Polydisperse polymer fractionation between phases

Polymer mixtures fractionate between phases depending on their molecular weight. Consequently, by varying solvent conditions, a polydisperse polymer sample can be separated between phases so as to achieve a particular molecular weight distribution in each phase. In principle, predictive physics-based theories can help guide separation design and interpret experimental fractionation measurements. Even so, applying the standard Flory-Huggins model can present a computational challenge for mixtures with many polymeric components of different length, particularly for scarce components at the tails of a distribution. Here, we apply our recently-derived exact analytical solution of multi-component Flory-Huggins theory for polydisperse polymers to understand the principles of polymer fractionation for common molecular weight distributions. Our method reveals that polymer fractionation is highly sensitive to the shape, and in particular the tails, of this distribution. Our results highlight the need for considering the full molecular weight distribution in phase coexistence calculations.