Enhanced Colloidal Stability in RAFT Seeded Emulsion Polymerization.

In recent years, reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization has been regarded as a powerful technique in particle design. In RAFT emulsion polymerization, the surface density of the polymer stabilizer decreases with the growth of latex particles, which results in a decrease in particle stability and the aggregation of particles. Therefore, a major challenge in RAFT emulsion polymerization is to improve the stability of the synthesized particles. Herein, an approach to improving particle stability in the seeded emulsion polymerization process is reported. Seed latex particles with poly(N,N-dimethylacrylamide) (PDMA) shells and poly(methyl acrylate) cores are prepared through RAFT emulsion polymerization. Initiated by bromine groups at PDMA chain ends, zwitterionic poly(3-dimethyl(methacryloyloxyethyl)-ammonium propanesulfonate) (PDMAPS) blocks are synthesized on the seeds by in situ activator generated by electron transfer atom transfer radical polymerization. The seed particles are employed in the subsequent RAFT seeded emulsion polymerization of n-butyl acrylate. Experimental results demonstrate particle stability in the polymerization process. Upper critical solution temperature (UCST) behavior and salt-responsiveness of the zwitterionic blocks on the particle surfaces are studied.