rate of polymerization, minimize coagulum or fouling in the reactor and other process equipment, prevent an unacceptably high viscosity during polymerization (which leads to poor heat transfer), and maintain or even improve properties in the final product such as tensile strength, gloss, and water absorption. Anionic, nonionic, and cationic surfactants have been used, although anionic surfactants are by far most prevalent. Surfactants with a low critical micelle concentration (CMC) are favored; the polymerization rate shows a dramatic increase when the surfactant level is above the CMC, and minimization of the surfactant is preferred for economic reasons and the (usually) adverse effect of surfactant on the physical properties of the resulting polymer. Mixtures of surfactants are often used, including mixtures of anionic with nonionic surfactants. Mixtures of cationic and anionic surfactants form insoluble salts and are not useful. Examples of surfactants commonly used in emulsion polymerization include fatty acids, sodium lauryl sulfate, and alpha-olefin sulfonate. Non-surfactant stabilizers Some grades of polyvinyl alcohol and other water-soluble polymers can promote emulsion polymerization even though they do not typically form micelles and do not act as surfactants (for example, they do not lower surface tension). It is believed that growing polymer chains graft onto these water-soluble polymers, which stabilize the resulting particles. Dispersions prepared with such stabilizers typically exhibit excellent colloidal stability (for example, dry powders may be mixed into the dispersion without causing coagulation). However, they often result in products that are very water sensitive due to the presence of the water-soluble polymer. Other ingredients Other ingredients found in emulsion polymerization include chain transfer agents, buffering agents, and inert salts. Preservatives are added to products sold as liquid dispersions to retard bacterial growth. These are usually added after polymerization, however. Applications Polymers produced by emulsion polymerization can roughly be divided into three categories. Synthetic rubber Some grades of styrene-butadiene (SBR) Some grades of Polybutadiene Polychloroprene (Neoprene) Nitrile rubber Acrylic rubber Fluoroelastomer (FKM) Plastics Some grades of PVC Some grades of polystyrene Some grades of PMMA Acrylonitrile-butadiene-styrene terpolymer (ABS) Polyvinylidene fluoride Polyvinyl fluoride PTFE Dispersions (i.e. polymers sold as aqueous dispersions) polyvinyl acetate polyvinyl acetate copolymers polyacrylates Styrene-butadiene VAE (vinyl acetate – ethylene copolymers) See also International Union of Pure and Applied Chemistry Radical polymerization RAFT (chemistry) Robert Gilbert Dispersion polymerization Ray P. Dinsmore References Chemical processes Polymerization reactions fr:Procédé de polymérisation#Polymérisation en émulsion