Reviews & Analysis

Three super-tough gels and their deformation mechanism as revealed by small-angle neutron scattering

Precise synthesis of dendrimer-like star-branched polymers, a novel class of structurally well-defined hyperbranched polymers, by stepwise iterative methodologies based on the ‘arm-first’ divergent approach is described. The methodologies basically involve a linking reaction of chain-functionalized living anionic polymer(s) and a transformation reaction to regenerate the next reaction sites. By repeating the two reaction steps, high-generation and high-molecular-weight dendrimer-like star-branched polymers and their block copolymers were successfully synthesized. The resulting polymers were characterized by small-angle X-ray scattering, viscosity and atomic force microscopy measurements to estimate their sizes, shapes and solution behavior.

The metal-catalyzed living radical polymerization has now been developed diversely in terms of the catalytic systems, controllable monomers, well-defined polymer structures and combinations with stereospecific radical polymerization. This review describes a short overview of recent developments in metal-catalyzed living radical polymerization mainly focusing on our recent research studies related to the subject.

This article reviews the development of catalysts for ring-opening metathesis polymerization (ROMP), synthesis of polymers bearing amino acids and peptides by ROMP of functionalized norbornenes, formation of aggregates and micelles, and applications of the polymers to medical materials. It also describes the control of monomer unit sequences, that is, living polymerization to synthesize block copolymers, and alternating copolymerization that is achieved on the basis of acid–base interactions.

Hyperbranched poly(ether sulfone)s (HBPES) possessing sulfonic acid at the terminal point were prepared by the electrophilic reaction of sulfonium ions to electron-rich benzene rings starting two kinds of AB₂ monomers. First, linear and hyperbranched multiblock copolymers were successfully prepared by the reaction of oligomeric linear PES and AB₂ monomer. Next, from these multiblock copolymers, a linear and hyperbranched PES blend was prepared and applied as ion-exchange membranes for fuel cells. The blend films showed comparable ion-exchange capacity with Nafion 117 membrane.

To obtain a novel biomimetic polymer, we have been studying polymers with an autonomous self-oscillating function. We succeeded in developing a novel self-oscillating polymer and gel by using an oscillating reaction, called the Belousov–Zhabotinsky (BZ) reaction, which is recognized as a chemical model for understanding several autonomous phenomena in biological systems. The self-oscillating polymer is composed of a poly(N-isopropylacrylamide) network in which the catalyst for the BZ reaction is covalently immobilized. Under the coexistence of the reactants, the polymer undergoes spontaneous cyclic soluble–insoluble changes or swelling–deswelling changes (in the case of gel) without any on–off switching of external stimuli. Several kinds of functional material systems using the self-oscillating polymer and gel, such as biomimetic actuators, mass transport surface and so on, are expected.

The slow mode in semidilute neutral polymer solutions, dilute polyelectrolyte solutions and gels, is reviewed here. Our results suggest that the slow mode can be qualitatively considered as a hindered motion of interacting chains, even though the nature of interaction can be very different; namely, from the weak segment-segment interaction in a less good solvent to a strong electrostatic interaction among polyelectrolyte chains, and even to chemical crosslinking inside gel networks.

The design and preparation of azobenzene-containing polymers showing a large photoinduced change in refractive index, and their applications to rewritable Raman-Nath and Bragg holograms are reviewed. Holographic performance has been remarkably improved with regard to diffraction efficiency, response time and multiplicity by development of newly designed polymer systems.

At present, the lithium ion secondary battery is necessary as an energy storage device for cellular phones, notebook computers and so on. The key to even further disseminate LIB was to add a safety function to prevent thermal abuse; therefore, the separator was required to have the safety function. The Asahi Kasei Corporation has carried out the development of the safety function of the separator and succeeded in controlling the pore size of the separator for improving the performance of LIBs.

This article provides a short overview of researches in preparation of smart soft materials using molecular complexes that are reversibly formed and dissociated by environmental changes. Biomolecule-responsive hydrogels that undergo volume changes in response to target biomolecules such as glucose, antigen and glycoprotein were strategically designed by using biomolecular complexes as reversible crosslinks. A variety of complexes between hydrogel networks and biomolecules were useful tools for creating smart soft materials and for constructing controllable and self-regulated systems.

As a new conformational motif of vinyl polymers having side-chain π-electronic groups, we have introduced a ‘π-stacked structure’ in which side-chain chromophores are regularly stacked on top of each other and main-chain C-C bonds have a nearly all-trans, zigzag conformation. π-Stacked polymers can be prepared by vinyl polymerization of dibenzofulvene (DBF) and its derivatives. On the basis of the controlled structure, poly(DBF) and its derivatives exhibit unique photophysical and electronic properties as vinyl polymers. Introduction of chirality to π-stacked polymers was also achieved.

The recent remarkable progress in structural investigations of helical polymers by high-resolution atomic force microscopy provides their exact helical structures including helical pitch and handedness. Seeing is believing!