Improved colloidal stability by seeded emulsion copolymerization of styrene with acrylic acid

The incorporation of acrylic acid (AA) in styrene (S) latex particles was investigated to improve colloidal stability. AA was added at high S conversions (> 0.7), using a two-step seeded emulsion polymerization of S. The addition moment and amount of added AA were varied. Conductometric titrations were used to study the spatial distribution of AA in the particles. The reactions were monitored by reaction calorimetry, which showed a delayed gel-effect for reactions with AA. Good surface incorporation of AA was obtained. The amount of surface AA increases with the amount of added AA and the amount of water phase AA increases with the addition moment. All copolymer latexes showed a significant increase in latex stability against coagulation compared to a PS latex.