## 3 Results and Discussion  
As shown in Scheme 1, shape memory PBLG-PPG-PBLG was synthesized by the ring-opening polymerization of BLG-NCA using PPG (Poly Propylene Glycol)-diamine 400 as an initiator. \({}^{1}\)H NMR and FTIR spectra were used to characterize the structure of the obtained PBLG-PPG-PBLG. Figure 2 shows the \({}^{1}\)H NMR spectrum of PBLG-PPG-PBLG in CF\({}_{3}\)COOD. The characteristic resonances at 7.0 ppm and 4.9 ppm are assigned to CH\({}_{2}\) and phenyl in benzyl group, respectively, and that at 4.4 ppm is assigned to CH groups in amide linkage, while the signals at 3.2-3.8 ppm are assigned to CH and CH\({}_{2}\) groups in the PPG units. The molecular weight of the obtained PBLG-PPG-PBLG was calculated to be \(\sim\)5000 according to the integral area, which is close to the theoretical value. Figure 3 exhibits the FTIR spectrum of the resulting PBLG-PPG-PBLG. The amide I (backbone C=O stretch) region is present at 1600-1700 cm\({}^{-1}\), which could be used to determine the structure (e.g., \(\alpha\)-helix, \(\beta\)-sheet) of polypeptides [27]. The strong band of \(\alpha\)-helix occurs at \(\sim\)1668 cm\({}^{-1}\) (left-handed) or \(\sim\)1655 cm\({}^{-1}\) (right-handed). The amide I peak is located at lower wavenumbers for a parallel \(\beta\)-sheet (1636-1640 cm\({}^{-1}\)) compared to an antiparallel \(\beta\)-sheet (1622-1632 cm\({}^{-1}\)) [27]. It can be clearly observed from Figure 3 that the obtained PBLG-PPG-PBLG not only forms right-handed \(\alpha\)-helix, but also has antiparallel \(\beta\)-sheet structure, as reported for PBLG-\(b\)-poly(dimethylsiloxane)-\(b\)-PBLG [28]. The percent of \(\beta\)-sheet conformation was calculated to be \(\sim\)5.12% by the deconvolution of the amide I region (1620-1670 cm\({}^{-1}\)). Moreover, the strong absorptions at 3300 and 1730 cm\({}^{-1}\) are corresponding to the stretching vibration of N\(-\)H and C=O stretching vibration of benzyl ester group, respectively. The characteristic peaks at 1550 and 1320 cm\({}^{-1}\) are assigned to amide II and III bands, respectively [29]. The thermal properties of the obtained PBLG-PPG-PBLG film were measured by DSC and TGA. Figure 4 shows the DSC curve of the PBLG-PPG-PBLG film during heating and cooling. Only one glass transition temperature (\(T_{\text{g}}\)) was clearly observed, corresponding to the PBLG units [30]. The \(T_{\text{g}}\) taken  
Figure 3: Fourier transform infrared (FTIR) spectrum of PBLG-PPG-PBLG. Figure 2: \({}^{1}\)H NMR spectrum of PBLG-PPG-PBLG in trifluoroacetic acid (CF\({}_{3}\)COOD). from the first heating curve was higher than one from the second heating curve (26 \({}^{\circ}\)C). Additionally, the sample shows an endothermic peak around \(T_{\text{m}}\) = 100 \({}^{\circ}\)C in the first heating process, which may be due to \(\alpha\)-helical transition [30; 31]. Figure 5 displays the TGA analysis of the PBLG-PPG-PBLG film. The sample began to decompose at above 280 \({}^{\circ}\)C, as evidenced by the rapid decrease in weight, indicating good thermal stability. Mechanical property of the resulting PBLG-PPG-PBLG film was examined by tensile test. Figure 6 exhibits the stress-strain curve, and its tensile strength, elongation and Young's modulus are 8.0 MPa, 13.1%, and 208 MPa, respectively. The shape memory properties of the obtained PBLG-PPG-PBLG film were quantitatively evaluated by the bending test. The straight specimen was bent into a \"U\"-like shape at 100 \({}^{\circ}\)C, then cooled down to room temperature with an external force to maintain the deformation. After that, the recovery process was recorded with time at 100 \({}^{\circ}\)C, as shown in Figures 7 and 8.