(192a) Reversible Addition-Fragmentation Chain Transfer In Microemulsion Polymerizations: Kinetics And Critical Parameters

The ability to produce stable latex nanoparticles containing monodisperse polymer chains of predetermined molecular weight is desired for many applications such as coatings, adhesives and rheological modifiers. Reversible addition-fragmentation chain transfer (RAFT) can control polymerizations for a wide range of monomers and reaction conditions in homogeneous polymerizations. Incorporating RAFT in heterogeneous polymerizations, however, has led to poor control of molecular weight, high polydispersity, and loss of colloidal stability. This work shows that microemulsions are an attractive alternative for incorporating RAFT into heterogeneous polymerizations. RAFT microemulsion polymerizations of acrylates with xanthate chain transfer agents produced stable latex nanoparticles (20-30 nm in diameter) composed of low polydispersity polymer chains of predetermined molecular weight. The measured RAFT microemulsion polymerization kinetics, polymer molecular weight distributions, and latex particle sizes identified the key parameters for achieving control as the chain transfer agent per micelle ratio, and the water solubilities of the monomer and the chain transfer agent. Additionally, a simple kinetic model was developed, which provided new insight into the RAFT microemulsion polymerization mechanism.