SURFACE CHARACTERIZATION AND DISSOCIATION PROPERTIES OF CARBOXYLIC-ACID CORE-SHELL LATEX PARTICLE BY POTENTIOMETRIC AND CONDUCTOMETRIC TITRATION

Surface characterization of poly(n-butyl methacrylate) (PBMA) core-she ll latex particle with a shell rich in carboxylic acid groups has been investigated by means of potentiometric and conductometric titrations . PBMA core-shell latex particle was prepared by semicontinuous three- stage emulsion polymerization, Methacrylic acid (MA) was added at the final stage of the polymerization. Potentiometric titration was carrie d out on the latex aqueous dispersions containing various NaCl concent rations. Conductometric titration was carried out for the salt-free aq ueous dispersion. The total content of ionizable groups was determined by conductometric titration in 1,4-dioxane. The RIA content in the sh ell, determined by potentiometric titration, is equal to that by condu ctometric titration, This quantity is, however, slightly smaller than that determined by back titration. We conclude that about 27% of total ionizable groups is buried in the particle interior. The potentiometr ic titration behavior of MA groups on the latex surface is analyzed in detail and compared to theoretical results calculated from a smeared- charge model with spherical symmetry. We determine the negative logari thm of intrinsic dissociation constant of RIA at the surface, pK(0) = 4.8 +/- 0.2, in agreement with that of low molecular weight isobutylic acid or poly(methacrylic acid). We find that the electrostatic work r equired to remove H+ from the latex particle surface calculated from t he smeared-charge model is in good agreement with the experimental res ults. (C) 1995 Academic Press, Inc.