Modulated differential scanning calorimetry (MTDSC) was applied to investigate the phase transition behaviour of polyurethane/organoclay nanocomposites. The endotherm transitions located at 50-80 and 140 degrees C were re-analysed through revealed thermal features in the MTDSC reversing, non-reversing and dC(p)/dT curves. It was proposed that the diffused interfacial phase exists between hard and soft phases in the polyurethane system. The assignment of endotherm at 140 degrees C is attributed to the hard microphase domain transition, which is similar to an order-disorder transition. The transition in the region of 50-80 degrees C reveals the relaxation of segments in the interface resulted by annealing. The addition of organoclay resulted in a reduction of hard domain ordering level. A simple method for quantitatively estimating the amount of polymer chains intercalated into layers of clay was introduced, and the relationship between the weight fraction (omega(p)), of the polymer intercalated into layers and the weight fraction (omega(c)), of clay was established. (C) 2006 Elsevier B.V. All rights reserved.