Effect of 20°–200oC Fabrication Temperature on Microstructure of Hydrothermally Prepared LiCoO2 Films

Films of LiCoO₂ were directly fabricated by hydrothermal treatment of a cobalt metal plate in a 4 M LiOH aqueous solution at 20°–200°C, with no subsequent annealing, and the effect of fabrication temperature on the film microstructure was investigated for the films. Micro-Raman studies have indicated that increasing the fabrication temperature produces a phase change in LiCoO₂ from spinel to hexagonal. This change is revealed by a variation in the film thickness and the film surface morphology, as seen in the micrographs. The present scanning electron microscopy results showed a growth of spinel LiCoO₂ particles up to 125°C and the formation of hexagonal particles at >125°C, in good agreement with the Raman and X-ray photoemission spectroscopy results. A film-formation mechanism based on the dissolution of cobalt metal, followed by precipitation, as LiCoO₂, onto the cobalt substrate, is proposed. The mechanism is supported by experimental data, such as the one-step potential evolution (0 → 0.6 V, with respect to the Ag/AgCl reference electrode) of the cobalt electrode during hydrothermal treatment and the detection of dissolved cobalt species by atomic absorption and ultraviolet–visible-light absorption spectroscopic analyses. Apparently, the evolution of the film structure arises from different nucleation and growth rates of LiCoO₂ particles on the film, caused by the dissolution–precipitation mechanism, and a phase selection of spinel or hexagonal as the fabrication temperature increases.     

New thermosetting resin from poly(p‐vinylphenol) based benzoxazine and epoxy resin

Poly(p‐vinylphenol) (VP) based benzoxazine was prepared from VP, formaline, and aniline. The curing behavior of the benzoxazine with the epoxy resin and the properties of the cured resin were investigated. Consequently, the curing reaction did not proceed at low temperatures, but it proceeded rapidly at higher temperatures without a curing accelerator. The reaction induction time or cure time of the molten mixture from VP based benzoxazine and epoxy resin was found to decrease, compared with those from conventional bisphenol A based benzoxazine and epoxy resin. The curing reaction rate of VP based benzoxazine and epoxy resin increased more than that of conventional bisphenol A based benzoxazine and epoxy resin. The properties of the cured resin from neat resins and from reinforced resins with fused silica were evaluated. The cured resins from VP based benzoxazine and epoxy resin showed good heat resistance, mechanical properties, electrical insulation, and water resistance compared to the cured resin from VP and epoxy resin using imidazole as the catalyst. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 555–565, 2001     

Allylation of Carbon Pronucleophiles with Alkynes in the Presence of Palladium/Acetic Acid Catalyst

We have developed an efficient and eco‐chemical process for the allylation of carbon pronucleophiles with alkynes. The reaction of alkynes with various active methynes and methylenes in the presence of Pd(PPh₃)₄/acetic acid gave the corresponding allylated products in high yields and high regioselectivities. In the present catalytic system, the key is the use of carboxylic acid which dramatically enhances the rate of the reactions. One of the important features of this process is that neither a leaving group is liberated nor is a stoichiometric amount of base needed to generate the nucleophiles.     

Phase Diagram and Oxygen-Ion Conductivity in the Y2O3-Nb2O5 System

The phase equilibria in the Y₂O₃-Nb₂O₅ system have been studied at temperatures of 1500° and 1700°C in the compositional region of 0-50 mol% Nb₂O₅. The solubility limits of the C-type Y₂O₃ cubic phase and the YNbO₄ monoclinic phase are 2.5 (±1.0) mol% Nb₂O₅ and 0.2 (±0.4) mol% Y₂O₃, respectively, at 1700°C. The fluorite (F) single phase exists in the region of 20.1-27.7 mol% Nb₂O₅ at 1700°C, and in the region of 21.1-27.0 mol% Nb₂O₅ at 1500°C, respectively. Conductivity of the Y₂O₃- x mol% Nb₂O₅ system increases as the value of x increases, to a maximum at x = 20 in the compositional region of 0 ≤ x ≤ 20, as a result of the increase in the fraction of F phase. In the F single-phase region, the conductivity decreases in the region of 20-25 mol% Nb₂O₅, because of the decrease in the content of oxygen vacancies, whereas the conductivity at x = 27 is larger than that at x = 25. The conductivity decreases as the value of x increases in the region of 27.5 ≤ x ≤ 50, because of the decrease in the fraction of F. The 20 mol% Nb₂O₅ sample exhibits the highest conductivity and a very wide range of ionic domain, at least up to log p _O2=−20 (where p _O2 is given in units of atm), which indicates practical usefulness as an ionic conductor.     

A mutant D-amino acid aminotransferase with broad substrate specificity: construction by replacement of the interdomain loop Pro119- Arg120-Pro121 by Gly-Gly-Gly

D-amino acid aminotransferase (EC 2.6.1.21) catalyzes the interconversion of various D-amino acids and 2-oxo acids. Each homodimer subunit consists of two domains, which are connected by a single loop, Asn118-Pro119-Arg120-Pro121. The loop has no direct contact with the active site region or the cofactor, pyridoxal 5'- phosphate. We attempted to increase the conformational flexibility of this loop through a triple glycine substitution. The resultant mutant P119G-R120G-P121G has features clearly different from the wild-type enzyme under overall as well as half-reaction conditions. The pre- steady-state kinetic analyses of half reactions showed that the mutant enzyme has kmax values higher than the wild-type enzyme towards most D- amino acids examined. A concomitant decrease in substrate affinity (1/Kd), particularly for acidic amino acids, was also observed. A putative binding site for the distal carboxyl group of acidic amino acids in the wild-type enzyme was incidentally displaced by the loop mutation, indicating a functional linkage between the interdomain loop and the active site region. This study has exemplified the usefulness of engineering relatively distant loops as a means to modify substrate specificity of an enzyme.      

Preparation of polyimides derived from biphenyltetracarboxylic dianhydrides and aromatic diamines bearing alkylene spacers

Four series of aromatic polyimides (PIs V–VIII) composed of biphenyltetracarboxylic dianhydrides (BPDAs) and aromatic diamines bearing alkylene spacers were prepared by two methods. Most polymers could be readily prepared in a one‐step method for the combination of a‐BPDA with α,ω‐bis(3‐aminophenoxy)alkanes, a‐BPDA with α,ω‐bis(4‐aminophenoxy)alkanes, and s‐BPDA with α,ω‐bis(3‐aminophenoxy)alkanes. However, the polymerization of s‐BPDA with α,ω‐bis(4‐aminophenoxy)alkanes gave powders. On the other hand, all four monomer combinations afforded the desired polyamic acid solution in a two‐step method. These polymer solutions could be cast into tough and flexible films, which were characterized by their inherent viscosity, differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical spectrometry measurements. The glass transition temperatures (T_gs) of the polymers were in the range of 110–240°C, but they were not clearly defined for PIs VIII and VI. The 5% weight loss temperatures were around 450°C for all prepared PIs. For PI VIII an “odd–even” behavior of the tensile properties of the films was detected, corresponding to the reported behavior of the melting temperatures. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2404–2413, 1999     

Dynamic Analysis of Phorbol Esters in the Manufacturing Process of Fatty Acid Methyl Esters from <Emphasis Type="Italic">Jatropha curcas</Emphasis> Seed Oil

Jatropha curcas seed oil, which is unsuitable as an edible oil but has received attention as a novel vegetable fat and oil resource, contains tumor-promoting phorbol esters. Currently, six types of derivatives of 12-deoxy-16-hydroxyphorbol (DHPEs) in J. curcas oil have been identified, and their toxicological safety for humans is being discussed. However, it is reported that most DHPEs disappear during the transesterification process. We investigated the dynamics of phorbol esters in the manufacturing process of fatty acid methyl esters from J. curcas seed oil. With the assumption that the precursor ion was the fragment ion (m/z = 311) from the frame unit of phorbol esters and their derivatives, we developed an LC–MS method for detecting the product ion (m/z = 165), which was obtained by cleavage of the fragment ion. The derivatives generated from the structural changes of the phorbol esters existed in fractions of glycerine–water in the manufacturing process; however, phorbol esters and their derivatives were not detected in the fatty acid methyl esters that were produced via a high-vacuum distillation process. Investigation into the dynamics of phorbol esters confirmed that the contents of phorbol esters, including DHPEs, in the fatty acid methyl esters were under detection limits.     

Strong orientation correlation and optical anisotropy in blend of cellulose ester and poly(ethylene 2,6‐naphthalate) oligomer

Molecular orientation of two aromatic additives in cellulose acetate propionate (CAP) matrix was investigated from orientation birefringence data and an intermolecular orientation correlation represented by nematic interaction (NI) was evaluated. Poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) oligomers with low molecular weight (ca. 400 g mol^?1) were used as the additives. The NI strengths of CAP‐PET and CAP‐PEN were determined to be 0.28 ± 0.05 and 0.96 ± 0.15, respectively. In particular, compared with other polymer/polymer and polymer/small additive blends, the NI value in CAP/PEN blend is much stronger and represents the perfect orientation correlation. The strong orientation correlation is possibly due to the rigid naphtalate structure in PEN. Contrary, a relation between birefringence and orientation function for CAP in bulk and blend showed the same trend, suggesting that the orientation behavior of CAP determines the orientation birefringence. As two ester groups in CAP are responsible for birefringence, the alignment of the ester groups is affected by only the main chain orientation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40570.