Fluorinated graft stabilizers for polymerization in supercritical carbon dioxide: The effect of stabilizer architecture

We describe the synthesis of new stabilizers for the free radical polymerization of methyl methacrylate in supercritical carbon dioxide. The stabilizers are based on commercially available copolymers containing maleic anhydride moieties. The maleic anhydride moieties undergo thermal ring opening in the presence of a fluorinated alcohol to form graft copolymers containing pendant fluorinated chains and carboxylic acid groups. We have investigated different polymer backbones to fabricate a range of materials that have been tested in scCO(2) for their effectiveness as stabilizers. FTIR analysis indicates that the mode of stabilization is through an interaction between the carbonyl group of monomer (methyl methacrylate) and the carboxylic acid group of the stabilizer. Our results confirm that the correct choice of stabilizer backbone and fluorinated chain length leads to effective stabilization and production of poly(methyl methacrylate) in high yield, with an acceptable molecular weight, and with spherical particle morphology even at very low stabilizer concentrations (ca. 0.1 wt % with respect to monomer). The balance between the length of the grafted chain and hydrocarbon content of the polymer backbone is found to be particularly important.