Koichiro Yonetake

New liquid crystals based on calixarenes

New liquid crystals based on calixarenes (7 and 8) were prepared by the reaction of calixarene, tert-butylcalix[8]arene and C-methyloctakis(2-hydroxyethyl)calix[4]resorcinarene, and 11-[(4′-cyano-1,1′-biphenyl-4-yl)oxy]undecanoyl chloride in the presence of triethylamine. The structures of 7 and 8 were characterized by IR, 1H NMR, 13C NMR, and MALDI-TOF mass spectroscopies. Compounds 7 and 8 had glass transitions at approximately –30 and 25 °C, respectively. Both of them exhibited smectic liquid crystals. Compound 8 was found to adopt a specific molecular structure due to the rigid bowl calix[4]resorcinarene core, i.e., a cone-like structure with mesogenic units aligned within the molecule. Moreover, the smectic A phase of 8 was transformed to nematic. The supercooling of 8 for the phase transition was very small due to the molecular structure.

Synthesis of head-to-tail polyurethanes from nonsymmetric diisocyanate and ethylene glycol with organotin catalysts

An ordered head-to-tail (HT) polyurethane was successfully prepared by the polyaddition reaction of p-isocyanatobenzyl isocyanate with ethylene glycol with dibutyltin dilaurate as a catalyst. Furthermore, the HT regularity of polyurethane was improved to 83% with 1,1,3,3-tetraphenyl-1,3-dichlorodistannoxane. The polymerization was conducted in N,N-dimethylformamide at 30 °C with both monomers mixed at once. The microstructure of the polymer was investigated by 1H and 13C NMR spectroscopy, and the polymer obtained by the polyaddition reaction had the expected HT linkages. The constitutional regularity of the polymers influenced the thermal properties and crystallinity.

Optically driven translational and rotational motions of microrod particles in a nematic liquid crystal

Significance This paper addresses light-driven dynamic motions of microrods suspended in a liquid crystal (LC) host. The results presented in this paper advance molecular-assisted manipulations of colloidal particles and their assemblies, which is a key concept for smart microdevices, using their interplay with the topology of the nematic director field. Almost all previous studies on colloids in LC (except some work by Yamamoto et al.) have dealt with the observation and analysis of defect structures around colloid particle(s) with fixed anchoring conditions. Herein we use a photoactive surfactant, which enables control of the LC anchoring by light irradiation. The induced reversible anchoring transition is accompanied by a reorientation of the rods and/or their translational motion. A small amount of azo-dendrimer molecules dissolved in a liquid crystal enables translational and rotational motions of microrods in a liquid crystal matrix under unpolarized UV light irradiation. This motion is initiated by a light-induced trans-to-cis conformational change of the dendrimer adsorbed at the rod surface and the associated director reorientation. The bending direction of the cis conformers is not random but is selectively chosen due to the curved local director field in the vicinity of the dendrimer-coated surface. Different types of director distortions occur around the rods, depending on their orientations with respect to the nematic director field. This leads to different types of motions driven by the torques exerted on the particles by the director reorientations.

Synthesis and characterization of ordered polyurethanes from nonsymmetric diisocyanate and ethylene glycol

An ordered polyurethane with a head-to-head (H-H) or tail-to-tail (T-T) content over 95% was prepared by polyaddition reaction of a nonsymmetric monomer, p-isocyanatobenzyl isocyanate (1) with a symmetric monomer, ethylene glycol (2). The model reactions were studied in detail to demonstrate the feasibility of polymer formation. The polymerization was conducted in THF in the presence of triethylamine (TEA) at 0 °C by slow addition of a half amount of 2 to 1, followed by removing THF and then adding the rest of 2 in DMF at once at 30 °C in the presence of dibutyltin dilaurate (DBTL). The microstructure of the polymer obtained was investigated by 13C NMR spectroscopy, and it was found that the polymer had the expected structural regularity. The constitutional regularity of polymers influenced their thermal properties.

Optical manipulation of the nematic director field around microspheres covered with an azo-dendrimer monolayer.

We report here the optical manipulation of the director and topological defect structures of nematic liquid crystals around a silica microparticle with azobenzene-containing dendrimers (azo-dendrimers) on its surface. We successfully demonstrate the successive switching processes from hedgehog, to boojum, and further to Saturn ring configurations by ultraviolet (UV) light irradiation and termination. The switching time between these defect structures depends on the UV light intensity and attains about 50 ms. Since the pretreatment of microparticles is not necessary and the surface modification is spontaneously performed just by dissolving the azo-dendrimers in liquid crystals, this dendrimer supplies us with a variety of possible applications.

Synthesis and Characterization of Polyamidoamine-Based Liquid Crystalline Dendrimers

Poly(amidoamine)-based liquid crystalline dendrimers (LCDs) with mesogenes on the surface were successfully prepared by the reaction of poly(amidoamine) dendrimers with 40-cyanobiphenyl hydrogen glutarate in the presence of a condensing agent, diphenyl(2,3- dihydro-2-thioxo-3-benzoxazolyl)phosphonate. The structures of LCDs were characterized by IR, 1H-NMR and MALDI-TOF mass spectroscopy and elemental analysis. These LCDs did not show a thermotropic liquid crystalline nature but exhibited a lyotropic liquid crystalline property in the 80 wt% DMF solutions of LCDs containing lithium bromide.

Structures and properties of dendrimers having peripheral 2,3‐difluorobiphenyl mesogenic units: effects of dendrimer generation

1st–5th generation poly(propyleneimine) dendrimers having peripheral 2,3‐difluorobiphenyl mesogenic groups have been synthesized. They exhibited smectic liquid crystalline behaviour. All the liquid crystalline dendrimers exhibited a smectic A (SmA) phase and a crystal E (E) phase. The SmA–isotropic phase transition temperature increased with increasing generation. In addition, a homeotropic structure was spontaneously formed on a glass plate in the SmA phase for the 2nd, 3rd, and 4th generation dendrimers. The hometropic structure remained unchanged in the phase.

Synthesis and characterization of ordered poly(amine thioether)s from 1,4-phenylene diacrylate and 4-aminobenzenethiol

An ordered head-to-head (H-H) or tail-to-tail (T-T) poly(amine thioether) was prepared by direct polyaddition of a non-symmetric monomer, 4-aminobenzenethiol (XabX) (1) with a symmetric monomer, 1,4-phenylene diacrylate (2). The reaction was conducted in m-cresol in the presence of a catalytic amount of acetic acid. The authentic ordered H-H or T-T polymer and the random polymer were prepared to verify the structure of the ordered polymer. 1 H and 13 C NMR spectroscopy confirmed the formation of the expected polymers. The con-stitutional regularity of polymers influenced the crystallinity.

Synthesis and characterization of 6-[4-(trans -4-pentylcyclohexyl)phenoxy]hexyl acrylate homopolymer and copolymers

The compound 6-[4-(trans -4-pentylcyclohexyl)phenoxy]hexyl acrylate (2) was prepared and homopolymerized. The block copolymer and copolymer of 2 with styrene were synthesized by photopolymerization and solution techniques, respectively. These polymers were characterized by IR and 1H NMR spectra and size exclusion chromatography. Polarizing optical microscopy (POM) and X-ray diffraction (XRD) studies revealed that these polymers exhibited smectic A (SmA) phases. POM showed that the homopolymer showed a higher order SmA phase than did the block copolymer and copolymer. After magnetically forced alignment the samples exhibited similar optical texture but the domain size of the liquid crystalline phase increased. Differential scanning calorimetry, POM and XRD data suggest that the SmA domain size decreased in the order hompolymer > block copolymer > copolymer.

Photoinduced Dewetting in Thin Films of Liquid Crystalline Dendritic Azobenzene Derivatives

We report in this paper photoinduced-dewetting phenomena observed for thin films (thickness < 100 nm) of a series of dendritic liquid crystalline materials with different spacer length (carbon number changing from n = 6 to 12) at their azobenzene units in the periphery. Spincast films of these dendrimers were prepared and exposed to UV light (365 nm) at various photon doses at room temperature. Atomic force microscopic observations of the dewetting forming process were performed step by step with increasing the UV illumination time for the dendrimer with the shortest spacer (n = 6). We observed how the dewetting bumps appeared from an initially flat spincast film and finally reached ca. eightfold of the initial film thickness. The dendrimer with n = 8 exhibited dewetting but the mass migration distance was significantly limited than that of n = 6. Dendrimers with longer spacer lengths (n = 10 and 12) did not exhibit dewetting behavior in the same conditions. These differences were discussed in terms of thermophysical properties of the materials.