Some aspects of tailoring flame retardancy in HET-acid-based flame retardants

HET acid was condensed with either ethylene glycol or 1,4-butanediol to yield the respective oligoesters. These oligoesters were characterized by molecular weight, measured by vapor-pressure osmometry. The degradation mechanism of oligoesters of HET acid with either ethylene glycol or 1,4-butanediol was elucidated. The thermal properties of these polyesters were studied using differential thermal analysis and thermal volatilization analysis. The mechanism of degradation was proposed on the basis of pyrolysis–gas chromatography studies, the degradation products being subsequently identified by mass spectrometry. It turned out that in the course of decomposition, hexachlorocyclopentadiene was formed, which is believed to be the active substance for flame retardance in these systems. The aspect of tailoring flame retardancy by changing the chemical environment, i.e., by using different diols, is discussed.     

Reverse micelles dissolved in supercritical xenon: an NMR spectroscopic study

Reverse micelles currently gain increasing interest in chemical technology. They also become important in biomolecular NMR due to their ability to host biomolecules such as proteins. In the present paper, a procedure for the preparation of high-pressure NMR samples containing reverse micelles dissolved in supercritical xenon is presented. These reverse micelles are formed by sodium bis(2-ethylhexyl) sulfosuccinate (AOT). For the first time, NMR spectroscopy could be applied to reverse micelles in supercritical xenon. The AOT/H(2)O/Xe system was studied as a function of experimental parameters such as xenon pressure, water content, and salt concentration. Optimum conditions for reverse micelle formation in supercritical xenon could be determined. It is, furthermore, demonstrated that biomolecules such as amino acids and proteins can be incorporated into the reverse micelles dissolved in supercritical xenon.     

Synthese und Charakterisierung neuer intramolekular stickstoffstabilisierter Organoaluminium‐ und Organogalliumalkoxide

Synthesis and Characterization of New Intramolecularly Nitrogen‐stabilized Organoaluminium‐ and Organogallium Alkoxides The intramolecularly nitrogen stabilized organoaluminium alkoxides [Me₂Al{μ‐O(CH₂)₃NMe₂}]₂ ( 1a ), Me₂AlOC₆H₂(CH₂NMe₂)₃‐2,4,6 ( 2a ), [(S)‐Me₂Al{μ‐OCH₂CH(i‐Pr)NH‐i‐Pr}]₂ ( 3a ) and [(S)‐Me₂Al{μ‐OCH₂CH(i‐Pr)NHCH₂Ph}]₂ ( 4 ) are formed by reacting equimolar amounts of AlMe₃ and Me₂N(CH₂)₃OH, C₆H₂[(CH₂NMe₂)₃‐2,4,6]OH, (S)‐i‐PrNHCH(i‐Pr)CH₂OH, or (S)‐PhCH₂NHCH(i‐Pr)CH₂OH, respectively. An excess of AlMe₃ reacts with Me₂N(CH₂)₂OH, Me₂N(CH₂)₃OH, C₆H₂[(CH₂NMe₂)₃‐2,4,6]OH, and (S)‐i‐PrNHCH(i‐Pr)CH₂OH producing the “pick‐a‐back” complexes [Me₂AlO(CH₂)₂NMe₂](AlMe₃) ( 5 ), [Me₂AlO(CH₂)₃NMe₂](AlMe₃) ( 1b ), [Me₂AlOC₆H₂(CH₂NMe₂)₃‐2,4,6](AlMe₃)₂ ( 2b ), and [(S)‐Me₂AlOCH₂CH(i‐Pr)NH‐i‐Pr](AlMe₃) ( 3b ), respectively. The mixed alkyl‐ or alkenylchloroaluminium alkoxides [Me(Cl)Al{μ‐O(CH₂)₂NMe₂}]₂ ( 6 ) and [{CH₂=C(CH₃)}(Cl)Al{μ‐O(CH₂)₂NMe₂}]₂ ( 8 ) are to obtain from Me₂AlCl and Me₂N(CH₂)₂OH and from [Cl₂Al{μ‐O(CH₂)₂NMe₂}]₂ ( 7 ) and CH₂=C(CH₃)MgBr, respectively. The analogous dimethylgallium alkoxides [Me₂Ga{μ‐O(CH₂)₃NMe₂}]₂ ( 9 ), [(S)‐Me₂Ga{μ‐OCH₂CH(i‐Pr)NH‐i‐Pr}]_n ( 10 ), [(S)‐Me₂Ga{μ‐OCH₂CH(i‐Pr)NHCH₂Ph}]_n ( 11 ), [(S)‐Me₂Ga{μ‐OCH₂CH(i‐Pr)N(Me)CH₂Ph}]_n ( 12 ) and [(S)‐Me₂Ga{μ‐OCH₂(C₄H₇NHCH₂Ph)}]_n ( 13 ) result from the equimolar reactions of GaMe₃ with the corresponding alcohols. The new compounds were characterized by elemental analyses, ¹H‐, ¹³C‐ and ²⁷Al‐NMR spectroscopy, and mass spectrometry. Additionally, the structures of 1a , 1b , 2a , 2b , 3a , 5 , 6 and 8 were determined by single crystal X‐ray diffraction.     

Polymerization of w/o microemulsions for the preparation of transparent SiO2/PMMA nanocomposites

Reverse w/o microemulsions composed of methyl methacrylate (MMA) forming the oil phase, nonionic surfactants, and water are used for the synthesis of transparent SiO2/PMMA nanocomposites. An inorganic precursor, tetraethoxysilane (Si(OEt)(4), TEOS), is hydrolyzed in the reverse micelles containing aqueous ammonia. During the hydrolysis of TEOS, polymerization of the continuous MMA phase is initiated using AIBN (azobisisobutyronitrile), and after thermal polymerization at 333 K for 12 h, solid blocks of PMMA are obtained in which nanometer-sized silica particles are trapped in the solid polymer matrix. According to small-angle X-ray and dynamic light scattering experiments, the water droplets in MMA microemulsions are 12 nm (R(W) = 13) in diameter, whereas after polymerization of the microemulsion, the SiO2 particles in the transparent SiO2/PMMA composites are 26 nm in diameter. Transmission electron micrographs demonstrate a low degree of agglomeration in the composites. In comparison with materials generated from micelle-free solutions, the particle size distribution is narrow. The reverse micelle-mediated approach produces composites of high transparency comparable with that of pure PMMA.     

Perdeuterated Conjugated Polymers for Ultralow‐Frequency Magnetic Resonance of OLEDs

The formation of excitons in OLEDs is spin dependent and can be controlled by electron‐paramagnetic resonance, affecting device resistance and electroluminescence yield. We explore electrically detected magnetic resonance in the regime of very low magnetic fields (<1 mT). A pronounced feature emerges at zero field in addition to the conventional spin‐ Zeeman resonance for which the Larmor frequency matches that of the incident radiation. By comparing a conventional π‐conjugated polymer as the active material to a perdeuterated analogue, we demonstrate the interplay between the zero‐field feature and local hyperfine fields. The zero‐field peak results from a quasistatic magnetic‐field effect of the RF radiation for periods comparable to the carrier‐pair lifetime. Zeeman resonances are resolved down to 3.2 MHz, approximately twice the Larmor frequency of an electron in Earth's field. However, since reducing hyperfine fields sharpens the Zeeman peak at the cost of an increased zero‐field peak, we suggest that this result may constitute a fundamental low‐field limit of magnetic resonance in carrier‐pair‐based systems. OLEDs offer an alternative solid‐state platform to investigate the radical‐pair mechanism of magnetic‐field effects in photochemical reactions, allowing models of biological magnetoreception to be tested by measuring spin decoherence directly in the time domain by pulsed experiments.     

Synthesis and characterization of the open-framework barium bisphosphonate [Ba3(O3PCH2NH2CH2PO3)2(H2O)4].3H2O

Following the strategy of using polyfunctional phosphonic acids for the synthesis of open-framework metal phosphonates, the phosphonocarboxylic acid (H2O3PCH2)2NCH2C6H4COOH was used in the hydrothermal synthesis of new Ba phosphonates. Its decomposition led to the first open-framework barium phosphonate [Ba3(O3PCH2NH2CH2PO3)2(H2O)4].3H2O. The synthesis was also successfully performed using iminobis(methylphosphonic acid), (H2O3PCH2)2NH, as a starting material, and the synthesis was optimized to obtain as a pure material. The reaction setup as well as the pH are the dominant parameters, and only a diffusion-controlled reaction led to the desired compound. The crystal structure was solved from single-crystal data: monoclinic; C2/c; a=2328.7(2), b=1359.95(7), and c=718.62(6) pm; beta=98.732(10) degrees ; V=2249.5(3)x10(6) pm3; Z=4; R1=0.036; and wR2=0.072 (all data). The structure of [Ba3(O3PCH2NH2CH2PO3)2(H2O)4].3H2O is built up from BaO8 and BaO10 polyhedra forming BaO chains and layers, respectively. These are connected to a three-dimensional metal-oxygen-metal framework with the iminobis(methylphosphonic acid) formally coating the inner walls of the pores. The one-dimensional pores (3.6x4 A) are filled with H2O molecules that can be thermally removed. Thermogravimetric investigations and temperature-dependent X-ray powder diffraction demonstrate the stability of the crystal structure up to 240 degrees C. The uptake of N,N-dimethylformamide and H2O by dehydrated samples is demonstrated. Furthermore, IR, Raman, and 31P magic-angle-spinning NMR data are also presented.     

<!?tlsb=‐0.06pt>Zigzag polymer chains in catena‐poly[[[triaqua(isobutyrato‐κO)magnesium(II)]‐μ‐isobutyrato‐κ2O:O′] monohydrate]

The structure of the title compound, {[Mg(C₄H₇O₂)₂(H₂O)₃]·H₂O}_n, features one‐dimensional ...(μ₂‐ib)Mg(μ₂‐ib)Mg... zigzag chains (ib is isobutyrate) parallel to the c axis. The octahedral Mg environment is completed by three fac‐oriented terminal water ligands, as well as one further monodentate end‐on coordinated ib ligand. In the crystal structure, the hydrophobic ib groups are all oriented within one half of the coordination perimeter of each chain, whereas the water ligands, together with hydrogen‐bonded noncoordinated solvent water molecules, define the other half. Along the a axis, neighbouring strands are oriented so that both the hydrophilic and hydrophobic sides are adjacent to each other. This results in an extensive hydrogen‐bonding network within the hydrophilic areas, also involving an additional solvent water molecule per formula unit. There are van der Waals contacts between the aliphatic isopropyl groups of the hydrophobic areas.