Effect of surfactant concentration and monomer polarity on particle nucleation in emulsion step polymerization of dithiol with diene

The dependence of the number of particles N p as a function of the surfactant concentration [S] is investigated for the step polymerization of dithiol-diene emulsions. A sigmoidal curve for log N p vs log [S] is found for a range of monomers regardless of their polarity. Above the critical micellar concentration (6–20 mM), a N p ∝ [S] x relationship is established with an exponent x dependent on the polarity of the two co-monomers. When the two co-monomers are highly water insoluble, x varies typically between 0.6 and 1. With two relatively water soluble co-monomers, x is close to 0. When two co-monomers with contrasting water solubility are involved, the power dependence is more difficult to predict and ranges from 0 to 1, but high x value are generally found when one of the two monomers is highly hydrophobic. This overall trend can be reconciled with the behavior of a conventional emulsion radical chain polymerization. Graphical abstract