Crystallization kinetics for semicrystalline random copolymers of vinylidene chloride (VDC) with methyl acrylate (MA), and the effects on the internal morphology of the resin particles formed during synthesis

Isothermal crystallization kinetics for random copolymers of vinylidene chloride (VDC) with methyl acrylate (MA) is reported. Syntheses of many semicrystalline polymers follow heterogeneous reaction paths in which the macromolecule chains phase separate from the reaction mixtures. The internal particle morphology (the internal structure of the resin bead) from this type of reaction is granular and porous, as a result of the demixing processes accompanying polymer formation. Demixing in these polymers involves either liquid-liquid (L-L) phase separation followed by liquid-solid (L-S) transformation (crystallization) or L-S transformation alone. Crystallization (L-S transformation) must be an indispensable part of the process if a porous granular structure is to be expected. This is because L-S transformation is the most probable means by which the demixed structure can be stabilized against complete coalescence or agglomeration, which would lead to totally fused bead internal structure. This is particularly true if the glass transition temperature (T_g) is lower than the polymerization temperatures, as is the case with the VDC-MA copolymers. Copolymers that crystallize the fastest will have the finest (most porous) resin bead morphology. The result of this work is consistent with expectation. The homopolymer (PVDC) that crystallizes the fastest has the finest resin bead internal morphology. The copolymers show slower crystallization rates with increasing noncrystallizable MA content. Correspondingly, resin morphology measured by specific surface area decreased with increasing amounts of the noncrystallizable (MA) comonomer unit in the copolymer. This is clearly seen in SEM photographs of the internal bead structures of these copolymers. ©1995 John Wiley & Sons, Inc.     

Magnetic and electrical properties of several Mn-based amorphous alloys

Magnetic and electrical properties of amorphous Mn-Y, Mn-Zr, and Mn-Nb alloys have been investigated. All these alloys have a temperature-dependent susceptibility which is well fitted by a Curie-Weiss law. This implies the existence of localized magnetic moments associated with the Mn atoms. In addition, amorphous Mn-Y alloys exhibit spin-glass characteristics at low temperature. The experimental results of the electrical resistivity show that the temperature coefficient of resistivity (TCR) of both Mn-Y and Mn-Zr are negative, while Mn-Nb has a positive TCR. On the other hand, the resistivity-temperature curves of Mn-Zr and Mn-Nb have nearly the same tendency but are different from that of Mn-Y.     

Comparing vortex methods and finite difference methods in a homogeneous turbulent shear flow

The vortex method is applied to the calculation of a homogeneous shear turbulence, and compared with a finite difference code using identical calculation conditions. The core spreading method with spatial adaptation is selected as the viscous diffusion scheme of the vortex method. The shear rate is chosen so that it matches the maximum value observed in a fully developed channel flow. The isosurface, anisotropy tensors, and joint probability density functions reflect the ability of the present vortex method to quantitatively reproduce the anisotropic nature of strongly sheared turbulence, both instantaneously and statistically. Copyright © 2009 John Wiley & Sons, Ltd.     

The stress effect on magnetic domain structure of Fe-Co amorphous alloys

The stress effect on magnetic domain structure has been studied for the Fe-Co amorphous alloy system. The domain structure was dominated by the magnetostriction-internal stress coupling. By applying the tensile stress, the domain structure was changed significantly according to the magnitude and sign of magnetostriction. The value of internal stress estimated was about 3×10⁸ dyn/cm² and nearly constant for all the alloy composition.     

Exploration on the characteristics of cellulose microfibers from Palmyra palm fruits

To obtain cellulose microfibers from Palmyra palm fruit fibers, a new succession of specific chemical treatments including acidified chlorination, alkalization, and acid hydrolysis have been developed. Cellulose microfibers obtained were characterized by different techniques. The chemical analysis indicated an increase in α-cellulose content and decrease in lignin and hemicellulose for the cellulose microfibers over raw fibers. Fourier transform infrared and ¹³C NMR spectra confirmed the removal of non-cellulosic (lignin and hemicellulose) components after chemical treatments. The X-ray diffraction results revealed that the cellulose I was partly transformed into cellulose II by chemical treatments and the crystallinity index of cellulose microfibers was significantly increased as compared to raw fibers owing to removal of non-cellulosic components. Thermogravimetric analysis results demonstrated that the thermal stability was enhanced noticeably for cellulose microfibers than for the raw fibers. The scanning electron micrographs illustrated cleaner and rough surfaces for the cellulose microfibers when compared to those of raw fibers.     

The flourescence lifetime of the benzyl radical

Time resolved fluorescence of the benzyl, monomethylbenzyl and dimethylbenzyl radicals strapped in rigid solvents at low temperatures has been observed using the second harmonic of the ruby laser at the exciting source. The fluorescence lifetimes of these radicals are very long (10^?7–10^?6 sec), which are influenced considerably by the methyl substituents. The long fluorescence lifetimes of the benzyl radical and its methyl derivatives are interpreted in terms of the forbidden character of the first doublet-doublet electronic transition.     

Effects of 32-oxygenated lanosterol derivatives on 3-hydroxy-3-methylglutaryl coenzyme A reductase activity and cholesterol biosynthesis from 24,25-dihydrolanosterol.

The effects of 32-oxygenated lanosterol derivatives on 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity and cholesterol biosynthesis from [24,25-3H]24,25-dihydrolanosterol were studied. Among the derivatives, 3 beta-hydroxylanost-7-en-32-oic acid was the most active in depressing HMG-CoA reductase activity (IC50: 0.7 microM) and cholesterol biosynthesis (IC50: 0.4 microM) from 24,25-dihydrolanosterol.     

Fluorescence lifetime and quantum yield of diphenylketyl radical at low temperature

The fluorescence lifetimes of the diphenylketyl radical trapped in ethanol and EPA matrices are 16.8 ± 0.5 and 21.1 ± 0.6 ns, respectively in the temperature region of 77–130 K. The fluorescence quantum yield in ethanol matrix is 0.16 ± 0.6. These values are consistent with the radiative lifetime calculated from the absorption spectrum.     

Desulfurizative stannylation of uracil derivatives

Phenylthio group in the C-6 or C-5 position of uracil moiety can be removed by radical mediated stannylation with tributyltin hydride followed by protonolysis, providing a new route to 5-substituted uridines.