bluuebunny/crossref_metadata_2025 huggingface dataset:
On axisymmetric deformations of the electric arc column in an accelerating flow
Authors: D R Topham  , H D Pite
Published: August 2002

A review of axial flow arcs which exhibit well defined varicose oscillations suggests that, although these have frequently been attributed to shear instabilities, their observed phase speeds are an order of magnitude less than those expected for shear driven phenomena. It is suggested that the coupling between the energy balance of arc and the cold flow conditions the response of the arc column to oscillatory forcing, delaying the onset of shear instability. A linearized mathematical analysis of the thermal coupling alone confirms that, in common with many of the observations, such disturbances travel at the cold flow speed.
Current-zero behaviour of an SF6gas-blast arc. II. Turbulent flow
Authors: M T C Fang  , Q Zhuang  , X J Guo
Published: August 2002

The conservation equations of turbulent gas-blast nozzle arcs based on local thermal equilibrium and on boundary layer assumptions have been solved numerically. A Prandtl mixing length model of turbulence has been adopted because of its simplicity and its success when applied to turbulent rounded jets. The investigation is aimed at an understanding of the arc in a gas-blast circuit-breaker, where the key problem is the arc behaviour during the current-zero period. Emphasis has been placed on quantitative analysis of turbulence-enhanced cooling and its influence on arc behaviour during the current-zero period. The dominant energy transport processes and the critical region for thermal interruption within the nozzle have been identified. The critical rate of rise of recovery voltage as a function of stagnation pressure has been studied and the physical mechanism responsible for this functional relationship discussed. Good agreement between the prediction and experimental measurements has been achieved for the two nozzle geometries investigated.
The effect of thermocapillarity on the flow of a thin liquid film on a rotating disc
Authors: B S Dandapat  , P C Ray
Published: August 2002

Gradual formation of a thin liquid film on a hot/cold rotating disc under the action of thermocapillary force is studied analytically. It is found that the thermocapillary force acting on the free surface enhances the thinning rate for cooling the disc.
The significance of the lifetime and collection time of free electrons for the recombination correction in the ionometric dosimetry of pulsed radiation
Authors: E Hochhauser  , O A Balk  , H Schneider  , W Arnold
Published: August 2002

The collection of free electrons in an ionization chamber results in a deficit of negative ions. The recombination of the ions in the chamber gas is therefore smaller than maintained by the classical recombination theory, which assumes an equal number of positive and negative ions. Under certain conditions the current induced by the electrons in the outer circuit of the chamber can be measured. If the lifetime and the drift velocity of the free electrons in the chamber gas are known, the collected electron-charge and therefore the deficit of negative ions can be found. The determination of the lifetime and the drift velocity is achieved by analysing the decay of the induced current following a short radiation pulse.
Measurement of the Townsend first ionization coefficient in tetraethoxysilane
Authors: K Yoshida  , T Ohshima  , H Ohuchi  , H Tagashira
Published: August 2002

The present paper reports the ionization coefficient in tetraethoxysilane determined experimentally by the steady state Townsend method for E/N in the range 450-2000 Td. Low-temperature plasmas of tetraethoxysilane mixtures may be used to perform plasma-enhanced chemical vapour deposition of silicon dioxide thin films for microelectronics at low substrate temperatures. Since tetraethoxysilane is a low-vapour-pressure liquid at room temperature, heating coils are attached to the ionization chamber to maintain the temperature of the chamber higher than that of the tetraethoxysilane source so that the required vapour pressure is obtained yet no condensation of tetraethoxysilane occurs on the chamber walls. Measurements indicate that the ionization coefficient increases very rapidly at about E/N of 450 Td, at which the value is 7.7*10-18cm2, then the increase tends to saturate and reaches a value of 4.9*10-16cm2at E/N of 2000 Td. Furthermore, it is found that the logarithm of the current has a linear dependence on electrode separation. This suggests that electron attachment is very small or practically absent in this vapour.
AC magnetization analyses in iron-rich amorphous wires
Authors: D -X Chen  , N M Dempsey  , A Hernando  , M Vazquez
Published: August 2002

Domain wall depinning and propagation in a long wire of amorphous Fe77.5Si7.5B15 alloy in the as-quenched state are studied during AC magnetization under a DC biasing field produced by a solenoid perpendicular to the wire. The active walls undergoing the depinning and propagation are classified into positive and negative ones. Consequently there are alternating and unidirectional magnetic reversal modes, both having two distinct types. The alternating mode can easily be induced by an external magnetic pole equidistant from the wire ends. The experimental data obtained in this work and published elsewhere are discussed in detail. It is concluded that the eventual depinning of the closure domain wall from the end is induced by its elongation and transverse movements. The latter process is essentially the same as domain wall propagation. Both are dynamic with a dominant eddy current damping and domain wall shape-dependent DC critical field.
The study of damage profiles in MeV -implanted crystals by Rutherford backscattering and oxygen resonance scattering
Authors: Bo-Rong Shi  , Nelson Cue
Published: August 2002

X-cutcrystals were implanted with 1.0 MeVusing doses ranging fromto. The 3.3 MeVRutherford backscattering/channelling technique was used to analyse the implantedcrystals. The spectra obtained demonstrate that the scattering peaks of the elastic resonance of 3.045 MeVwithshow a broadened half-width. With increasing implant dose, the damage peak of the Nb atoms shifts to the lower-energy side, and the apparent half-width of the resonance peak becomes narrower. The results are explained as being due to the different reduction of stopping power in a channelling direction for He ions after different dose implantations. The reduction of the stopping power for channelled ions can be deduced from the different half-widths of the resonance scattering peaks for spectra corresponding to aligned and random beam directions. The damage depth distributions for implantedcrystals were obtained after considering the corresponding reductions of channelled stopping power. The result shows that the damage profiles for lower dose implantation were shallower than these predicted by TRIM'90 (Transport of Ions in Matter 1990), but they were in good agreement with our calculation.
Studies of excitation, optical bleaching and thermal annealing of OSL in natural quartz
Authors: A Shmilevich  , M Abu-Rayya  , R Chen  , N Kristianpoller
Published: August 2002

Optically stimulated luminescence (OSL) was excited at LNT by monochromatic light in x-irradiated natural quartz crystals. Excitation maxima appeared at 290 and 310 nm. The phototransferred thermoluminescence (PTTL) of these crystals showed excitation maxima at the same wavelengths, indicating that carriers are optically stimulated from the same traps. This is supported by the finding that the same wavelengths are most efficient for optical bleaching caused by prolonged illumination. The effects of thermal annealing to gradually increasing temperatures on the OSL were investigated and a correlation to thermoluminescence (TL) peaks was found. The OSL intensities showed sharp decreases after annealing to 160, 190 and 280 K; these temperatures coincide with the temperatures of the main TL glow peaks. It appears therefore that the OSL and the main TL peaks between liquid nitrogen temperature (LNT) and room temperature (RT) are due to the same donor levels. The emission spectrum of the OSL showed that this emission is composed of some bands, which appear also in PTTL as well as in x- and photoluminescence, indicating that the same luminescence centres are responsible for these emissions.
Influence of anisotropic scattering on the size of time-dependent systems in monoenergetic neutron transport
Authors: Cemal Yildiz
Published: August 2002

Criticality type eigenvalues of the one-speed transport equation in a homogeneous slab with anisotropic scattering and Marshak boundary conditions are considered. The connection between the transport equations for a critical and for a time-decaying system is established, and thus the time-dependent equation is reduced to the stationary one. Variation of the size of the time-dependent system with anisotropic scattering is studied numerically. Calculations for different combinations of the scattering parameters and the selected values of the time decay constant using themethod are reported. Results are discussed and compared with those already obtained using various methods available in the literature.
PNsolutions of the time-dependent neutron transport equation with anisotropic scattering in a homogeneous sphere
Authors: Cemal Yildiz
Published: August 2002

In an earlier paper, the spherical harmonics method for the solution of the time-dependent transport equation with the Marshak boundary conditions was presented in order to investigate the effect of a strongly anisotropic scattering law on the slab thickness. Here, the previous work is extended to the study of the time-dependent problems in a homogeneous sphere with the same scattering function as used in the previous work. The time-dependent neutron transport equation is solved in the manner used for a critical sphere and all radii for a given time-dependent system are determined by finding the critical radii for the corresponding critical system.

ThePNcalculations of the critical radii were carried out for various combinations of the anisotropy parameters and the fundamental time eigenvalues. Some indications of the accuracy of the method were given for the problem of interest and the variation of the radius with anisotropic scattering was studied. We also obtained numerical values of the critical radii in the range of (1-),1. Finally, some results were discussed and compared with those already obtained by various methods.
Intensity-dependent characteristics of a picosecond laser-produced Cu plasma
Authors: J Badziak  , J Makowski  , P Parys  , L Ryc  , J Wolowski  , E Woryna  , A B Vankov
Published: August 2002

The interaction of a 1 ps laser pulse of moderate contrast ratio (~104) with a Cu target is investigated at laser intensitiesIof up to 3×1016 W cm-2with the use of corpuscular, x-ray and optical diagnostics. Intensity-dependent characteristics of ion and x-ray emission as well as reflectivity, electron temperature and average charge state of plasma produced by the laser pulse are presented and discussed. It is found that (a) the specular reflectivity dependence on intensity for a moderate-contrast ultrashort (⩽1 ps) pulse is qualitatively and quantitatively different from that for a high-contrast ultrashort pulse; (b) the scaling laws for parameters of thermal ions are essentially different from those for fast ions; (c) the soft x-ray yield scales asIαwith α≈2-2.5 in the intensity range 1014-3×1016 W cm-2; and (d) electron temperature scales asI0.44at 1015<I<3×1016 W cm-2.
Electrostatic image theory for the conducting prolate spheroid
Authors: I V Lindell  , G Dassios  , K I Nikoskinen
Published: August 2002

Electrostatic image theory is developed for a point charge at the
axis of revolution of a perfectly conducting prolate spheroid. A previous
theory, introduced in 1995, presenting the image as a line charge between the
focal points, was seen to be numerically stable only when the charge is far
enough from the spheroid and when the eccentricity of the spheroid is large
enough. The theory is improved by extracting a point charge from the line
image, whence the remaining line charge becomes numerically better behaved, as
demonstrated by some examples. Because the extracted point image theory
reduces analytically to the classical Kelvin image in the case when the
spheroid reduces to a sphere, and the line image simultaneously vanishes, the
present theory can be seen as a generalization of the Kelvin image theory.
Determination of the gas-phase Si atom density in radio frequency discharges by means of cavity ring-down spectroscopy
Authors: A Schwabedissen  , A Brockhaus  , A Georg  , J Engemann
Published: August 2002

Absolute densities of eroded silicon in the gas phase from the interaction of a target with a radio frequency (rf) plasma have been measured by cavity ring-down (CRD) spectroscopy. As a target either a quartz plate or a silicon wafer was used, which was attached on the powered electrode of an asymetrically driven argon rf discharge. The Si density was determined from the decrease in the CRD decay time when tuning the laser wavelength across one of the transitions of the silicon resonance line multiplet (centred at 252 nm). Typical Si densities were in the range from 107to 108 cm-3only, demonstrating the sensitivity of our method. The Si distribution in the plasma extended over a wider area than the dimensions of the target and the densities increased with rf power and argon pressure, but saturated at higher pressures and rf powers. Similar densities of Si were measured when using the quartz plate or the Si wafer.
Processable Poly(Keto-Imide)s Having Bulky Pendent Ether Groups
Authors: Tamai S , Yamashita W , Yamaguchi A
Published: August 2002

1, 3-Bis(3-aminobenzoyl)benzene (BAB), 1, 3-bis(3-amino-4-phenoxybenzoyl)benzene (BAPB) and 1, 3-bis(3-amino-4-biphenoxybenzoyl)benzene (BABB) were synthesized from 1, 3-bis(3-nitro-4-chlorobenzoyl)benzene. By using these three diamines and commercially available tetracarboxylic dianhydrides such as 3, 3′, 4, 4′-benzophenone tetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA), several kinds of poly(keto-imide)s were synthesized. Thermal properties and processability such as melt-flowability and solubility in organic solvents of the obtained poly(keto-imide)s were investigated by focusing on the chemical structures of their repeating structure units. Inherent viscosities of poly(keto-imide)s ranged from 0.54 to 0.75 dl g−1. These poly(keto-imide)s displayed glass transition temperatures ( Tg) between 219 and 256 °C, and only the poly(keto-imide) prepared from BAB and PMDA showed a melting point ( Tm)at 451 °C. Melt-flowabilities of these poly(keto-imide)s except for BAB/PMDA poly(keto-imide) were observed between 285 and 330 °C. The poly(keto-imide)s having bulky pendent ether groups were soluble in chloroform, 1, 1, 2-trichloroethane, N, N-dimethylacetamide and m-cresol at ambient temperature.
Preparation of Polyimide Films from A-BPDA/ODA by One-Pot and Two-Step Imidization Methods
Authors: Takahashi Takuji , Takabayashi Seiichirou , Inoue Hiroshi
Published: August 2002

Polyimide films were prepared from 2, 3, 3′, 4′-biphenyl tetracarboxylic dianhydride (a-BPDA) and 4, 4′-oxydianiline (ODA) by a two-step method (thermal and chemical imidization) and a one-pot method. In the case of the polyimide films prepared from polyamic acid solution by the two-step method, the molecular weight of the films decreased before achieving its final value. In the case of polyimide films prepared by the one-pot method, the molecular weight increased smoothly to its final molecular weight during cure. The inflection point in the viscosity curve was observed between 215 and 250 °C in the polyimide prepared by the two-step method, and the range of the inflection temperature was very different from the Tg of the polyimide (340 °C). So, this inflection of molecular weight was considered to be independent of the Tg of the polyimide. The films prepared from three methods had almost the same molecular weight and properties in spite of the different preparation processes. For this reason it is thought that the polyimide from a-BPDA/ODA has less crystallinity and less phase orientation.
Synthesis and Properties of Polyamide-Imide Based on 2, 2-Bis[4-(4-Aminophenoxy)Phenyl]Hexafluoropropane and 2, 2-Bis[4-(4-Aminophenoxy)Phenyl]Propane
Authors: Negi Yuvraj Singh , Suzuki Yoshi-Ichi , Kawamura Ichiro , Kakimoto Masa-Aki , Imai Yoshio
Published: August 2002

Aromatic polyamide-imides having hexafluoroisopropylidene and isopropylidene groups in the main chain of the polymer were prepared by reacting 4-chloroformylphthalic anhydride (CPA) and fluorine or non-fluorine containing diamines using low-temperature polycondensation. Polyamide-imides were obtained with high molecular weight and high yield. Thermal decomposition temperature and glass transition temperatures of polymers were above 460 °C and 275 °C respectively. Fluorine and non-fluorine containing polyamide-imides were cast into transparent films which were characterized by mechanical and water absorption analysis.
Improvement of Thermal Insulation for Polyurethane Foam by the Conversion of Carbon Dioxide to an Organic Carbonate Compound
Authors: Hashida T , Ueno T , Nakamoto H , Suzuki M
Published: August 2002

A new method to improve the thermal insulation of polyurethane rigid foam blown by a non-ozone depleting agent—an alternative to chlorofluorocarbon—has been developed. This method involves the reduction of the gas thermal conductivity for polyurethane foam by the conversion of gaseous carbon dioxide in the foam to an organic carbonate. We tried to perform the cyclization of carbon dioxide in foam with an epoxy compound, and then the reduction of the thermal conductivity of the polyurethane foam was ascertained as carbon dioxide was chemically fixed in the foam. Consequently, this method led to a reduction of about 10% in the thermal conductivity in comparison with that of the conventional foam including carbon dioxide. In addition, the degree of progress of reaction in the foam was investigated by a quantitative analysis of carbon dioxide, epoxide and the resulting cyclic carbonate in the polyurethane foam. It was observed that unnecessary reactions, which consumed epoxide other than for the fixation of carbon dioxide, existed in the process of urethane polymerization. The main unnecessary reaction was presumed to be a side reaction of epoxide with isocyanate. Furthermore, the unnecessary reactions were affected by the type of urethane catalyst, the selection of which has been of importance in this method.
Polyimide/Polyimide Molecular Composite Films: Difference between Reactive Oligoimide and Reactive Polyimide as the Matrix Component
Authors: Takeichi Tsutomu , Nakajima Kohji , Zuo Min , Yokota Rikio
Published: August 2002

Polyimide/polyimide molecular composite (MC) films were prepared by blending precursor solutions of a rigid polyimide and a reactive oligoimide or a reactive polyimide that contains acetylene units in the backbone in a 7:3 ratio, followed by casting, drying and thermal imidization at 300 °C. 3, 3′, 4, 4′-Biphenyltetracarboxylic dianhydride (BPDA), pyromellitic dianhydride (PMDA), p-phenylenediamine (PDA), oxydianiline (ODA) and 3, 3′-diaminodiphenylacetylene ( m-intA) were used as acid dianhydride and diamine monomers for the preparation of polyimide. The rigid components were prepared from PMDA or BPDA and PDA. The matrix components were prepared from PMDA or BPDA and ODA or m-intA. The polyimide/polyimide MCs have exotherm on DSC due to the reaction of internal acetylene units, which indicates that the MC films are laminate processable. Tensile measurements revealed that the tensile modulus of the MCs utilizing reactive oligoimides is 20–30% higher than that of the MCs utilizing reactive polyimides. Viscoelastic analyses of the MC films showed that the crosslinking of the acetylene units gave polyimides that have a very high glass transition temperature.
Side-Chain LC Block Copolymers with Well Defined Structures Prepared by Living Anionic Polymerization. 2: Effect of the Glass Transition Temperature of Amorphous Segments on the Phase Behaviour and Structure of the LC Segment
Authors: Yamada Masayuki , Itoh Tomomichi , Hirao Akira , Nakahama Sei-Ichi , Watanabe Junji
Published: August 2002

We have prepared two classes of LC diblock copolymers, OcSt-b-LC and MeStb-LC, by living anionic polymerization. These are composed of the side-chain LC polymer as one segment and two different amorphous polymers, poly(octyl styrene) (OcSt) and poly(α-methyl styrene) (MeSt), as the other segment. OcSt and MeSt segments have glass transition temperatures of −60 °C and 160 °C respectively, which are relatively lower and higher than the transition temperatures of crystal–SA (∼90 °C) and SA–isotropic (∼130 °C) in the LC segment. In OcSt-b-LC the lamellar domain size decreases gradually from that of the crystal phase to that of the isotropic phase, indicating that the global conformation of the backbone changes throughout the SA temperature region. In MeSt-b-LC, in contrast, no change in the lamellar size is observed and the crystallinity of the LC segment is reduced in comparison with that in OcSt-b-LC while the liquid crystal is well formed. Such a distinction between two copolymer systems, arising from an interplay between the LC and amorphous segments, shows that the global conformation of the backbone is significant for understanding the phase behaviour and structure of side-chain LC polymers.
Recent Technological Developments in Cyanate Ester Resins
Authors: Hamerton Ian , Hay John N
Published: August 2002

Although they are relative newcomers to the composites industry, cyanate ester (CE) resins are enjoying unprecedented success in certain applications. Several major space and radome manufacturers have qualified CE resins despite the extensive database on epoxies and the inherently conservative nature of the industry. Increasing demands on the materials used in these areas have stimulated the use of CE resins over other more conventional polymers. The aim of this review is to bring to the reader’s attention the more recent developments in the processing, toughening, properties and applications of cyanate esters, an exciting, versatile and important class of resins.
New Polymer Synthesis 99. Hyperbranched Poly(Ester-Imide)S Derived from 4,5-Dichlorophthalic Acid
Authors: Kricheldorf Hans R , Bolender Oliver , Wollheim Thomas
Published: August 2002

A new trifunctional monomer was prepared from ethyl-4-(4,5-dichlorophthalimido) benzoate and 4-mercaptophenol. The phenolic OH groups were acetylated, and the carboxylic group was silylated to reduce the melting temperature. A successful homopolycondensation yielding a completely soluble hyperbranched poly(ester-imide) was only obtained when the silylated monomer was used. This branching monomer was polycondensed with a difunctional imide monomer to yield co(polyester-imide)s having a variable degree of branching. Furthermore, copolycondensations with 3-acetoxybenzoic acid or 3,5-bisacetoxybenzoic acid (and their trimethylsilyl esters) were studied. The composition of the resulting copolyesters were checked by elemental analyses and 1H NMR spectra. The glass transition temperatures ( T g s) showed a systematic variation between the values of the parent homopolyesters.
Synthesis and Characterization of Polyamidoamine-Based Liquid Crystalline Dendrimers
Authors: Suzuki Kazuhiro , Haba Osamu , Nagahata Ritsuko , Yonetake Koichiro , Ueda Mitsuru
Published: August 2002

Poly(amidoamine)-based liquid crystalline dendrimers (LCDs) with mesogenes on the surface were successfully prepared by the reaction of poly(amidoamine) dendrimers with 40-cyanobiphenyl hydrogen glutarate in the presence of a condensing agent, diphenyl(2,3- dihydro-2-thioxo-3-benzoxazolyl)phosphonate. The structures of LCDs were characterized by IR, 1H-NMR and MALDI-TOF mass spectroscopy and elemental analysis. These LCDs did not show a thermotropic liquid crystalline nature but exhibited a lyotropic liquid crystalline property in the 80 wt% DMF solutions of LCDs containing lithium bromide.
New Polymer Synthesis VI: Synthesis, Characterization and Morphology of New Polyoxaloylesters Derived from Diarylidenecycloalkanones
Authors: Aly Kamal I
Published: August 2002

New polyoxaloylesters have been synthesized via interfacial polycondensation of oxaloyl chloride with 2,5-bis( p-hydroxybenzylidene)cyclopentanone I, 2,5-divanillylidenecyclopentanone II, 2,6-bis( p-hydroxybenzylidene)cyclohexanone III, 2,6-divanillylidenecyclohexanone IV, and 2,7-bis( p-hydroxybenzylidene)cycloheptanone V at ambient temperature. These polyoxaloylesters were characterized by elemental analysis, IR spectra, 1H NMR, solubility measurements, viscometry, DSC and thermogravimetric analyses. The crystallinity of the polymers was examined by x-ray analysis. The morphology of a high-performance polyoxaloylester, namely poly[oxyoxaloyloxy- p-phenylenemethylidyne (2-oxo-1,3-cyclohexanediylidene)methylidyne- p-phenylene], has been investigated by scanning electron microscopy. Electrical conductivity is in the range 10−11 -10−13Ω−1 cm−1.
Application of Thermosetting Copolyimides as Coatings for Protection of Semiconductor Devices
Authors: Furukawa Nobuyuki , Katayama Hisashi , Kitamura Ken-Ich
Published: August 2002

Six kinds of end-capped thermosetting copolyimides were prepared and applied as a junction coating resin for protection of semiconductor devices. The copolyimides are composed of aromatic dianhydrides, aromatic diamines, bis(γ-aminopropyl)tetramethyldisiloxane and reactive end-capping agents. Maleic anhydride and γ-aminopropyltrimethoxysilane were used as the reactive end-groups due to increasing their crosslinking reactivity. The copolyimides were cured at 200 °C, then the thermal and mechanical properties of the hardened copolyimides were characterized. The thermosetting copolyimides exhibited good adherence to a silicon wafer and an encapsulant without an adhesion promoter due to their incorporated disiloxane composition. The residual interface stress between the copolyimides and a silicon wafer was 3.5–3.6 MPa. The copolyimides were applied as a junction coating for protection of a semiconductor device and exhibited good reliability.
Syntheses of Soluble Tert-Butyl substituted Poly(p-Oxybenzoate)s
Authors: Yamanaka Kazuhiro , Jikei Mitsutoshi , Kakimoto Masa-Aki
Published: August 2002

Soluble poly( p-oxybenzoate)s (POBs) were synthesized by direct solution polycondensation using thionyl chloride and pyridine as condensation agents starting from tert-butyl substituted p-hydroxybenzoic acids (3- tert-butyl-4-hydroxybenzoic acid (BuHB) and 3, 5-di- tert-butyl-4-hydroxybenzoic acid (Bu2HB)). Tert-butyl substituted homopolymers (homo-POBs) had poor solubility in organic solvents, whereas solubility of resulting copolymers (co-POBs) was improved in comparison with that of homo-POBs. In particular, the co-POBs with the weight average molecular weight ( Mωw) value of 20 000 from BuHB/Bu2HB in the monomer feed ratio of 40/60–50/50 were soluble in various organic solvents such as tetrahydrofuran, chloroform, N, N-dimethylformamide, and 10 wt% loss and glass transition temperatures of co-POBs in nitrogen were at 375 °C and 190 °C, respectively.
Synthesis of Fully Aliphatic Polyimides
Authors: Seino Hiroshi , Sasaki Takeshi , Mochizuki Amane , Ueda Mitsuru
Published: August 2002

Fully aliphatic polyimides (APIs) have been synthesized. APIs were prepared by poly(addition-condensation) of the alicyclic dianhydride bicyclo[2.2.2]octane-2, 3, 5, 6-tetra-carboxylic 2, 3:5, 6-dianhydride with the aliphatic diamine 5-amino-1, 3, 3-trimethylcyclo-hexanemethylamine, the mixture of 2, 5- and 2, 6-bis(aminomethyl)bicyclo[2.2.1]heptane or 1, 4-cyclohexanebis(methylamine) in m-cresol at high temperature. The polymerization proceeded smoothly at 200 °C and produced APIs with inherent viscosities up to 0.48 dl g−1. The APIs were soluble in a wide range of polar solvents and showed high thermal stability and excellent transparency.
Photoinduced Nonlinear Optical Effects in 1, 4-cis-Polybutadiene Polymers
Authors: Tkaczyk S , Kityk I V , Benet S , Mefleh A
Published: August 2002

Photoinduced nonlinear optics phenomena in 1, 4- cis-polybutadiene have been investigated. Both an external electrostatic field as well as UV laser photoinducing light lead to enhancement of the local non-centrosymmetry determining optical second harmonic generation (SHG). Using ab initio quantum chemical calculations and experimental nonlinear optics data we have shown that there exist values of the external fields corresponding to the maximal SHG values. Low-temperature ordering (below 10 K) (due to decrease of thermoreorientation) and hydrostatic pressure-induced strength also favour photoinduced SHG. Time-resolved SHG measurements indicate an existence of at least two short-time components (about picosecond range), that may be caused by different mechanisms of the observed phenomenon. It has been shown both experimentally and theoretically that the degree of non-centrosymmetry for the corresponding butadiene bonds is closely connected with the UV-photoinducing power, temperature, hydrostatic pressure and delaying time between the photoinducing and probing beams.
Luminescence Studies of Polymer Matrices: 4. Phosphorescence of Benzophenone Dispersed in Acrylic Acid Based Polymer Films
Authors: Ebdon John R , Lucas David M , Soutar Ian , Lane Anthony R , Swanson Linda
Published: August 2002

The thermal dependence of the phosphorescence characteristics of benzophenone (BP) dispersed in thin films of poly(acrylic acid), PAA, and acrylic acid-methyl methacrylate, AA-MMA, copolymers is described. At all temperatures (between 77 K and 410 K), and in each of the systems studied, the triplet state decay kinetics of the phosphor are complex: a minimum of three exponential terms is required for adequate modelling of the time dependence of BP phosphorescence. This complexity is considered to reflect the breadth and heterogeneity of the distribution of sites accessed by the probe within each of the polymer matrices.

Both phosphorescence intensity and lifetime measurements are affected by the onset of macromolecular relaxations within each of the film samples. However, the temperature dependence of the BP phosphorescence data seems to also reflect the presence of specific interactions between the probe and polymer. Consequently the data do not allow a definitive picture of the relaxation behaviour or phase morphology of the copolymer samples to be derived. The data also illustrate the fact that, in designing a high-performance phosphorescent coding system, trends in the photophysical characteristics of one dopant in a given matrix do not necessarily translate into predictions of the behaviour of another phosphor even in the same matrix.
Atomic Oxygen Resistant Films for Multi-Layer Insulation
Authors: Schuler Peter , Mojazza H Bob , Haghighat Ross
Published: August 2002

A series of advanced polymer films from Triton Systems is being developed to meet the challenges of harsh space environmental effects, lighter weight requirements and superior thermal control performance demands. With support from NASA, Triton Systems Inc has developed advanced new materials for thermal control films with exceptional properties and durability in the space environment. These films known as TOR™ and TOR-LM™ are amber coloured, mechanically sound, produced in continuous rolls and have undergone substantial ground-based simulation and confirming space validation tests. These films are highly resistant to atomic oxygen erosion, and have excellent vacuum ultraviolet radiation stability in ground-based simulation tests. Two applications for these films include large inflatable structures that are either deployed in low earth orbit (LEO) or travel through a LEO orbit into higher orbits, and as outer metallized layers in multi-layer insulation (MLI) blankets.

This paper discusses the processing of these advanced materials into thin films, metallization of the films and characterization of their environmental durability as well as other physical, optical, thermal and mechanical properties.
The Curing Process and Moisture Transport in a Tetrafunctional Epoxy Resin as Investigated by FT-NIR Spectroscopy
Authors: Musto Pellegrino , Martuscelli Ezio , Ragosta Giuseppe , Russo Pietro
Published: August 2002

An epoxy resin formulation composed of tetraglycidyl-4, 4′ diaminodiphenylmethane (TGDDM) and 4, 4′ diaminodiphenylsulfone (DDS) was investigated by Fourier transform near-infrared (FT-NIR) spectroscopy. In situ isothermal measurements allowed us to obtain the concentration versus time curves of the various reactive groups present in the system, thus affording a complete characterization of the curing process. The same experimental approach was used to monitor the transport of moisture into the resin at several temperatures. The data gathered in this way revealed a good agreement with conventional gravimetric measurements, which verifies the reliability and accuracy of FT-NIR spectroscopy for the study of these transport processes.
Preparation and Properties of Novel Aromatic Polyimides from 4,4′-Diamino-4″ -Hydroxytriphenylamine and Aromatic Tetracarboxylic Dianhydrides
Authors: Akimoto Satoshi , Jikei Mitsutoshi , Kakimoto Masa-aki
Published: August 2002

Novel aromatic polyimides containing hydroxytriphenylamine units were prepared from 4,4′-diamino-4″-hydroxytriphenylamine 1 and various aromatic tetracarboxylic dianhydrides 2. The glass transition temperatures ( Tgs) of these polyimides were in the range of 274–388 °C and the 10% weight loss temperatures ( T d10s) were above 462 and 511 °C in air and nitrogen respectively. Polyimide 4f prepared from diamine 1 and 4,4′-hexafluoroisopropylidenebis(phthalic anhydride) (6FDA) was soluble not only in organic solvents such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, 1, 3-dimethyl-2-imidazolidone and dimethyl sulfoxide but also in tetramethylammonium hydroxide aqueous solution. Other resulting polyimides were not soluble in organic solvents. The resulting polyimides 4 possessed Tgs about 20–70 °C higher and poorer solubilities than the previously reported polyimides prepared from 4,4′-diaminotriphenylamine and various aromatic tetracarboxylic dianhydrides. These results indicated that polymer properties such as thermal behaviour and solubilities were influenced by the intermolecular interaction of hydrogen bonding due to hydroxy units.
Synthesis and Characterization of New Functional Bismaleimides
Authors: Hulubei Camelia , Gaina Constantin
Published: August 2002

Functional bismaleimides containing γ-lactone, carboxyl, aldehyde, hydroxyl, azomethine or cinnamoyl groups were synthesized from maleimido benzoic acid via its acid chloride with phenolphtaleine, 5,5′-methylene-bissalicylic acid, 5,5′-methylene-bissalicylaldehyde, glycerol, tartaric acid and 3,4-bis(hydroxyethan-2-tioether)- p-maleimidobenzoic acid, by simple condensation or polymer analogous reactions on some of these reactive bisimides.

The monomers were characterized by IR, 1H-NMR and elemental analysis. The DSC curves of all the samples showed an exotherm in the temperature range of 134–310 °C, which is attributable to curing reactions. Thermogravimetric analysis of the uncured resins indicated good thermal stability and a char yield of bismaleimide resins in accordance with the calculated C/H ratio. Their relative thermoxidative stability was evaluated by isothermal gravimetric analysis.
Azo Dyes Based on 2-Naphthol-Formaldehyde Oligomer
Authors: Desai C K , Desai K R
Published: August 2002

A series of new oligomeric disperse dyes were prepared by coupling various diazonium salts of aryl ether to a 2-naphthol-formaldehyde oligomer. They were characterized in terms of their softening points, colour, solubility and infrared and UV–visible spectral studies. The structural property relationships were discussed. The dyeing on polyester and nylon resulted in yellow, orange and pink-to-redcolouration having good to excellent light-fastness and washing-fastness properties.
Physico-Chemical Investigation of Multiple Asymmetric Amphiphilic Diblock Copolymer Morphologies in Solution
Authors: Burke Susan , Eisenberg Adi
Published: August 2002

Asymmetric amphiphilic diblock copolymers are able to form self-assembled crewcut aggregates of multiple morphologies in selective solvents. Micelles are formed by the slow addition of a poor solvent, for the core-forming block, to a solution of the copolymer dissolved in a solvent suitable for both polymer segments. The morphology of the aggregates is affected by a number of factors, such as the solvent composition, the block lengths, the presence of additives, and the temperature. Some of the resulting structures are considered to be equilibrium or near-equilibrium morphologies, which can be kinetically frozen using a number of different techniques. The thermodynamics of micelle formation has been investigated, and equations for the standard Gibbs free energy, enthalpy, and entropy have been formulated. Partial phase diagrams have been constructed, giving the morphological phase boundaries. Knowledge of the location of the boundaries has paved the way for the study of the kinetics and mechanisms of the sphere to rod and rod to vesicle transitions. Both processes have two-step mechanisms, with the second step being rate determining in each case.
Synthesis and Characterization of a Conductive Polyaniline/Clay Hybrid System
Authors: Frisch Harry L , Xi Bangwei , Qin Yingchuan , Rafailovich Miriam , Yang Nan-Loh , Yan Xingzhong
Published: August 2002

This paper presents the synthesis and characterization of polyaniline/montmorillonite hybrid polymer. Montmorillonite is a natural clay mineral. By an intercalative polymerization reaction the hybrid is synthesized. In our study, electron paramagnetic resonance (EPR) spectra were examined together with controls (PANI and clay) with the EPR signals from all the PANI/clay samples showing very high spin density (1019 spins /g polymer). PANI/clay samples show g-values higher than that of pure PANI control. Dc conductivity was measured by a four-point probe method and it was found not to be a linear function of PANI content, but the values are consistent with a percolation threshold.
X-Ray Scattering from Liquid–Liquid Interfaces
Authors: Schlossman Mark L , Li Ming , Mitrinovic Dragoslav M , Tikhonov Aleksey M
Published: August 2002

We present our recent progress in using synchrotron x-ray surface scattering to study several different aspects of ordering at liquid–liquid interfaces. (1) The interfacial width at the water–alkane interface has been measured for a series of different chain length alkanes. The variation of interfacial width with the carbon number can be described by combining the capillary wave prediction for the width with a contribution from the intrinsic structure. (2) Under appropriate conditions, a surfactant monolayer forms at the interface between water and a hexane solution of a fluorinated surfactant. Reflectivity measurements that probe the electron density profile normal to the interface provide information on the surfactant ordering. This monolayer undergoes a solid to gas transition as a function of temperature. Diffuse scattering near the transition reveals the presence of islands. (3) Equilibrium interfaces between two aqueous phases containing polyethylene glycol and potassium phosphate salts can be studied. We present studies of conformal capillary wave fluctuations between two interfaces of a thin film of this biphase system. We also demonstrate that ferritin can be trapped and studied at this aqueous–aqueous interface.
Time–Temperature Superposition of Phase Separating Polymer Blend Films
Authors: Winesett D A , Zhu S , Sokolov J , Rafailovich M , Ade H
Published: August 2002

We have examined the structure formations in symmetric blend films of polystyrene and poly(methyl methacrylate) during phase separation and coalescence in the melt. We qualitatively verify the principle of time–temperature superposition by observing morphology development in which characteristic structures develop independently of annealing temperature and initial morphology. Domain structures proceed to qualitatively similar morphologies regardless of the initial morphology due to the intrinsic viscosity of the blend films.
Preparation and Properties of Poly(Amide-Imide) Containing Acetylene Units in the Main Chain
Authors: Takeichi Tsutomu , Suefuji Kyoko , Zuo Min
Published: August 2002

Poly(amide-imide) containing internal acetylene units in the backbone was prepared from trimellitic anhydride chloride and bis(3-aminophenyl)acetylene in N-methyl-2-pyrrolidone at room temperature, followed by thermal imidization. Differential scanning calorimetry measurements of the poly(amide-imide) showed an exotherm due to the crosslinking reaction of the internal acetylene units. With higher heat treatment, the exotherm shifted to higher temperatures and the amount of the exotherm decreased. The exotherm finally disappeared after 400 °C treatment. Viscoelastic measurements revealed that the crosslinked polymer had a higher glass transition temperature and maintained a storage modulus up to higher temperatures. The thermogravimetric analyses profile showed that the crosslinking of internal acetylene units gave a thermally stable structure.
Architecturally Driven Properties Based on the Dendritic State
Authors: Tomalia Donald A
Published: August 2002

This new architectural class of macromolecules has received substantial attention during the past decade. Three dendritic subclasses, which include: (a) random hyperbranched (i.e. one-pot AB x polymerizations), (b) dendritic grafted (i.e. Combburst® polymers) and (c) regular dendrons/dendrimers (e.g., Starburst® dendrimers) have been synthesized and characterized at a well-defined level in our laboratory. It is clear that their precisely controlled, nanoscale dimensions and architecture play critical roles in influencing physical properties and performance characteristics. Furthermore, these parameters have also distinguished dendrimers as fundamental modules for many nanotechnology applications, as well as for the construction of a new class of larger nanoscale entities which we have termed core–shell tecto(dendrimers). This paper will overview these activities and focus on certain unique de Gennes dense packing (or congestion phenomena) and nanoscale container properties that have emerged from this novel architecture.
Ring-Closing Polycondensations
Authors: Kricheldorf Hans R , Rabenstein M , Langanke D , Schwarz G , Schmidt M , Maskos M , Krüger R-P
Published: August 2002

The role of cyclization in polycondensations is discussed for two different scenarios: thermodynamically-controlled polycondensation (TCPs) on the one hand and kinetically-controlled polycondensations (KCPs) on the other. The classical Carothers–Flory theory of step-growth polymerization does not include cyclization reactions. However, TCPs involve the formation of cycles via ‘back-biting degradation’, and when the ring–chain equilibrium is on the side of the cycles the main reaction products of the TCP will be cyclic oligomers. Two groups of examples are discussed: polycondensations of salicyclic acid derivatives (e.g. aspirin) and polycondensations of dibutyltin derivatives with long α-, ω-diols or dicarboxylic acids. Furthermore, various kinetically-controlled syntheses of polyesters and polyamides were studied and carefully optimized in the direction of high molecular weights. High fractions of cyclic oligomers and polymers were found by MALDI-TOF mass spectrometry, and their fractions increased with optimization of the process for molecular weight. These results disagree with the Carothers–Flory theory but agree with the theoretical background of the Ruggli–Ziegler dilution method (RZDM). When poly(ether-sulfone)s were prepared from 4,4′-difluorodiphenylsulfone and silylated bisphenol-A two different scenarios were found. With CsF as catalyst at a temperature of more than 145°C cyclic oligoethers were formed under thermodynamic control. When the polycondensation was promoted with K2CO3 in N-methylpyrolidone at ≤145°C the formation of cyclic oligoethers and polyethers occurred under kinetic control. A new mathematical formula is presented correlating the average degree of polymerization with the conversion and taking into account the competition between cyclization and propagation.
Control of the Length of Aromatic Polyester Whiskers
Authors: Sarker Ashim Kumer , Kimura Kunio , Yokoyama Fumiyoshi , Yamashita Yuhiko
Published: August 2002

The control method of poly( p-oxybenzoyl) (POB) whisker length is reported, with the main focus being on how to make the length of the whiskers longer. The POB whiskers were prepared by the polymerization of p-acetoxybenzoic acid in LPF at 330°C. The increase in whisker length is caused by the way oligomer lamellaepileupalongthelongaxisoftheneedle-likecrystalswithspiralgrowth. From the present detailed morphological observations during polymerization, the tip angle of the whiskers is constant at 80° up to a time 10 min, whereas it becomes significantly sharper to 12° at 30 min. This sharpening of the tip angles seems to be highly related to the degree of supersaturation of the oligomers dissolved in solution. In order to depress the sharpening of the tip angle and to extend the steady-state growth for increase of the whisker length, oligomers were added twice into the polymerization system, after 10 min just before the tip angle becomes sharper and then after 20 min. The addition of oligomers extended the steady-state growth period, and the length was increased from 40 μm to 47 μm with the first addition and then to 50 μm with the second addition. The addition of oligomers during steady-state growth gives the most favourable conditions for continuous growth with spiral growth.
Surfactants Based on Recycled Poly(Ethylene Terephthalate) for Breaking Water-in-Oil Emulsions
Authors: Abdel-Azim Abdel-Azim A , El-Sukkary M M A
Published: August 2002

Poly(ethylene terephthalate), waste was depolymerized with propylene glycol to an oligoester. The glycolyzed product was reacted with polyethylene glycol of different molecular weights, namely 600, 1000 and 4000, to form surfactants having different hydrophile–lipophile balances and hence different surface activities. The interfacial tension at the aqueous–benzene interface was determined. It was found that the demulsifier concentration that causes a minimum interfacial tension is always less than that inducing maximum efficiency. The data revealed that the efficiency increases on increasing the concentration of demulsifier, contact time and hydrophilicity.
Morphology of Elastic and Plastic Poly(Urethane-Imide) Films Observed with TEM and FE-SEM
Authors: Takeichi Tsutomu , Kawai Takeshi , Tsuchiya Hajime
Published: August 2002

Direct observation of the morphology of poly(urethane-imide) films, prepared by the reaction of a polyurethane prepolymer and poly(amide acid) as a precursor of polyimide, was performed using transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM). The poly(urethane-imide) films were plastic or elastic depending on the ratio of the two components. In the plastic films, TEM and FE-SEM analyses clearly showed the presence of urethane-rich domains in the imide-rich continuous phase. Under the higher magnification of TEM, a lamella structure was clearly observed inside the urethane-rich domains. The size and the number of the urethane-rich domains varied with the chemical structure and the ratio of the two components. It was confirmed that the size of the urethane-rich domains in the poly(urethane-imide) films observed with TEM and FE-SEM was almost the same as that of the pores in the porous polyimide films obtained by pyrolyzing the poly(urethane-imide) films at 300–400 °C. In the elastic films, imide-rich domains were clearly seen in the urethane-rich continuous phase by the FESEM observation.