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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Imide/Arylene Ether Copolymers

New imide/arylene ether copolymers prepared by reacting anhydride-terminated poly(amic acids) with amine-terminated poly(arylene ethers) in polar aprotic solvents. Each resulting copolymer may have one glass-transition temperature or two, depending on chemical structure and/or compatibility of block units. Most of copolymers form tough, solvent-resistant films with high tensile properties. Films cast from solution tough and flexible, and exhibit useful thermal and mechanical properties. Potentially useful as moldings, adhesives, or composite matrices. Because of flexible arylene ether blocks, these copolymers easier to process than polyimides.

Jensen, Brian J.↗
NASA NTRS1993

Freeze-Drying Makes Improved IPN And Semi-IPN Polymers

Novel process developed for production of interpenetrating polymer networks (IPN's) or semi-IPN's with greater fracture toughness and resistance to microcracks. Process controls degree of phase separation in IPN's. In experiment, IPN's and semi-IPN's formed by dissolving constituents in another common solvent in traditional method. Resins and composite materials produced were tested for both traditional and freeze-drying processes. Glass-transition temperatures and data from dynamic mechanical tests of freeze-dried IPN's and semi-IPN's demonstrated freeze-drying process provided much improved IPN's and semi-IPN's.

Pater, Ruth H.↗
NASA NTRS1994

Polyimides Containing Pendent Ethynyl Groups

Series of novel diamines containing pendent ethynyl groups synthesized and reacted with various dianhydrides to form polyamide acids cyclodehydrated to form polyimides containing pendent ethynyl groups. Copolyimides of these diamines and other diamines also prepared. Upon heating, ethynyl groups in these polymers react with one another to form cross-linked molecular structures. As result of curing reaction, resistance to solvents, glass-transition temperature, and modulus of elasticity of polymer of this type generally increase, accompanied by corresponding decrease in tensile elongation and toughness. Cured polymers used as films, moldings, adhesives, and composite matrices.

Hergenrother, Paul M.↗
NASA NTRS1994

Acetylene- and Phenylacetylene-Terminated Poly(Arylene Ether Benzimidazole)s (PAEBI's)

Polymers prepared by first synthesizing polymers terminated with hydroxy groups, then reacting them with either 4-ethynylbenzoyl chloride or 4-fluoro-4'-phenylethynylbenzophenone. Endcapped polymers thermally cured to yield materials with attractive combination of properties. Cured acetylene-and phenylacetylene-terminated PAEBI's exhibit higher glass-transition temperatures and better retention of mechanical properties at high temperatures. Cured acetylene- and phenylacetylene-terminated polymers exhibit excellent adhesion to copper foil and polyimide film. Potentially useful as adhesives, coatings, composite matrices, fibers, films, membranes, and moldings.

Connell, John W.↗
NASA NTRS1994

Modified LaRC(TM)-IA Polyimides

Modified versions of thermoplastic polyimide LaRC(TM)-IA incorporate various amounts of additional, rigid moieties into backbones of LaRC(TM)-IA molecules. Modified versions more resistant to solvents and exhibit higher glass-transition temperatures, yet retain melt-flow processability of unmodified LaRC(TM)-IA.

St. Clair, Terry L.↗
NASA NTRS1994

Oligomers Terminated By Maleimide And Acetylene

Oligomeric molecules terminated with maleimide and acetylene groups synthesized and thermally treated to form cross-linked polymers exhibiting high or undetectable glass-transition temperatures and high thermo-oxidative stabilities. Compounds used to make thermally stable, glassy polymers.

St. Clair, Terry L.↗
NASA NTRS1994

Phenylethynyl-Terminated Polyimides

Phenylethynyl-terminated polyimides exhibit properties suitable for films, moldings, adhesives, and composite-material matrices. Polyimides synthesized at various molecular weights, selected to obtain desirable properties for specific applications. Thermally cured to form cross-linked molecular structures typically increasing resistance to solvents, glass-transition temperatures, and moduli of elasticity. Also have low molecular weights and low melt viscosities for easier processing into composites and adhesive bonds.

Jensen, Brian J.↗
NASA NTRS1995

Poly(Arylene Ether)s Containing Pendent Ethynyl Groups

Poly(arylene ether)s containing pendent ethynyl groups synthesized. Offer advantage over linear poly(arylene ether)s in upon heating, pendent ethynyl groups react to form cross-linked molecular structures exhibiting greater resistance to solvents and higher glass-transition temperatures and tensile moduli. Polymers useful as adhesives, moldings, films, and matrices of composite materials.

Hergenrother, Paul M.↗
NASA NTRS1995

LaRC(TM)-IA Copolyimides

Copolyimides modified versions of LaRC(TM)-IA thermoplastic polyimide formulated by incorporating moieties of 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and, alternatively, isophthaloyldiphthalic anhydride (IDPA) into LaRC(TM)-IA polymer backbones. Exhibit higher glass-transition temperatures and retain greater fractions of lower-temperature shear moduli at higher temperatures. Copolyimides spun into fibers or used as adhesives, molding powders, or matrix resins in many applications, especially in fabrication of strong, lightweight structural components of aircraft.

St. Clair, Terry L.↗
NASA NTRS1995

A polyimide molecular composite

A polyimide is a hard and sturdy thermoplastic made from the combination of tetracarboxylic dianhydrides and diamines in a polar aprotic solvent. A series of polyimide blends comprising of a tough moldable, wholly aromatic polyimide and a highly crystalline rigid polyimide were prepared. The flexible polyimide was based on LaRC-SI with a 2% offset, and the rigid polyimide as based on para-phenylenediamine and biphenyltetracarboxylic dinnhydride encapped with pthalic anhydride. The polyimide blends were cast as films and cured at 100, 200, and 300 C in air. These films were characterized by finding their glass-transition temperature, melting temperature, coefficient of thermal expansion, tensile modulus, tensile strength, and percent elongation. These characterizations found out which polyimide blend had exceptional mechanical and thermal properties. Experimental results showed the following: (1) A blend with increasing amounts of flexible polyimide produced a better film; (2) A blend with increasing amounts of rigid polyimide produced a brittle film; (3) LaRC-SI (2% offset) tended to phase separate during film casting; (4) Most of the films produced were brittle; and (5) There was an inability to obtain mechanical and thermal properties due to having brittle film. These conclusions demonstrate the difficulty in producing a polyimide blend comprising two physically distinct polyimides. Combining a polysmide with a poly(amic acid) thermosett could be the next phase of research in polyimide synthesis.

Hart, Aprill J.↗
NASA NTRS2006

Polyimides From a-BPDA and Aromatic Diamines

Polymers having low color and a favorable combination of other properties, including high glass-transition temperature (Tg) and high mechanical properties (strength, tensile modulus, and toughness) will find use in a variety of terrestrial and space applications. Some of the space applications will be in thin films used as membranes on antennas, solar concentrators, coatings on second-surface mirrors, solar sails, sunshades, thermal and optical coatings, and multi-layer thermal insulation blankets. Depending upon the application, the film will be required to exhibit a unique combination of such properties as resistance to degradation by ultraviolet light, visible light, and electrons; low color and/or low solar absorptivity; resistance to tearing and/or wrinkling during packaging and deployment; and high mechanical properties (e.g. high strength, stiffness, and toughness).

Hergenrother, Paul M.↗
NASA NTRS2006

Automated Low-Gravitation Facility Would Make Optical Fibers

A report describes a proposed automated facility that would be operated in outer space to produce high-quality optical fibers from fluoride-based glasses, free of light-scattering crystallites that form during production in normal Earth gravitation. Before launch, glass preforms would be loaded into a mechanism that would later dispense them. A dispensed preform would be melted, cooled to its glass-transition temperature rapidly enough to prevent crystallization, cooled to ambient temperature, then pushed into a preform tip heater, wherein it would be reheated to the softening temperature. A robotic manipulator would touch a fused silica rod to the softened glass to initiate pulling of a fiber. The robot would pull the fiber to an attachment on a take-up spool, which would thereafter be turned to pull the fiber. The diameter of the fiber would depend on the pulling speed and the viscosity of the glass at the preform tip. Upon depletion of a preform, the robot would place the filled spool in storage and position an empty spool to pull a fiber from a new preform. Pulling would be remotely monitored by a video camera and restarted by remote command if a break in the fiber were observed.

Tucker, Dennis S.↗
NASA NTRS2005

Reactive Additives for Phenylethynyl-Containing Resins

Phenylethynyl-containing reactive additive (PERA) compounds and mixtures have been found to be useful for improving the processability of oligomers, polymers, co-oligomers, and copolymers that contain phenylethynyl groups. The additives can be incorporated in different forms: A solution of an amide acid or an imide of a PERA can be added to a solution of phenylethynyl-containing oligomer, polymer, co-oligomer, or copolymer; or An imide powder of a PERA can be mixed with a dry powder of a phenylethynyl-containing oligomer, polymer, co-oligomer, or copolymer. The effect of a given PERA on the processability and other properties of the resin system depends on whether the PERA is used in the amide acid or an imide form. With proper formulation, the PERA reduces the melt viscosity of the resin and thereby reduces the processing pressures needed to form the adhesive bonds, consolidate filled or unfilled moldings, or fabricate fiber-reinforced composite laminates. During thermal cure, a PERA reacts with itself as well as with the phenylethynyl-containing host resin and thereby becomes chemically incorporated into the resin system. The effects of the PERA on mechanical properties, relative to those of the host resin, depend on the amount of PERA used. Typically, the incorporation of the PERA results in (1) increases in the glass-transition temperature (Tg), modulus of elasticity, and parameters that characterize behavior under compression, and (2) greater retention of the aforementioned mechanical properties at elevated temperatures without (3) significant reduction of toughness or damage tolerance. Of the formulations tested thus far, the ones found to yield the best overall results were those for which the host resin was the amide acid form of a phenylethynyl-terminated imide (PETI) co-oligomer having a molecular weight of 5,000 g/mole [hence, designated PETI-5] and a PERA denoted as PERA-1. PETI-5 was made from 3,3',4'4'-biphenyltetracarboxylic dianhydride, 3,4'-oxydianiline (3,4'-ODA), 1,3-bis(3-aminophenoxy) benzene (1,3-APB), and 4-phenylethynylphthalic anhydride (PEPA). PERA-1 was made from 3,5-diamino- 4.-phenylethynylbenzophenon and equimolar amounts of phthalic anhydride and PEPA. To make PERA-1 in the imide form, the aforementioned ingredients were processed by refluxing in glacial acetic acid. To make the amide form of PERA-1, the ingredients were reacted in N-methyl-2-pyrrolidinone (NMP) under nitrogen at a temperature of 23 C (see figure). On the basis of the processability and other properties, a blend comprising 20 weight percent of PERA-1 and 80 weight percent PETI-5 was selected for further evaluation. Relative to neat PETI-5, the blend exhibited an increase in Tg; improved processability; and comparable values of shear strength in adhesion to titanium panels, open-hole compressive properties, compression properties after impact, and resistance to microcracking.

Connell, John W.↗
NASA NTRS2005

Stable Polyimides for Terrestrial and Space Uses

Polyimides of a recently developed type have an attractive combination of properties, including low solar absorptivity (manifested as low color) when cast into thin films, resistance to atomic oxygen and ultraviolet radiation, solubility in organic solvents, high glass-transition temperatures, and high thermal stability. The focus of the development work was on polymers that can endure the space environment and that have specific combinations of properties for use on Gossamer spacecraft. Because of their unique combination of properties, these polymers are also expected to find use in a variety of other applications on Earth as well as in space. Examples of other space applications include membranes on antennas, second-surface mirrors, thermal optical coatings, and multilayer thermal insulation. For both terrestrial and space applications, these polyimides can be processed into various forms, including films, fibers, foams, threads, adhesives, and coatings.

Connell, John W.↗
NASA NTRS2005

Improved Charge-Transfer Fluorescent Dyes

Improved charge-transfer fluorescent dyes have been developed for use as molecular probes. These dyes are based on benzofuran nuclei with attached phenyl groups substituted with, variously, electron donors, electron acceptors, or combinations of donors and acceptors. Optionally, these dyes could be incorporated as parts of polymer backbones or as pendant groups or attached to certain surfaces via self-assembly-based methods. These dyes exhibit high fluorescence quantum yields -- ranging from 0.2 to 0.98, depending upon solvents and chemical structures. The wavelengths, quantum yields, intensities, and lifetimes of the fluorescence emitted by these dyes vary with (and, hence, can be used as indicators of) the polarities of solvents in which they are dissolved: In solvents of increasing polarity, fluorescence spectra shift to longer wavelengths, fluorescence quantum yields decrease, and fluorescence lifetimes increase. The wavelengths, quantum yields, intensities, and lifetimes are also expected to be sensitive to viscosities and/or glass-transition temperatures. Some chemical species -- especially amines, amino acids, and metal ions -- quench the fluorescence of these dyes, with consequent reductions in intensities, quantum yields, and lifetimes. As a result, the dyes can be used to detect these species. Another useful characteristic of these dyes is a capability for both two-photon and one-photon absorption. Typically, these dyes absorb single photons in the ultraviolet region of the spectrum (wavelengths < 400 nm) and emit photons in the long-wavelength ultraviolet, visible, and, when dissolved in some solvents, near-infrared regions. In addition, these dyes can be excited by two-photon absorption at near-infrared wavelengths (600 to 800 nm) to produce fluorescence spectra identical to those obtained in response to excitation by single photons at half the corresponding wavelengths (300 to 400 nm). While many prior fluorescent dyes exhibit high quantum yields, solvent-polarity- dependent fluorescence behavior, susceptibility to quenching by certain chemical species, and/or two-photon fluorescence, none of them has the combination of all of these attributes. Because the present dyes do have all of these attributes, they have potential utility as molecular probes in a variety of applications. Examples include (1) monitoring curing and deterioration of polymers; (2) monitoring protein expression; (3) high-throughput screening of drugs; (4) monitoring such chemical species as glucose, amines, amino acids, and metal ions; and (5) photodynamic therapy of cancers and other diseases.

Meador, Michael↗
NASA NTRS2003

Lightweight, Self-Deployable Wheels

Ultra-lightweight, self-deployable wheels made of polymer foams have been demonstrated. These wheels are an addition to the roster of cold hibernated elastic memory (CHEM) structural applications. Intended originally for use on nanorovers (very small planetary-exploration robotic vehicles), CHEM wheels could also be used for many commercial applications, such as in toys. The CHEM concept was reported in "Cold Hibernated Elastic Memory (CHEM) Expandable Structures" (NPO-20394), NASA Tech Briefs, Vol. 23, No. 2 (February 1999), page 56. To recapitulate: A CHEM structure is fabricated from a shape-memory polymer (SMP) foam. The structure is compressed to a very small volume while in its rubbery state above its glass-transition temperature (Tg). Once compressed, the structure can be cooled below Tg to its glassy state. As long as the temperature remains <Tg the structure remains compacted (in a cold hibernated state), even when the external compressive forces are removed. When the structure is subsequently heated above Tg, it returns to the rubbery state, in which a combination of elasticity and the SMP effect cause it to expand (deploy) to its original size and shape. Once thus deployed, the CHEM structure can be rigidified by cooling below Tg to the glassy state. The structure could be subsequently reheated above Tg and recompacted. The compaction/deployment/rigidification cycle could be repeated as many times as needed.

Chmielewski, Artur↗
NASA NTRS2003

Soft Landing of Spacecraft on Energy-Absorbing Self-Deployable Cushions

A report proposes the use of cold hibernated elastic memory (CHEM) foam structures to cushion impacts of small (1 to 50 kg) exploratory spacecraft on remote planets. Airbags, which are used on larger (800 to 1,000 kg) spacecraft have been found to (1) be too complex for smaller spacecraft; (2) provide insufficient thermal insulation between spacecraft and ground; (3) bounce on impact, thereby making it difficult to land spacecraft in precisely designated positions; and (4) be too unstable to serve as platforms for scientific observations. A CHEM foam pad according to the proposal would have a glass-transition temperature (Tg) well above ambient temperature. It would be compacted, at a temperature above Tg, to about a tenth or less of its original volume, then cooled below Tg, then installed on a spacecraft without compacting restraints. Upon entry of the spacecraft into a planetary atmosphere, the temperature would rise above Tg, causing the pad to expand to its original volume and shape. As the spacecraft decelerated and cooled, the temperature would fall below Tg, rigidifying the foam structure. The structure would absorb kinetic energy during ground impact by inelastic crushing, thus protecting the payload from damaging shocks. Thereafter, this pad would serve as a mechanically stable, thermally insulating platform for the landed spacecraft.

Sokolowski, Witold↗
NASA NTRS1977

Thermochemical characterization of some thermoplastic materials

The thermochemical and flammability characteristics of some typical thermoplastic materials currently in use or being considered for use in aircraft interiors are described. The properties studied included thermomechanical properties such as glass-transition and melt temperature, changes in polymer enthalpy, thermogravimetric analysis in anerobic and oxidative environments, oxygen index, smoke evolution, relative toxicity of the volatile products of pyrolysis, and selected physical properties. The generic polymers evaluated included acrylonitrile butadiene styrene, bisphenol A polycarbonate, 9,9 bis (4-hydroxyphenyl) fluorene polycarbonate-poly (dimethylsiloxane) block polymer, phenolphthalein-bisphenol A polycarbonate, phenolphthalein polycarbonate, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyaryl sulfone, chlorinated polyvinyl chloride homopolymer, polyvinyl fluoride, and polyvinylidene fluoride. Processing parameters, including molding characteristics of some of the advanced polymers, are described. Test results and relative rankings of some of the flammability, smoke, and toxicity properties are presented. Under these test conditions, some of the advanced polymers evaluated were significantly less flammable and toxic than or equivalent to polymers in current use.

Kourtides, D. A.↗