bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of molar mass and molar mass distribution of blood plasma substitutes (plasma expanders)
Authors: Lemmes R. , Schwengers D. , Weimann B. 
Published: March 2011

AbstractBlood plasma substitutes, such as dextran and hydroxyethyl starch, cause an expansion of the liquid volume in blood vessels due to their high colloid‐osmotic pressure and water‐binding potential, and are therefore applied clinically as so‐called plasma expanders for rapidly increasing the liquid volume. This potentially life‐saving effect only applies while the plasma substitute is present in the bloodstream. For this reason knowledge of the retention time is of great importance. As the retention time is directly related to the molecular weight distribution of polydisperse hydrocolloids, an estimation of the parameters of this distribution is therefore of crucial significance in the quality control of plasma expanders.Besides absolute methods (e.g. GPC/LALLS), there is special interest in GPC as a relative method with calibration against narrow molecular weight standards. This is because of its wide distribution, the speed at which it can be carried out, and the low expenditure on apparatus. Furthermore, there are advantages if commonly accepted pharmacopoeial methods can be performed in a manner that allows the results to be compared easily. In order to implement the molecular weight determination method in Pharmacopoeia Nordica's (Ph.Nord, or Svensk Läkemedelsstandard “SLS”) dextran monograph, a suitable software for VAX computers was developed at the Max Planck Institut für Kohlenforschung in Mülheim/Ruhr.
Evaluation of K⊖ from [η]‐M‐data of binary and ternary polymer systems
Authors: Zisenis Mathias , Springer Jürgen 
Published: March 2011

AbstractUnperturbed dimensions of flexible linear macromolecules can be obtained from [η]‐M‐data in any solvent, good or poor, single or mixed. Usually Kθ is estimated by a relationship between [η]/MW0.5 and Mw0.5 first proposed by Burchard and by Stockmayer and Fixman. But, it is well‐known that the Burchard‐Stockmayer‐Fixman‐plot shows downward curvature, especially for good solvent systems. Various efforts have been made to achieve relations with better linearity. One of the first was the semi‐empirical relation between ([η]/Mw0.5)0.5 and Mw/[η] by Berry. Predicting a relationship of the excluded volume parameter z to the viscosity expansion factor by α5η instead of α5η Tanaka obtains that ([η]/Mw0.5)5/3 is linear in Mw0.5. By allowing for the dependence of the viscometric interaction parameter B, which is correlated to the second virial coefficient A2, on molar mass, Gavara, Campos and Figueruelo predict a linear dependence of [η]/Mw0.5 against A2.Mw0.5. It is not our intention here to discuss the validity of these theories, but to compare them with experimental data.
Molecular characterization of starch polysaccharides
Authors: Vorwerg W. , Burchard W. 
Published: March 2011

AbstractLight scattering and rheologic measurements have been carried out with native starch in DMSO and with degraded amylopectin of a starch hydrolysate in water at different temperatures. The measurements of dilute solutions in DMSO were made to get a reference for the molecularly dispersed state. In water association take place which under certain conditions leads to gelation. An aqueous solution of about 11.5% (w/w) degraded amylopectin was investigated in detail. Structural change was observed during cooling the solution below 20°C with both techniques. A fractal dimensions of about 2.5 was found at temperatures above 20°C indicating non‐swollen random aggregates. Light scattering proved to be the more sensitive method than rheology, but in both experiments a structural collapse was detectable. A fractal dimension of about 1 was now obtained which is characteristic for rigid, elongated supra‐structures. A certain time after this collapse an increase of loss and storage module and particle growth in light scattering were obtained. The crossing of the G' and G” was taken as point of gelation and the same gelling time was estimated from light scattering. Hence, the combination of oscillatory rheology with light scattering is an appropriate procedure for a thorough investigation of such complex, structure forming systems.
Preparation and characterization of latices with hydrophobic core and hydrophilic shell
Authors: Hashemzadeh A. 
Published: March 2011

AbstractAnionic and non‐ionic copolymer latices with a hydrophobic core and hydrophilic shell were prepared using emulsifier‐free emulsion polymerization. Styrene was used as the hydrophobic monomer; acrylic acid, acrylamide, and methacrylamide were employed as the hydrophilic monomers. The amount of chemically bound hydrophilic monomers in latex and unbound homopolymers in water were determined. The salt stability and redispersability of latices in water after spray‐drying were also investigated.
Aggregation of flexible‐rigid‐flexible triblock copolymers
Authors: Raphael E. , de Gennes P. G. 
Published: March 2011

AbstractWe discuss the aggregation behavior of flexible‐rigidflexible triblock copolymers in a selective solvent of low molecular weight. Aggregation may lead either to plates of (R) covered by brushes of (F), or to large “needles” (as a consequence of the Skoulios effect). In the absence of anisotropic bonding between adjacent rods, the “fence” morphology is not expected.
Comments on fluctuations of cross‐links in gels
Authors: Rubinstein M. , Ajdari A. , Bastide J. , Leibler L. 
Published: March 2011

AbstractLocalization of cross‐links is an important issue in the theory of rubber elasticity. We consider freely‐hinged rigid rod networks and show that in some cases they behave like critical objects: junctions fluctuate on all length scales. Such networks exhibit anomalously low shear modulus and cannot resist shear deformations. These conclusions are very different from the classical picture and might be of some significance for gels near the critical point of volume transition. We comment on the reasons for the different behavior of gels under more usual conditions and raise questions concerning the ability of cross‐links to rearrange on scales larger than the mesh size.
Exploring the domain validity of the equations relating the intrinsic viscosity to the molecular weight by using the characteristic numbers of polymers
Authors: Dondos Anastasios 
Published: March 2011

AbstractPlotting log[η] versus logM (Mark‐Houwink‐Sakurada equation) we observe a crossover region in which a continuous variation of the exponent of this equation takes place. This crossover region is delimited by two characteristic numbers: Nc (or Mc), the number of statistical segments (or the molecular weight) in the onset of excluded volume behavior and Nc' (or Mc') the number of statistical segments (or the molecular weight) in the onset of the complete excluded volume behavior. Relations are given in order to obtain these numbers. The Stockmayer‐Fixman‐Burchard equation is valid for the flexible and wormlike polymers in the molecular weight region which lies above the crossover region while the Dondos‐Benoit equation is valid in the medium and low‐molecular‐weight region including the crossover region.
Structure of iPP‐PS composites with specific dispersion of PS component
Authors: Kryszewski M. , Pluta M. , Trznadel M. , Milczarek P. 
Published: March 2011

AbstractThe results of structure investigations of two‐component iPP‐PSa) systems obtained by UV‐initiated polymerization of liquid styrene diffused into unoriented and oriented iPP matrices have been presented. Initial structure of iPP matrices was modified by different preparation and various conditions of orientation. Presented results show that the final structure of the composites strongly depends on the initial structure of the matrices and employed conditions of styrene polymerization process.
Model macromolecules
Authors: Rempp Paul , Lutz Pierre 
Published: March 2011

AbstractThe interest for tailor ‐ made macromolecules arises from their use as calibration samples for characterization techniques, and from their prominent role in the investigations of structure/properties relationships. The conditions most appropriate for the synthesis of model macromolecules of various kinds are reviewed. Two cases of controlled polymer synthesis are considered in greater detail: Cyclic macromolecules and star shaped polymers
A challenge to novel fluoropolymers
Authors: Yamabe Masaaki 
Published: March 2011

AbstractPerfluoro(vinyl ether) derivatives are extremely versatile monomers in preparing a variety of functional fluoropolymers. In this paper, two challenging topics in the development of novel fluoropolymers will be introduced. Carboxylated perfluoro(vinyl ether) can be copolymerized with tetrafluoroethylene to afford perfluorinated ion‐exchange membranes, which realize the innovative process for pollution‐free and energy‐saving chlor‐alkali production. Another topic includes the discovery of selective cyclo‐polymerization of specially designed difunctional perfluoromonomers such as perfluoro(allyl vinyl ether) which is readily derived from the carboxylated perfluoro(vinyl ether). The novel perfluoropolymer with a cyclic structure in the main chain is characterized by an exceptional transparency, and has been commercialized with expectation of major applications in electronics industries.
Dedicated polymers for future progress in microelectronics
Authors: Rubner Roland , Ahne Hellmut , Sebald Michael , Sezi Recai 
Published: March 2011

AbstractThe continuous miniaturization in microelectronics requires advanced materials and processes. Novel specifically functionalized anhydride‐containing filmforming polymers which spontaneously react with bisaminoalkylsiloxanes were synthesized for use in photolithographic processes. This allows the modelling of photoresist patterns and thus enhancement of practical resolution. In addition, efficient polymeric dielectrics with improved solubility in environmentally safe solvents were developed. The latter can be patterned using the above mentioned photolithographic process.
Water‐soluble polymers for hostile environment enhanced oil recovery applications
Authors: Hsieh H. L. , Moradi‐Araghi A. , Stahl G. A. , Westerman I. J. 
Published: March 2011

AbstractThis paper describes polymerization and properties of a number of water‐soluble polymers suitable for enhanced oil recovery applications. The polymers described here can tolerate long‐term exposure to hostile environment conditions of elevated temperatures and high salinity and hardness levels encountered in deeper petroleum reservoirs. The stable polymers reported here, in principle contain two or more of the following monomers: acrylamide, N‐vinyl‐2‐pyrrolidone, sodium 2‐acrylamido‐2‐methylpropanesulfonate and N,N‐dimethylacrylamide in proper ratios. The polymers reported here can be used directly to increase the viscosity of the injected water and consequently reducing its mobility to recover additional oil from petroleum reservoirs. Alternatively, these polymers can be used in combination with a suitable crosslinker to produce gels in‐situ to block high permeability channels or fractures under hostile environment applications.
Oligomers of stereoregular polymers
Authors: Garner Charles M. , Bartus Jan , Simonsick William J. , Ute Koichi , Hatada Koichi , Vogl Otto 
Published: March 2011

AbstractThe embryonic state of the ionic methyl methacrylate (MMA) and of trihaloacetaldehyde polymerization was studied. The composition of the oligomer mixtures, the end groups and the stereochemistry of individual compounds of the oligomers was investigated. Depending upon the initiating systems the oligomerization of methyl methacrylate can give either isotactic or syndiotactic oligomers. Trihaloacetaldehye oligomerization is highly dependent on the ceiling temperature of polymerization. The oligomerization of fluoral and chloral is compared with a more detailed study of the bromal polymerization and even more interestingly with the cooligomerization of chloral and bromal.
Constant pressure molecular dynamics: Instantaneous external stress tensor in systems with periodic boundary conditions
Authors: Winkler Roland Georg 
Published: March 2011

AbstractA stress tensor for systems with periodic boundary conditions is presented, which is different from the wellknown Irving‐Kirkwood expression. It is shown that it represents the external stress for particles initially in one of the cells of the periodic system. The statistical properties of the pressure, derived from the stress tensor, are discussed. It is demonstrated that this pressure can be used to simulate a constant pressure ‐ constant enthalpy ensemble. Constant pressure computer simulations on the basis of the proposed stress tensor are free of artificial parameters and the internal pressure is not constrained, in contrast to previously existing constant pressure simulation schemes.
Simulation of first‐ and second‐order transitions in asymmetric polymer mixtures
Authors: Deutsch H.‐P. , Binder K. 
Published: March 2011

AbstractThe critical properties of dense asymmetric binary polymer mixtures are studied by grand canonical simulations within the framework of the 3‐dimensional bond fluctuation lattice model. The monomers interact with each other via a potential ranging over the entire first peak of the pair distribution. An asymmetry is realized by giving the ratio of interactions λ = ∈AA/∈BB between monomers of the A‐species and of the B‐species a value different from 1. Using multiple histogram extrapolation techniques for the data analysis, the two phase region, which is a line of first‐order transitions driven by the chemical potential difference, and the critical point are determined for a mixture of chains with 32 monomers each. At a critical potential difference Δμc unmixing occurs below a critical temperature Tc. It is found that Δμc is proportional to the asymmetry (1 ‐ λ) and that the quantity 4kBTc/(3 + λ)∈ is independent of the asymmetry, consistent with the prediction of the Flory theory.
Relation between amorphous structure of polymers and penetrant diffusion: A molecular dynamics simulation
Authors: Takeuchi Hisao , Okazaki Keiji 
Published: March 2011

AbstractMolecular dynamics simulation has been performed for studying the relation between amorphous structure of polymers and penetrant diffusion. The self‐diffusion coefficients of O2 and He in various polymer models, which differ from each other in view of the amorphous structure, were calculated above their glass transition temperatures. The amorphous structure was characterized by considering the percolation of the unoccupied volume. A good correlation was found between the self‐diffusion coefficients and the number of clusters in the unoccupied volume at the critical point of the percolation. Based on the simulated cluster size distribution at the critical point, we defined a parameter into which effects of both the amorphous structure and the penetrant size are well incorporated. It was confirmed that the penetrant diffusion is intimately associated with the amorphous structure of polymers.
Modeling plasticizer diffusion in rubbery PVC
Authors: Vaz Roy J. , von Meerwall Ernst D. 
Published: March 2011

AbstractIn recent work4, the trace diffusion, Do of 14 plasticizers dissolved in rubbery PVC, CCl4 and neat, was determined and well correlated with estimated static minimal molecular diameter further reduced to account for cooperation between sidegroups and host chain segments. Here numerical molecular modeling has been used in an effort to put this correlation on a firmer basis. The modeling accounts for plasticizer major and minor axis bond flexibility, plasticizer shape in terms of steric and electrostatic fields surrounding the diffusants and the van der Waals volume. The correlation with experimental results of the diffusants is found to be good except for a single molecule with disk‐like geometry in PVC for which a different geometry may be operative.
Modeling the conformations and motions of isolated polymer chains in the narrow channels of their crystalline inclusion compounds with small‐molecule, host clathrates
Authors: Tonelli Alan E. 
Published: March 2011

AbstractThe narrow channels occupied by polymer chains in their crystalline inclusion compounds(IC) with small‐molecule, host clathrates, such as urea and perhydrotriphenylene(PHTP), provide a unique, solid state environment. Single polymer chains are confined to occupy narrow cylindrical channels whose walls consist of a crystalline matrix of the small‐molecule, host clathrate. Because the IC channels are well‐separated, each included polymer chain is isolated from its neighbors, and is therefore free from cooperative, interpolymer interactions which often dominate and complicate the behavior of bulk polymers. We have modeled polymer chains included in their IC channels by restricting the conformations accessible to small chain fragments(9–20 backbone bonds) to those which fit into a cylinder whose diameter(5.5Å) mimics the observed channel cross‐section. After establishing the population of channel conformers, a test is performed to determine the possibility of interconverting between them without any portion of the polymer chain fragment leaving the channel during any step in the interconversion process. The results of our modeling are compared to observations made on a variety of polymer‐IC's formed with either or both of the host clathrates, urea and PHTP. General agreement is found between the modeled conformations and mobilities of cylindrical polymer chain fragments and those observed directly from the crystalline polymer‐IC's, principally by solid state NMR, DSC, and X‐ray diffraction.
Twiston vs. random fluctuation as the source of the rapid motion of polyethylene in the inclusion complex with perhydrotriphenylene
Authors: Zhan Yongjian , Mattice Wayne L. 
Published: March 2011

AbstractRecently molecular dynamics simulations were performed for polyethylene in the inclusion complex with perhydrotriphenylene. The system contained ninety molecules of perhydrotriphenylene, arranged in six stacks of fifteen molecules each, and one molecule of n‐tetracontane, C40H82. The internal CH2‐CH2 bonds in n‐tetracontane have a very strong preference for the trans state. Nevertheless, the chain exhibits a high degree of internal flexibility. This motion produces a characteristic pattern in δ|ψ N + i ψi| vs. N, where ψi describes the instantaneous angle of a C‐H bond vector at carbon atom i about the axis defined by the channel, and δ denotes the fluctuation. The pattern expected for δ|ψ N + i ψi| vs. N is derived for the case where the rapid internal motion is produced by a twiston. It is compared with the results from the simulation and from the expectation for the case where the rapid motion arises from uncorrelated internal fluctuations within the trans state at each CH2‐CH2 bond.
Polyelectrolyte brushes
Authors: Borisov O.V. , Birshtein T.M. , Zhulina E.B. 
Published: March 2011

AbstractThe simple scaling theory of weakly‐charged polyelectrolyte brush (the layer of polyelectrolyte chains grafted at one end onto an impermeable surface) immersed into a good solvent has been developed.The asymptotic scaling dependences of the free layer thickness on charge density and solvent strength are obtained.The behavior of polyelectrolyte brush subjected to normal and tangential external forces is considered. New “polyelectrolyte effect” is predicted: shear of a free polyelectrolyte brush leads to a decrease in brush thickness in contrast to the case of a free neutral brush. Such behavior is equivalent to that of a neutral brush subjected to external normal stretching force. This force in the case of polyelectrolyte brush is created by the osmotic pressure of mobile counterions neutralizing grafted chain charges.
Docking of a polymer chain on a surface with Monte Carlo methods illustrated by polyimide on silicon
Authors: Hädicke Erich , Brode Stefan 
Published: March 2011

AbstractA computer simulation technique for docking small molecules in the cavities of zeolites has been used for modelling the arrangements of a single polymer chain on a crystalline solid substrate in atomistic detail. This Monte Carlo procedure calculates a large number of polymer/solid arrangements and eliminates identical aggregates. We model only the physicosorption between the two phases by taking only the nonbonding van der Waals interactions into account. The interface of a single polyimide chain and the Si (100) plane is used as a test case. We found, that the aromatic rings of the deposited polyimide prefer a coplanar arrangement to the Si surface. In this arrangement the polymer chain is distorted compared with the conformation in vacuum.
Structure, conformation and dynamics of polymer chains at solid melt interfaces
Authors: Pan Chongmin , Bitsanis Ioannis 
Published: March 2011

AbstractWe have performed molecular dynamics, and lattice Monte Carlo simulations of polymeric melts in the vicinity of solid surfaces. The structural features of the solid‐melt interface were very simple. The interfacial width was comparable to the segment size. Inside this narrow interface the segment density profile was oscillatory. The density oscillations were much less pronounced than those present at solid‐atomic liquid interfaces. On a scale much larger than the segment size, chain conformations were found to be identical with those of ideal chains next to a reflective barrier. In particular, the number of surface‐segment contacts scaled like the square root of the molecular weight. Extensive molecular dynamics simulations showed that chain desorption times increase with molecular weight but at a rate much slower than the longest relaxation time of Rouse chains. Therefore, sufficiently long chains desorbed almost freely from the surface despite the presence of attractive surface‐segment interactions. A study of chain relaxation dynamics confirmed that the Rouse modes constitute an appropriate set of normal coordinates for chains in the melt interacting with a solid surface. The effect of the surface on mode relaxation was significant. All relaxation processes of chains located within a couple of radii of gyration from the surface were slowed down considerably. This effect, however was approximately the same for fast and slow modes and independent of molecular weight for sufficiently long chains.
Anionic polymerization of butadiene: A MNDO study of the potential energy surface of the propagation reaction in polar and non‐polar media
Authors: Siggel Lorenz , Knoll Konrad , Hädicke Erich , Brode Stefan 
Published: March 2011

AbstractThe anionic polymerization of butadiene, to both the 1,2‐ and 1,4‐addition products, is an important industrial process. It is known that the reaction can be steered to either the 1,2‐ or 1,4‐product by the addition, or absence, of a complexing solvent such as ether. The goals of the current study were to map the MNDO Potential Energy Surfaces (PES) of the propagation reactions both in the presence and absence of dimethyl ether to gain insight into the factors influencing the reaction's selectivity. Single point ab initio calculations at the DZP level were run on all reactants, products and transition states as a cross check on the MNDO results.