CONTROL OF SURFACTANT LEVEL IN STARVE FED EMULSION POLYMERIZATION .4.MATHEMATICAL-MODEL AND EXPERIMENTAL TEST

In emulsion polymerization processes it is important to control the su rfactant level to avoid secondary nucleation (too much surfactant) and coagulation (too little), Seeded emulsion polymerizations are especia lly sensitive since the buffering effect of micellar soap is absent an d the surfactant concentration is generally low, Surface tension measu rements were employed to monitor the instantaneous free surfactant con centration, A previously developed Langmuir site adsorption model was employed to relate surface tension to surfactant concentration from fi rst principles, This model describes the partition of added sodium dod ecylbenzenesulfonate (SDBS) and mobile in situ surfactant between the aqueous phase and the particle surface in the presence of anchored sul fate groups, High solids contents in typical synthetic reactions resul t in significant contributions from the in situ surfactant and anchore d groups, In a model MMA/BA latex, the agreement between observed and calculated surface tension was similar to 1 dyn/cm, enabling design co ntrol of starve fed emulsion polymerization, When the surface tension was maintained at 45-57 dyn/cm, the process successfully generated 500 nm to 3 mu m monodisperse particles. (C) 1996 Academic Press, Inc.