## 4 Conclusions  
Modified TPUs, with different chain extenders, can be prepared using the one-shot solvent-free bulk polymerization method. Examination of their structures, thermal properties, morphology, and rheological properties revealed that the changing of chain extenders did not affect the structure of the main polymer chain segments; this was also applicable to the synthesizing of high molecular polymers. FT-IR results indicated that the two are structurally similar. Thermal analysis performed using DSC and DMA revealed that the \(\mathrm{T_{g}}\) of TPUs prepared using 1,3-BDO as the chain extender was approximately 10-15 \({}^{\circ}\)C higher than that of the TPUs prepared using 1,4-BDO as the chain extender. The main reason was that rotation difficulties in the branched chain structure resulted in an increase of \(\mathrm{T_{g}}\). Additionally, the \(\mathrm{T_{g}}\) point would also slightly increase, by 1 to 2 \({}^{\circ}\)C, with the increase in the TPU's hard chain segment. The DSC scanning data also revealed that the \(\mathrm{T_{m}}\) of TPU made with 1,3-BDO belongs to the category of amorphous materials; the DMA testing spectrum revealed that a TPU containing 1,3-BDO exhibits the characteristic of viscoelasticity. The  
Figure 8: Rheological properties. (**a**) Storage modulus and (**b**) loss modulus of TPUs prepared using 1,3-BDO or 1,4-BDO during the synthesizing of PBA, PTMG, or PCDL. Figure 7: Shear thinning characteristics of TPUs produced by applying 1,3-BDO or 1,4-BDO during the synthesizing of PBA, PTMG, or PCDL. differences in the thermal properties results prompted the researchers to perform further study on the viscoelastic and rheological properties. Subsequently, investigations related to morphological analysis and rheological measurement were conducted. Detailed morphological analysis was performed using AFM scanning. In PBA and PTMG, TPUs that contained 1,3-BDO exhibited an obvious microphase separation, which was a clear difference between hard and soft zones; the separation phenomenon did not change even when the hard chain content was increased. However, in the PCDL group, the microphase separation was not obvious; we believe that the reason for this is that the polycarbonate bonds in PCDL have excellent stiffness, which could help maintain structural stability. The results of the rheological measurements (to examine the viscoelasticity behavior) were similar to those obtained using the morphological test. For PBA and PTMG groups, TPUs that contained 1,3-BDO had poor viscoelasticity. The rheological results clearly confirmed that for PCDL, even when 1,3-BDO was employed as a chain extender during the synthesizing process, the TPUs synthesized were similar to the TPUs synthesized using 1,4-BDO as a chain extender; the reason behind this is that PCDL has a side methyl group, resulting in a high free volume rotation obstacle--thus, the increase of T\({}_{\text{g}}\). In addition, T\({}_{\text{g}}\) range of the TPUs synthesized using PCDL is within room temperature (15-20 \({}^{\circ}\)C). Another factor is that the carbonate group of the PCDL structure contains three oxygen atoms with the six lone pairs of electrons that will mutually repel each other; this causes the compatibility of TPUs synthesized using PCDL to be better than that of the TPUs synthesized using polyester or polyether. The conclusions of this study indicate that PCDL could be used in conjunction with 1,3-BDO as a candidate material for future smart material development.