Transparent nanolatexes by polymerization of precursor emulsions

Stable, transparent/translucent microlatexes of butyl acrylate–acrylonitrile copolymer, mimicking the properties of thermodynamically stable microemulsions were prepared by polymerizing precursor emulsions with relatively high weight ratio (10:1) of polymer to surfactant. The latex particle size as determined by the dynamic light scattering and transmission electron microscopy was observed to be 20–60 nm. No phase separation was observed during or after polymerization. Kinetics of the polymerization was studied using potassium persulphate, a water-soluble free radical initiator. Rate of polymerization, percentage conversion and particle size were found to be dependent on initiator concentration, reaction temperature and acrylonitrile concentration in the monomer feed. Unimolecular termination mechanism was found operative in the polymerization reactions. Overall energy of activation (ΔE) was found to be 13.6 kJ/mol. The products were characterized by IR, 13C NMR and thermal analysis. The unusual decrease in the particle size with increased conversion was explained on the basis of the nucleation mechanisms and coemulsifier role of butyl acrylate monomer.