A region of broad nonlinear curvature is observed in DSC traces of ABA copolymers during temperature sweeps between the glass transition temperatures of the two principal microphases. This curvature is attributed to a smoothly varying composition profile through the interfacial region lying between microphases. The shape of the DSC curve is proposed to be a fingerprint for a given profile. This curvature is, however, shown to be a possible source of uncertainty in precise evaluation of T-g for the microphases and the reported enhanced breadth of these transitions. In addition, microphase separation temperatures are readily identifiable from DSC traces, and their values correspond well to the predictions of Leary-Williams theory.