Free radical polymerization of styrene in supercritical CO2 requires addition of a surfactant to produce polystyrene (PS) in high conversion and molecular weight with well-defined particle sizes. In this work, we examined a new stabilizer that can provide effective stabilization for the polymerization of styrene. A commercially available poly(dimethylsiloxane) macromonomer has been employed as a stabilizer for dispersion polymerization of PS in scCO2. The reactions were conducted in a 225-mL stainless steel autoclave over the temperature range 60–80°C and under pressures of 1,500 to 3,000 psi. After 2–12 h of polymerization, the conversion determined by gravimetrical method was between 20 and 80%. These preliminary results suggest that this macromonomer offers satisfactory stabilization for the styrene system. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 545–549, 2004