Water-compatible molecularly imprinted polymers (MIPs) for caffeine were synthesized in aqueous medium with a new functional monomer, 1-(alpha-methyl acrylate)-3-methylimidazolium bromide (1-MA-3MI-Br), which had pi-pi and hydrogen-bonding interactions. Caffeine-imprinted polymers were prepared in suspension polymerization with 1-MA-3MI-Br and methacrylic acid (MAA), which only had hydrogen bonding, as a functional monomer. For the specific binding characteristics of the new functional monomer 1-MA-3MI-Br, the adsorption capacity and relative separation factor (beta) of MIPs for caffeine were significantly enhanced. The maximum adsorption capacities of 1-MA-3MI-Br-MIP and MAA-MIP imprinted microspheres for caffeine were 53.80 and 28.90 mu mol/g, respectively. Moreover, the relative separation factors were measured by comparison of the separation characteristics under competitive adsorption conditions. The results showed that the beta of MAA-MIP for caffeine relative to theophylline was only 1.65; this showed a very poor recognition selectivity for caffeine, but beta of 1-MA-3MI-Br-MIP for caffeine with respect to theophylline was remarkably enhanced to 3.19; this showed an excellent recognition selectivity and binding affinity toward caffeine molecules in an aqueous environment. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 127: 2884-2890, 2013