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At least 343 records · Page 19

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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

Adhesive evaluation of new polyimides

During the past 10 to 15 years, the Materials Division at NASA Langley Research Center (LaRC) has developed several novel high temperature polyimide adhesives for anticipated needs of the aerospace industry. These developments have resulted from fundamental studies of structure-property relationships in polyimides. Recent research at LaRC has involved the synthesis and evaluation of copolyimides which incorporate both flexibilizing bridging groups and meta-linked benzene rings. The purpose was to develop systems based on low cost, readily available monomers. Two of these copolyimides evaluated as adhesives for bonding titanium alloy, Ti(6Al-4V), are identified as LARC-STPI and STPI-LARC-2. Lap shear strength (LSS) measurements were used to determine the strength and durability of the adhesive materials. LSS results are presented for LARC-TPI and LARC-STPI lap shear specimens thermally exposed in air at 232 C for up to 5000 hrs. LARC-TPI was shown to perform better than the copolymer LARC-STPI which exhibited poor thermooxidative performance possibly due to the amines used which would tend to oxidize easier than the benzophenone system in LARC-TPI.

Stclair, Terry L.↗

NASA NTRS1988

Processable Aromatic Polyimide Thermoplastic Blends

Method developed for preparing readily-processable thermoplastic polyimides by blending linear, high-molecular-weight, polyimic acid solutions in ether solvents with ultrafine, semicrystalline, thermoplastic polyimide powders. Slurries formed used to make prepregs. Consolidation of prepregs into finsihed composites characterized by excellent melt flow during processing. Applied to film, fiber, fabric, metal, polymer, or composite surfaces. Used to make various stable slurries from which prepregs prepared.

Baucom, Robert M↗

NASA NTRS1987

Structure property behavior of polyimide siloxane segmented copolymers

Procedures were developed for preparing soluble fully imidized polyimide-polydimethyl siloxane segmented copolymers of wide ranging compositions. At low siloxane levels, the materails behave as modified polyimides. At higher concentrations, the materials are analogous to thermoplastic elastomers. Characterization by dynamic mechanical and thermal analysis methods will be reported along with an assesment of the bulk mechanical properties and the surface behavior. The surface behavior is particularly interesting since the materials can be tailored to have siloxane surfaces even at rather low siloxane contents. This influences a number of properties such as the coefficient of friction and, importanly, the degradation of these materials under aggressive oxygen environments (e.g., atomic oxygen, oxygen plasma).

Arnold, C. A.↗

NASA NTRS1987

Soluble aromatic polyimides for film and coating applications

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 NTRS1987

Electrical properties of polyimides containing a near-surface deposit of silver

Films containing a surface or near-surface deposit of palladium, gold or copper metal as well as tin, cobalt, copper, or lithium oxides have been prepared by dissolving appropriate metal salts into poly(amide-acid)/N,N-dimethylacetamide solutions and curing the solvent cast films to temperatures up to 300 C. This preparation technique has been extended to evaluate the thermal, spectroscopic, and electrical characteristics of condensation polyimide films modified with silver nitrate. A near-surface deposit of metallic silver results but the reflective surface has high electrical resistivity (sheet resistivity) due to a polymer coating or overlayer above the metal. Details pertaining to the silver nitrate modified condensation polyimides are presented. Also, the applicability of the structural model and electrical model previously proposed for the cobalt oxide system are assessed.

Rancourt, J. D.↗

NASA NTRS1988

Characterization of microcomposite polyimide films

Thermally stable microcomposite polyimide films were prepared by the homogeneous incorporation of either a soluble metal salt or a metal complex into a poly(amide-acid)/N,N-dimethylacetamide solution. The thermal processing of films solvent cast onto glass substrates and cured in an appropriate atmosphere yields films containing not only a fairly uniform dispersion of submicrometer particles, but also a new surface layer of metal or metal oxide. These polymeric systems have been characterized using X-ray photoelectron spectroscopy, Auger electron spectroscopy with depth profiling via argon ion etching, transmission electron microscopy of ultramicrotomed cross-sections, scanning electron microscopy, elemental analysis, thermal analysis, and variable temperature electrical resistivity determinations. The data from these techniques were used cooperatively to develop a model for these microcomposite polyimide films.

Rancourt, J. D.↗

NASA NTRS1988

A review of dynamic mechanical characterization of high temperature PMR polyimides and composites

This paper reviews the applications of dynamic mechanical characterization for high-temperature PMR polyimides and their graphite-fiber-reinforced composites. This characterization technique provides insights into the processability, performance, and structure property relationships of the polyimides and composites. The dynamic mechanical properties of various molding powders, commercially obtained prepregs, neat resins, and as-fabricated as well as aged composites are presented. Some applied aspects of the dynamic mechanical data are discussed.

Pater, Ruth H.↗

NASA NTRS1988

A study of thermal transitions in a new semicrystalline thermoplastic polyimide

A polyimide derive from 4,4'-isophthaloyl diphthalic anhydride (IDPA) and 1,3-bis (4-aminophenoxy 4'-benzoyl) benzene (1,3-BABB) having semicrystalline behavior was prepared and characterized by differential scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS). Thus a poly(amic acid) film cured in air for one hour each at 100 and 200 C displayed an endotherm at 286 C, followed by a crystallization exotherm at 317 C, and a second melting transition at 350 C. The 286 C melting point appeared to result from earlier solvent-induced crystallization. Films cast from DMAc, air dried, and soaked in methylene chloride could not be induced into semicrystallinity. The fully cured polyimide has a Tg of 216 C. Films heated to temperatures as high as 100 C for one hour in air were transparent and light yellow in color. Those films heated to or above 125 C were translucent. Polarized light microscopy revealed the presence of spherulites 608 micrometers in diameter in a sample cured to 275 C in air. Two film samples, one cured to 275 and the other to 325 C, were evaluated for tensile and ultimate strength, modulus, and percent elongation at 25 and 200 C. These values remained essentially constant at each test temperature.

Pratt, J. Richard↗

NASA NTRS1989

Polyimide Matrix composites: Polyimidesulfone/LARC-TPI (1:1) blend

Polyimide matrix composites were fabricated from unidirectional unsized AS-4 carbon fiber and a doped 1:1 blend of two polyimides: benzophenone dianhydride-3,3'-diamino diphenylsulfone (PISO2) and benzophenone dianhydride-3,3'-diamino benzophenone (LARC-TPI). To enhance melt flow properties, the molecular weight of the PISO2 was controlled by end-capping with phthalic anhydride and addition of 5 percent by weight p-phenylene diamine-phthalic anhydride bisamic acid dopant. Prepreg was drum-wound using a diglyme slurry comprised of the soluble polyamideacid of PISO2, the soluble bisamideacid of the dopant, and the insoluble imidized LARC-TPI powder. Melt flow studies with a rotary rheometer and parallel plate plastometer on neat resin and prepreg helped develop an optimum cure cycle. Composite mechanical properties at room and elevated temperatures, dry and moisture-saturated, were evaluated, including short beam shear strength and flexure, tensile, shear, and compression properties. Two 18 in. x 24 in. skin-stringer panels were fabricated, one of which was tested in compression to failure.

Johnston, Norman J.↗

NASA NTRS1988

Soluble and colorless polyimides

Results are reported in the form of reaction diagrams, graphs, and tables of research being conducted to synthesize and characterize linear aromatic polyimides which are soluble in common organic solvents and optically transparent in the 400-600 nm spectral range. These flexible and high-temperature polymeric films and coatings are needed for specific applications on space components such as antennas, solar cells, and thermal control coating systems. Several series of these polyimide films have been produced by making variations in the polymer molecular structure aimed at reducing the electronic interactions between the polymer chains.

St. Clair, Anne K.↗

NASA NTRS1990

Polyimides Containing Carbonyl And Ether Connecting Groups

Polyimides of new class made from chemical reactions of aromatic dianhydrides with novel aromatic diamines in which carbonyl and ether groups connect aromatic rings. New polyimides melt-processable, strong, resistant to impacts, and resistant to solvents and other chemicals. Useful as adhesives, coatings, films, membranes, and composite matrices.

Hergenrother, Paul M.↗

NASA NTRS1989

New Condensation polyimides containing 1,1,1-triaryl-2,2,2-trifluoroethane structures

The invention relates to a condensation polyimide containing a 1,1,1-triaryl 2,2,2-trifluoroethane structure and other related condensation polyimides. The process for their preparation, which comprises polymerization of a cyclic dianhydride with a diamine is also covered.

Alston, William B.↗

NASA NTRS1989

Fracture toughness of polyimide films

Two aromatic polyimides and an aromatic polyamide-imide were tested in single edge notched tension. Fracture toughnesses, normalized to 25 micron film thickness ranged from 1.65 to 5.4 MPa m sup 1/2. LARC-TPI, a thermoplastic polyimide, showed evidence of crazing ahead of a growing crack whereas the other materials formed a shear yielded zone.

Hinkley, J. A.↗

NASA NTRS1989

Aromatic polyimides containing a dimethylsilane-linked dianhydride

A high-temperature stable, optically transparent, low dielectric aromatic polyimide is prepared by chemically combining equimolar quantities of an aromatic dianhydride reactant and an aromatic diamine reactant, which are selected so that one reactant contains at least one Si(CH3)2 group in its molecular structure, and the other reactant contains at least one -CF3 group in its molecular structure. The reactants are chemically combined in a solvent medium to form a solution of a high molecular weight polyamic acid, which is then converted to the corresponding polyimide.

St.clair, Anne K.↗

NASA NTRS1989

Low dielectric thermoplastic polyimide resin

NASA-Langley studies of polymer structure-property relationships have led to the development of a method for the reduction of dielectric constants in polyimides through chemical alterations of polymer backbone composition to reduce chain-chain electronic interactions, as well as through the incorporation of fluorine atoms into the polymer molecular structure. Still-greater dielectric constant reductions are obtainable by means of a physical incorporation of diamic acid additives into these low-dielectric polyimide systems; the resulting thermoplastic resins are applicable to polymer matrices for composite structural materials.

Stoakley, D. M.↗

NASA NTRS1989

LARC-CPI, a new semi-crystalline polyimide

As part of a program on high performance/high temperature structural resins for aerospace applications, work was performed with a new semi-crystalline polyimide (LARC-CPI) to improve the compression moldability while retaining high mechanical properties and thermooxidative stability. Various molecular weight versions of LARC-CPI polyamide acid were prepared, end-capped with different groups, converted to polyimide and evaluated for film properties, thermooxidative stability and melt flow. One controlled molecular weight, end-capped version of LARC-CPI was evaluated more comprehensively in adhesive and composite work and exhibited good compression moldability, reasonable crystallization rates and high mechanical properties.

Hergenrother, P. M.↗