bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of monofunctional and trifunctional modifiers on a phase mixed polyurethane system
Authors: Fedderly Jeffry J. , Lee Gilbert F. , Ferragut David J. , Hartmann Bruce 
Published: August 2005

AbstractThe dynamic mechanical behavior of a phase mixed polyurethane system modified with trifunctional and monofunctional alcohols was investigated and compared with a typical polyurethane system with a difunctional alcohol. Of interest was verifying that the average functionality of the alcohol would determine the dynamic mechanical properties and not whether that functionality was achieved by an equimolar blend of trifunctional and monofunctional alcohols or by a purely difunctional alcohol. The base system consisted of poly(tetramethylene ether)glycol (PTMG) cured with 4,4′‐diphenylmethane diisocyanate (MDI). The trifunctional alcohol was trimethylol propane (TMP). The monofunctional alcohol was decyl alcohol (DA). Samples with a typical difunctional alcohol, 2,2‐dimethyl‐1,3‐propanediol (DMPD), were prepared and their properties compared with those of the above samples. To a first approximation, the properties of TMP‐DA modified polymers are identical to those of DMPD polymers of the same hard segment concentration. These results confirm our hypothesis that the dynamic properties obtained from a combination of a trifunctional alcohol with a monofunctional alcohol are essentially equivalent to those of a difunctional alcohol.
Epoxy and glass composites in water studied with 2H‐NMR
Authors: Klotz Jürgen , Brostow Witold , Hess Michael , Veeman Wiebren S. 
Published: August 2005

AbstractThe amount, behavior, and localization of water in epoxy resin composites largely influence the mechanical properties and aging. Gravimetric analysis combined with 2H‐NMR of heavy water in epoxy resin glass fabric composites provides direct information about types of water, which can be distinguished by their mobility. Three different epoxy composites were analyzed with this technique. The results are correlated with mechanical properties.
Thermally stimulated oxidative degradation of high impact polystyrene with nitric acid
Authors: Hace Drago , Kovacevic Vera , Pajc‐Liplin Davorka 
Published: August 2005

AbstractThe practical application of high impact polystyrene (HIPS) depends on the resistance to aging in aggressive environments. The investigation of morphological, mechanical, and chemical properties was made on HIPS samples of various thickness. The property deterioration of HIPS caused by concentrated nitric acid and heat was studied. The diffusion through micropores formed visible cracks that finally led to the complete destruction into a powder. The rapid loss in mechanical properties was explained in terms of scission reaction of the graft polybutadiene (PB) with the homopolystyrene (PS) matrix. Comparative measurements of pure PS and PB under the same conditions were helpful in resolving parallel reactions that preferentially take place in PS and/or in PB sequences. It was established that higher degree of nitration caused by higher temperature results in increased insolubility owing to parallel crosslinking reactions. The nitric acid attack on HIPS caused scission reactions, which also led to the oxidative degradation, more pronounced in the PS phase in the soluble part of HIPS.
Stereochemical analysis of acrylic copolymers with large polar side groups by NMR spectroscopy
Authors: Román Julio San , Gallardo Alberto 
Published: August 2005

AbstractNMR spectra give abundant information at the microstructural level. When pseudoasymmetric carbon atoms are present in the monomeric repeating units, it is possible to obtain valuable information about the relative stereochemical configuration of the side substituents of the pseudoasymmetric center. This is the best way to know the tacticity of a polymer and the cotacticity parameters of copolymers, as well as the average distribution of comonomeric units along the chains, according to the polymerization mechanism. In this work, we present the microstructural and stereochemical characterization of acrylic copolymers prepared by free radical copolymerization of 2‐hydroxyethyl methacrylate with a methacrylic ester or methacrylamide derivative, bearing polar side groups of biomedical interest. These copolymer systems were analyzed by 1H‐NMR spectroscopy to determine the average molar composition, and the corresponding reactivity ratios, and by 13C‐NMR to study the microstructural and stereochemical configuration of comonomer sequences in terms of triads and pentads. Analyses account for the mechanism of polymerization, which fits first order Markov statistics for the addition of comonomers to free radical growing ends. The stereochemical distribution is described by a Bernoullian trial.
Synthesis, characterization and properties evaluation of copolymers of 2,3,4,5,6‐pentafluorostyrene and N‐phenylmaleimide
Authors: Agarwal Seema , Becker Mathias , Tewes Friederike 
Published: August 2005

AbstractCopolymers of 2,3,4,5,6‐pentafluorostyrene (PFS) having a combination of high hydrophobicity and high glass transition temperature (Tg) are reported here for the first time. The copolymerization was carried out using N‐phenylmaleimide (NPM) as the comonomer and azobisisobutyronitrile (AIBN) as the initiator under both conventional thermal heating and microwave heating. The initial copolymerization rate was found to be higher under microwave heating than under thermal heating. The copolymerization parameters were determined using the Fineman–Ross method and were found to be r1 (NPM) = 0.28 and r2 (PFS) = 0.86. Increased incorporation of NPM in the copolymers led to an increase in Tg of the copolymers without significantly affecting the hydrophobicity of poly(2,3,4,5,6‐pentafluorostyrene). Thermal stability of the copolymers is also reported. Copyright © 2005 Society of Chemical Industry
Synthesis and evaluation of new ditopic cyclophane receptors for benzoic acid
Authors: Stetson Christopher M. , Nishikawa Shiro , Purkiss David W. , Dalley N. Kent , Bartsch Richard A. 
Published: August 2005

AbstractAs potential receptors for a benzoic acid guest, new ditopic cyclophane host molecules, each with a π electron‐rich portion and a pyridine ring‐containing portion, are synthesized. Complexation of benzoic acid guest by the potential molecular receptors is probed by infrared spectroscopy, proton magnetic resonance titration experiments and solid‐state structure determination. Copyright © 2005 John Wiley & Sons, Ltd.
Heat capacity and chemical equilibria of liquid selenium
Authors: Shu Hua‐Cheng , Gaur Umesh , Wunderlich Bernhard 
Published: August 2005

AbstractHeat capacities of liquid selenium have been measured by computer interfaced differential scanning calorimetry in the metastable region with an accuracy of ± 1% from 330 to 520°K. To avoid crystallization, the measurements were done on cooling. A semiquantitative fitting of the heat capacity to vibrational energy contributions, free volume (hole) effects, and heats of reaction from the changes in the ring‐chain and depolymerization equilibria was possible to within ±5% of the newly measured and literature data between the glass transition temperature (ca. 303°K) and 1000°K. It could be established that the shift in the ring‐chain equilibrium is not the major reason for the overall decrease in heat capacity above the glass transition temperature. The floor temperature, which was earlier placed at about 356°K, is possibly below the glass transition temperature. The increase in heat capacity beyond 800°K has been linked with the depolymerization reaction.
Intramolecular excimer formation in macromolecules. II. Energy migration and excimer formation in acenaphthylene‐methyl methacrylate copolymers
Authors: Reid R. F. , Soutar I. 
Published: August 2005

AbstractExcimer formation has been studied in a series of ancenaphthylene—methyl methacrylate copolymers of content varying over the total composition range. In accord with a previous model [Reid and Soutar, J. Polym. Sci. Polym. Lett. Ed., 15, 153 (1977)], the excimer formation has been described by a composite function representative of energy migration and excimer site concentration. In tramolecular energy migration in glassy solutions of the polymers was characterized by use of fluorescence depolarization measurements. The extent of energy migration in the acenaphthylene copolymers is determined by the mole fraction of aromatic chromophore fa. A function Σ descriptive of the excimer site concentration has been generated on the assumption that excimer formation results predominantly from next‐ to nearest‐neighbor interactions. Σ is based upon the pentad distribution of aromatic chromophores in the chain and contains pentad fractions appropriately weighted according to the frequency and relative importance of their potential excimer sites. Reactivity ratios of acenaphthylene and methyl methacrylate in copolymerization at 70°C were ra = 0.80 and rm = 0.57.
Proton spin‐relaxation study of the polymerization of diacetylene in a single crystal
Authors: Höptner W. , Von Schütz J. U. , Wolf H. C. 
Published: August 2005

AbstractProton spin‐lattice relaxation experiments on the bis‐(p‐toluenesulfonate) of 2,4‐hexadiyne‐1,6‐diol (TSHD) as a function of temperature (25 to 353 K), of frequency (22 and 44 MHz), and of conversion to polymer were performed to determine the molecular motions in this crystal and to follow the conversion via the changes in the relaxation time T1. It was found that T1 is dominated below 125 K by weakly hindered (ΔE = 2.8 kJ/mole) tunneling (Λ = 220 MHz) CH3 groups, at about 160 K by order‐disorder fluctuations around the phase‐transition temperature ϑc which depends strongly on the conversion, and above 200 K by the motion of the whole side group. T1 can be used as sensitive probe for the conversion: The change in T1 at about 44 K is directly proportional to the conversion, whereas the change at high temperatures (e.g., 353 K) occurs essentially at low conversions (⩽10%). This is explained by distorted (stressed) areas around the isolated polymer chains, which are estimated to be about 16 times the size of the chains. After an induction period the stresses are relieved by further polymerization.
Thermoelasticity of networks in swelling equilibrium with mixed diluents: Specific polymer‐diluent interactions
Authors: Britton A. T. , Sullivan J. L. , Smith K. J. 
Published: August 2005

AbstractThermoelasticity studies of poly(vinyl alcohol) networks swollen in aqueous glycol indicate that the effects of specific polymer‐diluent interactions diminish at high swelling, much as in the situation of poly(vinyl alcohol) in pure water reported earlier. In 20% glycol, the ratio of the energy component fe of the force to the total force f was found to be −0.59 at high swelling. Swelling was controlled by the degree of network crosslinking. Evidence that fe/f could be determined under the condition of a null thermal expansion coefficient was not obtained; in fact, the contrary was indicated.
Triple helix of a schizophyllum commune polysaccharide in aqueous solution
Authors: Norisuye Takashi , Yanaki Toshio , Fujita Hiroshi 
Published: August 2005

AbstractFrom sedimentation equilibrium, light scattering, and viscosity measurements on a series of native and sonicated samples of schizophyllan, and extracellular β‐1,3‐D‐glucan, the following results were obtained: (i) weight‐average and z‐average molecular weights (M̄w and M̄z) in water are about three times as large as those in dimethylsulfoxide (DMSO); (ii) the exponent in the Houwink‐Mark‐Sakurada intrinsic viscosity relation in water is close to 1.7, whereas in DMSO it is 0.68; (iii) intrinsic viscosities of samples with M̄w below 5 × 105 in water at 25°C can be fitted by Yamakawa's theory for along rigid rod if the pitch (1.836 nm) of the triple helix of Atkins et al. and the diameter (3 nm) estimated from the model triple helix are used; (iv) intrinsic viscosities in water‐DMSO mixtures at 25°C undergo and almost discontinuous decrease when the weight fraction of DMSO in the mixture increases to about 87%. These results combined lead to the conclusion that schizophyllan dissolves in water as a triple helix similar to that proposed by Atkins et al. and that the triple helix in aqueous DMSO solution “melts” abruptly to single chains when the DMSO coposition reaches about 87 wt%. It was also found that the triple helix is not recoverable once it is broken in DMSO.
Solid‐State coextrusion of high‐density polyethylene. II. Effect of molecular weight and molecular weight distribution
Authors: Zachariades Anagnostis E. , Kanamoto Tetsuo , Porter Roger S. 
Published: August 2005

AbstractThe recently developed technique of solid‐state coextrusion for ultradrawing semicrystalline thermoplastics has been applied in the preparation of self‐reinforced high‐density polyethylene extrudates. The extrudates consist of definite core and sheath phases composed of different molecular weights (Mw) in the range of 60,000–250,000 and different molecular weight distributions (Mw/Mn = 3.0–20). Concentric billets of two different phases were prepared for extrusion by in serting a polyethylene rod within a tubular billet of a different high‐density polyethylene followed by melting the two phases to obtain bonding between them. The billet was then split longitudinally to increase extrusion speed and extruded at 120°C, 0.23 GPa through a conical die of extrusion draw ratio 25. Extrudates of high tensile modulus (38 GPa) and strength (0.50 GPa) could be produced in a steady state process at a rate near 0.25 cm/min. The tensile properties of the extrudates from either the single or concentric billets increased with average molecular weight and were insensitive to the molecular weight distribution of the constituent phases. Thermal analysis indicated a high deformation efficiency for the sheath and core phases of the extrudates by the coextrusion technique.
Fourier transform infrared investigation of the effects of irradiation on the 19 and 30°C phase transitions in polytetrafluoroethylene
Authors: Vanni H. , Rabolt J. F. 
Published: August 2005

AbstractFourier transform infrared spectroscopy has been used in conjunction with differential scanning calorimetric measurements to investigate the nature of molecular degradation and its effect on the phase transition temperatures in irradiated polytetrafluoroethylene (PTFE). Both the 19 and 30°C transitions are observed to exhibit similar shifts to low temperatures upon irradiation. Infrared absorbance subtraction data from irradiated PTFE indicate a continual decrease in sample crystallinity accompanied by an increase in the number of free and bonded COOH groups with increasing dose consistent with molecular degradation by chain scission. By comparing infrared band intensities on a number of irradiated PTFE samples with those from short chain perfluoro n‐alkanes, it was determined that the overall reduction in chain length caused by irradiation was primarily responsible for the observed reduction in both phase transition temperatures.
Influence of chain conformation on translational diffusion of poly(2‐vinyl pyridine) in dilute solution
Authors: Chao D. Y. , Jamieson A. M. 
Published: August 2005

AbstractA comparative photon correlation spectroscopy study is reported of the concentration‐dependent translational diffusion coefficient Dt of atactic poly(2‐vinyl pyridine) in tetrahydrofuran and in aqueous solution, in the form of the poly(2‐vinyl pyridinium)chloride salt (α = 0.4). The limiting Stokes radius of the polymer is observed to be identical within experimental error in tetrahydrofuran (THF) at temperatures below 30°C and in aqueous solutions at high ionic strength. This numerical value is comparable to expectation for an unperturbed atactic vinyl polymer chain and indicates a compact, possibly micellar, conformation. Raising the temperature in THF above 30°C and decreasing the ionic strength or increasing the ionization above α = 0.4 in aqueous solvents causes a discontinuous cooperative transition to a more expanded structure. The effect of the conformational change is also manifest in the concentration dependence of Dt. Using experimental estimates of the second osmotic virial coefficients obtained by total scattered intensity measurements, the experimental data for dDt/dc are compared with prediction based on hydrodynamic theory. Substantial disagreement is found between theory and experiment, especially in the aqueous system. In 0.01M NaCl, decrease in polyion concentration induces the transition from the compact form to a highly extended structure. Angle‐dependent quasielastic light scattering data from the expanded state provides information about the intramolecular chain dynamics.
Effects of spinning conditions on the mechanical properties of ultrahigh‐molecular‐weight polyethylene fibers
Authors: Ohta Yasuo , Murase Hiroki , Hashimoto Takeji 
Published: August 2005

AbstractWe investigated the tensile strength and modulus of ultrahigh‐strength polyethylene (UHSPE) fibers obtained by using the special two‐step‐drawing process of as‐spun fiber (ASFs) which were prepared by the so‐called gel‐spinning method. We have found that the higher the ASF's spinning speed is, the higher the attainable tensile strength σf and modulus E are. For all the fibers drawn from ASFs with various spinning speed except for 120 m/min, we have found a master curve for the inverse of σf which is plotted as a function of T1/4E−1/2, where T is the linear density of the drawn fibers, in consistent with the Griffith theory: a thicker fiber obtained with a lower spinning speed exhibits lower strength, although all the AFSs possess the same value of E. This also suggests that a thicker fiber contains more defects which would lead to the Griffith‐type crack propagation breakage. Moreover, from morphological observation of ASFs under transmission electron microscopy, the ASF obtained at a relatively low spinning speed possesses a heterogeneous cross‐sectional morphology, whereas that obtained at relatively high spinning speed possesses a relatively homogenous morphology. We propose that this morphological evidence may account for the experimental findings of the behavior of the mechanical properties described above. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2639–2652, 2005
Gas permeability and selectivity of hexafluoroisopropylidene aromatic isophthalic copolyamides
Authors: Carrera‐Figueiras Cristian , Aguilar‐Vega Manuel 
Published: August 2005

AbstractThe synthesis, thermal, and gas transport properties of poly(hexafluoroisopropylidene isophthalamide), HFA/ISO homopolymer, and HFA/TERT‐co‐HFA/ISO copolyamides with different poly(hexafluoroisopropilydene‐5‐t‐butylisophthalamide), HFA/TERT, ratios are reported. The results indicate that the glass transition temperatures of the copolyamides increase as the concentration of HFA/TERT in the polyamide increases. The gas permeability coefficients in the polyamides and copolyamides are independent of pressure or decrease slightly particularly with CO2, N2, and CH4. It was seen that HFA/TERT is 2–6 times more permeable than HFA/ISO, depending on the gas being considered. This was assigned to the presence of the bulky lateral substituent, t‐butyl group in HFA/TERT and HFA/TERT‐co‐HFA/ISO copolyamides. This substituent increases fractional free‐volume, as expected. Therefore, the gas permeability and diffusion coefficients generally increase with increasing fractional free‐volume. The experimental results for the gas permeability and permselectivity for the copolyamides was well represented by a logarithmic mixing rule of the homopolyamides permeability coefficients and their volume fraction. The selectivity of gas pairs, such as O2/N2, CO2/CH4, and N2/CH4 decreased slightly with the addition of HFA/TERT. The temperature dependence of permeability for homopolyamides and copolyamides can be described by an Arrhenius type equation. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2625–2638, 2005
Experimental study of a pulsed microwave plasma assisted chemical vapour deposition of carbon nanotubes
Authors: Belmahi M. , Le Brizoual L. , Assouar M. B. , Tousch T. , Vergnat M. , Bougdira J. , Alnot P. 
Published: August 2005

AbstractIn this study we present the first results achieved on the growth of carbon nanotubes (CNT) in both continuous mode (CM) and pulsed mode (PM) microwave plasma assisted chemical vapour deposition (MPACVD). The interest of this work is to determine the influence of the discharge parameters on the CNT properties such as diameter, length, density … etc. The experiments were carried out at a sustrate temperature around 900 °C. The catalyst used was nanostructured Fe–SiO deposited on silicide. It was found that the formation of multiwalls carbone nanotubes (MWCNTs) occurs when varying the discharge parameter from the CM to the PM and a selective growth of bundles of MWCNTs is obtained in the optimal PM plasma mode conditions. The measured diameter of isolated MWCNTs in the CM is around 20 nm. We measured a decrease of the amorphous carbon structures by a factor 7 and an increase of the CNT density by a factor 3 from the CM to the PM, confirming that the pulsed mode is more suitable for the MWCNT growth. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
TL, OSL, Raman spectroscopy and SEM characterization of boron doped diamond films
Authors: Pedroza‐Montero M. , Chernov V. , Castañeda B. , Meléndrez R. , Gonçalves J. A. N. , Sandonato G. M. , Bernal R. , Cruz‐Vázquez C. , Brown F. , Cruz‐Zaragoza E. , Barboza‐Flores M. 
Published: August 2005

AbstractHot filament chemically vapor deposited (HFCVD) boron doped diamond films were grown on monocrystalline silicon (111) doped with B/C ratios of 4000, 8000 and 12,000 ppm. Scanning electron micrographs show that the films are composed of well‐faceted microcrystallites ranging in size from about 1 to 5 µm with no correlation with B/C concentration. The Raman spectra exhibit a sharp dia‐ mond band at 1332 cm–1 which shifts to lower wave numbers, broaden and decreases as the B/C ratio increases. An additional broad band is observed around 1200 cm–1. The beta irradiated diamond films exhibit thermoluminescence (TL) and optically stimulated luminescence (OSL) and the TL glow curves can be fitted well with four glow peaks. The kinetic parameters of these TL peaks as well as their intensities depend on B/C ratio. The OSL curves of the diamond films grown with 4000 and 8000 ppm of B/C exhibit standard decay behaviour for continuos stimulation with light of 470 nm. However, the OSL signal of the 12,000 ppm film increases initially with light stimulation, reaching a maximum to decay afterwards. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Improvement of the electrical properties of compensated phosphorus‐doped diamond by high temperature annealing
Authors: Chevallier J. , Saguy C. , Barbé M. , Jomard F. , Ballutaud D. , Kociniewski T. , Philosoph B. , Fizgeer B. , Koizumi S. 
Published: August 2005

AbstractWe have followed the evolution of the electrical and infrared absorption properties of two phosphorus‐doped epitaxial layers under a series of isochronal annealings between 800 °C and 1400 °C. In the as‐grown state, one sample is weakly compensated (Na/Nd= 0.15) while the other one is highly compensated (Na/Nd = 0.73). Under thermal annealing, both the electrical and infrared properties of the weakly compensated remain unchanged. On the contrary, the highly compensated sample becomes weakly compensated (Na/Nd = 0.15) after annealing at 1000 °C, 30 min while the neutral phosphorus concentration remains constant. This result is explained in terms of a migration of negatively charged acceptors followed by trapping on P+ donors. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)