bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermotropic Cholesteric Liquid Crystals in Ester Derivatives of Hydroxypropylcellulose
Authors: Kosho Hiroshi , Hiramatsu Sotaro , Nishi Takuya , Tanaka Yasuyuki , Kawauchi Susumu , Watanabe Junji
Published: August 2002

We have synthesized the ester derivatives of hydroxypropylcellulose by a reaction with alkanoic acids with a carbon number of 2 to 9. All these ester derivatives formed a thermotropic cholesteric liquid crystal. The temperature dependence of the cholesteric pitch was studied and discussed in relation to the side-chain length and molecular weight.
Ground-Based Testing of Replacement Thermal Control Materials for the Hubble Space Telescope
Authors: Townsend Jacqueline A , Hansen Patricia A , McClendon Mark W , de Groh Kim K , Banks Bruce A
Published: August 2002

The mechanical and optical properties of the metallized Teflon® FEP thermal control materials on the Hubble Space Telescope (HST) have degraded over the nearly seven years the telescope has been in orbit. Given the damage to the outer layer of the multilayer insulation (MLI) blanket that was apparent during the second servicing mission (SM2), the decision was made to replace the outer layer during subsequent servicing missions. A Failure Review Board was established to investigate the damage to the MLI and identify a replacement material. The replacement material had to meet the stringent thermal requirements of the spacecraft and maintain mechanical integrity for at least ten years.

Ten candidate materials were selected and exposed to ten-year HST-equivalent doses of simulated orbital environments. Samples of the candidates were exposed sequentially to lowand high-energy electrons and protons, atomic oxygen, x-ray radiation, ultraviolet radiation and thermal cycling. Following the exposures, the mechanical integrity and optical properties of the candidates were investigated using optical microscopy, scanning electron microscopy (SEM), a laboratory portable spectroreflectometer (LPSR) and a Lambda 9 spectroreflectometer. Based on the results of these simulations and analyses, the Failure Review Board selected a replacement material and two alternatives that showed the highest likelihood of providing the requisite thermal properties and surviving for ten years in orbit.
Electrically Conductive Space-Durable Polymeric Films for Spacecraft Thermal and Charge Control
Authors: Lennhoff John , Harris George , Vaughn Jason , Edwards David , Zwiener James
Published: August 2002

There is a significant requirement for an electrically conductive thermal control film for the dissipation of spacecraft charging. The present state-of-the-art technology for charge control is based upon thin vapour-deposited indium tin oxide (ITO) conductive coatings on Teflon or Kapton films. These ITO coated films suffer from a range of problems, including no bulk conductivity, poor space durability and a propensity of the coating to crack. A new blended polymer film developed at Triton Systems combines the properties of an intrinsically electrically conductive polymer with that of a space-durable polymer. The resulting film, called C-COR for conductive colourless oxygen resistant, has bulk electrical resistance adjustable between 1012 and 108 ( Ω cm), atomic oxygen (AO) resistance, low absorptance, high emittance, vacuum stability, and good mechanical and UV resistant properties. The C-COR polymer is produced as a free-standing film. Data are presented on the space durability, optical, mechanical and electrical properties of the C-COR film.
Important Factors Controlling Synthesis of Imides in Water
Authors: Dao Buu , Hodgkin Jonathan , Morton Trevor C
Published: August 2002

Four amine/anhydride models have been studied in order to understand the critical factors which control the synthesis of imides and polyimides in water. This synthesis method has been proposed recently as a convenient, environmentally friendly method of producing both thermosetting and thermoplastic polyimides. The key starting step in the synthesis is the formation of a salt/complex between the hydrolysed anhydride and the amine. The results from a combination of quantitative 1H NMR, HPLC and DSC analysis have shown that the reactions are reversible, and that the important factor in driving the reaction to completion in water is the insolubility of the imide product. Analysis of the precipitated imides shows them to be free of significant amounts of the considerably more water soluble amic acids (i.e. the uncyclized amide acids), which often contaminate imides made in conventional aprotic solvents. Of the models investigated, only the imidization of the second amino group in 2, 4, 6-trimethyl-1, 3-phenylene diamine (TMPDA) was subject to kinetic control.

A general conclusion from these experiments is that where a different result is observed in water synthesis of imides compared with conventional aprotic solvent synthesis, it is likely to reflect the vastly different solvation powers of the two solvents rather than a difference in reaction mechanism.
Experimental Verification of the End-Effect Weibull Model as a Predictor of the Tensile Strength of Kevlar-29 (Poly p-Phenyleneterephthalamide) Fibres at Different Gauge Lengths
Authors: Newell James A , Sagendorf Matthew T
Published: August 2002

This paper describes the first application of the four-parameter end-effect Weibull model as a predictor of tensile failure frequency at a gauge length different from that used to generate the model parameters. As-received Kevlar-29 fibres were tensile tested at gauge lengths of 10, 25 and 40 mm. The resulting failure data were used to determine four empirical constants using a maximum-likelihood regression. The model and parameters were used to predict failure frequency at a gauge length outside the initial range (5 mm). The results show that the end-effect Weibull model accurately represents the data from which its parameters are evaluated and that the model may be applied as an effective predictor for gauge lengths beyond the original testing range.
New Thermostable Systems: 2. Structure/Properties Relationship of Nadimide-Terminated Fluorinated Polyimides
Authors: Loustalot Marie Florence Grenier , Billon Laurent , Sillion Bernard
Published: August 2002

The thermomechanical properties of 12 nadimide endcapped oligomers synthesized by polycondensation of nadic anhydride (NA), hexafluoroisopropylidene-2, 2′-diphthalic acid anhydride (HFDA) and phenylene diamines, meta ( mPDA), para ( pPDA) or 9, 9-bis(4-aminophenyl)fluorene (cardo diamine) have been studied. The rheological curves obtained showed the presence of two relaxations: α, associated with the glass transition temperature, and β, due to local molecular movements with the glass transition. The temperature of the loss modulus G″ associated with these two relaxations varied in the domain of molecular weight M n according to a Fox-Flory relation.

By studying the relationship between chemical structures and mechanical properties, the influence of endo/exo isomerization of the nadimide end groups on the glass transition temperature T g has been demonstrated. For a given oligomer, the T g value increases with increasing percentage of exo isomers. The thermo-oxidative stability of the HFDA, PDA and NA oligomers increases when the molecular weight increases.
Liquid Crystalline Polymers: 2. Synthesis and Thermotropic Studies of Poly(Arylidene-Ether)s Containing a Cyclopentanone Moiety in the Main Chain
Authors: Aly Kamal I
Published: August 2002

A novel series of poly(arylidene-ether)s containing cyclopentanone was synthesized by polycondensation of 4, 4′-diformyl-α, ω-diphenoxyalkane and 4, 4′-diformyl-2, 2′-dimethoxy-α, ω-diphenoxyalkane with cyclopentanone. The polymers were characterized by elemental and spectral analyses, inherent viscosity, solubility and thermal analyses. Their thermotropic liquid crystalline properties were examined by DSC, optical polarizing microscopy using a heated stage and thermogravimetric analyses. Almost all the polymers exhibited thermotropic liquid crystalline properties. In most cases the mesophase extends up to 358°C, where thermal decomposition prevents further observations. In addition, the crystallinity of some polymers was examined by x-ray analysis; all showed some degree of crystallinity. The morphology of one polymer was examined by scanning electron microscopy (SEM).
Development and Testing of in situ Materials for Human Exploration of Mars
Authors: Kim M-H Y , Thibeault S A , Wilson J W , Simonsen L C , Heilbronn L , Chang K , Kiefer R L , Weakley J A , Maahs H G
Published: August 2002

Interplanetary space radiation poses a serious health hazard in long-term manned space missions. Natural Martian surface materials are evaluated for their potential use as radiation shields for manned Mars missions. The modified radiation fluences behind various kinds of Martian rocks and regolith are determined by solving the Boltzmann equation using NASA Langley’s HZETRN code along with the 1977 Solar Minimum galactic cosmic ray environmental model. To make structural shielding composite materials from constituents of the Martian atmosphere and from Martian regolith for Martian surface habitats, schemes for synthesizing polyimide from the Martian atmosphere and for processing Martian regolith/polyimide composites are proposed. Theoretical predictions of the shielding properties of these composites are computed to assess their shielding effectiveness. Adding high-performance polymer binders to Martian regolith to enhance the structural properties also enhances the shielding properties of these composites because of the added hydrogenous constituents. Laboratory testing of regolith simulant/polyimide composites is planned in order to validate this prediction and also to measure various structural properties.
Collision-Assisted Erosion of Hydrocarbon Polymers in Atomic-Oxygen Environments
Authors: Minton Timothy K , Zhang Jianming , Garton Donna J , Seale James W
Published: August 2002

Molecular beam–surface scattering experiments have been used to study the mechanisms of material removal when a hydrocarbon polymer surface erodes in the highly oxidizing environment of low Earth orbit or in a simulated space environment on Earth. During steady-state oxidation, CO and CO2 are produced. Formation of these volatile species is believed to account for a significant fraction of the mass loss of a polymer that is under atomic-oxygen attack. The rate of production of CO and CO2 is dramatically enhanced when a continuously-oxidized polymer surface is bombarded with Ar atoms or N2 molecules possessing translational energies greater than 8 eV. The yield of volatile products from the surface appears to increase exponentially with the collision energy of the inert atoms or molecules. Collisions of energetic inert species may accelerate the erosion of polymers in some exposure environments (e.g. in low Earth orbit, where N2 may strike oxidized surfaces with collision energies greater than 8 eV, and in certain atomic-oxygen test facilities that subject oxidized surfaces to bombardment by O2 molecules with average translational energies of approximately 10 eV).
Tailoring Thin-Film/Lacquer Coatings for Space Applications
Authors: Peters Wanda C , Harris George , Miller Grace , Petro John
Published: August 2002

Thin-film coatings have the capability of obtaining a wide range of thermal radiative properties, but the development of thin-film coatings can sometimes be difficult and costly when trying to achieve highly specular surfaces. Given any space mission’s thermal control requirements, there is often a need for a variation of solar absorptance (αs), emittance (∊) and/or highly specular surfaces. The utilization of thin-film coatings is one process of choice for meeting challenging thermal control requirements because of its ability to provide a wide variety of αs/∊ ratios. The radiative properties of thin-film coatings can be tailored to meet specific thermal control requirements through the use of different metals and the variation of dielectric layer thickness. Surface coatings can be spectrally selective to enhance radiative coupling and decoupling. The application of lacquer to a surface can also provide suitable specularity for thin-film application without the cost and difficulty associated with polishing.
Structure–Property Relationships in Epoxy-Amine Networks of Well-Controlled Architecture
Authors: Halary Jean Louis
Published: August 2002

Series of epoxy-amine networks of well-controlled architecture were prepared by varying (a) the chemical nature of both diepoxide and primary diamine, (b) the nature and relative amount of the difunctional amine co-hardener and (c) the stoichiometric ratio. The 22 systems under study here proved to be very suitable for establishing connections between network structure and various physical and mechanical properties including glass transition, primary and secondary mechanical relaxations, modulus in the glassy state, plasticization and antiplasticization effects, water uptake and development of residual stresses. Most of these relationships were based on the consideration of the cross-link density, which affects the properties to a larger extent than the chain flexibility.
Polyimide Containing an Acetal Structure with a Photoacid Generator: A Novel Positive Polyimide Photoresist
Authors: Akimoto Satoshi , Kato Daisuke , Jikei Mitsutoshi , Kakimoto Masa-aki
Published: August 2002

A main-chain degradable photosensitive polyimide containing an acetal structure which degrades by the action of acid coming from a photoacid generator has been developed. Polyimides 4 were prepared by the reaction of bis(4-aminophenoxy)methane 1 and various tetracarboxylic anhydrides 2, followed by thermal treatment. In the resulting polyimides 4, 4f filmderivedfrom 4,4′-hexafluoroisopropylidenebis(phthalicanhydride)(6FDA)and 1 showedgood solubility in organic solvents and transparency to UV light. The acid-catalysed degradation reaction was confirmed by the model imide compound in the presence of p-toluenesulfonic acid. The system of the polyimide 4f containing 30 wt% of diphenyliodonium 9,10-dimethoxyanthracene-2-sulfonate (DIAS), which is a photoacid generator (PAG) showed a sensitivity of 150 mJ cm−2 with 436 nm light, when it was post-exposure baked at 140°C for 30 min, followed by development with 5% tetramethylammonium hydroxide solution at 45°C.
Polyimides Containing an s-Triazine Ring
Authors: Patel H S , Patel V C
Published: August 2002

A series of new polyimides containing an s-triazine nucleus were prepared via Diels–Alder (DA) intermolecular polymerization of 2,6-bis(2-furanyl methyl imino)-4-ethoxy-1,3,5-triazine with different bis(maleimide) compounds. The DA reaction was carried out in tetrahydrofuran as solvent, as well as in bulk followed by aromatization of poly(tetrahydrophthalimido)-intermediates in the presence of acetic anhydride. All the poly(imino- s-triazine imide)s were characterized by elemental analysis, IR spectral studies and thermogravimetry. Glass fibre reinforced composites were prepared via in situ Diels–Alder intermolecular reaction between 2,6-bis(2-furanyl methyl imino)-4-ethoxy-1,3,5-triazine and different bis(maleimide) compounds without evolution of by-products. The prepared composites were characterized by chemical resistivity and mechanical properties.
New Fluorinated Poly(Imide-Ether-Amide)s
Authors: Hamciuc Corneliu , Hamciuc Elena , Sava Ion , Diaconu Ilie , Bruma Maria
Published: August 2002

A series of fluorinated poly(imide-ether-amide)s has been synthesized by solution polycondensation of aromatic diamines containing ether bridges between phenylene rings with a diacid chloride incorporating imide, hexafluoroisopropylidene and methylene groups. The polymers were readily soluble in organic solvents like N, N-dimethylformamide (DMF), N-methylpyrrolidinone (NMP), and even in less polar solvents like pyridine or tetrahydrofuran and gave flexible films by casting of such solutions. These polymers exhibited high thermal stability, with the decomposition temperature being above 360 °C and the glass transition temperature in the range 221–246 °C. The polymer films displayed a low dielectric constant, in the range 3.52–3.81, and tough mechanical properties.
Polymer Synthesis via a Diels–Alder Reaction between Bis(Isobenzofuran)s and Bis(Phenylacetylene)s Containing Preformed Phthalimide Rings
Authors: Watson Kent A , Bass Robert G
Published: August 2002

Polymers have been prepared by the Diels–Alder reaction between novel bis(isobenzofuran)s and bis(phenylacetylene)s containing preformed phthalimide rings. The initial polymer undergoes a thermal rearrangement without volatile evolution that effectively prevents a retro Diels–Alder reaction from occurring. The polymers were soluble in common organic solvents such as chloroform, N-methyl-2-pyrrolidinone, N, N-dimethylacetamide and chlorinated aromatic solvents. The polymers exhibited glass transitions ranging from 251 to 359 °C and a 10%weightloss ranging from 451 to 486 °C in air and 482 to520 °C in helium as determined by thermogravimetric analysis. Thissynthetic approach offers advantages over other Diels–Alder polymerizations since no volatile by-products are generated and a thermal rearrangement eliminates a retro Diels–Alder reaction.
Synthesis, Characterization and Application of Monomeric and Polymeric Dyes Based on N-Arylmaleimides
Authors: Maradiya Hari R , Patel Vithal S
Published: August 2002

Novel monomeric dyes have been prepared by diazotization of 2,6-dibromo-4-nitroaniline and coupled with various N-arylmaleimides. The polymeric dyes were prepared by free radical polymerization of monomeric dyes. The resultant dyes were characterized by IR spectral studies, intrinsic viscosity, thermogravimetry analysis, elemental analysis and molecular weight was characterized by VPO. The monomeric dyes were also characterized by elemental analysis and IR spectra. The purity of all the dyes were checked by thin layer chromatography and they have also been applied on nylon and polyester fibres as a disperse dye. These dyes have been found to give various colour shades with good to very good depth and levelness on each fibre. The percentage dye bath exhaustion on different fibres have been found to be good to very good. The light, washing, rubbing, perspiration and sublimation fastness properties of the dyed fibres has been found to be very good to excellent.
Silicon-Containing Polyesterimides
Authors: Bruma Maria , Schulz Burkhard , Kopnick Thomas , Robison Jenifer
Published: August 2002

New silicon-containing polyesterimides have been synthesized by a solution polycondensation reaction, in a high-boiling-point solvent, of a silicon-containing diacid chloride (namely bis(p-chlorocarbonyl-phenylene)-diphenylsilane) with certain dihydroxy-compounds having preformed imide rings. All these polymers were soluble in polar amidic solvents, such as N-methylpyrrolidinone and dimethylformamide, and gave thin transparent films on casting their solutions. The polymers exhibited high thermal stability, with the initial decomposition temperature being above 400 °C for fully aromatic structures. Most of these polymers did show a glass transition: those containing only aromatic rings being in the range of 180–236 °C, while those having some ethylene units along with aromatic ones being in the range of 160–178 °C. The dielectric constants of the free-standing polymer films are in the range of 3.04–3.19. Very thin coatings, in the range of tens of nanometres, which were deposited onto silicon wafers, exhibited smooth and pinhole-free surfaces in atomic force microscopy investigations. All these characteristics are discussed and compared with those of related polyester-imides which do not contain silicon.
Novel Soluble Ethynyl-Terminated Ester-Imide Prepolymers: Their Syntheses and Characteristics
Authors: Furutani Hiroyuki , Ida Junya , Tanaka Koichiro , Nagano Hirosaku
Published: August 2002

Novel soluble ester-imide prepolymers consisting of bisphenol-A bis(trimellitate) dianhydride (ESDA), aromatic diamine, and 3-ethynylaniline(3-EA) as the thermosetting groups were synthesized. The prepolymers were quite soluble in DMAc, DMF, m-cresol, NMP, CHCl3, and THF. The Tg’s of the various prepolymers were from 200 to 250 °C. The properties of the cured resins of the prepolymers were evaluated, and showed a range of cured Tg’s from 262 to 285 °C and flexural strengths of 112–138 MPa. A low moisture absorption of 0.45% and a low dielectric constant of 3.1 were also observed. Properties of glass-cloth-reinforced composites using the ester-imide prepolymers as the matrix resin were evaluated, and excellent mechanical and thermal properties were observed. An SEM photograph of a cross section of either the cured resin or the glass-cloth-reinforced composite showed good resin flow. Synthesis and some molecular orbital energies of ESDA were also studied.
Novel Soluble Propargylether-Terminated Ester-Imide Prepolymers: I. Their Syntheses and Characteristics
Authors: Furutani Hiroyuki , Ida Junya , Nagano Hirosaku
Published: August 2002

Novel ester-imide prepolymers terminated by 3-(4-aminophenoxy)-propane-1-yne (4-APE) as a thermally curable group were successfully synthesized. The practical preparation route for 4-APE via tosylate (2) is newly developed. Prepolymers were prepared from bisphenol-A bis(trimellitate)dianhydride (ESDA) having an ester moiety of dianhydride, aromatic diamine, and 4-APE. The properties of the cured resins of the prepolymers were evaluated and showed excellent mechanical and thermal properties, i.e. flexural strength of 269–370 MPa and Tg’s of 225–269 °C. Moisture absorption of 0.20–0.78%, and dielectric constants of 3.0–3.2 were also measured.
Microthermal Probing of Ultrathin Polymer Films
Authors: Gorbunov V V , Fuchigami N , Tsukruk V V
Published: August 2002

We present the results of microthermal studies of ultrathin polymeric films deposited on a silicon substrate. We propose the procedure for microthermal analysis of ultrathin polymer films, elucidate limits of applicability of this technique to study their microthermal properties, and observe the thermomechanical response during local heating for films with thicknesses above 10 nm. The glass transition temperature of ultrathin polystyrene (PS) films deduced from experiments decreases for film thicknesses below 200 nm. For the thinnest PS film with clearly detectable response(25nm), the glass transition temperature is 20 °C below its bulk value. Our estimation of heat dissipation in the tip–surface contact area supports the conclusion that the observed micro-thermal-analysis response for polymer films is associated mainly with temperature-induced elastic variation of the contact area.
Aromatic Polyimides Containing p-Quarterphenyl and p-Sexiphenyl Units
Authors: Morikawa Atsushi , Ono Katsumichi
Published: August 2002

We have prepared aromatic polyimides PI-Ar- m containing p-quarterphenyl ( m = 2) and p-sexiphenyl ( m = 4) units.

[ILLEGIBLE]

These polyimides are characterized by having long phenylene units and the introduction of these has a strong influence on the properties of polyimides. In this paper, the properties of polyimides are compared with those of polyimides from 3,3″,4,4″- p-terphenyltetracarboxylic dianhydride ( m = 1) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride ( m = 0), which had been previously prepared, and discussed on the basis of the number ( m) of phenylene units in the dianhydrides.
Aliphatic Polyimides Derived from Polyalicyclic Monomers
Authors: Matsumoto Toshihiko
Published: August 2002

Tetracarboxylic dianhydrides bearing a polyalicyclic structure, bicyclo[2.2.1]-heptane-2,3,5,6-tetracarboxylic 2,3:5,6-dianhydrides (BHDA), bicyclo[2.2.2]-octane-2,3,5,6-tetracarboxylic 2,3:5,6-dianhydrides (BODA), (4arH,8acH)decahydro-1t,4t:5c,8c-dimethanonaphthalene-2,3,6,7-tetracarboxylic 2,3:6,7-dianhydrides (DNDA), and bicyclo[2.2.1]heptane-2-exo,3-exo,5-exo-tricarboxyl-5-endo-acetic 2,3:5,5-dianhydride (BSDA) were synthesized and polycondensated with aromatic diamines or a polyalicyclic diamine, bis(aminomethyl)bicyclo[2.2.1]heptane (BBH), in DMAc, NMP, DMI or HMPA at room temperature or 60–105°C under nitrogen. The polymerization solutions gave the flexible and free-standing polyimide films after being cast on glass plates and then cured. The films were soluble in aprotic polar solvents such as DMAc and NMP at room temperature. Among the films, some dissolved in CHCl3 or 1,4-dioxane. The polyimides showed good thermal stability and the 5% weight loss temperatures in N2 were over 450°C. The polyimide films exhibited Tg values in the range of 280–400°C. The cutoff wavelengths of the non-aromatic polyimides such as PI(DNDAdx-BBH) and PI(BHDAdx-BBH) were shorter than 235 nm, and around 290–330 nm for the semi-aromatic polyimides. The transparencies in the visible region (400–780 nm) were over 85%. The flexible polyimide films possessed an average refractive index range of 1.522–1.617, and the optical anisotropies were 0.000–0.017. The dielectric constant ε values that were estimated from the refractive indices according to the modified Maxwell’s equation were 2.55–2.87.
Poly(Aryl Ether Ketones) Bearing Alkyl Side Chains
Authors: Gronewald Scott , Cassidy Patrick E , Fitch John W , Arbaugh Jesse , Herbold Heath , Jurek Dennis
Published: August 2002

Poly(aryl ether ketones) containing pendant alkyl side chains were prepared by the nucleophilic displacement reaction of 2,2-bis(4-hydroxphenyl)tridecane, 2-2,bis(4hydroxyphenyl)nonadecane and bisphenol AF with 2,2-bis-[4-(4-fluorobenzoyl)phenyl]propane and 2,2-bis[4-(4-fluorobenzoyl)phenyl]hexa-fluoropropane in the presence of potassium carbonate in N,N-dimethylacet-amide. The polymers had inherent viscosities up to 1.04 dl g−1 in chloroform, formed creaseable films and were soluble in common organic solvents. Their dielectric constants were below 2.60 (at 10 GHz). The inclusion of the alkyl side chains lowered the Tg, thermal stability and char yield of fluorinated poly(ether ketone) as expected.
Unexpected Discovery of the Formation of High-Molecular-Weight Aromatic Polyamides from Unstoichiometric Diacyl Chloride/Diamine Components
Authors: Liou Guey-Sheng , Hsiao Sheng-Huei
Published: August 2002

Two bis(ether-benzoylchloride)s, 4,4′-(1,4-phenylenedioxy)dibenzoylchloride (I) and 4,4′-(1,4-naphthalenedioxy)dibenzoyl chloride (II), were unexpectedly synthesized through nucleophilic substitution reaction of p-fluorobenzonitrile with 2-(6-oxido-6H-dibenz〈c,e〉〈1,2〉oxaphosphorin-6-yl)-1,4-benzenediol (1) and 2-(6-oxido-6H-dibenz〈c,e〉〈1,2〉oxaphosphorin-6-yl)-1,4-naphthalenediol (2), respectively, followed by hydrolysis and chlorination. A series of aromatic poly(ether-amide)s, having inherent viscosities of 0.65–0.99 dl g−1, prepared by the low-temperature solution polycondensation from the diacid chloride I with various aromatic diamines in an initial feeding molar ratio of diamine:diacyl chloride of 1:1 and 1:1.55, respectively. All resultant poly(ether-amide)s showed high and similar inherent viscosity regardless of the great stoichiometric imbalance. The unexpected results could be attributed to the very slow dissolution rate of the diacid chloride I in the reaction solvents such as N-methyl-2-pyrrolidone and N,N-dimethylacetamide.
Solid-Phase Thermal Polymerization of Macrocyclic S-Aryl Thioester Trimer with 5-t-Butylisophtaloyl Skeleton Using Crown Ether Complexes
Authors: Kameyama Atsushi , Kimura Kentarou , Nishikubo Tadatomi
Published: August 2002

Thermal polymerizations of macrocyclic S-aryl thioester trimer with a 5- t-butylisophtaloyl skeleton ( m-CTE-3) were investigated. The polymerization of m-CTE-3 without catalysts occurred at over 260°C in the solid state and heating at 280°C for 10 min produced a polymer with a Mw of 370 000. Quaternary onium salts or crown ether complexes enhanced the solid-phase thermal polymerization of m-CTE-3. In the case of the polymerization using 18-crown-6 ether (18-C-6)/potassium halide complexes, the polymerization occurred at around 200°C. It was proved that 18-C-6/KBr was the most effective catalyst to produce high molecular weight polymers with Mw as much as 850 000. It was also suggested that the solid-phase polymerization proceeded in a chain-growth reaction mode.
Synthesis and Properties of Copolyesters Based on Hydroquinone, Sebacic Acid and p-Hydroxybenzoic Acid
Authors: Nagata Minoru
Published: August 2002

A series of thermotropic liquid crystalline copolyesters were prepared by a melt-polycondensation of 1,4-diacetoxybenzene (HQ) and sebacic acid (SA) with various amounts of p-acetoxybenzoic acid (HBA) in the presence of p-toluene sulfonic acid as a catalyst. The chemical structure, phase transition behaviours, liquid crystallinity and thermal stability were examined by Fourier transform infrared absorption spectroscopy, 1H nuclear magnetic resonance, differential scanning calorimetry, thermogravimetry and polarized-light microscopy. With increasing HBA content, the glass transition temperature and melting temperature increased slightly, while the crystallinity decreased significantly. The copolyesters with HBA contents higher than 30 mol% could show a nematic phase and their isotropization temperatures increased markedly with increasing HBA content. The environmental degradability has been ascertained by testing the resistance of copolyester films to both alkaline hydrolysis and activated sludge. The degradation rate and the extent of the hydrolysis of the above copolyesters were evaluated by their weight losses. Weight loss and scanning electron microscope observation could not exhibit any significant change in the activated sludge during the test period, while the copolyesters with HBA contents higher than 30 mol% showed a dramatical weight loss in alkaline aqueous solution.
Chemistries for High Reliability in Electronics Assemblies
Authors: Herr Donald E , Nikolic Nikola A , Schultz Rose Ann
Published: August 2002

This article provides a review of the attitude of the scientific community towards reliability in electronic packages, with emphasis on the prevailing mechanisms for package failure under highly stressed environmental conditioning. Once this failure mechanism is fully developed, approaches to the resolution can be more rigorously applied. Overall, the predominant evidence points to moisture, both diffusivity and equilibrium weight gain, as the key factor in reduced reliability performance. Other fundamental polymer properties are important, but generally, methods are well established for adjusting these parameters. Moisture uptake is somewhat inherent to a particular chemistry type and this can direct the use of resin systems that are more suited to particularly moist environments. Epoxy resin systems, while pervasive in the electronics industry, do have limitations under humid environmental test conditions. Cyanate ester resin chemistry is claimed to have low moisture uptake by virtue of a non-hydrophilic cure mechanism. However, certain aspects of the cure chemistry and side reactions with water can result in misleading predictions on humid environment performance. Siloxane-based materials present an attractive solution to many moisture related issues. Traditional condensation and addition cure silicone systems have, thus, found widespread use as packaging adhesives and encapsulants. Siloxane-functional polyimides have also been successfully utilized in a number of application areas. Relatively new siloxane/hydrocarbon resins, developed specifically for electronics applications, further address the shortcomings of classic silicone adhesives and coatings.
Semi-Fluorinated Epoxy Thermoplastics Containing the α-Methylstilbene Linkage
Authors: Nelson Erik J , Foulger Stephen H , Smith Dennis W
Published: August 2002

The reaction of the mesogenic epoxy monomer, p-bis(2,3-epoxypropoxy)-α-methylstilbene, with bis(hydroxyphenyl)- iso-propylidene and bis(hydroxyphenyl)hexafluoro- iso-propylidene affords new semifluorinated poly(hydroxy aryl ether) thermoplastics with controlled properties dependent upon fluorine incorporation. Step-growth polymerization in a DMAc solution (33 wt%) gave linear polymers with molecular weights ranging from 29 000–60 000 Mw and polydispersities ( Mw/Mn) from 1.7–2.1 (gel permeation chromatography). The polymers can be solution or melt processed, exhibit Tg’s ranging from 78 to 105 °C (dynamic scanning calorimetry) and maintain thermal stability above 390 °C (thermogravimetric analysis). The polymerization, characterization, and potential mesophase formation as a function of polymer dimensions and semifluorination is discussed.
Structure–Properties Relationship of Some Polyimidazopyrrolones Foils
Authors: Schab-Balcerzak Ewa , Sek Danuta , Grabiec Eugenia , Jarzabek Bożena , Mazurak Zbigniew
Published: August 2002

A series of semiladder polyimidazopyrrolones having amide, ester and ether linkages in the main chain have been synthesized using low-temperature polycondensation in dimethylacetamide (DMA). Solutions of prepolymers in the form of proper polyamideamino acid in DMA were cast onto a glass plate, heated in vacuo at 200 °C for 8 h and then at 280 °C for 2 h to cause evaporation of the solvent and thermal cyclization. Free-standing foils were characterized by Fourier-transform infrared spectroscopy and their mechanical, thermomechanical and optical properties were investigated.
Evaluation and Analysis of Thermal Control Materials under Ground Simulation Test for Space Environment Effects
Authors: Nakayama Youichi , Imagawa Kichiro , Tagashira Minoru , Nakai Muneaki , Kudoh Hisaaki , Sugimoto Masaki , Kasai Noboru , Seguchi Tadao
Published: August 2002

Thermal control materials such as white paint comprising silicone resin matrix (NASDA-1049/101-S), black paint comprising urethane resin matrix (NASDA-1049/201-U-I), aluminized polyimide adhesive tape (Sheldahl G408810) and silver-backed fluorinated ethylene propylene (silvered FEP) adhesive tape (Sheldahl G402500) were exposed to electron beam (EB), proton (H+), iron ion (Fe5+), ultraviolet (UV) and atomic oxygen (AO) radiation with ground simulation test facilities. Combined irradiation of EB → UV and another combined irradiation of EB → AO, where EB was irradiated at first and then UV or AO was irradiated, were also examined for white paint and black paint. Irradiation energies were 0.5 and 1.9 MeV for EB; 1, 3 and 10 MeV for H+; 15 MeV for Fe5+; equal to or larger than 3.1 eV for UV; and 5 eV for AO. Fluences of EB, H+ and Fe5+ were selected to simulate the environment of geostationary orbit (GEO) for 10 years. UV irradiation was equal to 300 equivalent solar days. AO fluence corresponded to the environment of low Earth orbit (LEO) for about 1 year. The solar absorptance (αS) and normal infrared emittance (εN) of the examined materials both before and after irradiation were acquired. The durability of the materials against each irradiation treatment was judged by evaluating the changes in αS and εN. White paint and black paint were strongly affected by AO, EB → UV, EB → AO and UV irradiation. White paint was also affected by EB and weakly by H+ and Fe5+. Aluminized polyimide and silvered FEP were degraded most by AO and EB. EB had a stronger effect than ions (H+,Fe5+) in all the samples, the reason for which can be explained by the larger absorbed dose with EB compared with ions. The mass loss caused by the irradiation treatment was also measured for white paint and black paint. Analytical techniques such as scanning electron microscopy (SEM), electron spectroscopy for chemical analysis (ESCA) and Fourier transform infrared spectroscopy (FTIR) were applied to identify morphology and composition of the materials to obtain a deeper understanding of the mechanism of space environment effects on the materials.
Comparative Analysis of Solar Array Fragments Degradation at Different Structure Scales during and after Long-Term Exposure Overboard the ‘Mir’ Space Station
Authors: Letin Vladimir A , Babayevsky Petr G
Published: August 2002

Generalized comparative analysis of the results of model specimens and fragments of standard solar array degradation studies before and after prolonged exposure and during operation in low Earth orbits (LEOs) is made. The studies gave a unique opportunity to reveal new information on the influence of the space environment on solar array materials and components, determine the degree of degradation and understand the mechanism of their degradation. It was determined that the degrees of power and current degradation in the MSA1 wing of the Mir space station mountable solar array and its panels are high and non-uniform. Most of the solar cell blocks and single cells (about 70%), materials, structure assemblages and components had stood up to more than 10 years exposure in LEO environment satisfactorily. Thermocycle effects and optical performance decrease are the main causes of power and current losses in undamaged solar cells. About 30% of the cell blocks had suffered severe damage to their structure and interconnects from hot-spotting processes due to strip shadowing of the blocks by space station structure elements such as pantograph members. These processes governed the power and current losses in solar arrays.
Phenylethynyl Terminated Arylene Ether Oxadiazole and Triazole Oligomers and Their Cured Polymers
Authors: Thompson C M , Hergenrother P M
Published: August 2002

Several novel phenylethynyl terminated arylene ether oligomers containing oxadiazole and triazole rings were prepared as part of an effort to develop high performance polymers with an attractive combination of properties (e.g. processability and mechanical performance) for future NASA applications. The oligomers displayed low melt viscosities and good solubilities. Thin films cast from solutions of the oligomers and cured for one hour at 350 °Cinairgave good tensile properties. Titanium to titanium (6Al-4V) tensile shear specimens were readily fabricated and provided moderate strengths. The chemistry and properties of these new materials are discussed.
Polybenzimidazole Prepreg: Improved Elevated Temperature Properties with Autoclave Processability
Authors: Steiner Paul A. , Sandor Robert
Published: August 2002

Polybenzimidazoles (PBI) are heterocyclic polymers which are known for their outstanding thermal and chemical stability. Hoechst Celanese has recently developed PBI (2,2'-(m-phenylene)-5,5'-bibenzimidazole) as an engineering plastic with the trade name CelazoleTM. The polymer has excellent compressive strength, high tensile strength and modulus, and a glass transition temperature of 425°C. Low molecular weight, oligomeric forms of PBI have been used in the past as a composite matrix material. The prepregs produced were stiff and board-like at ambient temperature. In addition, in situ polymerization resulted in large amounts of condensation by-products (phenol and water) which meant that high pressure curing conditions were needed to minimize voids. More recently, medium molecular weight PBI (12 000-20 000 g molweight average) has been used in combination with NN-dimethylacetamide (DMAc) solvent to produce prepregs with excellent tack and drape. These prepregs have significantly reduced condensation by-products, resulting in improved processability and properties. Reported in this article are polymer modifications which enhance the ability to cure PBI prepreg at standard autoclave pressures and have the added benefit of improved high temperature composite properties.
Synthesis and Biological Activity of Polyketone Resins. Part II: Systems Based on o-xylene with Carbon Disulphide as Solvent
Authors: Patel N. Z. , Patel J. N. , Ray R. M. , Patel R. M.
Published: August 2002

Friedel-Crafts resins have been prepared by reactidg o-xylene, chloroacetyl chloride, 1,2-dichloroethane and dichloromethane using anhydrous aluminium chloride as catalyst and carbon disulphide as solvent. Polymers were characterized with IR and showed the presence of carbonyl and chlorine in the polymer backbone. Thermal analysis indicated good thermal stability of the resins. Microbial study indicated the ability of the resins to inhibit the growth of microorganisms.
Properties of Glass-fibre-reinforced Composites of Epoxy Resins Cured with Different Amines
Authors: Patel Sandeep R. , Patel Ranjan G.
Published: August 2002

Glass-fibre-reinforced epoxy composites were fabricated from the matrix resins diglycidyl ether of bisphenol A (DGEBA) and tetraglycidyl diaminodiphenyl methane (TGDDM) using different amines as curing agents. The characteriation of these epoxy laminates included resistance to chemical reagents, mechanical properties [e.g. shore-D hardness, flexural strength and interlaminar shear strength (ILSS)] as well as dielectric properties including dielectric constant, loss tangent (tan δ), electrical resistance and breakdown voltage.
Aromatic Poly(ether imide oxadiazole)s
Authors: Mercer F. W.
Published: August 2002

Two oxadiazole containing aromatic diamines were synthesized. The diamines were prepared by reaction of aminophenols with 2,5-bis(4-fluorophenyl)-4l3,4-oxadiazole in a polar aprotic solvent in the presence of potassium carbonate. Reaction of the resulting 2,5-bis(4-(aminophenoxy)phenyl)-1,3,4-oxadiazoles with dianhydrides gave a series of polymeric amic acids. Thermal treatment yielded poly(imide ether oxadazole) films which displayed good thermal stability, flexibility, and glass transition temperatures ranging from 241 to 344C. The dielectric constants of the films were characterized as a function of relative humidity.
Synthesis and Biological Activity of Polyketone Resins-IV. Systems Based on m-Xylene with Nitrobenzene as Solvent
Authors: Patel N. Z. , Patel J. N. , Patel R. M.
Published: August 2002

Seven chlorine-terminated polyketones of low molecular weight were prepared from m-xylene, chloroacetyl chloride and ao-dichloroalkanes, i.e. dichloro-methane and 1,2-dichloroethane, by the Friedel-Crafts reaction using nitrobenzene as solvent. The polyketones were characterized by [R spectra and vapour pressure osmome-t'y. The thermal properties were studied by thermogravimetry and differential scanning calorimetry. The kinetic parameters for the decomposition reactions were evaluated by the Broido and Doyle methods. The polyketones were found to be thermally sable up to 220°C but decompose beyond this temperature. All the resins were screened for their biological activity against plant pathogens (Pseudomonas fluorescens, Bacillus subtilis, Aspergillus niger and Trichoderma viride). The biological screening against bacteria has indicated that these polyketones have biocidal properties.
The effect of high-energy electron radiation on poly(arylene ether)s
Authors: Connell J W , Siochi E J , Croall C I
Published: August 2002

Thin films of four experimental poly(arylene ether)s of similar chemical structure were exposed to 1 MeV electrons while under high vacuum. The films received total exposures of 5 x 107 and 1 x 109 rads at a dose rate of 5 x 107 rads h-1 and a pressure of 2 x 10-7 torr. Films exposed to 5 x 107 rads showed dramatic changes in molecular weight distribution. After exposures of 1 x 109 rads the films were only partially soluble in chloroform and exhibited no detectable changes in the glass transition temperatures. Thin-film tensile properties were also altered by the exposure to electron radiation. The effect of the exposures as determined by various analyses is discussed.
Recent advances in polyimide composites
Authors: Wilson Doug
Published: August 2002

Polyimide matrix composites possess an excellent balance of physical and thermal properties. However, currently available systems suffer from a number of drawbacks. Much of R & D is aimed at overcoming these drawbacks and developing new and novel polyimide materials. This review paper will examine recent developments in polyimide composites in the areas of thermo-oxidative stability, resistance to microcracking, toughness, toxicity and processability.
Extended Poly(Phenylquinoxalines) Containing Earbonyl and Sulfide Connecting Groups
Authors: Mehta Rooma Mago , Basst R G , Singh Rajendra K
Published: August 2002

Novel poly(phenylquinoxalines) (PPQs) containing carbonyl and sulfide connecting groups between the aromatic rings were prepared by condensation of various aromatic bis(o-diamines) with novel extended bis(phenyl-1.2-diketones) in m-cresol. An objective of the work was to determine the effect of replacing oxygen by sulfur in extended PPQs. The polymers prepared were soluble in m-cresol, dimethylsulfoxide, N,Ndimethylacetamide, 1-methyl-2-pyrrolidinone and chlorinated hydrocarbon solvents, and had inherent viscosities as high as 1.23 dl g-1. The PPQs exhibited glass transition temperatures ranging from 217 to 245 C and polymer decomposition temperatures (10% weight loss) as measured by thermogravimetric analysis of 526-568 in air and 510-549 CC in helium. A tough transparent yellow fingernail creasable film with a tensile strength of 94.7 MPa, a tensile modulus of 2562 MPa and elongation at break of 6.4% at 25 "C was cast from a chloroform solution of the polymer prepared from 1,3-bis(phenylglyoxalyl-4phenylthio-4'-benzoyl)benzene and 3,3'-diaminobenzidine. Little difference in properties was observed in the PPQs prepared as compared to the PPQs containing carbonyl and ether connecting groups between the aromatic rings, in spite of the difference in the bonding characteristics of carbon to sulfur and to oxygen.
Preparation and characterization of poly(arylene ether isoxazole)s by fluoride ion-mediated aromatic nucleophilic displacement reactions
Authors: Herbert C G , Bass R G
Published: August 2002

As part of a continuing effort to prepare novel thermally stable high-performance polymers, poly(arylene ether isoxazole)s have been prepared by fluoride ion-catalysed aromatic nucleophilic substitution reactions with bis(trimethylsiloxyphenyl) isoxazoles and activated bisarylhalides in diphenyl sulphone. Initial investigations involving the preparation of these materials with isoxazole bisphenols and activated bisarylhalides in the presence of potassium carbonate indicated that, under reaction conditions necessary to prepare high-molecular-weight materials, the isoxazole monomer was converted to an enamino ketone. This side reaction was avoided by using fluoride as a base. However, trimethylsilyt ether derivatives of the isoxazole bisphenols were required in these polymerizations for the preparation of high-molecular-weight materials. Moderate to high inherent viscosity (htAh: 0.43-0.87 dl g -) materials with good thermal stability (air: 409-477C, helium: 435-512C) can be prepared by the silyl ether method. Glass transition temperatures ranged from 182 to 225 C for polymers with phenyl pendants and from 170 to 214 C for those without. Molecular weight control by 2% endcapping and the incorporation of a phenyl pendant at the 4 position of the isoxazole is necessary to yield polymers soluble in polar aprotic solvents at room temperature. There is evidence, however, indicating the existence of crosslinks between the polymer chains when the silyl ether approach is utilized.
Soluble poly(imide)s based on the phenylindane structure element
Authors: Maier Gerhard , Yang Dazhong , Wolf Martin , Nuyken Oskar
Published: August 2002

This paper describes the synthesis and characterization of several poly(imide)s containing different phenylindane structural elements. A comparison with known polymers of similar structure but no indane rings reveals the influence of the presence of the indane system on polymer properties. In general, solubility is improved and the glass transition temperature is increased by the introduction of the bulky indane groups. Crystallization of the polymer chains is prevented by the presence of 1,1,3-trimethylindane units. Variation of the indane structure itself allows some adjustment of the solubility behaviour. 1,3-Dicyclohexyl-l-methyl units in place of the trimethylindane groups decrease the range of possible solvents, but still allow solubility at room temperature in DMAc. All polymers in this study can be cast into tough. clear, flexible films, either directly as poly(imide) solution or via the poly(amic acid) precursor. The thermal stability is decreased compared with fully aromatic polyimides. Decomposition temperatures (5% weight loss) are between 450 and 480C in air.