# Shape-Memory Property Acting as a Switch to Change the Surface Property of the Film
## 3 Results
### Elucidating the Shape-Memory Mechanism of PNIPAAm-Grafted Polyester Composite  
PCL-based shape-memory exhibits shape-memory properties due to the softening of the film caused by crystal melting [35; 36]. Therefore, the endothermic peak originating from crystal melting was confirmed by DSC measurements. Before graft polymerization, a clear unimodal endothermic peak appeared at 44.8 \({}^{\circ}\)C in the film (3b-PCL-Cl in Figure 6a). Before crosslinking, the polymer exhibited a bimodal DSC curve at the peak top of the endothermic peak (Tm: 42.2 \({}^{\circ}\)C and 47.2 \({}^{\circ}\)C, AH: 47.5 J/g). The crystalline melting temperature and enthalpy of crosslinked polymers are lower than those of non-crosslinked polymers [35]. In this study, copolymers with a composition ratio of 20:80 (feed ratio) of \(\alpha\)-ClCL to \(\varepsilon\)-CL were primarily used. However, when copolymers with other composition ratios were synthesized, the crystal melting temperature at room temperature disappeared once the \(\alpha\)-ClCL to \(\varepsilon\)-CL ratio reached 40:60 (feed ratio) at the maximum. The disappearance of the crystal melting temperature in \(\alpha\)-ClCL and \(\varepsilon\)-CL copolymers with increasing \(\alpha\)-ClCL composition was also reported by [PERSON] et al. [37].  
In this study, a composition ratio of 20:80 (feed ratio) between \(\alpha\)-ClCL and \(\varepsilon\)-CL was adopted to evaluate shape-memory properties, as the polymer exhibits an appropriate crystal melting temperature and allows for sufficient initiation of graft polymerization. The shape-memory property of a film is influenced by the thermophysical properties of film constituent polymers. The properties of polymers can be controlled by the copolymerization ratio of monomers. Copolymer confirmed that an increase in the copolymerization ratio of \(\alpha\)-ClCL, then the polymer was losing crystallinity at room temperature. Therefore, the copolymer ratio used in this study is considered to be capable of modifying as many  
Figure 5: Explanatory diagram of contact-angle measurements for shape changes in P24 and P48. * The test was not measurable.  
Figure 6: The results of crystalline evaluation for shape-memory properties: (a) DSC curves; (b) XRD diffraction patterns.  
polymers as possible by graft polymerization and shape memory at room temperature. For example, graft polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) with a betaine structure on the side chain produces highly anti-thrombogenic surfaces through poly(MPC). Additionally, pH-responsive polymers are used in sensors and other applications because they change shape and color in response to environmental pH. Graft polymerization onto 3b-PCL-Cl film enables the modification of its properties through shape-memory effects. For PNIPAAm-grafted films prepared using a poor solvent, the onset of the crystal melting temperature was confirmed by DSC, regardless of the graft polymerization reaction time (Figure 6a). Furthermore, XRD measurements of the sample polymerized in a poor solvent showed the same PCL-derived crystal diffraction peaks as those of the sample before polymerization [35]. However, no crystal melting peak appeared in the sample polymerized using a good solvent (Figure 6-G3) when measured by DSC, and the XRD diffraction pattern showed a halo peak observed in the sample synthesized with a good solvent. Therefore, the use of a good solvent inhibits the crystallinity of the film by impregnating the NIPAAm monomer and randomly polymerizing it at the chloro groups present in the film as grafting points. The results for the samples synthesized using a good solvent suggest that graft polymerization with poor solvent proceeds clearly and selectively on the surface. These results suggest that the choice of solvent for graft polymerization can influence the material properties when graft polymerization of soft materials, such as gels, is carried out, regardless of whether the polymers are in film or sheet form.