Results for “polyimide” — Page 11

NASA NTRS1987

DC electrical, thermal, and spectroscopic properties of various condensation polyimides containing surface cobalt oxide

Doping polyimides with cobalt ion causes the room temperature direct current electrical resistivity to decrease relative to the polymer alone, the reduction being most pronounced for the air-side of the cobalt modified polyimides. At a constant electrical field, resistivity for the volume, air-side and glass-side modes decreases yet further with an increase in temperature as expected for semiconductors and insulators. X-ray photoelectron spectroscopy indicates the air-side of the cobalt modified polyimides is predominantly Co3O4. The bulk resistivity of the air-side and activation energy of conduction for this surface are comparable to high purity sintered Co3O4. Charging characteristics at room temperature indicate a substantial polymer matrix contribution to both the glass-side and volume mode measurements but a negligible contribution to the air-side electrical properties. Volume electrical resistivity for similar additive levels is reduced by increasing the molecular flexibility of the host polymer.

Rancourt, J. D.↗

NASA NTRS1988

Developing Crystallinity In Linear Aromatic Polyimides

New technique improves melt flow of polyimide. Uses chemical imidization or cyclodehydration techniques that do not cause significant decrease in molecular weight. Process involves dissolution of polyamide acid in amide solvent or mixture of ether and amide solvent at low percentage of solids followed by treatment of this solution with aprotic organic base, such as triethylamine or pyridine, for period of time prior to treatment with organic dehydrating agent. Latter treatments facilitates formation of polyimide. Useful for production of polyimide molding materials. Expected to have widespread application in preparation of easily processed adhesives, molding powders, and matrix resins.

St. Clair, Terry L.↗

NASA NTRS1988

Adhesive properties of LARC-CPI, a new semi-crystalline polyimide

As part of an effort on high temperature structural resins for aerospace applications, a new family of polyimides containing carbon and ether connecting groups between aromatic rings were prepared. Several of these polyimides were semicrystalline. One polyimide, designated LARC-CPI, with a glass transition temperature of 222 C and a crystalline melt temperature of 350 C, was evaluated in the form of an adhesive, film, and molding. Unoriented films exhibited excellent resistance to solvents and strong bases and high tensile properties. Compact tension specimens gave very high fracture toughness values. Titanium tensile shear specimens provided exceptional strength under a variety of test conditions. The chemistry and the physical and mechanical properties of LARC-CPI are discussed.

Hergenrother, P. M.↗

NASA NTRS1989

Low-Dielectric Polyimides

New process developed to produce aromatic condensation polyimide films and coatings having dielectric constants in range of 2.4 to 3.2. Materials better electrical insulators than state-of-the-art commercial polyimides. Several low-dielectric-constant polyimides have excellent resistance to moisture. Useful as film and coating materials for both industrial and aerospace applications where high electrical insulation, resistance to moisture, mechanical strength, and thermal stability required. Applicable to production of high-temperature and moisture-resistance adhesives, films, photoresists, and coatings. Electronic applications include printed-circuit boards, both of composite and flexible-film types and potential use in automotive, aerospace, and electronic industries.

St. Clair, Anne K.↗

NASA NTRS1989

Soluble Aromatic Polyimides For Film Coating

Because of toughness, flexibility, and remarkable thermal stability, linear all-aromatic polyimides excellent candidate film and coating materials for advanced electronic circuitry and wires. Study determined effects on solubility of changing isomeric points of attachment of phenoxy units in diamine portions of several all-aromatic polyimides. Tough, flexible, transparent films produced by thermally converting polyamic acids to polyimides at 300 degree C in air. Potential for electronic applications excellent.

St. Clair, Anne K.↗

NASA NTRS1988

Isomeric oxydiphthalic anhydride polyimides

Much of the polyimide research at Langley Research Center has focused on isomeric modification of the diamine component; polyimides having considerably improved processability and adhesion have resulted. The present structure-property study was designed to investigate how isomeric attachment of the three oxydiphthalic anhydride (ODPA) polyimides affects their properties. Each dianhydride, 3,4,3',4'-oxydiphthalic anhydride (4,4'-OPDA,I), 2,3,2',3'-oxydiphthalic anhydride (3,3'-ODPA,II), and 2,3,3',4'-oxydiphthalic anhydride (3,4'-OPDA,III), was reacted with p-phenylenediamine, 4,4'-oxydianiline, 3,3'-diaminodiphenylsulfone, 3,3'-diaminobenzophenone, and 4,4'-bis(3-aminophenoxy)benzophenone in DMAc. The inherent viscosities of the resulting poly(amic acids) were determined. Thermally imidized films were studied for their creasability and solubility, as well as by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and wide angle X-ray scattering (WAXS). A comparison of these properties will be made.

Gerber, Margaret K.↗

NASA NTRS1988

Flexible backbone aromatic polyimide adhesives

Continuing research at Langley Research Center on the synthesis and development of new inexpensive flexible aromatic polyimides as adhesives has resulted in a material identified as LARC-F-SO2 with similarities to polyimidesulfone, PISO2, and other flexible backbone polyimides recently reported by Progar and St. Clair. Also prepared and evaluated was an endcapped version of PISO2. These two polymers were compared with LARC-TPI and LARC-STPI, polyimides research in our laboratory and reported in the literature. The adhesive evaluation, primarily based on lap shear strength (LSS) tests at RT, 177 C and 204 C, involved preparing adhesive tapes, conducting bonding studies and exposing lap shear specimens to 204 C air for up to 1000 hrs and to a 72-hour water boil. The type of adhesive failure as well as the Tg was determined for the fractured specimens. The results indicate that LARC-TPI provides the highest LSSs. LARC-F-SO2, LARC-TPI and LARC-STPI all retain their strengths after thermal exposure for 1000 hrs and PISO2 retains greater than 80 percent of its control strengths. After a 72-hr water boil exposure, most of the four adhesive systems showed reduced strengths for all test temperatures although still retaining a high percentage of their original strength (greater than 60 percent) except for one case. The predominant failure type was cohesive with no significant change in the Tgs.

Progar, Donald J.↗

NASA NTRS1990

Additives Lower Dielectric Constants Of Polyimides

Dielectric constants as low as 2.43 make polyimides more attractive for electronic applications. Process makes aromatic condensation polyimide films and coatings with dielectric constants lowered by incorporation of diamic acid additives. Materials provide better electrical insulation without sacrificing temperature stability of polyimide binders. Applicable whenever high temperature, low absorption of moisture, and high electrical-insulation properties needed. Applications include semiconductors and printed-circuit boards for computer industry and possibly automotive industry.

Stoakely, Diane M.↗

NASA NTRS1989

Novel polyimide compositions based on 4,4': Isophthaloyldiphthalic anaydride (IDPA)

A series of twelve high temperature, high performance polyimide compositions based on 4,4'-isophthaloyl diphthalic anhydride (IDPA) was prepared and characterized. Tough, film-forming, organic solvent-insoluble polyimides were obtained. Three materials were semicrystalline. Several gave excellent long-term thermooxidative stability by isothermal thermogravimetric analysis (ITGA) at 300 C and 350 C in air when compared to Kapton H film (duPont). One extensively studied material displayed different levels of semicrystallinity over a wide range of final cure time/temperatures. The polyimide from IDPA and 1,3-bis (4-aminophenoxy 4'-benzoyl) benzene exhibited multiple crystallization and melting behavior, implying the existence of two kinetic and two thermodynamic crystallization and melting transitions by differential scanning calorimetry (DSC).

Pratt, J. Richard↗

NASA NTRS1990

LARC-IA: A flexible backbone polyimide

A new linear, aromatic, thermoplastic polyimide, prepared from oxydiphthalic anhydride (ODPA) and 3,4'-oxydianiline (ODA) in diglyme and identified as LARC-IA, was synthesized and evaluated. The monomers are relatively inexpensive and physiologically safe. Molecular weight was controlled by use of a monofunctional anhydride, phthalic anhydride (PA), in order to promote controlled flow and wetting properties. The polymer is considered a safe alternative to commercially available LARC-TPI which is prepared with an expensive diamine of uncertain carcinogenicity. The evaluation was based primarily on the polymer's adhesive properties as determined by thermal and water boil exposure of lap shear specimens. Strengths were determined at room temperature, 177, 204 and 232 C before and after exposure to determine the adhesive system's durability to adverse environments over a period of time. Other properties (FWT, G(1c), film and composite properties) were examined which were determined to be typical of a high temperature polyimide. Results of the study show a favorable comparison to LARC-TPI, a commercially available polyimide.

Progar, Donald J.↗

NASA NTRS1990

Process for lowering the dielectric constant of polyimides using diamic acid additives

Linear aromatic polyimides with low dielectric constants are produced by adding a diamic acid additive to the polyamic acid resin formed by the condensation of an aromatic dianhydride with an aromatic diamine. The resulting modified polyimide is a better electrical insulator than state-of-the-art commercially available polyimides.

Stoakley, Diane M.↗

NASA NTRS1989

Characterization of a thermally imidized soluble polyimide film

A soluble aromatic poly(amic acid) film was converted to a soluble polyimide by staging at 25 deg intervals to 325 C and characterized at each interval by several analytical methods. The behavior observed was consistent with an interpretation that a reduction occurred in molecular weight of the poly(amic acid) during the initial stages of cure before the ultimate molecular weight was achieved as a polyimide. This interpretation was supported by the results of solution viscosity, gel permeation chromatography, low angle laser light scattering photometry and infrared spectroscopy analysis. The results serve to increase the fundamental understanding of how polyimides are thermally formed from poly(amic acids).

Young, Philip R.↗

NASA NTRS1989

Flexible backbone aromatic polyimide adhesives

Continuing research at Langley Research Center on the synthesis and development of new inexpensive flexible aromatic polyimides as adhesives has resulted in a material identified as LARC-F-SO2 with similarities to polyimidesulfone, PISO2, and other flexible backbone polyimides recently reported by Progar and St. Clair. Also prepared and evaluated was an endcapped version of PISO2. These two polymers were compared with LARC-TPI and LARC-STPI, polyimides research in our laboratory and reported in the literature. The adhesive evaluation, primarily based on lap shear strength (LSS) tests at RT, 177 C and 204 C, involved preparing adhesive tapes, conducting bonding studies and exposing lap shear specimens to 204 C air for up to 1000 hrs and to a 72-hour water boil. The type of adhesive failure as well as the Tg was determined for the fractured specimens. The results indicate that LARC-TPI provides the highest LSSs. LARC-F-SO2, LARC-TPI and LARC-STPI all retain their strengths after thermal exposure for 1000 hrs and PISO2 retains greater than 80 percent of its control strengths. After a 72-hr water boil exposure, most of the four adhesive systems showed reduced strengths for all test temperatures although still retaining a high percentage of their original strength (greater than 60 percent) except for one case. The predominant failure type was cohesive with no significant change in the Tgs.

Progar, Donald J.↗

NASA NTRS1991

New Polyimide Has Many Uses

Low-toxicity and low-mutogenicity monomer key to new high-performance polyimide. LaRC-IA is thermoplastic polyimide made from 3-4'-oxydianiline and 4,4'-oxydiphthalic anhydride. Good processing characteristics, low toxicity, and no mutagenicity. Adhesives, composite matrix resins, heat resin moldings, and coating films made of new polymer found to exhibit properties identical or superior to commercially available polyimides. Potential applications wide ranging. With and without end capping, employed to prepare unfilled moldings, coatings and free films, adhesive tape, adhesively bonded substrates, prepregs, and composites.

St. Clair, Terry L.↗

NASA NTRS1991

Long term isothermal aging and thermal analysis of N-CYCAP polyimides

The N-CYCAP polyimides utilize a (2,2) paracyclophane endcap that polymerizes and does not generate volatile gases during the cure process. These polyimides have both high glass temperatures (390 C) and an onset of decomposition in air of 560 C. Thermal oxidative stability (TOS) weight loss studies show that replacing 25 percent by weight of the paraphenylene diamine in the polymer backbone with metaphenylene diamine improves the weight loss characteristics. N-CYCAP neat resin samples performed better than PMR-II-50 when exposed at 343 and 371 C in air for up to 1000 hours. Preliminary composite studies show that both PMR-II-50 and N-CYCAP have better thermal stability when fabricated on T-40R. Higher isothermal aging temperatures of longer aging times are needed to determine the differences in TOS between composite samples of PMR-II-50 and N-CYCAP polyimides.

Sutter, James K.↗

NASA NTRS1990

Characterization of a thermally imidized soluble polyimide film

A soluble aromatic poly(amic acid) film was converted to a soluble polyimide by staging at 25 deg intervals to 325 C and characterized at each interval by several analytical methods. The behavior observed was consistent with an interpretation that a reduction occurred in molecular weight of the poly(amic acid) during the initial stages of cure before the ultimate molecular weight was achieved as a polyimide. This interpretation was supported by the results of solution viscosity, gel permeation chromatography, low angle laser light scattering photometry and infrared spectroscopy analysis. The results serve to increase the fundamental understanding of how polyimides are thermally formed from poly(amic acids).

Young, Philip R.↗

NASA NTRS1992

Polyimides with pendent ethynyl groups

Several new polyimides containing pendent ethynyl groups were prepared and characterized. The new polyimides were prepared from the following novel ethynyl containing diamines; 1,1-bis(p aminophenyl)-1-(p ethynylphenyl) 2,2,2-trifluoroethane, and 1,1-bis(p aminophenyl)-1-(p phenylethynylphenyl)-2,2,2 trifluoroethane, and 1,1-bis(p aminophenyl)-1-(p hexynylphenyl)-2,2,2 trifluoroethane by reacting with either 3,3',4,4' benzophenone tetracarboxylic dianhydride or 2,2-bis(3,4 dicarboxyphenyl) hexafluoropropane dianhydride (6FDA). Inherent viscosities for the polymers ranged from 0.26 to 0.94 dL/g. Three copolymers prepared by reacting 10 mole pct. of one of the ethynyl containing diamines and 90 mole pct. of 2,2-bis-(4-(4 aminophenoxy)phenyl) hexafluoropropane with 6FDA were also prepared and characterized. Inherent viscosities for these copolymers ranged from 1.08 to 1.54 dL/g. Original polyimide glass transition temperatures were approx. 265 C while curing at 300 to 350 C for 1 hr in air increased the Tgs by approx. 10 C. Film properties and thermal stability were also measured for these copolyimides.

Jensen, Brian J.↗

NASA NTRS1992

The mechanical properties of polyimide films after exposure to high pH

Wiring failures linked to insulation damage have drawn much attention in the aerospace industry and concerns have developed regarding the stability and safety of polyimide insulated electrical wire. Several polyimides were selected for evaluation for resistance to degradation by various aqueous alkaline solutions. The polyimides under evaluation include commercially available films such as Kapton (tk), Apical (tk), LaRC(tk)-TPI, and Upilex(tk)R and S, as well as a number of experimental films prepared by NASA Langley. Thermally imidized films were studied for their retention of mechanical properties after exposure to high pH solutions under stressed conditions.

Croall, Catharine I.↗