AbstractThe occupied area (Am) of a sodium dodecyl benzene sulfonate molecule adsorbed on particles was measured by the soap titration method. TheAmvalues are 214, 133, and 53 Å2for poly(methyl acrylate) (I), poly(methyl methacrylate) (II), and polystyrene (III), respectively. For methyl metharylate‐styrene copolymer emulsions the additivity was established between theAmvalue and copolymer composition. Composite emulsion particles consisting of I/II, I/III, and II/III were prepared by seeded emulsion polymerization. For these emulsions the relationship between polymer composition at the surface layer calculated from theAmvalue and that in a particle calculated from the polymerization process was investigated. This relationship is remarkably affected by the order of polymerization, the hydrophilicity of polymer, the flexibility of the seed polymer, and the monomer addition method. The models of the morphology of these composite particles explain the results successful