To improve the heat resistance of thermoplastic polyurethane (TPU), in the melt blending process polyamide 1212 (PA1212) and trace amount of 4, 4'-diphenylmethane diisocyanate (MDI) were used as modifier and reactive solubilizer, respectively. Compared with pure TPU, the combinatorial addition of PA1212 and MDI resulted in remarkable improvement of mechanical, thermal, environmental, and aging properties of the TPU matrix. The reactive MDI contributes to the better interfacial adhesion between TPU and PA1212, and the dispersed PA1212 particles act as fillers as well as crosslinking points in the TPU/PA1212/MDI ternary blend. It was revealed that the synergetic effect of PA1212 and MDI is responsible for the enhanced performance of modified TPU. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012