Non-Migratory Surfactants in Emulsion Polymerization

摘要

Surfactants are one of the essential components in the synthesis of emulsion polymers. They provide colloidal stability and control the particle size of the latex. Common surfactants used in emulsion synthesis are either non-ionic or anionic (or combination) in nature. Free surfactants in water can adsorb onto the monomer droplet and polymer particle surface, form micelles in the aqueous phase, or migrate to the air/water interface. Surfactants at interfaces are in equilibrium with surfactant dissolved in the water. This equilibrium can be disrupted by environmental factors such as temperature, pH, or mixing. Surfactants can desorb from the polymer droplet surface, causing particle flocculation. During film formation, the adsorbed surfactant is released from the particle surface and has a dramatic negative effect on dry film properties. As a result, porous films can be formed with poor protective properties. Particle flocculation, phase separation, and accumulation of surfactant into hydrophilic domains during film formation adversely affect water resistance, blocking resistance, adhesion, and mechanical properties. Non-migratory surfactants (NMS) are reactive and become grafted onto the surface of polymer particles during polymerization. The final latex stability is enhanced with positive effects on shelf life, mechanical, and barrier properties. Use of reactive surfactants is relevant for various application areas. In architectural coatings, better pigment binding properties and scrub resistance can be achieved. In protective coatings, superior barrier properties, or lower water diffusion rates are often observed. Application data comparing conventional and copolymerizable surfactants is presented. NMS technology maximizes the development of waterbome polymer systems and dry film properties, and minimizes the drawbacks commonly associated with the presence of conventional surfactants.