Effect of chain transfer agents on the kinetics and mechanism of particle nucleation in the emulsion polymerization of vinyl pivalate

We have studied the kinetics and mechanism of particle nucleation in the emulsion polymerization of vinyl pivalate (VPi) under a wide variety of conditions. Quantitative comparisons between the theoretical and experimental estimations of the average number of radicals per polymer particle, as a function of the amounts of surfactant were performed. The relationship between and the parameter α _w, the ratio of radical production in the aqueous phase to termination per particle, can be explained by assuming that chain-transferred monomer radicals escape from the particle. We studied the influence of the chain transfer agents (CTA), namely, n-dibutyl disulfide, t-dibutyl disulfide and l-cysteine in the emulsion polymerization. The addition of a CTA had a strong influence on the resulting degree of polymerization. The experimental results can be accounted on the basis of a kinetic analysis of the chain transfer reaction, assuming an increase of the rate of escape of chain-transferred radicals from the polymer particle.