Predicting Multi‐Component Phase Equilibria of Polymers using Approximations to Flory–Huggins Theory

The rational development of sustainable polymeric materials demands tunable properties using mixtures of polymers with chemical variations. At the same time, the sheer number of potential variations and combinations makes experimentally or numerically studying every new mixture impractical. A direct predictive tool quantifying how material properties change when molecular features change provides a less time‐ and resource‐consuming route to optimization. Numerically solving Flory–Huggins theory provides such a tool for mono‐disperse mixtures with a limited number of components, but for multi‐component systems the large number of equations makes numerical computations challenging. Approximate solutions to Flory–Huggins theory relating miscibility and solubility to molecular features are presented. The set of approximate relations show a wider range of accuracy compared to existing approximations. The combination of the analytical, lower‐order, and more accurate higher‐order approximations together contribute to a broader applicability and extensibility of Flory–Huggins theory. A direct predictive tool quantifying how polymer concentrations change when molecular features change provides a route to optimization. Numerically solving Flory–Huggins theory provides such a tool for mono‐disperse mixtures with a limited number of components. This paper presents approximations relating concentrations and molecular features based on Flory–Huggins solution theory, which can be used for multi‐component systems.