LAUSR

Abstract Relatively monodisperse spherical poly(styrene-co-acrylonitrile) (SAN) particles may be prepared using phase inversion from water-in-oil (W/O) to oil-in-water (O/W) emulsions containing water-soluble methyl ethyl ketone (MEK) as the oil phase. In this study, we investigate how mixed solvents containing MEK and water-insoluble methylcyclohexane (MCH) affect the shape of SAN particles produced by the same phase-inversion process. We demonstrate that phase separation between MEK-rich and MCH-rich phases in oil droplets of O/W emulsions occurs during phase inversion and that the state of phase separation is controlled by the MCH:MEK ratio and concentration of SAN. In addition, SAN heterogeneously distribute in the oil droplets of O/W emulsions because SAN is soluble in MEK but not in MCH. We show that the uneven distribution of SAN in the oil droplets produces semispherical, disc-like, and multiporous SAN particles.