Effect of water solubility of monomer on reaction kinetics in oil–water microemulsion copolymerisation

A partially water soluble monomer acrylonitrile (AN) and a hydrophobic monomer butyl acrylate (BuA) were copolymerised in oil–water microemulsions prepared with anionic emulsifier sodium dodecyl sulfate. The effect of initiator type and concentration, polymerisation temperature, monomer feed composition and cosurfactant concentration on kinetics was investigated. Stable and translucent latexes were obtained. Rate of polymerisation (Rp) was found higher for water-soluble initiator potassium persulfate than for oil-soluble initiator 2,2,azo-bis-isobutyronitrile. Rp was observed to be directly proportional to the initiator concentration and BuA concentration in feed whereas it was inversely proportional to the AN concentration in feed. The particle size was found dependent on the initiator type, polymerisation temperature and monomer feed composition. The overall energy of activation (Δ̄Ea) was found to be dependent on the initiator type. The decrease in the percentage conversion and Rp and increase in the particle size was observed with increasing cosurfactant (hexanol) concentration. The latexes were characterised by dynamic light scattering and transmission electron microscopy for particle size. Latex particles were found to contain macromolecules of 105 molecular masses with polydispersity 1.6.