Thermodynamics of solutions of cyclic polymethylene ester oligomers inp-dioxane and chloroform

Abstract

Differential vapor pressures were measured for mixtures of two cyclic polymethylene ester oligomers in p-dioxane and chloroform at 25, 30, 35, and 40 °C at five different concentrations ranging from 1 to 20 wt %. The Flory-Huggins interaction parameter ( X ) as well as Leonard's interaction parameter ( X' ) for flexible and semiflexible rings were calculated and compared to one another. A new method for the estimation of the number of segments of a cyclic polymer is proposed that allows Leonard's equations to be applied correctly to a particular cyclic compound. Consistent differences between X and X' were observed for all studied mixtures, and the differences became smaller if the cyclic oligomers were considered semiflexible. Interestingly, the enthalpic parameter (K) deduced from values of X and X' did not differ within their uncertainties. This supports the prediction that mixing cyclic polymer compared to its linear counterpart is mainly due to a molecular configurational entropy difference and that this difference should become less pronounced as the cyclic compound becomes larger.