The colloidal properties of alkaline-soluble waterborne polymers

Waterborne polymer dispersions are widely used in coatings and graphic arts markets as environmentally friendly and more sustainable alternatives to solvent borne binders. Traditionally, waterborne (meth)acrylic dispersions are prepared by emulsion polymerization using low molar mass surfactants as a key ingredient to control particle size. However, these surfactants can have a negative influence on the performance of coatings such as reduced water resistance and adhesion. To mitigate the negative effects of surfactants, polymer latexes have been developed that employ alkaline-soluble polymers as the sole stabilizer for a subsequent emulsion polymerization step. In this way surfactant-free polymer dispersions are obtained. Despite the high commercial impact and relevance of this technology, fundamental studies regarding the physicochemical properties of the alkaline-soluble polymers are lacking. In this article, the synthesis and colloidal properties of alkaline-soluble waterborne methacrylic copolymers are reported. The dissolution behavior and colloidal properties of these alkaline-soluble polymers were studied as function of molar mass, acid content, and pH. The dissolving polymer particles were characterized using static and dynamic light scattering, static and dynamic surface tension measurements, and cryogenic-transmission electron microscopy analysis. It is concluded that the dissolution mechanism of alkaline-soluble polymers follows a gradual process. As the pH increases deprotonation of the carboxylic acid groups swells the particle enhancing the further swelling with water. At a certain amount of base, the particles disintegrate into small polymer aggregates while the most water-soluble polymer chains are dissolved in the water phase. An important learning is that part of the alkaline-soluble polymer resides in very small particles (<5 nm). The formation of these polymer particles below 5 nm was not reported previously and offers a new insight into the dissolution mechanism of alkaline soluble polymers. The most important parameter steering this process is the acid value of the polymer, while the molar mass plays a modest role. The understanding gained in this study can be used to further advance alkaline-soluble polymers as stabilizer in surfactant-free emulsion polymerization technology, improving the performance of a wide range of industrially relevant coatings. (c) 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46168.