A series of segmented polyurethanes (PUs) with novel thermosensitive shape-memory behavior were synthesized via the in situ addition of a small amount of Ioctadecanol (ODO) to a PU system. For comparison, liquid paraffin (LP) modified PUs were also synthesized. The effects of a small amount of ODO or LP on the PU suprastructure and the thermosensitive shape-memory properties were studied with X-ray diffraction, differential scanning calorimetry, dynamic mechanical analysis, and shape-memory studies. The results indicated that the in situ addition of a small amount of ODO (e.g., 0.3 wt %) remarkably promoted microphase separation, facilitating the ordered packing of soft segments and the formation of perfect hard-segment domains and thus significantly improving the shape-memory properties. In contrast, LP had less significant influence on the shape-memory behavior because of the macrophase separation of these nonpolar alkyl chains from the PU system. (c) 2006 Wiley Periodicals, Inc.