KINETICS OF PARTICLE GROWTH IN EMULSION POLYMERIZATION SYSTEMS WITH SURFACE-ACTIVE INITIATORS

The seeded kinetics of particle growth in an emulsion polymerization of styrene where initiation is by a surface-active initiator ("inisurf") were investigated. These systems are characterised by a low NBAR (average number of radicals per latex particle). The rate coefficient for free-radical exit was obtained using gamma-radiolysis relaxation by replacing the inisurf with its (noninitating) surfactant moiety. The resulting value was then used to determine the rate coefficient for radical entry and the initiator efficiency in seeded studies initiated by an inisurf, with varying amounts of surface coverage. The initiator efficiency, calculated using these entry rate coefficients and the measured initiator decomposition rate coefficient, was very low (ca. 0.04%) and independent of surface coverage. This result is readily explained qualitatively and quantitatively by comparison of the time for geminate recombination of the two free radicals formed by inisurf decomposition with the time for escape by diffusion of one of those free radicals from the vicinity of the particle.