Solvent-Driven Microdomain Ordering in PI–PS–PMMA Miktoarm Star Polymers

High Resolution Image Download MS PowerPoint Slide The bulk morphology of ABC star polymers composed of polyisoprene (PI), polystyrene (PS), and poly(methyl methacrylate) (PMMA) was investigated, examining the influence of the casting solvent on microphase separation. The lengths of the PI and PS arms were held constant, while the PMMA arm length varied systematically. Small-angle X-ray scattering (SAXS) and scanning transmission electron microscopy (STEM) reveal that solvent choice affects the resulting morphology. Acetone casting induces enhanced long-range order in the sample with the lowest PMMA volume fraction, characterized by a morphology exhibiting both hexagonal and lamellar-like periodicities, consistent with a hexagonally perforated lamella structure. This coexistence persists after thermal annealing, as SAXS profiles show no significant change upon heating and cooling. This behavior indicates a morphology that does not readily reorganize toward a single equilibrium structure, but instead reflects a nonequilibrium morphology resulting from solvent-dependent segregation pathways. Dissipative particle dynamics (DPD) simulations support this interpretation by reproducing pathway-dependent structural transitions.