Reviews & Analysis

Soft interfaces formed by polymer materials are important interfaces for biological systems (biointerfaces). Controlled radical polymerization (CRP) is highly suited for designing biointerfaces composed of polymer chains because it enables precise control of the polymer architecture at the nanoscale. This focus review describes the design of functional soft interfaces based on investigations of the structure-property relationships of CRPs. In particular, polymer brush surfaces showing autonomous property changes, comb-type copolymer-driven 2D/3D transformations of lipid bilayers, and molecular interactions in bactericidal cationic polymer brushes are depicted.

In this short review, we focus on the development of CO₂ separation materials consisting of hydrogel particles. The review starts with development of stimuli responsive micro- and nano-gel particles that reversibly absorb CO₂ isn response. The next chapter focuses on the development of temperature-responsive hydrogel films consisting of gel particles that reversibly absorb CO₂ and the importance of optimizing the pK_a values of the amines in the particles. In the end, assembly of defect-free nano-meter-thick CO₂ separation membranes consisting of the amine containing hydrogel particles are introduced.

Photochemically adaptable polymer materials are widely used in the fields of medicine, electronics, and engineering due to their precise and remote processability. Diverse designs of light-responsive units have been developed to fabricate various photocontrollable materials with low-energy, rapid, and reversible photoreactivity. Recently, multiple stimuli-responsive materials have been demonstrated to further control their photoreactivity by combining light with another stimulus, leading to advanced photocontrollable capabilities. This Focus Review summarizes the recent progress in developing photochemically adaptable polymer network materials by designing photoresponsive units, focusing on the chemical structures of cleavable moieties.

Photoinduced transitions between the solid, glass, and liquid states based on molecular photoswitches promise an enormous variety of applications, such as photoswitchable adhesives, which contribute to material recycling for a sustainable future in the era of composite materials. In this review, we highlight recent progress in the photoinduced transitions of small molecules and polymers and systematically discuss the molecular designs, mechanisms, applications, merits and demerits, and future challenges in each photoswitch and the whole field.

Mechanochemistry is a promising technology to tackle current and future polymer waste streams for a sustainable future. With this review, we take into account synthetic, computational, technical, and engineering perspectives to converge trituration and polymer mechanochemistry with a particular focus on the fate of commodity polymers and potential technologies to monitor mechanochemical reactions while they occur. We highlight the need for future transdisciplinary research to tackle the high-leverage parameters governing an eventually successful mechanochemical polymer degradation approach for a circular economy.

Our recent studies on the synthesis, characterization, degradation and applications of vinyl polyperoxides are reviewed. Primarily, the recent achievements in the design, biocompatibility, thermal and enzymatic degradation of water-soluble vinyl polyperoxides and copolyperoxides are described. Finally, future development possibilities and challenges of vinyl polyperoxides for various potential applications are summarised.

In this review, we show that reversibility of charge storage occurs in polymers with bistable redox-active groups populated in the repeat units of a nonconjugated backbone, especially when an electron self-exchange reaction spreads throughout the polymer. We will also show that extending the idea of electron exchange to electron/proton exchange leads to reversible hydrogen storage based on the bistability of hydrogenated and dehydrogenated states and the equilibrium for hydrogenation.

In this review article, an overview of recent studies on heat-responsive and photoresponsive adhesive materials and the characteristics of other external stimuli used for dismantlable adhesive systems are described. Then, research on dismantlable adhesive materials using polyperoxides is introduced as an example of early material design. Next, the development of a dual-stimuli responsive dismantlable adhesive material is interpreted as a material design for achieving stability during use and degradability during dismantling. Finally, recent studies on heat-responsive, dismantlable adhesive materials, which are thermally stable during use while responding quickly during disassembly by heating, are described.

A new concept for controlling the energy level of conjugated materials without extending the π-conjugated system is described. By performing aza-substitution at the “isolated frontier molecular orbitals (FMOs)”, which are defined in this manuscript, one energy level of FMOs can be selectively and efficiently lowered. Based on this protocol, advanced conjugated polymers with pure-blue or near-infrared luminescent properties were obtained.

Crystalline porous molecular frameworks formed through intermolecular hydrogen bonding calling hydrogen-bonded organic frameworks (HOFs) have recently been investigated as a new family of functional porous materials. In this review, HOFs composed of tritopic, tetratopic, and hexatopic carboxylic acid derivatives, which form H-bonded network such as those with hcb, sql, and hxl topologies depending on the numbers, positions, and orientations of the carboxy groups and conformational flexibility of the molecular skeletons, are reviewed by considering structural aspects such as isostructurality.

For uniform and flat materials, heavier plates show higher sound insulation performance because of the mass law. Acoustic metamaterials with periodic resonance structures have attracted attention as ultra-lightweight sound insulators that can break the mass law limit. Recently, practical acoustic metamaterial sheets that allow high-throughput fabrication and single-step implementation on target objects have been developed based on polymer materials. In this Focus Review, the polymer-based material design, the control of acoustic functions based on polymer properties, and applications as sound insulators and vibration dampers are described.

Peptides are versatile molecular tools with molecular recognition capabilities, high designability, and the capacity for self-assembly. In this focus review, the construction of new bio-nanoarchitectures using our peptide-based technologies is described. First, the construction of functional microtubules was achieved by molecular encapsulation using a Tau-derived peptide. Second, light-induced peptide nanofiber growth was used for the development of artificial motile systems of micrometer-sized spheres. The development of bio-nanoarchitectures by these peptide-based approaches is useful for understanding, mimicking, and controlling natural nano/microstructures.

In the first part of the review, continuous and length-controllable discrete one-dimensional channels, two-dimensional sheets, and three-dimensional vesicles, bulk-state complexation based on the versatile functionalization of pillar[n]arenes are discussed. In the second part of the review, functionalized pillar[n]arene crystals showing guest-responsive changes in color, state, and water contact angle, as well as serving as reaction media for the spontaneous polymerization of cyclic monomers are discussed.

Functional polymers such as semiconducting polymers and polyelectrolytes are essential materials for various polymer thin-film devices. Here we discuss the relationship among the aggregation states, the thermal molecular motion, the carrier properties of their thin films, and the interfacial effects.

Our recent studies on high-performance semiconducting polymers are reviewed. In the first part of this article, the correlations between semiconducting polymer structures and charge transport properties in thin film transistors are described. The second part of this report summarizes our recent results on the near-infrared emission properties of carefully designed semiconducting polymers.

In this Focus Review, we summarize our new strategy to create electroresponsive soft materials using electroresponsive dopants. Dopants can change the property of the LC material only with a minute amount and do not need to have an LC property by itself, allowing a simple molecular design. Based on this new concept, we developed cholesteric displays with rewritable color memory functions and quick color modulation functions. We also utilized this concept to create new columnar LC systems and realized multiresponsive columnar LC materials.

This focus review described recent research on cinnamate-based polymers. Polyesters derived from hydroxycinnamic acid showed characteristic ultraviolet response behavior. The mechanism of photodeformability and found that polyesters derived from 3-hydroxycinnamic acid are deformed by photoexpansion. By using dimers of bioproduced cinnamates, polyimides and polyamides were synthesized. The biobased polyimides and polyamides were found to exhibit high transparency, mechanical strength, and good chemical modification properties due to the cyclobutane main chain and carboxylic acid side chains, which are not present in other high-performance polymers.

A newly discovered nanostructure (island-nanomatrix structure) is introduced based on previous studies on the structure of natural rubber. Effects of the proteins and phospholipids that form the nanomatrix on the mechanical properties of natural rubber are described using a model island-nanomatrix structure of natural rubber. Furthermore, a synthetic cis-1,4-polyisoprene with island-nanomatrix structure is prepared; its mechanical properties are similar to those of natural rubber.

We have developed innovative new phosgenation reactions and their special reaction systems with the key objective of “safe application” to organic synthesis. This focus review summarizes our recent studies on in situ photo-on-demand phosgenation reactions of alcohols and amines for synthesizing polycarbonates, polyurethanes, and their precursors such as chloroformates, carbonate esters, and diisocyanates, in batch reaction systems, which are preferable for laboratory or small-scale industrial syntheses.

Atomic force microscopy (AFM)-based nanomechanical characterization techniques have been extensively used to investigate the mechanical properties and mechanisms of polymeric materials. This technique enables direct visualization of the micromechanical properties of material surfaces and is referred to as the AFM nanomechanics technique. This review article discusses the application of this technique to studying polymer composites with a specific focus on the significant advances made in tracking the microscopic deformation behavior and visualizing the microscopic stress distribution of materials.