Phase Separation and Aggregation in Random Block Copolymers Using Monte Carlo Simulations

Control of solution phase behavior in synthetic polymer systems is crucial to new soft materials engineering. Complex polymer architectures can be formed by microphase and macrophase separation as a response to environmental stimuli, such as temperature or solution composition. Recent experiments of styrene/isoprene copolymers in selective solvents have shown various micro- and macrophase separation outcomes dependent on block compatibility and sequence.¹ In this work, we model these styrene/isoprene copolymers using a coarse-grained lattice model and use grand canonical Monte Carlo simulations to analyze phase behavior and compare to experimental results. To match the behavior of the styrene- and isoprene-selective solvents used in the experimental work, a single solvent selectivity parameter that controls model interaction strengths and appropriate scaling parameter was used. The results indicate that even at fixed composition and chain length, variations in the monomer sequence, achieved by placing solvophilic or solvophobic homopolymer blocks in the middle or end of a sequence, affects whether the system undergoes phase separation or aggregation. Solvophilic midblock sequences increase T_c and display UCST phase behavior, in quantitative agreement with experimental results, whereas sequences with long solvophilic endblocks undergo aggregation and form large hollow-center micelles.



References

[1] L. W. Taylor; R. D. Priestley; R.A. Register, Macromolecules, 57 (2024) 916.