Design of Molecularly Imprinted Polymeric Materials: The Crucial Choice of Functional Monomers

The choice of the functional monomer is addressed in the present study. It is not only dictated by its ability to interact with the template molecule. Its reactivity towards the cross-linker in the radical polymerization reaction is also to be considered in order to yield a suitable distribution of the monomer bearing binding groups within the material and also to adjust the cross-linking degree which provides rigidity to MIP network. MIPs prepared using two functional monomers of very different reactivity in radical polymerization allowed to investigate the criteria for the optimum choice of the functional monomer. MIPs were made of cross-linked poly(methacrylic acid) or poly(maleic acid) bound as thin films to a silica solid support. Ethylene glycol dimethacrylate was the cross-linker. Calculations of the composition drift of the copolymer material from monomers reactivity ratios give new insights into the control of MIP properties by the choice of the functional monomer. As a consequence of the lower reactivity of maleic acid than methacrylic acid for copolymerization with methacrylic esters, the incorporation of maleic acid is low, the cross-linking density is very high, the polymer coating is very thin, and the specific area is high. The final structure of the MIP network with a predominance of isolated functional units closely surrounded by cross-links yields a rigid material capable of preserving the memory of the model molecule of patulin in molecular imprints. Low reactivity of the functional monomer has beneficial effects regarding the binding selectivity for the target molecule compared to materials prepared from the more reactive methacrylic acid which lead to the formation of flexible polymer formed of short poly(methacrylic acid) sequences.