A novel polymerization procedure, the concentrated-emulsion graft polymerization of styrene monomer with poly(butyl acrylate) seed, was proposed for the production of a self-compatibility macromolecule alloy. The effects of the butyl acrylate content, sodium dodecyl sulfate concentration, and polymerization temperature on the graft ratio were investigated. Scanning electron microscopy, transmission electron microscopy, and impact strength were used to characterize the microstructure and mechanical performance of the self-compatibility macromolecule alloy. The results showed that increasing the butyl acrylate content, reducing the sodium dodecyl sulfate concentration, and improving the polymerization temperature all favored an increased graft ratio, which resulted in increased impact strength of the self-compatibility macromolecule alloy. Therefore, the concentrated-emulsion polymerization method is particularly suitable for seed-graft polymerization. 2002 John Wiley Sons, Inc.