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 CO 2 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.