Fire- and heat-resistant matrix resins based on ethynyl-substituted aromatic cyclotriphosphazenes

A novel class of fire- and heat-resistant matrix resins has been synthesized by thermal polymerization of ethynyl-substituted aromatic cyclotriphosphazenes. Thermal polymerization of new tris[4-(4′-ethynylbenzanilido)phenoxy]tris(phenoxy) cyclotriphosphazene ( III ) and tris[4-(4′-ethynylphthalimido)phenoxy]tris(phenoxy)cyclotriphosphazene ( VII ) at 250°C for 1–1.5 h gave tough polymers. The thermal stabilities of the polymers were evaluated in nitrogen and in air by thermogravimetric analysis (TGA). The synthesised polymers were stable to 400–410°C and showed char yield of 78–65% at 800°C in nitrogen and of 78–69% at 700°C in air. The ethynyl-substituted polymer precursor ( III ) was synthesised by the reaction of tris(4-aminophenoxy)tris(phenoxy)cyclotriphosphazene ( I ) with 4-ethynylbenzoyl chloride. The polymer precursor ( VII ) was synthesised by a solution condensation of I with 4-ethynylphthalic anhydride followed by in situ thermal cyclodehydration at 150°C. The structure of polymer precursors was characterized using proton nuclear magnetic resonance (¹H-NMR), infrared (IR) spectroscopy, and elemental analysis. The curing of polymer precursors was monitored by differential scanning calorimetery (DSC) and IR spectroscopy. The synthesised matrix resins are potential candidates for the development of heat- and fire-resistant fiber-reinforced composites. © 1993 John Wiley & Sons, Inc.     

Amino acid functionalized ionomeric materials in biomedical applications

Several N-acryloyl and N-methacryloyl substituted amino acids have been prepared and copolymerized with acrylic acid and itaconic acid to prepare new polyelectrolytes. Due to an acid-base reaction, mixing of the water soluble copolymers with glass powders, having leachable Ca²⁺, Al³⁺, etc., type cations, produces inorganic-organic composites hardened by salt -bridge formation. These heretofore unexplored polyelectrolytes are shown to be very useful for preparing improved dental biomaterials.     

Synthesis and spectral characterization of zinc(II) complexes of N(4)-substituted thiosemicarbazone derived from salicylaldehyde: Structural study of a novel –OH free Zn(II) complex

Five novel zinc(II) complexes of salicylaldehyde 3-hexamethyleneiminyl thiosemicarbazone were synthesized and physico-chemically characterized. The complexes were given the formulae [Zn(HL)₂] (1), [Zn(L)py] (2), [Zn(L)bipy] · 3.5H₂O (3), [Zn(L)phen] · H₂O (4) and [Zn(L)γ-pic] (5). The thiosemicarbazone binds the metal as a dianionic ONS donor ligand in all the complexes, except in 1. Compound 1 is a homoleptic complex with zinc occupying the center of a distorted tetrahedral environment and being coordinated by two azomethine nitrogen and two thiolate sulfur atoms.     

Resistance anomaly and structural disorder in NiSi2 under high pressure

Results of X-ray diffraction, electrical resistance, thermoelectric power measurements and electronic band structure calculations on NiSi₂ under high pressure are reported. The thermoelectric power (TEP) changes sign near 0.5 GPa (from +30 to −20 μV/K). As the pressure is increased, the value of TEP increases further in magnitude and near 7 GPa it becomes −50 μV/K. The pressure vs. resistance curve measured up to 30 GPa using diamond anvil (DAC)-based technique exhibits a broad hump near 12 GPa and exhibits hysteresis on pressure release. The ADXRD patterns up to 42 GPa show a gradual irreversible loss of long-range order in NiSi₂ with the diffraction lines progressively broadening under pressure. The FWHM of the diffraction lines show a rapid increase in the half-widths close to 0.5 GPa and also near 12 GPa. The computed band structure at a compression (without any disorder) corresponding to 12 GPa, exhibits an electronic topological transition (ETT). The rapid increase in disorder above 12 GPa implies that the ETT may be facilitating the structural disorder. It is suggested that the pressure drives the material through a region of entropic and energetic barriers and induces disorder in the material.     

Thermal lens technique to evaluate the fluorescence quantum yield of a schiff base

The fluorescence spectrum of the schiff base obtained from salicylaldehyde and 2-aminophenol is studied using an argon-ion laser as the excitation source and its fluorescence quantum yield (Q_f) is determined using a thermal lens method. This is a nondestructive technique that gives the absolute value of Q_f without the need for a fluorescence standard. The quantum-yield values are calculated for various concentrations of the solution in chloroform and also for various excitation wavelengths. The value of Q_f is relatively high, and is concentration dependent. The maximum value of Q_f obtained is nearly 0.78. The high value of the fluorescence quantum yield will render the schiff base useful as a fluorescent marker for biological applications. Photostability and gain studies will assess its suitability as a laser dye. PACS 42.55.Mv; 42.62.Cf; 42.62.Fi; 42.70.Hj     

Excited atomic state of Li

An optical transition of 3489 A has been shown to arise from Li using beam foil spectroscopic technique. The mean life of the state emitting this radiation has been measured to be 2.23 ä 0.08 n sec.     

A crystallographic study of 2-hydroxyacetophenone N(4)-cyclohexyl thiosemicarbazone

The crystal structure of 2-hydroxyacetophenone N(4)-cyclohexyl thiosemicarbazone is described. The compound crystallizes in the triclinic crystal system, space group , Z = 4, V = 1569.6(3) ?³ with unit cell parameters a = 6.9436(8) ?, b = 12.4762(15) ?, c = 18.588(2) ?, α = 100.187(2)°, β = 97.069(2)° and γ = 92.340(2)°. There are two independent molecules in the asymmetric unit. The crystal structure reveals that the compound exists in the thione form and S1 and N1 are at E configuration to each other with respect to N2-C8 bond. Similarly, S2 and N4 are trans to each other with respect to N5-C23 bond in the second molecule of the asymmetric unit. The packing of the molecules in the crystal lattice is stabilized by intermolecular hydrogen bonds.     

Electrical resistance measurements under pressure on NbTe2 single crystal

Transition metal dichalcogenides, because of their layered structure, are well suited for extreme pressure lubrication. These materials being semiconducting and of layered structure may undergo structural and electronic transitions under pressure. Here we report the details of the preparation and characterization of single crystals of NbTe₂ and the results of electrical resistance measurements under pressure carried out on it to investigate this possibility. Single crystals were grown by the chemical vapor transport technique, using iodine as a transporting agent. The composition of the grown crystals was confirmed on the basis of Energy Dispersive Analysis by X-ray (EDAX) and remaining structural characterization was also accomplished by X-ray Diffraction (XRD) studies. Electrical resistance was measured employing a Bridgman anvil set up to 10?GPa and diamond anvil cell (DAC) assembly up to 25?GPa. A technique slightly modified from that described in the literature for carrying out electrical resistivity measurements in the diamond anvil cell (DAC) under pressure has been standardized.     

KINETIC EFFECTS OF SURFACTANT / POLYMER MIXTURES UPON ACIDIC HYDROLYSIS OF HYDROXAMIC ACIDS

The influence of surfactant / polymer (polyethylene glycol, PEG, mol. wt. = 400) mixtures upon the acidic hydrolysis of two N-substituted hydroxamic acids, i.e., R(CO). N(OH)R' : R = C₆H₅, R' = C₆H₅;4-CH₃C₆H₄ has been studied using cationic (CTAB, TTAB and CPC) and nonionic (TX-100 and Brij-35) surfactants. An inhibitory effect was observed. The results have been explained by Porinoy - Menger model. The critical aggregation concentration and polymer saturation point of the corresponding systems have also been measured with the conductivity and surface tension methods.     

Dialkyl (Alkylene) Dithiophosphate Adducts of Anhydrous Stannous Chloride: Synthesis,Characterization, and Biological Activities

Abstract

Dialkyl (alkylene) dithiophosphate adducts of stannous chloride were synthesized by the reaction of anhydrous tin(II) chloride (SnCl₂) and dialkyl (alkylene) dithiophosphoric acid in a 1:1 molar ratio, under anhydrous reaction conditions, below 5 °C in a closed vessel. The newly synthesized adducts were characterized by physicochemical and spectroscopic techniques [FT-IR, NMR (¹H, ³¹P, and ¹¹⁹Sn), and mass spectrometry]. Coordination modalities have indicated a donor–acceptor interaction between sulfur and tin(II) moieties, where tin(II) acts as a Lewis acid. The adducts were found to have significant antibacterial activity against Escherichia coli and Pseudomonas aeruginosa, and antifungal activity against Aspergillus niger and Candida albicans.

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