High-Modulus Wholly Aromatic Fibers. I. Wholly Ordered Polyamide-Hydrazides and Poly-1,3,4-oxadiazole—Amides

Several completely ordered polyamide-hydrazide copolymers were prepared via low temperature poly condensation of aromatic diacid chlorides with symmetrical aromatic diamines containing preformed dihydrazide linkages. Highly crystalline, hot-drawn fibers of the polyamide-hydrazide containing only para-oriented phenylene units showed unusually high strength and exceptionally high initial modulus: 10.8 and 508 g/den, respectively, at 2.9% elongation-to-break. The as-spun fibers also exhibited rather high tensile strength and unusually high initial modulus: 8.2 and 291 g/den, respectively, at 9.4% elongation-to-break. The hot-drawn fiber retained considerable strength at elevated temperatures, exhibiting a tenacity of 1.4 g/den and an initial modulus of 169 g/den at 350°C. Heat-aging of the as-spun fiber at 185°C in air showed that 66% of the original tenacity, 41% of the elongation, and 86% of the modulus were retained even after 336 hr. Substitution of as little as 25 mole % meta-oriented phenylene rings for para-oriented ones resulted in loss of the ultra-high strength and modulus, giving tensile properties comparable to those of fibers from wholly aromatic polyamides of the meta-oriented type. Fibers from the polyamide-hydrazides containing 50 mole % meta-oriented rings showed similar properties. Although ordered oxadiazole-amide copolymers were obtained from diamines containing two preformed oxadiazole linkages separated by m-phenylene rings, fibers could not be spun from them. Fiber of an ordered oxadiazole-amide copolymer was obtained, however, by heat treatment of the wholly p-phenylene ordered poly amide-hydrazide copolymer precursor fiber. Such a fiber exhibited a tenacity of 15.3 g/den, 3.6% elongation-to-break, and 564 g/den initial modulus.     

Formal hydride transfer mechanism for photoreduction of 3-phenylquinoxalin-2-ones by amines. Association Of 3-phenylquinoxalin-2-one with aliphatic amines

The photophysical and photochemical behavior of 1-methyl-3-phenylquinoxalin-2-one (MeNQ) and 3-phenylquinoxalin-2-one (HNQ) in the presence of amines is reported. While HNQ fluorescence shows an auxochromic effect and a bathochromic shift with added amines, explained by association of HNQ with amine in the ground state and emission from both excited species HNQ and [HNQ-amine], both MeNQ and HNQ are photoreduced efficiently on irradiation in the presence of amines, leading to the semireduced quinoxalin-2-ones, MeNQH(-) and HNQH(-), respectively, via an electron-proton-electron transfer, with unit quantum yields at high amine concentrations. The semireduced quinoxalin-2-ones XNQH(-) (X = H, Me) revert almost quantitatively to the parent XNQ in a dark thermal reaction with an activation free energy for MeNQH(-) of 17.4 and 25.9 kcal/mol in acetonitrile and benzene, respectively. Kinetic and spectroscopic (UV and NMR) evidence supports the proposed reaction mechanism for the reversible photoreduction.     

Preparation and electrical and magnetic properties of Sr2−xNaxCuO3 (0 ≤ x ≤ 1) solid solutions

Mixed-valence copper(II/III) oxide solid solutions Sr_2?xNa_xCuO₃ (0 ≤ x ≤ 1) have been prepared by solid-state reactions in oxygen atmosphere. All solid solutions exhibit the structure of Sr₂CuO₃ (S.G. Immm). Electrical conductivity and thermoelectric power measurements show a semiconducting behavior in the whole composition range. The electronic structure of Sr₂CuO₃ is compared with that of La₂CuO₄ on the basis of an iono-covalent model. Interpretation of transport properties suggests the formation of small polarons. Magnetic susceptibility and EPR measurements show that the antiferromagnetic ordering of Sr₂CuO₃ tends to vanish as x increases, however magnetic interactions are still strong for a concentration of Cu²⁺ ions corresponding to x = 0.8.     

Electrochemical properties of perovskite and A<Subscript>2</Subscript>MO<Subscript>4</Subscript>-type oxides used as cathodes in protonic ceramic half cells

Three selected materials have been prepared and shaped as cathode of half cells using the proton-conducting electrolyte BaCe_0.9Y_0.1O_3 − δ (BCY10): two perovskite compounds, Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3 − δ (BSCF) and La_0.6Sr_0.4Fe_0.8Co_0.2O_3 − δ (LSFC), and the praseodymium nickelate Pr₂NiO_4 + δ (PRN) having the K₂NiF₄-type structure. The electrochemical properties of these compounds have been studied under zero current conditions (two-electrode cell) and under polarization (three-electrode cell). Their measured area-specific resistances were about 1–2 Ω cm² at 600 °C. Under direct current polarization, it appears that the three compounds show almost similar values of current densities at 625 °C; however, at lower temperatures, BSCF appears to be the most efficient cathode material.     

Investigation on double perovskite Ba4Ca2Ta2O11

The structure, conductivity and water uptake of the oxygen-deficient perovskite-type compound Ba₄Ca₂Ta₂O₁₁ have been investigated. Ba₄Ca₂Ta₂O₁₁ crystallizes in the cryolite structure (cubic, Fm3m SG) with a = 8.4508(2) Å, under dry air. The compound can be partially hydrated up to a maximum water content of approximately 0.52 mol H₂O per mol Ba₄Ca₂Ta₂O₁₁. In moist air, the structure symmetry becomes monoclinic (C2/m) and the temperature dependence of total conductivity shows a different behavior because of changes in transport mechanism. Three regions can be observed as a function of temperature. For the low temperature range 200–400 °C, the protonic conduction is prevailing with an activation energy E_A = 0.85 eV. In the intermediate temperature range (400–600 °C), O²⁻ anionic and protonic conductions are mixed with an activation energy E_A = 0.45 eV and in the third region, for temperatures above 600 °C, O²⁻conduction is prevailing with an activation energy E_A = 0.85 eV.     

ABSORPTION AND EMISSION STUDIES OF ELECTRONIC STATES OF N-ARYLBENZAMIDES

Abstract— Absorption and emission spectra of several N-arylbenzamides have been measured. The quantum yields for their fluorescence were found to be dependent on matrix viscosity and temperature. Singlet-triplet splittings for these compounds were determined from their emission spectra and found to be abnormally small for π. π* states (˜ 1500 cm^-1). Indeed, the phosphorescence maxima of N-arylbenzamides occur slightly to the blue relative to their fluorescence maxima. Intersystem crossing efficiencies were determined for several of these compounds and are consistent with S₁→ S ₀ radiationless decay.     

Photolyse stéréosélective des [α-tétrahydropyrannyloxy] -2 tétrahydropyrones-3

The photochemical irradiation of the 2-[sα-tetrahydropyrannyl-oxy]-3-tetrahydropyrones (3) gives the -3-tetrahydropyrone (6)and the α-valerolactone (7). the structures (S*, R*) or (S*, S*) which were determined by mmr and by comparison with the 2-[α-tetrahydropyrannyloxy]-2tetrahydropyrannes (5) (S*, R*) and (S*, S*) influence the rate of the photolysis     

Detection of beta-1,3-glucanase activity after native polyacrylamide gel electrophoresis: application to tobacco pathogenesis-related proteins

Beta-1,3-Glucanase (laminarinase) activity was detected after polyacrylamide gel electrophoresis under native conditions by using laminarin as substrate. Following incubation of gels, laminarin was stained with Aniline Blue. Under UV illumination, lysis zones appeared as dark bands against a fluorescent background. As low as 0.001 unit of commercial Penicillium laminarinase could be observed after incubating the polyacrylamide gel for 45 min at pH 5.0. Extracts of commercial Penicillium laminarinase exhibited four bands with lytic activity towards laminarin. Analysis of intercellular fluid extracts of tobacco mosaic virus-infected tobacco leaves revealed four beta-1,3-glucanases corresponding to three acidic pathogenesis-related proteins, b4 (2), b5 (N) and b6b (0), and one basic protein. The presence of laminarin in gels retarded the migration of some proteins with beta 1,3-glucanase activity. This change in electrophoretic mobility could be used as a complementary affinity test for identifying proteins with beta-1,3-glucanase activity.