| The kinetics of the emulsion polymerization of styrene in the presence of mixtures of SLS and Triton X-405 were studied under various conditions.; The competitive adsorption of SLS and Triton X-405 on polystyrene particles was studied. At low surfactant content, Triton X-405 adsorbed preferentially on the surface of the PS particles. In some cases, it was able to displace some of the SLS from the surface. As the surface coverage increased with increasing total surfactant concentration, cooperative adsorption occurred and a large excess of the two surfactants was noted at the surface of the particles.; These mechanisms affected particle nucleation and particle growth in the presence of a mixed anionic-nonionic emulsifier mixture. When the emulsion polymerization of styrene was started with a mixture of the SLS and Triton X-405, most of the Triton X-405 was associated with the oil phase prior to polymerization. However, the partitioning of the nonionic surfactant in the oil phase was decreased by the presence of SLS. At low SLS contents, the nucleation was homogeneous. However, the number of particles initially formed with the mixed surfactant system was much higher than when the nonionic surfactant was used alone. As a consequence, no secondary nucleation was observed at the disappearance of the droplets. At higher SLS contents, there was enough Triton X-405 initially in the aqueous phase to form mixed micelles. The resulting kinetics were fast.; During particle growth, the continuous feeding of increasing amounts of Triton X-405 in neat monomer did not significantly affect the rate of polymerization of the semi-batch emulsion polymerization of styrene using SLS as the initial surfactant for various feed rates. However, the addition of a shot of Triton X-405 in the seeded emulsion polymerization of styrene using SLS as the initial surfactant, lead to a small increase in the rate of polymerization. Local instability may have occurred in the system resulting from the removal of SLS from the surface. Secondary nucleation was likely to be the cause for the increase in the rate, even though the new particles may have not been stable enough to survive until the end of polymerization.; Differences in the composition of the mixed surfactant layer did not seem to affect significantly the pseudo first order entry and exit rate coefficients of the free radicals into and from the particles as determined by the “slope-intercept” approach. Similarly, even though the chain transfer constant to Triton X-405 was large, it did not influence significantly the kinetics of polymerization, both in bulk and emulsion polymerization. |
