Chain Connectivity Contributions to Many-Body Interactions and Osmotic Pressure in Polymer Solutions

    Polymer chains undergo coil-to-globule transitions near the θ-temperature, coupling chain conformation with phase separation. Knowledge of second and third virial coefficients is crucial for reliable predictions and interpretation of experimental results, as they quantify polymer–solvent interactions.

    We use coarse-grained simulations to determine these coefficients. In single-chain simulations across solvent qualities, we capture the coil–globule collapse and extract virial coefficients by fitting chain size to mean field theory. In multi-chain simulations near the θ-point spanning dilute to semidilute concentrations, we measure osmotic pressure and apply a virial expansion to isolate two- and three-body interactions. We find the third virial coefficient is significantly smaller than the prediction of Flory-Huggins theory and molecular weight dependent, which highlights chain connectivity contributions to many-body interactions. Our refined virial values will help to improve the polymer solution phase diagram and guide experimental design.