Physical Form of Imprinted Polymers

Molecularly imprinted polymers can be prepared in a variety of forms to suit the final application desired. The most common, and indeed the crudest, method for preparing molecularly imprinted polymers is via solution polymerization followed by mechanical or manual grinding of the monolithic block generated, to give small, molecularly imprinted particles. If required, sizing of the particles through sieving and/or sedimentation can then be performed. Besides being time consuming and wasteful, this method produces particles of irregular shape which are not ideal for chromatographic applications. The grinding process may also destroy a few of the binding sites. Improved polymerization methods which obviate the need for grinding are therefore being investigated.

One seemingly general method which has been developed, and which overcomes the grinding problem completely, involves the suspension polymerization of imprinting mixtures in liquid perfiuorocar-bon continuous phases. Spherical beads of controlled, regular diameters (down to ca. 5 |im) can be prepared reproducibly by this technique, and are isolated simply by filtration. In the same way, imprinted beads can also be obtained via emulsion, seeded emulsion or precipitation polymerization methodologies.

For chromatographic applications, another solution to the grinding problem is to perform the polymerization directly inside the chromatographic column,

Table 3 Crosslinkers commonly used in molecular imprinting

Cross-linker Structure

Ethyleneglycol dimethacrylate 0 n


Divinylbenzene (DVB)

Trimethylolpropane trimethacrylate (TRIM)

i.e. in-situ polymerization. This approach is particularly attractive for capillary electrophoresis applications, where filling of the capillary can often be problematic.

One final format, which is finding increasing interest, involves imprinted membranes. Generally they are composed either of crosslinked polymers which have been prepared in the standard way, or of linear polymers which have been precipitated in the presence of the analyte. They can be either free-standing or supported.

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