Fabrication of nanofibers through a unique morphological transformation of poly(lactic acid) particles in water

Poly(lactic acid) (PLA) particles dispersed in water were transformed into nanofibers by simply heating above the glass transition temperatures of the hydrated PLAs.     

Chitosan‐Hydroxybenzotriazole Aqueous Solution: A Novel Water‐Based System for Chitosan Functionalization

Summary: A chitosan‐hydroxybenzotriazole (HOBt) aqueous solution prepared by simply mixing chitosan and HOBt in water provides an effective system to functionalize chitosan in an aqueous environment. This aqueous solution in combination with water‐soluble carbodiimide (WSC) allows the conjugation of functional groups onto chitosan under mild conditions without requiring any organic solvents or acid and heat. In this contribution, a series of model reactions that use a novel water‐based system of chitosan to functionalize the polymer with boc‐L ‐phenylalanine, poly(ethylene glycol) methyl ether, and dicarboxylated poly(ethylene glycol) is demonstrated.

Chitosan‐HOBt is effectively conjugated with R‐COOH via a water‐soluble carbodiimide (WSC) conjugating agent.     

Kinetics of the γ-radiation-induced polymerization of ethylene in liquid carbon dioxide

The γ-radiation-induced polymerization of ethylene with the use of liquid carbon dioxide as a solvent, was studied from the viewpoint of kinetics. The polymerization was carried out at conversions less than 10% under the pressure ranging from 100 to 400 kg./cm.², dose rates 1.3 × 10⁴?1.6 × 10⁵ rad/hr., and temperatures of 20–90°C. The concentration of carbon dioxide varied up to 84.1 mole-%. The polymerization rate and the polymer molecular weight were observed to increase with reaction time. This observation, however, becomes less pronounced with increasing concentration of carbon dioxide and with rising temperature. The exponents of the pressure and the dose rate were determined to be 2.3 and 0.85 for the rate, and 2.0 and ?0.20 for the molecular weight, respectively. From the kinetic considerations for these results, the effect of carbon dioxide on the initiation and termination reaction in the polymerization was evaluated.     

Polymerization of propylene with TiCl3–AlEt2Cl–polymeric electron donor catalyst

Polymeric donors having ether or carbonyl groups were added to the TiCI₃–AlEt₂CI catalyst system as the third component, and the effects on the polymerization of propylene were investigated in comparison with the effect of the electron donors with low molecular weight. The polymeric donors were effective in making the catalyst more active, but the donors of low molecular weight depressed the catalyst activity. In the case of poly(propylene glycol dimethyl ether) (PPG-DME), PPG–DME with a number of propylene oxide units (n) of more than 6.7 was effective in enhancing the catalyst activity. These effects were considered to be due to the different reactivities between TiCI₃ and AlEt₂CI-polymeric donor complexes having various chain lengths.     

Effect of competing alkali metal cations on neutral Host's anion binding ability

Anion binding by neutral hosts in organic solvents can be inhibited by the presence of alkali metal cations. The binding inhibition is due to salt ion-pairing which increases in the order Cs(+) < K(+) < Na(+). The binding inhibition can be reversed by using heteroditopic hosts that simultaneously bind both the metal cation and the anion. The largest cation-induced enhancements are observed with the less basic anions.     

Short-chain branching in γ-radiation-induced polymerization of ethylene

In an attempt to elucidate the mechanism of chain-branch formation in the polymerization of ethylene, the effect of reaction conditions on short-chain branching in γ-radiationinduced polymerization of ethylene was investigated by using infrared spectroscopy. The concentration of methyl groups, i.e., the frequency of short-chain branching, increases with temperature and pressure and is independent of ethylene conversion to polymer and radiation intensity. The number of methyl groups per polymer molecule increases almost proportionally with the degree of polymerization. These facts indicate that short-chain branching occurs mainly by the mechanism of intramolecular hydrogen transfer. The effect of pressure on the rate of chain branching can be postulated by considering the transition state to be six-membered rings in hydrogen transfer reactions. The activation energy of chain branching is found to exceed that of propagation by 6 kcal./mole.     

Novel chiral bisoxazoline ligands with a biphenyl backbone: preparation, complexation, and application in asymmetric catalytic reactions

Novel C(2)-symmetric chiral bisoxazoline ligands 1 were easily prepared from enantiomerically pure 2-amino alcohols and achiral 2, 2'-biphenyldicarboxylic acid via the corresponding amide and mesylate as intermediates. Since these ligands bear only two ortho-substituents on the biphenyl backbone, the biphenyl axis is not fixed, and the two diastereomers of these ligands exist in equilibrium in solution. Interestingly, when the ligands 1 were coordinated with a metal ion, only one of the two possible diastereomer complexes, an (S,aS,S)-complex, can be formed depending on the combination of the ligand and the metal ion. Thus, copper(I) afforded only the (S,aS,S)-complexes with all ligands 1, while zinc(II), palladium(II), and silver(I) afforded the (S,aS, S)-complexes as the sole product only with 1b, which has a bulky tert-butyl group on the oxazoline ring, and a mixture of the two diastereomer complexes with 1a,c,d. The copper(I)-catalyzed asymmetric cyclopropanation of styrene with diazoacetate proceeded successfully with these ligands and good to excellent enantioselectivities were afforded.     

New method of anatomic localization of scintigram of various organs by simultaneous combination of emission scanning and transmission scanning]

When the photoscintillo-roentgenography is used for relating the scintigram of internal organs to the anatomic structures, this method is found to have some defects--the difference of magnification between the emission scan and the roentgenogram, the inaccuracy due to the geometric distortion of the X-ray image, the impossibility of the simultaneous photographing of the scan and the X-rays, etc. Then, to diminish the influence of these defects we improved on the photographic recording system of a dual-heal scanner, and made use of the transmission scanning method. That is, we combined the recording parts, Ch1 and Ch2, into one system, using Ch1 for the light source of transmission scan and Ch2 for that of emission scan. In this way, we managed to make the two incident rays from those light sources converge into a focus upon a film. Thus we could perform a simultaneous emission-transmission scanning, by moving, at the same time in the same direction, the scanning detector over the patient and the small radioactive source (241Am) under him. This method can be applied to any radioactive nuclide to be used in transmission scanning and emission scanning. As the result of applying this method clinically in our department, the method has proved to be very useful for anatomic localization.