Dispersion polymerisation beads produced

Unfortunately, to date, this technique has received little attention from the molecular imprinting community and only one report of a dispersion polymerisation method had appeared until very recently [26]. This is probably better classified as a precipitation polymerisation, since random aggregates were produced rather than beads. No colloidal stabilisers were included in this procedure. The aggregates were made in situ in chromatography columns, which avoided the need to grind and sieve the polymer and pack the columns. Due to the rather polar nature of the solvent mixtures used (cyclohexanol, dodecanol, isopropanol), good imprints were only achieved for compounds which interact strongly with functional monomer... 

Overall, the dispersion polymerisation approach might offer an effective solution to bead production in many situations if the precise balance of solvent composition, imprinting recipe and synthetic conditions can be appropriately matched to produce particles with the desired size, morphology, porosity and binding characteristics. 

Aqueous two-step swelling is a technique for producing monodisperse polymer particles over a size range much greater than that achievable by direct dispersion polymerisation. The properties of the particles, such as porosity, can also be controlled. The concept was first introduced by Ugelstadt and Mork [28] and has since been adopted by many workers. It is used to produce a number of commercial products for chromatography and bioseparations, such as Mono-beads by Pharmacia and Dynabeads by Dynal. 

Using a similar philosophy to the perfluorocarbon liquid approach, Piletsky carried out suspension polymerisations in silicone oil. This liquid is also immiscible with some organic liquids, although the range of immiscible combinations is much smaller than for perfluorocarbons. Beads were successfully produced containing imprints of ATP and poly-A in an EDMA/A,A-diethyl-2-aminoethylmethacrylate system with DMF as solvent and an excess of silicone oil as dispersant [21]. 

The suspension polymerisation approach is often used in the production of polyvinyl chloride dispersions for use in plastic pipes. Polystyrene and styrenic copolymers are also produced by suspension polymerisation. The polystyrene beads are often prepared by suspension polymerisation for use as packing material in gel permeation chromatography (GPC) columns. Ion exchange resin beads are also commonly produced by suspension polymerisation. Because suspension beads are relatively large, it is easier to separate the polymer by coagulation than in the case of emulsion polymerisation. 

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