Miniemulsion copolymerization of styrene and butyl acrylate initiated by redox system at lower temperature: Reaction kinetics and evolution of particle-size distribution

The kinetics of the miniemulsion copolymerization of styrene (St) and butyl acrylate (BA) initiated by redox initiators, (NH4)(2)S2O8/NaHSO3, at lower temperature (45 degrees C) was studied. The polymerization rate in miniemu lsion copolymerization is lower than that of the corresponding conventional emulsion copolymerization. In regard to the rate of polymerization, the in itiator concentration plays a more important role in miniemulsion copolymer ization than in conventional emulsion polymerization, while the surfactant concentration has a more important role in conventional emulsion polymeriza tion than in miniemulsion polymerization. These are attributed to their dif ferent nucleation mechanisms, which are the same as those found in the mini emulsion polymerization carried out at higher temperatures. While by elimin ating nucleation via micelle and ensuring against homogeneous nucleation, m iniemulsion polymerization can be carried out by the sole nucleation mechan ism-monomer droplet nucleation-at lower temperature. Because of this, the p articles become narrower during the polymerization and, finally, monodisper se polymer particles are obtained. The result of the particle numbers indic ated that a continuous nucleation will cease at about 60% conversion. (C) 1 999 John Wiley & Sons, Inc.