SEARCH · Engineering Papers

Results for “polyimide”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 595 records · Page 33

All sources NASA NTRS DOE OSTI

NASA NTRS1987

A mechanistic study of polyimide formation from diester-diacids

Previous work has noted the presence of anhydride during the imidization step of polyimide polymer processing from diester-diacids and diamines. Comparison of the relative rates of reactions among model compounds demonstrates the intermediacy of anhydride in the imidization reaction. IR and NMR observations of mixtures of monomers confirm the production of anhydride as a necessary intermediate in the imidization reaction.

Johnston, James C.↗

NASA NTRS1988

Readily Processable Polyimide

Polymer exhibits resistance to hydraulic fluid, excellent processability, and extremely high adhesive strength. Synthesis involves reaction of new diamine, 1,3-bis 2-ethyl ether, with 3,3',4,4'-benzophenonetetracarboxylic dianhydride to form polyamic acid and subsequent conversion to polyimide.

Hergenrother, Paul M.↗

NASA NTRS1987

Synthesis and characterization of processable polyimides with enhanced thermal stability

Many of the emerging applications of polymers on space vehicles require materials with outstanding thermal stability. These polymers must also be readily processable in order to facilitate their use. The syntheses and polymerization of a cardo dianhydride were investigated. This monomer was prepared via the reaction of N-methyl 4-nitrophthalimide with a cardo diol. Polyimides containing oxyalkylene linkages were studied. The effects of two additional structural modifications on the polymers' properties were investigated. The effects of carrying out the preparation of poly(amic acid)s under non-equilibrium conditions were examined. Approaches that were investigated included the in-situ neutralization of the generated amic acid and its in-situ esterification.

Harris, Frank W.↗

NASA NTRS1987

An investigation of physical properties of thermoplastic polyimides

Thermoplastic polyimides are a class of promising high temperature polymers for aerospace applications. NASA-developed LARC-TPI is a prominent member of this family of polymers. Its physical characteristics have been measured as a function of its curing schedule. The results and their possible interpretations are discussed.

Singh, Jag J.↗

NASA NTRS1988

Correlations of norbornenyl crosslinked polyimide resin structures with resin thermo-oxidative stability, resin glass transition temperature and composite initial mechanical properties

PMR (polymerization of monomeric reactants) methodology was used to prepare 70 different polyimide oligomeric resins and 30 different unidirectional graphite fiber/polyimide composites. Monomeric composition as well as chain length between sites of crosslinks were varied to examine their effects on resin thermo-oxidative stability and glass transition temperature (Tg) of the cured/postcured resins. A linear correlation of decreasing 316 C resin weight loss/surface area versus (1) decreasing aliphatic content, or (2) increasing benzylic/aliphatic content stoichiometry ratio over a wide range of resin compositions was observed. An almost linear correlation of Tg versus molecular distance between the crosslinks was also observed. An attempt was made to correlate Tg with initial composite mechanical properties (flexural strength and interlaminar shear strength). However, the scatter in mechanical strength data prevented obtaining a clear correlation. Instead, only a range of composite mechanical properties was obtained at 25, 288, and 316 C. Perhaps more importantly, what did become apparent during the correlation study was (1) the PMR methodology could be used to prepare composites from resins containing a wide variety of monomer modifications, (2) that these composites almost invariably provided satisfactory initial mechanical properties as long as the resins formulated exhibited satisfactory processing flow, and (3) that PMR resins exhibited predictable rates of 316 C weight loss/surface area based on their benzylic/aliphatic stoichiometery ratio.

Alston, William B.↗

NASA NTRS1987

Polyimide processing additives

A method has been found for enhancing the melt flow of thermoplastic polyimides during processing. A high molecular weight 422 copoly(amic acid) or copolyimide was fused with approximately 0.05 to 5 pct by weight of a low molecular weight amic acid or imide additive, and this melt was studied by capillary rheometry. Excellent flow and improved composite properties on graphite resulted from the addition of a PMDA-aniline additive to LARC-TPI. Solution viscosity studies imply that amic acid additives temporarily lower molecular weight and, hence, enlarge the processing window. Thus, compositions containing the additive have a lower melt viscosity for a longer time than those unmodified.

Pratt, J. R.↗

NASA NTRS1987

Cure study of soluble aromatic polyimide films

Several soluble aromatic poly(amic acid) films were staged at intervals to 325 C and characterized by IR spectroscopy and various solution property techniques. A series of films in which the polymer had been endcapped in an effort to control chain extension was also examined. Much of the behavior observed is consistent with an interpretation that a reduction in molecular weight occurred during cure before the ultimate molecular weight was achieved as a polyimide.

Young, Philip R.↗

NASA NTRS1987

High temperature polyimide blends

In a continuing effort to synthesize polymers that are readily processable and that exhibit state-of-the-art characteristics, LARC-TPI (Mitsui) and polyimidesulfone (PISO2) were blended and subjected to a limited melt flow and thermal properties characterization. Mitsui Toatsu of Japan, working under a licensing agreement with NASA, synthesized an imidized version of LARC-TPI molding powder that exhibited an extraordinarily high level of softening when heated to 300 C. Subsequently, a study of the calorimetric and rheological properties was accomplished by NASA-Langley on that material. The thermoplastic polyimidesulfone that possesses processability similar to polysulfones and the solvent resistance of the polyimides was synthesized and characterized at NASA-Langley in the early 1980's.

Burks, Harold D.↗

NASA NTRS1987

Tearing of thin polyimide films

Films of BTDA-ODA polyimide up to 58 microns thick were torn at constant cross-head speed in 'trousers' tests. In common with previous results on polyolefins, the work of tearing was found to increase markedly with specimen thickness. A model for the increase, based on the volume of plastically deformed material adjacent to the crack plane, was found to be only qualitatively valid. The experimental slope of a plot of tearing energy (per unit area) against thickness was 70 MJ/cu m. Optical and scanning electron micrographs of torn films are discussed in regard to the modes of failure.

Hinkley, J. A.↗

NASA NTRS1989

Additives Lower Pickup Of Moisture By Polyimides

Series of new polyimide-processing additives decrease free volume and pickup of moisture in new 422 copolyimide. Physical properties of several copolyimides synthesized from linear BDSDA/ODA/MPD homopolymers investigated previously, by positron-annihilation spectroscopy, with results indicating copolyimides have unique transition molecular structure characterized by higher electron densities and stronger bonds. Transition structure permits both physical and chemical entry of water molecules into it.

St. Clair, Terry L.↗

NASA NTRS1988

Characterization of cobalt(II) chloride-modified condensation polyimide films

The effect of solvent extraction on the properties of cobalt(II) chloride-modified polyimide films was investigated. Solvent-cast films were prepared from solutions of cobalt chloride in poly(amide acid)/N,N-dimethylacetamide (DMAc) and were subsequently dried and cured in static air, forced air, or inert gas ovens with controlled humidity. The films were extracted by either of the three processes (1) soaking in a tray with distilled water at room temperature, (2) soxhlett extraction with distilled water, or (3) soxhell extraction with DMAc. Extraction with DMAc was found to remove both cobalt and chlorine from the films and to slightly increase bulk thermal stability and both surface resistivity and electrical resistivity.

Rancourt, J. D.↗

NASA NTRS1987

Adhesive properties of a semi-crystalline polyimide

Adhesive and film properties of a new semi-crystalline polyimide, designated LARC-CPI, having a glass transition temperature of 222 C and a crystalline melt temperature of 350 C are presented. The films exhibited excellent resistance to solvents and strong base. Compact tension specimens from LARC-CPI moldings displayed a fracture energy of 37.8 lb/sq in. Titanium tensile shear specimens gave strengths of 6250 psi initially at 25 C, 7120 psi at 25 C after 1000 hours at 232 C, 2800 psi at 232 C after annealing for 5 hours at 300 C, and 3670 psi at 232 C after 100 hours at 316 C in air.

Hergenrother, P. M.↗

NASA NTRS1990

High-Temperature Polyimide Resin

Improved polyimide resin used at continuous temperatures up to 700 degrees F (371 degrees C). PMR-II-50, serves as matrix for fiber-reinforced composites. Material combines thermo-oxidative stability with autoclave processability. Used in such turbine engine components as air-bypass ducts, vanes, bearings, and nozzle flaps. Other potential applications include wing and fuselage skins on high-mach-number aircraft and automotive engine blocks and pistons.

Vanucci, Raymond D.↗

NASA NTRS1990

LARC-I-TPI: A New Thermoplastic Polyimide

"LARC-I-TPI" denotes improved version of LARC-TPI class of thermoplastic polyimides: high-performance polymers developed for manufacture of strong, lightweight aircraft structures. Melt-flow and adhesive properties of new polymers make them attractive for use as matrix resins for composites, molding powders, adhesives, and coating films. Less toxic, improved LARC-I-TPI polymers formulated without 3, 3'-diaminobenzophenone, which is mutagenic and commercially unavailable.

St. Clair, Terry L.↗

NASA NTRS1990

A study of physical properties of ODPA-p-PDA polyimide films

Physical properties were investigated of ODPA-p-PDA polyimide films, including their lower molecular weight versions with phthalimide endcaps. Free volume, determined by low energy positron annihilation in the test films, was the major parameter of interest since all other physical properties are ostensibly related to it. It affects the dielectric constant as well as the saturation moisture pickup of the test films. An empirical relation was developed between the free volume and molecular weight of the test films, comparable to the Mark-Houwink relation between the polymer solution viscosity and the molecular weight. Development of such a relation constitutes a unique achievement since it enables researchers to estimate the molecular weight of an intractable polymer in solid state for the first time.

Singh, Jag J.↗

NASA NTRS1990

Computed structures of polyimides model compounds

Using a semi-empirical approach, a computer study was made of 8 model compounds of polyimides. The compounds represent subunits from which NASA Langley Research Center has successfully synthesized polymers for aerospace high performance material application, including one of the most promising, LARC-TPI polymer. Three-dimensional graphic display as well as important molecular structure data pertaining to these 8 compounds are obtained.

Tai, H.↗

NASA NTRS1990

LARC-TPI 1500 series controlled molecular weight polyimide

LARC-TPI, a linear high temperature thermoplastic polyimide, was developed several years ago at NASA Langley Research Center. This material has been commercialized by Mitsui Toatsu Chemicals, Inc., Tokyo, Japan, as a varnish and powder. More recently, a melt-extruded film of a controlled molecular weight of this same polymer has been supplied to NASA Langley Research Center for evaluation. This new form, called LARC-TPI 1500 series, has been prepared in three molecular weights - high, medium and low flow polymers. The subject of this investigation deals with the rheological properties of the high and medium flow powders and the adhesive properties of the medium flow melt-extruded film. Rheological studies indicate that the high and medium flow forms of the polymer fall in the flow range of injection moldable materials. Adhesive data generated on the medium flow extruded film shows this form to be well suited for structural adhesive bonding. The data are as good or better than that for LARC-TPI data of previous studies.

Progar, Donald↗

NASA NTRS1990

Effects of additives on the processing and properties of LARC-TPI polyimide

The blending of LARC-TPI polyimide with the thermotropic liquid crystal polymer designated Xydar and with four different oligomeric imide materials has facilitated the resulting resin systems' processing into films while enhancing their mechanical properties and lowering their coefficient of thermal expansion to virtually zero. Two film-formation processes have been evaluated: (1) the casting of polyamic acid films followed by thermal imidization and biaxial stretching, and (2) the blown-film melt-extrusion of fully imidized LARC-TPI polymer. The best results have been obtained through the use of Xydar as a processing aid at levels in the 10-30 percent range.

Elandjian, L.↗