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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Chemistry and properties of blends of acetylene terminated materials

As part of a NASA program to develop new high temperature/high performance structural materials, the chemistry and properties of acetylene-containing materials and their cured resins are under investigation. The objective of this work is to develop materials that are readily processable (i.e., 200-300 C and about 1.4 MPa or less) and possess usable mechanical properties at temperatures as high as 177 C. An acetylene-terminated aspartimide (ATA) was blended with an equal weight of an acetylene-terminated arylene ether (ATAE) oligomer. The blend was subsequently thermally cured to yield a resin which was evaluated in the form of neat resin moldings, adhesive specimens, and laminates. Adhesive specimens and laminates gave good mechanical properties to temperatures as high as 177 C. In addition, preliminary laminate work is presented on the resin from a blend of a new N-methyl substituted ATA and an ATAE.

Connell, John W.↗
NASA NTRS1992

Oligomeric baroeffect and gas aggregation states

The baroeffect is analyzed to include a gas that aggregates into higher-order polymers or oligomers. The resulting pressure change is found to vary independently of the molecular weight of the gas components and to depend only on the aggregation or oligomeric order of the gas. With increasing aggregation, diffusive slip velocities are found to increase. The calculations are extended to include general counterdiffusion of two distinct aggregation states (k-, j-mer) for the gas, and the pressure change is derived as a function that is independent of both molecular weight and the absolute aggregation. The only parameter that determines the baroeffect is the ratio of aggregated states, beta = k/j. For gases that reversibly aggregate, possible oscillatory behavior and complex dynamics for pressure are discussed. Gas aggregation may play a role for low-temperature crystal-growth conditions in which vapor concentrations of one (or more) species are high.

Noever, David A.↗
NASA NTRS1991

Preliminary properties of a resin from ethynyl terminated materials

A blend composed of an ethynyl terminated aspartimide (brittle component) and an ethynyl terminated arylene ether oligomer (tough component) was thermally cured to yield a resin which underwent preliminary evaluation to determine the potential for use in structural applications on aerospace vehicles. The blend exhibited good compression moldability, allowing for fabrication of neat moldings, adhesive specimens and composites at temperatures of 250 C under a pressure of 1.4 MPa (200 psi). Neat resin moldings and adhesive specimens provided relatively high mechanical properties. Composite specimens provided promising results in spite of fiber misalignment, fiber washout, and a small amount of panel warpage.

Hergenrother, Paul M.↗
NASA NTRS1992

Comet outbursts and polymers of HCN

Dramatic cometary outbursts have been noted by observers for many years. These outbursts can sometimes increase the apparent brightness of a comet up to 9 mag and release energy on the order of 10 exp 19 ergs. A number of mechanisms have been suggested for outburst activity; however, none has been generally accepted. HCN is a known constituent of both interstellar icy grain mantles and cometary nuclei, and HCN polymers have been postulated to exist on the dark surface of comets such as P/Halley. Since polymerization is a strongly exothermic process, we investigate the possibility that HCN polymerization can provide the energy needed for outbursts. Polymerization may be continuing in the inhomogeneous interior of comets. In addition, the reactive CN groups in these oligomers can be hydrolyzed and may contribute to CO2 and CO pressure buildup in the interior of comets.

Rettig, Terrence W.↗
NASA NTRS1992

Benzonorbornadiene end caps for PMR resins

Several ortho-disubstituted benzonorbornadiene derivatives are described. These molecules contain acid, ester, or anhydride functionality permitting their use as end caps in PMR (polymerization of monomer reactants) polyimide systems. The replacement of the currently used norbornenyl end caps with benzonorbornadienyl end caps affords resins of increased aromatic content. It also allows evaluation of some mechanistic aspects of PMR cross-linking. Initial testing of N-phenylimide model compounds and of actual resin formulations using the benzonorbornadienyl end cap reveals that they undergo efficient thermal crosslinking to give oligomers with physical properties and thermal stability comparable to commercial norbornene-end-capped PMR systems.

Panigot, Michael J.↗
NASA NTRS1993

Unexpected substrate specificity of T4 DNA ligase revealed by in vitro selection

We have used in vitro selection techniques to characterize DNA sequences that are ligated efficiently by T4 DNA ligase. We find that the ensemble of selected sequences ligates about 50 times as efficiently as the random mixture of sequences used as the input for selection. Surprisingly many of the selected sequences failed to produce a match at or close to the ligation junction. None of the 20 selected oligomers that we sequenced produced a match two bases upstream from the ligation junction.

Harada, Kazuo↗
NASA NTRS1994

Phenylethynyl End-Capping Reagents And Reactive Diluents

Compounds containing phenylethynyl group serve as thermally reactive polymer end caps and reactive diluents. Useful in preparation of adhesives, composite matrices, and molding compounds. These reagents transform arylene ether oligomers and polymers into readily processable reactive materials that convert thermally to thermosets. Compounds synthesized for subsequent use in making thermoset polymers. Phenylethynyl group found to offer several unexpected advantages over ethynyl-based analog.

Bryant, Robert G.↗
NASA NTRS1994

Phenylethynyl-Terminated Poly(Arylene Ethers)

Phenylethynyl-terminated poly(arylene ethers) synthesized in wide range of molecular weights by adjusting monomer ratios and adding appropriate amounts of 4-phenylethynyl-4'-fluorobenzophenone to monomers to end-cap oligomers during polymerization. Have low molecular weights and low melt viscosities, and are easily processed as adhesives, composites, and moldings. Thermally cured to provide materials that are crosslinked and insoluble in common organic solvents. Exhibit increased resistance to solvents, greater tensile moduli, and better high-temperature properties. Useful as adhesives, composite matrices, and moldings, especially in applications in which combination of toughness and resistance to solvents needed.

Jensen, Brian J.↗
NASA NTRS1993

Synthesis of novel electrically conducting polymers: Potential conducting Langmuir-Blodgett films and conducting polymers on defined surfaces

Based on previous results involving thiophene derived electrically conducting polymers in which it was shown that thiophene, 3-substituted thiophenes, furans, and certain oligomers of these compounds showed electrical conductivity after polymerization. The conductivity was in the order of up to 500 S/cm. In addition, these polymers showed conductivity without being doped and most of all they were practically inert toward ambient conditions. They even could be used in aqueous media. With these findings as a guide, a number of 3-long-chain-substituted thiophenes and 1-substituted-3-long-chain substituted pyrrols were synthesized as monomers for potential polymeric electrically conducting Langmuir-Blodgett films.

Zimmer, Hans↗
NASA NTRS1994

Solventless, curable fluid oligomeric systems for high performance microwave, acoustical and mechanical applications

While establishing the basis for a 'Technology 2000' product plan several years ago we plugged in the usual factors contributing toward product success: price/performance justifiable; profitable, warranting high quality maintenance, enhancement, and specific property improvement; narrow inventory requirements; and raw material integrable backwards with easily variable properties (molecular weight, functionality, and isomer control). We resolved this by selecting radical functional, low molecular weight polybutadiene liquid polymers. Encouraged by the need for solid rocket binders, several companies embarked on various perceptions of binder performance requirements over four decades ago. Initially dominated by progress of liquid polysulfides, soon a few settled primarily upon polybutadiene based binders. Such an approach in a few instances was exploited quite viably with a series of functional group terminated liquid polybutadienes: hydroxyl, mercaptan, carboxyl, vinyl, and amine. Good results are obtained for oligomers, liquid polymers, and their hybrids. The only significant limits on compounded products has been solvent resistance and oxidative sensitivity, unless sufficient proportion of sulfide or nitrile moiety is incorporated. For convenience, they have been grouped under the trademarks Nylane, Seamax, Oligomax, and Castomax.

Lefave, G. M.↗
NASA NTRS1994

Archean geochemistry of formaldehyde and cyanide and the oligomerization of cyanohydrin

The sources and speciation of reduced carbon and nitrogen inferred for the early Archean are reviewed in terms of current observations and models, and known chemical reactions. Within this framework hydrogen cyanide and cyanide ion in significant concentration would have been eliminated by reaction with excess formaldehyde to form cyanohydrin (glycolonitrile), and with ferrous ion to formferrocyanide. Natural reactions of these molecules would under such conditions deserve special consideration in modeling of primordial organochemical processes. As a step in this direction, transformation reactions have been investigated involving glycolonitrile in the presence of water. We find that glycolonitrile, formed from formaldehyde and hydrogen cyanide or cyanide ion, spontaneously cyclodimerizes to 4-amino-2-hydroxymethyloxazole. The crystalline dimer is the major product at low temperatue (approximately 0 C); the yield diminishes with increasing temperature at the expense of polymerization and hydrolysis products. Hydrolysis of glycolamide and of oxazole yields a number of simpler organic molecules, including ammonia and glycolamide. The spontaneous polymerization of glycolonitrile and its dimer gives rise to soluble, cationic oligomers of as yet unknown structure, and, unless arrested, to a viscous liquid, insoluble in water. A loss of cyanide by reaction with formaldehyde, inferred for the early terrestrial hydrosphere and cryosphere would present a dilemma for hypotheses invoking cyanide and related compounds as concentrated reactants capable of forming biomolecular precursor species. Attempts to escape from its horns may take advantage of the efficient concentration and separation of cyanide as solid ferriferrocyanide, and most directly of reactions of glycolonitrile and its derivatives.

Arrhenius, T.↗
NASA NTRS1993

The RNA-world and co-evolution hypothesis and the origin of life: Implications, research strategies and perspectives

The applicability of the RNA-world and co-evolution hypothesis to the study of the very first stages of the origin of life is discussed. The discussion focuses on the basic differences between the two hypotheses and their implications, with regard to the reconstruction methodology, ribosome emergence, balance between ribozymes and protein enzymes, and their major difficultites. Additional complexities of the two hypotheses, such as membranes and the energy source of the first reactions, are not treated in the present work. A central element in the proposed experimental strategies is the study of the catalytic activites of very small peptides and RNA-like oligomers, according to existing, as well as to yet-to-be-invented scenarios of the two hypothesis under consideration. It is suggested that the novel directed molecular evolution technology, and molecular computational modeling, can be applied to this research. This strategy is assumed to be essential for the suggested goal of future studies of the origin of life, namely, the establishment of a `Primordial Darwinian entity'.

Lahav, Noam↗
NASA NTRS1995

Oligonucleotides as probes for studying polymerization reactions in dilute aqueous solution. 2: Polycondensations

We have prepared a (P-32)-labeled oligonucleotide probe carrying a ureido (-NH-CO-NH2) function at its 3'-terminus. This labeled oligomer was used to study polycondensations of urea and formaldehyde and of various phenols and formaldehyde in aqueous solution. The formation of formaldehyde copolymers attached to the amido-function of the probe was monitored by gel electrophoresis. Our results are generally in agreement with those obtained using conventional techniques. Our method is suitable for monitoring potentially prebiotic polycondensation reactions involving formaldehyde.

Kolb, Vera↗
NASA NTRS1996

Processing and Properties of Fiber Reinforced Polymeric Matrix Composites: Processing Robustness of IM7/PETI Polyimide Composites - Part 2

The processability of a phenylethynyl terminated imide (PETI) resin matrix composite was investigated. Unidirectional prepregs were made by coating an N-methylpyrrolidone solution of the amide acid oligomer onto unsized IM7. Two batches of prepregs were used: one was made by NASA in-house, and the other was from an industrial source. The composite processing robustness was investigated with respect to the effect of B-staging conditions, the prepreg shelf life, and the optimal processing window. Rheological measurements indicated that PETI's processability was only slightly affected over a wide range of B-staging temperatures (from 250 C to 300 C). The open hole compression (OHC) strength values were statistically indistinguishable among specimens consolidated using various B-staging conditions. Prepreg rheology and OHC strengths were also found not to be affected by prolonged (i.e., up to 60 days) ambient storage. An optimal processing window was established using response surface methodology. It was found that IM7/PETI composite is more sensitive to the consolidation temperature than to the consolidation pressure. A good consolidation was achievable at 371 C/100 Psi, which yielded an OHC strength of 62 Ksi at room temperature. However, processability declined dramatically at temperatures below 350 C.

Hou, Tan-Hung↗
NASA NTRS1995

Enzymatic synthesis of polymers containing nicotinamide mononucleotide

Nicotinamide mononucleoside 5'-diphosphate in its reduced form is an excellent substrate for polynucleotide phosphorylase from Micrococcus luteus both in de novo polymerization reactions and in primer extension reactions. The oxidized form of the diphosphate is a much less efficient substrate; it can be used to extend primers but does not oligomerize in the absence of a primer. The cyanide adduct of the oxidized substrate, like the reduced substrate, polymerizes efficiently. Loss of cyanide yields high molecular weight polymers of the oxidized form. Terminal transferase from calf thymus accepts nicotinamide mononucleoside 5'-triphosphate as a substrate and efficiently adds one residue to the 3'-end of an oligodeoxynucleotide. T4 polynucleotide kinase accepts oligomers of nicotinamide mononucleotide as substrates. However, RNA polymerases do not incorporate nicotinamide mononucleoside 5'-triphosphate into products on any of the templates that we used.

Liu, Rihe↗
NASA NTRS1997

Adhesive Properties of Cured Phenylethynyl containing Imides

As part of a program to develop structural adhesives for high performance aerospace applications, several phenylethynyl containing oligomer blends of Larc(TM) MPEI and a reactive plasticizer designated LaRC LV-1 21 were prepared and evaluated. The fully imidized blends exhibited minimum melt viscosity as low as 1000 poise at 371 C. Ti/Ti lap shear specimens fabricated at 316 C under 15 psi gave RT strength of approx. 4300 psi and no change in strength was observed at 177 C. The chemistry and properties of this new MPEI as well as some blends of MPEI with LV-121 are presented and compared to the linear version, LARC(TM)-PETI-5.

Chang, Alice C.↗
NASA NTRS1996

Catalysis of the Oligomerization of O-Phospho-Serine, Aspartic Acid, or Glutamic Acid by Cationic Micelles

Treatment of relatively concentrated aqueous solutions of 0-phospho-serine (50 mM), aspartic acid (100 mM) or glutamic acid (100 mM) with carbonyldiimidazole leads to the formation of an activated intermediate that oligomerizes efficiently. When the concentration of amino acid is reduced tenfold, few long oligomers can be detected. Positively-charged cetyltrimethyl ammonium bromide micelles concentrate the negatively-charged activated intermediates of the amino acids at their surfaces and catalyze efficient oligomerization even from dilute solutions.

Bohler, Christof↗
NASA NTRS1997

Redox Energy and Sulfur Chemistry in Prebiotic Polymer Synthesis and Replication

In the past year we have made significant progress in three research areas: (1) Most importantly, we discovered a new pathway of prebiotic amino acid synthesis in which formaldehyde and glycolaldehyde (substrates of the formose reaction) react with ammonia yielding alanine and homoserine in the presence of thiol catalysts. This thiol-dependent synthesis of amino acids undoubtedly occurs via amino acid thioester intermediates capable of forming peptides. This 'one-pot' reaction system operates under mild aqueous conditions, and like modern amino acid biosynthesis, uses sugar intermediates which are converted to amino acids by energy-yielding redox disproportionation. (2) Finally, in preparation for the analysis of Martian meteorite samples, we upgraded our HPLC system and developed an improved method capable of detecting a I femtomole of amino acid enantiomers. (3) We completed our analysis of the energetics of metabolism that revealed that life depends on biosynthetic processes driven by chemical energy made available by the redox disproportionation of carbon groups of sugars. We established that the favorable energy of redox disproportionation is based on the universal reduction potentials of carbon groups. We concluded that it is hard to imagine any other organic molecule besides sugars (formaldehyde oligomers) having the energy and reactivity needed to drive either modem biosynthesis or the chemical processes behind its origin.

Weber, Arthur L.↗