Narrow or Monodisperse, Highly Cross-Linked, and "Living" Polymer Microspheres by Atom Transfer Radical Precipitation Polymerization

A facile, general, and efficient one-pot approach to obtaining narrow or monodisperse, highly cross-linked, surface-functionalized, and "living" polymer microspheres with uniformly cross-linked structures by atom transfer radical precipitation polymerization (ATRPP) is described for the first time. The simple introduction of atom transfer radical polymerization (ATRP) mechanism into precipitation polymerization system allows the direct generation of uniformly crosslinked "living" polymer microspheres with their number-average diameters ranging from 0.73 to 3.25 mu m and their polydispersity indices being typically lower than 1.01. The polymerization parameters (including stirring rate, monomer loading, initiator and catalyst concentrations, molar ratio of cross-linker to monovinyl functional comonomer, and polymerization scale and time) have proven to show significant influence on the morphologies of the resulting polymer microspheres, which makes it very convenient to control the particle sizes by easily tuning the reaction conditions. The general applicability of ATRPP was demonstrated by synthesizing a series of uniform functional copolymer rnicrospheres with different incorporated functional comonomers (i.e, 4-vinylpyridine, acrylamide, and 2-hydroxyethyl methacrylate). Moreover, the "livingness" of the resulting polymer microspheres was confirmed by their direct grafting of hydrophilic polymer brushes via surface-initiated ATRP under mild reaction conditions. Furthermore, a "grafting from" particle growth mechanism is proposed for ATRPP, which is considerably different from the "grafting to" particle growth mechanism in the traditional precipitation polymerization.