Radical polymerization of polar unsaturated monomers in direct microemulsion systems

Polymerization in o/w microemulsions is a new polymerization technique which allows preparation of ultrafine latex particles within the size range 5 nm<particle radius<50 mm. This article presents a review of the current literature in the field of radical polymerization of polar traditional monomers in direct microemulsion systems. Besides a short introduction into some kinetic aspects of polymerization in microemulsions, we mainly focus on the formation of o/w microemulsions and the radical polymerization and copolymerization of alkyl (meth)acrylates and other polar monomers. We present kinetic data of radical polymerization of hydrophilic or polar monomers which are partly soluble in water and contribute to the surface activity of reactants. Effects of initiator, emulsifier and monomer concentration, and the type of additive are evaluated. The influence of several parameters, such as temperature, intensity of the incident light, the nature of emulsifier, monomer and initiator, etc., were also investigated. These results indicate that the nature of the emulsifier and the surface activity of monomer play a decisive role in the polymerization process. The surface active monomer dominates the formation of stable monomer microemulsion, improves the colloidal stability of final polymer microemulsion and decreases the critical amount of emulsifier in the microemulsion monomer droplets. It has been recognized that photopolymerization in the micellar systems is a very attractive way to prepare polymers displaying high molecular weights with high rates of reaction. Besides variation of kinetic, colloidal and molecular weight parameters with the reaction conditions, the type of components of reaction mixture or microemulsion, etc. are discussed.