bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nuclear magnetic resonance monitoring of chain‐end functionality in the atom transfer radical polymerization of styrene
Authors: Lutz Jean‐François , Matyjaszewski Krzysztof 
Published: January 2005

AbstractThe evolution of the bromine end functionality during the bulk atom transfer radical polymerization (ATRP) of styrene [in the presence of the catalyst CuBr/4,4′‐di‐(5‐nonyl)‐2,2′‐bipyridine] was monitored with 600‐MHz 1H NMR. A decrease in the functionality versus the conversion was observed. The loss of functionality was especially significant at very high conversions (>90%). The experimental data were compared with a kinetic model of styrene ATRP. The latter indicated that the loss of chain‐end functionality was partly due to bimolecular terminations but was mainly due to β‐H elimination reactions induced by the copper(II) deactivator. These elimination reactions, which occurred later in the reaction, did not significantly affect the polymer molecular weights and the polydispersity. Therefore, a linear evolution of the molecular weights and low‐polydispersity polymers were still observed, despite a loss of functionality. Understanding these side reactions helped in the selection of the proper conditions for reducing the contribution of the elimination process and for preparing well‐defined polystyrene (number‐average molecular weight ∼10,000 g mol−1; weight‐average molecular weight/number‐average molecular weight ∼1.1) with a high functionality (92%). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 897–910, 2005
Synthesis, characterization, and degradation of silicon(IV) phthalocyanines conjugated axially with poly(sebacic anhydride)
Authors: Lee Priscilla P. S. , Ngai To , Yang Cheng , Wu Chi , Ng Dennis K. P. 
Published: January 2005

AbstractA novel silicon(IV) phthalocyanine with two axial poly(sebacic anhydride) chains has been synthesized by melt condensation of silicon phthalocyanine dihydroxide and oligo(sebacic anhydride). The polymer has been spectroscopically characterized and its molecular weights have been determined by gel permeation chromatography (GPC) and 1H NMR spectroscopy. Nanoparticles with an intensity‐average apparent hydrodynamic radius of 65 ± 1 nm have been prepared from this polymer via a microphase inversion method with sodium dodecyl sulfate as the surfactant. The spherical nanoparticles contain loosely aggregated polymer chains, trapping about 90% of the water. On treatment with NaOH, these nanoparticles undergo degradation that has been monitored by laser light scattering and fluorescence spectroscopy. Because of the axial substitution, the change in the aggregation state of the phthalocyanine core of this polymer during nanoparticle formation and degradation is relatively small compared with that of the zinc(II) phthalocyanine analogue reported earlier, in which poly(sebacic anhydride) chains are linked to the periphery of the phthalocyanine ring. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 837–843, 2005
New polyphenylene‐g‐polystyrene and polyphenylene‐g‐polystyrene/poly(ε‐caprolactone) copolymers by combined controlled polymerization and cross‐coupling processes
Authors: Yurteri Seda , Cianga Ioan , Demirel A. Levent , Yagci Yusuf 
Published: January 2005

Abstract1,4‐Dibromo‐2‐(bromomethyl)benzene and 1,3‐dibromo‐5‐(bromomethyl)benzene were used as initiators in the atom transfer radical polymerization of styrene in conjunction with CuBr/2,2′‐bipyridine as a catalyst. The resulting polystyrene (PSt)‐based macromonomers, possessing at one end a 2,5‐dibromophenylene or 3,5‐dibromophenylene moiety, were used in combination with 2,5‐dihexylbenzene‐1,4‐diboronic acid for Suzuki coupling in the presence of Pd(PPh3)4 as a catalyst or with the system NiCl2/2,2′‐bipyridine/triphenylphosphine/Zn for Yamamoto polymerization. Polyphenylenes (PPs) with PSt chains as substitution groups were obtained. The same macromonomers were used in Yamamoto copolycondensation reactions, in combination with a poly(ε‐caprolactone) (PCL) macromonomer, and this resulted in PPs with PSt/PCL side chains. The obtained PPs had good solubility properties in common organic solvents at room temperature similar to those of the starting macromonomers. The new polymers were characterized with 1H (13C) NMR, IR, and gel permeation chromatography. The optical properties of the polymers were monitored with UV and fluorescence spectroscopy. The thermal behaviors of the macromonomers and final PPs were investigated with differential scanning calorimetry and compared. The morphology of PPs containing PSt and PCL blocks was characterized with atomic force microscopy, and a microphase‐separated layered morphology was observed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 879–896, 2005
Controlled anionic synthesis of star‐shaped polystyrene by the incremental addition of divinylbenzene
Authors: Lee Hyung‐Jae , Lee Kwanyoung , Choi Namsun 
Published: January 2005

AbstractStar polystyrenes were synthesized from polystyryllithium with an incremental procedure in which equally divided portions of divinylbenzene (DVB) were added periodically. When the addition of DVB was repeated, the content of the unreacted polystyryllithium dramatically decreased, and complete conversion was readily achieved. In the conventional linking reaction, however, in which all the required amounts of DVB were added at once, there was an incomplete conversion of the arm polymer. The arm number of star polymers also continuously increased upon the subsequent addition of DVB. The incremental‐addition method effectively synthesized star polystyrene, minimizing uncoupled polystyrene and reproducibly controlling the arm number of star polystyrene without the formation of gel polymers. The intrinsic viscosity of star polystyrene was measured to determine the highly branched structure of star polystyrene prepared by incremental or one‐shot addition. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 870–878, 2005
DFT LCAO and plane wave calculations of SrZrO3
Authors: Evarestov R. A. , Bandura A. V. , Alexandrov V. E. , Kotomin E. A. 
Published: January 2005

AbstractThe results of the density functional (DFT) LCAO and plane wave (PW) calculations of the electronic and structural properties of four known SrZrO3 phases (Pm3m, I4/mcm, Cmcm and Pbnm) are presented and discussed. The calculated unit cell energies and relative stability of these phases agree well with the experimental sequence of SrZrO3 phases as the temperature increases.The lattice structure parameters optimized in the PW calculations for all four phases are in good agreement with the experimental neutron diffraction data. The LCAO and PW results for the electronic structure, density of states and chemical bonding in the cubic phase (Pm3m) are discussed in detail and compared with the results of previous PW calculations. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Site inequivalence for Mn2+substitution on Zn sites in ZnGeP2and ZnSiP2
Authors: Gehlhoff W. , Azamat D. , Voevodin V. G. , Hoffmann A. 
Published: January 2005

AbstractThe magnetic site‐inequivalence of the both Zn sites in ZnGeP2(ZnSiP2) could be resolved for MnZn2+(S=$ \textstyle 5 \over 2 $) by electron paramagnetic resonance (EPR) measurements. The EPR spectra are analyzed with the generalized spin Hamiltonian (SH) for S4symmetry. We found that the Mn substitu‐tion on Zn site causes a strong local distortion of the free parameterxf, which describes the positions of the anions in chalcopyrite structures withc/a≠ 2. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Low‐energy (0.1 eV) electron attachment SS bond cleavage assisted by Coulomb stabilization
Authors: Sawicka Agnieszka , Berdys‐Kochańska Joanna , Skurski Piotr , Simons Jack 
Published: January 2005

AbstractElectron capture by the ion H3C–S–S–CH2–CH2–NH at either the −NH site (to form the Rydberg radical H3C–S–S–CH2–CH2–NH3) or into the S–S antibonding σ* orbital is shown to be able to produce the same S–S bond fragmentation products H3C–S and HS–CH2–CH2–NH2, albeit by very different pathways. Capture into the S–S σ* orbital is, in the absence of the nearby positive site, endothermic by approximately 0.9 eV and leads to an electronically metastable anion that can undergo dissociation or autodetachment. In contrast, in the presence of the stabilizing Coulomb potential provided by the nearby NH site, electron attachment into the S–S σ* orbital is rendered exothermic. As a result, as we have shown in this paper, the effective cross sections for forming the H3C–S and HS–CH2–CH2–NH2 products via attachment at the −NH and S–S σ* sites are predicted to be comparable for our model compound. Moreover, we predict that the σ* site will become more amenable to electron attachment compared with the −NH site for compounds in which the distance between the S–S bond and the protonated amine is larger than in our cation. These findings and insights should be of substantial value to workers studying bond cleavage rates and fragmentation patterns in gaseous positively charged samples of peptides and proteins. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Quantum chemistry study of monomer electronic properties in water clusters and liquid water and methanol
Authors: Tu Yaoquan , Laaksonen Aatto 
Published: January 2005

AbstractA self‐consistent quantum chemistry approach is presented to study the electronic properties of a single molecule in condensed phases where Coulomb interaction is predominant in the intermolecular interactions. Using the approach, implemented in this work in a self‐consistent charge way, the electronic properties of a single water molecule in water clusters, liquid water, and those of a single methanol molecule in liquid methanol are studied at the second‐order Møller–Plesset level. The average monomer dipole moments for water and methanol in their liquid phases are calculated to be 2.65 D and 2.39 D, respectively. The changes in quadrupole moments are also discussed. For water monomer, the polarizability changes upon going from gas state to interaction systems are reported, as well. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Memory formulas for perturbations in time‐dependent density functional theory
Authors: Maitra Neepa T. 
Published: January 2005

AbstractExact time‐dependent density functionals depend on both the entire history of the density and the initial wave function. Recently we have shown that the two effects are entangled by an exact condition that should be useful as a test in building accurate memory‐dependent functionals. Here we consider this condition for small perturbations and derive an exact relation connecting the exchange‐correlation kernel with initial‐state derivatives. We discuss other exact conditions on the initial‐state derivatives which shed some light on the elusive memory‐dependence in time‐dependent density functional theory. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Transmetatarsal Amputation: Three‐year Experience At Groote Schuur Hospital
Authors: Mwipatayi B.P. , Naidoo N.G. , Jeffery P.C. , Maraspini C.D. , Adams M.Z. , Cloete N. 
Published: January 2005

AbstractTransmetatarsal amputation (TMA) for peripheral vascular disease has the reputation of being an operation with a poor outcome. This retrospective study reviewed a 3‐year consecutive series of TMA in diabetic and nondiabetic patients. All amputations performed for peripheral vascular disease at Groote Schuur Hospital from January 1999 to December 2002 were reviewed. Data were obtained from hospital records and operating theatre books. The following groups were defined for the purpose of this retrospective study: group 1, TMAs performed in diabetic patients; group 2, TMAs done in nondiabetic patients. Altogether, 43 TMAs were performed: 27 in group 1 and 16 in group 2. Perioperative mortality rates were 7% and 4%, respectively. Overall, the healing rate was 67%: 62% (17/27) in group 1 and 75% (12/16) in group 2. The median times to healing were 8 months in group 1 and 7 months in group 2. Toe pressure and the presence of advanced tibioperoneal disease influenced the outcome of TMA in diabetic patients.Transmetatarsal amputation with a healed stump provided our patients with good mobility. Prediction of healing after operation is unreliable. There was no statistical difference in outcome in diabetic (group 1) versus nondiabetic (group 2) patients.
The evidence for emergency obstetric care
Authors: Paxton A. , Maine D. , Freedman L. , Fry D. , Lobis S. 
Published: January 2005

AbstractPurposeWe searched for evidence for the effectiveness of emergency obstetric care (EmOC) interventions in reducing maternal mortality primarily in developing countries.MethodsWe reviewed population‐based studies with maternal mortality as the outcome variable and ranked them according to the system for ranking the quality of evidence and strength of recommendations developed by the US Preventive Services Task Force. A systematic search of published literature was conducted for this review, including searches of Medline, PubMed, Cochrane Database of Systematic Reviews, the Cochrane Pregnancy and Childbirth Database and the Cochrane Controlled Trials Register.ResultsThe strength of the evidence is high in several studies with a design that places them in the second and third tier in the quality of evidence ranking system. No studies were found that are experimental in design that would give them a top ranking, due to the measurement challenges associated with maternal mortality, although many of the specific individual clinical interventions that comprise EmOC have been evaluated through experimental design. There is strong evidence based on studies, using quasi‐experimental, observational and ecological designs, to support the contention that EmOC must be a critical component of any program to reduce maternal mortality.
Argon—Nitrogen Phase Diagram
Authors: Barrett C. S. , Meyer Lothar 
Published: January 2005

The phases and phase transformations in the argon—nitrogen system have been determined by x-ray diffraction with results very different from previous published phase diagrams. The solid phase in equilibrium with the liquid between 1% and 100% N2 is close-packed hexagonal in spite of the fact that pure argon is face-centered cubic. The argon-rich solid solutions with 1% to 55% N2 undergo a strain-induced martensitic transformation from cph (stable at high temperatures) to fcc at low temperatures. The highest temperatures at which this transition becomes possible are those at which the combination of thermal expansion plus solid solution expansion gives a lattice constant for the fcc phase of a0=5.486 Å, which corresponds to that obtained by extrapolating the curve of a0 for pure argon to a point 5° above the melting point. The c/a value for the cph argon-rich phase is 1.633 within experimental uncertainty at all compositions and temperatures.
Stacking faults are infrequent in the as-frozen samples but are very numerous in the deformed samples. At temperatures and compositions where fcc and cph have nearly equal free energies it is possible to destroy the crystalline diffraction pattern by cold work, leaving only an amorphous pattern.
The α-N2 solid solution forms spontaneously and isothermally from the β-N2 solid solution at N2 contents above 77.5% N2. The transformation appears to be that known in metallic systems as a ``massive'' type, and presumably involves only short-range diffusion in the phase interface. The curve of distance between nearest molecular centers in the β phase is not an extension of the curve for the argon-rich phase. The α phase, which is cubic, is not continuous with the cubic argon-rich solid solution; samples with 55%—75% N2 do not transform from the hexagonal form even when cold worked at 4.2°K.
Rate-of-Growth Technique for the Measurement of Molecular Dipole Moments from Microwave Spectra at Weak Modulation Fields
Authors: Lindfors Karl R. , Cornwell C. D. 
Published: January 2005

Under suitable conditions, commonly met in practice, rotational lines observed with low amplitude zero-based square-wave Stark modulation have the shapes of the first or second derivatives of the zero-field absorption lines. From the rate of growth of the peak-to-peak spectrometer deflection as a function of the modulation amplitude, the molecular electric dipole moment may be calculated. As this procedure does not require the resolution of individual Stark components, it should prove useful when the analysis of Stark splittings is not feasible, as in the case of cluttered spectra, spectra complicated by nuclear quadrupole hyperfine splittings, and spectra for which no low-J transitions are accessible. Working equations are given for the case where the Stark shifts, when smaller than the linewidths, are linear or quadratic in the field.
The method has been tried with OCS, CH3Br, and SO2. It appears that an accuracy of the order of several percent in the dipole moment can be achieved. Several experimental precautions and techniques are described, including a null method for measurement of the square wave voltage amplitude.
Gaseous Diffusion. The Systems He–Ar, Ar–Xe, and He–Xe
Authors: Malinauskas A. P. 
Published: January 2005

Relative values of the diffusion coefficients of the systems He–Ar, Ar–Xe, and He–Xe have been determined over the temperature range 0° to 120°C by a two-bulb method. The experimental diffusion coefficients, at 1 atm pressure, can be described by the following equations: He–Ar: log10D=1.684log10T−4.2902,Ar–Xe: log10D=1.955log10T−5.7807,He–Xe: log10D=1.720log10T−4.5251.
The apparatus was calibrated with the He–Ar diffusion data; the results for the system Ar–Xe are in essential agreement with the data reported by other workers, but the He–Xe diffusion coefficients are about 9% lower than previously published values. The present He–Xe coefficients are in good agreement, however, with results which have been determined from a consideration of the composition dependence of the viscosities of He–Xe mixtures.
On the Relative Roles of Free Volume and Activation Energy in the Viscosity of Liquids
Authors: Macedo P. B. , Litovitz T. A. 
Published: January 2005

The rate-theory approach of Eyring and the free-volume theory of Cohen and Turnbull for liquid viscosities have been reconsidered. The rate theory has been reformulated using the Cohen and Turnbull expression for the probability of finding a vacant site and yields an equation of the form η=A0exp[Ev*/RT+γV0/Vf].This result has been applied to many liquids ranging from fused silica to liquid argon and including polyatomic van der Waals as well as hydrogen-bonded liquids.
Consistent fits to both temperature and pressure dependence of viscosity were obtained. A significant conclusion is that the free volume of liquids is considerably higher than that suggested by the WLF and Cohen and Turnbull equations.
Viscosity of Moderately Dense Gases
Authors: Kim Shoon Kyung , Ross John 
Published: January 2005

At moderate densities the viscosity of a gas may be represented by a virial expansion in density η=η0+bρ+···, and we present a calculation of the contribution of triple collisions to the coefficient b. We approximate three-body encounters by two-body collisions between a single molecule and a dimer. We derive the equilibrium constant for dimers, according to classical statistical mechanics for spherically symmetric short-range potentials, which include bound, metastable, and orbiting pairs. Numerical results are obtained for the Lennard-Jones (6–12) potential and the equilibrium constant is found to be approximately proportional to T−32. We then apply the Chapman—Enskog theory of the viscosity of a binary mixture of dilute gases, one component being the monomer, the other the dimers. Collisional transfer in binary collisions is not taken into account.
The analysis based on this simple model yields substantial agreement with experiment, in particular the temperature dependence of b∼T−1 at high reduced temperature, and the near invariance of b with T at moderate reduced temperatures. In comparison, Enskog's theory of hard spheres predicts b∼T½ and the anomalous behavior at high reduced temperature is not removed by ad hoc variation of the hard-sphere diameter with temperature. For given parameters (σ, ε) of the Lennard-Jones intermolecular potential, good agreement with experiment is obtained, if the monomer—dimer interaction is represented by a similar potential with parameters 1.02σ, 1.23ε. The results are essentially independent of the use of other potential parameters which maintain the magnitude of the attractive potential. We conclude that the physical origin of the initial density dependence of viscosity requires consideration of not only repulsive but also attractive forces between molecules.
Inhibited Dissolution of {100} Surfaces of Single Crystals of Lithium Fluoride
Authors: Ives M. B. , Plewes J. T. 
Published: January 2005

A technique is described for the determination of the dissolution rates of {100} lithium fluoride surfaces in dilute aqueous solutions of ferric fluoride. The effect of ferric ion content of the etchant on the rate is found to be constant for ion concentrations substantially in excess of the optimum for the production of smooth-faced square etch pits at dislocations. The results correlate well with recent theories concerning the adsorption of ferric ions during etching.
The effect of lithium fluoride undersaturation varies greatly from specimen to specimen and demonstrates the heterogeneous nature of hole nucleation in the close-packed surfaces.
Effect of Electrical Fields and Density in the Radiolysis of Ethane
Authors: Carmichael Halbert H. , Gorden R. , Ausloos P. 
Published: January 2005

The gamma-ray radiolysis of C2H6–C2D6–NO and CH3CD3−NO mixtures has been investigated as a function of applied electrical field. In the saturation current region, a number of products resulting from the decomposition of neutral excited molecules increase about fivefold before the onset of secondary ionization while several other products, which can be ascribed to ion molecule reactions, remain essentially unchanged. The modes of decomposition of the excited ethane molecules formed by electron impact, as derived from the applied field experiments, are the same as those observed in the vacuum ultraviolet photolysis at 1470 and at 1236 Å. From the isotopic composition of the products it could be deduced that the average energy transferred to ethane by electron impact is greater than 10 eV. A value of 0.5 was derived for the number of neutral excited molecule decompositions per ion pair.
A change in density has a pronounced effect on the product distribution, both in the photolysis at 1236 Å and the radiolysis. In the radiolysis, several of the changes can be ascribed to the diminishing fragmentation of the parent ion with an increase in density. However, products resulting from the fragmentation of the neutral excited ethane molecules formed in the radiolysis also show a strong dependence on density because of collisional stabilization of the primary fragments and of the products formed in secondary reactions. For instance, the propane which could be entirely ascribed to the insertion reaction CH2+C2H6+M→C3H8+M increases with an increase in density in the photolysis as well as in the radiolysis.
Phonon Spectrum of Graphite
Authors: Young James A. , Koppel Juan U. 
Published: January 2005

The phonon spectrum of reactor grade graphite is computed by means of the essentially exact root sampling technique for a sampling 47 788 points in an irreducible segment of the Brillouin zone.
Measurements of the specific heat (over the range 100°—1000°K) are used to determine the force constants, resulting in good agreement of the calculated phonon spectrum, and neutron scattering measurements.