VAPOR-PHASE ADDITION METHOD TO INVESTIGATE THE MONOMER TRANSPORT AT THE LATEX PARTICLE INTERFACE

In emulsion polymerization, monomer can be transferred into the polyme r particles either by the diffusion from the aqueous phase or by the c ollision between the monomer droplets and the polymer particles. To in vestigate only the diffusional monomer transfer rate at the latex part icle interface, a vapor phase addition method was developed. In this m ethod, monomer is transferred from a separate reservoir to the aqueous phase, and then into the latex particles. Because there ape no monome r droplets in the aqueous phase, the monomer transfer occurs only by d iffusion. The vapor and the water phase resistances were minimized to the extent that the particle interfacial resistance dominated. Using t his method, overall mass transfer coefficient of the particle-water in terphase, K-wp, can be calculated using conventional mass transfer exp ressions. For example, vinyl acetate monomer mass transfer coefficient , for monodisperse polystyrene latex particles stabilized with ionic s urfactant, sodium lauryl sulfate, was determined. K-wp was found to be independent of the agitator speed in the range of 400-500 rpm. The ca lculated value of K-wp was in the order of 10(-7) cm/min.