Efficient synthesis of narrow or monodisperse, physically cross-linked, and “living” spherical polymer particles via one-stage ambient temperature photoiniferter-RAFT precipitation polymerization and its particle formation mechanism

Abstract

The efficient synthesis of narrow or monodisperse, physically cross-linked, and “living” spherical polymer particles via one-stage ambient temperature photoiniferter-reversible addition-fragmentation chain transfer precipitation polymerization (pRAFTPP) and its particle formation mechanism are reported. The pRAFTPP of acrylic acid (AA) and methacrylic acid (MAA) in a mixed solvent of acetonitrile and toluene using a trithiocarbonate unit-containing photoiniferter readily afforded uniform poly(AA-co-MAA) micro/nanospheres with surface-bound trithiocarbonate groups, easily tunable sizes and compositions, and low molecular weights under blue light irradiation at room temperature by simply adjusting polymerization parameters (including molar ratio of monomers to photoiniferter, monomer loading, and light intensity). The addition of toluene into the pRAFTPP system largely accelerated the polymerization rate but inhibited the reactivity of trithiocarbonate groups on particle surfaces. Nevertheless, the resulting poly(AA-co-MAA) particles proved to be “living” in pure acetonitrile and they were successfully used as sacrificial templates for fabricating well-defined polymer capsules. Remarkably, the limited light penetration depth of this photoinduced heterogeneous polymerization led to inefficient activation of the photoiniferter and its presence in the reaction solution during the polymerization process. These features of pRAFTPP enabled the polymerization of monomers mainly occurring in the continuous phase instead of on polymer particles, suggesting the existence of a unique “grafting to” particle growth mechanism thereof. This newly developed pRAFTPP, with advantages over thermo-induced RAFTPP such as lower polymerization temperature, faster polymerization rate, and higher monomer loading, can not only address the challenging slow-polymerization-rate issue of the photoinduced heterogeneous polymerizations but also provide a versatile platform for preparing “living” sacrificial templates highly useful for developing advanced polymer micro/nanocapsules that hold much promise in many bioanalytical and biomedical applications.