Stereocontrol during the free‐radical polymerization of methacrylamides in the presence of Lewis acids

The effects of Lewis acids, that is, rare earth metal trifluoromethanesulfonates, on the free‐radical polymerization of N‐methylmethacrylamide (MMAM), N‐isopropylmethacrylamide (IPMAM), N‐tert‐butylmethacrylamide (tBMAM), N‐phenylmethacrylamide (PMAM), and methacrylamide were examined under various conditions. A catalytic amount of Yb(OSO₂CF₃)₃ significantly affected the stereochemistry during the radical polymerization. Polymerization solvents strongly influenced the effect of the Lewis acids. Methanol was the best solvent for increasing the isotactic specificity during the polymerization of MMAM and IPMAM, whereas tetrahydrofuran was more effective for the tBMAM and PMAM polymerizations. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1027–1033, 2003     

Preparation and chiral recognition ability of cellulose 3,5-dimethylphenylcarbamate immobilized on silica gel through radical polymerization

Polysaccharide-immobilized chiral stationary phases (CSPs) were prepared by the polymerization of cellulose 3,5-dimethylphenylcarbamate, having a polymerizable vinyl group, such as 4-vinylphenylcarbamate or 2-methacryloyloxyethylcarbamate, at the 6-position, with a vinyl monomer, such as styrene, isoprene, t-butyl acrylate, or t-butyl methacrylate, on silica gel under various conditions. Their chiral recognition abilities were then evaluated with high-performance liquid chromatography. The immobilized cellulose 3,5-dimethylphenylcarbamate remained on the silica gel even if washed with tetrahydrofuran, which could dissolve the cellulose derivative. The chiral recognition abilities of the immobilized CSPs were similar to those of the coated CSPs when the vinyl monomer content was low. The chiral recognition abilities of the obtained immobilized CSPs slightly depended on the vinyl monomers. The immobilization of the cellulose derivatives was more efficiently attained on the silica gel modified with a vinyl compound. The cellulose derivatives, randomly having a vinyl group at the 2-, 3-, or 6-position of the glucose unit, were prepared by a one-pot reaction. The immobilization efficiency of these derivatives was slightly lower than that of the derivative with the vinyl group at the 6-position. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3703–3712, 2003     

Effect of korteweg stress in miscible liquid two-layer flow in a microfluidic device

Miscible liquid two-layer flow in a Y-shaped microfluidic device, which consists of microchannels with 120 μm in width and 35 μm in depth, is investigated by particle image velocimetry (PIV) to clarify the flow characteristics at fluid interfaces. The obtained velocities with a spatial resolution of 5.9 x 1.5 μm² around the interface between water and ethanol indicate an imbalance in shear stress at interface. The reason of the imbalance is to be the Korteweg stress generated by interfacial tension gradient due to a concentration gradient by diffusion in a miscible two-layer flow. The stress may cause an interfacial instability and destroy a uniform mixing in two flowing fluids in the case of large concentration gradient.     

Improvement in Light Output of Thin-Film Vertical-Cavity Surface-Emitting Lasers Transferred onto A1N Substrates

Thin-film 850-nm vertical-cavity surface-emitting lasers (VCSELs) were improved in light output power by designing both the reflectivity of the distributed Bragg reflector on the light-emitting side and also the degree of de-tuning between the photoluminescence peak and the etalon wavelength. Thin-film VCSELs, which were fabricated on A1N substrates by a functional layer transfer technique, are attractive components for the hybrid integration of optoelectronic devices. Their maximum output power was 2.8 mW and their slope efficiency was 0.40 W/A for the 15μm diameter VCSEL devices that we studied. Uniform spontaneous emission over the entire mesa area, and a single transverse laser mode up to 1.3 times the threshold current were confirmed by observing the near-field images.     

A study of 50V using the direct reactions 49Ti (3He,d) and 51V(d,t)

Energy levels in ⁵⁰V up to 4.3 MeV have been studied using the ⁴⁹Ti(³He, d)⁵⁰V and ⁵¹V(d,t)⁵⁰V reactions with ³He particles of 22 MeV and deuterons of 19.5 MeV incident energy. More than eighty levels are seen, with angular distributions taken for forty-one levels in the (³He, d) reaction and for the ten lowest levels in the (d, t) reaction. The angular distributions are compared with the distorted-wave Born approximation (DWBA) to extract the l-values of the transferred nucleons and obtain the spectroscopic strengths. In the stripping reaction, a small amount of l = 0 and l = 2 strength is seen, indicating the presence of s and d proton holes in the g.s. of ⁴⁹Ti. The results are compared with a recent shell-model calculation based on an $\text{(}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{)}{}^{\mathrm{n}}$ configuration, and show qualitative agreement.     

Effects of t-butyl substituents on valence tautomerism of 7-t-butyl-7-cyano-1,3,5-cycloheptatrienes to the norcaradiene form

Introduction of t-butyl groups to the 2-, 3-, 2,4-, or 2,5-positions of 7-t-butyl-7-cyano-1,3,5-cycloheptatriene dramatically shifts the cycloheptatriene - norcaradiene equilibrium to the norcaradiene form. The nonbonded interaction is an important factor.     

Mass spectra of some alkyl isoxazoles

The mass spectra of several compounds obtained during the process of Stork's isoxazole synthesis9 as well as the related isoxazoles have been investigated. The fragmentations of simple alkyl isoxazoles are nicely formulated via azirine intermediates. A striking difference between the spectra of isoxazoles and those of methylfurans as to the relative abundance of [M — l] peaks is noteworthy. The very low abundance of these peaks in the former reflects the unique character of isoxazole nucleus due to the preferential cleavage of N? O linkage rather than a benzylic C? H bond rupture. If an alkyl substituent is present at 4-position in 3,5-dimethylisoxazoles, strong peaks at m/e 110, 68 and 43 are common in their spectra. The analyses of metastable transitions and high resolution measurements have demonstrated that the formation of these ions can be interpreted by a mechanism involving the cleavage of N? O linkage.