POLYMERIZATION OF STYRENE IN TERNARY MICROEMULSION USING CATIONIC GEMINI SURFACTANTS

The use of cationic dimeric (''gemini'') surfactants in the oil in mat er (o/w) microemulsion polymerization of styrene is reported, Gemini s urfactants of the alkanediyl-alpha,omega(dimethylalkylammonium bromide ) type (m-s-m) with m being 12 and s being 2, 4, 6, 8, 10, and 12 were used. The phase behavior of the microemulsion is decisively influence d by the spacer length s. All surfactants form single-phase form micro emulsions with styrene in a temperature range from 25 to 60 degrees C. For s being 2, only very small stable microemulsion regions were obse rved, while for s being 4, 6, and 8, the clear and stable regions were gradually increased. The shape of the single-phase regions was very s imilar to that of the analogous single tail surfactant dodecyltrimethy lammonium bromide. For s being 10, the microemulsion region was distin ctly extended, while for s being 12, it was decreased again at low tem perature, but even more increased at high temperature. Polymerization of the monomeric microemulsions led to spherical latex particles, whos e size range could be easily controlled by the monomer/surfactant rati o. A significant dependence of the particle size on the surfactant spa cer length was observed. At 25 degrees C, the particle size was maximu m for s being 10, at 60 degrees C the particle size increased with s. Therefore, the particle size was directly correlated with the size of the single-phase microemulsion region. The molecular weight was maximu m at medium spacer length. The experimental results are discussed by t aking into account hydrophobic and electrostatic effects and the respe ctive microdroplet structure resulting from the varying interfacial sp ontaneous curvature due to the different surfactant shapes.