Effect of living polystyrene costabilizer on styrene miniemulsion polymerization

RAFT miniemulsion polymerizations of styrene with living polystyrene (PS_lc) serving as both RAFT reagent and polymer costabilizer were investigated. The miniemulsion upon aging at 25 °C showed satisfactory stability against the Ostwald Ripening process. The rate of polymerization for RAFT miniemulsion polymerization initiated by oil-soluble AIBN is much slower than that for the water-soluble SPS counterpart. In addition to the predominant monomer droplet nucleation, much stronger particle nucleation taking place in the continuous aqueous phase (homogeneous nucleation) for the run with AIBN was observed. It is the different extents of homogeneous nucleation that is responsible for the quite different kinetic behaviors between the RAFT miniemulsion polymerizations initiated by different types of initiator (AIBN versus SPS). Furthermore, increasing initial molar ratio of RAFT reagent to AIBN greatly enhances the characteristics of RAFT polymerization (i.e., better control over polymer chain growth with the progress of polymerization).