Dispersion polymerization of styrene in CO2-expanded ethanol

Abstract Dispersion polymerization of styrene has been performed in CO 2 -expanded ethanol at ≤9 MPa and 70 °C using PVP as stabilizer. The polymerizations proceeded with good colloidal stability, resulting in spherical particles of diameters of ∼2 μm. Pressurization with CO 2 leads to an increase in particle size (∼1 μm in the corresponding CO 2 -free system), and a decrease in both polymerization rate and molecular weight. The main effect of CO 2 is proposed to be its influence on the partitioning of monomer between the continuous and the particle phase–the results indicate that CO 2 -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.