Thermodynamics of polyisobutylene solutions. II. Vapor pressures and polymer order

The Maron theory of nonelectrolyte solutions has been used to examine the vapor pressure behavior of solutions of polyisobutylene in benzene and in cyclohexane between 25 and 65°C and in n-pentane between 25 and 55°C. The results show that the theory can predict the vapor pressures of these solutions over the full concentration range, provided the polymers involved are amorphous. When the polymers are not completely amorphous, then discrepancies between theory and experiment are observed at high solution concentrations which are due to persistence of polymer order in the highly concentrated solutions. A method is described by means of which these discrepancies can be used to obtain on an absolute basis both the degree of polymer order in solution and in the original polymer samples used.