Effects of thermal cycling on mechanical properties of graphite polyimide
Previously cited in issue 13, p. 2034, Accession no. A82-30101
Tompkins, S. S.↗
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Preparation and characterization of siloxane-containing thermoplastic polyimides
Copolyimides and homopolyimides of bis(gamma-aminopropyl)tetramethyldisiloxane and 3,3'-diaminobenzophenone have been prepared with benzophenonetetracarboxylic dianhydride. The properties of the copolyimides were compared with those of the homopolyimides to assess the effect of incorporation of siloxane groups in the backbone. Applications of the polymers as adhesives and mouldings are discussed.
Maudgal, S.↗
Effect of substituted phenylnadimides on processing and properties of PMR polyimide composites
Three nitrophenylnadimide cure initiators and two phenylnadimides (without nitros) were evaluated as additives to PMR-15 resins and Celion 6000 graphite fiber composites. The results of a resin screening study eliminated all of the additives except 3-nitrophenylnadimide (NO2PN) for use as a low temperature curing additive for PMR-15. Thus, NO2PN and the two control additives were investigated in PMR-15 formulations from which Celion 6000 graphite fiber/PMR-15 composites were processed both with low temperature (274 C) and normal (316 C) cure cycles. Comparisons of the two processing cycles, the resultant glass transition temperatures (Tg), the ambient, 274 and 316 C composite mechanical properties determined before and after 316 C postcure, the 316 C thermo-oxidative weight losses and the retention of 316 C composite mechanical properties are presented. Empirical correlations of the type and amount of nadimide additives with processing parameters, Tg, composite mechanical properties, composite thermo-oxidative stability and long term retention of 316 C composite mechanical properties are also presented.
Alston, W. B.↗
Polyimides containing oxyethylene units. II - Polymerization of 3.3', 4.4'-benzophenonetetra carboxylic dianhydride and pyromellitic dianhydride
The study is concerned with the polymerization of diamines 2a-d with readily available dianhydrides, i.e., 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA). The synthesis and polymerization of asymmetric diamines containing substituted alkylene ether linkages are also investigated. It is assumed that the flexibility introduced into the polymer chain through the use of such diamines would result in moderate glass transition temperatures that would allow the systems to be melt processed. Mixtures of diamines are also copolymerized so as to further disrupt the polymer's symmetry and recurrence regularity. The properties of the resulting polymers are briefly discussed.
Harris, F. W.↗
Polyimide of Modified Melt Flow and Toughness
Linear aromatic polyphenylene ether sulfideimide (BDSDA/APB) polymer molded, used as resin, and cast into thin films. In effort to improve further both use properties and amenability to process BDSDA/APB, molecular weight of polymer varied by variations in percentage of end capping. Effect of end capping BDSDA/APB determined by measurement of polymer melt viscosity and fracture-energy values for different number average synthesized molecular weights.
St. Clair, T. L.↗
Evaluation of a high temperature adhesive for fabricating graphite/PMR-15 polyimide structures
Tests are conducted to measure shear strength, shear modulus and flatwise tensile strength of the A7F (amide-imide modified LARC-13) adhesive system. An investigation is also conducted to determine the effect of geometric material parameters, and elevated temperature on the static strength of standard joints. Single-lap and double-lap composite joints, and single, double and step lap composite to metal joints are characterized. A series of advanced joints consisting of preformed adherends, adherends with scalloped edges and joints with hybrid interface plies are tested and compared to baseline single and double-lap designs.
Hill, S. G.↗
New processable modified polyimide resins for adhesive and matrix applications
A broad product line of bismaleimide modified epoxy adhesives which are cured by conventional addition curing methods is described. These products fill a market need for 232 C (450 F) service adhesives which are cured in a manner similar to conventional 177 C (350 F) epoxy adhesives. The products described include film adhesives, pastes, and a primer. Subsequent development work has resulted in a new bismaleimide modified epoxy resin which uses a unique addition curing mechanism. This has resulted in products with improved thermomechanical properties compared to conventional bismaleimide epoxy resins. A film adhesive, paste, and matrix resin for composites using this new technology are described. In all cases, the products developed are heat cured by using typical epoxy cure cycles i.e., 1 hour at 177 C (350 F) followed by 2 hours postcure at 246 C (475 F).
Landman, D.↗
Effect of substituted phenylnadimides on processing and properties of PMR polyimide composites
Three nitrophenylnadimide cure initiators and two phenylnadimides (without nitros) were evaluated as additives to PMR-15 resins and Celion 6000 graphite fiber composites. The results of a resin screening study eliminated all of the additives except 3-nitrophenylnadimide (NO2PN) for use as a low temperature curing additive for PMR-15. Thus, NO2PN and the two control additives were investigated in PMR-15 formulations from which Celion 6000 graphite fiber/PMR-15 composites were processed both with low temperature (274 C) and normal (316 C) cure cycles. Comparisons of the two processing cycles, the resultant glass transition temperatures (Tg), the ambient, 274 and 316 C composite mechanical properties determined before and after 316 C postcure, the 316 C thermo-oxidative weight losses and the retention of 316 C composite mechanical properties are presented. Empirical correlations of the type and amount of nadimide additives with processing parameters, Tg, composite mechanical properties, composite thermo-oxidative stability and long term retention of 316 C composite mechanical properties are also presented.
Alston, W. B.↗
PMR polyimide compositions for improved performance at 371 deg C
Studies were conducted to identify matrix resins which have potential for use at 371 C (700 F). Utilizing PMR methodology, neat resin moldings were prepared with various monomer reactants and screened for thermo-oxidative stability at 371 C (700 F) under both ambient and a four-atmosphere air pressure. The results of the resin screening studies indicate that high molecular weight (HMW) formulated resins of first (PMR-15) and second (PMR-II) generation PMR materials exhibit lower levels of weight loss at 371 C (700 F) than PMR-15 and PMR-II resins. The resin systems which exhibited the best overall balance of processability, Tg and thermo-oxidative stability at 371 C were used to prepare unidirectional Celion 6000 and T-40R graphite fiber laminates. Laminates were evaluated for thermo-oxidative stability and 371 C mechanical properties. Results of the laminate evaluation studies indicate that two of the resin compositions have potential for use in 371 C applications. The most promising resin composition provided laminates which exhibited no drop in 371 C mechanical properties and only 11 percent weight loss after 200 hr exposure to 4 atmospheres of air at 371 C.
Vannucci, Raymond D.↗
Quantitative analysis of PMR-15 polyimide resin by HPLC
The concentration of individual components and of total solids of 50 wt pct PMR-15 resin solutions was determined using reverse-phase HPLC to within + or - 8 percent accuracy. Acid impurities, the major source of impurities in 3,3', 4,4'-benzophenonetetracarboxylic acid (BTDE), were eliminated by recrystallizing the BTDE prior to esterification. Triester formation was not a problem because of the high rate of esterification of the anhydride relative to that of the carboxylic acid. Aging of PMR-15 resin solutions resulted in gradual formation of the mononadimide and bisnadimide of 4,4'-methylenedianiline, with the BTDE concentration remaining constant. Similar chemical reactions occurred at a reduced rate in dried films of PMR-15 resin.
Roberts, Gary D.↗
A quantum theoretical study of polyimides
One of the most important contributions of theoretical chemistry is the correct prediction of properties of materials before any costly experimental work begins. This is especially true in the field of electrically conducting polymers. Development of the Valence Effective Hamiltonian (VEH) technique for the calculation of the band structure of polymers was initiated. The necessary VEH potentials were developed for the sulfur and oxygen atoms within the particular molecular environments and the explanation explored for the success of this approximate method in predicting the optical properties of conducting polymers.
Burke, Luke A.↗
Evaluation of a thermoplastic polyimide (422) for bonding GR/PI composite
A hot-melt processable copolyimide previously studied and characterized as an adhesive for bonding Ti-6Al-4V was used to bond Celion 6000/LARC-160 composite. Comparisons are made for the two adherend systems. A bonding cycle was determined for the composite bonding and lap shear specimens were prepared which were thermally exposed in a forced-air oven for up to 5000 h at 204 C. The lap shear strengths (LSSs) were determined at RT, 177, and 204 C. After thermal exposure at RT, 177, and 204 C the LSS decreased significantly; however, a slight increase was noted for the 204 C tests. Initially the LSS values are higher for the bonded Ti-6Al-4V than for the bonded composite, however, the LSS decreases dramatically between 5000 and 10,000 h of 204 C thermal exposure. Longer periods of thermal exposure up to 20,000 h results in further decreases in the LSSs. Although the bonded composite retained useful strengths for exposures up to 5000 h, based on the poor results of the bonded Ti-6Al-4V beyond 5000 h, the 422 adhesive bonded composites would most likely also produce poor strengths beyond 5000 h exposure. Adhesive bonded composite lap shear specimens exposed to boiling water for 72 h exhibited greatly reduced strengths at all test temperatures. The percent retained after water boil for each test temperature was essentially the same for both systems.
Progar, Donald J.↗
PMR polyimide compositions for improved performance at 371 C
Studies were conducted to identify matrix resins which have potential for use at 371 C (700 F). Utilizing PMR methodology, neat resin moldings were prepared with various monomer reactants and screened for thermo-oxidative stability at 371 C (700 F) under both ambient and a four-atmosphere air pressure. The results of the resin screening studies indicate that high molecular weight (HMW) formulated resins of first (PMR-15) and second (PMR-II) generation PMR materials exhibit lower levels of weight loss at 371 C (700) than PMR-15 and PMR-II resins. The resin systems which exhibited the best overall balance of processability, Tg and thermo-oxidative stability at 371 C were used to prepare unidirectional Celion 6000 and T-40R graphite fiber laminates. Laminates were evaluated for thermo-oxidative stability and 371 C mechanical properties. Results of the laminate evaluation studies indicate that two of the resin compositions have potential for use in 371 C applications. The most promising resin composition provided laminates which exhibited no drop in 371 C mechanical properties and only 11 percent weight loss after 200 hr exposure to atmospheres of air at 371 C.
Vannucci, Raymond D.↗
Evaluation of polyimide films as adhesives
A commercially available LARC-TPI film and an experimentally prepared film of LARC-TPI with 5 mol pct of 4,4-prime-oxydianiline (ODA), designated as LARC-TPI/ODA, were evaluated as thermoplastic adhesive films for bonding Ti-6Al-4V. Lap shear strength was used to evaluate the materials as adhesives. They were characterized after fracture by determining the glass transition temperature, T(g). The mode of failure is also reported. Thermal exposure at 240 C for 500 and 1000 h and a 72-h water-boil were conducted on lap shear specimens prepared with the two adhesive films. Lap shear tests were conducted at room temperature, 177 C, 204 C, and 232 C before and after exposures.
Progar, Donald J.↗
Evaluation of a thermoplastic polyimide (422) for bonding GR/PI composite
A hot-melt processable copolyimide previously studied and characterized as an adhesive for bonding Ti-6Al-4V was used to bond Celion 6000/LARC-160 composite. Comparisons are made for the two adherend systems. A bonding cycle was determined for the composite bonding and lap shear specimens were prepared which were thermally exposed in a forced-air oven for up to 5000 h at 204 C. The lap shear strengths (LSSs) were determined at RT, 177, and 204 C. After thermal exposure at RT, 177, and 204 C the LSS decreased significantly; however, a slight increase was noted for the 204 C tests. Initially the LSS values are higher for the bonded Ti-6Al-4V than for the bonded composite, however, the LSS decreases dramatically between 5000 and 10,000 h of 204 C thermal exposure. Longer periods of thermal exposure up to 20,000 h results in further decreases in the LSSs. Although the bonded composite retained useful strengths for exposures up to 5000 h, based on the por results of the bonded Ti-6Al-4V beyond 5000 h, the 422 adhesive bonded composites would most likely also produce poor strengths beyond 5000 h exposure. Adhesive bonded composite lap shear specimens exposed to boiling water for 72 h exhibited greatly reduced strengths at all test temperatures. The percent retained after water boil for each test temperature was essentially the same for both systems.
Progar, Donald J.↗
X-ray diffraction studies of model compounds of thermoplastic polyimides
Several model compounds which represent aspects of the chemical structure of the Langley Research Center thermoplastic (LARC-TPI) have been synthesized for comparison studies using wide angle X-ray scattering (WAXS) as the discriminatory tool. The model compounds included N-phenylphthalimide, 3,3',4,4'-benzophenonetetracarboxylic diphthalimide, and N,N'-diphenyl-3,3',4,4'-benzophenonetetracarboxylic diphthalimide. X-ray diffraction studies of appropriate model compounds can yield information to aid in the understanding of polymeric crystallographic structure. Crystallinity and physical property changes can thus be induced into materials having complicated structures by chemical and thermal processes.
Wakelyn, N. T.↗
An e.s.c.a. study of atomic oxygen interactions with phosphazene-coated polyimide films
Metallic as well as most nonmetallic materials experience oxidation and mass loss via surface erosion in low earth orbit as shown in previous Space Shuttle flights. This study is an evaluation of select polyphosphazene polymers and their resistance to atomic oxygen attack. Electron spectroscopy for chemical analysis examinations of the surfaces of polyphosphazene coatings were monitored for microstructural changes induced during exposures to atomic oxygen. Sample exposures in oxygen plasmas and O(3P) beam were compared as to their effect on surface compositional changes in the polyphosphazene coating. High resolution line scans revealed rearrangements in the polymer backbone and scissioning reactions involving fluorocarbon units of long chain fluoroalkoxy pendant groups. Atom percents and peak areas of all species provided a detailed profile of the microstructural changes induced in phosphazene polymers as a result of exposures to atomic oxygen.
Fewell, Larry L.↗
Polyimides from a methylene-bridged dianhydride
High-molecular weight, high-temperature, highly optically transparent films suitable for electronic and aerospace applications were prepared based on a novel methylene-bridged dianhydride 3,3-prime bis(3,4-dicarboxyphenoxy) diphenylmethane dianhydride (PDMDA). All films had lower dielectric constants and significantly higher optical transparency than the commercial Kapton H film, with air-cured films having slightly higher dielectric constants and lower optical transparency than vacuum films, due to oxidative cross-linking.
Boston, Harold G.↗