ABSTRACT
Themajority of traditional molecularly imprinted polymers (MIPs) are in the format of irregular particulates obtained by grinding cross-linked polymer monoliths. The widely used grinding and sieving procedures are time-consuming, and often lead to a poor yield of useful MIP particles. In chromatographic uses, the nonuniform (wide variation of ) particle shape and size make it di⁄cult to achieve an optimum column packing. Also the cross-linking polymerization in bulk is only applicable in small laboratory scale. For mass production of MIPs, scalable preparation methods are needed.The most common methods for preparing polymer beads are emulsion polymerization, dispersion polymerization, and suspension polymerization (Table 1). Emulsion polymerization normally leads to uniform latex particles with diameters smaller than 1 mm. Dispersion polymerization and suspension polymerization give larger beads and a broader distribution in particle size, although the latter can be controlled to certain extent by optimizing the reaction condition. In many cases, an aqueous medium serves as a continuous phase in the polymerization system to both support the resulting polymer beads and to provide easy temperature control during the polymerization. In principle, all the above-mentioned methods can be adopted for making molecularly imprinted polymer beads, though under certain circumstances polar or aqueous media do interfere with weak molecular interactions, as represented by the devastating e¡ect of water on the hydrogen bond interaction between template and functional monomers. In addition to the above-mentioned methods, there have been investigations for new polymerization systems that are suitable for making molecularly imprinted polymer beads, for example by using preformed beads as supporting skeleton to generate hybrid materials. These will be discussed in the following sections.
