## 3 Results and Discussion
Next, AFM was used to identify the microphase distribution of the TPUs. The surfaces of TPUs that were subjected to thermal processing and those not subjected to thermal processing were analyzed to confirm their phase separation condition and structure. The annealing was conducted at 100 \({}^{\circ}\)C. With the increase of annealing time, changes in the crystal could be evaluated. All the captured images were uniformly modified to the same scale for direct comparison. Figure 5 presents the AFM images of TPUs synthesized from PBA and PTMG; the images clearly indicate that obvious microphase separation was present in TPUs synthesized using 1,3-BDO. Because the miscibility between the hard and soft chain segments is poor, the differentiation between the dark and light zones is fairly apparent. After being subjected to 10 and 20 h of thermal processing, only the dark-colored aggregates increased substantially. According to the surface structure, the crystals aggregated with the increase of thermal processing time. AFM images of thermal treatment were presented in Figure S1 for TPU composed by PBA and Figure S3 for TPU composed by PTM. The increase in the number of TPU hard chain segments resulted in the formation of more crystals, which in turn led to more aggregates. The AFM scanned images of TPUs with disparate R value were presented in Figure S2 for TPU synthesized from PBA, and Figure S4 For TPU synthesized from PTMG to address the results of aggregation. Compared with the AFM images of TPUs synthesized with PCDL, the constituents of TPUs synthesized with PBA and PTMG are slightly different; the AFM images indicate that regardless of whether TPUs were synthesized using 1,4-BDO or 1,3-BDO, the aggregate of crystals was present in both types of TPU. The aggregate condition of the two types of TPU is depicted in Figure 6; TPUs synthesized using 1,3-BDO as a chain extender exhibit a more obvious phase separation phenomenon. It has the same phenomenon that more aggregates with the increase of the hard phase presented in Figures S5 and S6. In all the synthesized TPU series, an increase in hardness resulted in an increase of crystallization. The microphase separation of the TPUs synthesized using PCDL revealed that regardless of whether the TPUs were synthesized using 1,3-BDO or 1,4-BDO, the aggregation of crystallizations was readily observable in the synthesized products; this is because the polarized structure of polycarbonate bonds is beneficial for the production of hard chains [48]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Chain Extender** & \multicolumn{2}{c}{**1,3-BDO**} & \multicolumn{2}{c}{**1,4-BDO**} \\ \hline
**[NCO]/[OH]** & **1.00** & **1.02** & **1.00** & **1.02** \\
**(R Value)** & & & & \\ \hline PBA-1000 & \(-2.8\)\({}^{\circ}\)C & \(-1.2\)\({}^{\circ}\)C & \(-31.3\)\({}^{\circ}\)C & \(-28.3\)\({}^{\circ}\)C \\ PCDL-1000 & \(8.1\)\({}^{\circ}\)C & \(10.6\)\({}^{\circ}\)C & \(-3.5\)\({}^{\circ}\)C & \(-1.3\)\({}^{\circ}\)C \\ PTMG-1000 & \(-19.1\)\({}^{\circ}\)C & \(-13.9\)\({}^{\circ}\)C & \(-44.9\)\({}^{\circ}\)C & \(-38.4\)\({}^{\circ}\)C \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The tan \(\delta\) crest peak location on the DMA spectrum was used as the glass transition temperature (T\({}_{\text{g}}\)). Relevant numerical values associated with TPU prepared through the polymerization of different butanetolids with different R values. Figure 5: Atomic force microscope (AFM) scanned images: (**a**) PBA-1,3-BDO, (**b**) PBA-1,4-BDO, (**c**) PTMG-1,3-BDO, (**d**) PTMG-1,4-BDO. Next, the researchers performed a rheological analysis using two methods to understand the shear-thinning behaviors via frequency sweep and the viscoelastic characteristics under the oscillatory mode; the shear-thinning data related to the shear rate are presented in Figure 7. The results indicate that for the PBA and the PTMG groups, the melt viscosity of TPUs synthesized using 1,4-BDO was higher than the melt viscosity of TPUs synthesized using 1,3-BDO.