Kensuke Sakurai

Interactions between spiropyrans and room-temperature ionic liquids: photochromism and solvatochromism.

A series of imidazolium-based room-temperature ionic liquids (RTILs) containing anions from organic carboxylic acids were prepared. A set of dye probes, including Reichardts dye (30), 4-nitrioaniline, and N, N-diethyl-4-nitroaniline, were used to determine the ET(30) scales and the Kamlet-Taft parameters (pi*, alpha, and beta) of the RTILs. On the basis of the polarity properties, these RTILs were categorized into three groups: group A with beta >0.9, alpha <0.9; group B with beta <0.9, alpha <0.9; and group C with beta <0.9, alpha >0.9. Interactions of these RTILs with four photochromic spiropyran derivatives (SP-I, SP-II, SP-III, and SP-IV) were investigated. It was found that the spiropyrans could present photochromism (positive or negative) or not, depending mainly on the polarity properties of the RTILs and also on the structure itself. A new spectroscopic method based on the molecular transition energy of the spiropyran probes (ESP) was proposed to determine the polarity of those protic or fluorine-containing RTILs, which were failed with the Reichardts dye (30) probe.

Crystal transformation of styrene-butadiene block copolymer

Abstract The crystal transformation of styrene-butadiene block copolymer, which has the attribute of shape-memory, has been studied. It is demonstrated from differential scanning calorimetry and wide-angle X-ray diffraction measurements that reversible crystal transformation takes place with temperature; two distinct crystal forms exist above and below the crystal transformation temperature of ∼45°C.

Morphology of a wholly aromatic thermoplastic, poly(ether nitrile)

Abstract The morphology of solution-cast, solution-grown and melt grown crystals of poly(ether nitrile) (PEN) was studied using mainly transmission electron microscopy. Fibrous, lamellar crystals (F crystals) develop during casting from solution followed by heat treatment, and via crystallization from solution and the melt. Electron diffraction studies indicate that PEN crystals grow rapidly along the a ∗ axis, along which the cyano groups are aligned. It can be suggested that an interaction between cyano groups and phenyl rings along the a ∗ axis should favour nucleation on the (200) growth front. F crystals coalesce to form wide lamellar crystals (L crystals) during heat treatment at temperatures above 250°C. PEN formed spherulites with positive birefringence from solution and the melt: the radial growth direction of the spherulites corresponds to the a ∗ axis. In view of the orientation of the cyano groups in the unit cell, it can be suggested that the refractive index along the radial direction is larger than that in the tangential direction. Stacked lamellar structures are formed from the melt under shear; the a ∗ axis is parallel to the transverse direction and the b axis is parallel to the thickness direction. It seems reasonable to assume that preferential nucleation at the bc plane occurs on the substrate during oriented crystallization.

Banded structure of gel-drawn poly(vinyl alcohol) fibers

Abstract During gel spinning/drawing of PVA fiber, a series of bands with ∼1 μm spacing are formed at angles of 75–90° to the fiber axis. Band angle varies depending on drawing temperature. The banded structure can be interpreted in terms of a model in which molecular axes are alternatively kinked from band to band. The stress-strain curve during drawing-contraction suggests that the formation of the banded structure is due to contraction strain of the deformed fiber, which is induced during stress relaxation. It is suggested that crystallographic, (101)〈010〉 slip plays an important role in the formation of the banded structure of gel-drawn PVA fibers.

Chitosan derivatives/calcium carbonate composite capsules prepared by the layer-by-layer deposition method

Core/shell capsules composed of calcium carbonate whisker core (rod-like shape) and chitosan/chitosansulfate shell were prepared by the layer-by-layer deposition technique. Two chitosan samples of different molecular weights (Mw = 9.7 × 104 and 1.09 × 106 gċmol-1) were used as original materials. Hollow capsules were also obtained by dissolution of the core in hydrochloric acid. Electron microscopy revealed that the surface of the shell is rather ragged associated with some agglomerates. The shell thickness l obeys a linear relation with respect to the number of deposited layers m as l = md + a(a > 0). The values of d (thickness per layer) were 4.0 and 1.0 nm for the higher and lower Mw chitosan materials, respectively, both of which are greater than the thickness of the monolayer. The results suggest that the feature of the deposition does not obey an ideal homogeneous monolayer-by-monolayer deposition mechanism. Shell crosslinked capsules were also prepared via photodimerization reaction of cinnamoyl groups after a deposition of cinnamoyl chitosan to the calcium carbonate whisker core. The degree of crosslink was not enough to stabilize the shell structure, and hollow capsule was not obtained.

Supermolecular structure of a new, wholly aromatic thermoplastic polyimide

Abstract Polyimides are one of the important heat-resistant polymers. A large number of wholly aromatic and aromatic/aliphatic polyimides have been developed since this class of polymer was first reported in the 1960s. These polyimides are in general either not processable or processable with great difficulty. In most cases, solutions of the corresponding polyamic acid (PAA) in polar solvents are used for processing.

Chitosan derivatives/calcium carbonate composite capsules prepared by the layer-by-layer deposition method II stabilization of the shell by crosslinking

The layer-by-layer deposition method is utilized to prepare rodlike core/shell capsules. Chitosan (polycation) and chitosansulfate (polyanion) were alternatively deposited on the surface of calcium carbonate whisker (rodlike particle). The thickness of the obtained shells ranged from 26 to 42 nm. After the deposition, the shell was treated with diisocyanate to form crosslink between the chitosan or chitosansulfate chains in order to stabilize the deposited shell. The obtained shell crosslinked rodlike capsules were successfully converted to hollow particles by immersing them into hydrochloric acid due to the enhanced shell stability, whereas from noncrosslinked shells, no hollow capsules were yielded: the shell was removed by dissolution in hydrochloric acid. It is revealed that the crosslinking reactivity is higher for 1,6-diisocyanatehexane than for tolylene 2,4-diisocyanate, suggesting that the reactivity depends on the size and flexibility of the crosslinking molecule.

Morphology of solution-cast thin films of wholly aromatic thermoplastic polyimides with various molecular weights

The morphology of solution-cast thin films of wholly aromatic thermoplastic polyimides (TPIs) with various molecular weights ( M w =3490-85 800) was studied using transmission electron microscopy (TEM). Thin TPI films suitable for TEM studies were prepared from 0.3% solution in p -chlorophenol/phenol cast onto hot polyphosphoric acid, where the solvent was evaporated. A TPI oligomer of M w =3490-6500 forms droplet-like structure (D structure) during casting, whereas TPIs with higher molecular weights ( M w =23 900-85 800) form ellipsoidal and elongated structures. On heating the as-cast film of TPI with M w =3490, the D structure is converted into a flat, layer structure with extended chains, which gives an electron diffraction pattern of the single-crystal type. On the other hand, long curved crystals with folded chains develop in the D structure of a TPI with molecular weight of 6500. The supermolecular structures of TPIs with higher molecular weights ( M w =23 900-85 800) are noticeably affected by the molecular orientation in the original structure of the as-cast films. Oriented crystallization occurs in the elongated structure, while lamellar crystals develop in the D structure or ellipsoidal structures.

Crystal morphology and polymorphism of a wholly aromatic thermoplastic polymer, poly (ketone sulfide)

Abstract The thermal behavior, morphology of the melt-grown crystals, and polymorphism of poly(ketone sulfide) (PKS) were studied and compared with those of poly(ether ketone) (PEK), using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and wide-angle x-ray dif- fractometry (WAXD). The following results were obtained: (1) The melting temperature of PKS is somewhat lower than that of PEK, suggesting that the sulfide linkage ([sbnd]S[sbnd]) has a relatively shallower rotational conformational energy than that of the ether linkage ([sbnd]O[sbnd]). (2) The spherulites of PKS and PEK are composed of long, narrow lamellar crystals. It has been confirmed by electron diffraction (ED) studies that the longitudinal, transverse, and thickness directions of the long lamellar crystals correspond to the b, a, and c-axes, respectively. (3) The melt-grown and the melt- quenched and subsequently heat-treated PKS and PEK have a similar two- chain orthorhombic unit cell. The orthorhombic uni...

Photophysics of novel 2,6-disubstituted benzobisthiazoles possessing chromophoric groups

A series of 2,6-disubstituted benzo[1,2-d:4,5-d′]bisthiazoles that have two photofunctional groups was synthesized, and their absorption and emission spectra in chloroform solution were examined. An anthracene derivative, 2,6-di(9-anthryl)benzo[1,2-d:4,5-d′]bisthiazole (DABBT), as well as a mono-substituted compound, 2-(9-anthryl)benzothiazole (ABT), showed a broad emission band at a long wavelength without any monomer emission of an anthryl group even for a concentration as low as 5 × 10−7 M. In contrast, naphthalene derivatives, 2,6-di(1-naphthyl)benzo[1,2-d:4,5-d′]bisthiazole (D1NBBT) and 2,6-di(2-naphthyl)benzo[1,2-d:4,5-d′]bisthiazole (D2NBBT), showed entirely monomer emission of a naphthyl group with no broad emission band at longer wavelengths. The broad emission bands observed for DABBT and ABT are attributed to an excited charge-transfer state in which an electron has transferred from a benzothiazole unit to an anthryl group.