Die Bestimmung des Arsens in Pflanzenmaterialien

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Synthesis of ether‐linked bisoxazolines and their use in step‐growth polymerization reactions with phenolics

Six new ether‐linked bisoxazolines have been synthesized via reaction of p‐hydroxyphenyl‐2‐oxazoline with dihalides. These bisoxazolines may be used as chain extenders or crosslinkers for resins, monomers or polymers containing various acidic groups, including phenolics, via step‐growth (1 : 1) reactions. As an illustration, a phenol‐formaldehyde polycondensate (Alnovol) and an enzyme oligomerized bisphenol A resin, as well as poly (p‐hydroxystyrene), was chain extended and crosslinked to produce thermosets with high glass transition temperatures. The new bisoxazolines were also polymerized with diphenol compounds, such as diphone D and bisphenol P to generate linear or branched oligomers and polymers. Differential scanning calorimetry was used to evaluate the potential for polymerization and crosslinking reactions. Preliminary results showed that the new, ether‐linked bisoxazolines have potential for formulating high performance thermosets. Copyright © 2002 John Wiley & Sons, Ltd.     

Temperature dependence of the field effect mobility of solution-grown germanium nanowires

The temperature dependence of the field effect mobility was measured for solution-grown single-crystal Ge nanowires. The nanowires were synthesized in hexane from diphenylgermane by the supercritical fluid-liquid-solid process using gold nanocrystals as seeds. The nanowires were chemically treated with isoprene to passivate their surfaces. The electrical properties of individual nanowires were then measured by depositing them on a Si substrate, followed by electrical connection with Pt wires using focused ion beam assisted chemical vapor deposition. The nanowires were positioned over TaN or Au electrodes covered with ZrO2 dielectric that were used as gates to apply external potentials to modulate the conductance. Negative gate potentials increased the Ge nanowire conductance, characteristic of a p-type semiconductor. The temperature-dependent source/drain current-voltage measurements under applied gate potential revealed that the field effect mobility increased with increasing temperature, indicating that the carrier mobility through the nanowire is probably dominated either by a hopping mechanism or by trapped charges in fast surface states.     

Direct Carousel Flight Calorimeter for Metabolic Investigations of Small Insects

An isoperibolic heat flow calorimeter is described for the determination of heat production rates during the tethered flight of small insects such as flies, honeybees or hornets. The insects are fixed with their thoraces to one arm of a low-friction carousel. A sensor counts the number of revolutions per time and determines the speed of flight. Wing sound is monitored by a microphone with an audio recorder, so that wing beat frequencies and hence locomotor activities can be determined. Different illumination means are incorporated to guarantee the illumination levels necessary for flight.This revised version was published online in November 2005 with corrections to the Cover Date.     

Click Chemistry: A Potential Platform for Development of Novel Dental Restorative Materials

The main aim of this study is to develop novel polymer modified glass-ionomer cement (GIC) glasses utilizing click chemistry and RAFT polymerization. These novel glasses can serve as a platform to improve the properties of GIC's by incorporating chemistries and formulations that are not normally compatible with GIC's. Aluminofluoro-silicate glasses utilized in glass-ionomer dental cements were coated with azide terminated silane groups. In addition, a copolymer of acrylic acid-itaconic acid containing alkyne groups was synthesized by RAFT polymerization and was coupled via ‘click’ chemistry with the azide-coated GIC glass particles. FT-IR spectroscopy was used to characterize the synthesized materials and to confirm completion of the ‘click’ coupling reaction. The experimental cements cured, demonstrating that these modified glasses could be utilized in GIC formulations. The long setting and working times compared to control groups indicate that further improvements are necessary to fully utilize this chemistry. Our initial results in this study demonstrated the successful application of click chemistry in developing novel dental restorative materials, specifically glass-ionomer cements.     

Protein adhesion of block copolymer surfaces

Atomic force microscopy studies on the adhesion between various novel poly(methyl methacrylate)/poly(acrylic acid)-based block copolymers and the proteins fibronectin and bovine serum albumin are presented for the first time. Random, diblock, and triblock copolymers exhibit distinct adhesion profiles although their chemical compositions are identical, implying that biomaterial nanomorphology can be used to control protein–polymer interactions and potentially cell adhesion.     

Synthesis and Characterization of Homopolymers and Copolymers Containing closo‐[B12H12]2− Boron Cage Derivatives

Chains of cages : Neutral/ionic [B₁₂H₁₂]^2? boron‐cage‐functionalized methacrylate and styrene homopolymers or copolymers (see picture) are non‐crystalline solids, T_g increases as the number of B₁₂ cages in the chain of polystyrene increases, and homopolymers retain more weight than the copolymers when heated to 400 °C.

     

Synthesis and ring‐opening reactions of tetraphenyl‐substituted bisoxazoline monomers for preparing new thermosets and composites

To develop new monomers for formulating thermosetting composites, three new tetraphenyl‐substituted bisoxazoline monomers were synthesized via the direct reaction of 2‐(diphenylmethyl)oxazoline with bromoalkyls, using tert‐butyllithium. The structures were confirmed by Fourier transform infrared, nuclear magnetic resonance and mass spectrometry. These bisoxazolines have different melting points with varied molecular chain flexibility. They functioned well as crosslinkers when heated with phenolic resins or poly(acrylic acid), providing a path to new thermosetting materials with controlled glass transition temperature. To clarify the crosslinking reaction mechanism, the model reactions of these monomers with phenol and acetic acid were investigated. Copyright © 2000 John Wiley & Sons, Ltd.     

Effect of Methacrylated Hyperbranched Polymers on the Fracture Properties of Denture Base Materials

Hyperbranched polymers have the potential to reinforce crosslinked polymeric materials. In this study several concentrations of a methacrylated hyperbranched polyether are formulated with a denture base resin and cured. The denture base resin is a polymethyl methacrylate based resin. The fracture toughness of each of these concentrations was measured and compared to control. Only the 1% concentration had a significantly higher fracture toughness compared to the control. This is similar to other results that are found in the literature.     

Heat Dissipation of Flying Wax Moths (Galleria Mellonella) Measured by Means of Direct Calorimetry

Heat production rates and flight speed of adult wax moths (Galleria mellonella) were investigated by means of direct calorimetry at T_A=20 and 30°C. Specific heat production rates were not significantly different between males and females at T_A=20°C (p_TH=747±123.7 mW g^-1, n=5 for males and p_TH=791±169 mW g^-1, n=5 for females) even with females having a higher body mass (M_B=83.8±21.6 mg, n=9 for males and M_B=146.4±25.7 mg, n=11 for females) and wing load. In females, heat production rates were dependent on temperature with higher heat production rates at T_A=20°C (p_TH=791±169 mW g^-1, n=5) than at T_A=30°C (p_TH=441±74 mW g^-1, n=6). Flight speed was also clearly correlated with T_A. Both males and females flew more slowly at T_A=20 than at 30°C. This revised version was published online in August 2006 with corrections to the Cover Date.