Inverse miniemulsion polymerization is a water-in-oil (W/O) heterogeneous polymerization process that forms kinetically stable macroemulsions at, below, or around the critical micellar concentration (CMC). This process contains aqueous droplets (including water-soluble monomers) stably dispersed, with the aid of oil-soluble surfactants, in a continuous organic medium. Stable inverse miniemulsions are formed under high shear by either a homogenizer or a high speed mechanical stirrer. Oil-soluble nonionic surfactants with hydrophilic-lipophilic balance (HLB) value around 4 are used to implement colloidal stability of the resulting inverse emulsion. Upon addition of radical initiators, polymerization occurs within the aqueous droplets producing colloidal particles (Fig. 2) [83]. Several reports have demonstrated the preparation of stable particles of hydrophilic and water-soluble polymers [86–89], polyaniline nanoparticles [90], and organic–inorganic hybrid particles [91–93]. This method also allows for the preparation of crosslinked microgels in the presence of difunctional crosslinkers [27,94–100]. In addition, CRP techniques including ATRP [78,79,82,101,102] and RAFT [103] in inverse miniemulsion have been explored to prepare well-defined nanoparticles and nanogels.
