Emulsion polymerization of butyl acrylate. Kinetics of particle growth

The kinetics of the seeded emulsion polymerization of butyl acrylate have been studied dilatometrically at 50 °C, using both persulphate and γ-radiolysis for initiation. Kinetic data obtained for steady state polymerization and for the approach to (and, for γ-radiolysis, relaxation from) a steady state, gave rate coefficients for entry, exit, termination and propagation, using data-fitting techniques which have been shown to yield unambiguous rate parameters from such results. The system is found to have a high average number of free radicals per article (ranging from 3 to 9). The rate coefficient for exit (desorption) of free radicals from the particles is in accord with transfer/diffusion theory; exited free radicals tend to undergo subsequent re-entry. The entry rate shows that the free-radical capture efficiency is high but significantly less than 100% at the higher initiator concentrations studied; this is quantitatively interpreted by considering competing aqueousphase events. Values for the propagation and termination rate coefficients at 60% weight fraction polymer are reported, the latter being an order of magnitude less than predicted by current theory.