bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ethylene Polymerization Catalyzed by Titanium(IV) Complexes of a Triaryloxoamine Ligand [TiX{(OArCH2)3N}]
Authors: Wang Wei , Fujiki Michiya , Nomura Kotohiro 
Published: February 2004

AbstractSummary: Titanium complexes containing a triaryloxoamine ligand, [TiX{(O‐2,4‐R2C6H2‐6‐CH2)3N}] (R = Me, tBu; X = OiPr, O‐2,6‐iPr2C6H3), exhibited notable catalytic activity for ethylene polymerization in the presence of MAO, especially at temperatures between 100 and 120 °C. Their activity increased upon the addition of a small amount of AlMe3.
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Green Polymer Chemistry: Microwave‐Assisted Single‐Step Synthesis of Various (Meth)acrylamides and Poly(meth)acrylamides Directly from (Meth)acrylic Acid and Amines
Authors: Goretzki Christian , Krlej Andrea , Steffens Christopher , Ritter Helmut 
Published: February 2004

AbstractSummary: Various (meth)acrylamides were synthesized in good yields directly from (meth)acrylic acid and an amine using microwave irradiation in a solvent‐free environment. Under the applied conditions the (meth)acrylic function is preserved. Furthermore, the addition of an initiator like 2,2′‐azoisobutyronitrile (AIBN) to the starting mixture leads directly to poly(meth)acrylamides in a single step.General reaction scheme for the formation of poly(meth)acrylamides from the microwave‐assisted reaction of (meth)acrylic acid and various amines.magnified imageGeneral reaction scheme for the formation of poly(meth)acrylamides from the microwave‐assisted reaction of (meth)acrylic acid and various amines.
Controlled/Living Radical Polymerization of Methacrylic Monomers in the Presence of Lewis Acids: Influence on Tacticity
Authors: Lutz Jean‐François , Jakubowski Wojciech , Matyjaszewski Krzysztof 
Published: February 2004

AbstractSummary: Atom transfer radical polymerization (ATRP) and reversible addition‐fragmentation transfer (RAFT) polymerization of N‐methyl methacrylamide and methyl methacrylate were investigated in the presence of rare‐earth triflates known to enhance polymer isotacticity. Poly(N‐methyl methacrylamide) with controlled molecular weight, low polydispersity, and enhanced isotacticity was prepared by ATRP and RAFT in the presence of catalytic amounts of yttrium trifluoromethanesulfonate or ytterbium trifluoromethanesulfonate. The tacticity of poly(N‐methyl methacrylamide) depends on the Lewis acid concentration: well‐defined polymers with predominantly either syndiotactic, atactic, or isotactic triads were prepared by adjusting the concentration of the Lewis acid. Simultaneous control of molecular weights, polydispersities, and tacticities in the polymerization of methyl methacrylate was less successful.Free radical propagation in the presence of a Lewis acid (LA) giving rise to chelate control.magnified imageFree radical propagation in the presence of a Lewis acid (LA) giving rise to chelate control.
The Resting State Makes the Difference: The Influence of the Anchor Group in the ROMP of Norbornene Derivatives
Authors: Slugovc Christian , Demel Sandra , Riegler Silvia , Hobisch Josefine , Stelzer Franz 
Published: February 2004

AbstractSummary: A model study with four norbornene derivatives with different groups connecting a functional unit to the norbornene reveals that the “anchor groups” influence the polymerisation rate constants of ring opening metathesis (ROM) polymerisations. Consequently, polydispersities and molecular weights are affected. The observed effects are explained by different tendencies of the anchor groups to coordinate to the ruthenium centre during the resting state of the propagation.A functionalised monomer where F is the functional unit, S is a spacer, A is an anchor group and P is the polymerisable group.magnified imageA functionalised monomer where F is the functional unit, S is a spacer, A is an anchor group and P is the polymerisable group.
Kinetics of the Thermal and Thermo‐Oxidative Degradation of a Polystyrene–Clay Nanocomposite
Authors: Vyazovkin Sergey , Dranca Ion , Fan Xiaowu , Advincula Rigoberto 
Published: February 2004

AbstractSummary: Thermogravimetry and differential scanning calorimetry have been used to study the thermal and thermo‐oxidative degradation of polystyrene (PS) and a PS–clay nanocomposite. An advanced isoconversional method has been applied for kinetic analysis. Introduction of the clay phase increases the activation energy and affects the total heat of degradation, which suggests a change in the reaction mechanism. The obtained kinetic data permit a comparative assessment of the fire resistance of the studied materials.The change in activation energy for the degradation of PS and the PS–clay nanocomposite with the extent of polymer conversion.magnified imageThe change in activation energy for the degradation of PS and the PS–clay nanocomposite with the extent of polymer conversion.
Cover Picture: Macromol. Rapid Commun. 2/2004
Authors: Kihara Hideyuki , Miura Toshiaki , Kishi Ryoichi 
Published: February 2004

Cover: The picture on the cover shows SEM images of LC polymer films consisting of rotating fine fibers, which were prepared by photopolymerization‐induced phase separation under a cholesteric LC ordering field. The background images are polarizing optical micrographs of the fingerprint (left) and Grandjean (right) textures of the cholesteric phase that were used as the templates for preparation of the respective polymer films.Details can be found in the Communication by H. Kihara,* T. Miura, and R. Kishi* on page 445.
Cover Picture: Macromol. Rapid Commun. 3/2004
Authors: Wang Wei , Fujiki Michiya , Nomura Kotohiro 
Published: February 2004

Cover: Titanium complexes containing triaryloxoamine ligands of the type, TiX‐[(OArCH2)3N], exhibited notable catalytic activity for ethylene polymerization in the presence of MAO, especially at higher temperatures. The activity further increased upon the addition of a small amount of AIMe3, and dissociation of the one σ bond to generate the catalytically active species occurred.Further details can be found in the Communication by W. Wang, M. Fujiki, and K. Nomura* on page 504.
Modeling Investigation of Hydrogel Volume Transition
Authors: Wu Shunnian , Li Hua , Chen J. Paul , Lam K. Y. 
Published: February 2004

AbstractSummary: This paper provides an overview of the latest development in modeling and simulation of volume transition behaviors of hydrogels with models at both macroscopic and molecular levels. Energy conservation law, mass conservation law and momentum conservation law provide good starting points for developing models for hydrogel volume transition. Thermodynamic models, transport models, multiphasic mixture theory and molecular simulation are discussed. Thermodynamic models provide qualitative description of equilibrium volume transition of hydrogels. Both transport models and multiphasic mixture theory can predict transient and equilibrium volume transition of hydrogels. Molecular simulation provides mechanistic understanding of hydrogel volume transition. Several key parameters are summarized for future model development.
Binary Polymer Mixtures in Selective Solvents: Interfacial Structure
Authors: Abramchuk Sergei S. , Semenov Alexander N. , Khokhlov Alexei R. 
Published: February 2004

AbstractSummary: The interaction of a large polymer droplet (formed by a poorly soluble polymer A) with a soluble polymer additive (polymer B) is investigated in the framework of a mean‐field approach. We found that polymer B may tend to adsorb on the surface of the droplet even when it is immiscible with polymer A in the droplet and is soluble in the solvent surrounding the droplet. We calculated the concentration profiles of both polymers A and B near the interface and established conditions for polymer B accumulation at the interface. The dependencies of the surface tension and the interfacial excess of polymer B on its bulk concentration are also calculated. We found that even a very small amount of homopolymer B additive may result in a significant reduction of the interfacial tension (by a factor of 2). The effect is stronger if the additive is more flexible than the insoluble polymer.The region of parameters where B from dilute solution is adsorbed at the A/solvent interface (II).imageThe region of parameters where B from dilute solution is adsorbed at the A/solvent interface (II).
Theoretical Study of the Effects of Templated Materials on Aggregate Formation
Authors: Chen Yong , Shew Chwen‐Yang , Gbemudu Chukwunonso , Chauhan Bhanu P. S. 
Published: February 2004

AbstractSummary:We have conducted Monte Carlo simulations to investigate a greatly simplified model for a blend composed of templated materials (polymers or monomers), smaller reacting particles and solvents on a two‐dimensional lattice. In the simulations, we compute the mean chain conformation of flexible templated polymers, and the distribution of the number of adjacent reacting particles aligned along the same axis to rationalize how templated materials affect the physical aggregation of smaller particles in a blend. We first examine the effects of the effective interactions between templated materials and smaller reacting particles. For repulsive interactions, flexible templated polymers tend to contract to reduce repulsions arising from smaller reacting particles, but for attractive interactions, mean chain dimension increases to maximize attraction. When templated material composition is increased, the conformational deformation of templated polymers becomes more pronounced. Moreover, in the presence of attractive interactions, reacting particles are more dispersed in the blend. In contrast, repulsive interactions increase the probability of aggregation of reacting particles. Also, our findings show that templated monomers (without chain connectivity) interact with reacting particles more effectively than with templated polymers due to the greater interacting area per monomer, which enhances the dispersion and segregation of reacting particles in the blend due to the attractive and repulsive interaction, respectively. In addition, as templated material composition is increased, the probability of forming a larger aggregate decreases. This simple model allows us to elucidate the role of templated materials on the physical aggregation of smaller particles in a blend.Probability distributionP(m) of findingmadjacent reacting particles along the same axis in the presence of templated polymers (open symbols) and templated monomers (solid symbols) for different monomer‐reacting particle ratio, 1:3 (□/▪), 1:1 (○/•) and 3:1 (▵/▴):.imageProbability distributionP(m) of findingmadjacent reacting particles along the same axis in the presence of templated polymers (open symbols) and templated monomers (solid symbols) for different monomer‐reacting particle ratio, 1:3 (□/▪), 1:1 (○/•) and 3:1 (▵/▴):.
Multi‐Objective Optimization of Semi‐Batch Copolymerization Reactors Using Adaptations of Genetic Algorithm
Authors: Nayak Arpan , Gupta Santosh K. 
Published: February 2004

AbstractSummary: The polymerization of styrene‐acrylonitrile (SAN) random copolymers in semi‐batch reactors is optimized using multiple objective functions that are often conflicting and non‐commensurate in nature. These include the average composition of the copolymer product, its number‐average molecular weight, its polydispersity index, and the conversion of monomers attained in the reactor. Two decision/control variables are used, namely, the rate of continuous addition of a monomer‐solvent‐initiator mixture (having a specified and fixed composition) and the history of the temperature in the reactor. The elitist non‐dominated sorting genetic algorithm, NSGA‐II, is adapted and used for decision variables that are functions of time (trajectory optimization). This robust, AI (artificial intelligence)‐based technique, enables the solution of far more complex optimization problems than those reported in the literature. A set of several non‐dominating (equally good) Pareto optimal solutions was obtained. These provide insights into the conflicting nature of the objective functions. An engineer (decision maker) can then use his judgment (often intuitive) to choose the preferred solution from among these possibilities.Pareto set of optimal solutions and some corresponding state variables for a Reference Problem.imagePareto set of optimal solutions and some corresponding state variables for a Reference Problem.
Monte Carlo Simulations of Polymers in Nanoslits
Authors: Vacatello Michele 
Published: February 2004

AbstractSummary:Monte Carlo computer simulations have been performed for model polymers confined in slits of thickness comparable to the transverse diameter of the chains. The density of polymer within the slits is allowed to vary with the slit thickness in such a way that the content of the slits is always in equilibrium with a large reservoir of bulk polymer. The calculations reveal the presence of polymer‐mediated attractive or repulsive interactions between the slit plates, oscillating with the slit thickness in good agreement with experimental results.The base cell used in the simulations.imageThe base cell used in the simulations.
Conformational Polymer Statistics from the Geometrical Scaling of Monomeric Units and the Characteristic Ratio from Circle Maps. Application to Carbohydrate Macromolecules
Authors: Mezzasalma Stefano A. , Angioletti Carmela , Cesàro Attilio 
Published: February 2004

AbstractSummary: Basic results on conformational chain statistics were formerly derived from scaling concepts for geometry and a relativistic picture of Brownian self‐diffusion in liquids. A polymer conformation was interpreted as a geometrical scaling law of its monomer shape, where the concept of characteristic ratio identifies a mean metric coefficient, originating topologically from rotational degrees of freedom internal to single molecules. Here, we add the former theoretical results to first numerical calculations. They are performed for three polysaccharides, provided with different chain topologies and constrained conformationally to identical square‐well energy states with increasing width. The spatial coil dilation‐contraction has been described satisfactorily by dihedral sine‐like rotations on a circle at dimeric length scales. New intrinsic quantities, like inner characteristic ratio and angular Kuhn step, both belonging to the shape of single molecules, have been finally defined. The geometrical mechanism bringing them at larger scales, to point out the chain shape size, is still unknown and under consideration.Conformational energy landscape of nigerose.imageConformational energy landscape of nigerose.
Multiple Histogram Method and Static Monte Carlo Sampling
Authors: Inda Márcia A. , Frenkel Daan 
Published: February 2004

AbstractSummary: We describe an approach to use multiple‐histogram methods in combination with static, biased Monte Carlo simulations. To illustrate this, we computed the force‐extension curve of an athermal polymer from multiple histograms constructed in a series of static Rosenbluth Monte Carlo simulations. From the complete histogram of the distribution function of the end‐to‐end vectors of the polymer chain, we can efficiently compute the polymer force‐extension curve.Comparison of the stress‐strain curves for the stress ensemble (symbols) and the strain ensemble (lines). Results obtained for N = 100, 200, 400, and 600. For small x, f(x) = −F′(x) was computed by aproximating F(x) by a second degree polynomial and then taking the derivative. For large x, f(x) = −F′(x) was computed numerically.imageComparison of the stress‐strain curves for the stress ensemble (symbols) and the strain ensemble (lines). Results obtained for N = 100, 200, 400, and 600. For small x, f(x) = −F′(x) was computed by aproximating F(x) by a second degree polynomial and then taking the derivative. For large x, f(x) = −F′(x) was computed numerically.
Cover Picture: Macromol. Theory Simul. 1/2004
Authors: Inda Márcia A. , Frenkel Daan 
Published: February 2004

Cover: Histograms of the x‐coordinate of the end‐to‐end vector of an athermal polymer subject to an external force. Above: raw data – Rosenbluth sampling. Below (reflected(: improved histograms after applying the multiple histogram method.Further details can be found in the Full Paper by M. A. Inda and D. Frenkel* on page 36.
Experimental study of thermal effects on the mechanical behaviour of a clay
Authors: Cekerevac Cane , Laloui Lyesse 
Published: February 2004

AbstractThe paper presents the results of an experimental study of thermal effects on the mechanical behaviour of a saturated clay. The study was performed on CM clay (Kaolin) using a temperature‐controlled triaxial apparatus. Applied temperatures were between 22 and 90°C. A comprehensive experimental program was carried out, including: (i) triaxial shear tests at ambient and high temperatures for different initial overconsolidation ratios; (ii) consolidation tests at ambient and high temperatures; and (iii) drained thermal heating for different initial overconsolidation ratios. The obtained results provide observations concerning a wide scope of the thermo‐mechanical behaviour of clays. Test results obtained at 90°C were compared with tests performed at ambient temperature. Based on these comparisons, thermal effects on a variety of features of behaviour are presented and discussed. Focus is made on: (i) induced thermal volume change during drained heating; (ii) experimental evidence of temperature influence on preconsolidation pressure and on compressibility index; (iii) thermal effects on shear strength and critical state; and (iv) thermal effects on elastic modulus. Thermal yielding is discussed and yield limit evolution with temperature is presented. The directions of the induced plastic strains are also discussed. Several remarks on the difference in the mechanical behaviour at ambient and high temperatures conclude the paper. Copyright © 2004 John Wiley & Sons, Ltd.
About Darcy's law in non‐Galilean frame
Authors: Geindreau C. , Sawicki E. , Auriault J.‐L. , Royer P. 
Published: February 2004

AbstractThis paper is aimed towards investigating the filtration law of an incompressible viscous Newtonian fluid through a rigid non‐inertial porous medium (e.g. a porous medium placed in a centrifuge basket). The filtration law is obtained by upscaling the flow equations at the pore scale. The upscaling technique is the homogenization method of multiple scale expansions which rigorously gives the macroscopic behaviour and the effective properties without any prerequisite on the form of the macroscopic equations. The derived filtration law is similar to Darcy's law, but the tensor of permeability presents the following remarkable properties: it depends upon the angular velocity of the porous matrix, it verifies Hall–Onsager's relationship and it is a non‐symmetric tensor. We thus deduce that, under rotation, an isotropic porous medium leads to a non‐isotropic effective permeability. In this paper, we present the results of numerical simulations of the flow through rotating porous media. This allows us to highlight the deviations of the flow due to Coriolis effects at both the microscopic scale (i.e. the pore scale), and the macroscopic scale (i.e. the sample scale). The above results confirm that for an isotropic medium, phenomenological laws already proposed in the literature fails at reproducing three‐dimensional Coriolis effects in all types of pores geometry. We show that Coriolis effects may lead to significant variations of the permeability measured during centrifuge tests when the inverse Ekman number Ek−1 is 𝒪(1). These variations are estimated to be less than 5% if Ek−1<0.2, which is the case of classical geotechnical centrifuge tests. We finally conclude by showing that available experimental data from tests carried out in centrifuges are not sufficient to determining the effective tensor of permeability of rotating porous media. Copyright © 2004 John Wiley & Sons, Ltd.
Comparison of non‐local and polar modelling of softening in hypoplasticity
Authors: Maier Th. 
Published: February 2004

AbstractThe paper deals with the comparison of a non‐local and a polar (Cosserat) hypoplastic model. The hypoplastic constitutive law in the version of von Wolffersdorff is chosen as local reference model. For the comparison the results of biaxial tests on dense Hostun Rf sand are predicted with both enhanced models. The comparison is based on a strict separation of input data from triaxial‐ and oedometer tests and output data from biaxial tests. The comparison is drawn in terms of the shear band width, the load–displacement curves and the influence of the pressure level. Finally, the non‐local and the polar hypoplastic model are applied on the strip foundation problem. Copyright © 2004 John Wiley & Sons, Ltd.
On the evolution of simple shear in saturated soils
Authors: Lu X. B. , Wang S.Y. , Peng Cui 
Published: February 2004

AbstractDevelopment of shear bands in saturated soils is a multi‐stage process based on the theoretical and numerical investigations in this paper. The soil is initially in homogenous shear strain state, and the instability can be characterized by a dimensionless number D. The inhomogenous distribution of shear strains appears when D>1, and the shear band will initiate and develop gradually. Numerical solutions show that only single shear band that is finally formed in the central region of the specimen even several disturbances (distributed along the specimen) appear in the beginning. Copyright © 2004 John Wiley & Sons, Ltd.
Functionalization of a poly(vinyl alcohol) in the solid state with a swelling agent by methacrylic anhydride
Authors: Becquart F. , Taha M. , Zerroukhi A. , Kaczun J. , Stebani U. 
Published: February 2004

AbstractPoly(vinyl alcohol‐co‐vinyl acetate) was functionalized by methacrylic anhydride to introduce functional groups by a new process that consisted of modifying a polymer directly from a powder form in the solid state. To favor the diffusion of the reagents, a swelling agent composed by a mixture of ethylene carbonate and propylene carbonate was used. N‐methylimidazole was used as a basic catalyst of the esterification reaction, adjusting the reaction times. This work presents the process and the effects of the formulation on anhydride conversion. The side reactions were also determined; they all involved N‐methylimidazole. Decarboxylation reactions of the carbonates were characterized, that is, going from ethylene carbonate to ethylene glycol, which is able to react with two anhydride molecules by esterification reactions to, respectively, form 2‐hydroxyethyl 2‐methylpropenoate and ethyl 1,2‐bis(2‐methyl propenoate). The same side reactions are possible with propylene carbonate but are less reactive than the starting ethylene carbonate. Model anhydrides such as hexanoic and heptanoic anhydrides, less reactive than methacrylic anhydride, were used to characterize a new anhydride decarboxylation reaction. The homogeneity of the grafting is also discussed, especially its dependence on the polymer properties, the diffusion modes of the reagents (carbonate mixture and the anhydride), and the competition between the diffusional and chemical kinetics of methacrylic anhydride. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1618–1629, 2004