Fraktionierung und Charakterisierung von ungehärteten Epoxidharzen aus Bisphenol A und Epichlorhydrin

Gel permeation chromatography and thin layer chromatography have been used respectively to separate and characterize the first seven members of an epoxy resin polymer homologous series on a preparative and analytical scale. The epoxy resin was formed by the reaction between Bisphenol-A and epichlorhydrin. NMR was used to identify the oligomers. The relationship between extinction coefficient and degree of polymerisation was also determined.     

Field bioassay ofexo- andendo-brevicomin withDendroctonus ponderosae in lodgepole pine

Bothexo- andendo-brevicomin reduced the response of flyingDendroctonus ponderosae (Coleoptera: Scolytidae) to an attractant composed oftrans-verbenol and terpenes or oftrans- andcis-verbenol and terpenes in a stand ofPinus contorta var.murrayana. These data suggest that racemicexo- andendo-brevicomin may interrupt aggregation in populations of mountain pine beetle colonizing lodgepole pine; functions of the natural chiral compounds are unknown.Research supported by NSF grants DEB 77-11367 and PCN 79-21708 and the O.S.U. School of Forestry. O.S.U. Agric. Exp. Sta. Tech. Paper No. 5713.     

Improved mechanical properties of shape‐memory polyurethane block copolymers through the control of the soft‐segment arrangement

High‐performance shape‐memory polyurethane block copolymers, prepared with two types of poly(tetramethylene glycol) (PTMG) used as soft segments, were investigated for their mechanical properties. Copolymers with a random or block soft‐segment arrangement had higher stresses at break and elongations at break than those with only one kind of PTMG. Random copolymers with fewer interchain interactions showed higher elongation than block copolymers. All the copolymers had shape‐recovery ratios higher than 80%. In dynamic mechanical testing, the glass‐transition behavior clearly depended on the soft‐segment arrangement: random copolymers had only one glass‐transition peak, whereas block copolymers showed two separate glass‐transition peaks. Overall, the control of the soft‐segment arrangement plays a vital role in the development of high‐performance shape‐memory polyurethane. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2410–2415, 2004     

Synergic influence of a surfactant and ultrasonication on the preparation of soluble,conducting polydiphenylamine/silica‐nanoparticle composites

Conducting polydiphenylamine was used to encapsulate silica nanoparticles through the oxidative polymerization of diphenylamine in the presence of ultrasonic irradiation. The polymerization was performed in the presence of sodium lauryl sulfate as a surfactant. Experiments performed in the absence of ultrasound clearly demonstrated that the application of ultrasonication played multiple roles in the preparation of a composite of polydiphenylamine with silica nanoparticles. Ultrasonication dispersed the silica nanoparticles, converted sodium lauryl sulfate to lauryl alcohol, and augmented the dispersion of the silica‐nanoparticle/polydiphenylamine composite in an organic medium. Silica‐nanoparticle/polydiphenylamine composites were also prepared in the absence of ultrasound and/or sodium lauryl sulfate. The silica‐nanoparticle/polydiphenylamine composites were characterized with Fourier trans form infrared spectroscopy, ultraviolet–visible/near‐infrared spectroscopy, and thermogravimetric analysis. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3912–3918, 2006     

Kinetic parameters estimation for cure reaction of epoxy based vinyl ester resin

A new graphical estimation technique is proposed for the determination of the kinetic parameters describing an autocatalytic reaction. A differential scanning calorimeter was used to monitor the reaction kinetics of an epoxy-based vinyl ester resin. The method utilizes information from a zero initial reaction rate, conversation at vitrification, the ratio of reaction rate constants under different isothermal conditions, and characteristics of the phenomenological kinetic model with assumptions being made about the overall reaction order. By fitting data to the integrated reaction rate equation with adjustments for the isothermal conditions, the kinetic parameters are estimated without using a linear or nonlinear regression method. Different kinetic parameters can be estimated from data before and after the gel point which was obtained from the relationship between the glass transition temperature and the degree of cure.     

Effect of La/K A-site Substitutions on the Ordering of Ba(Zn1/3Ta2/3)O3

The 1/3 <111>-type ordering of Ba(Zn_1/3Ta_2/3)O₃ (BZT) can be transformed to 1/2 <111>–type ordering by substituting the La³⁺ cation into the A site. The 1/3 <111> ordering in BZT is shown to be reduced, discontinued, and then replaced by 1/2 <111> ordering, using X–ray diffraction, electron microscopy, and Raman spectroscopy. On the other hand, potassium–substituted BZT only displays a reduction in the degree of ordering.     

Oxygen evolution and hypochlorite production on Ru-Pt binary oxides

The electrocatalytic activities of Ru-Pt binary oxide electrodes prepared by thermal decomposition for both oxygen and chlorine evolution reactions (OER and CER) were investigated by cyclic voltammetry (CV) and log i/E relationships (Tafel study). Both CV and Tafel studies revealed that the electrodes from the coating solutions with 60 and 20 mol % Pt content possessed the maximum apparent activity for OER and optimal apparent activity for CER/hypochlorite production, respectively. The specific activity (i/q ^*) revealed that mixing of the RuO₂ and PtO _x had no synergistic effects for OER due to the occurrence of phase segregation, which was revealed by element mapping/surface morphologies and Auger electron spectroscopy. Lower current efficiencies for hypochlorite production were found on the freshly prepared binary electrodes (type I electrodes) than on those having been treated by repetitive CVs (type II electrodes). Stability testing of both type I and II electrodes was measured in 0.5 m NaCl solution at 300 mA cm^–2 for 480 h, indicating that both type I and II electrodes are quite stable under the above conditions.     

Persistence of nonprotein seed amino acid s-(β-carboxyethyl)-cysteine in young leaves ofCalliandra rubescens Ecological implications

The insecticidal nonprotein amino acid S-(-carboxyethyl)-cysteine (S-CEC) is the major free amino acid in the seeds of severalCalliandra spp. where it accounts for up to 2.9 % of dry weight. Lesser amounts of other related S-containing amino acids and an array of nonprotein imino acids derived from pipecolic acid are other constituents. High concentrations of imino acids, which also show insecticidal activity, are maintained in the mature leaves, but sulfur compounds are lacking. In this study the disappearance of S-CEC from the germinating seeds and young seedlings ofC. rubescens was monitored over time. After 10 weeks, S-CEC continues to be found in high concentrations in the stems and new leaves. As young leaves mature, sulfur compounds quickly decrease in concentration. Traces of S-CEC are found in new leaves of plants up to nine months after germination. Whether high concentration of S-CEC in young leaves is due to transportation from the seed or de novo synthesis is unclear. The ecological implications are discussed.     

Preparation of stable polyurethane-polystyrene copolymer emulsions via RAFT polymerization process

Stable polyurethane-polystyrene (PU-PS) copolymer emulsions were prepared by the polymerization of 2-hydroxyethyl acrylate (HEA)-capped PU macromonomer and styrene, using azobis(isobutyronitrile) (AIBN), a radical initiator, and 4-((benzodithioyl)methyl)benzoic acid, a reversible addition-fragmentation chain transfer (RAFT) agent. As the molar ratio of the RAFT agent to AIBN increased, the zeta potential of the resulting copolymer emulsion increased, but the average size and size distribution of the emulsion droplets decreased. A living polymerization of HEA end-capped PU macromonomer and styrene was characterized by a linear increase in the molecular weight and decrease in the molecular weight distribution with consumption of monomers. The tensile strength, hardness and water-resistance of the copolymer films, prepared from the PU-PS copolymer emulsions, were much greater than those of the films prepared from the pure PU emulsion. The copolymer emulsions, prepared via the RAFT polymerization process, are expected to exhibit better storage stability than those prepared via the conventional free radical polymerization process, due to the presence of carboxyl groups derived from the RAFT agent at the PS block termini.     

Kinetics of cellobiose decomposition under subcritical and supercritical water in continuous flow system

The effects of reaction temperature, pressure and residence time were investigated with a flow apparatus. Cellobiose decomposition kinetics and products in suband supercritical water were examined at temperatures from 320 to 420 °C at pressures from 25 to 40 MPa, and at residence times within 3 sec. Cellobiose was found to decompose via hydrolysis and pyrolysis. The yield of desired hydrolysis product, glucose, was the maximum value of 36.8% at 320 °C, 35 MPa, but the amount of 5-(hydroxymethyl)furfural (HMF), fermentation inhibitor increased too because residence time increased in the subcritical region owing to decrease of reaction rate. Meanwhile, though the yield of glucose is low in the supercritical region, the yield of HMF decreased compared with the subcritical region; and at the minimum yield of HMF (380 °C, 25 MPa), the yield of glucose was 21.4%. The decomposition of cellobiose followed first-order kinetics and the activation energy for the decomposition of cellobiose was 51.05 kJ/mol at 40MPa.