| Abstract: | An emulsion polymerization process is reported for the production of high-solids, surfactant-free styrene/butadiene latices. With this procedure latices require no surfactants, for stabilization is built into the emulsion particles by means of copolymerized acid monomers. This “pH variable” method is a two-step, batch-on-batch polymerization. In the first step, all the ingredients are present in the reaction mixture; however, only enough styrene and butadiene is added to reach a low solids content. This step, carried out at low pH, produces a carboxylated seed latex. On raising the pH of this low-solids emulsion, the copolymerized carboxyl groups ionize, and the now highly charged latex particles provide an expedient locus for the generation of stable, highsolids latices. Neutralizing the carboxyl groups of the seed latex before adding the remaining monomers induces the highly hydrophilic carboxyl anions to remain on the surface of the latex particle, nearer to the aqueous environment of the surrounding media. Hence, the maximum stabilization capacity of the acid monomers is utilized. The process was evaluated to ascertain the effects of the following variables: the particle size and solids content of the first step, the nature of the base used to raise the pH, the pH of the dispersion prior to the second step, and the effect of the acid monomer on the latex stability. |
