A polystyrene (PS)/poly(butyl acrylate) (PBA) composite emulsion was produced by seeded emulsion polymerization of butyl acrylate (BA) with PS seed particles which were prepared by emulsifier-free polymerization of styrene with potassium persulfate (KPS) under a nitrogen atmosphere at 70degreesC for 24 h with stirring at 60 rpm and swelled with the BA monomer in an ethanol/water medium. The structure of the PS/PBA composite particles was confirmed by the presence of the characteristic absorption band attributed to PS and PBA from FTIR spectra. The particles for pure PS and PS/PBA with a low content of the BA monomer were almost spherical and regular. As the BA monomer content was increased, the particle size of the PS/PBA composite particles became larger, and more golf ball-like particles were produced. The surface morphology of the PS/PBA composite particles was investigated by AFM and SEM. The T-g's attributed to PS and PBA in the PS/PBA composite particles were found at 110 and -49degreesC, respectively. The thermal degradation of the pure PS and PS/PBA composite particles occurred in one and two steps, respectively. With an increasing amount of PBAI the initial thermal decomposition temperature increased. On the contrary the residual weight at 450degreesC decreased with an increasing amount of PBA. (C) 2003 Wiley Periodicals, Inc.