers with concentration; (c) the abnormally large vapor pressure of solvent above concentrated solutions of such polymers; (d) the fact that surface tension becomes independent of the molecular weight for long molecules; (e) the volume and entropy changes of swelling of polymers. The theory for the effect of concentration of solvent is developed and segment lengths are calculated. All effects indicate segments of the order of 20 atoms in length, the length varying with the nature of the polymer. According to the theory each of these properties can be used as a basis of a method for testing the rigidity of the structure of macromolecules.