Electron Microscopic Study of the Locus of Latex Reaction

The outstanding example of the study of reaction loci in an emulsion system is Harkins's work in the field of emulsion polymerization. A simpler case presents itself for study when chemical reactions are carried out with preformed polymer emulsions (latexes), as in the hydrochlorination of polyisoprene latex. Here the reaction consists in the progressive conversion of the individual unsaturated isoprene units to their hydrochlorinated form: (see PDF for diagram) the polymer particles preserving their identity throughout the reaction. The hydrochloric acid arrives at the site of reaction by a series of diffusion processes from the vapor phase and through the continuous aqueous phase. In principle there are still two loci at which the isoprene units may react with this reagent: in the bulk of the particle and at (or near) the interphase between the aqueous acid and the polymer particle. We were led by kinetic experiments to conclude that the two loci do react at different rates and by different mechanisms, and it is the purpose of this report to provide quantitative evidence for this conclusion. At the same time we wish to put on record some observations connected with the electron microscopic technique used in the investigation.