The network rigidity inherent to a polymer-supported reagent affects its ability to distinguish among a family of substrates with varying electron density at the functional group. The dimethylamine ligand is bonded to a polystyrene network whose rigidity is increased by increasing the crosslink level from 2% to 25% divinyl-benzene. The ability of the ligand to complex substituted benzoic acids of increasing acidity is correlated with the network's rigidity. The initial ratio of substrate to ligand sites is varied from 0.1 to 1.0. At the highest ratio, the amount complexed decreases with increasing network rigidity but the molecular recognition pattern remains constant. with a ten-fold excess of ligands to substrates, the polymer network plays a critical role in setting the molecular recognition pattern: as network rigidity increases, the specificity of the substrate−−ligand interaction increases. It is proposed that increasing network rigidity decreases multi-site inter actions between the substrate and two or more ligands; this decreases complexation of weakly interacting substrates while not affecting those which interact strongly.