Free Radical Polymerization of Methyl Methacrylate in Supercritical Carbon Dioxide Using a Pseudo-Graft Stabilizer:  Effect of Monomer, Initiator, and Stabilizer Concentrations

This paper describes the free radical polymerization of methyl methacrylate [MMA] in supercritical carbon dioxide [scCO2] using a commercially available acid-terminated perfluoropolyether [Krytox 157FSL] as a polymerization stabilizer. We have investigated the effect of varying the concentrations of monomer, initiator, and stabilizer upon the molecular weight and morphology of the resultant poly(methyl methacrylate). The results obtained are compared to those observed for other stabilizers used for polymerization in scCO2. Krytox 157 FSL is shown to be an effective stabilizer leading to discrete spherical particles with diameters in the range expected from dispersion polymerization. Unusual morphologies are observed at high initiator concentration and at lower stabilizer concentration. Surprisingly, high yields of polymer are still formed even at very low concentrations of stabilizer (e.g., 10-4 wt % with respect to monomer).