Can a Simple Two-Letter Model Predict Complex Solution Phase Behavior of Block-Random Copolymers?

Control of synthetic polymer solution phase behavior is crucial for soft materials engineering. Recent experiments on styrene-isoprene block-random copolymers [ Taylor, L. W. Macromolecules 2024, 57, 916-925 ] revealed various sequence-dependent phase behavior outcomes. This work aims to provide a quantitative description of those experimental findings using a simple two-letter lattice model with grand canonical Monte Carlo simulations. The results demonstrate that this can be achieved using a single solvent selectivity parameter and appropriate temperature scaling. Predictions of critical temperatures, phase diagrams, and certain micelle radii agree well with the corresponding experimental results. However, the model cannot reproduce large experimental crew-cut micelles, instead predicting large hollow-cored aggregates that disassemble into smaller micelles, raising questions about the equilibrium nature of the remarkably large experimental micelles. The model’s ability to quantitatively describe phase and aggregation behavior demonstrated in this work would be valuable for designing synthetic polymers with desirable properties.