Narrow or Monodisperse, Physically Cross-Linked, and Living Spherical Polymer Particles by One-Stage RAFT Precipitation Polymerization

Controlled preparation of narrow or mono disperse, physically cross-linked, and living spherical polymer particles by one-stage reversible addition fragmentation chain transfer (RAFT) precipitation polymerization (RAFTPP) is described for the first time. The introduction of RAFT polymerization mechanism into precipitation polymerization system, together with the use of methacrylic acid (MAA) (capable of forming hydrogen bonding) as the monomer, allows ready generation of uniform spherical poly(MAA) (PMAA) particles with surface-bound living dithioester groups, easily tunable sizes, and low molecular weights in the absence of any cross-linking monomer. The polymerization parameters (i.e., monomer loading, molar ratio of the RAFT agent to free radical initiator, and polymerization temperature) showed much influence on the morphologies and yields of PMAA particles, and their simple adjustment allows fine-tuning of living PMAA particle sizes. The presence of dithioester groups on such PMAA particles was confirmed not only by their light pink color and characteristic UV-vis absorbance peak of dithioester units but also by their capability of directly grafting cross-linked apolar polymer shells. Some uniform living PMAA-based functional copolymer microspheres were also prepared in a one-stage process by simply incorporating glycidyl methacrylate, 2-hydroxyethyl methacrylate, or a fluorescent monomer into the RAFTPP of MAA, demonstrating the high versatility and general applicability of the RAFTPP system. The polymerization of MAA in RAFTPP proved to occur both in the continuous phase and on PMAA particle surfaces instead of inside particles, and a combined grafting from and grafting to particle growth mechanism is proposed for RAFTPP.