DETERMINATION OF THE INTERFACIAL MASS-TRANSFER COEFFICIENT OF VINYL-ACETATE MONOMER DIFFUSION INTO POLY(VINYL ACETATE) AND POLYSTYRENE LATEX-PARTICLES STABILIZED WITH DIFFERENT STABILIZATION MECHANISMS USING AVAPOR-PHASE ADDITION METHOD

A vapor phase monomer addition method was used to measure the monomer transfer rate into latex particles. The classical mathematical model f or the diffusion process was used to calculate the overall mass transf er coefficients of monomer between the vapor and the water phases, and between the water and the polymer particle phases. At the initial sta ge of the monomer transfer into the glassy polystyrene latex particles at 60 degrees C, the rate-determining step was the monomer transfer i nside the polymer. As more monomer transferred into the latex particle s and the glass transition temperature of the swollen latex particles decreased below the experimental temperature, the rate-determining ste p became the monomer transfer across the interfacial surfactant layer. This transition was not observed with poly(vinyl acetate) latex, whic h was rubbery at the experimental temperature. The diffusion coefficie nts calculated were in the order of 10(-13) to 10(-14) cm(2)/s. These low values correspond to molecular diffusion of small molecules throug h a solid or glassy membrane. This was attributed to the resistance of the adsorbed surfactant layer. The mass transfer rates into latex par ticles stabilized with ionic, nonionic surfactants, and a water-solubl e polymer were compared. In the case of the ionic surfactant, sodium d odecyl sulfate, when a large amount of electrolyte was added, the mass transfer rate decreased compared to the electrolyte addition free cas e. This was attributed to the formation of a ''condensed'' layer of ad sorbed surfactant. Adsorbed nonionic surfactant or water-soluble polym er showed larger resistance to monomer transport compared to the ionic surfactant layer. (C) 1995 John Wiley & Sons, Inc.