Oil-in-water microemulsion polymerizations of styrene initiated by ammonium peroxodisulfate (APS) and sodium thiosulfate (STS) redox system with and without the macromonomeric azoinitiator [4,4'-azobis-valeronitrile (4-vinylbenzyl(poly(ethylene glycol)ether), macroinimer or MIM] were investigated. The microemulsion polymerizations were performed with either sodium dodecyl sulfate (SDS) or the nonionic Tween 20 as stabilizer. The polymerization kinetics is characterized by two nonstationary rate intervals determined from conversion-time curves. This behavior is the result of continuous particle nucleation during the entire reaction. The macroinimer favors additional particle nucleation and thus influences the kinetics of microemulsion polymerization considerably. The rate of polymerization is strongly influenced by the choice of the stabilizer where the nonionic Tween 20 causes much higher rates than the anionic SDS.