Reviews & Analysis

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  • Recent developments in the one-step synthesis of structurally controlled hyperbranched polymers (HBPs) in terms of molecular weight, dispersity, number of branching points, branching density, and number of chain-end groups by radical polymerization are summarized. Copolymerization of conventional vinyl monomers and a vinyl telluride, which induces the branching structure, under organotellurium-mediated radical polymerization (TERP) affords HBPs with dendrimer and dendron structures. The same synthetic strategy under atom transfer radical polymerization is also discussed.

    • Shigeru Yamago
  • Recently, controlled/living supramolecular polymerization has been evolved by many research groups; however, the principles of monomer design remain elusive. In this focused review, I present a case study of a series of porphyrin-based monomers that we have investigated over the past 10 years. By systematically designing monomers, we have been able to gain deep insights into the mechanisms of controlled/living supramolecular polymerization, and we have even been able to apply the developed method to synthesize two-dimensional supramolecular nanosheets with controlled areas and aspect ratios.

    • Kazunori Sugiyasu
    Focus Review
  • This focused review provides an overview of our recent work and related research regarding the precise anionic ring-opening polymerization (AROP) of substituted epoxides, including alkylene oxides, glycidyl ethers, and glycidyl amines, using t-Bu-P4 as the phosphazene base catalyst to produce functional polyethers, such as homopolymers, block copolymers (BCPs), and topologically unique polymers. First, the fundamental aspects and applicable monomer scope of the t-Bu-P4-catalyzed AROP are discussed. Subsequently, the applications of the AROP system for synthesizing functional materials and architectural polymers are presented.

    • Takuya Isono
    Focus Review
  • Despite the tremendous efforts made in recent decades to remove imperfections from gels, discernible signs of spatial defects have been persistently observed in gels. Researchers believe that gels are inherently heterogeneous. In this focus review, I briefly introduce a recent finding from our research group’s efforts to fabricate polymer gels free of spatial heterogeneities via “bond percolation”. The commonly observed scattering profiles for the spatial defects disappeared in the homogeneous gels. The newly observed scattering profiles are a benchmark for gel structures.

    • Xiang Li
    Focus Review
  • Our recent development on healable soft materials that utilize block copolymer self-assembly in ionic liquids is reviewed. We begin by discussing photohealable ion gels that respond to specific wavelength of light irradiation by forming and collapsing stimuli-responsive networks. Then, we highlight on the self-healing ion gels based on synergetic combination of supramolecular interaction and block copolymer self-assembly, which realize high mechanical strength and fast self-healing ability in the absence of any external stimuli.

    • Ryota Tamate
    Focus Review
  • The functionalization methods of polymeric materials using various types of cross-links, such as supramolecular cross-links, photo cross-links, and associative dynamic covalent bonded cross-links, were described. First, the enhancement and precise tuning of the thermal and mechanical properties are demonstrated in the supramolecular cross-link-based and photo cross-link-based designs. In the latter section, the design and physical property tuning of functional materials based on a special type of cross-linked materials with associative dynamic covalent bonded cross-links, known as vitrimers, are demonstrated.

    • Mikihiro Hayashi
    Focus Review
  • Poly(ethylene-2,6-naphthalate) (PEN) nanofibers were prepared by carbon dioxide laser supersonic drawing (CLSD). The CLSD method was carried out by irradiating the as-spun PEN fiber with a laser in a low-temperature supersonic jet, which was generated by blowing the air from the fiber supplying orifice into a vacuum chamber. The DSC curve of the PEN nanofibers produced by CLSD showed two melting peaks: 260 °C and 285 °C. The increase in melting temperature is attributed to the supramolecular sequence effect, which is a nanoscale effect.

    • Akihiro Suzuki
    • Yasutaka Oshiro
    Focus Review
  • Biological membranes that tailor their morphology to environmental stimuli are nature’s ultimate smart molecular systems. This focused review describes the design and function of smart biomembrane nanohybrids. Specifically, liposomes and exosomes can be functionalized with inorganic substances and polymers to afford hybridized artificial cell membranes. These membranes have a tailorable morphology and can incorporate functional integral membrane proteins.

    • Yoshihiro Sasaki
    • Kazunari Akiyoshi
    Focus Review
  • This paper reviews our X-ray and neutron scattering experiments on the molecular structure and dynamics of a supramolecular assembly, polyrotaxane (PR) composed of polyethylene glycol (PEG) and α-cyclodextrin (CD). Inclusion complex formation with CDs increases the stiffness of the PEG backbone and restricts the diffusion of the PEG monomers that are covered by or in close proximity to the CD molecules.

    • Koichi Mayumi
    Focus Review
  • Polyrotaxane (PRx) has a necklace-like structure, which exhibits many features (e.g., cyclic molecule slippage) that are not found in other supramolecular structures. In this review, we report that the number of cyclic molecules, the length (molecular weight) of the linear molecules, and the combination of the cyclic molecules and linear molecules in PRx can be precisely controlled to maximize cyclic molecule slippage. In addition, we created a material that quickly recovers its material strength because of the cyclic molecule slippage of PRx.

    • Yuichiro Kobayashi
    Focus Review
  • Water-soluble Naphthalene diimide (NDI) binds to the DNA duplex via threading intercalation mode. This has provided unique DNA analytical techniques, functional DNA polymers, and supramolecular polymers. Especially the ferrocene-containing NDIs, having electrochemically active sites, has been applied to an electrochemical gene detection system and also utilized in the precision analysis of genes and single nucleotide polymorphisms. Recently, NDI derivatives have been recognizing as potential candidate for anticancer therapeutics and for designing a unique cancer-detection system.

    • Shigeori Takenaka
    Focus Review
  • This focus review describes the synthetic routes to cyclic compounds and cyclic polymers via spontaneously occurring cyclization processes using (1) rotaxane chemistry and (2) dynamic covalent chemistry. Systems with rotaxane-based structures proceed via the spontaneous and selective cyclization of two self-complementary molecules and a macromolecular rotaxane switch, which results in a topology change from linear to cyclic. Systems based on dynamic covalent chemistry use exchange reactions of bis(2,2,6,6-tetramethylpiperidin-1-yl)disulfide (BiTEMPS) units. Controlling the dynamic nature of BiTEMPS-based molecules provides cyclic topologies via spontaneously and selectively occurring cyclization processes.

    • Daisuke Aoki
    Focus Review
  • Direct CO2 capture from the air (DAC), is inevitable to reduce the concentration of CO2 in the atmosphere. Recent reports of ultrahigh CO2 permeances in gas separation membranes indicate a potential of new technology for DAC (m-DAC). In this paper, we use chemical process simulation to discuss the potential of m-DAC considering the state-of-the-art performance of organic polymer membranes. Based on the analysis, we propose the target properties for separation membranes required for m-DAC with competitive energy expenses as well as the direction of future membrane development for DAC.

    • Shigenori Fujikawa
    • Roman Selyanchyn
    • Toyoki Kunitake
    Focus Review Open Access
  • Polyhydroxyalkanoates (PHAs) are biobased and biodegradable materials. The artificial PHAs, such as lactate-based polymers, synthesized by engineered platforms expand the range of physical properties. The artificial polymers with superior properties are produced mainly from CO2-derived biomass using microbial platform with engineered enzymes. The oligomers can be secreted from cells and derivatized into high-molecular-weight polymers through assembling with other segments. The review summaries recent advances in the biosynthesis and biodegradation of artificial PHAs and oligomers.

    • Seiichi Taguchi
    • Ken’ichiro Matsumoto
  • To shift from a petroleum-dependent society to a sustainable society using eco-friendly materials, polysaccharides from natural products are important candidates as alternative materials. We have researched one of the cyanobacterial polysaccharides, “sacran,” which is extracted from Aphanothece sacrum. In this review, the unique characteristics, structures, and preparation of sacran LC gels are introduced. These matters are discussed especially from the perspectives of polymer science, colloidal science, gel science, etc. We hope that sacran will be used in a variety of fields, such as tissue engineering, pharmacodynamics, and biomedical materials, with possible contributions to the development of a sustainable material society.

    • Kosuke Okeyoshi
    • Maiko K. Okajima
    • Tatsuo Kaneko
  • Our recent studies on the cellulose nanofibrils (CNFs)/polymer nanocomposites prepared via Pickering emulsion templating are reviewed. CNF-stabilized monomer-in-water emulsions were used as starting materials to design the composite structures. In the first part of this review, we summarize the preparation of transparent films. The second part describes the approaches to prepare a composite microparticles having CNF shells.

    • Shuji Fujisawa
    Focus Review Open Access
  • To establish a sustainable material production system and preserve the Earth’s environment, “biomass plastics” that are made from renewable biomass instead of petroleum and “biodegradable plastics” that are completely degraded into carbon dioxide and water by enzymes secreted by microorganisms in the environment are desirable products. This miniature review describes a series of studies on microbial polyesters and polysaccharide ester derivatives, including the synthesis of novel polymers, development of new processing techniques for high-performance films and fibers, elucidation of the relationship between structure and properties using synchrotron radiation, and control of the rate of enzymatic degradation.

    • Tadahisa Iwata
    • Hongyi Gan
    • Yuya Fukata
  • Our recent studies on how nanostructures can be self-assembled in discotic liquid crystals to create self-organizing functional systems of discotics with tuned physical properties are reviewed. In the first part of the article, charge carrier and semiconducting properties of discotic liquid crystals in the form of 1-D molecular wires are described. The second part of this report summarized our recent results on self-assembly of Ag, Au, Cu, and graphene nanoparticles, carbon dots, CdTe and CdSe quantum dots, gold nanorods, CdS nanoribbons, silver nanodisks, and graphene sheets in discotics.

    • Manish Kumar
    • Shalaka Varshney
    • Sandeep Kumar
    Focus Review
  • Recent studies on exploration of mechanical deformation of microtubules under tensile and compressive stress, using a newly developed methodology, have been reviewed. In the first part of this review article, development of the methodology and its utility in studying the mechanoresponsiveness of microtubules have been described. In the second part, applications of the recently developed methodology in studying dynamic soft interfaces have been elaborately discussed.

    • Arif Md. Rashedul Kabir
    • Akira Kakugo
    Focus Review
  • Our recent studies on the zincate complex dilithium tetra-tert-butylzincate-catalyzed transesterification and polymerization are reviewed. In the first part of this report, the ROP of ε-caprolactone catalyzed by TBZL is described. In the second part of this report, the acylation and transesterification of alcohols with vinyl acetate and carboxylic esters catalyzed by TBZL are summarized. Next, TBZL-catalyzed polycondensations of diphenyl carbonate (DPC) with diols are discussed. In the last part of this report, the transesterifications of poly(phenyl methacrylate) (PPhMA) side chains with alcohols catalyzed by TBZL are described.

    • Miyuki Oshimura
    Focus Review