This plot shows a measurement on TPU. During the 1st heating, the endothermic step at -42°C (mid-point) reflects the glass transition of the soft segments of the sample.
Additionally, the curve exhibits an endothermic double peak between 100°C and 210°C. The reversible part of it, which can be detected again in the 2nd heating (7.40 J/g), is caused by the melting of the hard (thermoplastic) segments. The irreversible part is probably due to evaporation of volatiles or distribution of additives in the polymer matrix. This process explains the fact that the glass transition was detected at a higher temperature (mid-point at -28°C) in the 2nd heating.