New side-chain poly(methacryl-rotaxanes) bearing cyclodextrins as non-covalently anchored ring components. Chemoenzymatic synthesis and degradation

The chemoenzymatic synthesis of new side-chain polyrotaxanes ( 6 ) bearing non-covalently attached cyclodextrins is described. Starting from 11-methacryloylaminoundecanoic acid, up to 8 units of 12-hydroxylauric acid were condensed in the presence of a lipase from Candida antarctica. They were copolymerized with methyl methacrylate to comb-like polymers ( 4 ) bearing free carboxylic groups at the end of the oligoester side chains. These free carboxylic groups were then condensed chemically with a nucleophilic barrier group, N-(4-aminobutanoyl)-4-triphenylmethylaniline ( 5 ), in the presence of dimethylated β-cyclodextrin, yielding new polyrotaxanes that contain statistically more than 1 ring component per side chain.     

Na0.74Ta3O6, ein niedervalentes Oxotantalat mit einer Ta–Ta‐Mehrfachbindung

Na_0.74Ta₃O₆, a Low‐Valent Oxotantalate with Multiple Ta–Ta Bonds The title compound was prepared in a sealed tantalum tube through the reaction of Ta₂O₅, tantalum and Na₂CO₃ in a NaCl flux at 1570 K within 5 d. The crystal structure of Na_0.74Ta₃O₆ (a = 713.5(1), b = 1027.4(2), c = 639.9(1) pm, Immm, Z = 4) was determined by single crystal X‐ray means. The structure is isomorphous with NaNb₃O₅F [1]. The characteristic structural units are triply bonded Ta1₂ dumb‐bells with eight square‐prismatically co‐ordinated O ligands. Four Ta2, each octahedrally surrounded by O atoms, are side‐on bonded weakly to the binuclear Ta₂O₈ complex, thus forming a Ta₆ propellane‐like cluster. The lattice parameters of three additional M_xTa₃O₆ phases, M = Li, Mn, and Yb, are reported.     

Cyclodextrins in polymer chemistry: Influence of methylated β-cyclodextrin as host on the free radical copolymerization reactivity ratios of isobornyl acrylate and butyl acrylate as guest monomers in aqueous medium

Methylated β-cyclodextrin (me-β-CD) was used to complex the hydrophobic monomers isobornyl acrylate ( 1 ) and butyl acrylate (2) yielding the water-soluble host/guest complexes isobornyl acrylate/me-β-CD ( 1a ) and butyl acrylate/me-β-CD ( 2a ). The included monomers were copolymerized in water by free-radical mechanism and the kinetics were studied. In order to evaluate these results, the corresponding uncomplexed monomers 1 and 2 were also copolymerized in organic solution. The reactivity ratios of 1a and 2a (r _1a = 0.3, r _2a = 1.7) differ significantly from the reactivity ratios of the corresponding uncomplexed acrylates 1 and 2 in organic solution (r ₁ = 1.3, r ₂ = 1.0). In addition, we found that the weight averages of the copolymers prepared by using me-β-CD are significantly higher than those of the corresponding polymers prepared from uncomplexed monomers in organic solution.     

Elements of the Phase Diagram of YbInCu4

To clearify how the valence transition temperature of YbInCu₄ is connected with the composition of the grown crystals, we investigated the phase diagram. Since elements of the liquidus curve of the system Yb-In-Cu were already known we focused on the solidus curve in the surrounding of the valence changing YbInCu₄. Bridgman-technique for crystal growth was used. The composition of the solidified crystals was determined by means of wavelength-dispersive X-ray analysis. The valence transition temperature is measured via the lattice constant by low temperature X-ray diffraction. Results are, that the assumed exchange of Yb and In, which is indicated in the formula Yb_xIn_2-xCu₄ seems to be not correct. Not the quasi-binary section for constant Copper content should be used, but one for constant Ytterbium content. Starting compositions with an excess of Ytterbium lead to the substitution of Indium by Copper. The valence transition temperature of these crystals is shifted from 40K to 70K.     

DNS and LES of spark ignition with an automotive coil

The cycle to cycle combustion variability which is observed in spark-ignition engines is often caused by fluctuations of the early flame development. LES can be exploited for a better understanding and mastering of their origins. For that purpose appropriate models taking into account energy deposition, mixture ignition and transition to propagation are necessary requirements. This paper presents first DNS and LES of spark ignition with a real automotive coil and simplified pin-pin electrodes. The electrical circuit characteristics are provided by ISSIM while the energy deposition is modelled by Lagrangian particles. The ignition model is first evaluated in terms of initial spark radius on a pin-pin ignition experiment in pure air performed at CORIA and EM2C laboratories, showing that it pilots the radius of the torus formed by the initial shock wave. DNS of a quiescent lean propane/air mixture are then performed with this ignition system and a two-step mechanism. The impact of the modelled transferred energy during glow phase as well as the initial arc radius on the minimum ignition energy (MIE) are examined and compared to experimental values. Replacing the two-step chemistry by an analytically reduced mechanism leads to similar MIE but shows a different ignition kernel shape. Finally, LES of turbulent ignition using a Lagrangian arc model show a realistic prediction of the arc shape and its important role on the energy transfer location and thus on the flame kernel shape.     

Microwave‐Sensitive Foamable Poly(ionic liquids) Bearing tert‐Butyl Ester Groups: Influence of Counterions on the Ester Pyrolysis

Several poly(ionic liquids) have been synthesized based on poly(1‐vinyl‐3‐tert‐butoxycarbonylmethylene imidazolium) salts with different counterions to investigate the tert‐butyl ester pyrolysis of these compounds. It is found that the counterions strongly influence the temperature of the pyrolysis. The pyrolysis temperature shifts to higher or lower temperatures depending on the nature of the counterions. The use of microwave irradiation was employed to accelerate the gas release because of the high dipolar interaction of amorphous salts with microwaves. The result of these reactions is the formation of organic foams that could be of industrial interest.

     

Polymerizable Ionic Liquid Crystals

Polymerizable vinylimidazolium ionic liquids (ILs) that contain mesogenic coumarin and biphenyl units, respectively, have been synthesized. The N‐alkylation of N‐vinylimidazole with bromoalkylated mesogenic units 7‐(6‐bromohexyloxy)coumarin ( 1 ) and 4,4′‐bis(6‐bromohexyloxy)biphenyl ( 2 ) was then carried out. The thermal behavior of the obtained ILs 3 and 4 was investigated by differential scanning calorimetry and polarizing optical microscopy. These measurements showed that the attached mesogenic units induce the self‐assembly of ILs and, therefore, the occurrence of liquid crystalline phases. Subsequently, the ionic liquid crystals (ILCs) 3 and 4 were polymerized by a free‐radical mechanism.