Radical mediated thiol ene emulsion polymerizations for the synthesis of aqueous dispersion of polymer particles with narrow particle size distributions are reported. Submicrometer polymer particles comprising of cross-linked or linear chains were obtained using a water-soluble thermal initiator, without the need for a high-intensity emulsification step. Particles were prepared using 1,3,S-trially1-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, pentaerythritol tetrakis(3-mercaptopropionate), trimethylolpropane diallyl ether, 1,6-hexanedithiol, and 3,6-dioxa-1,8-dithiooctane monomers. Potassium persulfate was used as the water-soluble initiator, and sodium dodecyl sulfate was used as the surfactant. The effects of surfactant, initiator, and comonomer concentrations on the particle diameters in the emulsion polymers are reported. The order of dependence of particle diameter on the surfactant concentration was -(0.44 +/- 0.03) and on the initiator concentration was -(0.53 +/- 0.04). The particle size distributions in the cross-linked latexes were generally broad. A seeded emulsion polymerization reaction, consisting of delayed addition of the cross-linker, was found to result in cross-linked thiol ene latexes with narrow particle size distribution.