The polymerization of styrene in oil-in-water microemulsions made with the cationic surfactants dodecyltrimethylammonium bromide or chloride is studied as a function of inorganic electrolyte (KBr, KCl, or K2SO4) concentration. The resulting microlatex is stable, but as the electrolyte concentration increases, both the average radius and the polymer molecular weight decrease. The presence of electrolyte slows the polymerization rate and diminishes final conversion as followed by gravimetry, dilatometry, and calorimetry. Both particle radius, determined by quasielastic light scattering, and molecular weight show only limited growth as styrene conversion increases, suggesting continuous nucleation of latex particles and termination by chain transfer to monomer. Small-angle neutron scattering (SANS) of undiluted parent and polymerized microemulsions shows that a unimodal population of swollen micelles evolves into a bimodal population of empty micelles coexisting with large polymer particles. Structural details of the parent and polymerized microemulsions as determined by SANS are used to assess nucleation mechanisms previously proposed for emulsion polymerization.

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Tetrahydrofurfuryl methacrylate (THFM) polymerizes at 60 0 C when initiated with potassium persulfate in three-component microemulsions made with Aerosol-OT (AOT) and water. The resulting monodisperse microlatex contains particles with mean diameters from 25 to 34 nm and polymer molecular weights of order 107. Each particle consists of approximately one polymer molecule in a collapsed state. Polymerization kinetics are followed by calorimetry, dilatometry, and internal reflectance infrared spectroscopy. Reaction rate curves show two intervals only: an interval of increasing rate immediately followed by an interval of decreasing rate. Weight-average molecular weight as measured by size-exclusion chromatography and particle size as measured by quasielastic light scattering increase during polymerization. Transmission electron microscopy (TEM) shows the in situ formation of lamellar and multilamellar structures when excess AOT from micelles depleted of monomer exceeds its solubility in water. These findings confirm that latex particles grow by recruiting monomer from uninitiated microemulsion droplets.

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