Fairly uniform copolymer particles of methyl acrylate (MA), butyl acrylate (BA), or butyl methacrylate (BMA) were synthesized via Shirasu porous glass (SPG) membrane and followed by suspension polymerization. After a single-step SPG emulsification, the emulsion composed mainly of the monomers. Hydrophobic additives of dioctyl phthalate (DOP), polystyrene molecules, and an oil-soluble initiator, suspended in an aqueous phase containing poly(vinyl alcohol) (PVA) stabilizer and sodium nitrite inhibitor (NaNO2), were subsequently subjected to suspension polymerization. Two-phase copolymers with a soft phase and, hard phase were obtained. The composite particles of poly(St-co-MA)/PSt were prepared by varying the St/PSt ratios or the DOP amount. The addition of PSt induced a high viscosity at the dispersion phase. The molecular weight slightly increased with increasing St/pst concentration. The multiple-phase separation of the St-rich phase and PMA domains, observed by transmission electron microscopy, was caused by composition drift because the MA reactivity ratio is greater than that of St. The addition of DOP revealed the greater compatibility between the hard-St and soft-MA moieties than that without DOP. The phase morphologies of poly(St-co-MA), poly(St-co-BMA), and their composites with PSI were revealed under the influence of DOP. (c) 2005 Wiley Periodicals, Inc.