bluuebunny/crossref_metadata_2025 huggingface dataset:
Outcome of patients with new-onset diabetes mellitus after liver transplantation compared with those without diabetes mellitus
Authors: John Preeti R. , Thuluvath Paul J.
Published: August 2002

In liver transplant recipients, new onset of diabetes mellitus (posttransplant diabetes mellitus or PTDM) is estimated to occur in 9% to 21% of recipients. The limited published data on survival and posttransplant complications in liver transplant recipients who develop PTDM show conflicting results. The objective of our study was to compare the morbidity and mortality of 46 patients who developed PTDM with 92 age- and sex-matched patients without pretransplant or posttransplant diabetes mellitus (DM). The demographics of both groups were similar except that there were more blacks with PTDM. The incidence of following complications was higher in the PTDM group compared with the control group: cardiac (48% v 24%; P = .005), major infections (41% v 25%; P = .07), minor infections (28% v 5%; P = .001), neurologic (22% v 9%; P = .05), and neuropsychiatric (22% v 6%; P = .009). Acute rejection was seen more commonly in the PTDM group (50% v 30%; P = .03). The duration of hospital stay, cost of hospitalization, retransplantation rate, and graft survival were similar in both groups. Patient survival also was similar in the PTDM and control groups at 1 year (93.5% v 83.5%), two years (88.1% v 77.9%), and 5 years (75% v 77.2%); Kaplan-Meier survival analysis also did not show survival difference. In conclusion, PTDM was associated with significant morbidity, and our findings suggest that patients with PTDM should be monitored very closely to improve long-term outcome.
Combined Omental Pedicle Grafts and Thoracodorsal Axial Pattern Flaps for the Reconstruction of Chronic, Nonhealing Axillary Wounds in Cats
Authors: Lascelles B. Duncan X. , White Richard A. S.
Published: August 2002

Objective—To assess the results of an omental pedicle graft in combination with a thoracodorsal axial pattern flap for the reconstruction of chronic nonhealing axillary wounds in 10 cats caused by forelimb entrapment within a collar.

Study Design—A prospective, clinical trial.

Animals Used—Ten client‐owned domestic shorthair cats.

Methods—Routine biochemical and hematologic evaluation was performed on each cat, and all were tested for feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV). Microbial culture was performed on samples from the wounds. After surgical debridement, omentalization using a vascular pedicle of greater omentum, and closure of the chronic axillary wounds, using a thoracodorsal axial pattern flap, was performed. All excised tissue was examined histologically.

Results—The sex distribution was 7 males and 3 females, with a mean age of 3.5 years. The cats had undergone a median number of 3 previous repair attempts over a 1.5‐ to 25‐month period before referral (mean, 10.2 months). No hematologic or biochemical abnormalities were noted apart from moderately elevated creatine kinase and aspartate transaminase concentrations in some cats. All cats were negative for FIV and FeLV. Histologic examination of resected tissue revealed hair (foreign body) in 2 cats and an unidentified foreign‐body reaction in 3 other cats. Complete healing occurred in all cats (mean follow‐up period of 21.7 months), with 2 cats requiring further surgery: 1 for flap dehiscence at 4 days after surgery, and 1 for donor‐site dehiscence at 4 days after surgery. One other cat developed a large seroma in the axilla that resolved by 10 days following surgery.

Conclusion—The use of an omental pedicle graft in combination with a thoracodorsal axial pattern flap is the first consistently successful 1‐step technique for the management of chronic nonhealing axillary wounds in cats.
Modelling Macrophage Infiltration into Avascular Tumours
Authors: Kelly C. E. , Leek R. D. , Byrne H. M. , Cox S. M. , Harris A. L. , Lewis C. E.
Published: August 2002

In this paper a mathematical model that describes macrophage infiltration into avascular tumours is presented. The qualitative accuracy of the model is assessed by comparing numerical results with independent experimental data that describe the infiltration of macrophages into two types of spheroids: chemoattractant‐producing (hepa‐1) and chemoattractant‐deficient (or C4) spheroids. A combination of analytical and numerical techniques are used to show how the infiltration pattern depends on the motility mechanisms involved (i.e. random motion and chemotaxis) and to explain the observed differences in macrophage infiltration into the hepa‐1 and C4 spheroids. Model predictions are generated to show how the spheroid′s size and spatial structure and the ability of its constituent cells influence macrophage infiltration. For example, chemoattractant‐producing spheroids are shown to recruit larger numbers of macrophages than chemoattractant‐deficient spheroids of the same size and spatial structure. The biological implications of these results are also discussed briefly.
Regulation of Cytochrome c Oxidase by Adenylic Nucleotides. Is Oxidative Phosphorylation Feedback Regulated by its End‐Products?
Authors: Beauvoit Bertrand , Rigoulet Michel
Published: August 2002

Cytochrome c oxidase, which catalyzes an irreversible step of the respiratory chain, is one of the rate‐controlling steps of oxidative phosphorylation on isolated mitochondria. The rate of electron transfer through the complex is primarily controlled by the associated thermodynamic forces, i.e., the span in redox potential between oxygen and cytochrome c and the protonmotive force. However, the electron flux also depends on the various kinetic effectors, including adenylic nucleotides. Although the number of binding sites for ATP and ADP on cytochrome oxidase is still a matter of debate, experiments performed on the solubilized and reconstituted enzyme provide strong functional evidence that the mammalian cytochrome c oxidase binds adenylic nucleotides on both sides of the inner membrane. These effects include modification in cytochrome c affinity, allosteric inhibition and changes in proton pumping efficiency. Immunological studies have pointed out the role of subunit IV and that of an ATP‐binding protein, subunit VIa, in these kinetic regulations. In yeast, the role of the nuclear‐encoded subunits in assembly and regulation of the cytochrome c oxidase has been further substantiated by using gene‐disruption analysis. Using a subunit VIa‐null mutant, the consequences of the ATP regulation on oxidative phosphorylation have been further investigated on isolated mitochondria. Taken together, the data demonstrate that there are multiple regulating sites for ATP on the yeast cytochrome oxidase with respect to the location (matrix versus cytosolic side), kinetic effect (activation versus inhibition) and consequence on the flow‐force relationships. The question is therefore raised as to the physiological meaning of such feedback regulation of the respiratory chain by ATP in the control and regulation of cellular energy metabolism.
Structure and Thermal Behaviour of a Thermotropic Liquid Crystalline Polyimide (PI-LC)
Authors: Tanaka M , Konda M , Miyamoto M , Kimura Y , Yamaguchi A
Published: August 2002

Anomalous solid structures formed by a thermotropic liquid crystalline polyimide (PI-LC) were investigated by thermal analysis, polarized light microscopy and x-ray analysis. It was revealed that PI-LC should undergo a phase transition from the crystalline to the isotropic phase through the smectic or nematic phase in the temperature range 277–300 °C. The PI-LC filament extruded at 280 °C, at which temperature the polymer was in liquid crystalline phase, was formed to have a structure similar to the smectic C phase, while that extruded and melt-drawn at 310 °C, at which temperature the polymer was in the isotropic phase, had a structure similar to the smectic A phase.
Arylene Azo p-Hydroxy Benzoic Acid–Formaldehyde Oligomer Dyes
Authors: Patel P S , Patel S K , Patel K C
Published: August 2002

A series of oligomeric azo dyes has been synthesized by coupling various aromatic diazonium salts to p-hydroxy benzoic acid–formaldehyde ( p-HBAF) oligomer. They were evaluated in terms of their softening points, yields, colour, UV–visible spectra, IR spectra and PMR spectra. Dyeing on wool and nylon resulted in yellow to red shades having moderate to good fastness to light and good to very good fastness to washing.
Effects of Radiation and Thermal Cycling on Teflon ® FEP
Authors: Dever Joyce A , de Groh Kim K , Banks Bruce A , Townsend Jacqueline A
Published: August 2002

Surfaces of the aluminized Teflon® FEP (fluorinated ethylene propylene) multilayer thermal insulation on the Hubble Space Telescope (HST) were found to be cracked and curled in some areas at the time of the second servicing mission (SM2) in February 1997, 6.8 years after HST was deployed in low Earth orbit (LEO). In an effort to understand what elements of the space environment might cause such damage, pristine second-surface aluminized Teflon® FEP was tested for durability to various types of radiation, to thermal cycling and to radiation followed by thermal cycling. Types of radiation included synchrotron vacuum ultraviolet and soft x-ray radiation, simulated solar flare x-ray radiation, electrons and protons. Thermal cycling was conducted in various temperature ranges to simulate HST orbital conditions for Teflon® FEP. Resultsoftensiletestingoftheexposedspecimensshowedthatexposuretohighfluencesofradiation caused degradation in tensile properties of FEP. However, exposure to radiation alone in exposures comparable to those experienced by HST did not produce reduction in ultimate tensile strength and elongation of Teflon® similar to that observed for HST-retrieved aluminized Teflon®. Synergism of radiation exposure and thermal cycling was evident in the results of three experiments: thermal cycling following electron and proton irradiation, thermal cycling following x-ray exposure, and additional thermal cycling of a sample retrieved from HST. However, irradiation and thermal cycling with comparable HST SM2 exposure conditions did not produce the degradation observed in the FEP material retrieved during HST SM2.
Molecularly Oriented Films for Space Applications
Authors: Fay Catharine C , Stoakley Diane M , St Clair Anne K
Published: August 2002

Because of their inherent toughness and flexibility, low density, thermal stability, radiation resistance and mechanical strength, aromatic polyimides have excellent potential for use as advanced materials on large space structures. Polyimides were uniaxially and biaxially oriented to further enhance their dimensional stability, stiffness, elongation and strength. Both unoriented and oriented polymeric thin films were also cryogenically treated to temperatures below -184 °C to show their stability in cold environments. Successful stretching depended on film quality, film thickness, soak time, grip pressure, stretching rate and stretching temperature. In-plane birefringence increased with increased stretch ratios as expected. Coefficients of thermal expansion (CTEs) decreased with increased stretch ratio by as much as 31%. Tensile strengths increased by up to 85% with increasing stretch ratio. Elongations increased by as much as 95% with stretching. Significant improvements in elongation were obtained with only a 2× uniaxial orientation. Moduli did not change significantly with stretching. Mechanical properties increased more with uniaxial stretching than biaxial stretching. Cryogenic treatment increased the tensile strength of some stretched samples by a maximum of 10–20%. Properties such as modulus and CTE did not change significantly after the films had been slow cooled to cryogenic temperatures.
Synthesis and Characterization of Short Carbon Fibre-Reinforced PMR-Type Polyimide Composites
Authors: Gao Sheng Q , Zhang Yi L , Li Jia Z , Yang Shi Y
Published: August 2002

Short carbon fibre-reinforced polyimide composites were prepared by wet impregnating chopped short carbon fibres with PMR-type polyimide matrix resin solution followed by evaporating the solvent with strong stirring. The processing properties of the prepolymer moulding powders were investigated. The mechanical properties and thermo-oxidative stability of the fabricated composite were also studied. Experimental results demonstrate that the short fibre filled moulding powders exhibit good melt resin flowing characteristics and can be processed by a hot press moulding technique to produce small-size, complicated composite structures which are difficult to produce using continuous fibre-reinforced composite prepregs by an autoclave technique. The composites exhibit outstanding mechanical properties and excellent thermal and thermo-oxidative stabilities at temperatures as high as 320 °C.
New Thermostable Systems: 1. Mechanism and Kinetics of Polycondensation and Characterization of Fluoro-Nadimide End-Capped Oligomers
Authors: Loustalot Marie Florence Grenier , Billon Laurent , Sillion Bernard
Published: August 2002

The reactivity of monomers in PMR (polymerization of monomeric reactants) mixtures has been investigated in methanol at room temperature. The monomers used were three aromatic diamines, meta-phenylene diamine ( mPDA), para-phenylene diamine ( pPDA), the 9, 9-bis (4-amino phenyl) fluorene (Cardo diamine), hexafluoroisopropylidene-2, 2 bis phthalic ether (HFDE) and nadic anhydride mono methyl ester (NE). Using titration, and 13C and 19F NMR, it was found that NE rapidly reacts with the three aromatic diamines to yield bisnadimides; the corresponding acid-amide intermediates were not detected. The diester HFDE, on the other hand, reacts only very slowly with the same diamines at room temperature in methanol.

Telechelic polyimides with nadic terminations were prepared from these monomers and characterized with liquid phase 1H and 13C NMR and HPLC. This physico-chemical study showed that during synthesis, the endo (N) nadimides isomerize giving off a mixture of endo endo (NN), endo exo (NX) and exo exo (XX) end groups. In addition, a fine high-performance liquid chromatography analysis led to the separation of oligomers as a function of their polymerization degree, and for each molecular weight a mixture of isomeric chain end groups NN, NX, XX were separated.
Study on Novel Polyamides Based on Ester Terminated Epoxy Resin
Authors: Patel Sanjay V , Raval Dipak K , Thakkar Jatin R
Published: August 2002

The bisester 1, 1′-(1-methylethylidene)bis[4-{1-imino-4-ethylbenzoate-2-propanolyloxy}]benzene (DGEBA-4-AEB), synthesized by the reaction of the epoxy resin diglycidyl ether of bisphenol-A (DGEBA) with 4-amino ethyl benzoate (4-AEB), was condensed with different aromatic diamines, namely 4, 4′-diamino diphenyl methane (DDM), 4, 4′-diamino diphenyl sulfone (DDS) and benzidine (Ben) to yield novel epoxy based curing agents. The resultant novel epoxy based polyamides (PAs) were characterized by infrared spectroscopy along with the estimation of number average molecular weight ( Mn) by gel permeation chromatography (GPC). Using differential scanning calorimetry (DSC), the kinetics of the curing reactions of PAs–epoxy resin systems were established by evaluating the usual kinetic parameters. The thermal behaviour of PAs–epoxy cured products was also studied by thermogravimetric analysis (TGA).
Chemistry and Properties of Imide Oligomers from Phenylethynyl-Containing Diamines
Authors: Smith J G , Connell J W
Published: August 2002

As an extension of work on pendent phenylethynyl-containing imide oligomers, three new diamines containing pendent phenylethynyl groups were prepared and characterized. These diamines were used to prepare pendent and pendent and terminal phenylethynyl imide oligomers via the amide acid route in N-methyl-2-pyrrolidinone at a calculated number average molecular weight of 5000 g mol−1. The pendent phenylethynyl groups were randomly distributed along the oligomer backbone and provided a means of controlling the distance between reactive sites. The imide oligomers were characterized and thermally cured, and the cured polymers evaluated as thin films and compared with materials of similar composition prepared from 3,5-diamino-4′-phenylethynylbenzophenone. This work was performed as part of a continuing research effort to develop structural resins for potential aeronautical applications.
Aromatic Polyazomethines Containing Phenylquinoxaline Rings
Authors: Bruma Maria , Hamciuc Elena , Mercer Frank , Köpnick Thomas , Schulz Burkhard
Published: August 2002

New aromatic polyazomethines have been synthesized by polycondensation of terephthalic dialdehyde with aromatic diamines containing preformed phenylquinoxaline rings. These polymers are easily soluble in polar aprotic solvents such as N-methylpyrrolidinone and dimethylacetamide, and even in less polar liquids like tetrahydrofurane and can be cast into thin flexible films or coatings from such solutions. They show high thermal stability with the initial decomposition temperature being above 500 °C and glass transition temperatures in the range 240–292 °C. The very thin polymer coatings deposited by a spin-coating technique onto silicon wafers show a very smooth, pinhole-free surface in atomic force microscopy investigations. The free-standing films of 20–30 μm thickness show a low dielectric constant, which is in the range 3.25–3.56, which is promising for a future application as high-performance dielectrics.
Neat Resin, Adhesive and Composite Properties of Reactive Additive/PETI-5 Blends
Authors: Connell John W , Smith Joseph G , Hergenrother Paul M , Rommel Monica L
Published: August 2002

PETI-5 (5000 g mol −1) is a relatively new adhesive and composite matrix that exhibits good processability and excellent properties. However in the fabrication of complex composite parts (i.e. skin stringer and support frames), better processability would offer distinct advantages. In an effort to improve the processability of PETI-5, a novel reactive additive was prepared and used to formulate blends. The reactive additive is a mixture of relatively simple phenylethynyl containing imides. As such, it exhibited solubility in a variety of solvents such as N-methyl-2-pyrrolidinone, a relatively low softening temperature ∼185°C) and a low melt viscosity (∼0.1–0.3 Pa s at 250°C). Neat resin blends prepared by physically mixing imide powders of the reactive additive and PETI-5 were thermally and rheologically characterized. Blends were also prepared by mixing NMP solutions of PETI-5 amide acid and the reactive additive (imide form). These solutions were subsequently used to prepare adhesive film and unidirectional carbon fibre tape using unsized IM7 fibre. The reactive additive/PETI-5 blends were used to fabricate titanium adhesive panels and composites under 0.54 MPa or less for 1 h at 350–371°C. The effect of reactive additive content on the physical, rheological, adhesive and carbon fibre laminate properties was determined. One formulation exhibited a decrease in melt viscosity (i.e. improved processability) without effecting open hole compression, compression properties after impact or microcrack behaviour. The neat resin, adhesive and composite properties of these reactive additive/PETI-5 blends and their cured polymers will be discussed.
Preparation and Properties of PMR-II Polyimide/Chopped Quartz Fibre Composites
Authors: Gao S Q , Wang X Ch , Hu A J , Zhang Y L , Yang S Y
Published: August 2002

High-temperature polyimide composites with low and stable dielectric properties were produced by thermally curing prepolyimide moulding compounds which were prepared by the wet impregnation of chopped short quartz fibres with a PMR-II polyimide matrix resin solution, followed by the evaporation of the solvent with vigorous stirring. The mechanical properties, thermo-oxidative stability as well as the dielectric and electric properties of the composites were studied. The experimental results showed that the composites exhibit outstanding mechanical properties and excellent thermal and thermo-oxidative stability at temperatures as high as 371 °C. It was revealed that both the dielectric constant (∼3.0) and loss tangent (∼10−3) of the composites were not obviously changed with a frequency in the broadband wavelength (1 kHz–20 GHz).
Novel Propargylether-Terminated Ester-Imide Prepolymers: III. Thermoset/thermoset blend prepolymers as matrix resins for composites
Authors: Furutani Hiroyuki , Ida Junya , Nagano Hirosaku
Published: August 2002

Glass-cloth-reinforced composites were prepared from prepolymers of various weight ratio blends of the state-of-the-art propargylether-terminated ester-imide (1) and bismaleimide (MB-8000). The Tg of a composite is directly related to the weight ratio of MB-8000 present. The composites demonstrated excellent initial mechanical properties. The chemical and electrical properties under severe long-ageing conditions were demonstrated.
Application of Hyperbranched Block Copolymers as Templates for the Generation of Nanoporous Organosilicates
Authors: Mecerreyes D , Huang E , Magbitang T , Volksen W , Hawker C J , Lee V Y , Miller R D , Hedrick J L
Published: August 2002

A general route to organic–inorganic hybrids with nanophase morphologies has been elaborated with the objective of ultimately generating nanoporosity in organosilicates. Hyperbranched block copolymers prepared by either the sequential or concurrent polymerization of an ABC monomer ( γ-( ∊-caprolactone) 2-bromo-2-dimethylpropionate) with a BCD monomer (2-hydroxyethyl methacrylate) were used as the macromolecular templates. The two monomers, each polymerizing by different chemistries, for example ring-opening polymerization and atom transfer radical polymerization, bear initiating centres that are targeted for the functionality located on the accompanying monomer. Consequentially, a branched polymer is obtained which avoids the traditional multistep procedures. The branching density was altered simply by the addition of the appropriate AB ( ∊-caprolactone) and/or CD (methyl methacrylate) comonomers. These polymers were readily soluble initially in the organosilicate prepolymer (methyl silsesquioxane), however, upon the onset of crosslinking, both the solubility parameters and molecular weight of the organosilicate (polymethylsilsesquioxane) change, causing the hyperbranched polymer to phase separate by a nucleation and growth process. The organic polymer was selectively removed by thermolysis, producing a nanoporous inorganic structure. The size and shape of the pores are identical to those of the initial hybrid morphology. A significant reduction in the dielectric constant was achieved by simply replacing a portion of the glass matrix with air, which has a dielectric constant of 1.0.
Hyperbranched Poly(Ether Amide)s via Nucleophilic Ring Opening Reaction of Oxazolines
Authors: Böhme Frank , Clausnitzer Carola , Gruber Freddy , Grutke Stefan , Huber Thomas , Pötschke Petra , Voit Brigitte
Published: August 2002

The nucleophilic ring opening addition reaction of phenol groups towards oxazoline units has been used for the preparation of hyperbranched poly(ether amide)s. For this the AB2 monomer 2-(3,5-bishydroxyphenyl)-1,3-oxazoline was synthesized and converted in a highly branched polymer in bulk or solution at temperatures above 190°C. The resulting hyperbranched polymers exhibit a degree of branching of 50%, as verified by high-resolution NMR spectroscopy, and are highly soluble in polar organic solvents, for example DMF and DMAc, with low solution viscosity. Their glass transition temperatures are in the region of 170°C and degradation does not start below 300°C. Melt rheology measurements revealed a predominantly elastic behaviour with a relatively high viscosity at low frequency. A lower melt viscosity was achieved by end group modification. Hyperbranched poly(ether amide)s with phenolic and acetate end groups are fully miscible with linear polyamide 6. When a small amount of the hyperbranched material is added to the PA6 matrix a significant reduction of the melt viscosity could be achieved without changing the mechanical properties of the matrix polymer.
Hyperbranched Aramids by the A2 + B3 versus AB2 Approach: Influence of the Reaction Conditions on Structural Development
Authors: Monticelli Orietta , Mariani Alberto , Voit Brigitte , Komber Hartmut , Mendichi Raniero , Pitto Valentina , Tabuani Daniela , Russo Saverio
Published: August 2002

Hyperbranched aromatic polyamides (pPDT) from A2 ( p-phenylene diamine)+ B3 (trimesic acid) reactants have been prepared using direct polycondensation in solution. The influence of various polymerization parameters on the polymer structure development and the sol content, as well as on gel formation, has been thoroughly investigated. Prior to the attainment of the gel point, whose occurrence is linked quite strongly to the reaction conditions, the resultant hyperbranched polymers are fully soluble even at room temperature, not only in concentrated H2SO4, but also in aprotic polar solvents (DMF, NMP, DMAc, DMSO). At 80°C, under typical experimental conditions, gel formation starts just under 120 min. At a higher temperature (115°C), the attainment of crosslinking reactions is accelerated (gel point occurs at about 20 min). Both the presence of added salt (LiCl) to the reaction medium at 80°C and the use of highly purified reagents promotes earlier gel occurrence. By increasing the molar ratio of primary amino to carboxyl groups from two-thirds to one, the network formation is delayed. A molar ratio of 1/2 leads to the formation of oligomers only.

Both the polymer structure development and the degree of branching of pPDT have been evaluated by NMR spectroscopy as functions of reaction conditions. As compared to pPDT, polymers prepared from the homologous AB2 monomer show similar intrinsic viscosity and glass transition temperature, but higher molecular weights and distinct differences in the relative ratio of the various structural units. The lyotropic and thermotropic behaviour of both polymers has been found.
Semi-Aromatic Polyimides with Low Dielectric Constant and Low CTE
Authors: Hasegawa Masatoshi
Published: August 2002

Semi-aromatic polyimides (PIs) possessing simultaneously a low dielectric constant ( K) and low linear coefficient of thermal expansion ( CTE) were molecularly-designed. Two PI systems were focused on, i.e. the s-BPDA/CHDA polyimide derived from 3,3′,4,4′-biphenyltetracarboxylic dianhydride with trans-1,4-cyclohexanediamine and CBDA/TFMB derived from 1,2,3,4-cyclobutanetetracarboxylic dianhydride and bis(2,2′-trifluoromethyl)benzidine. In the s-BPDA/CHDA system, poly(amic) acid (PAA) polymerization using the common procedure was prevented by strong salt formation at the initial stage. However, heating the salt-forming reaction mixture at a selected temperature for a short period allowed the system to polymerize and resulted in a high-molecular-weight PAA (reduced viscosity ηred > 2 dl g−1). On the other hand, in the CBDA/TFMB system, a high-molecular-weight PAA ( ηred > 3 dl g−1) was readily obtained by choosing the solid content without any salt formation. The chosen PIs almost achieved the current goal; CTE < 20 ppm K−1, K < 3.0, and Tg > 300°C concurrently with adequate film flexibility. In particular, CBDA/TFMB accomplished a very low K (∼2.6). Although these PIs have a much lower thermo-oxidative stability than wholly aromatic PIs, the results suggested that there is no serious problem for the short-term thermal stability required for soldering processes.
Quadruple Aliphatic Polyamide Systems Prepared by a Layer-by-Layer Alternating Vapour Deposition Method
Authors: Nagai Ayako , Shao Huli , Umemoto Susumu , Kikutani Takeshi , Okui Norimasa
Published: August 2002

Quadruple nylon systems, nylon-6688, nylon-661010 and nylon-6668, were prepared by layer-by-layer alternating vapour deposition polymerization (AVDP). In the AVDP process, four bi-functional monomers, two dichloride monomers and two diamine monomers were deposited alternately onto the substrate with layer-by-layer polycondensation. The films showed a highly ordered structure with the molecular orientation tilting to the substrate. The film thickness could be effectively controlled by the number of deposition reaction cycles. The intensities for characteristic IR band peaks and for x-ray diffraction peaks associated with the layer structure showed good linear relationship to the film thickness.
Synthesis and Characterization of Ordered Polyurethanes from a Pair of Diisocyanate Monomers and Ethylene Glycol
Authors: Nishio Akinori , Mochizuki Amane , Sugiyama Jun-Ichi , Takeuchi Kazuhiko , Asai Michihiko , Ueda Mitsuru
Published: August 2002

We have studied the synthesis of ordered polyurethane from 4,4′-methylenebis(phenyl isocyanate) (MDI), hexamethylene diisocyanate (HMDI) and ethylene glycol (EG). It was found that the regularity of polyurethanes was affected by the feed speed of the monomer and catalyst species. Using a triethylamine (TEA) catalyst, a multi-block copolymer was produced by the slow addition of EG to a mixture of MDI and HMDI, and a statistical copolymer was obtained by the rapid addition of EG to a mixture of MDI and HMDI. On the other hand, the rapid addition of EG to a mixture of MDI and HMDI in the presence of an alkyltin catalyst produced an alternating copolymer. The structural regularity of the polymers has an effect on their thermal properties and crystallinity.
Synthesis and Phase Separation Behaviour of High Performance Multiblock Copolymers
Authors: Pospiech Doris , Häußler Liane , Eckstein Kathrin , Komber Hartmut , Voigt Dieter , Jehnichen Dieter , Friedel Peter , Gottwald Antje , Kollig Wolfram , Kricheldorf Hans R
Published: August 2002

The phase separation behaviour of block copolymers of the type (A–B) n(segmented block copolymers, multiblock copolymers) containing segments with different degrees of flexibility was investigated using a stepwise variation of the incorporated blocks A and B. Amorphous/rigid blocks (polysulfone segments) were systematically combined with amorphous/flexible blocks (poly(tetramethylene glycol), semiflexible/nematic blocks (different kinds of aromatic polyesters and poly(ester imides) as well as semicrystalline fluorinated polyester blocks). All multiblock copolymers were synthesized using a conventional transesterification polycondensation in the melt and the polycondensation results are discussed.

The phase separation in the synthesized block copolymers was investigated both experimentally and theoretically. Flory–Huggins interaction parameters of the block copolymers were calculated and used together with mean field calculations in order to understand the phase separation behaviour of all block copolymers correlated to their chemical structure. On the other hand, the onset of phase separation in a series of block copolymers with a systematic variation of block molecular weights was examined experimentally, mainly by DSC and SAXS.

Finally, the question is discussed whether or not the degree of phase separation in the investigated systems determines the properties of the polymers or not. This is for example outlined for the mechanical properties and, in particular, the surface properties of fluorinated block copolymers.
Effect of Hydroxyphenylmaleimide on the Curing Behaviour and Thermomechanical Properties of Rubber-Modified Polybenzoxazine
Authors: Agag Tarek , Takeichi Tsutomu
Published: August 2002

Hydroxyphenylmaleimide (HPMI) and/or amine terminated butadiene acrylonitrile (ATBN)-modified polybenzoxazine were prepared by mixing benzoxazine monomer (Ba), HPMI and ATBN. The onset of the ring opening of the pristine Ba started with differential scanning calorimetry at 223°C with a maximum at 247°C. The incorporation of ATBN lowered the onset and the maximum of the exotherm to 180°C and 216°C respectively. The incorporation of HPMI initiated the ring opening of Ba at a temperature as low as 160°C with a maximum at 200°C. Viscoelastic measurements showed that the incorporation of HPMI increased the Tg and the storage modulus compared to that of the unmodified polybenzoxazine and ATBN-modified polybenzoxazine. Tensile property measurements indicated that the tensile modulus was enhanced with the addition of HPMI to ATBN-modified polybenzoxazine accompanied with little decrease in the elongation at break. Thermogravimetric analysis showed that the addition of HPMI enhanced the thermal stability of polybenzoxazine.
Synthesis and Characterization of a Fully Aromatic Polyazomethine with Main Chain Rotaxane Architecture
Authors: Farcas Aurica , Grigoras Mircea
Published: August 2002

A new aromatic polyazomethine with rotaxane architecture containing a blocking group in every structural unit has been synthesized by polycondensation of 3,6-diformyl-9-butyl carbazole with p,p′-diaminobiphenyl (benzidine)/β-cyclodextrin adduct. As compared with polymers obtained in the absence of β-cyclodextrin, this polymer is more hygroscopic and soluble in polar solvents such as DMF and DMSO. The IR, 1H-NMR, GPC and DSC data support the presence of β-cyclodextrin in the polymer chain. Measurements made by gel permeation chromatography of the DMF soluble main-chain polyrotaxane show high molecular weight. This polymer is a light-yellow coloured product and its electrical conductivity is as high as 10−9 S cm−1. Doping with iodine markedly increased the conductivity of the orange-brown coloured semiconductive polyazomethine with a maximum conductivity of 10−6 S cm−1.
Processable Polyimides with High Glass Transition Temperature and High Storage Modulus Retention at 400°C
Authors: Hao J Y , Hu A J , Gao S Q , Wang X Ch , Yang S Y
Published: August 2002

End-capped polyimide precursor solutions in ethyl alcohol were prepared by incorporating carbonyl groups into the polymer backbone of a second-generation PMR ( in situ polymerization of monomer reactants) polyimide, PMR-II-50, which exhibited good features as a matrix resin for carbon-fibrereinforced composites. Cured polyimides were prepared in an analogous process as the PMR-II polyimides. The thermal and thermo-oxidative stability of the cured polyimides was systemically investigated. It was found that the cured polyimide containing a 1:1 mole ratio of the carbonyl group [–C(O)–] to the hexafluoroisopropyl group [–C(CF3)2–] in the polymer backbone possessed a very high glass transition temperature (440 °C) and an excellent thermal decomposition temperature (576 °C). The onset temperature of the storage modulus curve was measured at about 400 °C with high retention ( >55%) of the storage modulus at 400 °C, compared to 10–15% of the corresponding PMR-II polyimide. Carbon-fibre-reinforced composites also showed a high onset temperature of the storage modulus (420 °C) and high storage modulus retention ( >85%) at 400 °C. Preliminary results indicated that the composite laminate exhibited excellent mechanical strength retention at 371 °C, which was superior to that of CF/PMR-II composites.
Mechanical Properties of Teflon® FEP Retrieved from the Hubble Space Telescope
Authors: Dever Joyce A , de Groh Kim K , Messer Russell K , McClendon Mark W , Viens Michael , Wang L Len , Gummow Jonathan D
Published: August 2002

Teflon® FEP (fluorinated ethylene propylene) surfaces on the Hubble Space Telescope (HST) have experienced significant degradation in mechanical properties during nearly ten years of exposure in the low Earth orbit environment. This paper describes results of mechanical properties testing of Teflon® FEP materials exposed on HST for 9.7 years between launch and the third servicing mission (SM3A) and for 2.8 years between the second servicing mission (SM2) and SM3A. The results of tensile testing, bend testing and microscopic examination of crack morphology are described. The effects of post-retrieval heating and air compared with vacuum storage on the mechanical properties of the FEP surfaces are described as they significantly affect the interpretation of the results regarding the durability of FEP on HST. This paper provides comparisons of the properties of FEP surfaces retrieved during SM3A to previously reported results for FEP materials retrieved during the first servicing mission (SM1) and SM2. The environmental exposure conditions for the HST exposed materials are also described.
Thermal Contributions to the Degradation of Teflon® FEP on the Hubble Space Telescope
Authors: de Groh Kim K , Dever Joyce A , Sutter James K , Gaier James R , Gummow Jonathan D , Scheiman Daniel A , He Charles
Published: August 2002

Metallized Teflon® fluorinated ethylene propylene (FEP) thermal control material on the Hubble Space Telescope (HST) is degrading in the space environment. Teflon® FEP insulation was retrieved during servicing missions, which occurred in 1993, 1997 and 1999. During the second servicing mission (SM2), the 5 mil aluminized-FEP (Al-FEP) outer layer of multilayer insulation (MLI) covering the telescope was found to be cracked in many locations around the telescope. Teflon® FEP retrieved during SM2 was more embrittled than the FEP retrieved 2.8 years later from a different location, during the third servicing mission (SM3A). Studies have been conducted to understand the degradation of FEP on HST, and the difference in the degree of degradation of FEP from each of the servicing missions. The retrieved SM2 material experienced a higher temperature extreme during thermal cycling (200 °C) than the first servicing mission (SM1) and SM3A materials (upper temperature of 50 °C), therefore an investigation on the effects of heating FEP was also conducted. Samples of pristine FEP and SM1, SM2 and SM3A retrieved FEP were heated to 200 °C and evaluated for changes in properties. Heating at 130 °C was also investigated because FEP bi-stem thermal shields are expected to cycle to a maximum temperature of 130 °C on-orbit. Tensile, density, x-ray diffraction crystallinity and differential scanning calorimetry data were evaluated. It was found that heating pristine FEP caused an increase in the density and practically no change in tensile properties. However, when as-retrieved space samples were heated, the density increased and the tensile properties decreased. Upon heating, all samples experienced an increase in crystallinity, with larger increases in the space-exposed FEP. These results indicate that irradiation of FEP in space causes chain scission, resulting in embrittlement, and that excessive heating allows increased mobility of space-environment-induced scissioned chains. Thermal exposure was therefore found to have a major impact on the extent of embrittlement of FEP on HST.
Synthesis and Characterization of Aromatic Polyimide Containing 3,6-Diamino-9-Alkylcarbazole and Aromatic Tetracarboxylic Dianhydrides
Authors: Watanabe Shinji , Yamamoto Taizoh , Murata Miki , Masuda Yuzuru
Published: August 2002

New soluble polyimides with inherent viscosities of 0.25–0.62 dl g−1 were synthesized from 3,6-diamino-9-alkylcarbazole and various aromatic tetracarboxylic dianhydrides by the conventional two-step method, including ring-opening polyaddition and subsequent thermally cyclodehydration. Most of the polyimides having hexyl alkyl chains were soluble in N-methylpyrrolidinone and m-cresol, while the polymers having ethyl chains were not soluble in organic solvents. The glass transition temperatures and 10% weight loss temperatures under argon of the polyimides having hexyl chains were in the ranges 232–269 °C and 485–518 °C, respectively.
Surface Contamination of Some Materials of the Space Station ‘MIR’
Authors: Skurat V E , Tantsyreve G D , Beriozkina N G , Volkov A V , Jigatch A N , Leipunsky I O , Pshechenkov P A , Samsonov P V , Toropov V P , Demidov S A , Naumov S F , Sokolova S P
Published: August 2002

About 60 samples of various materials exposed to low Earth orbit (LEO) conditions for 997 days on board the orbital space station ‘Mir’ were investigated. The aim was to determine the properties of the contamination layers formed during LEO exposition.

The following methods were used: optical and scanning electron microscopy, local x-ray microanalysis, secondary ion mass spectrometry in fast atom bombardment ionization mode, electron spectroscopy for chemical analysis, temperature programmed desorption mass spectrometry, x-ray phase analysis, spectral reflectance, solar absorbance and relative emittance measurements.

Two effects were observed for all samples: the formation of contamination deposits and the erosion of the substrate–original surface. The relative contribution of both effects changes depending on the sample type and on exposure conditions. The deposit thickness varies on the sample surface over a very wide range (at least five decimal orders of magnitude), changing from values exceeding 100 μm to values of less than 2 nm (possibly these regions do not contain any deposit at all).

The main element of contamination is silicon; the others are potassium and calcium. Evidence of a chemical reaction between the Teflon FEP substrate and the contamination was observed.
Imide/Arylene Ether Copolymers-Part I
Authors: Jensen B. J. , Hergenrother P. M. , Bass R. G.
Published: August 2002

Two series of imide/arylene ether block copolymers were prepared using an arylene ether block and either an amorphous or semi-crystalline imide block. The resulting copolymers were characterized, and selected physical and mechanical properties were determined. These resuls, as well as comparisons with the homopolymer properties, are discussed.
The Toughness and Morphology Spectrum of Bismaleimide/Polyetherimide Carbon Fabric Laminates
Authors: Rakutt D. , Fitzer E. , Stenzenberger H. D.
Published: August 2002

The paper describes the fracture energy (G1c) spectrum of bismaleimide (BMI)/thermoplastic polyetherimide (PEI) carbon fabric laminates. The PEI concentration was varied between 0% and 100% by weight. Only negligible G1c improvements were obtained for BMI/PEI matrices with 30% or less PEI content. This was probably due to the fact that the large PEI/BMI clusters are concentrated in the crossover regions between the warp and fill strands of the fabric. BMI/PEI matrices with 40% or more PEI content show the expected neat resin/composite G1c correlation in that an increased PEI content improves the toughness of both laminate and neat resin because the morphology of the neat resin and laminate are similar. Poor phase adhesion between BMI and PEI was used to explain mechanical property losses for BMI/PEI fabric laminates with low BMI content.
Polyimide Matrix Composites: Candidates for High Speed Commercial Aircraft or not?
Authors: Wilson Doug
Published: August 2002

Several aerospace companies are actively pursuing the development of a 'high speed civil transport aircraft' (HSCT). Flight profiles and weight considerations dictate the use of high temperature advanced composites. This paper briefly examines two such contenders-PMR-15 and bismaleimides (BMIs). Materials are compared in the categories of thermo-oxidative stability, resistance to thermal cycling, damage tolerance, toxicity and ease of fabrication. At present, it would appear that neither PMR-15 nor BMIs, in general, are capable of meeting HSCT requirements. PMR-15 seems to be hampered by its susceptibility to microcracking, monomer toxicity and difficult fabrication. On the other hand, the use of BMIs seems to be hampered by their relatively poor thermo-oxidative stability. These views assume an aircraft with a maximum operating temperature of about 350°F. Should this requirement change, then the picture will change also and other materials could be considered.
Synthesis and Properties of Hexafluoroisopropylidenecontaining Polyarylates and Copolyarylates
Authors: Kane Kevin M. , Wells Lisa A. , Cassidy Patrick E.
Published: August 2002

A homologous series of four aromatic polyesters and two series of copolyarylates were synthesized under phase-transfer conditions from monomers containing the isopropylidene (IP) and/or the hexafluoroisopropylidene (HFIP) moiety. The homopolymers were obtained in good yields, were soluble in common organic solvents, and would readily form clear, colorless films from solution. Thermal stabilities in air (dynamic-10% weight losses at 440°C-490°C; isothermal-100 h at 350°C, 7%-86% weight loss) revealed that resistance to thermo-oxidation was highest when the HFIP group replaced the IP moiety in the bisphenol rather than in the diacid. Other properties of the homopolymers which were measured were water absorption of 0.07%-0.35% (by weight), and the dielectric constant of 2.32 for the fully fluorinated polymer. Copolymers were prepared from mixtures of bisphenols A and AF, and each of the two diacids. The thermal stability and water absorption of both series were measured as functions of BPAF content. No significant change in properties was observed for copolymers with less than 70 mol.% BPAF comonomer.
LaRCTM-ITPI/Arylene Ether Copolymers
Authors: Jensen Brian J. , Working Dennis C.
Published: August 2002

A series of novel imide/arylene ether copolymers were prepared from the reaction of an amine-terminated amorphous arylene ether oligomer and an anhydrideterminated amorphous imide oligomer. These copolymers were thermally characterized with Tgs ranging from 224 to 2S7°C and mechanical properties were measured on thin films. One block copolymer was end-capped and the molecular weight was controlled to provide a material that displayed good compression moldability. Adhesive properties were determined with Ti/Ti tensile shear strength as high as 3750 psi at room temperature and graphite composite properties were good.
Polybenzimidazole (PBI) Prepreg II: Improved Elevated Temperature Properties with Autoclave Processability
Authors: Steiner Paul A. , Sandor Robert
Published: August 2002

Polybenzimidazoles 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 Celazole. The polymer has excellent compressive strength, high tensile strength and modulus, and a glass transition temperature of 453°C (P. A. Steiner and R. B. Sandor, High Perf. Polym., 3, 139 (1991)). Low molecular weight, oligomeric forms of PBI have been used in the past as a composite matrix material to produce stiff and boardy prepregs. More recently medium molecular weight PBI (12 000-20 000 weight average) has been used in combination with N,N-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 herein are composite mechanical properties on the low molecular weight PBI prepregs illustrating their improved performance and processability.
Mechanism of endo-exo isomerization of nadimide end-capped oligomers
Authors: Bertholio Frédéric , Mison Pierre , Pascal Thierry , Sillion Bernard
Published: August 2002

Before polymerization, nadimide end-capped polyimide oligomers exist in the endo form. During the cure, an endo-exo equilibrium takes place. This paper discusses the relationship between endo-exo isomerization and the reverse-Diels-Alder reaction of the nadinaide system. As a consequence of the experimental results, an explanation for cyclopentadiene evolution during the polymerization of nadimide systems is given.
Synthesis and characterization of aromatic poly(ether ketone oxadiazole)s
Authors: Mercer Frank W
Published: August 2002

A general method for the preparation of oxadiazole containing aromatic poly(ether ketone)s has been developed. Polymerization is based on a ketone-activated halo displacement in oxadiazole containing bis(4-fluorobenzoyl) moieties by phenoxides. 2,5-bis[4-(4-fluorobenzoyl-(4-phenoxyphenyl)]-1,3,4-oxadiazole was prepared by reaction of 4-fluorobenzoyl chloride with 2,5-bis(4-phenoxyphenyl)-1,3,4-oxadiazole in dichloromethane in the presence of aluminium chloride. Reaction of 2,5-bis[4-(4-fiuorobenzoyl)-(4-phenoxyphenyl)]-1,3,4-oxadiazole with diphenols in an aprotic solvent in the presence of potassium carbonate gave a series of aromatic poly(ether ketone oxadiazole)s. Films of the aromatic poly(ether ketone oxadiazole)s displayed good thermal stability, flexibility, and Ts s ranging from 172 to 218 C. The dielectric constants of the films were characterized as a function of relative humidity (RH).