Solvents imprinted matrices

In an alternative approach, MIP membranes can be obtained by generating molec-ularly imprinted sites in a non-specific matrix of a synthetic or natural polymer material during polymer solidification. The recognition cavities are formed by the fixation of a polymer conformation adopted upon interaction with the template molecule. Phase inversion methods have used either the evaporation of polymer solvent (dry phase separation) or the precipitation of the pre-synthesised polymer (wet phase inversion process). The major difficulties of this method lay both in the appropriate process conditions allowing the formation of porous materials and recognition sites and in the stability of these sites after template removal due to the lack of chemical cross-linking. 

Both of these MIP preparation procedures have their advantages and limitations [20, 21]. For instance, the size of the analyte molecule is not a discriminating criterion in covalent imprinting since the template selectively determines the interaction sites. In contrast, non-covalent imprinting has the advantage of being simpler since an additional synthetic step is not required to introduce the template into the polymer matrix. Moreover, removal of the template via extraction with the suitable solvent solution is simple and mostly complete for the non-covalent imprinting. 

There are two processes by which the bulk imprinted polymers are formed covalent imprinting and noncovalent imprinting. In the former, the template molecule is first covalently functionalized with the monomer, and then copolymerized with the pure monomer. After that the covalent bond is broken and the template molecule is removed by extraction. In order to facilitate the extraction step, a so-called porogenic solvent is used. It effectively swells the polymer matrix. 

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