Polymerization of oil (styrene and methylmethacrylate) in-water microemulsions

The polymerization of styrene-in-water and methylmethacrylate-in-water micr oemulsions stabilized by nonionic surfactants was investigated using differ ent initiation techniques. Thermally induced initiation was carried out usi ng potassium persulfate (water soluble) and azobisiso-butyronitrile (AIBN) (oil soluble) at 60 degrees and 50 degrees C, respectively. When the monome r concentration was kept below a certain limit, the particle size of the na nolatex was similar to the droplet size of the microemulsion precursor. At higher monomer concentrations, the latex produced was significantly larger than the microemulsion droplets, as a result of the possible coalescence of the microemulsion droplets during polymerization. By using chemically indu ced polymerization (hydrogen peroxide + ascorbic acid) at temperatures belo w the cloud point temperature of the microemulsion or by photochemically in duced initiation at room temperature, it was possible to obtain nanolatex p articles with similar size to the droplets up to 10% monomer content. In al l cases, the particle size was determined using photon correlation spectros copy (PCS). Electron micrographs of the microlatex particles were taken and these confirmed the measurements obtained by PCS. The molecular weight of the polymers produced was determined by gel permeation chromatography. The average number of polymer molecules per particle was calculated. It was sho wn in some cases that the nanolatex contained one polymer chain per particl e. A mechanism was suggested for polymerization and particle growth.