Microemulsion polymerization: Phase behavior driven mechanistic changes

We have examined the phase behavior of anionic microemulsions of the general type water/NaCl-hexyl methacrylate (C₆ MA)-bis(2-ethylhexyl)sulfosuccinate (AOT)/sodium dodecyl sulfate (SDS) with respect to temperature and composition. Monomer partitioning measurements and kinetic experiments show good agreement with the Morgan model (de Vries et al. in Macromolecules 34:3233, 2001) for droplet-type microemulsions that do not phase separate as monomer is consumed. In contrast, balanced microemulsions, which efficiently solubilize large amounts of monomer, exhibit dramatic effects on the polymerization kinetics as the phase behavior changes. Our findings suggest that the appearance of a liquid crystalline mesophase in the binary water-surfactant system of the respective microemulsion causes a phase separation during polymerization and, thus, a severe deviation from previous mechanistic models.