PREPARATION AND CHARACTERIZATION OF SULFONATED POLYSTYRENE LATEXES

Abstract

The purpose of the work was the preparation of aqueous suspensions of model spherical particles stabilized by ionizable groups covalently bound to the surface. Starting material.was a 80/20 styrene/divinylbenzene latex. The latex had an average particle diameter of 500 Å as determined in the electron microscope. The copolymer was sulfonated in dichloroethane with a 3/1 SO₃/triethylphosphate complex in a concurrent-flow fast-reaction apparatus and was purified by dialysis and ion exchange.Three main fractions with neutralization equivalents, N_e of 0.9, 1.8, and 2.7 meq g⁻¹ were prepared. Elemental analysis revealed that the varying N_e in these fractions resulted from the absorption of Ca²⁺ and Mg²⁺ ions which were tightly bound to the inner-lying sulfonic groups of the particles. Treatment with strong acid followed by ion exchange eliminated the bivalent ions and increased N_e, but the titration pattern was markedly changed after such treatment. Sulfonation caused both the partial specific volume and the refractive index increment to decrease. Electron micrographs showed that the latex particles were only slightly polydisperse and that there was little change in size and shape after sulfonation. Light-scattering measurements established the absence of aggregates in the sulfonated latex. Particle sizes, determined from the intrinsic viscosities, indicated some swelling of the particles in 1 M aqueous NaCl. The extent to which the sulfonated latex satisfies the criteria required of a model colloid to be used for a study of electroviscous behavior is discussed.