AbstractThe compact → coil conformational transition of two series of hydrophilic‐hydrophobic copolymers derived from poly(methacrylic acid) was studied by potentiometric and conductimetric titrations. The samples used were poly(N‐methacryloylalanine‐co‐N‐phenylmethacrylamide) containing up to 50 mole‐% of the hydrophobic residue (P series) and poly(methacrylic acid‐co‐benzyl methacrylate) containing up to 25 mole‐% of the hydrophobic residue (S series). The determination of the free enthalpy of the transition and of the domain of the degree of ionization in which the transition occurs, show inportant differences in the behaviour of the two series of copolymers. These differences are explained by an entropy‐enthalpy compensation for the S series due to strong hydrophobic interactions between the aromatic side chains. Conductimetric titrations allow, in some cases, the determination of the degree of ionization at the beginning and at the end of the conf