In this study, thermoplastic polyurethanes (TPUs) were obtained in a torque rheometer (an instrumented batch mixer) at 70, 80, and 90 degrees C, and the thermal properties were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC results showed that the glass transition temperature (Tg) of the rubber phase is not affected by the synthesis temperature. The increase in synthesis temperature promoted side reactions, which modified the crystallization process and reduced nucleation and growth rate (k') during the first stage of crystallization. From TGA analysis, it was observed that the TPU prepared at 70 degrees C showed the highest activation energy (Ea) of decomposition, whereas the TPU synthesized at 80 degrees C showed the lowest Ea values. The rigid-phase decomposition mechanisms were mainly phase boundary controlled reaction (Rn) and random nucleation with one nucleus on the individual particle (F1). These results show that side reactions (other than formation of urethane groups) could occur during the synthesis of polyurethane at temperatures lower than 100 degrees C, and even a small amount of these side reactions influence the thermal properties. POLYM. ENG. SCI., 2012. (C) 2012 Society of Plastics Engineers