Thermal transitions of benzene in a hydrophobic polymer network have been explained by us in terms of the phase diagram of the polymer-solvent system. In this work, we executed a similar study on copolymers and interpenetrating polymer networks (IPNs) with controllable hydrophilic/hydrophobic ratios. Copolymers and IPNs were swollen with different amounts of benzene and subjected to cooling and heating scans with differential scanning calorimetry (DSC). Synthesis of the IPNs was carried out in such a way that phase separation appeared, and three qualitatively different types of DSC thermograms were identified depending on the benzene content of IPN. Thermal transitions of benzene in the hydrophilic/hydrophobic copolymers can also be explained as a consequence of the phase diagram of the system, but an increase in the glass-transition temperature of the system can be correlated with the interactions among the hydrophilic groups of the copolymer. (C) 2003 Wiley Periodicals, Inc.