The Challenges of Using COSMO-RS To Describe Polymer Solution Behavior

This work discusses the ability and limitations of the conductor-like screening model for realistic solvation (COSMO-RS) to predict the thermodynamic properties of polymer solutions over the entire concentration range. For that purpose, aqueous mixtures of polyethylene glycol (PEG) are used as a case study. The activity coefficients of PEG + water mixtures were calculated as functions of molecular weight and temperature. The influence of the conformations of the solvated polymer molecules, the inclusion of a combinatorial term, and the description of the volume dependence were assessed. Molecular dynamics simulations of water-solvated polymer molecules were performed to obtain representative polymer conformers. COSMO-RS is shown to be able to quantitatively predict the activity coefficients of these systems with the inclusion of a combinatorial term when the conformational and density dependence are well described. It is also shown that the scaleup of the polymer to large molecular weights can be achieved from the sigma profiles of oligomers with low molecular weight.