Focus Review in 2016

Angle-independent colored materials based on Christiansen effect was successfully prepared using phase-separated polymer membrane and thermotropic liquid crystal. Because this system displays angle-independent color and can act as a multi-color polymer-dispersed liquid crystal, I believe that this system may be applicable for energy-saving multi-color displays.

In this focus review, alternating copolymers of carbon dioxide with epoxides have been synthesized and studied as novel ion-conductive polymers. The Li salt electrolytes of poly(ethylene carbonate) (PEC) and of other polycarbonates having different side groups exhibited remarkable ion-conductive properties including the following: increased conductivity with increasingly higher salt concentrations, very high values for the Li⁺ transference number, and good electrochemical stability. The Li-ion conductivity of a highly concentrated PEC-LiFSI electrolyte was estimated to be greater than 10⁻⁴ S cm⁻¹, and excellent battery performance was demonstrated at room temperature.

In this focused review, we provide an overview of our recent work on the design and synthesis of a new type of side-chain liquid crystal π-conjugated polymeric system associating regioregular poly(3-alkylthiophene) backbones with laterally pending π-conjugated mesogenic groups. Several polymeric architectures have been prepared based on different polymer backbone structures and various side groups, providing important insight into the relationships among the polymeric architecture, nano- and macroscale organization and charge transport properties in such self-organized multi-lamellar macromolecular systems.

The state-of-the-art atomic force microscopy allows us to observe inner structures of single molecules. Such observation is quite beneficial to study single and self-assembled molecules on surface as well as on-surface chemical reaction. This focus review describes recent technical improvement and achievements in the field of on-surface molecule studied with high-resolution atomic force microscopy.

Liquid crystalline organic semiconductors are good candidates for organic transistors because the materials have properties that are beneficial compared with those of polymer materials. Liquid crystalline materials show good solution processability for the fabrication of uniform crystalline thin films. The novel liquid crystalline material 2-phenyl-7-decyl[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-10) exhibits a highly ordered liquid crystal phase, and has good solution processability and high thermal durability to use for creating transistor devices with high mobility, over 10 cm² Vs⁻¹, following thermal annealing.

A series of dioxocycloalkene-annelated thiophenes was designed to utilize as noble acceptor units in donor–acceptor (D–A) copolymers, and D–A copolymers containing these acceptor units were systematically developed for the application to organic photovoltaics (OPVs). Photophysical and electrochemical properties of these copolymers as well as their photovoltaic performance under the combination with [6,6]-phenyl-C_x-butyric acid methyl ester (x=61 or 71) were summarized. These systematic investigations provide important clues for the development of high-performance D–A-type OPV materials.

Various conjugated polymers self-assemble to form well-defined microspheres that act as optical resonators. Upon focused laser irradiation, the single isolated microspheres exhibit whispering gallery mode photoluminescence (PL), where sharp and periodic emission lines appear in the PL spectra. Efficient and long-range intersphere light energy transfer is demonstrated using coupled microspheres. Conjugated polymer microspheres are advantageous as optical resonators in terms of their high refractive index, photoabsorptivity, and PL efficiency, as well as simple and low-energy fabrication processes, beneficial for the practical application.

The adhesion of hydrogels has attracted attention for use in building three-dimensional (3D) constructs, such as scaffolds for cell culture, carriers of drug release system and soft actuators. Electrophoretic hydrogel adhesion, which is the electrophoretic manipulation of a polyelectrolyte to form an adhesive layer at the interface of two gels, was developed. To apply this adhesive method to build 3D materials, rapid and free-form fabrication of hydrogel constructs was achieved by the electrophoretic adhesion of microgels. The development of a novel adhesion strategy will be useful for the fabrication of novel 3D hydrogel architectures.

Biodegradable aliphatic carbonyl polymers, such as polylactides, polylactones and polycarbonates, have been studied for applications in a broad range of resorbable medical devices. This review mainly highlights the synthesis and application of poly(trimethylene carbonate) (PTMC) analogs with various substituents derived from 2,2-bis(methylol)propionic acid. In addition, organocatalytic transesterification is discussed as an indispensable tool for further functionalization and sophistication of the PTMC analogs.

Silkworms produce silk fibroin fiber from an aqueous silk fibroin solution by applying shear stress within the spinneret at ambient temperature. Here the structures of silk fibroin before and after spinning determined by solution and solid-state nuclear magnetic resonance. The solution structure was determined by using native liquid silk extracted from silkworm larvae and the lamellar structure of fibroin after spinning was determined. Moreover, a silk-based small diameter vascular graft was developed by electrospinning. These studies provide a perspective for investigations of energy-conserving fiber processing techniques and silk-based biomedical materials.

This review focuses on the factors that determine the molecular weight of polyhydroxyalkanoate (PHA), an aliphatic polyester synthesized by bacteria for carbon and energy storage. Because the mechanical strength of PHA increases with its molecular weight, high-molecular weight PHA polymers are preferred. The synthesis of high-molecular weight PHA should consider the following factors: the concentration of PHA synthase, occurrence of chain transfer reaction, catalytic activity of PHA synthase and simultaneous degradation of PHA during biosynthesis. These factors have a direct impact on the molecular weight of PHA.

Vibrational circular dichroism (VCD) is effective for analyzing the configuration and conformation of various bio(macro)molecules. In addition to a conventional VCD approach using theoretical calculations, this review explains how the use of an exciton-type VCD couplet can be employed to elucidate the structures of bio(macro)molecules, such as carbohydrates, glycerophospholipids, proteins and polyesters.

In this focus review, we overview our recent works on acyclic artificial nucleic acids (XNAs). Three acyclic XNAs, D-aTNA, SNA and L-aTNA have been developed. D-aTNA can form extremely stable homo-duplex, whereas it shows a high orthogonality with natural nucleic acids. SNA oligomers can change their helicity and chirality depending on sequences. L-aTNA can form stable duplexes with both DNA and RNA. Owing to unique properties of these XNAs, they should find application as tools in biology, biotechnology and nanotechnology.

This report reviews the seminal features and characteristics of free-standing polymeric ultrathin films (nanosheets), including fabrication methods, mechanical properties and biomedical and health-care applications (for example, wound dressings, tissue engineering materials and bioelectronic devices). ‘Nanosheet technology’ is a promising approach for the development of advanced medical applications and health-care practices in surgery and regenerative medicine, as well as for connecting the human body to electronic interfaces for future medical applications.

This review focused on the various polymers composed of trimethylene carbonate (TMC) units and ethylene glycol (EG) units. Poly(TMC) is a biodegradable polymer that is used in biomedical materials. It has been reported that its combination with oligo(EG) and poly(EG) would offer a useful approach. In addition, monomer design and polymer reactions are available. These polymers, including TMC and EG units, are useful in preparing various nanostructures and they have the potential for application in biomedical materials.

The antigen-loaded liposomes modified with pH-sensitive polymers and adjuvants were taken up by dendritic cells and induced fusion with endosomal membranes, responding to the acidic pH inside of the endosomes, thus causing the transfer of the antigen into the cytosol, as shown in the fluorescence microscopic image (green: fluorescein isothiocyanate-labeled antigen, red: liposome). As a result, cross-presentation is promoted, leading to the induction of cellular immunity. In addition, the dendritic cells are activated by adjuvants, which causes the activation of cellular immunity, resulting in therapeutic effects on tumor-bearing mice.

Our recent results in the concurrent cationic vinyl-addition and ring-opening copolymerization of vinyl ethers (VEs) and oxiranes are summarized with particular emphasis on the strategies required to generate crossover reactions between different types of monomers. Most importantly, carbocation generation via the ring-opening reaction of the oxonium ion is indispensable for the crossover reaction from oxirane to VE. This article also summarizes concurrent cationic vinyl-addition, ring-opening and carbonyl-addition terpolymerization, the copolymerization using an alkoxyoxirane through the alkoxy group transfer mechanism and the long-lived species-mediated polymerization using cyclic formals.

This focused review describes how surface properties can be manipulated by combining surface-initiated atom transfer radical polymerization (SI ATRP) and the very-large-scale integration (VLSI) lithography process. These fabricated surfaces with solvent-responsive or bio-inert/bioactive are applied to VOC sensors and non-biofouling/cell-growing surfaces. We also discussed the functionalization of renewable resources and how SI ATRP is extended to the applications of high-performance adsorbents.

Various cross-linkable poly(styrene-random-methyl methacrylate) (P(S-r-MMA)) that can neutralize substrates are reviewed. Four efficient cross-linkable random copolymers incorporated with benzocyclobutene (BCB), glycidyl methacrylate (GMA), azide and ketene functional groups can be used to prepare a thin, cross-linked neutral layer. On this cross-linked layer, polystyrene-block-poly(methyl methacrylate) (P(S-b-MMA)), thin films produce microdomains oriented perpendicular to the substrate, confirming the effective neutralization of the substrate to both PS and PMMA blocks.

The recent advances of AIE polymers, including structural design, synthetic approaches and practical applications have been summarized. A series of functional nonconjugated or conjugated AIE linear polymers with AIEgens on the side chains or main chains, and star-shaped or hyperbranched AIE polymers with AIEgens on the core or terminal parts are introduced. Their performances in a series of practical applications such as fluorescent sensors, stimuli-responsive materials, biological applications, porous materials and circularly polarized luminescence are updated.