Rapid-set, waterborne coatings from polyzwitterionic polymers formulated with a critical solvent combination

Abstract

Waterborne coatings that rapidly set and become tack-free can be prepared from polymers containing both pendant anionic (acidic, carboxylate, or strong-acid groups such as sulfonate) and cationic functionality (quaternary ammonium groups). This phenomenon is related to anion-cation interactions that function as ionic crosslinks and dramatically enhance the physical properties and water resistance of the coatings. We define this process as “controlled ionic-coacervation.” The best coating properties can only be obtained by using a “critical solvent combination.” The critical solvent combination requires water plus at least two organic solvents: (1) a lower boiling (70 to 134°C) water-soluble organic solvent having at least one hydroxyl group and (2) a higher boiling (135 to about 250°C) organic solvent. Loss of only a small amount of solvent causes a coating to rapidly become tack-free. Ionization of acid functionalities on the polymers by an increase in pH (e.g., through the loss of CO2) can initiate controlled ionic interactions. The influence of polymer and solvent compositions on coating properties is discussed.