bluuebunny/crossref_metadata_2025_split huggingface dataset:
Supramolecular structures and properties models of macrocyclic polymer complexes
Authors: Mubarak Ahmed T. , El‐Assiery Saeed A. 
Published: July 2004

AbstractTwo novel supramolecular complexes of types [Ru(L)(H2L)Cl·OH2] and [Ru(HLn)Cl3] (where H2L is a potential tetradentate ligand derived from hydrazine hydrate and diethyl malonate, and HLn is a potential bidentate ligand derived from coupling of allyl azo‐β‐diketone) have been synthesized and characterized by elemental analysis, conductance and magnetic measurements, followed by 1H NMR, to determine the effect of substituents on the intramolecular hydrogen bond. The electronic properties and models of the bonding of ligands and complexes were investigated by UV–Vis and IR spectroscopies. The first type of complex contains terminal hydrazinic nitrogen atoms with an unshared electron pair and may take part in nucleophilic condensations. Therefore, the reactions of allyl‐β‐diketone complexes with malonic dihydrazide have also been studied, as these cause ring closure and formation of supramolecular macrocyclic ligand complexes. The wavelengths of the principal electronic absorption peaks have been accounted for quantitatively in terms of crystal field theory, and various parameters have been evaluated. On the basis of the electronic spectra, an octahedral geometry has been established for the polymer complexes C. The macrocyclic polymer complexes D are pentacoordinate, and a trigonal‐bipyramidal environment (D3h) is suggested for the ruthenium(III) ion. The effect of the Hammett constant on the ligand field parameters is also discussed. Copyright © 2004 John Wiley & Sons, Ltd.
Solid‐state NMR study of [(Ph3SnF)2(Ph3SnO2PPh2)], a novel coordination polymer prepared from Bu4N[Ph3SnF2] and [Ph3SnOPPh2OSnPh3](O3SCF3)
Authors: Beckmann Jens , Dakternieks Dainis , Duthie Andrew , Mitchell Cassandra , Ribot François , d'Espinose de la Caillerie Jean Baptiste , Revel Bertrand 
Published: July 2004

AbstractThe coordination polymer [(Ph3SnF)2(Ph3SnO2PPh2)] (3), prepared by the reaction of [Ph3SnOPPh2OSnPh3](O3SCF3) (4) with Bu4N[Ph3SnF2] (5), was investigated by multinuclear magic angle spinning magnetic resonance spectroscopy and the results compared with those of the polymeric parent compounds Ph3SnF (1) and Ph3SnO2PPh2 (2). The crystal structure of 4 was determined by X‐ray crystallography. Copyright © 2004 John Wiley & Sons, Ltd.
Regioselective synthesis of symmetrical pyridyl selenium compounds by bromine–magnesium exchange of bromopyridines using isopropyl magnesium chloride: X‐ray crystal structure of 2,2′,5,5′‐tetrabromo‐3,3′‐dipyridyldiselenide
Authors: Bhasin K. K. , Arora Veena 
Published: July 2004

Abstract2,2′‐Dipyridyl‐3,3′‐dipyridyl,5,5′‐dipyridyl‐diselenides have been synthesized by a convenient method employing non‐cryogenic conditions. Various bromopyridines (2‐Bromopyridine, 2,5‐dibromopyridines and 2,3,5‐Tribromopyridines) undergo selective monobromine–magnesium exchange to yield the corresponding pyridyl magnesium chlorides at room temperature upon treatment with iPrMgCl. The resulting pyridyl magnesium chloride is quenched with elemental selenium, which upon further oxidation affords the above diselenides in good yields. The compounds prepared using this methodology have been characterized by elemental analysis, IR, NMR (1H, 13C, 77Se) and mass spectral analysis. The molecular structure of 2,2′,5,5′‐Tetrabromo‐3,3′‐dipyridyldiselenide has been established by single‐crystal X‐ray diffraction analysis. It exists as a dimeric form due to the non‐bonding interactions between the selenium of one pyridine moiety and the hydrogen of the other. Copyright © 2004 John Wiley & Sons, Ltd.
Synthesis, structure characterization and larvicidal activity of some tris‐(para‐substitutedphenyl)tins
Authors: Song Xueqing , Duong Quyen , Mitrojorgji Edlira , Zapata Alejandra , Nguyen Nhuvu , Strickman Daniel , Glass Jacqulin , Eng George 
Published: July 2004

AbstractA series of tris‐(para‐substitutedphenyl)tins (X − C6H4)3SnY, where X = Cl, F, CH3 and SCH3 and Y = Cl, OH and OAc, was synthesized. The structures of the compounds were primarily characterized by Mössbauer spectroscopy. Based on the spectroscopic data, the chloride derivatives were determined to be four‐coordinated monomers and the acetate and hydroxide compounds were found to be five‐coordinated polymers. The compounds were screened against the second larval instar of the Anopheles stephensi and Aedes aegypti mosquitoes. For the An. stephensi larvae, the compounds that had the highest toxicity were those that contained a single atom substituent on the phenyl ring, and the least effective compounds contained the SCH3 substituent. Toxicity was more dependent on the ring substituent than on the anion attached to the tin atom. Quantitative structure–activity relationships could be generated between the toxicity of the compounds and the surface area of the molecule, indicating that the toxicity was related to the size of the substituent on the ring. In the case of the Ae. aegypti, the toxicity was also more dependent on the ring substituent than on the anion group. However, the size of the substituent on the ring was not found to be the dominant factor in the toxicity of these compounds. Copyright © 2004 John Wiley & Sons, Ltd.
Synthetic and antimicrobial studies on new gold(I) complexes of imidazolidin‐2‐ylidenes
Authors: Özdemir İsmail , Denizci Akın , Öztürk H. Tansel , Çetinkaya Bekir 
Published: July 2004

AbstractSix new 1,3‐diorganylimidazolidin‐2‐ylidene (NHC) gold(I) complexes of the type [Au(NHC)2]+ (1–6), were synthesized by reacting [AuCl(PPh)3] with 1,3‐dimesitylimidazolidin‐2‐ylidene or bis(1,3‐dialkylimidazolidin‐2‐ylidene). The complexes 1–6 were fully characterized by elemental analyses and spectroscopic data. The placement of mesityl or para‐substituted benzyl groups on the nitrogen atoms of the ring of the complexes leads to the particularly active antibacterial agents evaluated in this work. It is worth noting that the p‐methoxybenzyl derivative (2) inhibited the growth of Pseudomona aeruginosa, Staphylococcus epidermidis, Staphylococcus aureus and Enterococcus faecalis with minimum inhibitory concentration (MIC) values of 3.12 µg ml−1, 6.25 µg ml−1, 3.12 µg ml−1 and 3.12 µg ml−1 respectively. In contrast, the analogous p‐dimethylaminobenzyl derivative (3) is effective only against Escherichia coli (MIC = 3.12 µg ml−1). Copyright © 2004 John Wiley & Sons, Ltd.
New insights into the degradation mechanism of poly(vinyl chloride), part II. Limited polyene sequence length during degradation and synergism between costabilizers
Authors: Santamaría E. , Edge M. , Allen N. S. , Harvey H. B. , Mellor M. , Orchison J. 
Published: July 2004

AbstractFluorescence spectroscopy has shown that the limited sequence length exhibited during the thermal degradation of poly(vinyl chloride) (PVC) was the result of an HCl readdition/splitting off equilibrium, especially in unstabilized PVC formulations. In the case of stabilized PVC, the type and mechanistic action of the stabilisers seemed to play an important role in HCl re‐addition. The possibility of a synergistic effect taking place between costabilisers for PVC, namely N‐phenyl‐3‐acetyl pyrrolidine‐2,4‐dione (P24D) and its derivative N‐isopropyl‐n‐phenyl‐3‐(1‐iminoethyl) pyrrolidine‐2,4‐dione (P24D‐d) has also been investigated by means of statistical design, degrading the samples at 170°C in air and measuring the induction time (Ti) of the degraded polymer. The results reveal that the stabilising efficiency is not only affected by the presence of the metal soap, but also by the nature of the substituents in the P24D derivatives. It may be concluded that P24D‐d on degradation operates as a “reservoir” for P24D, extending the Ti to higher values compared to their individual performances and giving rise to a synergistic combination. The ability of the costabiliser to form a keto‐enol tautomerism as well as its ability to interact with the PVC and the metal soap play a crucial role in controlling their stabilising effectiveness in the polymer. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2744–2763, 2004
Enhancing the strength of polypropylene fibers with carbon nanotubes
Authors: Moore Eric M. , Ortiz Diana L. , Marla Vishnu T. , Shambaugh Robert L. , Grady Brian P. 
Published: July 2004

AbstractSingle‐walled carbon nanotubes were added to two different grades of polypropylene to produce composites. The composites were then melt‐spun into fibers, and the fibers were tested with both a conventional tensile pull tester and dynamic mechanical analysis. The changes in tensile properties were related to the grade of polypropylene used. In addition to fibers being made from the mixes, coarse extrudates (i.e., undrawn, gravity‐spun filaments) were also produced. Density measurements on these extrudates showed that the addition of nanotubes increased the composite density in a highly nonlinear manner, which suggested interaction between the polypropylene and the carbon nanotubes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2926–2933, 2004
Poly(methyl methacrylate) nanoparticles prepared through microwave emulsion polymerization
Authors: Bao Jianjun , Zhang Aimin 
Published: July 2004

AbstractThe emulsifier‐free emulsion polymerization of methyl methacrylate (MMA) was conducted with microwave irradiation. Superfine and monodisperse poly(methyl methacrylate) (PMMA) microspheres were obtained. Microwave irradiation notably promoted the polymerization reaction. This phenomenon was ascribed to the acceleration of the initiator [potassium persulfate (KPS)] decomposition by microwave irradiation. The experimental results revealed that the apparent activation energy of KPS decomposition decreased from 128.3 to 106.0 kJ/mol with microwave irradiation. The average particle size of the prepared PMMA latex was mainly controlled with the MMA concentration; it increased linearly from 103 to 215 nm when the MMA concentration increased from 0 to 0.3 mol/L and then remained almost constant at MMA concentrations of 0.3–1.0 mol/L. The KPS concentration had no effect on the average particle size, but the particle size dispersity was significantly reduced by a high KPS concentration. With a mixed polymerization phase (water/acetone = 1:3 v/v) or a redox initiation system, PMMA nanoparticles were obtained with an average particle size of 45 or 67 nm, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2815–2820, 2004
Hydraulic resistance of rigid polyurethane foams. III. Effect of variation of the concentration of catalysts on foam structure and properties
Authors: Mondal Pravakar , Khakhar D. V. 
Published: July 2004

AbstractWater blown rigid polyurethane foams are made using dibutyltin dilaurate and triethanol amine as catalysts. The rate of carbon dioxide generation due to the reaction of isocyanate with water and the rate of polymerization are varied by changing the relative proportion of the catalysts keeping the total catalyst concentration fixed. The foams have densities in the range of 134 to 164 kg/m3. Foams are characterized for hydraulic resistance, “closed cell content,” and compressive modulus. A cell window is the lamella of the foam material that separates two adjacent cells. A strut is generated where three windows of three different cells meet. The cell window area and strut width of the foam cells are measured by optical microscopy. It is found that cell window area and strut width decrease and the respective distribution becomes narrower as the proportion of dibutyltin dilaurate in the total amount of the catalysts is increased. The hydraulic resistance and hence threshold pressure of the foams increases with increase in the proportion of dibutyltin dilaurate. The maximum threshold pressure of 1.81 MPa is observed for the foam made with dibutyltin dilaurate alone. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2838–2843, 2004
Hydraulic resistance of rigid polyurethane foams. I. Effect of different surfactants on foam structure and properties
Authors: Mondal Pravakar , Khakhar D. V. 
Published: July 2004

AbstractFoams used in buoyancy applications must resist penetration by water at significant depths of immersion. The behavior of water blown rigid polyurethane foam at different water pressures from 0 to 3 MPa are studied in this work. The effects of different surfactants on the cell structure and hydraulic resistance of the foams are examined. The foams have densities in the range of 145 to 160 kg/m3. With increasing applied hydraulic pressure, it is found that the foams have very small buoyancy losses at low pressures but beyond a threshold pressure, buoyancy losses increase rapidly. The threshold pressures of the foams increase with decrease in cell window area. A cell window is the lamella of the foam material that separates two adjacent cells. The cell sizes of the foam are found to correlate with the size of the air bubbles entrained during initial mixing. Surfactants, which reduce the surface tension of the polyol to the greatest extent, are found to give the finest initial bubbles, smaller cells, and foams with the highest hydraulic resistance. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2821–2829, 2004
Shear rheological properties of acrylic copolymers and terpolymers suitable for potentially melt processable carbon fiber precursors
Authors: Bortner Michael J. , Bhanu Vinayak , McGrath James E. , Baird Donald G. 
Published: July 2004

AbstractIn an effort to generate melt processable polyacrylonitrile (PAN) precursor fibers suitable for conversion to carbon fibers, an acrylonitrile/methyl acrylate (AN/MA) copolymer and two acrylonitrile/methyl acrylate/acryloyl benzophenone (AN/MA/ABP) terpolymers were synthesized at molar ratios of 85/15 and 85/14/1, respectively. The termonomer (ABP) was incorporated to accelerate crosslinking via UV irradiation, which serves to prevent relaxation of orientation and flow as the temperature of the fiber is raised during thermooxidative stabilization. Two molecular weights of the terpolymer and one molecular weight of the copolymer were studied to determine the effect of the termonomer, and the effect of molecular weight (MW), on the steady shear viscosity (η) and magnitude of the complex viscosity (η*). A higher rate of increase of η as a function of time was observed for the high MW terpolymer relative to that of the copolymer over the temperature range used. Using a temperature sweep and monitoring levels of η*, a minimum was observed at lower temperatures for both terpolymers. These results suggest that copolymerization with ABP significantly increased the thermally induced kinetics of crosslinking. Comparison of the η and η* data for the low and high MW terpolymers suggested that molecular weight also significantly reduced the melt stability (increased the kinetics of crosslinking). A chemorhelogical correlation was then used to quantify the effects of the termonomer and of molecular weight on the kinetics of crosslinking of the AN terpolymers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2856–2865, 2004
Influence of processing on ethylene‐propylene block copolymers: Structure and mechanical behavior
Authors: Maspoch M. Ll. , Gamez‐Perez J. , Gimenez E. , Santana O. O. , Gordillo A. 
Published: July 2004

AbstractThin plaques (1, 2, and 3 mm) made of polypropylene homopolymer (iPP) and three ethylene propylene block copolymers (EPBC) with different ethylene content (5.5, 7.4, and 12% in weight) have been obtained by different processing methods (injection molding, injection and annealing, and compression molding). The morphology of the plaques has been studied using polarizing microscopy (PLM), differential scanning calorimetry (DSC), and wide‐angle X‐ray scattering (WAXS). The results have been related with the mechanical properties of the plaques (MD and TD directions) in tension loading tests. We show the influence of the ethylene content, thickness, and processing method and conditions in the final morphology and how they affect the mechanical behavior. This knowledge can be used to tailor the final properties of a piece. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2866–2878, 2004
Copolymers derived from bismaleimide oligomer with active solvent
Authors: Wang Zhen , Deng Pengyang , Gao Lianxun , Ding Mengxian 
Published: July 2004

AbstractAn oligomer from 4, 4′‐bis(maleimido)diphenyl methane and methylenedianiline were dissolved in active solvent N,N‐dimethyl acrylamide in a solid content up to 50–70%; the solution was poured in a sheet‐shaped module and irradiated by 60Co with the dose from 20 to 350 kGy at room temperature. The polymerized sheet was postcured at 180°C to obtain a transparent red‐orange sheet with tensile strength above 100 MPa. The glass transition temperature before and after postcuring was around 100°C and 150–180°C, respectively. Styrene was used along with DMAA to decrease the water absorption for the copolymers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2879–2882, 2004
The effect of varied monomer composition on adhesive performance and peeling master curves for acrylic pressure‐sensitive adhesives
Authors: Gower M. D. , Shanks R. A. 
Published: July 2004

AbstractA group of pressure‐sensitive adhesives were prepared with constant glass transition temperature, using emulsion polymerization. The monomers chosen were butyl acrylate, 2‐ethylhexyl acrylate, and methyl methacrylate, along with a small amount of acrylic acid. The proportion of acrylic acid monomer was held constant for each polymer preparation but acrylic ester monomer levels were varied. The glass transition temperatures of the acrylate copolymers were measured by using differential scanning calorimetry. Drying and weighing the tetrahydrofuran‐insoluble polymer fractions were used to determine the polymer gel fractions. Films of constant coating thickness were applied to poly(ethylene terephthalate) film and adhesive properties (tack and shear) were examined. Peel was examined through the construction of master curves derived from peel tests conducted over a range of temperatures and peel rates. As the 2‐ethylhexyl acrylate content increased, the latex gel fractions were found to increase. With increasing EHA and gel fraction, peel shear was found to increase. When peel force master curves were compared, divergence in peel master curves occurred as peel rates increased where polymers with higher butyl acrylate contents reached greater peel stress values. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2909–2917, 2004
Thermal strain of high strength polyethylene fiber in low temperature
Authors: Yamanaka Atsuhiko , Kitagawa Tooru , Tsutsumi Masayuki , Kashima Toshihiro , Fujishiro Hiroyuki , Ema Kimiko , Izumi Yoshinobu , Nishijima Shigehiro 
Published: July 2004

AbstractHigh strength polyethylene fiber (Toyobo, Dyneema® fiber: hereinafter abbreviated to DF) has a negative thermal expansion coefficient. Relation between fiber structure and thermal strain of DF used as reinforcement of DF reinforced plastic (DFRP) for cryogenic use was investigated. The crystallinities and orientation angles of several kinds of polyethylene fibers having different modulus from 15 to 134Gpa (herein after abbreviated to DFs) were measured by NMR and X‐ray. We obtained the parameters of the mechanical series‐parallel model composed of crystal and amorphous by crystallinity and modulus. Thermal expansion coefficients of DFs were estimated by mechanical series‐parallel model. All DFs having different modulus showed negative thermal expansion coefficients in the temperature range from 180 to 300K, and absolute values of those markedly increased by increasing tensile modulus of DF. The estimated thermal expansion coefficients showed negative values, and thermal strains showed a similar curve to observed ones mostly. Average thermal expansion coefficients in the temperature range from 180 to 300K estimated by mechanical model agreed with the observed ones. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2918–2925, 2004
Long‐range dependence and performance in telecom networks
Authors: Conti Pier Luigi , Lijoi Antonio , Ruggeri Fabrizio 
Published: July 2004

AbstractTelecommunications systems have recently undergone significant innovations. These call for suitable statistical models that can properly describe the behaviour of the input traffic in a network. Here we use fractional Brownian motion (FBM) to model cumulative traffic network, thus taking into account the possible presence of long‐range dependence in the data. A Bayesian approach is devised in such a way that we are able to: (a) estimate the Hurst parameter H of the FBM; (b) estimate the overflow probability which is a parameter measuring the quality of service of a network: (c) develop a test for comparing the null hypothesis of long‐range dependence in the data versus the alternative of short‐range dependence. In order to achieve these inferential results, we elaborate an MCMC sampling scheme whose output enables us to obtain an approximation of the quantities of interest. An application to three real datasets, corresponding to three different levels of traffic, is finally considered. Copyright © 2004 John Wiley & Sons, Ltd.
Understanding endothelin‐1 function during craniofacial development in the mouse and zebrafish
Authors: Clouthier David E. , Schilling Thomas F. 
Published: July 2004

AbstractMorphogenesis of the face and neck is driven by an intricate relay of signaling molecules and transcription factors organized into hierarchical pathways. The coordinated action of these pathways regulates the development of neural crest cells within the pharyngeal arches, resulting in proper spatiotemporal formation of bone, cartilage, and connective tissue. While the functions of many genes involved in these processes were initially elucidated through the use of knockout technology in the mouse, increasing numbers of zebrafish craniofacial mutants have led to a rapid expansion in the identification of genes involved in craniofacial development. A comparative analysis of signaling pathways involved in these processes between mouse and zebrafish holds the potential not only to pinpoint conserved and therefore crucial gene functions in craniofacial development, but also to rapidly identify and study downstream effectors. These complementary approaches will also allow rapid identification of candidate genes and gene functions disrupted in human craniofacial dysmorphologies. In this brief review, we present a comparative analysis of one molecule involved in craniofacial development, endothelin‐1, a small, secreted protein that is crucial for patterning the neural crest cells that give rise to lower jaw and throat structures. Birth Defects Research (Part C) 72:190–199, 2004. © 2004 Wiley‐Liss, Inc.