The cohesive energy density of polymers and its relationship to surface tension, bulk thermodynamic properties, and chain structure

The cohesive energy density (CED) and the internal pressure (Pi) have similar values for most liquids at low pressures. For most polymers CED cannot be directly measured, unlike Pi which is readily obtained in the melt from PVT or other related data. Directly measured CED are available for the oligomer linear alkane series over a moderate molecular weight (MW) range. Scaling CED with measured surface tensions ((sic)) leads to separation into two universal scaling curves, which provides a measure of surface configurational entropy, as does the MW dependence of experimental surface tensions for two polymer series. A novel polymer scaling curve based on CED is shown to provide improved accuracy in the prediction of (sic) for any polymer or solvent. For polymers that interact predominately through Van der Waals forces, correlations between the average interchain separation distances and the magnitude of CED (or Pi), are shown to give a universal derivation of CED. In contrast, polymers like P4VP having strong polar interactions provide dramatic evidence of the different physical basis of CED and Pi. (C) 2016 Wiley Periodicals, Inc.