bluuebunny/crossref_metadata_2025_split huggingface dataset:
Separation properties and surface morphology of polyacrylonitrile membranes
Authors: Paul D. , Kamusewitz H. , Hicke H.‐G. , Buschatz H. 
Published: April 2003

AbstractThe formation of polyacrylonitrile membranes by phase inversion has been studied. The surface morphology, as investigated by atomic force microscopy, and the separation performance in ultrafiltration were correlated with the concentration of the polymer in the casting solution and a post‐treatment by annealing.
Determination of domain sizes in heterogeneous polymers by solid‐state NMR
Authors: Clauss J. , Schmidt‐Rohr K. , Spiess H. W. 
Published: April 2003

AbstractAdvanced solid‐state NMR techniques exploiting 1H spin diffusion are described, which rely on selecting 1H magnetization of one of the components on the basis of 1H chemical shift or mobility differences under multiple‐pulse irradiation. To monitor the progression of 1H spin diffusion, the higher resolution of 13C CP MAS spectra is exploited for NMR detection. For evaluation of the data, full quasi‐analytical solutions of the diffusion equation as well as initial‐rate approximations are derived, applied and discussed. In order to obtain quantitative results, the 1H spin‐diffusion constant has to be determined. To this end, the domain sizes in poly(styrene)‐poly(methyl methacrylate) systems including symmetrical diblock copolymers have been measured. The comparison of the NMR results with SAXS and TEM data yields the spin‐diffusion coefficient for PS and PMMA. The resulting value of D=0.8 nm2/ms is expected to be typical for rigid organic systems. The domain sizes investigated range from approximately 1 nm to ca. 100 nm.
A Diels‐Alder ladder polymer bridged by imino and ether groups
Authors: Löffler M. , Schlüter A.‐D. , Enkelmann V. 
Published: April 2003

AbstractThe synthesis of a Diels‐Alder ladder polymer with imino and ether bridges is described. The structure proof is based upon a comparison of its high resolution 13C‐NMR spectrum with those of model compounds. The molecular weights can reach values as high as M̄n = 52000 which are the highest ones observed so far for a double stranded polymer. The X‐ray structure of model compound 8 is also presented.
Detection of ferroelectric to paraelectric phase transition in copolymers of vinylidene fluoride by magnetic susceptibility
Authors: Flores A. , Ania F. , Cabarcos E. López , Calleja F. J. Baltá 
Published: April 2003

AbstractThe diamagnetic susceptibility of a series of random copolymers of vinylidene fluoride (VF2) with trifluoroethylene containing 60 to 100 mole‐% VF2 has been investigated, both as a function of composition and of temperature. Results show that at room temperature the molecular susceptibility of the series linearly decreases with VF2 content. Furthermore, the diamagnetic susceptibility for each composition rises gradually at the beginning of the Curie transition, reaching a plateau which characterizes the diamagnetism of the paraelectric phase. The percent increase in diamagnetism when passing from the ferroelectric to the paraelectric phase is primarily due to the changes occurring from the planar all‐trans polar conformation into the disordered molecular conformation of the high temperature phase. The reduced final increase in diamagnetism detected at the melting point suggests that conformational transformations occurring from the paraelectric phase into the molten state are small.
The influence of hydroxyethylcellulose on the diffusion of acetylsalicylic acid trihydromagnesium salt in aqueous solution
Authors: Pisárčik M. , Mikula M. , Marianiová D. , Lapčik L'. 
Published: April 2003

AbstractThe mean mutual diffusion coefficient of acetylsalicylic acid trihydromagnesium salt in water and in hydroxyethylcellulose aqueous solution is studied using optical refractometric Philpott Svensson method. It was found that the presence of the polymer increases the diffusion coefficient of the magnesium salt in the three‐component system. The self‐diffusion coefficient of hydroxyethylcellulose aqueous solution with and without addition of the magnesium salt was also measured using dynamic light scattering. The possible diffusion mechanism of the magnesium salt in aqueous solution with presence of the polymer is explained. Assuming the experimental data of the two‐component system with respect to the addition of a third component, it was found that the jumping distance of magnesium salt increases approximately linearly with the hydroxyethylcellulose concentration.
Thermal stability of poly(2‐acrylamido‐2‐methylpropanesulphonic acid) and polymer complexes of 2‐acrylamido‐2‐methylpropanesulphonic acid with some transition metal salts
Authors: Aggour Y. A. 
Published: April 2003

AbstractPoly(2‐acrylamido‐2‐methylpropanesulphonic acid) and polymer complexes of 2‐acrylamido‐2‐methylpropanesulphonic acid with nickel(II), copper(II), iron(III) chlorides and cobalt (II) sulphate, respectively, were prepared and characterized by spectroscopic techniques. Thermal stability of the formed polymer complexes was determined by means of thermogravimetric analysis. It was found that the thermal stability of the homopolymer is less than that of the polymer complexes. The activation energies of the degradation of the polymer complexes were determined by using the Arrhenius equation.
Investigations about dissolution of cellulose in the LiCl/N,N‐dimethylformamide system
Authors: Morgenstern B. , Berger W. 
Published: April 2003

AbstractUsing various cellulose samples, the conditions of cellulose dissolution in N,N‐dimethylformamide with added lithium chloride were established. The way of activation of cellulose influences decisively the dissolution. Complete dissolution of microcrystalline cellulose can only be achieved after treating with liquid ammonia. The required salt concentration amounts to approximately 10 wt‐%. Degree of polymerization and crystallinity of the cellulose influence significantly the solubility behaviour.
Biodegradable polymers. 7th comm. On the mechanism of ring‐opening polymerization of cyclic esters of aliphatic hydroxycarboxylic acids by means of different tin compounds
Authors: Dahlmann J. , Rafler G. 
Published: April 2003

AbstractTo elucidate the effect of tin compounds in the ring‐opening polymerization of lactides and lactones, D,L‐dilactide was taken as an example, and its reaction with different tin compounds at a molar ratio of 1:1 as well as the polymer formation and degradation in dependence of its concentration has been investigated. Two entirely different reaction courses were observed which are consequently influenced by compounds with alcoholic and/or carboxylic OH groups in different ways.
The role of interparticle distance in maximizing the toughness of high‐impact thermoplastics
Authors: Michler G. H. 
Published: April 2003

AbstractFor the two groups of rubber modified thermoplastics (toughness by multiple crazing as in HIPS and ABS polymers or by multiple shearing as in high‐impact PA) the local processes of plastic deformation have been studied by different techniques of electron microscopy, including scanning, transmission and high voltage electron microscopy. The processes have been investigated dependent on the morphology, in particular on the diameter D of the rubber particles and their interparticle distance A. For both groups critical values for the interparticle distance exist: a minimum critical value Amin (which has the same physical reason for both and is connected with the coupled movements of segments of the interconnected macromolecules) and a maximum critical value Amax (which is of a different nature in the two cases).
Conformation and shape of rigid‐rod polyesters substituted with flexible side chains as revealed by small‐angle neutron scattering
Authors: März K. , Lindner P. , Urban G. , Ballauff M. , Kugler J. , Fischer E. W. 
Published: April 2003

AbstractA small‐angle neutron study of liquid crystalline main chain polyesters with flexible side chains is presented. Investigations in solution have been performed using protonated material dissolved in deuterated tetrahydrofuran and deuterated nitrobenzene. To determine the conformation in bulk, mixtures of deuterated and protonated material have been investigated at ambient and at elevated temperature. For this purpose, a route for the synthesis of fully deuterated polyesters has been developed. It is shown that the form factor measured in solution is compatible with an extended, rod‐like conformation. Investigations in bulk show that a plate‐like conformation is adopted under these conditions. This observation is in full agreement with earlier findings from structural studies which indicate that in bulk the side chains of a given main chain are located in a plane; i.e., the polyester molecule assumes a plate‐like shape. Thus the present investigation demonstrates that there is a pronounced change of conformation when going from solution to bulk. The reason for this change are the packing constraints exerted by the neighbouring molecules in the bulk.
Dilute solution properties of alternating copolymers from acrylonitrile and α‐methylstyrene
Authors: Cincu C. , Ion L. , Trifan M. 
Published: April 2003

AbstractKuhn‐Mark‐Houwink‐Sakurada relations were obtained in various solvents for alternating copolymers from acrylonitrile and α‐methylstyrene. The values of the unperturbed dimension and the conformational parameter were determined using usual extrapolation techniques. The values of the unperturbed dimensions are dependent on the solvent and are quite different from the values calculated on the basis of additivity rules from the unperturbed dimensions of the parent homopolymers.
Biodegradable polymers. 8th comm. On the kinetics of ring‐opening polymerization of 1,3‐dioxane‐2‐one (trimethylene carbonate)
Authors: Rafler G. 
Published: April 2003

AbstractThe ring‐opening polymerization of 1,3‐dioxane‐2‐one was investigated in dependence on the most important reaction parameters. It was found that the monomer conversion is above all determined by the polymerization temperature and the initiator concentration. The molecular weight of the formed polycarbonate is determined not only by the kinetics of the polymerization reaction, but also by the extent of competitive side reactions. High molecular weight products are only obtained by high polymerization rates.
Small‐angle x‐ray analysis of latex particles using contrast variation
Authors: Dingenouts N. , Ballauff M. 
Published: April 2003

AbstractA study of a core‐shell latex consisting of a polystyrene core and a polymethylmethacrylate (PMMA) shell by small‐angle x‐ray scattering is presented. Since the electron density, i.e., the contrast of both polymers, can be easily matched by addition of sucrose to the dispersing agent water, the internal structure of the particles can be studied by contrast variation. The scattering intensities obtained at different contrast are all compatible with a concentric core‐shell model which exhibits a finite nonuniformity of the thickness of the shell. The present analysis furthermore reveals that the interfacial region between the polystyrene and the PMMA phase must be very small.
Increased biodegradation of LDPE with nonionic surfactant
Authors: Albertsson A.‐Chr. , Sares Chr. , Karlsson S. 
Published: April 2003

AbstractLDPE's with and without 0.5% nonionic surfactant (Tween 80) were subject to biodegradation in salt solutions with Pseudomonas aeruginosa. The degradation of LDPE was greater in samples with Tween 80 than in pure LDPE as observed by ATR‐FTIR, DSC and chemiluminescence (CL) measurements. In light microscopy a larger number of bacteria were observed on the surface of LDPE with Tween 80 incubated with Pseudomonas aeruginosa for 60 days than on the surface of pure LDPE. The results indicate a greater susceptibility to biodegradation in the LDPE samples with surfactant than in the corresponding pure LDPE.
Simultaneous measurements of small angle X‐ray scattering, wide angle X‐ray scattering and heat exchange during crystallization and melting of polymers
Authors: Bark M. , Zachmann H. G. 
Published: April 2003

AbstractExperimental equipment was constructed for simultaneous measurements of wide angle X‐ray scattering (WAXS), small angle X‐ray scattering (SAXS) and differential scanning calorimetry (DSC) using synchrotron radiation as a strong source of X‐rays. The crystallization occurring during heating of an initially amorphous sample with constant heating rate was investigated. Poly(ethylene naphthalene‐2,6‐dicarboxylate) (PEN), poly(ethylene terephthalate) (PET) and the copolymer PEN‐co‐PHB (90:10), where PHB stands for poly(p‐hydroxybenzoic acid), were used as materials. By comparing the change of the degree of crystallinity as measured by WAXS and DSC with the change of the SAXS power Q, it was shown that the primary crystallization, during which morphological units like spherulites axe growing, is followed by a secondary crystallization during which the degree of crystallinity with the lamellar stacks in the spherulites is increased. Assuming a two‐phase system for the semicrystalline structure, consisting of crystals and amorphous regions, three different processes were shown to be responsible for this increase: The formation of new crystal lamellae within the already existing lamellar stacks, the thickening of already existing crystals at the expense of the amorphous regions, and the complete melting of crystals followed by formation of new, thicker, crystals.
Structural aspects of oligothienyl series from X‐ray powder diffraction data
Authors: Porzio W. , Destri S. , Mascherpa M. , Brückner S. 
Published: April 2003

AbstractThe structures of the series of oligothienyls (T4‐T5‐T6) have been determined and refined from X‐ray powder diffraction data using the Rietveld full‐profile analysis. Unlike polythiophene, all the molecules in the isomorphous series display no internal symmetry, being only approximately planar within 12°. Packing is always achieved through a common molecular disposition, which is usually defined as a herringbone arrangement, with an angle between mean planes of adjacent molecules which spans from 60° to 70°.
The orientation distribution in an industrial sample of poly(p‐phenylenetere‐phthalamide) determined by two‐ and three‐dimensional NMR techniques
Authors: Wilhelm M. , de Lacroix S. Féaux , Titman J. J. , Schmidt‐Rohr K. , Spiess H. W. 
Published: April 2003

AbstractTwo new solid‐state NMR methods for measuring orientation distributions in partially ordered solids are applied to high tensile‐strength fibre polymers. Both methods use the anisotropy of the carbon‐13 chemical shift tensor as a probe for local molecular directions, but they differ in the manner in which the information is extracted and complement one other. The spectral resolution is higher in the ORDER (ORientation Distributions with Enhanced Resolution) experiment, which employs rotor‐synchronized three‐dimensional magic angle spinning (MAS) NMR, while the angular precision with which the orientation distribution can be determined is higher in the DECODER (Direction Exchange with Correlation of Orientation Distribution Evaluation and Reconstruction) experiment. The utility of the two techniques is demonstrated by their application to the study of industrially produced poly(p‐phenyleneterephthalamide) fibres. Both give the same result for the width (χ = 13°) and the order parameters (<P2>=0.85, <P4>=0.57, <P6>=0.34, <P8>=0.14) of the orientation distribution.
Thermal graft copolymerization of 4‐vinyl pyridine onto ethyl cellulose in homogeneous media. 1. Influence of ammonium persulfate
Authors: Abdel‐Razik E. A. 
Published: April 2003

AbstractGraft copolymerization of 4‐vinyl pyridine(4‐VP) onto ethyl cellulose (EC) using ammonium persulfate (APS) as free radical initiator was studied in the toluene: DMSO (4:l v/v) solvent system. The weight conversion, grafting percentage and grafting efficiency were determined as functions of the polymerization temperature and of the concentration of monomer, ethyl cellulose and initiator. The homopolymerization of 4‐VP in the presence ofAPS was also investigated. The graft copolymers were characterized by thin layer chromatography, IR spectroscopy, nuclear magnetic resonance and intrinsic viscosity measurements. The highest rate of propagation of graft copolymerization of 4‐VP onto EC in the presence of APS observed was 0.06 %/min. A suitable mechanism of grafting reaction is discussed.
New polyelectrolyte materials based on smectite polyoxyethylene intercalation compounds
Authors: Aranda P. , Ruiz‐Hitzky E. 
Published: April 2003

AbstractThe intercalation of poly(ethylene oxide), PEO, into homoionic phyllosilicates of the smectite group (montmorillonite and hectorite) gives composite materials able to act as solid polyelectrolytes. The synthesis and the structural characterization of new intercalation compounds belonging to this class of materials have been investigated. The resulting compounds exhibit good chemical and thermal stability, preserving their ion‐exchange properties. PEO intercalation produces an enhancement of the electrical conductivity associated with the interlayer cations compared to the parent silicates. Ionic conductivity determined by impedance spectroscopy measurements of different polyoxyethylene compounds (PEO and crown‐ethers) into homoionic 2:1 charged phyllosilicates reveals that the conductivity values can be correlated with the oxyethylene‐cation strength interaction.
Crystallinity of cellulose and its accessibility during deuteration
Authors: Loelovitch M. , Gordeev M. 
Published: April 2003

AbstractThe accessibility of cellulose samples with different supermolecular structure during deuteration has been studied by NMR. It has been established that the content of accessible regions is higher than the content of amorphous regions determined by the X‐ray method. A modified crystalline–amorphous model of cellulose structure is proposed to explain this result. According to this model, thin surface layers of crystallites are less ordered and are accessible during the deuterium exchange. The quantitative ratio between the accessibility and the crystallinity of cellulose has been established.
Neutron spin echo studies on the segmental diffusion behavior in the different chain sections of high molecular weight poly(dimethylsiloxane) melts
Authors: Ewen B. , Maschke U. , Richter D. , Farago B. 
Published: April 2003

AbstractUsing neutron spin echo spectroscopy, the dynamics of high molecular weight poly(dimethylsiloxane) in the melt (T=473 K) was investigated. In order to decide whether the lateral constraints are uniform or nonuniform with respect to the contour of a test chain, chains were labeled either completely or partially by a corresponding proton‐deuterium exchange. It was found that the central and the terminal chain sequences experience the same amount of lateral confinement, which–in the framework of the reptation or tube model–can be characterized by a tube diameter dt of about 70 Å. Nearly the same dt value is obtained from the plateau modulus of rheological measurements, too. Thus, these experiments show unambiguously that the lateral constraints, responsible for the reptational chain dynamics, are quite homogeneous, even in the case of extremely large tube dimensions.
General formulation of the statistical mechanics of multicomponent polymer systems
Authors: Vilgis T.A. , Haronska P. 
Published: April 2003

AbstractThis paper summarizes different approaches to strongly interacting polymer systems. The first part of the paper discusses repulsive systems, i.e. polymers in a good solvent, polymer melts and blends. Corresponding field theories are reviewed and critically revisited from different points of view. The second part of the paper is devoted to attractive systems, i.e. polymers in a poor solvent, ionomers, polyelectrolytes under certain conditions, etc. New types to field theories have to be developed as theories for repulsive polymer systems no longer lead to the appropriate physics. The technical approaches used in the paper are field theory and path integrals. Novel possibilities for a microscopic theoretical description of these systems are reported.
Liquid‐crystalline perylene oligomers: Synthesis and phase behavior
Authors: Pressner D. , Göltner C. , Spieß H‐W. , Müllen K. 
Published: April 2003

AbstractTwo selectively deuterated, liquid‐crystalline oligomers of different topology, containing the deep‐violet perylene mesogen 1, were prepared by two‐fold polymer‐analogous reaction of a suitable pre‐oligomer or by polycondensation of an ester‐functionalized monomer. The materials obtained were investigated by optical microscopy, DSC, X‐ray diffraction, and solid‐state 2H NMR spectroscopy. The structural changes in the mesophases formed and the dynamic phase behavior are discussed, and the results are compared with those obtained from low molecular weight model compounds.
Temperature evolution of the structure of a thermotropic main‐chain liquid crystalline copolyester
Authors: Antipov E.M. , Stamm M. , Abetz V. , Fischer E.W. 
Published: April 2003

AbstractX‐ray diffraction, differential scanning calorimetry and dynamic mechanical analysis are used to study the temperature evolution of the structure of the thermotropic copolyester poly[(phenyl‐pphenylene)‐co‐(terephthalate)‐co‐(p‐hydroxybenzoate)] (PES) prepared from terephthalic acid, phenyl‐hydroquinone and p‐hydroxybenzoic acid (molar ratio 45/45/10). Needle‐like crystals are developed in the quenched as‐spun fibers despite the random sequence of the monomers of the copolyester. Moreover, two other crystalline phases are observed at elevated temperatures, which may be explained by a phase separation process. X‐ray diffraction experiments show a significant temperature dependence of structural features, indicating some conformational disorder and mobility in this class of “rigid‐rod” liquid crystalline polymers. Changes in the X‐ray pattern are observed on heating, starting immediately above the glass transition temperature of the copolyester. Melting of PES reveals a two‐step character with transitions at 300 °C and 320 °C. The material becomes isotropic at 400 °C or higher.