The second DSC heating curves demonstrate that the pure SMPU shows an exothermic peak at −20 °C and an obvious endothermic peak at 50 °C (see Figure 5a), which correspond to the cold crystallization and crystal-melting temperature of the soft phase, respectively. Pure OOBA shows four obvious endothermic peaks (Figure 5a). Among them, the first two peaks at 78 °C and 101 °C can be attributed to the crystal-melting transitions of the α and β crystalline phases, respectively. The β crystal-melting transition also indicates that OOBA enters the smectic phase. The third peak at 107 °C indicates a smectic-nematic phase transition, and the fourth peak at 148 °C suggests a phase transition from the nematic phase to the isotropic phase. When OOBA is incorporated into the SMPU matrix, the two crystal-melting transitions in the composites (e.g., P3) at 49 °C and 74 °C can be attributed to the crystal-melting of the soft segment of SMPU and the α phase of OOBA, respectively. Meanwhile, a new weak exothermic peak which can be attributed to the β crystal-melting transition appears at 89 °C. When the molar ratio of OOBA/MDI is lower than 0.4 (m ≤ 0.4), the β crystal-melting transitions cannot be detected on the second DSC heating curve (see Figure 5b), because the SMPU polymer chain affects the order structure of OOBA. In addition, another weak exothermic peak is detected at 183 °C and is attributed to the crystal melting of the hard segment of SMPU. This result indicates that the crystallizability of the hard segment of SMPU is also enhanced, because the OOBA crystals provide the nuclear seeds of crystallization for the hard phase. However, the cooling curves demonstrate that pure SMPU shows two weak peaks at 105 °C and −14 °C (see Figure 5c), which are the crystallization temperatures of the hard and soft segments of SMPU, respectively; whereas SMPU-OOBAm shows a series of endothermic peaks upon cooling. For P5, the lowest and highest endothermic peaks at 15 °C and 133.6 °C are attributed to the crystallization temperatures of the soft phase and hard phase of SMPU, and these crystallization temperatures are also higher than those of pure SMPU. When the OOBA-content increases, the crystallization temperature of the soft phase of SMPU shifts to a higher temperature range. It is confirmed again that the soft phase of composites with higher OOBA-content has higher crystallinity. In addition, the endothermic peaks at 37 °C should be attributed to the crystallization temperature of the OOBA phase, whereas the endothermic peak at 80 °C shows the phase transition from the isotropic phase to the LC phase. These phase transitions are also verified by the following POM investigations.