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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Carbon-rich ceramic composites from ethynyl aromatic precrusors

A number of polyfunctional aromatic acetylenes thermally polymerize at low temperatures (180 C) and pyrolyze with greater than 90 char yield. In nonoxidizing environments, they are thermally stable to 1450 C. These monomers were chosen as the basis of a model system to study the fabrication and mechanical properties of continuous filament ceramic matrix composite. Composites were fabricated from aryl poly(acetylenes), SiC particulate filler and graphite, Avco SiC, Nicalon and Nextel fibers. Microstructure, physical and mechanical properties are reported.

Hurwitz, F. I.↗
NASA NTRS1985

A new emission feature in IRAS spectra and the polycyclic aromatic hydrocarbon spectrum

IRAS spectra of those sources which show strong 7.7 and 11.3 micron emission features also show a plateau of emission extending from 11.3 to about 13.0 microns. Like the 11.3 micron feature, this new feature is attributed to the CH out-of-plane bending mode in polycyclic aromatic hydrocarbons (PAHs). Its discovery reinforces the identification of the 'unidentified infrared emission features' as emission from PAHs. The wavelength of this new feature suggests that interstellar PAHs are not as partially hydrogenated as hitherto thought. It also constrains their molecular structure.

Cohen, M.↗
NASA NTRS1987

Cross-Linking Aromatic Polymers With Ionizing Radiation

Resistance to heat and solvents increased. Certain aromatic polymers containing radiation-sensitive methylene groups cross-linked through methylene groups upon exposure to ionizing radiation. Cross-linked polymers resistant to most organic solvents and generally more resistant to high temperatures, with less tendency to creep under load. No significant embrittlement of parts fabricated from these polymers when degree of cross-linking, as controlled by irradiation dose, kept at moderate level.

Bell, Vernon L.↗
NASA NTRS1986

Identification of polycyclic aromatic hydrocarbons

The nature of the Very Small Grains evidenced by K. Sellgren (1985) is discussed. Thsir stability suggests that they are graphitic material and specifically Polycyclic Aromatic Hydrocarbons (PAHs). The expected infrared emission of a typical PAH, coronene, gives an impressive spectroscopic agreement with the five observed Unidentified IR Emission Features, leading to an unambiguous identification. Those PAHs are the most abundant organic molecules detected to date (f is approximately .00001).

Leger, A.↗
NASA NTRS1986

The possible existence of interstellar Polycyclic Aromatic Hydrocarbons (PAHs) in collected interplanetary dust particles

Extraterrestrial dust particles which are 3 to 50 microns in size are routinely collected in the stratosphere and are now available for general laboratory study. These grains represent true Interplanetary Dust Particles (IDPs). Issues associated with the carbon containing components of IDPs which occur in a variety of physical forms, including amorphous mantles and matrix materials, are addressed. The observed properties of the hydrocarbon phase in IDPs are compared with those expected for polycyclic aromatic hydrocarbons (PAHs).

Sandford, S. A.↗
NASA NTRS1986

Soluble aromatic polyimides for film and coating applications

Linear all-aromatic polyimides have been synthesized and characterized which show much potential as films and coatings for electronic applications. Structure-property relations with regard to methods for obtaining solubility of fully imidized polymers will be discussed. Methods used to obtain solubility include variation of polymer molecular structure, variation of isomerism of the diamine monomer, modification of cure time/temperature and atmosphere. Other properties of soluble polyimides will be presented which include glass transition temperatures, thermooxidative stabilities, UV-visible spectra, and refractive indices.

St.clair, Anne K.↗
NASA NTRS1987

The oxidation degradation of aromatic compounds

A series of experiments were conducted which focused on understanding the role that the O atom addition to aromatic rings plays in the oxidation of benzene and toluene. Flow reactor studies of the oxidation of toluene gave an indication of the amount of O atoms available during an oxidation and the degree to which the O atom adds to the ring. Flow reactor studies of the oxidation of toluene and benzene to which NO2 was added, have shown that NO2 appears to suppress the formation of O atoms and consequently reduce the amount of phenols and cresols formed by O atom addition. A high temperature pyrolysis study of phenol has confirmed that the major decomposition products are carbon monoxide and cyclopentadiene. A preliminary value for the overall decomposition rate constant was also obtained.

Brezinsky, Kenneth↗
NASA NTRS1987

Polyenamines from aromatic diacetylenic diketones and diamines

The synthesis and characterization of several polyenamine ketones are discussed wherein conjugated diacetylenic diketones and aromatic diamines are used as a route to the formation of high molecular weight polyenamine ketones which exhibit good mechanical properties and can be cast into creasible films. Typical polymerization conditions involved the reaction of stoichiometric amounts of 1,4- or 1,3-PPPO and a diamine at 60 to 130 C in m-cresol at (w/w) solids content of 8 to 26% for a specified period of time under a nitrogen atmosphere. Novel polyenamine ketones were prepared with inherent viscosities as high as 1.99 dl/g and tough, clear amber films with tensile strengths of 12,400 psi and tensile moduli of 397,000 psi were cast from solutions of the polymers in chloroform. In most cases, the elemental analyses for the polyenamine ketones agree within + or - 0.3% of the theoretical values.

Hergenrother, Paul M.↗
NASA NTRS1986

Polycyclic aromatic hydrocarbons and the diffuse interstellar bands

The profiles, widths and positions of the Diffuse Interstellar Bands (DIB's) are discussed. It is shown that the carriers of the DIB's are molecular rather than impurities in grains. Polycyclic Aromatic Hydrocarbons (PAH's) are attractive candidates for the DIB's, in view of their likely abundance, their extreme stability, and the fact that these molecules, and their corresponding radicals, show visible transitions.

Van Der Zwet, G. P.↗
NASA NTRS1987

Anharmonicity and the interstellar polycyclic aromatic hydrocarbon infrared emission spectrum

The hypothesis that interstellar infrared emission originates from vibrationally excited polycyclic aromatic hydrocarbons (PAHs) requires that emission can arise from all vibrational levels that are energetically accessible. Due to anharmonicity, the emission from the upper vibrational levels is shifted to longer wavelengths from that of the v = 1-0 transition. It is shown that structure in the 3-micron region is readily and quantitatively explained by emission from upper vibrational levels of excited PAHs that contain a maximum of 20-30 carbon atoms. The asymmetrical broadening of the 11.3-micron emission band may also be due to anharmonicity.

Barker, John R.↗
NASA NTRS1987

Interstellar polycyclic aromatic hydrocarbons and carbon in interplanetary dust particles and meteorites

Raman spectra of interplanetary dust particles (IDPs) and meteorites containing material similar to polycyclic aromatic hydrocarbons (PAHs) show features that are similar in position and relative strength to interstellar IR emission features attributable to vibrational transitions in free molecular-sized PAHs. In addition, these spectra sometimes show red photoluminescence that has elsewhere been attributed to PAHs, and a part of the carbonaceous phase in IDPs and meteorites contain a degree of deuterium enrichment anticipated in small, free PAHs that are exposed to ISM UV radiation. These observations suggest that some of the IDPs' carbonaceous material may have been produced in circumstellar dust shells, and only slightly modified in interstellar space.

Allamandola, L. J.↗
NASA NTRS1987

Cure study of soluble aromatic polyimide films

Several soluble aromatic poly(amic acid) films were staged at intervals to 325 C and characterized by IR spectroscopy and various solution property techniques. A series of films in which the polymer had been endcapped in an effort to control chain extension was also examined. Much of the behavior observed is consistent with an interpretation that a reduction in molecular weight occurred during cure before the ultimate molecular weight was achieved as a polyimide.

Young, Philip R.↗
NASA NTRS1987

Soluble aromatic polyimides for film and coating applications

Linear all-aromatic polyimides have been synthesized and characterized which show much potential as films and coatings for electronic applications. Structure-property relations with regard to methods for obtaining solubility of fully imidized polymers will be discussed. Methods used to obtain solubility include variation of polymer molecular structure, variation of isomerism of the diamine monomer, modification of cure time/temperature and atmosphere. Other properties of soluble polyimides will be presented which include glass transition temperatures, thermooxidative stabilities, UV-visible spectra, and refractive indices.

St.clair, Anne K.↗
NASA NTRS1987

Soluble aromatic polyimides for film and coating applications

The effect of changing isomeric points of attachment of phenoxy units in the diamine portion of several all-aromatic polyimide systems on the solubility of these materials were investigated. It was found that solubility could be enhanced by the presence of meta and ortho isomer links in the diamine portion of the molecule. The soluble phenoxy-linked polyimides yield tough flexible colorless to pale-yellow transparent films from solutions of chlorinated solvents, with high potential for use in electronic applications.

St. Clair, Anne K.↗
NASA NTRS1988

Polyenamines from aromatic diacetylenic diketones and diamines

The synthesis and characterization of several ployenamine ketones are discussed wherein conjugated diacetylenic diketones and aromatic diamines are used as a route to the formation of high molecular weight polyenamine ketones which exhibit good mechanical properties and can be cast into creasible films. Typical polymerization conditions involved the reaction of stoichiometric amounts of 1,4- or 1,3-PPPO and a diamine at 60°-130° C. in m-cresol at (w/w) solids content of 8-26% for a specified period of time under a nitrogen atmosphere. Novel polyenamine ketones were prepared with inherent viscosities as high as 1.99 dl/g and tough, clear amber films with tensile strengths of 12,400 psi and tensile moduli of 397,000 psi were cast from solutions of the polymers in chloroform. The polymers exhibited T g s as high as 235° C. and weight losses of 14% after aging at 232° C. in circulating air for sixty hours. The specific conditions for the preparation of the various polyenamine ketones are presented in Table I. In most cases, the elemental analyses for the polyenamine ketones, shown in Table II, agree within ±0.3% of the theoretical values.

Paul M Hergenrother↗
NASA NTRS1988

Flexible backbone aromatic polyimide adhesives

Continuing research at Langley Research Center on the synthesis and development of new inexpensive flexible aromatic polyimides as adhesives has resulted in a material identified as LARC-F-SO2 with similarities to polyimidesulfone, PISO2, and other flexible backbone polyimides recently reported by Progar and St. Clair. Also prepared and evaluated was an endcapped version of PISO2. These two polymers were compared with LARC-TPI and LARC-STPI, polyimides research in our laboratory and reported in the literature. The adhesive evaluation, primarily based on lap shear strength (LSS) tests at RT, 177 C and 204 C, involved preparing adhesive tapes, conducting bonding studies and exposing lap shear specimens to 204 C air for up to 1000 hrs and to a 72-hour water boil. The type of adhesive failure as well as the Tg was determined for the fractured specimens. The results indicate that LARC-TPI provides the highest LSSs. LARC-F-SO2, LARC-TPI and LARC-STPI all retain their strengths after thermal exposure for 1000 hrs and PISO2 retains greater than 80 percent of its control strengths. After a 72-hr water boil exposure, most of the four adhesive systems showed reduced strengths for all test temperatures although still retaining a high percentage of their original strength (greater than 60 percent) except for one case. The predominant failure type was cohesive with no significant change in the Tgs.

Progar, Donald J.↗
NASA NTRS1989

Radiation-resistant, amorphous, all-aromatic poly(arylene ether sulfones) - Synthesis, physical behavior, and degradation characteristics

The effects of Co-60 gamma radiation on a series of poly(arylene ether sulfones) prepared by nucleophilic activated aromatic substitution are investigated experimentally. The preparation of the test compounds is described, and the test results are presented in extensive tables and graphs. Radiation-induced degradation, as measured by SO2 production, was found to be lowest in compounds based on biphenol rather than bisphenol A; these findings were also well correlated with ultimate-tensile-strain measurements.

Lewis, D. A.↗