bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crystallization kinetics for semicrystalline random copolymers of vinylidene chloride (VDC) with methyl acrylate (MA), and the effects on the internal morphology of the resin particles formed during synthesis
Authors: Obi Bernard E. , DeLassus Phillip T. , Howell B. A. , Dangel Brian 
Published: April 2003

AbstractIsothermal crystallization kinetics for random copolymers of vinylidene chloride (VDC) with methyl acrylate (MA) is reported. Syntheses of many semicrystalline polymers follow heterogeneous reaction paths in which the macromolecule chains phase separate from the reaction mixtures. The internal particle morphology (the internal structure of the resin bead) from this type of reaction is granular and porous, as a result of the demixing processes accompanying polymer formation. Demixing in these polymers involves either liquid‐liquid (L‐L) phase separation followed by liquid‐solid (L‐S) transformation (crystallization) or L‐S transformation alone. Crystallization (L‐S transformation) must be an indispensable part of the process if a porous granular structure is to be expected. This is because L‐S transformation is the most probable means by which the demixed structure can be stabilized against complete coalescence or agglomeration, which would lead to totally fused bead internal structure. This is particularly true if the glass transition temperature (Tg) is lower than the polymerization temperatures, as is the case with the VDC‐MA copolymers. Copolymers that crystallize the fastest will have the finest (most porous) resin bead morphology. The result of this work is consistent with expectation. The homopolymer (PVDC) that crystallizes the fastest has the finest resin bead internal morphology. The copolymers show slower crystallization rates with increasing noncrystallizable MA content. Correspondingly, resin morphology measured by specific surface area decreased with increasing amounts of the noncrystallizable (MA) comonomer unit in the copolymer. This is clearly seen in SEM photographs of the internal bead structures of these copolymers. ©1995 John Wiley & Sons, Inc.
Electron transport in acceptor doped polymers: The role of group dipole moments
Authors: Borsenberger P. M. , Gruenbaum W. T. , O'Regan M. B. , Rossi L. J. 
Published: April 2003

AbstractElectron mobilities have been measured in poly(styrene) doped with an isomer mixture of two diphenoquinone (DPQ) compounds over a range of fields, temperatures, and DPQ concentrations. The results are interpreted within the framework of a formalism based on disorder, due to Bässler and coworkers. The formalism is based on the assumption that charge transport occurs by hopping through a manifold of localized states with superimposed energetic and positional disorder. The key parameter of the formalism is the energy width of the hopping site manifold. For DPQ doped poly(styrene), the energy width is 0.118 eV and independent of the intersite distance or DPQ concentration. The width can be described by a model based on dipolar disorder, if it is assumed that the fluctuations of hopping site energies are due to group dipole moments associated with the carbonyl groups of the DPQ molecules. The interpretation of the experimental results leads to the further conclusion that polaronic effects need not be invoked to explain transport phenomena in this class of doped polymers. © 1995 John Wiley & Sons, Inc.
Dilute solution properties of asymmetric six‐arm star polystyrenes
Authors: Jackson Christian , Frater Donna J. , Mays Jimmy W. 
Published: April 2003

AbstractSix‐arm star polystyrenes having varying numbers of short and long arms attached to the same molecule have been synthesized by anionic polymerization. The molecules have been characterized by high resolution size exclusion chromatography using multiangle light scattering and viscosity detectors. This technique has allowed the radii of gyration and intrinsic viscosities to be measured for stars with each possible combination of arms. The branching parameters g and g′ are computed and compared with theoretical expectations. It is found that short arms add preferentially to the stars, because of reduced steric effects. The molecule with one long and five short arms exhibits behavior closest to that of a linear chain (largest branching ratios). The effect of arm polydispersity on solution properties of stars is discussed. © 1995 John Wiley & Sons, Inc.
Thickness of a silica‐tethered poly(ethylene oxide) layer measured by spin labeling
Authors: Hommel H. , Touhami A. , Halli A. , LeGrand A. P. 
Published: April 2003

AbstractEPR spectroscopy of labeled poly(ethylene oxide) (PEO) grafted on silica has been used to characterize the conformation and local dynamics of the chains. Grafted molecules of MW 2000 with grafting ratios of 0.045, 0.057, 0.126, and 0.42 molecules/nm2 were in contact with benzene. The mobility of the label was compared with that observed for solution of PEO from very diluted to highly concentrated and even bulk PEO. Thus, the concentration inside the grafted layer could be evaluated and also the thickness, which evolves rather linearly with the grafting ratio. © 1995 John Wiley & Sons, Inc.
Chain behavior of an amphoteric cellulose derivative: O‐carboxymethyl‐O‐2‐hydroxy‐3‐(trimethylammonio) propylcellulose
Authors: Zheng Guo‐Zhen , Meshitsuka Gyosuke , Ishizu Atsushi 
Published: April 2003

AbstractThe 13C NMR spin‐lattice relaxation times (T1) of anhydroglucose units vary with the number of substituents, and the T1 values of unsubstituted anhydroglucose units of O‐carboxymethylcellulose are longer than those of amylose. Those results indicate that in water, the rotational motions of anhydroglucose units of cellulose derivative are quite important local motions contributing to the 13C NMR spin‐lattice relaxation, and within a cellulose chain, anhydroglucose units rotate with different degrees of freedom depending on their environment. Moreover, the 13C NMR spin‐lattice relaxation data indicate that the mobilities of ionic substituents are dependent on substitution positions as well as their ionic interaction. © 1995 John Wiley & Sons, Inc.
Miscibility and cure kinetics studies on blends of bisphenol‐A polycarbonate and tetraglycidyl‐4,4′‐diaminodiphenylmethane epoxy cured with an amine
Authors: Su C. C. , Kuo J.‐F. , Woo E. M. 
Published: April 2003

AbstractDifferential scanning calorimetry (DSC) has been applied to characterize the glass transition behavior of the blends formed by bisphenol‐A polycarbonate (PC) with a tetrafunctional epoxy (tetraglycidyl‐4,4′‐diaminodiphenyl methane, TGDDM) cured with 4,4′‐diaminodiphenylsulphone (DDS). A rare miscibility in the complete composition range has been demonstrated in these blends. Additionally, the blend morphology was examined using scanning electron microscopy (SEM) and a homogeneous single‐phase PC/epoxy network has been observed in the blends of all compositions. Moreover, polycarbonate incorporation has been found to exert a distinct effect on the cure behavior of the epoxy blends. The cure reaction rates for the epoxy‐PC blends were significantly higher due to the presence of PC. In addition, the cure mechanism of the epoxy blends was no longer autocatalytic. An n‐th order reaction mechanism with n = 1.2 to 1.5 has been observed for the blends of DDS‐cured epoxy with PC of various compositions studied using DSC. The proposed n‐th order kinetic model has been found to describe well the cure behavior of the epoxy/PC blends up to the vitrification point. © 1995 John Wiley & Sons, Inc.
Comparison of dielectric theories that explicitly include viscoelastic parameters
Authors: Havriliak S. , Havriliak S. J. 
Published: April 2003

AbstractIn this work we compare four dielectric relaxation models that explicitly include the viscoelastic properties of the environment to define the dielectric relaxation process. These models are the Debye, Gamant, DiMarzio‐Bishop, and the Havriliak‐Havriliak models. Debye's model assumes a Newtonian viscosity and solves the hydrodynamic problem exactly leading to the venerable Debye function. Gamant's used heuristic arguments to include a time‐dependent viscosity. These results lead to a splitting of the relaxation process. DiMarzio‐Bishop solved the hydrodynamic equations which included a time‐dependent viscosity exactly and applied the results to poly(n‐octyl methacrylate). The Havriliak‐Havriliak approach is based on statistical mechanics arguments that take into account strain energy which is associated with the polarization process. This model also requires a knowledge of the viscoelastic properties of the system. The results of the four models are compared. © 1995 John Wiley & Sons, Inc.
Dielectric analysis of an epoxy resin during cross‐linking
Authors: Butta E. , Livi A. , Levita G. , Rolla P. A. 
Published: April 2003

AbstractThe dielectric behavior of an epoxide/ethylenediamine formulation has been studied during cross‐linking in the frequency range 103−1010 Hz at 25°C and 70°C. Dielectric data were collected both in the frequency and in the time domains and analyzed in terms of a combination of two Havriliak‐Negami functions. A complete description of the evolution of the relaxation parameters during the reaction was obtained. The nature of the information yielded by dielectrometry on the dynamics of the system is discussed. © 1995 John Wiley & Sons, Inc.
Water sorption/desorption kinetics in poly(ethylene naphthalene‐2,6‐dicarboxylate) and poly(ethylene terephthalate)
Authors: Rueda D. R. , Varkalis A. 
Published: April 2003

AbstractWater sorption/desorption experiments were carried out on films (∼ 220 μm thick) of amorphous poly(ethylene naphthalene‐2,6‐dicarboxylate) (PEN) stored in ambient conditions for different periods of time (0.5‐4 years) and of poly(ethylene terephthalate) (PET) with different degrees of crystalinity levels (0‐29%) by means of FTIR spectroscopy. Water sorption/desorption kinetics follows Fick's law for all samples investigated. Water sorption isotherms, obtained from gravimetric methods, indicate a larger sorption capacity in the case of PEN materials. The apparent diffusion coefficients (D) are larger in the case of PET samples. The observed D values decrease with storage time (physical aging) of PEN samples and with the crystallinity of PET samples. © 1995 John Wiley & Sons, Inc.
Thermal history and temperature dependence of viscoelastic properties of polymer glasses: Relation to free volume quantities
Authors: Higuchi H. , Yu Z. , Jamieson A. M. , Simha R. , McGervey J. D. 
Published: April 2003

AbstractThe dependence of physical properties on temperature and thermal history of glassy polycarbonate is examined. The average stress relaxation time increases during isothermal aging and with decreasing cooling rate. The temperature dependence of the stress relaxation time was compared with a free volume function calculated from specific volume data reported by Zoller by means of the Simha‐Somcynsky theory and with a fractional free volume measured by ortho‐positronium annihilation. We report in addition comparisons between free volume fractions extracted from volume data, and creep measurements for polystyrene, and stress relaxation data for poly(vinyl acetate) given by Kovacs et al., Schwarzl and Zahradnik, and Meyer et al. These investigations suggest that in the glassy state the Doolittle equation is valid only in isothermal aging experiments. It follows that in expressing the polymer mobility not only a temperature‐dependent free volume but additional temperature‐dependent processes need to be considered. © 1995 John Wiley & Sons, Inc.
Density functional theory of polymer‐polymer phase separation behavior
Authors: Nath Shyamal K. , McCoy John D. , Curro John G. , Saunders Randall S. 
Published: April 2003

AbstractPolyatomic density functional theory is applied to a binary polymer blend. The polymer reference interaction site model (PRISM) liquid state theory provides the homogeneous state correlation functions necessary for the application of density functional theory. An effective chi parameter can be recognized from the density functional expression; however, the phase separation criteria does not depend solely upon the chi parameter, rather it depends upon various combinations of the species‐dependent direct correlation functions of the blend. The Flory‐Huggins chi parameter along with the associated phase diagram is obtained when the monomer volumes of the blend species are equal and for a range of monomer‐monomer attractive interactions. Calculations are performed both with and without the assumption of incompressibility. The density functional theory along with the PRISM determined “input” predict that an isotopic polymer blend shows an upper critical solution temperature (UCST) phenomena. © 1995 John Wiley & Sons, Inc.
Mobility‐sensitive fluorescence probes for quantitative monitoring of water sorption and diffusion in polymer coatings
Authors: Miller Keith E. , Krueger Robert H. , Torkelson John M. 
Published: April 2003

AbstractThe fluorescent molecular rotor probes 4‐tricyanovinyl‐[N‐(2‐hydroxyethyl)‐N‐ethyl]‐aniline, tricyano‐4‐(dimethylamino) benzylidene, and tricyanovinyljulolidene have been used as extrinsic fluorescence probes for quantitative monitoring of water uptake in polymeric coatings. The presence of water causes plasticization of the polymer, which results in increased local mobility within the film. The nonradiative decay pathways of the rotor probes are increased as local mobility increases, and the resulting decrease in fluorescence intensity of the probes is directly proportional to the amount of water sorbed. Beyond allowing for the characterization of sorbent content, this fluorescence technique can be used to determine the diffusion coefficient of water in a polymer film. The relative change in fluorescence fits well to a Fickian diffusion model, yielding a diffusion coefficient for water of 3 × 10‐8 cm2/s in poly(vinyl acetate), and a value of 6 × 10‐9 cm2/s in a room‐temperature cured epoxypolyamide, in excellent agreement with diffusion coefficient values determined from gravimetric analysis. Preliminary studies also demonstrate the utility of molecular rotor probes to monitor water uptake in individual layers of multilayered polymer systems. © 1995 John Wiley & Sons, Inc.
Direct observation of a diblock copolymer‐induced microemulsion at a polymer/polymer interface
Authors: Xu Z. , Jandt K. D. , Kramer E. J. , Edgecombe B. D. , Fréchet J. M. J. 
Published: April 2003

AbstractWe have studied the segregation of a block copolymer of poly(d8‐styrene‐b‐2‐vinylpyridine) (dPS‐PVP) at the interface between polystyrene and a random copolymer of poly(styreneran‐4‐hydroxystyrene) (PS‐r‐PPHS). Forward recoil spectrometry (FRES) was used to measure the equilibrium excess (z*) of the dPS‐PVP chains at the interface as a function of its volume fraction in the bulk PS phase (ϕ∞). It was found that there is a sharp increase in z* at a critical value of ϕ∞. This upturn indicates the formation of a microemulsion of PS and the random copolymer PS‐r‐PPHS due to a vanishing of the interfacial tension caused by the strong adsorption of the block copolymer. Cross‐sectional transmission electron microscopy (TEM) of the interface shows that this microemulsion starts to form at the interface by forming a deeply corrugated structure where the “wavelength” of the corrugations is of the order of 50 nm. © 1995 John Wiley & Sons, Inc.
Neutron scattering from polymer blends under pressure
Authors: Hammouda B. , Benmouna M. 
Published: April 2003

AbstractA procedure is used to analyze small‐angle neutron‐scattering (SANS) data from a pressurized polymer blend mixture (deuterated polystyrene/polyvinylmethylether). The Lattice‐Fluid (LF) equation‐of‐state model is used along with a compressible random phase approximation (RPA) in order to obtain free volume fractions and intermonomer interaction potentials. Solving the two sets of equations (LF and RPA) self‐consistently within the fitting procedure to the SANS data provides an improvement over the familiar incompressible RPA model. In this approach, the free volume fraction is the main varying parameter. Intermonomer interaction potentials were found to depend on pressure (weakly) and temperature (linearly). © 1995 John Wiley & Sons, Inc.
Activation volumes associated with chromophore reorientation in corona poled guest–host and side‐chain polymers
Authors: Brower Shane C. , Hayden L. Michael 
Published: April 2003

AbstractThe decay of the second‐order optical susceptibility χ(2) as a function of temperature and pressure has been studied in a variety of corona poled guest–host and side‐chain polymeric materials using second harmonic generation (SHG). The specific systems studied include the side‐chain copolymer poly(disperse red 1 methacrylate‐co‐methyl methacrylate) (DR1‐MMA) as well as the series of guest–host materials formed by individually dissolving the dyes Disperse Red 1 (DR1), Disperse Orange 3 (DO3), and N,N dimethyl‐p‐nitroaniline (DpNA) in poly(methyl methacrylate) (PMMA), polycarbonate (PC), and polystyrene (PS). In each of these systems, the observed relaxation of χ(2) can be represented by a Kohlrausch‐Williams‐Watts stretched exponential, from which the decay time τ and decay distribution width β are determined. For pressures up to approximately 1000 atm, the natural log of the pressure shift factor is seen to vary linearly with applied pressure, yielding the activation volume for rotational reorientation of the chromophores in each system. The activation volumes are loosely correlated with dopant size in a given polymer host, but are not the same for a given dopant in different hosts. Modeling the chromophores as rotating cylinders, we show that the measured activation volumes do not correspond to the average volume swept out by the dye molecules as they reorient. On the other hand, the activation volumes for each of the three dyes dissolved in PS are seen to be in agreement with the measured activation volumes for the molecular motions associated with volume recovery in neat PS. Moreover, the activation volumes for DR1 and DpNA dissolved in PS are seen to correlate with the proposed couplings between the rotational reorientation of DR1 and the α‐relaxation dynamics of PS and the slight decoupling of DpNA from the α‐transition motion of PS. This correlation suggests a possible relationship between the activation volumes for chromophore reorientation and the size of the components of the host polymer or the volume swept through by the polymer components during structural reconfiguration. We demonstrate that assuming activation volumes for chromophore reorientation to be related to the size or motion of the polymer host constituents yields a consistent interpretation of the observed trends in the measured activation volumes. © 1995 John Wiley & Sons, Inc.
Autobiographisches Altgedächtnisinterview und semantisches Altgedächtnisinventar
Authors: Schmidtke Klaus , Vollmer-Schmolck Heike 
Published: April 2003

Autobiographical Memory Interview and the Semantic Memory Test Abstract: Two instruments for the evaluation of retrograde memory deficits are presented. The autobiographic memory test assesses childhood memories, as well as episodic and semantic memories of the most recent five-year-period. The semantic memory test assesses facts, i. e. general knowledge that is free of specific temporo-spatial context. Both tests are reproduced in an appendix. Both tests display maximum sensitivity for interindividual differences in the impaired performance range. In the interest of reliability, the number of items is comparatively high. In the interest of objectivity, questions and rating procedures are clearly defined. Administration requires comparatively little time and effort. Distributions and mean performances of two subject groups, i.e. normal subjects and amnesic patients, are given, as well as cut-off scores.
Der Neuropsychologe in der Akutklinik - Beschreibung eines Berufsbildes
Authors: Diehl Rolf R. , Wittlieb-Verpoort Elke , Ringendahl Hubert , Calabrese Pasquale , Wilhelm Hans 
Published: April 2003

The Acute Neuropsychologist: Description of a Profession Abstract: Cognitive and affective dysfunctions are frequent symptoms of neurological diseases. In the primary phase of neurological treatment these deficits can often not sufficiently be diagnosed or treated. During the past 15 years, the «acute neuropsycholgy» has emerged in Germany at larger neurological departments as a new clinical discipline in the diagnosis and management of neuropsychological disturbances. Acute neuropsychology emphasizes early diagnosis and therapy, follow-up measurements during neurological therapy, counseling, and the scheduling of further rehabilitation strategies. The differential diagnosis between psychosomatic related cognitive symptoms and neuropsychological disorders on the basis of brain-injury is another focus of interest. The «neuropsychological monitoring» of patients during interventional procedures is another area of major importance within the domain of primary neurological care. Neuropsychological visits and team conferences expand the communication with other clinical professionals and may help to underline the importance of neuropsychological disorders for nursing, physiotherapy, speech-therapy and neurological treatment.
Dissociation of Spatial Perception and Object Recognition in Humans
Authors: Bodenburg Sebastian 
Published: April 2003

Dissoziation von Raum- und Objektwahrnehmung beim Menschen Zusammenfassung: In dieser Studie wird untersucht, ob Patienten mit rechtshemisphärischen temporalen bzw. parietookzipitalen Läsionen in Testverfahren zur Raum- und Objektwahrnehmung ein unterschiedliches Testprofil zeigen. Acht Versuchspersonen mit umgrenzten Hirninfarkten der rechten Hemisphäre, davon vier mit fokalen temporalen Läsionen, vier mit fokalen parietookzipitalen Schädigungen, nahmen an der Untersuchung teil. Testmaterial waren der Dot-Position-Test (als Komponente der Raumwahrnehmung) und der Foreshortened-Silhouettes-Test (als Komponente der Objektwahrnehmung), beide aus der Testbatterie zur visuellen Raum- und Objektwahrnehmung. Patienten mit rechts-temporalen Läsionen waren in dem Test zur Objektwahrnehmung verhältnismäßig stärker eingeschränkt als in dem Test zur Raumwahrnehmung. Patienten mit rechts-parietookzipitalen Schädigungen wiesen demgegenüber ein umgekehrtes Leistungsprofil auf: Sie zeigten in dem Test zur Raumwahrnehmung deutlich geringere Leistungen als bei der Objektwahrnehmung. Die Ergebnisse dieser Dissoziation werden in Verbindung mit dem Konzept der Objektagnosien und dem Modell der zwei Hauptinformationswege im visuellen Kortex von Goodale und Milner (1992) erörtert.
Functional Reorganization after Training of Alertness in Two Patients with Right-Hemisphere Lesions
Authors: Longoni Francesca , Sturm Walter , Weis Susanne , Holtel Christiane , Specht Karsten , Herzog Hans , Willmes Klaus 
Published: April 2003

Funktionelle Reorganisation nach Alertness-Training bei zwei Patienten mit Läsionen der rechten Hemisphere Zusammenfassung: Bei Patienten mit Alertness-Defiziten nach rechtshemisphärischer vaskulärer Schädigung wurde die individuelle Veränderung des funktionellen Netzwerkes für Alertness nach einem spezifischen Training in einer PET-Aktivierungsstudie untersucht. Die Patienten wurden mit dem Unterprogram Alertness aus dem computergestützten AIXTENT Aufmerksamkeitstraining behandelt. Vor und nach dem Training erfolgte jeweils eine PET- und eine neuropsychologische Untersuchung zur Erfassung von Aufmerksamkeitsstörungen und Hemineglect. In dieser Arbeit präsentieren wir zwei Patienten, von denen einer signifikante Leistungsverbesserungen nach dem Training erzielte. Bei diesem Patienten zeigte sich nach dem Training eine teilweise Restitution des rechtshemisphärischen funktionellen Netzwerks, welches sich bei Gesunden als relevant für die intrinsische Alertness-Kontrolle erwiesen hat. Bei dem zweiten Patienten, der keine Verbesserung zeigte, ergab sich nach dem Training lediglich eine deutliche linkshemisphärische Aktivierung im PET.