Yuji Higaki

A dynamic (reversible) covalent polymer: radical crossover behaviour of TEMPO-containing poly(alkoxyamine ester)s.

A dynamic covalent polymer incorporating thermally alkoxyamine units in the main chain was synthesized. Due to a radical crossover reaction between the alkoxyamine units, an interchange of the main chains in poly(alkoxyamine ester) was observed on heating.

pH-Responsive and selective protein adsorption on an amino acid-based zwitterionic polymer surface

The synergistic interactions between the α-amine and the carboxylic acid in an amino acid have recently been studied as bio-based zwitterions. Here, we report a new amphiphilic polymer containing glutamic acid grafted to the end of a dodecyl polymer side chain, which contains the α-amine and the γ-carboxylic acid of the glutamic acid moiety. The polymer self-assembled into a multilayered structure in the thin film, and the glutamic acid moieties in the polymer side chains were exposed to the polymer film/water interface. Annealing the sample enhanced the formation of a well-oriented lamellar structure in the films. Due to the presence of the glutamic acid moieties at the interface, the surface charge was controllable by pH in buffer solutions, resulting in zwitterionic character at neutral pH. It has been widely accepted that zwitterionic surfaces can exhibit non-fouling for proteins. Interestingly enough, the polymer film showed charge-selective protein adsorption since the synergistic interaction between the α-amine and the γ-carboxylic acid was weaker than conventional amino acid-based zwitterionic systems. This is due to the separated state of the functional groups by a three carbon spacer.

Repeatable mechanochemical activation of dynamic covalent bonds in thermoplastic elastomers

Repeated mechanical scission and recombination of dynamic covalent bonds incorporated in segmented polyurethane elastomers are demonstrated by utilizing a diarylbibenzofuranone-based mechanophore and by the design of the segmented polymer structures. The repeated mechanochemical reactions can accompany clear colouration and simultaneous fading.

Structural effects of catechol-containing polystyrene gels based on a dual cross-linking approach

Based on efforts to develop synthetic materials with novel properties similar to the ingenious mussel adhesive, we present a structural study of gels with different cross-linking approaches, using a catechol-bearing polystyrene system. Prior studies have shown that catechol affords a dual cross-linking system based on Fe3+–catechol complexes and oxidative coupling. In this study, the structures of gels with different cross-linking ratios were investigated by field-emission scanning electron microscopy (FE-SEM), small angle X-ray scattering (SAXS), Raman spectroscopy, and dynamic viscoelastic measurements. These results revealed that Fe3+–catechol cross-linking leads to a more compact structure, which increased the gel rigidity. In addition, Fe3+–catechol cross-links could be removed from the hybrid cross-linking system by an acidifying process, yielding a catechol–catechol cross-linked gel with stable covalent bonds. A structure in which a continuous network of loosely folded poly(styrene-co-DOPMAm) chains is combined, with a cross-linking density varying from high (coordinative) to low (covalent), was achieved by balancing both oxidation and coordination. The work presented here will provide inspiration for those designing new classes of synthetic materials with advanced properties, biomimicking extensible byssal threads.

Electrospinning of non-ionic cellulose ethers/polyvinyl alcohol nanofibers: Characterization and applications

The morphology of spin-coated films and electrospun fibers of ethyl hydroxy ethyl cellulose (EHEC), hydrophobically modified ethyl hydroxy ethyl cellulose (HM-EHEC) and their blends with Poly(vinyl alcohol) (PVA) was examined by AFM, SEM and contact angle measurements. These polysaccharides upon blending with PVA exhibited smooth surface which was evidenced by Atomic Force Microscopy (AFM) observation. The electrospinnability of above polysaccharides with PVA was demonstrated for the first time. The oriented fibers could be obtained using a rotating disc collector. Contact angles of spin-coated films and electrospun fibers were discussed in terms of hydrophobicity and wetting characteristics. Further, The nanofibers of EHEC/PVA were in-situ crosslinked using citric acid and were used for controlled release of an antibacterial drug, Chlorhexidine Digluconate (ChD). In-vitro studies of cytotoxicity, cell growth and cell proliferation were performed using L929 mouse fibroblast cells. These nanofiber mats show potential in drug delivery and as scaffolds in tissue engineering applications.

Molecular design of environmentally benign segmented polyurethane(urea)s: effect of the hard segment component on the molecular aggregation states and biodegradation behavior

We investigated the molecular aggregation states, mechanical properties, and biodegradability of environmentally benign segmented polyurethane(urea)s [SPU(U)s], which contained bio-based monomers of an α-amino acid lysine-based diisocyanate (LDI). The SPU(U)s consisted of an aliphatic diisocyanate (LDI or 1,4-butanediisocyanate (BDI)), a chain extender (1,4-butanediamine (BDA) or 1,4-butanediol (BDO)), and a poly-e-caprolactone (PCL) segment. Four SPU(U)s, LDI–BDA, LDI–BDO, BDI–BDA, and BDI–BDO, were prepared by a standard two-step prepolymer method. Fourier transformed infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and small-angle X-ray scattering (SAXS) measurement indicated that the LDI-series SPU(U)s formed weakly aggregated hard segment domains, which readily dissociated under mechanical deformation and heating. The diamine chain extender, BDA, enhanced the stability of the hard segment domains, and the BDA-series SPU(U)s exhibited better mechanical properties than the BDO-series. The LDI-series SPU(U)s have notable biodegradability, and the BDI-based hard segments delayed the degradation rate because of the strongly segregated hard segment.

Ion-Specific Modulation of Interfacial Interaction Potentials between Solid Substrates and Cell-Sized Particles Mediated via Zwitterionic, Super-Hydrophilic Poly(sulfobetaine) Brushes

Zwitterionic polymer brushes draw increasing attention not only because of their superhydrophilic, self-cleaning capability but also due to their excellent antifouling capacity. We investigated the ion-specific modulation of the interfacial interaction potential via densely packed, uniform poly(sulfobetaine) brushes. The vertical Brownian motion of a cell-sized latex particle was monitored by microinterferometry, yielding the effective interfacial interaction potentials V(Δh) and the autocorrelation function of height fluctuation. The potential curvature V″(Δh) exhibited a monotonic increase according to the increase in monovalent salt concentrations, implying the sharpening of the potential confinement. An opposite tendency was observed in CaCl2 solutions, suggesting that the ion specific modulation cannot be explained by the classical Hofmeister series. When the particle fluctuation was monitored in the presence of free sulfobetaine molecules, the increase in [sulfobetaine] resulted in a distinct increase in hydrodynamic friction. This was never observed in all the other salt solutions, suggesting the interference of zwitterionic pairing of sulfobetaine side chains by the intercalation of sulfobetaine molecules into the brush layer. Furthermore, poly(sulfobetaine) brushes exhibited a very low V″(Δh) and hydrodynamic friction to human erythrocytes, which seems to explain the excellent blood repellency of zwitterionic polymer materials.

In situ ultra-small-angle X-ray scattering study under uniaxial stretching of colloidal crystals prepared by silica nanoparticles bearing hydrogen-bonding polymer grafts

The change in the crystal structure of polymer-grafted nanoparticles during uniaxial stretching was investigated by simultaneous ultra-small-angle X-ray scattering and stress–strain measurement.

Zwitterionic polymer brush grafting on anodic aluminum oxide membranes by surface-initiated atom transfer radical polymerization

A feasible processing of zwitterionic polymer-grafted anodic aluminum oxide (AAO) membranes by surface-initiated atom transfer radical polymerization (SI-ATRP) and the geometric effect on the polymer chain growth in the confined nanopores were investigated. A zwitterionic poly(3-(N-2-methacryloyloxyethyl-N,N-dimethyl)ammonatopropanesulfonate) (PMAPS) brush was produced on an AAO membrane via introduction of an initiator with a phosphonate group and subsequent SI-ATRP. The PMAPS-grafted AAO membranes were characterized by water droplet contact angle measurement, size exclusion chromatography (SEC), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and laser Raman micro-spectroscopy. The linear relationship between the grafting yield (Y) of the PMAPS brush and number-average molecular weight (Mn) of the unbound PMAPS indicates that there is no significant geometric effect on the chain growth under the spatial confinement inside the nanopores with diameters of ∼200 nm. The PMAPS brushes were diminished near the center section along the nanopores because the monomer supply was retarded. The capability of the PMAPS-grafted AAO membranes for inorganic nanoparticle immobilization was also demonstrated using gold nanoparticles (AuNPs) through ion-exchange and reduction processes.

Enhancement of the Hydrogen-Bonding Network of Water Confined in a Polyelectrolyte Brush

Water existing in the vicinity of polyelectrolytes exhibits unique structural properties, which demonstrate key roles in chemistry, biology, and geoscience. In this study, X-ray absorption and emission spectroscopy was employed to observe the local hydrogen-bonding structure of water confined in a charged polyelectrolyte brush. Even at room temperature, a majority of the water molecules confined in the polyelectrolyte brush exhibited one type of hydrogen-bonding configuration: a slightly distorted, albeit ordered, configuration. The findings from this study provide new insight in terms of the correlation between the function and local structure of water at the interface of biological materials under physiological conditions.