Polydisperse polymer fractionation between phases

TL;DR

This paper presents an analytical approach to understanding how polydisperse polymer mixtures fractionate between phases, aiding in the design of separation processes based on molecular weight distributions.

Contribution

It applies a recently derived exact analytical solution of multi-component Flory-Huggins theory to predict polymer fractionation behavior for common molecular weight distributions.

Findings

Fractionation sensitivity depends on the shape and tails of the molecular weight distribution.

The method enables systematic evaluation of molecular weight distributions in phase coexistence.

Analytical solutions simplify predictions compared to numerical computations.

Abstract

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 phase-diagram and fractionation measurements. Even so, applying the standard Flory-Huggins model can require numerical computations that hamper the predictions considering the full molecular weight distribution. Here, we apply a recently-derived exact analytical solution of multi-component Flory-Huggins theory for polydisperse homopolymers to understand the principles of polymer fractionation for common molecular weight distributions. Consistent with previous studies, the method highlights the sensitivity of polymer fractionation to the shape, and in particular the tails, of this distribution. Our results provide a systematic approach to evaluate the full molecular weight distribution in phase coexistence calculations over the possible composition space.