Two-step swelling polymerization

Two-step swelling polymerization starts with the preparation of sub-micron sized non cross-linked seed particles by emulsion polymerization. The seed particles are then added to a pre-polymerization mixture. The particles swell in the mixture and the polymerization takes place within the volume of the swollen particles [91]. The procedure, which results in monodisperse particles, has been used for the preparation of MIPs imprinted with a range of templates [92-97]. 

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Spherical beads possess better hydrodynamic and diffusion properties than irregularly shaped particles. It is, hence, desirable to apply MIPs in a spherical bead format, especially for flow-through applications. Methods to synthesize spherical polymer beads are often classified according to the initial state of the polymerization mixture (i) homogeneous (i.e. precipitation polymerization and dispersion polymerization) or (ii) heterogeneous (i.e. emulsion polymerization and suspension polymerization). In addition, several other techniques have been applied for the preparation of spherical MIP beads. The techniques of two-step swelling polymerization, core-shell polymerization, and synthesis of composite beads will be detailed here. 

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