Role of mixed anionic-nonionic systems of surfactants in the emulsion polymerization of styrene:: Effect on particle nucleation

The batch emulsion polymerization kinetics of styrene using various ratios and amounts of anionic surfactant sodium lauryl sulfate (SLS) and nonionic surfactant Triton X-405 (octylphenoxypolyethoxyethanol with an average number of ethylene oxide units of 40) were studied at 70 degrees C using the Mettler RC1 reaction calorimeter. The presence of 1 mM SLS in the emulsion polymerization of styrene using 6.4 mM Triton X-405 greatly affected the kinetics of the reaction. The initial rate of polymerization was faster in the presence of the mixture of surfactants, as 17 times more particles were initially created (1.7 x 10(16) versus 1.0 x 10(15) particles/dm(3)). This phenomenon was observed even though most of the nonionic surfactant was associated with the oil phase prior to the reaction. However, limited aggregation took place later in the reaction. No secondary nucleation was noted at the disappearance of the droplets when SLS and Triton X-405 were used in combination, as was reported when Triton was used as the sole surfactant. When increasing amounts of SLS (3 and 5 mM) were used in combination with 6.4 mM Triton X-405, the kinetics of the reaction became faster and the number of particles formed was high (1.1 x 10(16) particles/dm(3) using 5 mM SLS). No secondary nucleation was noted at the disappearance of the droplets, and the resulting latexes were stable. The initial partitioning of the Triton X-405 into the styrene monomer was affected by the presence of SLS. When no SLS was used, 95% of the Triton X-405 was associated with the oil phase as opposed to 78% when 5 mM SLS was used. The longer PEO chains were mostly located in the aqueous phase. Increasing amounts of Triton X-405 in the water phase allowed the formation of mixed micelles in the aqueous phase at higher SLS concentrations (3 and 5 mM). The resulting kinetics were fast.