Emulsion polymerization of styrene: Nucleation studies with nonionic emulsifier

The nucleation mechanism of styrene emulsion polymerization in the presence of the nonionic surfactant Emulphogene BC‐840 was investigated. It was found that the conversion‐time curves of this system show two rate regions. The change in rate occurs at ca. 40% conversion. Second‐stage nucleation leads to a faster rate and consequently to a bimodally dispersed latex. The particle size distribution is relatively narrow before 40% conversion. The bimodally dispersed latex shows a bimodal molecular weight distribution in gel permeation chromatography and the results from fractional “creaming” of the latex indicate that the small‐size particles contain the higher‐molecular‐weight polymer.