Abstract
Particle growth rates were analyzed for the dispersion polymerization of methyl methacrylate (MMA) in supercritical carbon dioxide at 65 C stabilized with a poly(dimethyl siloxane)-methyl methacrylate (PDMS-mMA) macromonomer. Although pure CO2 is a mediocre solvent for PDMS even at 4000 psia, the monomer behaves as a cosolvent to prevent flocculation. As pressure is decreased, the dispersion flocculates sooner, as expected due to the reduced solvent quality of CO2. Final particle size is only mildly dependent on pressure as a result of the solvation from the high monomer concentration during the particle formation stage, however particle coagulation increases with decreasing pressure. There exists both a minimum pressure (3000 psia) and stabilizer concentration (2 wt % stabilizer/monomer) below which particles are highly coagulated due to insufficient steric stabilization. Here polymerization rates are reduced due to diffusional restrictions. This threshold pressure and stabilizer concentration are requir...
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