AbstractDowfax* 2A1 is a branched C12‐alkylated diphenyl ether disulfonate surfactant widely used in industrial emulsion polymerization because of its electrolyte tolerance, stability in concentrated acids and alkalis, oxidation resistance, temperature stability, efficiency in solubilization, and moderate foaming. This surfactant and other similar surfactants were evaluated as emulsifiers in 60 : 40 styrene‐butadiene emulsion copolymerizations carried out at 70°C using persulfate ion initiator, and their solution properties were determined. The similar surfactants were Dowfax 3B2 (linear C10‐alkylated), XD‐8390 (linear C16), XD‐8292 (linear C6), XD‐8174 (linear C12), and various laboratory monoalkylated and dialkylated variations. Sodium lauryl sulfate, Aerosol MA, and Aerosol OT were used as standards for comparison. The emulsifier concentration required to give a 200‐nm particle diameter varied strongly with the degree of alkylation of the emulsifier; the linear C16‐monoalkylated diphenyl ether disulfonate emulsifier gave the desired diameter with the lowest concentration. The adsorption isotherms of these emulsifiers on the 60 : 40 styrene—butadiene copolymer particles were determined and correlated with the emulsifier structure. The interfacial tensions between styrene and the aqueous emulsifier solutions were measured and used to calculate the free energies of micellizat