bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthetic polymers in biology and medicine
Authors: Scheler W. 
Published: March 2011

AbstractSynthetic organic polymers have gained great importance as supports and separation materials in biochemical laboratory techniques, medical diagnostics and biotechnological procedures. Furthermore they are used as carriers for drugs and biologically active substances in pharmacy, medicine and agriculture. Classifying their biocompatibility it has to be distinguished between in vitro application of polymers interacting on the one hand with molecular biosystems such as proteins and on the other hand with living cells, and in vivo administration in higher organisms, especially in the human organism.
Multiplicity of active species in transition metal based catalysts: The various reaction processes involved
Authors: Sigwalt P. , Deffieux A. 
Published: March 2011

AbstractProducts resulting from the polymerization of α‐olefins and of styrene initiated by transition metal based catalytic systems may range from dimers of various structures to high mol. wt. polymers of different stereoregularities. In this report, it is shown that such a large variety of products may be obtained using the same transition metal compound.Initiating systems derived from tetrabenzylzirconium are first examined. The nature of the various mechanisms involved according to polymerization conditions are discussed. A rather similar situation is observed for systems derived from titanium trichloride. In this series, however, Ziegler‐type processes can be generated much more cleanly. This led us to examine the mechanisms in more detail in order to distinguish the various types of active species which may participate to these polymerizations.
On the reactivity of supported zirconium organic catalysts in the polymerization of ethylene
Authors: Ulbricht Joachim , Giesemann Jürgen 
Published: March 2011

AbstractThe ethylene polymerization with tetrabenzyl zirconium displays a higher concentration of active centres on catalysts obtained by supporting of the organometallic compound on alumina or silica‐alumina carriers than by activation without supporting. The active centres of the supported catalysts possess different polymerization reactivity. At the beginning of the polymerization in the presence of monomer, these active centres are formed from a small amount of the stable surface compounds originated in the carrier impregnation. The maximum polymerization rate depends on the pretreatment, the loading and the porosity of the carrier. The more active these centres, the quicker they lose their activity. A relation was found between a chemical deactivation reaction and the concentration of the hydroxyl groups remaining on the catalyst after impregnation. Addition of hydrogen or butyllithium can change the polymerization in a different manner. The addition of butyllithium causes an increase in the number and the reactivity of the active centres and a suppression of the chemical deactivation.
Prediction of phase equilibrium behavior of quasibinary polymer solutions
Authors: Fujita Hiroshi , Einaga Yoshiyuki 
Published: March 2011

AbstractA chronological review is given of typical contributions which played a role in approaching quantitative predictions of phase equilibria in binary and quasibinary polymer solutions. It describes step by step findings of the variables which govern phase separations in these systems. These variables are temperature, overall polymer concentration, and chain length distribution of the polymer mixture making up the solution. The last variable gives rise to a considerable difficulty in formulating the free energy of quasibinary solutions.
Polydispersity treated by continuous thermodynamics
Authors: Rätzsch Margit T. 
Published: March 2011

AbstractContinuous thermodynamics is a suitable concept for performing phase equilibrium calculations of polydisperse systems such as polymer solutions or polymer mixtures. In contrast to the traditional pseudo‐component method the continuous molar mass distribution density function obtained by fractionation or gel permeation chromatography is used directly for thermodynamic calculations. This paper describes the application of continuous thermodynamics to calculate cloud‐point curves, shadow curves and coexistence curves for solutions and mixtures of homopolymers and random copolymers. Particular attention is devoted to special problems such as fractionation or the transition from polymers to oligomers requiring the application of sophisticated Gibbs energy functions. In all cases the use of continuous thermodynamics leads to a drastic reduction of the required computer time. For Schulz‐Flory distributions the occurring integrals often may be calculated analytically leading to simple closed end formulas.
Changes in lignin and cellulose by irradiation
Authors: Fischer Klaus 
Published: March 2011

AbstractThe effect of high‐energy radiation on wood and cellulose was investigated. By irradiation of beech wood, changes in lignin, in carbohydrates and in wood structure take place. Furthermore, new lignin carbohydrate complexes are formed. A way is shown to prevent undesirable reactions. Irradiated pulp possesses a lower degree of polymerization and a higher accessibility for chemical reactions. Processing irradiated pulp to viscose fibres will be more efficient.
Biomedical behavior of some amino‐containing polymers in contact with blood constituents
Authors: Tsuruta Teiji 
Published: March 2011

AbstractThe present paper is concerned with studies for elucidation of the relationship between the structure of HA copolymers and their adsorption property toward lymphocyte subpopulations, B cell and T cell. HA is a polyamine graft copolymer of poly(hydroxyethyl methacrylate) as the backbone. In the earlier part of this paper, discussion will be made on our synthetic approach to HA copolymers having polyamine graft chains of controlled length and number, while, in the later part, the outline of our recent studies of biomedical behavior of HA copolymers in terms of selective adsorption of B cell against T cell will be presented. A possible mechanism for the cell separation will also be discussed.
Polymer modification to achieve novel properties
Authors: Vogl Otto , Sustic Andres 
Published: March 2011

AbstractPolymers have been modified, by subjecting them to reactions in solution, in the melt and in the solid state. Novel polymers with improved and optimized properties have also been created by copolymerization, chain transfer or by the design of chain termination. Even by manipulating the initiation step in polymerizations, functional and reactive groups have been introduced at the head of the polymer chain. Polymer properties have been modified by influencing physical properties of polymers by orienting, annealing and blending.
X‐ray crystallography at macromolecular resolution: A solution of the phase problem
Authors: Luzzati V. , Mariani P. , Delacroix H. 
Published: March 2011

AbstractThe problem of crystal structure analysis at macromolecular resolution is tackled using notions borrowed from small‐angle solution‐scattering studies. The mathematical procedure ‐ essentially a pattern recognition approach ‐ consists of generating all the phase combinations compatible with the data and screening them: the critical steps are the choice of the “pattern” and of the criteria which preside the “recognition”. Two strategies are adopted. One is based upon use of the histogram of the electron density maps, a function more dependent on chemical composition than on physical structure: the histograms of samples of different structure and similar chemical composition are compared in search for similarity. The other strategy operates on the electron density maps and involves the principle of maximum smoothness. From the practical viewpoint, one single parameter, (Δp)4, is found to play an outstanding role in the two cases. Algorithms are worked out, implemented on the computer and tested using a variety of lipid‐water phases. The comparison of samples of different structure and similar chemical composition is found to provide a powerful screening criterion. The principle of maximum smoothness is also of great help, at least to the extent that the electron density distribution is a fairly smooth function, devoid of sharp peaks (associated with heavy atoms). The practical aspects of the algorithms are discussed, as well as their possible application to crystallographic problems of more general interest.
Time‐of‐flight small‐angle scattering spectrometers on pulsed neutron sources
Authors: Ostanevich Yurii M. 
Published: March 2011

AbstractThe operation principles, constructions, advantages and shortcomings of the known Time‐of‐Flight Small‐Angle Neutron Scattering (TOF SANS) spectrometers built up on pulsed neutron sources are reviewed. The most important characteristics of TOF SANS apparatuses are rather a high luminosity and the possibility of measurement in an extremely wide range of the scattering vector at a single exposure. This is achieved by simultaneous employment of the white beam, TOF technique for Λ‐scan and the commonly known θ‐scan. However, the electronic equipment, data‐matching programs and the measurement procedure, necessary for accurate normalization of experimental data and their transformation into absolute cross‐section scale ‐ they all become more complex as compared with those for SANS apparatuses operating on steady‐state neutron sources, where only θ ‐scan is used.
A complete mapping of the positions of the proteins in the small ribosomal subunit of escherichia coli
Authors: Capel M.S. , Engelman D.M. , Freeborn B.R. , Kjeldgaard M. , Langer J.A. , Ramakrishnan V. , Schindler D.G. , Schneider D.K. , Schoenborn B.P. , Sillers I.‐Y. , Yabuki S. , Moore P.B. 
Published: March 2011

AbstractThe relative positions of the centers of mass of the 21 proteins of the 30S ribosomal subunit from Escherichia coli have been determined by triangulation using neutron scattering measurements in solution. This mapping is the first complete account of the quaternary structure of the small ribosomal subunit to be obtained by any method.
Small‐angle scattering in materials science
Authors: Kostorz Gernot 
Published: March 2011

AbstractThe use of small‐angle scattering techniques in the study of inhomogeneities and microstructural changes in inorganic materials is reviewed with emphasis on X‐ray scattering. Recent applications of anomalous scattering with synchrotron radiation and kinetic studies in amorphous and crystalline systems are stressed.
Small‐angle scattering from dense systems of non‐homogeneous particles, I
Authors: Syneček Vladimír 
Published: March 2011

AbstractThe introduction of the effective integral quantities characterizing non‐homogeneous particles and their volume fraction leads to an expression for the distance distribution function analogous to that for homogeneous particles. This significantly simplifies the determination of the structure characteristics of particles. The procedure is outlined for obtaining the distribution of excess electrons and the total number of electrons within the particle from relative SAXSb) intensity data. The mode of the spatial arrangement of the partially ordered system of particles can be estimated by comparing the characteristic numbers calculated for different structure types with that characteristic number determined from relative intensities, namely from the effective quantities of the system and from the position of the maximum of interference function.
Determination of compositions of Guinier‐Preston zones and matrix in Al‐Zn alloys using relative intensities, II
Authors: Truong Chu Thien. , Syneček V. , Wendrock G. , Löffler H. 
Published: March 2011

AbstractThe composition of Guinier‐Preston (GP) zones (cZ) and matrix (cM) in an Al‐15 mol‐% Zn alloy was determined for temperatures ranging between 80 and 180°C by applying a new method. The volume fraction of the GP zones is evaluated by their mean size and spacing. The latter quantity is computed from the position of the maximum of the interparticle interference function.
Analysis of small angle neutron scattering data from strongly interacting polydisperse ionic micellar solutions
Authors: Chen Sow‐Hsin , Sheu Eric Y. 
Published: March 2011

AbstractSmall angle neutron scattering (SANS) intensity distributions from ionic micellar solutions without added salt generally show a prominent interaction peak at finite Q (magnitude of the wave vector transfer) related to a certain inter‐micellar correlation distance. Analysis of this type of data requires, aside from the structural model of the micelle itself, a statistical mechanical theory for dealing with the inter‐micellar correlations. We present a method for a consistent analysis of SANS data taking into account the surfactant chain packing, the aggregation number polydispersity, and the effective micellar charge. The micelle is modelled as a two‐region spheroidal particle and the inter‐micellar correlations calculated according to a generalized one‐component macroion (GOCM) theory. GOCM uses an effective inter‐micellar pair potential which is a finite concentration extension of the well‐known Derjaguin‐Landau‐Verway‐Overbeek (DLVO) double layer interaction potential. Two micellar solutions are treated as examples, namely that of sodium dodecyl sulfate (SDS) and sodium 1,2‐bis(2‐ethylhexyloxycarbonyl)ethanesulfonate (AOT). The effects of polydispersity are appreciable immediately above the critical micellar concentrations (CMC). Both the structural parameters of the micelle and the free energies of micellization and micellar growth can be extracted from SANS data.
Neutron scattering studies of the structure and assembly of spherical viruses
Authors: Timmins Peter A. 
Published: March 2011

AbstractStudies of the structure of spherical viruses, using both classical solution scattering techniques, and in favourable cases, the technique of low‐resolution neutron crystallography, are described. Solution scattering studies, which began with the determination of the radial distribution of the various viral components, have evolved to the stage where it is now possible to follow the in vitro reassembly of virus particles. The limitations of spherical averaging present in solution scattering can in certain cases be overcome by the application of the contrast variation method to single crystals of a virus. Application of this technique to the structure of tomato bushy stunt virus (TBSV) is described.
Polymer blends ‐ current state of progress and future developments from an industrial viewpoint
Authors: Rudolph Hans 
Published: March 2011

AbstractTechnical and economic considerations have given polymer blends a major share in the increasing sales of plastics. This applies both to general‐purpose and to the higher value‐added materials. Thus it is scarcely surprising that almost all polymer manufacturers have now developed comprehensive ranges of blends having particular property profiles. The principal types of blends currently available are described.The variety of products already developed should not be allowed to obscure the fact that certain conceivable and highly attractive property combinations have not so far been realized. If progress is to be made in this area, interdisciplinary cooperation between chemists and physicists in the fields of polymer chemistry, polymer physics and materials science is essential.
Miscibility enhancement in polymers via ionic interactions: Dynamic mechanical and NMR studies
Authors: Natansohn Almeria , Murali Rajagopalan , Eisenberg Adi 
Published: March 2011

AbstractThe presence of ionic interactions can be used to control the degree of miscibility of otherwise immiscible polymer systems. This control, in turn, allows one to prepare blends with a very wide range of “tailor‐made” properties. Several examples are cited. In some of these, the interactions are based on proton transfer from a donor site on one polymer to an aceptor site on another leading to ion‐ion interactions. In others, the transfer of a metal cation from an ionomer to a polar polymer, as a result of ion‐dipole interactions, is involved. Systems studied to date include, among others, mixtures of polystyrene with poly(ethyl acrylate), polyisoprene, segmented poly urethanes, poly(ethyleneimine), and poly(ethylene oxide). The polyurethane blends with polystyrene are discussed in some detail, focussing especially on the mechanism of miscibility enhancement as determined by NMR. This technique has also been utilised to study the dynamics of the coil overlap process in solution as well as the proximity of the polymer coils to each other. Two particularly noteworthy applications involve mixtures of poly (tetrafluoroethylene) (PTFE) or of phenylated poly(phenylene oxide) with poly (ethyl acrylate), which are also discussed in some detail. Blends of this type may be of special interest in membrane applications.
On the compatibilization of polymer blends
Authors: Vilgis T. A. , Noolandi J. 
Published: March 2011

AbstractBy means of statistical thermodynamics we consider the effect of a diblock copolymer on the interface of a demixed homopolymer blend. In contrast to the usual case where the blocks are identical with the components of the homopolymers, we investigate the use of arbitrary blocks XY respective to the A‐B blend. As examples, we calculate interfacial properties such as the interfacial tension and the width of the interface as well as the concentration profiles of the blocks. We expect a strong compatibilization effect if the blocks are sufficiently long and have a preferential repulsive interaction with one of the two homopolymers.
Theory of crystallizable block copolymers
Authors: Whitmore Mark Douglas , Noolandi Jaan 
Published: March 2011

AbstractWe present an equilibrium theory of diblock copolymers in which one of the blocks is crystallizable and the other is amorphous. The material is assumed to order in a lamellar structure of alternating semi‐crystalline and amorphous layers with the chemical bonds which connect the copolymer blocks lying in the interfacial regions between the layers. The amorphous blocks are modelled as flexible chains, each with one end (the joint) anchored in an interface. Their contribution to the free energy is calculated via the self‐consistent solution of the modified diffusion equations. The crystalline regions are modelled as folded chains, also with one end in an interfacial region (bonded to the corresponding end of an amorphous block).We find that the calculated amorphous block‐free energies can be expressed as a single universal function depending on the total degree of polymerization of the amorphous block, its stretching, and a parameter proportional to the thickness of the interface. We have fitted an analytical form to this function, which can be used for any amorphous block, and we have combined it with our model of the crystallizable block to obtain scaling laws describing the equilibrium morphology.
The application of fracture mechanics to the impact behaviour of rubber‐toughened polyamides
Authors: Sunderland P. , Kausch H. H. , Schmid W. Arber E. 
Published: March 2011

AbstractRubber‐modification of polyamide is a widely‐applied method of improving material resistance under high strain rate loading. The processing conditions used for preparing such two‐phase blends strongly influence their structure and thus their subsequent impact properties. In the present work the relationships between production parameters, phase structure and impact resistance have been studied, and the rǒle of the rubber phase in promoting energy absorption investigated. It has been found that improved impact resistance, defined as a combination of high resistance to crack initiation and to crack propagation, is achieved by decreasing the polyamide phase viscosity while increasing the extrusion and injection temperatures, the mixing shear rate and the rubber phase volume fraction; an EPR modifier offers superior performance to a polybutadiene modifier; the dominant mechanisms of energy‐absorption are shearing and void formation, there being no clear evidence of crazing; the J‐integral technique of plastic fracture mechanics can be applied to Charpy impact testing; TEM allied with image analysis techniques provides quantitative morphological information on polymer blends.
Reversible and irreversible denaturation of proteins in chromatographic systems
Authors: Wetlaufer D.B. 
Published: March 2011

AbstractProtein denaturation in typical chromatographic mobile phases is examined from kinetic and equilibrium viewpoints, preliminary to consideration of the binding of proteins to stationary phases. Protein binding to a stationary phase may result in concomitant stabilization or destabilization. Experiments to clarify mechanisms and/or to lead to stabilization of proteins against denaturation are discussed. Among the work to be discussed are the ion exchange chromatography of α‐chymotrypsinogen and hen egg lysozyme with mobile phases containing urea; reverse phase HPLC of RNase A and serum albumin with conventional mobile phases; and hydrophobic interaction chromatography of enolase, carbonic anhydrase, lysozyme, RNase A, and bovine pancreatic trypsin inhibitor, mediated by the surfactant CHAPS.
Influence of pressure on protein conformation
Authors: Lüdemann H.‐D. 
Published: March 2011

AbstractThe pressure effects in aqueous solutions of biopolymers are presented. It is shown, that pressure in the range of 300 to 800 MPa leads for small monomeric proteins to irreversible denaturation. Larger oligomeric enzymes and structural proteins dissociate reversibly in the pressure range around 100 MPa. The sign of the volume effects of the various noncovalent interactions contributing to the observed reaction and activation volumes is discussed.
Forces and mechanisms in the adsorption of uncharged and ionizable macromolecules and of proteins
Authors: Fleer G.J. , Lyklema J. 
Published: March 2011

AbstractThe main energetic and entropic factors determining the adsorption behaviour of neutral polymers, polyelectrolytes, and proteins are discussed. The driving force is the segment adsorption energy, opposing forces are the loss of chain conformation entropy and the entropy of (de)mixing. Mutual interactions between the segments play an important role, especially if the macromolecules carry charged groups.Several examples are given of the dependency of the adsorption of flexible macromolecules on the adsorption energy, the solvent quality, the salt concentration, and the surface charge. In the case of proteins, the internal coherency of the molecule largely determines the adsorption behaviour. For relatively flexible proteins like HPA, entropic contributions are important and sometimes dominant; the nature of the surface is less critical. For rigid proteins like RNAse, the adsorption is mainly energetically determined, depending largely on the electrostatic interaction between protein and surface.