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At least 109 records · Page 6

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NASA NTRS1972

Polyimidazopyrrolone model compounds.

Study of model reactions between phthalic anhydride and o-phenylenediamine under conditions analogous to the polymerization and post cyclization of dianhydrides with bis(o-diamines) to form polyimidazopyrrolones (Pyrrones). Solid-state thermal conversion of the amide-acid-amine affords a unique dimeric species containing amide, imide, and benzimidazole functions. It was confirmed that melt techniques lead to disproportionation products. The application of these findings to related polymer syntheses is discussed.

Young, P. R.↗

NASA NTRS1972

Polyimidazopyrrolone model compounds.

The model reactions between phthalic anhydride and o-phenylenediamine were studied under conditions analogous to the polymerization and post-cyclization of dianhydrides with bis(o-diamines) to form polyimidazopyrrolones (Pyrrones). The route from the initial amide-acid-amine to the tetracyclic Pyrrone model when the reactions are conducted in aprotic solvents is highly competitive between isolatable benzimidazole-acid and imide-amine intermediates. Solid-state thermal conversion of the amide-acid-amine affords a unique dimeric species containing amide, imide, and benzimidazole functions. It was confirmed that melt techniques lead to disproportionation products. The application of these findings to related polymer synthesis is discussed.

Young, P. R.↗

NASA NTRS1973

Heat-resistant polymers containing bipyridyl units. II Polyamide-imides

Polyamide-amic acids containing bipyridyl units were prepared by polymerization of various bipyridyl diamines with trimellitic anhydride acid chloride. These polymers were converted to polyamide-imides by thermal cyclization. The resulting polyamide-imides exhibited very good solubility in organic solvents.

Kurita, K.↗

NASA NTRS1973

A novel imide synthesis via silyl-blocked diamines

Efforts have resulted in the production of some trimethylsilyl-blocked diamines, which have been employed in a novel manner for the synthesis of polyimide model compounds. Three new silicon-containing diamides were prepared by reacting 1 mol of bis-/N, N prime-bis (trimethylsilyl) -4-aminophonyl/-disubstituted silanes with 2 mol of phthalic anhydride, thus establishing the reactivity of fully silylated diamides in imide formation.

Pratt, J. R.↗

NASA NTRS1976

Polymeric foams stable at high temperatures

Crosslinked poly(N-arylenebenzimidazoles) are stable up to 370 C. Polymers are made by mixing appropriate stoichiometric amounts of tetramine and aromatic dicarboxylic acid anhydride with phenol or alkyl-substituted phenol.

Riccitiello, S. R.↗

NASA NTRS1975

Effect of polymer properties and adherend surfaces on adhesion

The surface properties associated with good adhesive joints were evaluated in terms of application of adhesive bonding in aerospace technology. The physical and chemical nature was determined of Ti and Al adherend surfaces after various surface treatments, and the effects on fracture surfaces of high temperature aging, and variations in amide, anhydride, and solvent during polymer synthesis. The effects were characterized of (1) high temperature during shear strength testing, (2) fiber-reinforced composites as adherends, (3) acid/base nature of adherends, (4) aluminum powder adhesive filler, and (5) bonding pressure.

Dwight, D. W.↗

NASA NTRS1976

Polycondensation of alpha-amino acids by pyrosulfuric acid

The thermal polycondensation of amino acids common to protein is promoted at 80 deg C by pyrosulfuric acid. This is in contrast to the noncondensation at 100 deg C in the presence of concentrated sulfuric acid. These results are in accord with an anhydride mechanism, as proposed earlier for copolycondensation promoted by polyphosphoric acid. The amino acid composition, molecular weight, near-homogeneity, and infrared absorption of the polymer formed are described. The potential significance of planetary pyrosulfuric acid is discussed.

Denes, F.↗

NASA NTRS1979

Low-temperature elastomer production and curing

Thermally and chemically stable polymers are needed for materials applications, particularly highly-stable elastomers for solid propellant binders where initial high temperature required for dissolving anhydride in polymer is deerimental. Solvent reactant system allows polymerization without condensation of products under low heat. Solvents utilized were dimethylacetamide, dimethyflormamide, etc.

Ingham, J. D.↗

NASA NTRS1978

Polymers with complexing properties. Simple poly(amino acids)

The free amino (0.3 equiv/residue) and carboxyl (0.5 equiv/residue) groups of thermal polylysine increased dramatically on treatment with distilled water. The total hydrolysis of such a polymer was abnormal in that only about 50% of the expected amino acids were recovered. Poly (lysine-co-alanine-co-glycine) under usual conditions hydrolyzed completely in 8 hours; whereas, when it was pretreated with diazomethane, a normal period of 24 hours was required to give (nearly) the same amounts of each free amino acid as compared with those obtained from the untreated polymer. The amino groups of the basic thermal poly(amino acids) were sterically hindered. The existence of nitrogen atoms linking two or three chains and reactive groups (anhydride, imine) were proposed.

Roque, J. M.↗

NASA NTRS1978

Polymeric foams from cross-linkable poly-N-ary lenebenzimidazoles

Foamed cross-linked poly-N-arylenebinzimidazoles are prepared by mixing an organic tetraamine and an ortho substituted aromatic dicarboxylic acid anhydride in the presence of a blowing agent, and then heating the prepolymer to a temperature sufficient to complete polymerization and foaming of the reactants. In another embodiment of the process, the reactants are heated to form a prepolymer. The prepolymer is then cured at higher temperatures to complete foaming and polymerization.

Harrison, E. S.↗

NASA NTRS1979

Development and evaluation of die and container materials

X = 0.75 Beta prime Sialon (a silicon aluminum oxynitride) and Sibeon (silicon beryllium oxynitride) are promising die materials. In sessile drop tests in contact with molten silicon, beryllium contamination was less than ppm and aluminum contamination 50 ppm. A shaping die of the Sialon material was successfully fabricated. Dry milling studies for the preparation of Si3N4-Al2O3-ALN mixtures were performed with butanol, acetic anhydride, oleic acid, and triethanolamine milling aids. Optimum mixing was achieved with 0.15 percent triethanolamine using a milling time of 8 hours. Preliminary evaluation of Sibeon materials indicates that they are more resistent to molten silicon attack than Sialon. Silicon contamination from the beryllium was less than aluminum contamination even though the aluminum impurity level in the Sibeon was only 450 to 1300 ppm. Work designed to produce an aluminum-free Sibeon is described.

Wills, R. R.↗

NASA NTRS1980

Experiments on the amplification of optical activity

Chemical mechanisms for the amplification of small, abiotically produced enantiomeric excesses leading to the complete stereo specificity of all biochemical reactions observed in the present-day biosphere are investigated quantitatively. Partial copolymerization of a mixture of R- and S-leucine or R- and S-valine N-carboxy anhydrides containing a known excess of one enantiomer was induced and the enantiomeric composition of the resulting oligomer was analyzed by gas chromatography. It is found that the 50% polymerization of leucine mixtures having excesses of 8 to 70% of either enantiomer leads to a significant enhancement of the enantiomeric excess of the polymer, accompanied by a corresponding decrease in the enantiomeric excess of the unpolymerized residue. On the other hand, 25-50% polymerization of valine mixtures is observed to result in polymers showing a decreased enantiomeric excess relative to the starting mixture and corresponding increases in those of the residue. Results of the leucine polymerization are interpreted as supporting the theory of steric interactions between the monomer and the helical structure of the polymer leading to the enrichment of one enantiomer, and possible mechanisms for the reverse stereospecificity observed in valine are discussed.

Blair, N. E.↗

NASA NTRS1980

Process for the preparation of fluorine containing crosslinked elastomeric polytriazine and product so produced

Crosslinking elastomeric polytriazines are prepared by a 4 step procedure which consists of (1) forming a poly(imidoylamidine) by the reaction, under reflux conditions, of anhydrous ammonia with certain perfluorinated alkyl or alkylether dinitriles; (2) forming a linear polytriazine by cyclizing the imidoylamidine linkages by reaction with certain perfluorinated alkyl or alkylether acid anhydrides or halides; (3) extending the linear polytriazine chain by further refluxing in anhydrous ammonia; and (4) heating to cyclize the new imidoylamidine and thereby crosslink the polymer.

Rosser, R. W.↗

NASA NTRS1981

Physical aging of linear and network epoxy resins

Network and linear epoxy resins principally based on the diglycidyl ether of bisphenol-A and its oligomers are prepared and studied using diamine and anhydride crosslinking agents. Rubber modified epoxies and a carbon fiber reinforced composite are also investigated. All materials display time-dependent changes when stored at temperatures below the glass transition temperature after quenching (sub-T/g/ annealing). Solvent sorption experiments initiated after different sub-T(g) annealing times demonstrate that the rate of solvent uptake can be indirectly related to the free volume of the epoxy resins. Residual thermal stresses and water are found to have little effect on the physical aging process, which affects the sub-T(g) properties of uniaxial carbon fiber reinforced epoxy material. Finally, the importance of the recovery phenomenon which affects the durability of epoxy glasses is considered.

Kong, E. S.-W.↗

NASA NTRS1981

Factors influencing the rate of non-enzymatic activation of carboxylic and amino acids by ATP

The nonenzymatic formation of adenylate anhydrides of carboxylic and amino acids is discussed as a necessary step in the origin of the genetic code and protein biosynthesis. Results of studies are presented which have shown the rate of activation to depend on the pKa of the carboxyl group, the pH of the medium, temperature, the divalent metal ion catalyst, salt concentration, and the nature of the amino acid. In particular, it was found that of the various amino acids investigated, phenylalanine had the greatest affinity for the adenine derivatives adenosine and ATP. Results thus indicate that selective affinities between amino acids and nucleotides were important during prebiotic chemical evolution, and may have played a major role in the origin of protein synthesis and genetic coding.

Mullins, D. W., Jr.↗

NASA NTRS1981

New interstellar molecular transitions in the 2 millimeter range

A Sgr B2 kinetic temperature of about 47 K is derived based on observations of K components of the 9K-8K transition of CH3CCH. Interstellar line emission is detected in the 2 mm wavelength region from SO, (S-34)O, SO2, CH3OH, CH3CCH, CH3CH2CN, HC3N, and nine unidentified transitions. The methylacetylene K component data combined with the derived data reduction technique, demonstrates the utility of the molecule as a temperature probe of molecular clouds when two or more rotational transitions are observed. Evidence for the existence of interstellar HNO is presented, and an attempt is made to detect sulfuric acid, formic anhydride, and the 0-18 isotopic for CO2 in interstellar clouds and in the Venusian atmosphere during inferior conjunction.

Hollis, J. M.↗

NASA NTRS1983

Epoxy hydantoins as matrix resins

Tensile strength and fracture toughness of castings of the hydantoin resins cured with methylenedianiline are significantly higher than MY 720 control castings. Water absorption of an ethyl, amyl hydantoin formulation is 2.1 percent at equilibrium and Tg's are about 160 C, approximately 15 deg below the final cure temperature. Two series of urethane and ester-extended hydantoin epoxy resins were synthesized to determine the effect of crosslink density and functional groups on properties. Castings cured with methylenedianiline or with hexahydrophthalic anhydride were made from these compounds and evaluated. The glass transition temperatures, tensile strengths and moduli, and fracture toughness values were all much lower than that of the simple hydantoin epoxy resins. Using a methylene bishydantoin epoxy with a more rigid structure gave brittle, low-energy fractures, while a more flexible, ethoxy-extended hydantoin epoxy resin gave a very low Tg.

Weiss, J.↗

NASA NTRS1983

Synthesis and characterization of a polyethersulfoneimide

Two similar polyimide systems were synthesized and characterized. The only structural difference was a sulfide linkage in the anhydride derived portion of the first system versus a sulfone linkage in the second. Their physical, mechanical, melt-flow and thermal properties were determined and also their resistance to some of the more common solvents. The flow properties of these polyimides indicate them to have potential for melt processability.

Burks, H. D.↗