AbstractThe compact → coil conformational transition of hydrophilic‐hydrophobic copolymers derived from poly(methacrylic acid) was studied by UV Spectroscopy. Two copolymers were used in this study: a Poly(N‐methacryloylalanine‐co‐N‐phenylmethacrylamide) (P50) and a poly(methacrylic acid‐co‐benzyl methacrylate) (S25). Both samples exhibit hypochromism in the absorption band of the aromatic chromophore when they are under the compact conformation: 7% and 30% hypochromism for P50 and S25, respectively. This difference is explained by differences in the hydrophobic side chain‐side chain interactions between the aromatic residues. Increasing the temperature was found to increase strongly the hypochromism of S25 and to have lit