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Abstract: Submicrometer-sized, polystyrene (PS) particles with controlled molecular weight distribution (MWD), were successfully obtained directly as powder state by iodine transfer dispersion polymerization (dispersion ITP) and reversible chain transfer catalyzed dispersion polymerization (dispersion RTCP) in supercritical carbon dioxide (scCO2) for the first time. These dispersion polymerizations proceeded similarly reaching 80% conversion in 21 h. In the dispersion ITP, the number-average molecular weight (Mn ) nonlinearly increased with the conversion, which were always higher than theoretical values, and the MWD at each conversion was comparatively narrow (Mw /Mn  = 1.5–1.7) throughout polymerization. In the dispersion RTCP, Mn also nonlinearly increased with increasing conversion and Mw /Mn values were in the range of 1.3–1.5, which were lower than those of the dispersion ITP. In chain extension tests in bulk systems, the degrees of livingness of PS prepared by the dispersion ITP and the dispersion RTCP in scCO2 systems were, respectively, estimated to be 56% and 48%. From these results, while more investigation is necessary, it was concluded that both polymerizations with scCO2 proceeded in a partly controlled manner. [Copyright &y& Elsevier]