Anomalous polymer particles with a partial protuberance like "octopus ocellams" were produced under alkaline conditions by seeded emulsion copolymerization for styrene and butyl acrylate, with styrene-butyl acrylate-methacrylic acid terpolymer emulsion as seed. The mechanism of production of the polymer particles was studied. By transmission electron microscopic observation of the particles at each conversion, it was observed that the anomalous polymer particles were produced by partial growth of each of the individual seed particles throughout polymerization. Ionization of the carboxyl groups and low viscosity in the growing particles during the process of polymerization were important factors for partial growth.

SynopsisIt was studied how to localize carboxyl groups at the particle surface in a preparation of styrene (S)/butyl acrylate (BA)/methacrylic acid (MAA) polymer emulsion. The relative distribution of carboxyl groups in the emulsion was determined by conductometric titration method: in serum, a t surface, and inside particle. By seeded (two-stage) emulsion polymerization that S-BA-MAA terpolymer emulsion was first prepared at low pH and then second stage polymerization of S-BA was continued at high pH, S/BA/MAA polymer emulsion particles in which carboxyl groups are localized predominantly at the surface could be prepared.

For the purpose of localizing carboxyl groups from inside to particle surface, styrene -butyl acrylate -methacrylic acid (74.3/17.0/8.7, mol ratio) terpolymer emulsion was kept under pH 9 at different temperatures. The amount of carboxyl groups at the particle surface, As, was remarkably increased by the alkali-treatment above 35 ~ On the other hand, As value of the alkalitreated emulsion was decreased by keeping under ph 3 above 45 ~ C, although in the case of the original emulsion without the alkalitreatment, it was not changed by the acid-treatment. These results suggest that a part of polymer segments which have ionized carboxyl groups is dragged out at the surface by an increase in the affinity of the groups against water, and the dragged segments turn back into the inside again when the carboxyl groups are deionized.