In this study, two low-molecular-weight diurethanes were synthesized and blended with thermoplastic polyurethane (TPU). The effects of the incorporation on the thermal and rheological properties of TPU were evaluated. The diurethanes were obtained from the reaction of 4,4'-diphenylmethane-diisocyanate (MDI) with 1-butanol (Additive 1) or 1-octanol (Additive 2). Blending of the additives with TPU was carried out in a torque rheometer, and the blends obtained were analyzed by differential scanning calorimetry (DSC), torque rheometry, and capillary rheometry. The torque rheometry showed that an increase in the amount of both additives displaced the charging peaks to longer times and reduced the torque values after melting. The DSC analysis showed that the incorporation of the additives did not affect the glass transition temperature (T-g) of the flexible phase of TPU. However, an increase in the amount of Additive 1 led to a reduction in the T-g of the rigid phase, while increasing the amount of Additive 2 caused an increase in the Tg of this phase. Capillary rheometry results showed that blends with up to 2 wt % of additive led to intrinsic viscosity and melt-flow stability values higher than those of processed TPU. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 2896-2905, 2009