bluuebunny/crossref_metadata_2025_split huggingface dataset:
Some aspects of graft copolymerization on holocellulose
Authors: Okieimen Felix , Idehen Kevin 
Published: April 2003

AbstractGraft copolymers of acrylonitrile and methyl methacrylate on unmodified holocellulose and holocellulose containing between 0.3 and 4.6% thiol groups were prepared by the use of Ce4 + initiator in aqueous medium at 29°C. It was found that although the extent of graft polymer formation on the holocellulose was appreciably reduced by the presence of thiol groups, thiolation showed little influence on the frequency of grafting. The molecular weight of grafted PMMA chains was higher than for PAN grafts; but the latter were more frequently grafted on the backbone polymer. The observed low frequency of grafting is thought to indicate that radicals formed on the cellulosic substrate may not be very reactive towards graft polymer formation.
Effect of thermal history on the crystallization behaviour of polyetheretherketone by the dynamic viscoelastometer
Authors: Wu Zhungwen , Zheng Yu Bin , Ni Zhuo , Nakamura Tomoki , Yosomiya Ryutoku 
Published: April 2003

AbstractThe effect of thermal history on the crystallization behaviour of PEEK is investigated by the dynamic viscoelastometer. The crystallization behaviour of PEEK shows significant influence on the α peak in the tan δ and the storage modulus. The α peak temperature is rapidly increased at shorter times with the annealing temperature at 160°C or higher, and is then constant. The storage modulus is more gently reduced in the α transition region as the annealing temperature is higher, and becomes then a constant value. It is suggested that the reduction in the storage modulus corresponds to some defect in the crystal structure of PEEK.
Effect of the viscosity of components on the phase structure and impact strength of polypropylene/ethylene‐propylene elastomer blends
Authors: Fortelný Ivan , Kamenická Danuše , Kovář Josef 
Published: April 2003

AbstractThe concentration dependences of particle size of the dispersed phase on rheological properties of the components were investigated by scanning electron microscopy for blends of polypropylene and ethylene‐propylene elastomers obtained by melt mixing. At very low concentrations the minority component is dispersed the more finely the lower its viscosity is. With increasing concentration of the dispersed phase the size of its particles in the given matrix increases the more quickly the lower the viscosity of the dispersed phase is.With increasing viscosity of the matrix the particle size of the minority phase decreases at all compositions of the blend. The results obtained were interpreted as a result of dynamic equilibrium between the break up and coalescence of particles in flow. At elastomer concentrations higher than 15% the differences between impact strength values of the blends are determined by the size of inclusions of the elastomeric modifier. Dispersions finer than the optimal one with respect to impact strength can be reached only with the polypropylene matrix possessing high viscosity.
The mechanism and kinetics of reactions in the initial stage of thermally initiated oxidation of caprolactam
Authors: Lánská B. , Šebenda J. 
Published: April 2003

AbstractIn the induction period of the autocatalytic, thermally initiated oxidation of caprolactam (90–155°C) the role of the catalyst is played by the primary oxidation product, caprolactam hydroperoxide.With increasing concentration of hydroperoxide the probability of its association by hydrogen bonds to a dimer also increases. This dimer is cleaved by a somewhat different mechanism than the monomeric form, or its associate with caprolactam; the oxidation of caprolactam assumes a stationary rate, with adipimide as the oxidation product. Its presence by no means affects the further oxidation course and adipimide alone is neither oxidized nor hydrolyzed.Similarly to the oxidation of N‐alkyl amides, carboxylic groups arise in the oxidation of caprolactam via an alkoxy radical formed by the homolysis of hydroperoxide. We found that the carboxylic groups are formed autocatalytically due to their cooperative effect in the decomposition of caprolactam hydroperoxide into adipic acid monoamide. With increasing concentration of carboxyl groups the rate of this decomposition increases so much that adipic acid monoamide becomes the predominant oxidation product. The rate of radical homolysis of hydroperoxide, i.e. of the initiation reaction and of the oxidation in general, also decreases.Consequently, the effect of carboxylic groups on the rate of oxidation of caprolactam is an inhibiting one. The reactions mentioned above describe the thermally initiated oxidation of caprolactam to the stage which corresponds to the conversion of 2% of caprolactam.
Systematic study of ion‐exchange properties and ligating behaviour of respropiophenone‐formaldehyde copolymers
Authors: Patel B. K. , Patel M. M. 
Published: April 2003

AbstractRespropiophenone‐formaldehyde copolymers (RPP‐F) were synthezised by the condensation of 2,4‐dihydroxypropiophenone (respropiophenone (RPP)) and formaldehyde (F) in the presence of NaOH or H2SO4 as catalyst with varied molar ratios of reacting monomers. The copolymers were characterized by elemental analysis, IR spectra, viscosity, and TGA studies. Their M̄n was determined by nonaqueous conductometric titrations and vapour pressure osmometry (VPO). Chelation ion‐exchange properties have also been studied employing the batch equilibration method. Polychelates of Cu(II), Ni(II), Co(II), Mn(II), Zn(II), VO(II), and UO2(II) with RPP‐F‐AI copolymer were prepared. The analytical data agree with 1 : 2 metal‐ligand stoichiometry. Elemental analysis, magnetic, spectral, and thermal properties of polychelates have been studied and probable structures are assigned to the polychelates. All the polychelates are amorphous powders, insoluble in common organic solvents.
Blends of chlorinated isotactic polypropylene with poly(ethylene‐co‐vinyl acetate) II. Phase studies of the miscible blends
Authors: Lee Seung Soo , Chung Ki‐Hyun , Kim Kwang Soo , Jung Jin Chul 
Published: April 2003

AbstractBy measuring Tg, Tm and Tc (cloud point) phase diagrams for the four miscible blends of chlorinated isotactic polypropylenes (chlorine content 39.2 (CPP‐40) and 49.8 wt.‐% (CP‐50)) with Poly(ethylene‐co‐vinyl acetate)s (vinyl acetate contents 40 (EVA‐40) and 45 wt.‐% (EVA‐45)) were investigated. The blend of CPP‐50 with EVA‐40 was the most compatible of the four blend pairs.
Radical concentration and efficiency of secondary photochemical reactions in modified polystyrene
Authors: Kamińska A. , Kaczmarek H. 
Published: April 2003

AbstractThe influence of acrylonitrile‐butadiene‐styrene‐terpolymer (ABS) and methyl methacrylate‐butadiene‐styrene‐terpolymer (MBS) modifying the polystyrene (PS) films on its resistance to UV radiation were investigated.On the basis of the results of ESR, IR, UV, mass spectroscopy, viscosimetric and solubility measurements it was found that 3% of ABS or MBS in polystyrene films have a clear influence on the course of photochemical processes. After UV‐irradiation of the samples, at the presence of this terpolymers, a greater concentration of free radicals with shorter half‐life times was observed.Both terpolymers increase the productivity of photooxydation of polystyrene as well as its crosslinking and decrease its dehydrogenation.
The hydrogenation of HO‐terminated telechelic polybutadienes in the presence of a homogeneous hydrogenation catalyst based on tris(triphenylphosphine)rhodium chloride
Authors: Bouchal Karel , Ilavský Michal , Žůková Eva 
Published: April 2003

AbstractThe hydrogenation kinetics of multiple bonds in HO‐terminated telechelic polybutadienes was investigated using two types of these prepolymers prepared by the anionic and radical polymerization. The rate of addition of hydrogen to the π‐bonds of these polydienes in the presence of tris(triphenylphosphine) rhodium chloride as a homogeneous hydrogenation catalyst was determined by the chemical structures of the starting polydienes, their concentration in the solvent, the partial hydrogen pressure, the concentration of the catalyst, and the temperature.The effect of kinetic parameters given above on the rate of hydrogenation reaction can be interpreted in the sense of Wilkinson's reaction mechanism of the hydrogenation of alkenes in the presence of the Rh(I)‐complex. Due to the predominant 1,2‐structural units, the anionic prepolymer reacted twice as quickly with hydrogen (k = 0.093 mol−1 dm3 s−1) compared with the radical prepolymer (k = 0.045 mol−1 dm3 s−1). During the hydrogenation of multiple bonds there is a partial loss of hydroxy groups in modified telechelic prepolymers; the extent of this reaction depends on reaction conditions of the hydrogenation reaction.
Structure and molecular dynamics of highly mobile polymer membranes
Authors: Fahmy Tarek , Wesser Joachim , Spiess Hans Wolfgang 
Published: April 2003

AbstractThe function of lipid bilayer membranes crucially depends on their mobility and their ability to incorporate components that, e.g., can change molecular order and dynamics or form channels. Since polymerization increases the stability of model membranes at the expense of their mobility a compromise must be sought. Therefore, the effect of different polymerization schemes on the structure and dynamics of polymer membranes has to be checked. To this end X‐ray scattering, DSC‐thermal analysis and a variety of spectroscopic techniques probing the dynamics on largely different time‐‐‐ and length scales were employed, i.e. 2H‐NMR, ESR, fluorescense anisotropy and FRAP. These studies showed that in model membranes polymerized in the hydrophylic region the head group mobility can be controlled by the length and the nature of the spacer connecting it to the polymer backbone. The head group region is much less affected, if the polymerization is achieved in the hydrophobic region. By use of a lipid analogue carrying a polymerizable group on only one of its two alkyl chains, membranes retaining high mobility in the hydrophobic region can be generated. Typical membrane constituents, i.e. cholesterol, gramicidin and ubiquinone can be incorporated and the mixtures show a behaviour similar to natural model membranes, although lateral diffusion of the lipids is frozen as a consequence of the polymerization.
Interaction of amphiphilic polymers with model membranes
Authors: Decher Gero , Kuchinka Ellen , Ringsdorf Helmut , Venzmer Joachim , Bitter‐Suermann Dieter , Weisgerber Christoph 
Published: April 2003

AbstractThe lipid bilayers of cell membranes are usually connected to two types of biopolymers: the cytoskeleton and the glycocalix. These structures are not only responsible for the stabilization of the lipid bilayer, they also alter the surface properties of the cells. Among the various attempts to mimick membrane properties using polymeric systems(1), one method is the fixation of amphiphilic polymers via hydrophobic anchor groups to lipid bilayers. In the experiments reported here the influence of amphiphilic polymers on the morphology of giant unilamellar liposomes has been investigated. Therefore a series of amphiphilic polyvinylpyrrolidone and dextran derivatives has been synthesized. The fixation of these polymers to the liposomal membranes could be shown with a fluorescence‐labelled derivative by using epifluorescence microscopy. The polymer‐membrane interaction caused by the insertion of the anchor groups leads to drastic morphological changes in this model membrane system. The exclusive interaction with the outer membrane of multilamellar liposomes could be demonstrated by freeze fracture electron microscopy. In addition, the anchoring of a natural capsular polysaccharide in liposomes has been proven by immunofluorescence. In these experiments, also a clustering (patching) of the antigen caused by the binding of the antibody could be observed.
Liquid crystals in biological systems
Authors: Hoffmann Siegfried 
Published: April 2003

AbstractNotwithstanding their more common beginnings, liquid crystals and molecular biology developed mainly parallel and independently during the last one hundred years.Molecule‐phase relationships on the one and complex static‐dynamic treatments on the other hand seem to forward mutually integrative views in our days.Biomesogen approaches will deepen our insights into the spatio‐temporal coherences of biological systems. They might contribute significantly to the understanding of life processes.
Preparation and characterization of microdisperse bioavailable carotenoid hydrosols
Authors: Horn Dieter 
Published: April 2003

AbstractThe application of carotenoids as natural additives in various water‐based or water‐compatible formulations for the pigmentation of foods and feeds is seriously hampered by their insolubility in aqueous systems.Therefore, in order to develop the full potential of colour strength and to achieve a high degree of bioavailability during gastro intestinal passage, the coarse crystalline material has to be transformed into a microdisperse state.Exemplified with β‐carotene, a novel non‐mechanical process is described that transforms the carotenoids into a colloidal hydrosol characterized by an average particle size of about 0.1 μm.The process is based on the preparation of a transient high temperature solute state of the carotenoid in a water‐miscible solvent, coupled with succeeding rapid aqueous precipitation in the presence of a stabilizing polymer colloid. The obtained hydrosols are characterized by photon‐correlation‐spectroscopy(size), and microelectrophoresis(colloidal stabilization).The bioavailability was tested by monitoring plasma levels of β‐carotene in veal calves.
Bioresorbable polymers for temporary therapeutic applications
Authors: Vert M. 
Published: April 2003

AbstractPolymer science is mature enough to allow one to think about tailor‐making macromolecular compounds aimed at interacting purposely with living systems. Reasons for developing bioresorbable polymers for temporary therapeutic applications are discussed with respect to property adjustments and economical factors. The field of the applications is first described and guidelines for tailor‐making multimeric macromolecules with desired properties are presented. The approach led to focuss investigations on poly(α‐hydroxy acids) and functional poly(β‐hydroxy acids) derived from natural hydroxy acids, namely lactic, glycolic and malic acids. Physical, mechanical and biological properties of some corresponding polymers and copolymers are presented. Last but not least, examples of applications currently investigated are recalled.
Polymere in der diagnostik
Authors: Batz Hans‐Georg , Hopp Herbert , Mang Thomas , Schmidt Brigitta 
Published: April 2003

AbstractDiagnostics are e. g. reagents or combinations of reagents or measure bloodcomponents down to concentrations of 10−15 mol/1 in reproducable form. To achieve this target diagnostics have to fullfill special requirements in purity, uniformity, producibility and reproducibility. These requirements are also valid for integrated polymers and plastics. Examples of the application of polymers and plastics in diagnostics are e. g. materials for the blood‐plasma‐separation, the stabilization of proteins, solid phases in immunoassays as reagent tubes, microtiterplates and latexparticles.Reciprocal actions between polymers, plastics, polymer additives, blood and bloodsubstances like proteins in diagnostic tests can be seen as indications to similar effects by the intracorporeal applications of plastics in surgery and in general for contacts of natural materials with plastics, as usual in the foodpacking.
The application of immobilized affinity ligands in high performance liquid chromatography
Authors: Josić Dj. , Reutter W. , Krämer D. M. 
Published: April 2003

AbstractUsing Eupergit, a synthetic resin, as an example, the necessary characteristics of a support for high performance affinity chromatography (HPAC) are demonstrated. To such a support different ligands can be immobilized and used for the separation of biopolymers.From the range of possible applications a few examples are chosen. Immunoglobulins are isolated in one step by protein A‐HPAC, the purified antibodies are immobilized and applied to immunoaffinity‐HPLC for the isolation of corresponding antigens. Concanavalin A‐HPAC of membrane proteins was chosen to represent chromatography with immobilized lectins. Antithrombin could be isolated from human plasma by the use of immobilized heparin. HPAC has the advantage of affinity chromatography, which is above all highly specific. As the support is resistant to high pressure and has well defined microparticles with a particular pore size, it provides a much higher yield at considerable flow rates. The handling of materials like this is simpler, the separation of the sample is quicker and can be reproduced more easily.
Polymers for the immobilization of whole cells and their application in biotechnology
Authors: Klein J. , Kressdorf B. 
Published: April 2003

AbstractImmobilization of whole cells has become an efficient tool for biosynthesis, biotransformation and analysis. High cell density, high operational stability, easy handling, propably in continuous systems, and multiple reuse are important advantages of immobilized cells. In comparison to other methods like adsorption, crosslinking and encapsulation, the entrapment within a polymeric network is the most widely applied technique in heterogeneous biocatalysis. For immobilizing mammalian cells nearly exclusively the adsorption onto micorcarriers is used. Requirements for the polymers to be used in such immobilized cell systems are discussed in detail.
Morphology and supermolecular structure of the polymer system PA‐6/PMA
Authors: Janicki Jarosław , Włochowicz Andrzej 
Published: April 2003

AbstractThe results of investigations of the supermolecular structure of the mixture of a semicrystalline polymer polyamide‐6 (PA‐6) and of an amorphous one, poly(methacrylic acid) (PMA), are presented. The determination of the supermolecular structure was realized using the correlation functions and the interface distribution functions calculated from SAXS patterns. It was stated that the introduction of poly(methacrylic acid) results in a transformation of the γ‐type crystalline structure into the α‐type structure. Until the PMA content is less than 46%, the blend has a lamellar structure, and an increase in the PMA content causes an increase in the long period. PMA and the amorphous phase of PA‐6 form a homogeneous phase, there are no microdomains of PMA.An increase in the PMA content results in a decrease of the crystallinity index. Simultaneously, the thickness of the transition layers between the crystalline regions and the phase composed of PMA and of the amorphous phase of PA‐6 increases. When the content of PMA is large, the lamellar structure disappears.
Mechanische Eigenschaften von Polyesterfasern bei kurzzeitiger Zugbeanspruchung, 1. Aufbau eines Meßplatzes für schnelle Zugbeanspruchung
Authors: Beier Manfred , Schollmeyer Eckhard 
Published: April 2003

AbstractKraft‐Dehnungs‐Graphen von Filamentgarnen für die Dehngeschwindigkeiten zwischen 10−1 und 105%/s werden ermittelt. Für die niedrigen Dehngeschwindigkeiten bis 10%/s wird eine übliche Zugprüfmaschine benutzt, die höheren Dehngeschwindigkeiten werden mit einer Fallschlagapparatur durch Variation der Fallhöhe und der Fadenlänge erreicht.Aufgrund der hohen Dehngeschwindigkeit und der Meßzeiten bis minimal 10−4 s sowie der Variation der Fallhöhe zwischen 0,6 und 166 cm treten Fehler auf, die eingehend diskutiert werden.
Mechanische Eigenschaften von Polyesterfasern bei kurzzeitiger Zugbeanspruchung, 2. Verformungsgeschwindigkeitsabhängige Kraft‐Dehnungs‐Diagramme von Polyester‐Multifilamentgarn
Authors: Beier Manfred , Schollmeyer Eckhard 
Published: April 2003

AbstractUntersucht werden Polyethylenterephthalat (PETP)‐Multifilamentgarne mit unterschiedlicher thermischer Vorgeschichte.Die Kraft‐Dehnungs‐Kurven für die Dehngeschwindigkeit von 0,1 bis 100 000%/s zeigen, daß die Höchstzugkraft mit der Dehngeschwindigkeit zunimmt und die Höchstzugkraftdehnung abnimmt. Für die Garne mit unterschiedlicher thermischer Vorgeschichte bestehen jedoch Unterschiede, was die Änderung der Höchstzugkraftund Höchstzugkraftdehnungswerte mit der Dehngeschwindigkeit betrifft. So weist ein spannungslos thermisch behandeltes Material eine geringere Änderung der Höchstzugkraft mit steigender Dehngeschwindigkeit auf als ein bei gleicher Temperatur, aber unter Spannung thermofixiertes Material. Die Höchstzugkraftdehnungswerte zeigen dagegen ein umgekehrtes Verhalten. Mit wachsendem Einfluß der Dehngeschwindigkeit auf die Bruchkraft nimmt das Verhältnis von Höchstzugkraft zu Höchstzugkraftdehnung stärker zu.Die Anfangssteigung, d. h. der Anfangsmodul der K‐D‐Kurven des Fadenmaterials, nimmt für alle Fixierspannungen und ‐temperaturen mit der Dehngeschwindigkeit zu. Das lokale Minimum der ersten Ableitung der K‐D‐Kurven (lokales Modulminimum) verlagert sich mit zunehmender Dehngeschwindigkeit zu höheren Modulwerten, die Lage des Minimums als Funktion der Dehnung bleibt jedoch konstant.
DSC studies on melt crystallized, drawn and fuming nitric acid oxidized polyethylene
Authors: Akar Ahmet , Aydoǧan A. Cevdet , Zaim Ömer , Tinçer Teoman 
Published: April 2003

AbstractMelting, recrystallisation and remelting of undrawn and drawn linear polyethylene with different molecular weight were studied by differential scanning calorimetry before and after oxidation with nitric acid.
Eine Studie über den Pyrolysevorgang bei organischen Bindemittelsubstanzen für die Herstellung von Kohlenstoffmaterialien
Authors: Popovska Nadeshda 
Published: April 2003

AbstractMittels Thermo‐ und Röntgenstrukturanalyse wird eine vergleichende Untersuchung des Pyrolysevorganges und der Mikrostruktur des aus zwei Gruppen organischer Bindemittel und deren Mischungen gewonnenen Koksrückstandes durchgeführt. Gruppe I umfaßt reine und mit Hydrolyselignin gefüllte Resol‐ und Novolak‐Phenol‐Formaldehydharze und Gruppe II Steinkohlenpech und ‐teer. Es wird festgestellt, daß sich die Mischungen Novolakharz‐Pech, Resolharz‐Teer und Resolharz‐Hydrolyselignin beim Erhitzen nicht wie mechanische Gemische verhalten und eine erhöhte Ausbeute an Koksrückstand liefern. Weiterhin wird gefunden, daß die integrale Endtemperatur der Pyrolyse (T) dieser Substanzen als quantitatives Maß für die Ausbeute an Koksrückstand im Anschluß an die Carbonisierung der Proben dienen kann.
Chemical modification of rice starch via its reaction with acrylamide
Authors: Haggag K. , Kantouch F. A. , El‐Thalouth I. Abd 
Published: April 2003

AbstractRice starch was carbamoyl ethylated via its reaction with acrylamide in presence of sodium hydroxide under a variety of conditions. Variables included the concentration of acrylamide, the reaction temperature and the preparation medium. It was found that the extent of the reaction increases by increasing the acrylamide concentration. The temperature plays a dominant role in the extent of the reaction. Carbamoyl ethylated starches are water soluble and can be precipitated by ethyl alcohol. Printing pastes thickened with carbamoyl ethyl starch samples are characterized by non‐Newtonian thixotropic behaviour. At a constant rate of shear, the values of the apparent viscosity increase as the nitrogen content of the product increases. Furthermore, increasing the reaction temperature is accompanied by a substantial decrease in the apparent viscosity at a constant rate of shear.