Dispersion polymerization of methyl methacrylate in supercritical carbon dioxide: An investigation into stabilizer anchor group

New stabilizers for the dispersion polymerization of methyl methacrylate (MMA) in supercritical carbon dioxide (scCO(2)) were prepared and studied in terms of their anchor group architecture. The same perfluoropolyether (PFPE) chain was used in each case as the CO2-philic portion of the stabilizer and four different PMMA-philic headgroups were investigated as anchoring units: an alcohol, an acetate group, a methacrylate unit, and a PMMA block. When compared to the stabilizing ability of PFPE-alcohol, incorporation of an anchor group as small as an acetate group, or a reactive group such as a methacrylate unit, was found to have a dramatic effect upon the dispersion polymerization of MMA in scCO(2). Their incorporation led to a significant increase in PMMA yield and molecular weight and an improvement of the morphology of the polymer product. A method for the synthesis of PFPE-b-PMMA diblock copolymers is reported via atom transfer radical polymerization (ATRP) from a PFPE-bromoester macroinitiator in a fluorinated solvent (pentafluorobutane). This method allows the controlled synthesis of PFPE-b-PMMA diblock copolymers with well-defined architecture. These copolymers were found to be effective stabilizers in scCO(2), leading to excellent PMMA yield with high molecular weight and a fine morphology. The effect of PFPE and PMMA block length on the copolymer stabilizing ability was also studied to probe the influence of the stabilizer anchor-soluble balance (ASB). In addition, the phase behavior of each stabilizer in CO2 or a mixture of CO2/MMA was studied to elucidate the effect of stabilizer structure on CO2-philicity and stabilizing ability.