Dispersion polymerization of styrene has been performed in CO2-expanded ethanol at <= 9 MPa and 70 degrees C using PVP as stabilizer. The polymerizations proceeded with good colloidal stability, resulting in spherical particles of diameters of similar to 2 mu m. Pressurization with CO2 leads to an increase in particle size (similar to 1 mu m in the corresponding CO2-free system), and a decrease in both polymerization rate and molecular weight. The main effect of CO2 is proposed to be its influence on the partitioning of monomer between the continuous and the particle phase-the results indicate that CO2-pressurization causes a reduction in monomer concentration in the particles. Overall, the results are consistent with literature data on the effects of the polarity of the continuous phase in dispersion polymerization of styrene in alcohols and alcohol/water mixtures. (C) 2013 Elsevier Ltd. All rights reserved.