Reviews & Analysis

This review focuses on the controlled radical polymerization of vinyl ether (VE) and the related self-assemblies. VE was long believed to be among the monomers that could not be radically homopolymerized. Under such circumstances, some groundbreaking polymerizations of VE have been discovered. Advances in research have made it possible to perform controlled radical polymerization with VE due to hydrogen bonds and/or cation-π interactions between VE monomers and the propagating radical. By using the resulting poly(VE)s, various functional polymers and nano-objects via polymerization-induced self-assembly can be obtained.

This focus review discussed our recent developments of unnatural glycopolymers based on polyoxazoline, protein–polymer conjugates, and protein stabilization. To develop new glycopolymers, a bicyclic monomer composed of glucosamine and 2-methyl-2-oxazoline (MeOx) was designed. This cationic ring-opening polymerization proceeded not by the mechanism for MeOx but by a new polymerization mechanism. This oligosaccharide has promise to be applied to a new glycomaterial owing to the polymer design. Additionally, protein conjugation and encapsulation by amphiphilic/fluorous chain-folding nanoparticles were investigated. Fluorous nature in random copolymers was useful for the protein conjugation and stabilization.

Among stimuli-responsive polymers, thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) is the most widely investigated. PNIPAAm-based polymers can undergo appropriate changes in response to their external environment. In this focus review, recent advancements in the applications of stimuli-responsive polymers based on PNIPAAm in biomedical fields are summarized, with an emphasis on our own research. In particular, a summary of the design of polymers for application in the separation and purification of (bio)pharmaceutical products and controlled cellular uptake is provided.

This review is focused on evolutions of precision radical polymerizations in various directions from metal-catalyzed Kharasch addition or atom transfer radical addition (ATRA). The developments include metal-catalyzed living radical polymerizations via reversible activation of carbon-halogen bonds, metal-catalyzed step-growth radical polymerizations of designed monomers having an unconjugated vinyl group and a reactive carbon-halogen bond, simultaneous metal-catalyzed chain- and step-growth radical polymerization for producing degradable vinyl copolymers with main-chain ester units, and vinyl monomer sequence control via combinations of iterative ATRAs and various controlled polymerizations.

Optically active polymers and supramolecules that form well-defined architectures are important materials with a wide range of applications. Amino acids and sugars are great candidates for the preparation of optically active functional materials because of their versatile structures and functional groups. In these chiral units, intra- and intermolecular noncovalent interactions play significant roles in the generation of smart functions. In this focus review, the author reviews his recent studies related to the fabrication and functions of chiral conjugated polymers and chiral supramolecules based on these natural chiral compounds.

Academia and industry are interested in using autotrophic microorganisms as a sustainable/green production platform to produce biochemical products and commercially relevant commodities, including biopolymers. Unlike heterotrophs that require carbohydrates and amino acids for growth, autotrophs have evolved to fix carbon dioxide and drive metabolic processes utilizing either light (photoautotrophs) or chemical compounds (chemolithotrophs) as energy sources. Here, we review the current state-of-the-art in the construction of autotrophic microbial cell factories for efficient biopolymer production and recent breakthroughs in natural autotrophs focusing on biopolymer production.

Reverse osmosis (RO) membranes composed of polyamides and cellulose acetates are used as separation layers in pure-water production. However, improving the separation performance and antifouling properties of RO membranes is necessary. This focus review described the composite reverse osmosis membranes with optimal amounts of polyhedral oligomeric silsesquioxanes (POSS), which are cage-shaped, subnanosized molecules exhibiting organic–inorganic hybrid structures, showed improved water flux, NaCl rejection, antichlorine and antifouling properties, and mechanical strength.

The encapsulation of polymer chains into MOF pores is a powerful strategy for controlling polymer chain assemblies at the molecular level. In this focus review, recent developments of hybridization of conjugated polymers and MOFs are described. This approach can facilitate the study of the inherent optoelectronic properties of conjugated polymers. Furthermore, the formation of nanocomposites can provide unprecedented material platforms to accomplish nano-synergistic functions.

In this review, recent developments in data-driven approaches for structure-property relationships in polymer science based on statistical/informatics methods are introduced. A concept and some methods in data-driven science to obtain the desired properties and understand the mechanisms in polymeric materials are first explained. Additionally, various examples, such as the description of a single chain, phase separations, network polymers, crystalline polymers, and machine learning potential are introduced.

This paper outlines recent progress in various solution-processed fluorescent polymer tandem organic light-emitting diodes (OLEDs), white phosphorescent tandem OLEDs, and perovskite nanocrystal (NC) LEDs. Tandem OLEDs, which comprise multiple light-emitting units stacked in series through a charge-generation layer, have attracted considerable attention for display applications owing to their high efficiencies and long operational lifetimes. Metal halide perovskite NCs have also been considered promising light-emitting materials owing to their excellent optoelectrical properties.

Dispersibility and interfacial interactions are the important factors to exploit the high potential of nanocarbons for polymer/nanocarbon nanocomposites. However, carbon backbone with low reactivity has often cause agglomerations and defects from the interfaces. The use of surfactants and the surface modifications of nanocarbons have widely been conducted to improve these issues. This paper reviews recent advances in the design of polymer/nanocarbon nanocomposites, focusing on our research on the reinforcement effect of nanodiamond on polymer nanocomposites.

Sacrificial bonds break to dissipate energy and can increase the toughness of materials. Incorporating sacrificial bonds into hydrogels through the double network process enabled the first extremely tough hydrogels. In this Focus Review, we discuss the nature of sacrificial bonds, and how they can be used on the macroscale to enable tough soft composite materials. By matching the essence of the double network concept, we can make tough materials from macroscale composites for biomedical and engineering applications.

In 1996, the author reported “self-oscillating” polymer gels that spontaneously repeat swelling–deswelling changes in a closed solution without any on–off switching by external stimuli, such as with heart muscle. The gel has an energy converting system provided by an oscillatory chemical reaction called the Belousov–Zhabotinsky (BZ) reaction, which induces periodic mechanical motion of the polymer chain. The author systematically developed self-oscillating polymer gels with approaches ranging from demonstrating fundamental behaviors to constructing material systems for potential applications in biomimetic materials such as autonomous soft actuators, automatic transport systems, and functional fluids causing autonomous sol-gel oscillations, as seen with amebas. In this review, these research developments and recent progress from the author’s group are summarized.

This focus review describes a biosensing strategy called “chemical tongue”, which mimics the human taste system by employing fluorogenic materials containing various chemical structures in conjunction with statistical techniques. The focus is on the design of polymer-based chemical tongues and their applications with various complex biological samples. The chemical-tongue strategy is capable of recognizing biological samples in a unique manner that does not, in contrast to conventional approaches, rely on specific interactions, thereby potentially opening avenues for unexplored uses of polymers in a wide range of research areas.

Reverse osmosis (RO) membranes are widely used as energy-saving and environmentally friendly materials for water purification. This Focus Review reports on the nanoscale structure and permeation mechanism of crosslinked fully aromatic polyamide RO membranes. First, the research on the morphology of protuberance structures of the polyamide separation functional layer is described. Next, hydrated structure of the functional layer is focused, which was analyzed using neutron scattering and molecular dynamics simulations. Innovative RO membranes are being developed that can obtain higher quality water with less energy by precisely controlling nanostructures.

In this review, we overview the recent advances associated with seminal findings in the development of nucleic acid-based fluorescent sensor systems aimed at application for exploring intracellular phenomena. We described the fluorescence signal generation mechanisms of each nucleic acid-based fluorescent sensor, including molecular beacon and quencher-free linear probes, as well as aptamer or DNAzyme-based systems. In addition, cascade hybridization chain reaction and catalyzed hairpin assembly are introduced as methods for amplifying fluorescence signals under isothermal conditions.

Bacterial cellulose (BC) has been utilized as a biopolymer matrix for various applications. The advancement of synthetic biology has brought new approaches for its production and functionalization. In this mini-review, we briefly discuss the conventional methods employed to improve BC production and functionalization as well as their challenges. We summarize the applications of synthetic biology to address the challenges and its use to develop novel hybrid living materials. Finally, we consider the opportunities and future prospects of synthetic biology and engineered biological materials.

Polysaccharides and “imogolite” (a natural aluminum silicate nanoclay) were used as building blocks to prepare environmentally benign (organic/inorganic) hybrid materials of natural origin. Cellulose nanocrystals (CNCs), cellulose fibers (CFs), and sacran were employed as polysaccharides. By utilizing oppositely charged organic and inorganic components, polysaccharide/imogolite hybrids were prepared by spin-assisted layer-by-layer assembly and solution blending. The fine dispersion and attractive interactions of imogolite with polysaccharides afforded hybrids with improved physicochemical properties.

The self-assembly of carbohydrate-based block copolymer systems has allowed recently the conception of novel glyconanoparticles and high-resolution patterning thin films with sub_10nm resolution (high χ) that has never been attained by petroleum-based copolymers and provides these new nanostructured biomaterials with novel properties such as next generation nanolithography, memory devices, OPV and biosensors. The glyconanoparticles can be designed to meet the targeted applications in terms of size, encapsulation and decoration. The control of the lamellar/cylindrical phases orientation can be achieved using thermal, solvent vapor or microwave annealing processes in thin films.

Random pH-responsive copolymers, P(A/AaU) have been prepared from a pH-responsive pendant fatty acid-containing monomer (AaU) and a pendant sulfonate-containing monomer (AMPS). In water, P(A/AaU) formed unimer micelles under acidic conditions. Under basic conditions, the P(A/AaU) polymer chains expand due to the electrostatic repulsions. Although pH-responsive sunscreen shows waterproof properties under neutral conditions, it disperses under weakly basic conditions such as soap water. pH-responsive diblock copolymers with a pendant fatty acid-containing block were prepared. This review also discusses pH-responsive gelling agents based on ABA triblock copolymers.