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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Isomer effects on polyimide properties

The effect of structure variation on the solubility and glass-transition temperature of polyimide polymers is investigated. The addition of alkyl substituents to an aromatic ring in the polymer molecule, the reduction in the number of imide rings per average polymer chain-length, and a variation in the symmetry of the polymer molecule are studied. The synthesis of key intermediates for the preparation of the monomers required in this investigation is reported along with progress made in the synthesis of polyimide-precursor amines that contain functional groups to allow for post-cure cross-linking.

Stump, B. L.↗
NASA NTRS1975

Flame resistant nontoxic polymer development

A number of homopolymers, copolymers, and terpolymers were synthesized employing styrene and four derivatives of diphenyl-p-styrylphosphine. The various polymeric compositions were prepared by two processes, (1) monomer bulk polymerizations and (2) substitution of preformed polydiphenyl-p-styrylphosphine. Results indicate that the majority of the compositions exhibit superior melting and flame retardant characteristics as compared to polystyrene, but are inferior in molding and film forming capability. Terpolymerization appears to result in the materials with the best overall combination of properties. Toxicological evaluation of three representative basic compositions in the form of molded washers showed that no mortalities occurred among the test animals exposed to the products of the oxidative thermal decomposition of the three materials.

Paciorek, K. L.↗
NASA NTRS1974

The origin of life

Research in the areas of precambrian paleontology, chemical evolution of genetically important monomers, prebiotic dehydration-condensation reactions, organic compounds in meteorites and interstellar space, and biological exploration of the planets is summarized. Fossils in precambrian cherts and findings of eukaryotic cells are described, and recent investigations of prebiotic conditions, energy sources, and starting materials for genetic molecules are outlined. Studies of homogeneous and heterogeneous dehydrations and of nonaqueous thermal dehydrations are described. The detection of amino acids, purines, and pyrimidines in meteorites and of biologically significant molecules in interstellar clouds is discussed, as well as the possibilities of life on Jupiter, Mars, and Titan.

Horowitz, N. H.↗
NASA NTRS1975

Low gravity synthesis of polymers with controlled molecular configuration

Heterogeneous chemical systems have been studied for the synthesis of isotactic polypropylene in order to establish baseline parameters for the reaction process and to develop sensitive and accurate methods of analysis. These parameters and analytical methods may be used to make a comparison between the polypropylene obtained at one g with that of zero g (gravity). Baseline reaction parameters have been established for the slurry (liquid monomer in heptane/solid catalyst) polymerization of propylene to yield high purity, 98% isotactic polypropylene. Kinetic data for the slurry reaction showed that a sufficient quantity of polymer for complete characterization can be produced in a reaction time of 5 min; this time is compatible with that available on a sounding rocket for a zero-g simulation experiment. The preformed (activated) catalyst was found to be more reproducible in its activity than the in situ formed catalyst.

Heimbuch, A. H.↗
NASA NTRS1975

Tailor making high performance graphite fiber reinforced PMR polyimides

Studies performed to demonstrate the feasibility of using the polymerization of monomer reactants (PMR) approach in order to 'tailor-make' processable polyimide matrix resins are described. Monomeric reactant solutions containing the dimethyl ester of 3, 3', 4, 4'-benzophenonetetracarboxylic acid, 4, 4'-methylenedianiline and the monomethyl ester of 5-norborene-2, 3-dicarboxylic acid were used to impregnate Hercules HTS graphite fiber. Six different monomeric reactant stoichiometries were studied. The processing characteristics and elevated temperature mechanical properties of the PMR polyimide/HTS graphite fiber composites are described.

Serafini, T. T.↗
NASA NTRS1975

Processable high temperature resistant polymer matrix materials

A review is presented of studies conducted with addition-cured polyimides, giving particular attention to an improved method involving in situ polymerization of monomer reactants (PMR) on the surface of the reinforcing fibers. The studies show that the PMR approach provides a powerful method for fabricating high performance polymer matrix composites. Significant advantages of the PMR approach are related to the superior high temperature properties of the obtained material, lower cost, greater safety, and processing versatility.

Serafini, T. T.↗
NASA NTRS1975

Effects of multifunctional crosslinking agents on the thermomechanical properties of polyimide films

The potential of high temperature resistant polymers such as polyimides (PI) and polyphenylquinoxalines (PPQ) as matrix resins in fiber-reinforced composites has not been fully realized to date. One of the problems associated with these resins is that they exhibit creep, or thermoplastic yielding under load at temperatures approaching 316 C (600 F). The purpose of this investigation was to further reduce thermoplastic behavior of polyimide resins by substituting a controlled amount of the diamine monomer with crosslinking agents having a higher amine functionality. The knowledge gained from a study of the thermomechanical properties of the crosslinked resins would then be used in the fabrication of fiber-reinforced polyimide composites. This report describes the synthesis and characterization of three new polyfunctional amines. Polyimide films containing varying amounts of the cross-linking agents were prepared, and their properties compared with those of control samples prepared with difunctional amines. The effect of crosslink density on isothermal weight loss, polymer softening, and glass transition temperatures is discussed.

Delvigs, P.↗
NASA NTRS1976

Utilization of oxygen difluoride for syntheses of fluoropolymers

The reaction oxygen difluoride, OF2, with ethylenically unsaturated fluorocarbon compounds is examined. Depending upon the fluorocarbon material and reaction conditions, OF2 can chain extend fluoropolyenes, convert functional perfluorovinyl groups to acyl fluoride and/or epoxide groups, and act as a monomer for an addition type copolymerization with diolefins.

Toy, M. S.↗
NASA NTRS1975

Preliminary evaluation of a novel polyimide adhesive for bonding titanium and reinforced composites

A novel polyimide has been developed which shows promise as an adhesive for bonding titanium-to-titanium, titanium-to-polyimide composite and composite-to-composite with excellent lap shear strengths at room temperature and moderate strengths at 288 C. The adhesive is a high molecular weight polyimide made from commercially available monomers. The use of an ether as the solvent for the polymerization and for application of the polyamic acid enhanced the adhesive properties of the polyimide. At room temperature, P13N/glass composite bonded to titanium or to itself failed primarily in the surface layer of the composite, whereas at 260 C the failure was primarily cohesive. Failure of the P13N/unidirectional HT-S graphite composite-to-titanium bonded composites occurred in the composite regardless of the test temperature. Preliminary shear results with cross-plied P13N/HT-S graphite composite-to-composite specimens showed failure in the bonded surface fibers.

Progar, D. J.↗
NASA NTRS1975

Plasma polymerization of an ethylene-nitrogen gas mixture

A procedure has been developed whereby nitrogen can be incorporated into an organic film from an ethylene-nitrogen gas mixture using an internal electrode capacitively coupled radio frequency reactor. The presence of nitrogen has been shown directly by infrared transmittance spectra and electron spectroscopic chemical analysis data, and further indirect evidence was provided by dielectric measurements and by the reverse osmosis properties of the film. Preparation of a nitrogen containing film did not require vapor from an organic nitrogen containing liquid monomer. Some control over the bonding and stoichiometry of the polymer film was provided by the added degree of freedom of the nitrogen partial pressure in the gas mixture. This new parameter strongly affected the dielectric properties of the plasma polymerized film and could affect the reverse osmosis behavior.

Hudis, M.↗
NASA NTRS1975

Moisture resistant and anti-reflection optical coatings produced by plasma polymerization of organic compounds

The need for protective coatings on critical optical surfaces, such as halide crystal windows or lenses used in spectroscopy, has long been recognized. It has been demonstrated that thin, one micron, organic coatings produced by polymerization of flourinated monomers in low temperature gas discharge (plasma) exhibit very high degrees of moisture resistence, e.g., hundreds of hours protection for cesium iodide vs. minutes before degradation sets in for untreated surfaces. The index of refraction of these coatings is intermediate between that of the halide substrate and air, a condition for anti-reflection, another desirable property of optical coatings. Thus, the organic coatings not only offer protection, but improved transmittance as well. The polymer coating is non-absorbing over the range 0.4 to 40 microns with an exception at 8.0 microns, the expected absorption for C-F bonds.

Hollahan, J. R.↗
NASA NTRS1976

Ice crystal growth in water vapor at high saturation

A simple technique is presented for estimating the energy of formation of monolayer icelike clusters at ice-vapor interfaces. Under the assumptions that the ice surfaces are smooth and sparsely covered with monomers, dimers, etc., in near equilibrium with the vapor, and that the bond energies and configurational entropy dominate the energy of formation, it is found that the basal surfaces prefer triangular embryos with an orientation which reverses from layer to layer, whereas the most stable clusters on the prism surfaces are rectangular in configuration. The preferred prism clusters are determined to have a significantly lower critical energy of formation than the basal clusters due to differences in both corner free energy and configurational entropy. This phenomenon provides a mechanism for strongly anisotropic crystal growth at high saturations.

Bartley, D. L.↗
NASA NTRS1976

Abiotic origin of biopolymers

A variety of methods have been investigated in different laboratories for the polymerization of amino acids and nucleotides under abiotic conditions. They include (1) thermal polymerization; (2) direct polymerization of certain amino acid nitriles, amides, or esters; (3) polymerization using polyphosphate esters; (4) polymerization under aqueous or drying conditions at moderate temperatures using a variety of simple catalysts or condensing agents like cyanamide, dicyandiamide, or imidazole; and (5) polymerization under similar mild conditions but employing activated monomers or abiotically synthesized high-energy compounds such as adenosine 5'-triphosphate (ATP). The role and significance of these methods for the synthesis of oligopeptides and oligonucleotides under possible primitive-earth conditions is evaluated. It is concluded that the more recent approach involving chemical processes similar to those used by contemporary living organisms appears to offer a reasonable solution to the prebiotic synthesis of these biopolymers.

Oro, J.↗
NASA NTRS1977

Soluble, thermally-stable aromatic polyimides

Solubility of aromatic polyimides in organic solvents is increased by additions of dianhydride monomers and substituted diamines. Thermal stability of polymers is retained.

St. Clair, T. L.↗
NASA NTRS1977

A new polyimide laminatine resin

Addition polyimide for composite materials is based on liquid monomers and has significant advantages over most existing high-temperature resins. Essentially solventless prepreg has improved drape, tack.

Barrick, J. D. W.↗
NASA NTRS1977

Metal/polyvinyl pyridine catalytic beads

Processed microspheres of polyvinyl pyridine (PVP), copolymers of PVP and other monomers are utilized as wide range of catalytic materials for different applications.

Rembaum, A.↗
NASA NTRS1976

Flame retardant polyphosphazenes

Three processes for the preparation of polyphosphazenes were investigated: (1) the reaction of bisphosphines with diazides, (2) the condensation of bisdichlorophosphoranes with diamines; and (3) the treatment of bisphosphines with diamines in the presence of carbon tetrachloride followed by base dehydrohalogenation. All products obtained were of low molecular weight; the degree of polymerization did not exceed twelve repeating units. However, several compositions exhibited good thermal stability. No weight loss was observed up to 390 C when heated in air at 5 C/min. Treatment of bisphosphines with either an excess of a diazide or an excess of a diamine in the presence of carbon tetrachloride resulted in the production of difunctional phosphazenes which were respectively, azido and amino terminated. The reaction of these azido terminated extended monomers with bisphosphines did not produce high molecular weight materials. The bis-aminophosphazene prepared for the first time under this contract was successfully incorporated into a polyimide.

Paciorek, K. L.↗