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

Abstract

ABSTRACT:The kinetics of the miniemulsion copolymerization of styrene (St) and butyl acrylate (BA) initiated by redox initiators, (NH 4 ) 2 S 2 O 8 /NaHSO 3 , at lower temperature (45°C) was studied. The polymerization rate in miniemulsion copolymerization is lower than that of the corresponding conventional emulsion copolymerization. In regard to the rate of polymerization, the initiator concentration plays a more important role in miniemulsion copolymerization than in conventional emulsion polymerization, while the surfactant concentration has a more important role in conventional emulsion polymerization than in miniemulsion polymerization. These are attributed to their different nucleation mechanisms, which are the same as those found in the miniemulsion polymerization carried out at higher temperatures. While by eliminating nucleation via micelle and ensuring against homogeneous nucleation, miniemulsion polymerization can be carried out by the sole nucleation mechanism-monomer droplet nucleation-at lower temperature. Because of this, the particles become narrower during the polymerization and, finally, monodisperse polymer particles are obtained. The result of the particle numbers indicated that a continuous nucleation will cease at about 60% conversion.

Alkoxysilane‐functionalized acrylic copolymer latexes. I. Particle size, morphology, and film‐forming properties

“…The same question discussed previously arises: why do the PBA/P(BA–MMA) composite latex particles become relatively monodispersed, whereas the P(BA–MMA) copolymers grow on multidispersed PB seed latex particles? At first glance, there is a striking similarity if this is compared to the evolution of the particle size distribution in the miniemulsion copolymerization of styrene and BA,10 for which the particle size distribution is broader at the beginning of the polymerization and becomes narrower as the polymerization proceeds. At the end of the polymerization, monodispersed particles are formed.…”

“…2 and Table IV), largely in the range of 50–100 nm. This is not expected because conventional emulsion polymerization normally leads to the formation of particles with wide distributions on account of the coexistence of micelle, homogeneous, and droplet nucleation mechanisms 9, 10. One possibility is that there are no new particles produced during the second stage of polymerization because of the good control over the addition of monomer emulsions; this assumes that micelle nucleation is the predominant mechanism, and homogeneous and droplet nucleation has been eliminated.…”

“…In the study reported here, however, the broad particle size distribution at the beginning of the seeded polymerization refers to PBA polymer latex particles only. In other words, there is no issue of molecular diffusion from larger monomer droplets to growing polymer particles, which become smaller and approach the mean population, as in the miniemulsion copolymerization of styrene and BA 10. Again, more effort is needed to determine the origins of this unusual behavior.…”