Pressure-induced binding sites in molecularly imprinted network polymers

Molecular imprinting in network polymers under high pressure was studied as a means of inducing selective binding sites for molecular recognition. Network polymers of methacrylic acid and ethylene glycol dimethacrylate were prepared in the presence of a template, atrazine or ametryn, by free radical polymerization at either 1 or 1000 bar in three different solvents. After washing, they were chromatographically evaluated for rebinding selectivity. In one case, a significantly stronger rebinding of the template to the polymer prepared at high pressure than to the polymer prepared at normal pressure was observed. On an ametryn-imprinted polymer prepared at 1 bar using 2-propanol as solvent, the capacity factor for ametryn was 2.3, whereas on a polymer prepared at 1000 bar the capacity factor was 3.2. The capacity factors of atrazine on these materials were 1.2 and 1.4, respectively. With atrazine as the template, no pressure effect was observed and the capacity factors were, within the experimental error, the same on the high-pressure and the normal-pressure materials. The polymers were characterized by porosimetry, swelling measurements, IR, and SEM. These data showed that the high-pressure polymers exhibited a more compact structure with lower pore volume, higher density, and higher swelling compared to the polymers prepared at normal pressure. The origin of the pressure effect on selectivity was discussed in terms of the monomer-template association tendency and in terms of polymer morphology.