Methylated beta -cyclodextrin (me-beta -cD) was used to complex the hydrophobic monomers n-butyl acrylate (I), n-hexyl acrylate (2) and cyclohexyl acrylate (3) yielding the corresponding water soluble host/guest complexes 1a-3a. The complexes were copolymerized in water by free radical mechanism and the reactivity ratios were determined by measuring the monomer consumption by HPLC. The following reactivity ratios were found: copolymerization of la and 2a: r(1) = 1.01 +/- 0.01; r(2) = 1.04 +/- 0.01; copolymerization of 3a and 2a: r(1) = 0.74; r(2) = 1.28; copolymerization of 3a and la: r(1) = 0.75 +/- 0.04; r(2) = 1.13 +/- 0.01. In contrast to that, the copolymerization of the uncomplexed monomers 1-3 in organic medium (DMF/H2O) leads to nearly ideal statistical copolymers in all cases.