In-situ investigation on the mechanism of dispersion polymerization in supercritical carbon dioxide

The effect of stabilizers on the particle formation stage in dispersion pol ymerization 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 stabi lizers poly(dimethylsiloxane)-b-poly(methyl methacrylate-co-methacrylic aci d) (PDMS-b-P(MMA-co-MA)) and poly(1,1-dihydroperfluorooctyl acrylate)-b-pol ystyrene (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 particl e number density changes little for conversions from 1% to completion for P DMS-b-P(MMA-co-MA) but increases for PFOA-b-PS due to formation of new part icles in block copolymer micelles.