Ordering and grain growth of FePt thin films by annealing

Microstructure variation of FePt thin film upon annealing at elevated temperatures was investigated by transmission electron microscopy (TEM). A special shape aperture was employed to observe the ordered L1₀ phase in the dark-field TEM images. With increasing the annealing temperature, crystal grains formed clusters with gathering of neighboring grains, and crystal grain growth proceeded within the cluster. L1₀ ordered crystal grains were preferentially formed near the grain boundaries, and their sizes grew with increasing the annealing temperature.     

Decisive factors for realizing atomic-column resolution using STEM and EELS

We demonstrate atomic-column imaging by scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS). The silicon atomic-columns of a β-Si₃N₄ (0 0 1) specimen are clearly resolved. The atomic-site dependence and the energy-loss dependence of the spatial resolution are elucidated on the basis of the experimental results and multislice calculations. We describe two decisive factors for realizing atomic-column imaging in terms of localization in elastic and inelastic scattering. One is the channeling of the incident probe due to dynamical diffraction, which has atomic-site dependence. The other is the localization in inelastic scattering; in addition to the energy-loss dependence of delocalization, we point out its dependence on the offset energy from the ionization energy, i.e., an additional localization factor concerning the Bethe surface. The present atomic-column observation of the Si-L core-loss image indicates that the local approximation, which can be interpreted intuitively, is achievable under appropriate experimental conditions, such as high-energy-loss, a small convergence angle and a large collection angle (e.g., 400 eV, 15 and 30 mrad, respectively).     

Free-radical polymerization of vinyl esters using fluoroalcohols as solvents: Effect of monomer structure on stereochemistry

Free-radical polymerization of vinyl esters including vinyl propionate (VPr), vinyl isobutylate (ViBu), vinyl 2,2-dimethylbutylate (VDMB), vinyl 2,2-dimethylvalerate (VDMV), vinyl 2,2-bis(trifluoromethyl)propionate (VF6Pi), and vinyl benzoate (VBz) was carried out using fluoroalcohols as solvents, and the tacticity of the obtained polymers was determined by NMR analysis of the produced poly(vinyl alcohol) (PVA). The polymerization of VPr, ViBu, VDMB, and VDMV, which are bulkier than VAc, in fluoroalcohols afforded polymers rich in heterotacticity (up to mr = 61%) similar to that of vinyl pivalate (VPi) whereas VAc is known to give a syndiotactic polymer under the reaction conditions used here. The polymerization of VF6Pi, which is the bulkiest among the monomers used in this study, gave a polymer rich in syndiotacticity in bulk and in fluoroalcohols regardless of the structure of the solvents. On the other hand, the polymerization of VBz in fluoroalcohols gave polymers with a higher isotacticity (up to mm = 33%) than bulk polymerization. Thus the monomer structure strongly affected the stereochemistry of the free-radical polymerization of vinyl esters in fluoroalcohols. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2677–2683, 1999     

Polysaccharide Derivatives for Chromatographic Separation of Enantiomers

The first resolution of enantiomers was performed 150 years ago–mechanically. Today a powerful method for carrying out this task is HPLC on polysaccharide derivatives as chiral stationary phases. Most racemates, from an analytical to a preparative scale, now appear to be resolved by this technique. As an example, the chromatogram for the enantiomeric resolution of a fullerene derivative is shown on the right.     

Synthesis and characterization of new soluble aromatic polyimides from diaminotetraphenylimidazolinone and aromatic tetracarboxylic dianhydrides

A series of new soluble aromatic polyimides with inherent viscosities of 0.65–1.12 dL/g were synthesized from 1,3-bis(4-aminophenyl)-4,5-diphenylimidazolin-2-one and various aromatic tetracarboxylic dianhydrides by the conventional two-step procedure that included ring-opening polyaddition and subsequent thermal cyclodehydration. These polyimides could also be prepared by the one-pot procedure in homogeneous m-cresol solution. Most of the tetraphenyl-pendant polyimides were soluble in organic solvents such as N,N-dimethylacetamide, 1,3-dimethyl-2-imidazolidone, and m-cresol. Some polyimides gave transparent, flexible, and tough films with good tensile properties. The glass transition temperatures and 10% weight loss temperatures under nitrogen of the polyimides were in the range of 287–326 and 520–580°C, respectively. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1767–1772, 1998     

Novel lipase-catalyzed ring-opening copolymerization of oxiranes and succinic anhydride forming polyesters bearing functional groups

Oxiranes, such as glycidyl phenyl ether (GPE) and benzyl glycidate (BG), were copolymerized with succinic anhydride (SA) by lipase at a temperature between 60 and 80°C to yield the corresponding polyesters bearing carboxyl or phenyl groups. Bulk polymerization, especially at the temperature of 80°C, and preferably using porcine pancreatic lipase gave biodegradable polyesters with a molecular weight greater than 5000.