Alkali-Soluble Resins as pH-Responsive Protective Colloids

Emulsion polymers are widely present in numerous applications such as adhesives, coatings, paints, and cementitious materials. In applications such as construction, they are favored in dry form that can be restabilized in the final formulation in the presence of water. This offers advantages in terms of storage, transportation, and final application. This work investigates a pH-switchable stabilizer. Turning off the stabilizer leads to latex particle coagulation and dry polymer isolation. Then, turning it back on recovers the restabilized particles in the form of an emulsion. The success of this process relies on the switchability of the colloidal stabilization system and the surface protection of low glass transition temperature (<i>T</i>_g < 20 °C) particles through a hard shell, ensuring particle integrity during coagulation and polymer isolation. Carboxyl-containing alkali-soluble resins are identified as promising candidates capable of providing both requirements simultaneously. Low <i>T</i>_g (14 °C) polymer particles of vinyl acetate and vinyl neodecanoate (VeoVa10) stabilized by high <i>T</i>_g alkali-soluble resins were synthesized in seeded semicontinuous emulsion polymerization. The polymer isolation was performed through a sequence of steps, including latex coagulation at pH ≤ 3, water filtration (resulting in approximately 70% water removal), drying, grinding, and reinforcement with kaolin as an anticaking agent. The isolated polymer product was then successfully restabilized in the presence of water by applying energy and increasing the pH.