In-Situ Investigation on the Mechanism of Dispersion Polymerization in Supercritical Carbon Dioxide

The effect of stabilizers on the particle formation stage in dispersion polymerization of methyl methacrylate in supercritical CO2 has been studied by in-situ turbidimetry. The average particle diameter (250 nm) and particle number density are similar at the end of this formation stage for the stabilizers poly(dimethylsiloxane)-b-poly(methyl methacrylate-co-methacrylic acid) (PDMS-b-P(MMA-co-MA)) and poly(1,1-dihydroperfluorooctyl acrylate)-b-polystyrene (PFOA-b-PS). Particle diameters are only about twice as large for perfluoropolyether acid (PFPE-COOH) but become much larger for grafted PDMS−monomethacrylate due to less effective surface coverage. The final particle number density changes little for conversions from 1% to completion for PDMS-b-P(MMA-co-MA) but increases for PFOA-b-PS due to formation of new particles in block copolymer micelles.