**1. Introduction**

Synthetic polymers have been investigated for the applications in the medical field as bioma‐ terials, and used for processing biomedical devices and artificial organs which could be used in living organs. However, most of the polymers are not suitable for a long-term implantation when the materials contact with flowing blood or internal organs, because the material surface could not avoid the initiation of the process leading to thrombosis. Therefore, the development of the materials, which are continuously showing a stable biocompatibility during the longterm use, is desired for the advanced medical devices. For example, segmented polyurethanes have been widely used in practical applications for medical devices due to their high mechan‐ ical strength and biocompatibility [1, 2].

On the other hand, the phosphorylcholine (PC) group is a polar component of phospholipid molecules, which cover the surface of cell membranes. It has been well known that synthetic polymer materials containing PC group exhibit biocompatibility including nonthromboge‐ nicity. Firstly, Ishihara *et al.* has been developed 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer as an excellent biocompatible material, which efficiently reduces the adhesion of cells and proteins to the polymer surface [3 – 7]. The design of the MPC polymer was inspired by the chemical structure of the phospholipid polar group in biomembranes. Then, in recent years, the MPC polymer has been widely applied in biological and medical fields. Furthermore, the applications of MPC polymer to medical devices and other uses have been greatly advanced in these years [8 – 15]. However, most of MPC polymers do not possess the thermal stability and the mechanical strength, which were derived from the polymethacrylate type main chain. Then, if these physical properties of MPC polymers improved satisfactorily while maintaining the excellent biocompatibility, novel biocompatible polymer materials could be developed.

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In these years, we have succeeded in the syntheses of novel diamine and diol monomers containing PC moiety for the preparations of polyamides, polyimides, polyesters and polyur‐ ethanes from these monomers [16 – 23]. It was found that the obtained polymers exhibited the excellent biocompatibility derived from PC unit in addition to the processability, the durability to solvents, the thermal stability and the mechanical strength, which were derived from the main chain components.

By the way, the development of practical biomaterials will desire the collaborations among chemists, biologists, material scientists. We focused in the field of nanotechnology, especially the processing for free-standing ultrathin films consisting of polymers with a thickness less than 100 nm (often called nanosheets), which exhibited the unique properties such as high adhesive strength, flexibility, transparency and smoothness [24-26]. If the nanosheets could be fabricated from such PC-containing polymers, the applications as new biomaterials would be significantly advanced. Then, we attempted to prepare the nanosheets from the obtained copoly(ester-urethane)s and to investigate the physical properties and the biocompatibility of the nanosheet surface.

This chapter covered the subject of our recent study to develop new biomaterials containing a phospholipid moiety. We describe the preparations of aromatic polyimides and segmented polyurethanes containing PC group, which are obtained by polycondensation or polyaddition using PC-containing diamine and diol monomers. In addition, the fabrication of ultra-thin films, so called nanosheets, composed of these PC-containing polymers is described in detail. The obtained nanosheets exhibited the high adhesive strength, indicating that the nanosheets could conform closely to the desired surfaces due to their exquisite flexibility and low roughness. In this chapter, the physical properties such as thermal stability, biological function as blood compatibility, and surface property of the obtained polymers and nanosheets are discussed to reveal the possibility of a new biocompatible polymer material.
