# Shape-Memory Property Acting as a Switch to Change the Surface Property of the Film
## 1 Introduction  
Composite materials using polymers have attracted wide attention, and various synthetic methods have been developed, including organic-inorganic composites [1; 2], polymer blends [3; 4], in-situ polymerization [5], and graft polymerization onto polymer substrates [6; 7; 8]. Graft polymerization can be used to prepare composites of different polymers and inorganic materials [9]. Grafting techniques can be broadly classified into two categories. The grafting-to technique involves modifying a functionalized polymer [10] by introducing a reactive moiety at the side chain or polymer terminal to the base material. In the grafting-from technique, polymerization occurs directly on the substrate after modifying it with a small-molecule initiator [11]. The grafting-to technique directly modifies a polymer with a larger hydrodynamic radius than the grafting-from technique, resulting in a mushroom-like structure that is highly dependent on the molecular weight. This approach limits the grafting density, which can result in the properties desired for an intended application not being achieved [4]. In particular, the grafting-from technique has led to significant progress in the development of living-radical polymerization (LRP) [12]. Before the advent of LRP, radical polymerization from the surface of substrates with peroxide or azo compound modification or irradiation with high-energy electron beams or \(\gamma\)-rays was common [13; 14; 15]. However, controlling the molecular weight distribution of grafted polymers and achieving surface uniformity were challenging. In contrast, LRP facilitates the creation of grafted surfaces with controlled molecular weights and molecular weight distributions, and numerous methods for preparing uniform surfaces have been developed. Notably, atom-transferradical polymerization (ATRP), in which ATRP-dormant groups such as haloesters and halosulfonyl groups are introduced into the base material, has enabled high-density graft polymerization and the development of polymer brushes, which had been difficult to achieve by the grafting-to technique [16; 17]. We previously reported the successful synthesis of a polyester-based shape-memory film with a surface capable of functional modifications [18]. This shape-memory film is based on poly(caprolactone), and the functional moiety is copolymerized with \(\alpha\)-chloro caprolactone (\(\alpha\)-CICL) as a comonomer to introduce chloro groups. The shape-memory property is exhibited by the softening point of the film due to crystal melting, and the chloro group is converted to an azide group by NaN\({}_{3}\), which allows for the click reaction known as Huisgen cycloaddition. If the azidation reaction occurs while the film swells in the presence of a good solvent, the chloro groups inside the film become azidized, leading to a reduction in shape memory. Therefore, to selectively react with the film surface, a solvent that is neither too good nor too poor should be used. The azidation reaction was performed using dimethylsulfoxide (DMSO) as a poor solvent for the film, which did not cause swelling. As a result, both shape-memory and surface functionalization were successfully achieved, although selective surface reactions remain challenging. In this study, we addressed the challenge of selective surface reactions on shape-memory films, confirming the functional expression of grafted polymers on surfaces and the control of surface states using shape-memory properties. Specifically, the surface of the shape-memory film serves as the starting point for ATRP due to the presence of chloro groups derived from \(\alpha\)-CICL. Poly(N-isopropylacrylamide) (PNIPAAm) exhibits a low critical solution temperature (LCST) of approximately 32 \({}^{\circ}\)C in water, and molecular-weight control of PNIPAAm is achieved through ATRP graft polymerization. The aim is to hybridize the shape-memory properties triggered by the softening point of the film and the solution properties of PNIPAAm in water by grafting.