EFFECT OF SURFACE ACID GROUP NEUTRALIZATION ON INTERDIFFUSION RATES IN LATEX FILMS

We report measurements of the kinetics of polymer diffusion in latex f ilms prepared from two pairs of poly(butyl methacrylate) (PBMA) latex particles. One set contains only a small amount of sulfate groups at t he surface; the other contains a significant amount of carboxylic acid groups at the surface. Neutralization of these acid groups with ammon ium, sodium, and barium hydroxide retards the interdiffusion rate at 1 00-degrees-C but does not suppress it. In these experiments, we employ pairs of particles identical in size, with very similar molecular wei ghts, molecular weight distributions, and surface charge densities, th at differ only in the fluorescent chromophore [phenanthrene (Phe) or a nthracene (An)] used to label the polymer. Each pair of latex allows u s to use direct nonradiative transfer (DET) experiments to follow poly mer interdiffusion in films prepared from their dispersions. Acid grou p neutralization in the latex converts an acid-rich phase at the inter particle boundary in the film into an ionomer phase. Ba2+ salts are mo re effective than Na+ at slowing down the polymer diffusion rate, and both metal ions are much more effective than NH4+. In the case of the carboxylated latex, this may point to loss of NH3 during film annealin g, regenerating free COOH groups.