# Shape-Memory Property Acting as a Switch to Change the Surface Property of the Film
## 3 Results
### Influence of PNIPAAm Grafting onto Polyester Films on Shape-Memory Properties  
Several previous studies of ATRP from the side chains of polyesters using \(\alpha\)-CICL have been reported [24; 37; 38], and all previous studies have shown successful graft polymerization onto degradable polyesters. In particular, [PERSON] et al. reported the self-assembly of PNIPAAm grafted onto polyester side chains in water and the relationship between this self-assembly and thermos-responsiveness [39]. The graft polymerization of PNIPAAm into polyester side chains resulted in a material that exhibited the properties of PNIPAAm; however, the polyester, which is the substrate for graft polymerization, still serves merely as a degradable material. Therefore, polymer modification by graft polymerization onto a polyester material with shape-memory properties will result in a composite material that can fully utilize both the thermos-responsiveness of the polyester material and the properties of the grafted polymer. The physical properties of the grafted PNIPAAm were evaluated, as discussed in Section 3.4. Therefore, the next step was to evaluate the bulk properties of the film, including its softening temperature (Figure 7) and shape-memory properties (Figure 8), using TMA.  
Figure 7: Film softening point measurement by TMA.  
First, the softening points of the films were evaluated by measuring temperature changes at a constant load of 20 kPa. The average softening points (\(n=3\)) for the 3b-PCL-Cl and P48 films were 52.2 \({}^{\circ}\)C and 49.4 \({}^{\circ}\)C, respectively. Samples with shape-memory properties were measured repeatedly using this program (Figure 7). During the first temperature increase (1 st scan), a lower softening point was observed compared to the other temperature-increase processes. The softening point of the first scan shifted to a lower temperature because of the thermal response, including the thermal history [40; 41]. As seen in Figure 7, G3 did not show a clear softening point at the first scan, unlike the other samples, and the shape changed gradually with increasing temperature from above 50 \({}^{\circ}\)C. The TMA results for G3 were consistent with the DSC and XRD results. The absence of crystalline melting peaks in the DSC results and the appearance of halo peaks in the XRD results indicate that G3 inhibited the crystallinity of 3b-PCL-Cl before grafting because of the progressive polymerization of PNIPAAm inside the film. Therefore, the film became rubbery, and no shape change due to the temperature was observed by TMA under a constant load.  
The shape-memory properties of the 3b-PCL-Cl and PNIPAAm-grafted films were first evaluated qualitatively by photographing the samples as their shape changed with temperature, as shown in Figure 8. As shown in the figure, 3b-PCL-Cl exhibited shape memory. However, although G3 could be deformed by heating to approximately twice its original size, the deformation did not persist upon cooling, resulting in the shape shown in the photograph being only slightly deformed due to shrinkage. Temperature ranges (1)-(3) in Figure 8A correspond to the temperature range in Figure 8B. The shape-memory properties of the 3b-PCL-Cl films were confirmed by TMA measurements, as evidenced by qualitative shape-memory characterization. R\({}_{\text{f}}\) for 3b-PCL-Cl and P48 were 99.5% and  
Figure 8: Evaluation of PNIPAAm-grafted film and 3b-PCL-Cl film shape-memory properties. (**A**); Qualitative view of shape memory. (**B**); Strain and Stress profiles for time.  
99.3%, respectively, and \(\rm R_{r}\) was 99.1% and 97.9%, respectively. 3b-PCL-Cl and P48 exhibited excellent shape-memory properties, with \(\rm R_{r}\) values close to 100%.