Crystalline titanium dichloride—an active catalyst in ethylene polymerization. II. Polymer structure,polymerization variables,and scope

Polymerization of ethylene with ball-milled titanium dichloride leads to a completely linear polymer with terminal unsaturation corresponding to approximately one carbon–carbon double bond per molecule. Polymerization rate is first-order in both monomer and catalyst concentration at 140°C. Due to a thermal deactivation of the catalyst, the polymerization rate falls sharply with temperature above 180°C. Propylene and butene-1 will copolymerization with ethylene in this system, propylene more efficiently than butene-1. Evidence for copolymerization of trans-2-butene, but not of the cis-isomer or of isobutene, in trace concentrations is presented. Propylene is homopolymerized to a product low in isotactic content. The significance of the structural and (limited) kinetic data in terms of the mechanism of polymerization are discussed.     

Macrocycle complexation chemistry. 37. The isolation and crystallographic characterization of the U4+ and UO2+ extraction complexes [(H5O2)(dicyclohexano-24-crown-8)]2[U02Cl4]⁗MeOH and [(H5O2) (dicyclohexano-24-crown-8)]2[UCl6]⁗MeOH

The reaction of dicyclohexano-24-crown-8 with UCl₄ in 3/1 THF:MeOH under anhydrous conditions and with exposure to air, resulted in the isolation of the hydronium ion complexes, [(H₅O₂)(dicyclohexano-24-crown-8)]₂[UO₂Cl₄]-MeOH and [(H₅O₂)(dicyclohexano-24-crown-8)]₂[UCI₆]-MeOH. The [UO₂Cl₄]^2? complex crystallizes in the monoclinic space group,P2₁/n, witha = 15.200(8),b = 26.565(9),c = 16.977(8)Å, β = 95.89(6)° andD _calc = 1.40 g cm^?3 forZ = 4 formula units. A finalR value of 0.051 was obtained utilizing 5913 independent observed [F _o ≥ 5σ(F _o)] reflections. One ether is complexed by an ordered H₅O _inf2 ^sup+ ion, while the second crown ether is hydrogen bonded to a disordered H₅O _inf2 ^sup+ ion. The [UCl₆]^2? complex is tetragonal,P4/n, with (at ?150°C)a = 16.320(4),c = 12.542(2)Å andD _calc = 1.47 g cm^?1 forZ = 2. A finalR value of 0.038 was obtained utilizing 2466 observed reflections. The anion resides on a four-fold axis and the crown ether cation around a crystallographic two-fold axis. The H₅O _inf2 ^sup+ ion is disordered into two orientations within the macrocycle cavity. All three crystallographically independent crown ether environments in these two structures have essentially identical conformations.     

Absorption and luminescence spectra of electroluminescent liquid crystals with triphenylene,pyrene and perylene units

New derivatives of triphenylene, perylene, and pyrene are described, some of which form columnar mesophases. The absorption spectra are investigated both experimentally and theoretically. The spectra calculated using the density functional tight binding (DFTB) theory are in good agreement with experimental results. The investigated compounds show photoluminescence of violet-blue (triphenylene), yellow-green (pyrene), and orange-red (perylene) colours. In addition, electroluminescence is observed in thin films of these compounds between a positively charged ITO electrode and a negatively charged aluminium electrode. The brightness of the electroluminescence decreases in the order perylene > pyrene > triphenylene. Threshold voltages below 20 V and a luminance up to 100 cd m^-2 were observed.     

On the evaluation of elasto-plastic strains measured with strain gages

The analysis of plane-stress conditions using strain gages is feasible even when the deformations of the materials are in the elasto-plastic range. The calculation of stresses from the measured strain values is based on an analysis which requires knowledge of the stress-strain curve of the material as obtained from a uniaxial tensile test. In this paper, the practical procedure of such an analysis is described together with the application of a nomograph to allow a simplified evaluation to be made of the results of measurements. A numerical example is also given.     

Fractionation of cadmium in tobacco and cigarette smoke condensate using XANES and sequential leaching with ICP-MS/MS

Analytical and Bioanalytical Chemistry - Fractionation data for cadmium in tobacco products, as obtained by sequential leaching of cadmium species with ICP-MS/MS analysis, and separately by X-ray...     

The direct precipitation of rhabdophane (REEPO<Subscript>4</Subscript>·<Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O) nano-rods from acidic aqueous solutions at 5–100 °C

The precipitation of lanthanum and neodymium phosphate phases from supersaturated aqueous solutions at pH ~1.9 was studied at 5, 25, 50, and 100 °C in batch reactors for up to 168 h. Crystalline La and Nd–rhabdophane phases precipitated immediately upon mixing of the initial aqueous La or Nd and PO₄ solutions. Changes in aqueous PO₄ and Rare Earth Element (REE) concentrations during the experiments were determined by ICP-MS and UV–Vis spectrophotometry, while the resulting solids were characterized via powder XRD, SEM, TEM, and FTIR. All precipitated crystals exhibited a nano-rod morphology and their initial size depended on temperature and REE identity. At 5 °C and immediately after mixing the La and Nd–rhabdophane crystals averaged ~44 and 40 nm in length, respectively, while at 100 °C lengths were ~105 and 94 nm. After 168 h of reaction, the average length of the La and Nd rhabdophanes increased by 23 and 53% at 5 °C and 11 and 59% at 100 °C, respectively. The initial reactive solutions in all experiments had activity quotients for rhabdophane precipitation: \textREE ³⁺ + \textPO₄^{3 -} + n\textH₂ \textO = \textREEPO₄ ·  n\textH₂ \textO {\text{REE}}^{ 3+ } + {\text{PO}}_{4}^{3 - } + n{\text{H}}_{2} {\text{O}} = {\text{REEPO}}_{4} \cdot\;n{\text{H}}_{2} {\text{O}} of ~10^−20.5. This activity quotient decreased with time, consistent with rhabdophane precipitation. The rapid equilibration of rhabdophane supersaturated solutions and the progressive rhabdophane crystal growth observed suggests that the REE concentrations of many natural waters may be buffered by rhabdophane precipitation. In addition, this data can be used to guide crystallization reactions in industrial processes where monodisperse and crystalline La or Nd rhabdophane materials are the target.     

Polarized electroluminescence of a discotic mesogenic compound

Polarized electroluminescence is observed for a uniaxially aligned sample of a discotic compound in its crystalline state. The alignment was achieved by coating the ITO anode with an aligned film of poly(tetrafluoroethylene) (PTFE) deposited using the friction method. Organic light emitting devices with the layer sequence glass/ITO/PTFE/tetraethyl perylene-3,4,9,10-tetracarboxylate (55 nm)/aluminium (100 nm) show linearly polarized emission of light with a dichroic ratio up to 3.2.