| POLYMERS Vol.70 No.4 |
| >> Japanese | >> English |
COVER STORY
2D Materials for the Bright Future |
| COVER STORY: Highlight Reviews |
| The Chemistry of Two-Dimensional Covalent Organic Frameworks | Donglin JIANG |
| <Abstract> Topology-directed polycondensation of knot and linker enables the growth of two-dimensional polymers, which crystallize and stack into covalent organic frameworks to create periodic skeleton and aligned channels. Covalent organic frameworks are unique as they predetermine both primary- and high-order structures by monomers, offering an irreplaceable platform for exploring novel organic materials. In this perspective, we briefly summarized the principles for structural design and methods to synthesize frameworks, with an aim to show the basis of the field. By elucidating specific interplays mediated by skeletons and channels, we scrutinized the framework materials with an emphasis on developing functions that are specific to the frameworks. We predicted the future directions and showed the key fundamental issues to be addressed. Keywords: Two-Dimensional Polymers / Covalent Organic Frameworks / Polycondensation / Topology Diagram / Adsorption / Mass Transport / Catalysis / Semiconductors |
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| Synthesis of Two-Dimensional Polymers | Junji SAKAMOTO |
| <Abstract> A single-molecule thick polymeric network that extends in two dimensions is defined as a 2D polymer. Although such sheet-like polymers have been reported in scientific literature, commercially viable large-scale production of 2D polymers is still unfeasible, mainly due to high cost and tedious synthetic procedures. Unique properties of 2D polymers, different from conventional materials, imply significant potential impact of this class of polymers in materials science. This article describes synthetic strategies, current technical challenges and future prospects of 2D polymers with examples from previous and recent milestone studies. Keywords: Graphene / Nanosheet / Monolayer / Exfoliation / Crystal / Topochemical Polymerization / Dynamic Bond Formation / Cohelical Crossover |
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| Organization of 2D Inorganic Nanosheets into Nano- to Mesoarchitectures and Their Functions | Takayoshi SASAKI |
| <Abstract> A diverse range of inorganic nanosheets has been synthesized through various processes. The obtained nanosheets can be organized into precisely designed nano- to mesoarchitectures. The mechanical transfer method enables the sheet-by-sheet assembly of graphene and chalcogenide nanosheets, in which intriguing electronic and quantum functions have been evolved. 2D nanosheets based on oxides, carbides and hydroxides are obtained as monodispersed charged colloidal materials and thus they can be assembled into precisely designed nanostructured systems based on multilayer and superlattice structures via various solution-based processes such as electrostatic self-assembly, Langmuir Blodgett deposition, spin-coating and flocculation method. These processes flexibly allow the layer-by-layer assembly and hybridization of multiple nanosheets to construct the artificial lattice-like systems and a range of useful functionalities related to electronics and energy storage/conversion have been developed. Keywords: 2D Materials / Nanosheets / Colloid Processes / Layer-by-Layer Assembly / Artificial Lattice / Liquid Crystal / Nano- to Mesoarchitectures / Electronics / Energy Storage and Conversion |
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| COVER STORY: Topics and Products |
| Creation of Pseudo-Polyrotaxane Nanosheet and Its Function | Shuntaro UENUMA |
| <Abstract> Nanosheets are 2D structures with thicknesses of up to 100 nm and lateral dimensions of over a few hundred nanometers. Herein, we report a novel nanosheet, called pseudo-polyrotaxane nanosheet （PPRNS）, which is fabricated via hierarchical self-assembly of bio-safe and accessible compounds. The PPRNS was formed by mixing β-cyclodextrin （CD） and carboxyl-terminated poly（ethylene oxide）75-b-poly（propylene oxide）29-b-poly（ethylene oxide）75 （EO75PO29EO75） in water. The β-CDs localized on a central PO segment of the axis and formed the thin layer with a thickness of 11 nm and the side length of ca. 2 μm. The thickness corresponded to the length of PO29 with all trans conformation. The PPRNS was isolated by Coulombic repulsion forces between the nanosheet surfaces. Interestingly, PPRNS exhibited a structural coloration and those orientations could be controlled by a strong magnetic field. Owing to the mass-producibility and biocompatibility, PPRNS has a great potential to develop new nanosheet engineering applications, particularly in optical materials, biomaterials, and drug delivery systems. Keywords: Supramolecules / Self-Assembly / Cyclodextrin / Structural Coloration / Magnetic-Field-Induced Orientation |
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| Top-Down Approaches for 2D Nanocarbons | Yuta NISHINA |
| <Abstract> Methods for preparing 2D nanocarbon from graphite are summarized. To obtain 2D nanocarbons in a stable state, it is necessary to weaken the interaction between graphene layers. Here chemistry-based methods that utilize chemical functionalization, electrochemical functionalization, and mixing with dispersants are discussed. Although these treatments enable us to produce 2D materials on a large scale, the obtained materials lack outstanding physical properties expected for high crystalline graphene. Nevertheless, the sophisticated use of these materials will bring the path to practical applications. Keywords: Graphene / Functionalization / Electrochemistry / Dispersant / Graphite / Exfoliation / Oxidation |
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| Synthesis and Properties of Inorganic Atomic Sheets | Tetsuya KAMBE, Kimihisa YAMAMOTO |
| <Abstract> In this report, we describe the bottom-up synthesis and properties of 2D materials focusing on borophene and metalladithiolene sheets. Such 2D atomically thin sheets, a representative analog of graphene, are attractive materials showing unique mechanical and electronic properties. The synthesized borophene-like sheet was found to have a completely planar skeleton with hexagonal network. Potassium cations between the layers enabled crystalline stacking of the layers, as well as dissolution in solvents as atomically thin layers. In contrast, stacked or atomically thin metalladithiolene sheets were prepared at the interface of solution of the organic ligand and corersponding metal salt. Metallic properties of both bottom-up sheets were revealed. Almost zero activation energy like a metal was suggested in the borophene-like sheet. In the case of metalladithiolene sheet, metallic nature was revealed by photoelectron emission spectroscopy. Keywords: 2D Sheet / Atomic Layer / Bottom-Up Synthesis / Borophene / Electronic Properties |
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| Two-Dimensional Carbon Material (Graphite) Made from Polyimide and its Applications | Masamitsu TACHIBANA |
| <Abstract> Highly crystalline artificial graphite thin films, which are two-dimensional carbon materials produced by the pyrolysis of polyimide films, are being developed for various applications due to advances in thinning and improvement of surface smoothness. For example, a graphite thin film with a size of 10 cm square and a thickness of 1.0 μm has been realized, and a graphite thin film with a mirror-like surface and 1.0 μm thickness has also been materialized. These graphite thin films have been commercialized as electrode membrane of ion beam shape measurement sensors and ion beam charge stripping foils for particle accelerators, taking advantage of their thinness and high heat durability in vacuum. Graphite thin films are also expected to be used as thermal interface material (TIM) with low thermal resistance due to their thinness and high thermal conductivity, and as high-frequency vibrators by making use of their lightness and large Young’s modulus. Keywords: Graphite / Polyimide / Particle Accelerator / TIM / Vibrator |
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| Polymer Science and I: A Personal Account |
| Discovery of Interest | Toshiyasu HIBINO |
| <Abstract> Looking back on my research life, when the research moves forward, it is a common situation where I am persistently struggling. In order to do that, I think it is necessary to find it interesting. |
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| Front-Line Polymer Science |
| Kinetically Controlled Supramolecular Coordination Chemistry | Yoko SAKATA |
| <Abstract> While molecular recognition and self-assembly are generally thermodynamically controlled events, kinetic control of such processes is essential for the development of new supramolecular functional systems. This review summarizes the recent development of the kinetic control of functions in supramolecular coordination chemistry. The introduction of caps or gates into the apertures of the host molecules enables the kinetic control of guest uptake/release of host-guest system. The methodology to investigate protein-ligand binding mechanism in biological system can be applied to unveil the mechanism of artificial host-guest binding where the host molecule uptakes the guest accompanied by the structural change. Investigation of coordination-driven self-assembly processes and control of kinetic stability of self-assembled metal complexes are also important for the design of well-defined new supramolecular hosts. Keywords: Supramolecular Chemistry / Metal Coordination / Kinetic Control / Host-Guest Binding / Molecular Recognition Mechanism / Self-Assembly |
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| Polymer Select |
| Development History and Latest Development Status of Cyclo Olefin Polymers | Takashi HOUKAWA |
| <Abstract> Cycloolefin polymer is a thermoplastic developed by Zeon Corporation for optical use and it was released in 1991. It was predominantly developed for optoelectronics application, mainly represented by CDs, digital cameras, LCD televisions, and smartphones. This paper introduces the initial development process, features, and the latest development status of cycloolefin polymer produced by Zeon Corporation. Keywords: COP / Tacticty |
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