Controlled Radical Polymerization of MIPs

The polymerization is initiated (1) by generating free radicals R using an initiator, a molecule that decomposes under heating or under UV or visible irradiation. A radical attacks the double bond of a monomer, resulting in the formation of an intermediate radical Mi . This is the rate-limiting step of the process. 

The propagation (2) is the main step of radical polymerization. Here, the macromolecular chain is formed by successive additions of monomers on the growing macroradical Mn . The result is a mixture of polymer chains with high molecular weights. 

The termination of the reaction can take place in two ways recombination (3) of two macroradicals Mn and Mp forming a macrochain Mll+p or disproportionation (4) yielding a double bond Mn = and a C-H bond at the chain terminus MpH. 

A number of controlled/living radical polymerization methods have been developed. These include  

It should be noted that the presence of cross-links results in the partial or complete loss of control over the size of the polymer molecules, even if the living character of the polymerization can sometimes be preserved. Incidently, one of the characteristics of MIPs is that they are cross-linked polymers. This cross-linking is necessary in order to maintain the conformation of the three-dimensional binding sites obtained through the molecular imprinting process, and thus the ability of the polymer to recognize specifically and selectively its target molecule. Nevertheless, even with cross-linked polymers, the use of CRP methods may be beneficial, as it can, up to a certain point, improve the structure of the polymer matrix. Indeed, all of the above CRP methods have been applied to MIPs. 

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