Preparations of polystyrene/aluminum hydroxide and polystyrene/alumina composite particles in an ionic liquid

Polystyrene (PS)/aluminum hydroxide (Al(OH)(3)) composite particles were successfully prepared by the sol-gel process of aluminum isopropoxide (Al(OPr(i))(3)) in a hydrophilic ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF(4)]) using ammonium hydroxide (NH(4)OH) as a catalyst in the presence of PS seed. Transmission electron microscopy observation of ultrathin cross-sections of the composite particles revealed that the composite particles had a core-shell morphology consisting of a PS core and a Al(OH)(3) shell having high crystallinity. The amount of secondary nucleated Al(OH)(3) could be reduced by dropwise addition of NH(4)OH. Moreover, PS/η-Al(2)O(3) composite particles were successfully prepared by heat treatment of PS/Al(OH)(3) at 300 °C in N(2) atmosphere, which is below the decomposition temperature of PS.     

Rheo-SANS studies on shear-thickening/thinning in aqueous rodlike micellar solutions

Shear-induced thickening/thinning phenomena of aqueous rodlike micellar solutions of cetyltrimethylammonium bromide (CTAB) and sodium p-toluene sulfonate (NapTS) were investigated by means of simultaneous measurements of rheology and small-angle neutron scattering (SANS), the so-called Rheo-SANS. The aqueous CTAB/NapTS solutions were classified into five different categories dependent on their flow behavior and micellar structure. By increasing salt concentration and/or shear rates, the micelles underwent morphological transition from (i) spherical or short rodlike micelles to (ii) long rodlike micelles without entanglements, followed by (iii) those with entanglements. These transitions were recognized as changes in flow behavior from Newtonian to shear-thickening and shear-thinning flow, respectively. In the latter two cases, anisotropic SANS patterns appeared around these critical shear rates. The physical meaning of the anisotropic SANS patterns accompanied by shear-thickening flow behavior is discussed in conjunction with other shear-thickening systems.     

Inhibitory effects of a novel ascorbic derivative, disodium isostearyl 2-O-L-ascorbyl phosphate on melanogenesis

We investigated the inhibitory effects of a novel amphiphilic ascorbic derivative, disodium isostearyl 2-O-L-ascorbyl phosphate (VCP-IS-2Na), synthesized from a hydrophilic ascorbic derivative, sodium-2-O-L-ascorbyl phosphate (VCP-Na), on melanogenesis in cultured human melanoma cells, normal human melanocytes, and three-dimensional cultured human skin models. Melanin synthesis in melanoma cells treated with VCP-IS-2Na at 300 muM and melanocytes treated with VCP-IS-2Na at 100 muM decreased to 23% and 52% of that in non-treated cells, respectively, and the cell viability was not affected. VCP-IS-2Na also significantly suppressed the cellular tyrosinase activity of melanoma cells and melanocytes. Melanin synthesis in human skin models was evaluated by macro- and microscopic observations of its pigmentation and quantitative measurements of melanin. Treatment of the human skin models with 1.0% VCP-IS-2Na did not inhibit cell viability, while melanin synthesis was decreased to 21% of that in the control. In contrast, L-ascorbic acid (VC) and VCP-Na did not seem to inhibit melanin synthesis and cellular tyrosinase activity. These results indicate that VCP-IS-2Na may be an effective whitening agent for the skin, and we expect the application of VCP-IS-2Na in the cosmetic industry.     

Synthesis and hybridization properties of 2′-O-(tetrazol-5-yl)ethyl-modified oligonucleotides

2′-O-(1H-Tetrazol-5-yl)ethyladenosine was synthesized using 2′-O-cyanoethyladenosine derivative as a key intermediate. The 2′-O-(1H-tetrazol-5-yl)ethyl modifications exhibited intriguing properties such as the change in the structure of the tetrazole residue between a protonated and a deprotonated form. The T_m experiments of various oligodeoxynucleotides having a 2′-O-(1H-tetrazol-5-yl)ethyl-modified adenosine showed reduced hybridization affinity in comparison to the unmodified oligonucleotides toward their complementary oligodeoxynucleotides. The mechanism of the reduced hybridization affinity was discussed on the basis of the structure and the physicochemical properties of the tetrazole moiety.     

Preparation and applications of novel fluoroalkyl end-capped 2-acrylamido-2-methylpropanesulfonic acid oligomer/clay nanocomposites

New fluoroalkyl end-capped 2-acrylamido-2-methylpropanesulfonic acid oligomers/clay composites were prepared by reaction of fluoroalkanoyl peroxide with the corresponding monomer in the presence of clay in aqueous solutions. These obtained fluorinated composites were nanometer size-controlled and were found to exhibit a good dispersibility in water and polar organic solvents such as methanol. The contents of clay in these nanocomposites were estimated to be 3～19% by the thermogravimetric analysis measurements. X-ray diffraction spectra showed the successful intercalation of fluorinated oligomers into the interlayer spaces of clay. These fluorinated clay nanocomposites were applied to the surface modification of poly(vinyl alcohol). In addition, these fluorinated nanocomposites were found to interact with methylene blue effectively to afford the fluorinated oligomers/clay/methylene blue nanocomposites.     

Preparation and exfoliation of layered titanium butyl phosphates

Titanium butyl phosphates (TiBP) synthesized by reacting Ti(SO₄)₂ with a mixture of mono-(C₄H₉PO₄H₂) and dibutyl phosphates ((C₄H₉)₂PO₄H) in aqueous ethanol solution at 25 °C were characterized by various conventional techniques. XRD pattern of TiBP possessed a peak at 2θ?=?5.5° and a broad hump at 2θ?=?15–30°. This fact indicated that the material was composed of a multilayer alternating bilayer of butyl groups of the phosphates and amorphous titanium phosphate phase. The TiBP was spherical particles with a size of ca. 100 nm and the chemical formula of this material was Ti((C₄H₉O)₂PO₂)_x(C₄H₉OPO₃)_y(OH)_z. The TiBP possessed a UV absorption property due to charge transfer of O^2? ? Ti⁴⁺. The layered structure of TiBP was exfoliated in ethanol at 25 °C up to TiBP concentration of 1.0?×?10⁵ ppm to form nanosheet. The nanosheet dispersing solution exhibited a UV absorption property and the property depends on nanosheet concentration.     

Pressure effects on the inhomogeneities of environmentally sensitive polymer gels

The effects of pressure at gel preparation on the inhomogeneities were investigated by small-angle neutron scattering. Poly(N-isopropylacrylamide) (PNIPA) gels, known as thermosensitive polymer gels undergoing volume transition, were prepared at various pressures ranging from 0.1 to 300 MPa. The scattering intensity increased with increasing P_prep, up to 200 MPa, then decreased by further increase in P_prep. The degree of inhomogeneities evaluated by the ratio of the static and dynamic correlators exhibited a similar behavior to that of the ensemble average light scattered intensity, <I>_E. The physical meaning of the gel inhomogeneities is discussed from the viewpoint of swelling thermodynamics. It will be shown that the increase in the swelling degree is due not to an increase in the miscibility of PNIPA with water but to the increase in inhomogeneities.     

Synthesis and Self-Association of Stimuli-Responsive Diblock Copolymers by Living Cationic Polymerization

The living cationic polymerization of several functional monomers in the presence of an added base is investigated as a possible preparation of a new series of water-soluble or stimuli-responsive copolymers. Under appropriate conditions, the polymerization allows the selective preparation of polymers with various shapes and different sequence distributions of monomer units, including stimuli-responsive block copolymers, gradient copolymers, poly(vinyl alcohol) graft copolymers, and star-shaped polymers. The stimuli-induced self-association of the diblock copolymers is also examined. An aqueous solution of the diblock copolymer with a thermo-sensitive segment undergoes rapid physical gelation upon warming to the critical temperature to give a transparent gel, and returns sensitively to the solution state upon cooling. The sharp transition of stimuli-responsive segments with highly controlled primary structure turns out to play an important role in the self-association. Small-angle neutron scattering, dynamic light scattering, and electron microscopy studies reveal that the physical gelation involves a thermosensitive micellization of diblock copolymers (core size: 18-20 nm) and subsequent micelle macrolattice formation (bcc symmetry). Based on the gelation mechanism, several stimuli-responsive gelation systems are achieved using other stimuli such as the addition of a selective solvent or compound, cooling, pH change, and irradiation with ultraviolet light.     

Ring-opening polymerization of six- and seven-membered cyclic pseudoureas

The cationic ring-opening polymerization of six-membered cyclic pseudoureas, 2-(1-pyrrolidinyl)- ( 2a ) and 2-morpholino-5,6-dihydro-4H-1,3-oxazine ( 2b ), was examined, which proceeded in two different ways, depending on the nature of initiator. The polymerization of 2 with methyl p-toluenesulfonate or trifluoromethanesulfonate (MeOTf) produced poly[(N-carbamoylimino)trimethylene], while that with benzyl chloride or bromide or methyl iodide gave a polymer consisting of 1,3-diazin-2-one-1,3-diylalkylene unit (the main component) and (N-carbamoylimino)trimethylene unit. The cationic ring-opening polymerization of seven-membered cyclic pseudourea, 2-(1-pyrrolidinyl)-4,5,6,7-tetrahydro-4H-1,3-oxazepine ( 3 ) was also examined. The polymerization of 3 with MeOTf as initiator gave poly{[N-(1-pyrrolidinycarbonyl)imino]tetra-methylene}. With benzyl chloride, on the other hand, no polymerization of 3 proceeded but, instead, the quantitative isomerization of 3 to 1,1′-carbonyldipyrrolidine took place. The polymerization mechanism of 2 and 3 as well as the isomerization mechanism of 3 were discussed with comparing them to the polymerization mechanism of five-membered pseudoureas. © 1977 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 933–945, 1997