bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lichtstreuung und polydispersität von polymerlösungen. I. Theoretische betrachtungen
Authors: Lechner M. D. 
Published: June 2010

AbstractThe influence of the type of molecular weight distribution function (Gaussian distribution, Schulz‐Flory distribution, log‐normal or Wesslau distribution) and of the distribution function itself on the light‐scattering behavior of polymer solutions is discussed. It is shown that the three types of distribution functions yield characteristic scattering functions Pθ, which permit us to determine the nonuniformity of the polymer and in some cases the type of distribution function.
Light scattering by solutions of tRNA molecules oriented in D.C. magnetic field
Authors: Dobek A. , Patkowski A. , Labuda D. 
Published: June 2010

AbstractLight scattering measurements of macromolecular reorientation in a d.c. magnetic field, predicted and calculated theoretically by Kielich, were carried out for yeast (unfractionated) transfer ribo‐nucleic acids (tRNA) solutions of concentrations ranging from 0.001 g/cm3 to 0.05 g/cm3. The vertical and horizontal intensity components of light, scattered at 90° to the incident beam, were measured. The d.c. magnetic field parallel to the direction of observation was fixed in the 0‐20 kOe interval. These studies, together with previously performed Rayleigh light scattering measurements, permitted evaluation of the NaCl and nucleic acid concentration range in aqueous solutions in which tRNA molecules occurred in the monomer form. In concentrated salt solutions tRNA molecules associate with the highest probability parallel to their long axes. Light scattering studies in an external d.c. magnetic field showed the anisotropy of optical and magnetic polarizabilities of tRNA molecules to be negative. The conclusion from scattering measurements concerning the conformational changes of tRNA molecules in solutions of different ionic conditions are compared and discussed with data from the literature. The described method is suggested for studies of biological macromolecular complexes in vitro.
Laser light scattering and polydispersity of polymers
Authors: Meyerhoff G. , Hack H. , Raczek J. 
Published: June 2010

AbstractThe application of lasers to light scattering improves the potentials of elastic scattering, especially in the high molecular weight range and enables the technique of inelastic scattering to be used.For elastic light scattering an experimental arrangement and an evaluation method is described which allows, within appropriate molecular weight ranges, the determination of the ratio Mw/Mn from the experimental scattering function with an accuracy down to 0.02.The newer technique of inelastic light scattering yields the coefficient of translational diffusion D. Besides D, the friction coefficient f is also directly accessible. The basic equations are reported, as well as an application to mixtures of two nearly monodisperse polymers. Always a z‐average is obtained.
Complete temperature dependence of the far infrared absorption spectrum of linear polyethylene from 14°k to the melting point
Authors: Frank W. , Schmidt H. , Wulff W. 
Published: June 2010

AbstractIn the far infrared, polyethylene shows two absorption bands: a very strong one at 73 cm−1 and a weak one centered at 109 cm−1 which is only observable below 160°K. From the frequency and temperature dependence of the 73 cm−1 band, the maximum frequency shift, the peak height, integrated absorption intensities, and the integral half‐width are determined. The frequency shift with temperature is shown to be a linear function of the related lattice parameter. A comparison with the temperature behavior of the CH2‐rocking vibration at 730 cm−1 is given.
Blends of poly(ϵ‐Caprolactone) with poly(vinyl chloride). I. Morphology
Authors: Ong C. J. , Price F. P. 
Published: June 2010

AbstractThe morphology of blends of poly(ϵ‐caprolactone) (PCL) with poly(vinyl chloride) (PVC) was investigated. The observations made with the optical microscope and electron microscopes indicate that for the blends rich in PCL, the samples are almost completely filled with spherulites composed of lamellas radiating from the spherulite center and twisting regularly. As the concentration of PVC increases, the texture of the spherulites becomes increasingly coarse and open. The results of the elementary analysis, made with an x‐ray spectrometer, indicate a uniform distribution of chlorine atoms in the blends regardless of the composition. X‐Ray diffraction studies reveal that the unit cell dimensions of PCL are not changed by the presence of PVC. It is believed that the PVC molecules were trapped within the spherulites and rejected preferentially into interlamellar regions. The results of differential scanning calorimetry measurement show that the crystallinity of PCL decreases with increasing PVC content. PCL in the blend containing more than 70% PVC exhibits no tendency to crystallize. The blends show a depression of the melting point of PCL. Over a wide range of composition, the blends display a single glass transition intermediate between the transition of the respective components. The glass transition shows a systematic increase with PVC concentration.
Effect of free‐volume fluctuations on polymer relaxation in the glassy state
Authors: Robertson Richard E. 
Published: June 2010

AbstractAs is most clearly seen in the results of A. J. Kovacs on the volumetric relaxation following changes in temperature, the initial relaxation in polymers is surprisingly rapid, considering how slowly relaxation becomes later. We suggest that this rapid initial relaxation is due to relaxing molecular rearrangements in regions of particularly high free volume produced by thermal fluctuations. The magnitude of thermal fluctuations increases as the size of the region decreases, and molecular rearrangements are described that probably contribute to most polymer relaxation and seem to be completely contained in regions as small as 2–3 nm.
Crystal nucleation and the crystalmelt interfacial tension in linear hydrocarbons
Authors: Turnbull David , Spaepen Frans 
Published: June 2010

AbstractRecent results on the homogeneous nucleation of crystals in n‐alkane (CnH2n+2) melts are used in conjunction with simple nucleation theory to calculate scaled crystal‐melt interfacial tensions, α (n), per CH2 group. α(n) falls off smoothly and, at first, sharply with n increasing to 12–15, where it levels and remains roughly constant at ca. 0.15 to n = 32, at least. We show that these results are accounted for satisfactorily by the Spaepen‐Meyer negentropic model for the crystal‐melt tension, if it is assumed that there is high probability for the occurrence, within the melt, of planar conformations persisting for 14–15 C atoms.
Formation properties of solid‐state extruded high density polyethylene fibers
Authors: Mead W. T. , Porter Roger S. 
Published: June 2010

AbstractExtrusion rates have been measured for high density polyethylene fibers prepared by solid‐state extrusion through a conical die with maximum draw ratio of 52, using constant pressure and temperatures ranging from 0.12 to 0.49 GPa and 60° to 140°C and molecular weights from 5 × 104 to 6 × 106. The processing variables are reported in terms of an apparent elongational viscosity. The logarithm of the extrusion rate was proportional to the applied pressure. Deviation from the Eyring theory of viscosity was found, since lowering of the extrusion temperature to 60°C produced an anomalous decrease in the extrusion rates. The anomaly was explained by the increased friction between die and polymer, the pressure dependence of the yield stress, and by the pressure dependence of the α‐relaxation mechanism. Apparent activation energies of 60 and 100 kcal/mole were calculated for the solid‐state extrusion in the region 100°–130°C and 80–100°C. Three modes of deformation were observed for each extrusion, consisting of an unsteady state, a second stage of drawing in which the extrusion rate approached a constant value, and a fracture region. The first mode corresponded to orientation and rotation of the crystalline lamellae, as shown by the rapid increase and plateau region of the crystalline and noncrystalline orientation functions. During the second stage of deformation, the apparent elongational viscosity ηE increased linearly with draw ratio, as did the modulus, and this mode was found necessary for the attainment of high modulus fibers. The second mode of deformation was associated with the deformation of the crystalline lamellae and strain hardening in which ηE‐approached that for a glass. Strain hardening readily occurred with decreasing temperature, and increasing draw ratio and molecular weight. Continuous extrusion producing uniform modulus fibers was only possible when the maximum draw ratio of the die was less than the fiber draw ratio, where strain hardening occurred. The third mode of deformation limited the maximum modulus obtainable and consisted of fracture or kink planes oblique to the fiber axis. The relations between the processing variables used in the solid‐state extrusion and the resulting fiber properties are discussed.
Topological model of the crystalline morphology in polyethylene with grafted defects
Authors: Drǎgan Gh. 
Published: June 2010

AbstractThe most important results obtained on polyethylene morphology as a function of thermal, mechanical and chemical treatments are reviewed. Amorphous–crystalline coupling in high density polyethylene with grafted defects by photochlorination is quantitatively studied by differential thermal analysis using six parameters. The model of this coupling is discussed in terms of the topological thermodynamics.
Contributions to vinyl chloride suspension polymerization with constant rate
Authors: Feldman D. , Macoveanu A. 
Published: June 2010

AbstractIn the present paper the authors study the possibility of conducting vinyl chloride suspension polymerization at constant rate using a temperature program, as well as some physical and morphological characteristics of the obtained polymer. The elaboration of the temperature program necessary for conducting vinyl chloride suspension polymerization with constant rate was realized by two different means: empirical, on the basis of experimental data, and theoretical, on the basis of a mathematical model, which describes the kinetics of suspension radical vinyl chloride polymerization. In performing the polymerization with constant rate, the design of caloric exchange surfaces becomes much easier, an optimal using of the reaction space being in the same time ensured during the whole time of the process. The interpretation of experimental data permits us to affirm that by polymerization with constant rate can be obtained a poly(vinyl chloride) similar to the polymer with the same average molecular weight synthesized at a constant temperature with slightly weaker volumetric properties but some better thermal stability.
Liquid–crystalline solutions of polyhydrazides and poly(amide‐ hydrazides) in sulfuric acids
Authors: Morgan P. W. 
Published: June 2010

AbstractPara‐linked aromatic polyhydrazides and poly(amide‐hydrazides) can be dissolved in sulfuric acid of about 100% concentration to form liquid–crystalline solutions, and if the solutions are not heated excessively, they are reasonably stable and can be spun into strong fibers. Similar results can be obtained in fluorosulfonic acid and its admixtures with sulfuric acid. Polyhydrazides and copolyhydrazides based on oxalyl, terephthaloyl, chloroterephthaloyl, and 2,5‐pyridinedioyl units and poly(amide–hydrazides) based in part on such intermediates as 4‐aminobenzhydrazide and terephthalic dihydrazide were examined for formation of optically anisotropic solutions. Polymers with high proportions of meta‐ and ortho‐linked ring units were highly soluble but did not yield liquid–crystalline solutions.
Synthesis, characterization, rheological, and fiber formation studies of p‐linked aromatic polyamides
Authors: Aoki Hiroshi , Coffin David R. , Hancock Tony A. , Harwood Daniel , Lenk Rudolph S. , Fellers John F. , White James L. 
Published: June 2010

AbstractAromatic polyamides are being extensively studied in our laboratories along the lines of synthesis, dilute solution viscosity and light scattering, concentrated solution optical and rheological measurements, and wet spinning of fibers. Several series of polymers have been synthesized, including those starting with chloro‐ and methyl‐substituted p‐phenylene diamine and also those starting with the monomer bisacid A2. Poly(chloro‐p‐phenylene terephthalamide) in dilute solution shows a marked hydrodynamic volume dependence on solvent when studied in DMA–5% LiCl versus H2SO4 At higher concentration, optical characterization shows that liquid crystal formation in the quiescent state corresponds to changes observed in the rheological behavior for Kevlar–H2SO4 solutions; these observations include a yield stress and the inversion of the order ofG/G' = tan 5. Fibers produced by wet spinning and subsequently studied in cross section via SEM have revealed that material continuity is easily attained with Kevlar‐H2SO4 spinning dopes under a variety of processing conditions.
Properties of a phenyl‐substituted polyphenylene in dilute solution
Authors: Work James L. , Berry Guy C. , Casassa Edward F. , Stille John K. 
Published: June 2010

AbstractThree preparations of a phenyl‐substituted polyphenylene were fractionated and studied in solution by light scattering, osmometry, viscometry, fluorescence depolarization, and exclusion chromatography. Three of the five main‐chain phenylene groups in the repeat unit are linked para, but the other two may be either meta or para, with the latter linkage predominating. The data are consistent with a chain structure characterized by rigid segments about 70–75Å long, on the average, joined with 120° bond angles, about which virtually free rotation is allowed. For chains of up to about 250 backbone phenylene units, the hydrodynamic behavior in tetrahydrofuran, and other solvents, is that of a freely draining coil with intrinsic viscosity proportional to molecular weight. The effect of intramolecular excluded volume on chain conformation is negligible, although intermolecular interactions are reflected by a positive second virial coefficient (in tetrahydrofuran). Study of polymers of higher molecular weight is hampered by formation of what appear to be metastable aggregates resembling randomly branched chains.
Effect of the length and structure of the side chain of soluble copolymers of the methacrylamide type on the mobility of the spin label bonded to the chain end
Authors: Labsky J. , Pilar J. , Kalal J. 
Published: June 2010

AbstractResults are reported obtained by the ESR study of the mobility of spin labels bonded at the side‐chain ends of copolymers of the polymethacrylamide type. The correlation times, γ, characterizing the mobility of the spin label were determined by analyzing the EPR spectra of 1% methanolic solutions of copolymers. The log γ vs 1/T dependences within the temperature interval 233‐313 K studied are linear and are characterized by the same activation energy, Ea = 3 kcal/mole (12.5 kJ/mole), for both types of the side chains. The mobility of the spin label bonded at the end of the side chain of the oligoglycine type is lower than that of the spin label bonded at the end of the equally long side chain of the methylene type.
Polyaspartamide — a potential drug carrier
Authors: Drobník J. , Saudek V. , Vlasák J. , Kálal J. 
Published: June 2010

AbstractThe molecular weight of polysuccinimide prepared by thermal polycondensation depends mostly on the reaction temperature. Antioxidants have no effect. Proteolytic enzymes do not degrade the main chain of N‐substituted polyaspartamides tested. Bacteria are capable of utilizing about 4% of aspartic acid from the 2‐hydroxyethyl derivative. Side chains are sensitive to enzymes as in the previously studied polyolefinic polymers.
Application of polysaccharides and their derivatives as supporting materials and auxiliary substances in medicine and nutrition
Authors: Philipp B. , Bock W. , Schierbaum F. 
Published: June 2010

AbstractGiven certain peculiarities of polysaccharides in comparison to synthetic polymers, a survey is made of the application of polysaccharides in the field of nutrition for calory‐reduced food, in pharmacy, and as auxiliary products in surgery, stressing to some extent recent results of the authors in cellulose and starch chemistry. In dealing with nutritional uses in calory‐reduced food, the problem of persorption of cellulose powders is discussed as well as properties and uses of recently developed starch products obtained by partial hydrolysis. In reviewing pharmaceutical uses of polysaccharides, we mention the active therapeutic effects of these substances, with detailed emphasis on the application of starch and cellulose products as carrier compounds. A survey of polysaccharide products as surgical auxiliaries is centered on their application as plasma expanders, as internal surgical dressings, and as external aids (glove powders). Finally, the need for further progress in polysaccharide chemistry is stressed as a prerequisite for finding and realizing new applications in restoring human health.
Problems of matrix activation in using the cyanogen bromide method
Authors: Pommerening K. , Jung W. , Kühn M. , Mohr P. 
Published: June 2010

AbstractThe CNBr used to activate carriers for covalent binding of biologically active substances must not contain free cyanide ions. Several carrier materials, such as poly‐2‐hydroxy‐ethyl methacrylate (Spheron) or cellulose, adsorb cyanide ions that cannot be removed by thorough washing. But when these carriers are incubated with substances or ions showing high affinity for cyanide ions, such as methemoglobin or Fe2+, then as a result of complexing, desorption from the carrier and inhibition of the fixed or incubated substances are effected.
The kinetic specificity of polyethylene terephthalate degradation in the living body
Authors: Rudakova T. E. , Zaikov G. E. , Voronkova O. S. , Daurova T. T. , Degtyareva S. M. 
Published: June 2010

AbstractThe kinetic specificity of polyethylene terephthalate (PET) degradation in a living body was investigated. The polyethylene terephthalate net implanted subcutaneously in the backs of rabbits and dogs usually degrades from the surface very slowly. The time of complete degradation of PET fibers in both dogs and humans amounts to 30 ± 7 yr. The time for loss of 50% of the initial filament strength under similar conditions is 10 ± 2 yr. An equation for promotion of changes in the mechanical properties of polyethylene terephthalate fibers in living animals and humans has been derived.
Synthetic polymers with anticoagulant activity
Authors: Van Der Does L. , Beugeling T. , Froehling P. E. , Bantjes A. 
Published: June 2010

AbstractPolymers with C=C bonds have been modified by reaction with chlorosulfonyl isocyanate (CSI). Addition products were obtained in yields varying from 60% to 75%. Reaction of these products with NaOH yielded polyelectrolytes with sulfamate and carboxylate groups, whereas from the reaction with NH4OH polyelectrolytes with sulfamate and carbonamide groups, were obtained. The polyelectrolytes showed anticoagulant activity depending on the structure and on the presence of both sulfamate and carboxylate groups. These groups are essential for the anticoagulant activity, because N‐S bond cleavage in the sulfamate groups as well as substitution of carboxylate by carbonamide groups resulted in loss of activity. From the recalcification times of bovine plasma, it could be concluded that the most active polyelectrolyte had an activity of 6‐7% compared with heparin. However, determination of the activated clotting time of blood from rabbits showed that this compound had an in vivo activity of 50% in comparison with heparin.
Blood‐compatibility‐water‐content relationships for radiation‐grafted hydrogels
Authors: Ratner B. D. , Hoffman A. S. , Hanson S. R. , Harker L. A. , Whiffen J. D. 
Published: June 2010

AbstractA series of radiation‐grafted hydrogels with water contents ranging from 10% to 90% have been prepared. When evaluated by the vena cava ring test, increasing amounts of adherent thrombus were found in rings with lower graft water contents. Using a baboon arteriovenous shunt evaluation system, platelet thromboembolic consumption was found to be directly proportional to graft water content. Hydrogels studied by the renal embolus ring test were found to cause numerous infarcts in the kidneys of test animals. Results from these studies do not support “water‐content‐blood‐compatibility” hypotheses which have been suggested for hydrogels. Results obtained with a series of hydrophilic‐hydrophobic copolymers suggest that a balance of polar and apolar sites at a polymer‐surface may be important for blood compatibility. The significance of results from the three evaluation systems used is discussed.
Platelet adhesion from human blood to bare and protein‐coated polymer surfaces
Authors: Neumann A. W. , Moscarello M. A. , Zingg W. , Hum O. S. , Chang S. K. 
Published: June 2010

AbstractA static platelet adhesion test using whole human blood was employed to assess the affinity of various bare polymer (sulfonated polystyrene, acetal resin, Teflon FEP, polystyrene) surfaces as well as various surfaces of glass and polymers that were coated with plasma proteins. Platelet adhesion to the bare polymer surfaces was found to increase with increasing solid surface tension of the substrate. With protein‐coated glass and polymer surfaces, however, platelet adhesion did not follow the above pattern; more platelets adhered to the fibrinogen‐coated surfaces than to albumin‐coated surfaces. The solid surface tension of the underlying substrate also influenced the adhesion of platelets to the protein‐coated surfaces; platelet adhesion to the proteincoated high‐energy sulfonated polystyrene substrates was found to be greater than to the corresponding protein‐coated lower‐energy substrates of acetal resin and Teflon FEP.
The interaction of polymer surfaces with blood
Authors: Beugeling T. 
Published: June 2010

AbstractSome general aspects of the interaction of foreign materials with blood are summarized. The role of protein adsorption in this interaction is briefly discussed. In an attempt to produce more stable antithrombogenic surface coatings than the well‐known heparin‐bonded surfaces, a method is described in which a high‐molecular‐weight polyelectrolyte is bound to polymer surfaces. In vitro experiments carried out with freshly drawn human blood show a reduced platelet adhesion on such surfaces.
The role of adsorbed proteins in platelet adhesion onto polymer surfaces
Authors: Kim Sung Wan , Lee Eun Soo 
Published: June 2010

AbstractPolymer surfaces adsorb plasma proteins upon contact with blood. The nature of this adsorbed layer may determine the extent of platelet adhesion onto these surfaces. It is proposed in this study that incomplete terminal oligosaccharides, galactose, and N‐acetyl‐glucos‐amine in adsorbed fibrinogen and γ‐globulin are mainly responsible for the platelet adhesion, possibly via glycosyl transferase reactions. In order to verify these proposed mechanisms, platelet–protein interactions in the bulk state and platelet aggregation caused by the interactions were studied. The study was further extended into the reactions of platelets with adsorbed proteins. Data on protein adsorption from blood plasma onto model polymers (Teflon FEP, silastic rubber, Avcothane, and Biomer) provide supportive evidence for the proposed mechanism. The results discussed in this paper emphasize the important role of protein adsorption onto polymer surfaces and the possible involvement of specific reactions in platelet adhesion.