Colloidal Structure-Property Relationships in Carboxylated Styrene-Butadiene Latexes

Abstract

Abstract 1. The hydrodynamic particle size of the latexes, measured by light transmission and liquid exclusion chromatography, was, in general, higher than the dry particle size measured by electron microscopy. At comparable high pH and acid level, a methacrylic latex swelled more than an itaconic latex, indicating difference in acid incorporation. 2. Carboxylic acid incorporation in batch-polymerized SB latexes containing itaconic and/or methacrylic acid was strongly influenced by the level and relative ratio of the two acid monomers in the recipe. Itaconic acid distributed primarily between the surface and the serum and none in the bulk polymer. Methacrylic acid distributed primarily between the surface and the bulk of the polymer and none in the serum. The acid distribution results can, in general, be understood in terms of the relative solubilities of the acid monomers in water and styrene. 3. It appeared that the percentage of the total acid bound to the surface could be maximized by the use of certain combinations of the two acid monomers rather than the sole usage of either acid monomer. 4. The latexes contained two kinds of surface-bound acid that differed slightly in ionization characteristics. In general, a direct relationship existed between the H+ ion stability and the ratio of type I to type II surface-bound acid concentration. Thus, the itaconic latex was the least H+ ion stable, while the methacrylic latex was the most H+ ion stable among the latexes. It is not clear at this point as to how exactly the two acid types are located on the particles. 5. The colloidal stability of a carboxylated latex depended on the type of cation, the amount of surface-bound acid and the extent of ionization. Both CCC and electrophoresis results showed that sodium chloride stability increased with the increase of surface-bound acid and pH of the latex. The calcium chloride stability, however, decreased with the increase of pH, indicating strong specific interaction between calcium and carboxylate ions. The interaction of a carboxylated latex with hydrogen, sodium, and calcium ions seemed to take place, respectively, through alteration of the surface acid dissociation equilibrium, reduction of the double layer potential, and surface charge reduction by chemical bonding.