bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cycle Formation in the Polycondensation of Potassium 3‐Bromomethyl‐5‐methylbenzoate
Authors: Sepulchre Maurice , Sepulchre Marie‐Odile , Belleney Joël 
Published: June 2004

AbstractPotassium 3‐bromomethyl‐5‐methylbenzoate 2K, preformed or obtained from 3‐bromomethyl‐5‐methylbenzoic acid 2 by exchange reaction with potassium undecanoate 5K, was polymerized in bulk or in 1‐methyl‐2‐pyrrolidone (NMP), in the presence or not of a trifunctional core molecule. GPC analyses of the reaction products have shown that small cyclic oligomers (usually from C2 to C6) are formed in all the cases. MALDI‐TOF MS of polymers have shown that, in the range of masses examined, those prepared by polymerization of 2K in bulk or in NMP are almost exclusively formed of cycles. In the polymer obtained by polymerization, in NMP, of 2 in the presence of 5K linear and cyclic species coexist. In the polymer resulting from the polymerization of 2K in the presence of 2,4,6‐tris(bromomethyl)mesitylene (TBMM) the expected three‐arm stars are predominant and the content in cycles is relatively low and obviously the lowest of all the other prepared polymers. The formation of cycles (large and/or small) is an inherent component of the polycondensation of 2K. Cyclization strongly contributes to the limitation of molar masses of the reaction products.
MALDI‐TOF mass spectrum (reflector mode) of PB2 (run 3, Table 1). Symbols: •, Cn; ×, (Cp[D])LqOCH3 and +, (Cp[D])LqBr.imageMALDI‐TOF mass spectrum (reflector mode) of PB2 (run 3, Table 1). Symbols: •, Cn; ×, (Cp[D])LqOCH3 and +, (Cp[D])LqBr.
Alternating Copolymerization Reaction of Propylene Oxide and CO: Variation of Polymer Stereoregularity and Investigation into Chain Termination
Authors: Allmendinger Markus , Eberhardt Robert , Luinstra Gerrit A. , Rieger Bernhard 
Published: June 2004

AbstractThe cobalt‐catalyzed alternating copolymerization reaction of racemic propylene oxide and CO affords regioregular but atactic poly(hydroxybutyrates). The application of enantiomerically pure (R)‐ or (S)‐propylene oxide results in the formation of isotactic, optically active and crystalline materials. In contrast to the perfect isotactic microstructures that are available via the microbial pathway, our approach allows to tailor the stereoregularity of the polymer products, and hence their melting points by application of mixtures of the epoxide enantiomers. Investigations into the polymer stereochemistry show that the epoxide units undergo a clean regioregular incorporation into the polymer chain with retention of configuration at the stereogenic carbon centers. MALDI‐TOF and online ATR‐IR experiments give insight into the mechanism of chain termination reactions.Sketch of regio‐ and stereoselective epoxide incorporation.imageSketch of regio‐ and stereoselective epoxide incorporation.
Strain Rate, Temperature, and Microstructure‐Dependent Yield Stress of Poly(ethylene terephthalate)
Authors: Lim Jung Yul , Donahue Henry J. , Kim Sang Yong 
Published: June 2004

AbstractYield stress of a series of poly(ethylene terephthalate) (PET) filament samples, which differ in molecular draw ratio, was observed at a range of strain rate and temperature to reveal the relation between microstructure and yield stress behavior. Based on the observations, a novel correlation between (quasistatic) tensile yield behavior and dynamic mechanical properties was proposed. Above secondary relaxation temperature and below primary relaxation temperature, changes in yield stress with strain rate and temperature could be described successfully with one activated rate process, Eyring's model of yielding, regardless of the microstructure of PET samples. The activation enthalpy of Eyring's model increased almost linearly with crystallinity, while the activation volume decreased with crystallinity in a sigmoidal fashion. We suggest that crystalline structural development elevates the energy barrier for yield, and that the scale of molecular motion for yield decreases with microstructural development, not only because of the decrease in molecular volume. Such a scale of molecular motion as Eyring's activation volume could possibly interpret the loss tangent (tan δ), i.e., as the activation volume increases, loss tangent maxima of both primary and secondary relaxation increase almost linearly.
Relation between the activation volume of Eyring's model of (quasistatic tensile) yield and loss tangent maximum of the dynamic mechanical behavior.imageRelation between the activation volume of Eyring's model of (quasistatic tensile) yield and loss tangent maximum of the dynamic mechanical behavior.
Water‐Swollen Hydrogels with Pendant Terthiophenes
Authors: Chen Li , Gong Jian P. , Ohsedo Yutaka , Osada Yoshihito 
Published: June 2004

AbstractA chemically cross‐linked and water‐swollen poly(AA3T‐co‐AA) gel having pendant terthiophenes was synthesized by radical copolymerization of [(2,2′:5′,2″‐terthiophen‐5‐yl‐)methyl acrylate] (AA3T) and acrylic acid (AA), and its swelling, dissociation, and doping behaviors were studied. The gel swells in high pH solution, which is associated with the dissociation and, hence, electrostatic repulsion of the AA units, and the pH value at which the swelling starts increases with increasing AA3T composition. The dissociation of the gels is suppressed, presumably due to the incorporation of the hydrophobic AA3T unit, and, once started, the dissociation could be promoted by AA3T in the low pH region. Poly(AA3T‐co‐AA) copolymers and gels can be easily electrochemically and chemically doped. The volume change of the gels is observed during doping/undoping and the maximum volume change reached was about 50%.
The pH dependence of the degree of swelling, q, for poly(AA3T‐co‐AA) gels with various F at 25 °C. (•) F = 0.11, DCL = 20%; (▪) F = 0.05, DCL = 20%; (▴) F = 0, DCL = 10%.imageThe pH dependence of the degree of swelling, q, for poly(AA3T‐co‐AA) gels with various F at 25 °C. (•) F = 0.11, DCL = 20%; (▪) F = 0.05, DCL = 20%; (▴) F = 0, DCL = 10%.
Ring‐Opening Copolymerization of 2‐Aryl‐1‐methylenecyclopropanes with Carbon Monoxide Initiated by Pd–bpy Complexes
Authors: Kim Sunwook , Takeuchi Daisuke , Osakada Kohtaro 
Published: June 2004

Abstract[PdCl(Me)(bpy)] and a mixture of the complex with cocatalysts; NaBARF (BARF = [B{C6H3(CF3)2‐3,5}4]−), NaBF4, AgBARF, AgBF4, and AgOTf, catalyze the copolymerization of 2‐phenyl‐1‐methylenecyclopropane with carbon monoxide to produce a new polyketone accompanied by ring opening of the monomer. 1H and 13C{1H} NMR spectra indicate that the polymers have two isomeric repeating units in which the phenyl substituents occupy different positions. The molecular weights of the polyketones formed by the reactions with a [Pd]/[cocatalyst]/[2‐phenyl‐1‐methyleneyclopropane] ratio of 1:3:70 are in the range of Mn = 13 100–86 000. The polymer obtained by the reaction promoted by [PdCl(Me)(bpy)]/MBARF, where M = Ag or Na, shows a narrow molecular weight distribution, Mw/Mn = 1.44 and 1.59, respectively. The catalysis is effective also for the ring‐opening copolymerization of 2‐aryl‐1‐methylenecyclopropanes bearing Me and F substituents on the phenyl ring. Isotope‐labeled experiments revealed the mechanism of the polymerization, which involves a 1,2‐insertion of the monomer into the Pd–acyl bond to produce a cyclopropylmethyl palladium intermediate, and subsequent β‐alkyl elimination to give the Pd–alkyl complex.image
Orientation of the Main Chain in Liquid‐Crystalline Side‐Chain Polyesters with Variation of Main‐Chain Spacer Length
Authors: Hempel Günter , Dimitrova Albena , Lindau Jürgen , Reichert Detlef , Schneider Horst 
Published: June 2004

AbstractPrevious X‐ray investigations on liquid‐crystalline side chain polyesters with variable spacer length in the side chain as well as in the main chain led to the assumption that the structure will change qualitatively if the main chain spacer length exceeds a certain value. We obtained indications supporting this assumption by applying two‐dimensional 13C NMR. It was shown that for a sample with main chain spacer shorter than the critical length, the main chain segments align perpendicular to the side chains (〈P2〉 = −0.46), and for spacer length larger than critical length, the main chain segments preferentially orient themselves parallel to the side chain (〈P2〉 = 0.28).Visualization of the main‐chain order as revealed by the values of Table 2. The opening angle of the cones corresponds to the average angle of deviation as defined in the text.imageVisualization of the main‐chain order as revealed by the values of Table 2. The opening angle of the cones corresponds to the average angle of deviation as defined in the text.
Mechanisms of Moisture Sorption in Barrier Polymers Used in Food Packaging: Amorphous Polyamide vs. High‐Barrier Ethylene‐Vinyl Alcohol Copolymer Studied by Vibrational Spectroscopy
Authors: Lagaron Jose M. , Gimenez Enrique , Catala Ramon , Gavara Rafael 
Published: June 2004

AbstractThe nature of the association between sorbed water and two high‐barrier hydrophilic polymers used in oxygen‐sensitive food packaging, and exhibiting opposite oxygen barrier behavior in the presence of moisture, has been studied by FT‐Raman and FT‐Infrared spectroscopy. The polymers considered in this work were an ethylene‐vinyl alcohol copolymer with superior oxygen barrier properties (32 mol‐% of ethylene EVOH) and an amorphous polyamide (aPA). The results revealed that for the latter glassy amorphous polymer, water molecules associate with the CO and NH groups of the ca. 10% “free” amide moieties, being the excess sorbed water self‐associated in clusters; thus, moisture sorption does not appear to disrupt the originally present hydrogen‐bonded amide groups. This “unusual” behavior leads to an overall increase in the extension of the hydrogen‐bonding, which may help explain the lower oxygen permeability displayed by the aPA with increasing relative humidity on the basis of the known free‐volume competing mechanism. Differently, water sorption appears to progressively disrupt the strong polymer self‐association present in the very efficient high‐barrier semicrystalline EVOH material by hydrogen‐bonding to hydroxyl groups, hence leading to the well‐known highly plasticized rubbery structure with much lower intermolecular cohesion and oxygen barrier.FT‐IR spectra of severely dried, dry (dotted), and water‐equilibrated (thicker line) aPA in the range 2 600–3 800 cm−1.imageFT‐IR spectra of severely dried, dry (dotted), and water‐equilibrated (thicker line) aPA in the range 2 600–3 800 cm−1.
Radical Grafting Polymerization of Vinylformamide with Functionalized Silica Particles
Authors: Meyer Torsten , Spange Stefan , Hesse Stephanie , Jäger Christian , Bellmann Cornelia 
Published: June 2004

AbstractTwo different radical polymerization techniques have been applied to covalently graft vinylformamide (VFA) onto silica particles. Grafting by the polymerization of VFA using an immobilized azo initiator on silica has been found less effective, because monomer conversion is limited in non‐aqueous solvents and grafting yields are low in water. Radical copolymerization of VFA with vinyltriethoxysilane (VTS)‐functionalized silica particles is suitable to produce poly(vinylformamide) (PVFA) silica hybrid particles in respectable yield. The VFA/VTS‐silica ratio determines the degree of grafting. The PVFA‐VTS‐co‐grafted silica particles can be acidically hydrolyzed into poly(vinylamine)‐grafted silica particles. Molecular structures of the surface groups and grafted polymer chains have been confirmed by means of solid state 13C{1H} cross‐polarization magic‐angle spinning (CP MAS) NMR spectroscopy. Zeta potential measurements show the altering of the former silica particles surface charges arising from the introduction of basic groups on the surface.image
Cover Picture: Macromol. Chem. Phys. 10/2004
Authors: Monaco Guglielmo , Viglione Rosario G. 
Published: June 2004

Cover: According to a theoretical analysis in terms of a three‐state rotational isomeric state model, in favorable cases variations of conformational statistics can be described by a mechanism as simple as a children's game, where r‐children are unfaithful messengers, m‐children are faithful ones and the behavior of the whole sequence is determined by the number (even or odd) of unfaithful messengers. This mechanism turns out to be operative in many vinyl polymers and helps considerably in sequencing their tacticity‐spread NMR signals. The artwork has been realized by Dr. P. Vanacore.Further details can be found in the Full Paper by G. Monaco* and R. G. Viglione on page 1327.
Equivalent conditions to the nonnegativity of a quadratic functional in discrete optimal control
Authors: Hilscher Roman , Zeidan Vera 
Published: June 2004

AbstractIn this paper we provide a characterization of the nonnegativity of a discrete quadratic functional ℐ with fixed right endpoint in the optimal control setting. This characterization is closely related to the kernel condition earlier introduced by M. Bohner as a part of a focal points definition for conjoined bases of the associated linear Hamiltonian difference system. When this kernel condition is satisfied only up to a certain critical index m, the traditional conditions, which are the focal points, conjugate intervals, implicit Riccati equation, and partial quadratic functionals, must be replaced by a new condition. This new condition is determined to be the nonnegativity of a block tridiagonal matrix, representing the remainder of ℐ after the index m, on a suitable subspace. Applications of our result include the discrete Jacobi condition, a unification of the nonnegativity and positivity of ℐ into one statement, and an improved result for the special case of the discrete calculus of variations. Even when both endpoints of ℐ are fixed, this paper provides a new result. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Factorization of operator valued Lp for 0 ≤ p < 1
Authors: Mezrag Lahcène 
Published: June 2004

AbstractIn [5], it is proved that a bounded linear operator u, from a Banach space Y into an Lp(S, ν) factors through Lp1 (S, ν) for some p1 > 1, if Y* is of finite cotype; (S, ν) is a probability space for p = 0, and any measure space for 0 < p < 1. In this paper, we generalize this result to uv, where u : Y → Lp(S, ν) and v : X → Y are linear operators such that v* is of finite Kašin cotype. This result gives also a new proof of Grothendieck's theorem. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Oscillation theorems for second order matrix differential systems
Authors: Wang Qi‐Ru 
Published: June 2004

AbstractBy employing the generalized Riccati technique and the integral averaging technique, new oscillation criteria are established for a class of second order matrix differential systems. These criteria extend, improve and unify a number of existing results and handle a number of cases not covered by known criteria. In particular, several interesting examples that illustrate the importance of our results are included. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Living Polymerization of α‐Amino Acid N‐Carboxyanhydrides (NCA) upon Decreasing the Reaction Temperature
Authors: Vayaboury Willy , Giani Olivia , Cottet Hervé , Deratani André , Schué François 
Published: June 2004

AbstractSummary: The n‐hexylamine‐initiated polymerization of Nε‐trifluoroacetyl‐L‐lysine N‐carboxyanhydride in N,N‐dimethyformamide was studied by nonaqueous capillary electrophoresis. A polypeptide with a broad molecular weight distribution was obtained and side reactions were clearly identified for polymerization at room temperature. The possibility of living polymerization at 0 °C was demonstrated.Synthesis of living polypeptides by primary amine initiated polymerization of NCA at low temperatures.imageSynthesis of living polypeptides by primary amine initiated polymerization of NCA at low temperatures.
Stimuli‐Responsive Semi‐Fluorinated Polymer Brushes on Porous Silica Substrates
Authors: Granville Anthony M. , Brittain William J. 
Published: June 2004

AbstractSummary: A diblock copolymer brush consisting of poly(methyl acrylate)‐block‐poly(pentafluoropropyl acrylate) (Si/SiO2//PMA‐b‐PPFA) was synthesized on a porous silica substrate. The brush was exposed to selective solvents, as well as thermal treatments, to induce a surface rearrangement. The rearrangement resulted in the selective loss or creation of an ultrahydrophobic layer by location of the fluoropolymer segment. This work demonstrates that surface rearrangements observed on flat surfaces can be transferred to porous substrates.Image of a water droplet in contact with an Si/SiO2//PMA‐b‐PPFA ultrahydrophobic polymer brush, synthesized from a porous silica substrate.magnified imageImage of a water droplet in contact with an Si/SiO2//PMA‐b‐PPFA ultrahydrophobic polymer brush, synthesized from a porous silica substrate.
Cover Picture: Macromol. Rapid Commun. 13/2004
Authors: Rettig Hartmut , Krause Eberhard , Börner Hans G. 
Published: June 2004

Cover: Integration of sequence‐defined oligopeptides into synthetic polymers opens a broad scope of possibilities for interfacing synthetic and biological systems. The cover picture features a two‐step procedure used to realize such chimera structures, with defined molecular weights and low polydispersity indices. The presented strategy includes the solid‐phase supported synthesis of an oligopeptide ATRP macroinitiator, subsequently followed by a solution‐phase atom transfer radical polymerization (ATRP).Further details can be found in the Communication by H. Rettig, E. Krause, and H. G. Börner* on page 1251.
Structure Formation in the Crystallization and Annealing of Tetracontane Nanoparticles
Authors: Vao‐Soongnern Visit , Xu Guoqiang , Mattice Wayne L. 
Published: June 2004

AbstractSummary: Crystallization, melting and annealing of nanoparticles of tetracontane were simulated via a Monte Carlo method on the second nearest neighbor diamond (2nnd) lattice by including short‐ and long‐range interactions. Nanoparticles can be obtained from an equilibrated tetracontane melt by increasing three periodic lengths to values that are effectively infinite. Nanoparticles, which contain 155 chains of C40H82, have been produced. After a deep quench from 473 K to 298 K, the crystallization process was investigated by the evolution of the density profile, fraction of bonds in the trans state, and the orientational order parameter. The vicinity of the center is less dense and less well ordered than portions of the nanoparticle located further from the center. The crystals form first in the region close to the surface. Each nanoparticle usually contains multiple crystalline domains. A melting phenomenon was observed at a temperature about 365 K when the nanoparticle crystal was heated. Annealing of the multiple domain crystal at 360 K can transform the structure to a more regular one without a grain boundary.Snapshot of the final structure containing a single domain crystal after 20 million MCS.imageSnapshot of the final structure containing a single domain crystal after 20 million MCS.
Today's sheet metal materials and their forming properties
Authors: Bach F.‐W. , Roßberg A. , Schäperkötter M. , Schaper M. , Walden L. , Weber J. 
Published: June 2004

AbstractThe production and processing of sheet metals of high‐strength steels, titanium, aluminum or magnesium alloys is investigated intensively at universities and in the industry. The main emphasis is put for example on the aluminum space frame concept as well as on the succeeding projects of the ULSAB‐study in the field of the steel sheet metals. Within this article the qualification of the above mentioned materials for the application as deep‐drawing materials will be discussed. The aim of the development for new deep‐drawing sheet metals is to decrease the elastic part of the forming, which means to lower the yield point. A high elastic portion would cause a high resilience after the forming of the sheet metals and therefore an increased requirement of force and form error during the forming process. Furthermore the optimized sheet metal material should have a great uniform elongation, so that it can be plastically deformed in a wide range. The beginning of the deformation should be possible at low forming forces but due to the deformation an increase of the hardening should be caused, so that the finished component has high strength. But it is not possible to realize both aims, high strength and great uniform elongation, at the same time.
Lasererwärmung zur Verbesserung des Umformergebnisses beim Kragenziehen von Aluminium‐ und Magnesiumknetlegierungen
Authors: Groche P. , Erhardt R. 
Published: June 2004

AbstractDie Halbwarmblechumformung hat sich bei der Herstellung von geometrisch komplexen Bauteilen aus Magnesium‐ und Aluminiumknetlegierungen als nützlich erwiesen. In vielen Fällen, z. B. beim Tiefziehen, ist eine großfläche Erwärmung sinnvoll. Sollen aber, wie beim Kragenziehen, nur kleine Bereiche eines größeren Bauteils ausgeformt werden, ist eine lokale Erwärmung mittels Laserstrahlung vorteilhafter. Auf diese Weise lässt sich die Wärmemenge zeitlich und örtlich gut dosiert einbringen. In Versuchen konnte das Aufweitverhältnis gegenüber dem kalten Zustand bei einer lokalen Bauteiltemperatur von rd. 200 °C je nach Werkstoff um mehr als das doppelte gesteigert werden. Es zeigte sich, dass hierbei ein relativ enges Prozessfenster einzuhalten ist, da Werkstoffversagen nicht nur bei zu geringer, sondern auch bei zu hoher Umformtemperatur auftritt.
Simulation der geometrischen Oberflächen‐ wandlung beim Drücken optischer Bauteile
Authors: Groche P. , Schäfer R. 
Published: June 2004

AbstractMit Hilfe umformtechnischer Verfahren werden oftmals Bauteile mit Spezifikationen sowohl im Hinblick auf Bauteilform, als auch die Oberflächengüte hergestellt. Die Realisierung der geforderten Oberflächeneigenschaften basiert aber auch heute noch vorwiegend auf Erfahrungswerten. Am Beispiel des Drückens soll in diesem Artikel eine Methode vorgestellt werden, mit deren Hilfe die Oberflächengüte durch Finite Element Simulation vorherbestimmt werden kann.
Plumbagin induces reactive oxygen species, which mediate apoptosis in human cervical cancer cells
Authors: Srinivas Priya , Gopinath Gokul , Banerji Asoke , Dinakar Abhilash , Srinivas Gopal 
Published: June 2004

AbstractThere is an emerging evidence that plumbagin (5‐hydroxy‐2‐methyl‐1, 4‐naphthoquinone) may have potential as a chemotherapeutic agent. However, the growth inhibitory mechanisms of plumbagin have remained unexplored. The aim of the study was to determine whether plumbagin‐induced cell death in human cervical cancer cell line, ME‐180, exhibited biochemical characteristics of apoptosis and to check whether N‐acetyl‐l‐cysteine (NAC), which is a free radical scavenger, can reverse the cytotoxic effects of plumbagin. It can be concluded from the results that plumbagin inhibits the growth of ME‐180 cells in a concentration and time‐dependent manner. The cytotoxic effect of plumbagin induced cell death is through the generation of reactive oxygen species (ROS) and subsequent induction of apoptosis as demonstrated by the present data. Treatment of cells with plumbagin caused loss of mitochondrial membrane potential (ΔΨm), and morphological changes characteristic of apoptosis, such as the translocation of phosphatidyl serine, nuclear condensation, and DNA fragmentation. Moreover, plumbagin‐induced apoptosis involved release of mitochondrial cytochrome c and apoptosis inducing factor (AIF), thus activation of caspase‐dependent and ‐independent pathways, as shown by the plumbagin‐mediated activation of caspase‐3 and ‐9. Our results also show that pretreatment of ME‐180 cells with NAC blocks plumbagin‐induced loss of ΔΨm and subsequent release of cytochrome c, AIF, and caspase‐9 and ‐3 activation, thus inhibiting the apoptotic ability of plumbagin. © 2004 Wiley‐Liss, Inc.