bluuebunny/crossref_metadata_2025_split huggingface dataset:
Properties of polypropylene fibers made from polymer homologue mixtures
Authors: Geleji Frigyes , Kóczy László , Fülöp István , Bodor Géza 
Published: June 2010

AbstractFibers from mixtures of two polypropylene types were produced with the same conditions. The polymer base was a normal fiber grade polymer to which a high molecular weight polypropylene was added in amounts of 25, 50, and 75%. The extensibility of the fibers changed considerably by increasing the high polymer amount. The tensile properties were measured and compared with measured structural properties, such as crystallinity, crystalline particle size, amorphous orientation, amorphous region derived from small and wide‐angle X‐ray scattering. New terms, the specific amorphous orientation and the structural deformability index, were proposed, and it was shown that the tensile properties, i.e., strength, elongation at break, initial modulus and sonic modulus, are in very good correlation with them.
Method for the quantitative characterization of the supermolecular structure of highly oriented polymers
Authors: Jungnickel B. J. 
Published: June 2010

AbstractThe morphology of polymers having fiber texture is commonly considered to consist of a fibrillar structure. The author proposes a method for the quantitative description of the internal structure of the fibrils by analysis of X‐ray small‐angle scattering patterns. A theoretically relevant quantity, “morphology index” (μ) characterizing the fibril morphology can be calculated from structure parameters. Microfibrillar (μ » 1) and lamellar (μ « 1) structures represent limiting cases of the actual structural order. The dependence of μ on the temperature was determined for a series of fixed ends annealed polyamide‐6 filaments. A distinct change from the microfibrillar to the lamellar structure was verified, with slight increase of the microfibrillar character up to 140°C. With drawn polyamide‐6 samples the morphology index remains unchanged, in spite of slight changes of individual parameters, such as crystallite size, and weak shearing of fibrils. This suggests that drawing does not lead to essential changes of the internal structure of fibrils.
Isothermal growth, thickening, and melting of polyethylene oxide) single crystals in the bulk. II
Authors: Kovacs A. J. , Straupe C. , Gonthier A. 
Published: June 2010

AbstractCharacteristic features of isothermal growth, thickening, and melting of melt‐grown single crystals of poly(ethylene oxide) fractions, as reported in a recent paper, are complemented and further discussed. A newly discovered phenomenon–isothermal superheating–is described and its implications are discussed. Growth and thickening rate data are analyzed in terms of the two independent molecular parameters which determine the lamellar thickness: the number, n, of folds per molecule and the total chain length, λ Current formulations of kinetic theories are critically analyzed in view of their applicability to the present growth rate data. The analysis reveals that, for the low‐molecular‐weight fractions, the theory only applies to fast growth obtained at high undercooling. At low undercooling, where molecules deposit in extended or n‐times folded‐chain conformation, however, growth proceeds by a nucleation mechanism which appears to be quite different from that implied by the theory.
Determination of the conformation of polyelectrolytes in solution by small‐angle neutron elastic scattering
Authors: Moan Michel , Wolff Claude , Cotton Jean‐Pierre , Ober Raymond 
Published: June 2010

AbstractThis is a survey of recent experimental results obtained by small‐angle neutron scattering on the conformation of polyelectrolytes in the dilute and semidilute regime, in solutions both with and without salt. Some scaling laws are included.
Phase‐separation phenomena in solutions of poly(2,6‐dimethyl‐1,4‐phenylene oxide). III. Pulse‐induced critical scattering of solutions in toluene
Authors: Koenhen D. M. , Smolders C. A. , Gordon M. 
Published: June 2010

AbstractFor the polymer‐solvent system poly(phenylene oxide) in toluene the mechanism and kinetics of crystallization have been studied with the Pulse Induced Critical Scattering technique. It was found that after a delay‐time τ the growth mechanism was diffusion controlled. The delay‐time is thought to be connected with the nucleation of the crystallites and it disappeared in the “seeded” crystallizations studied. After incomplete melting of crystallites the first stages of growth resemble a condensation reaction.
The form‐anisotropy in light scattering: Experimental study of the validity of the rayleigh‐gans‐debye type approximation
Authors: Ravey Jean‐Claude 
Published: June 2010

AbstractSome experimental evidence of the validity of the (extended) Rayleigh‐Gans‐Debye approximation when used to describe the anisotropic form of not very small particles (α < 5) is presented. This approximate theory affords results of reasonably good value for each case where exact analytical expressions occur for small particles (α < 1).
Light scattering by large ellipsoidal particles. II. Determination of optical anisotropy by polarization ratio
Authors: Petres J. J. , Deželić Gj. 
Published: June 2010

AbstractPolarization ratios of monodisperse ellipsoidal particles of barium sulfate were determined at wavelengths of 546 and 436 nm, and the optical anisotropy was determined. A significant increase of the optical anisotropy with the increasing axial ratio of particles was found. A part of the optical anisotropy can be ascribed to the anisotropic form, but the other portion is a consequence of the internal anisotropy of the barium sulfate particles.
Thermokinetics of formation of polymeric mesomorphous phases in block copolymers and polymer mixtures
Authors: Frenkel S. 
Published: June 2010

AbstractAn attempt is made to treat the formation of supercrystalline lattices in solution of melts of block copolymers on the macromolecular level using the effective flexibility parameters appearing in the equivalence principle of thermokinetics. All known data are in accord with the assumption which proposes an extremal dependence of the interaction of χ and χAB parameters on composition (χAB attaining its maximal value at A/B molar ratios close to unity). Therefore, the effective flexibility parameters fA and fB characterizing the corresponding blocks should pass through a minimum close to the χ maxima, the lines for fA and fB being, however, somewhat shifted along the composition axis. At first sight this type of behavior fits the experimental data, but closer consideration shows that the assumption of chain extension due to segreation inherently appearing in the whole concept does not hold.Therefore the situation is reconsidered, and it is shown that if the units (i.e., spheres, cylinders, and lamellae) occupying the sites of the superlattice are treated as “supermacromolecules” (or structons, following a somewhat improved definition of Huggins) the earlier theory holds.Moreover, it is shown that the supercrystals can be treated in terms of the kinetic theory of liquids and real crystals which leads to a understandable explanation of their unusual properties, especially their high thermal stability. Probably a general theory starting from ideal supercrystals may be developed by means of a stepwise introduction of paracrystalline defects (in the manner of Hosemann) in the lattice. The most disordered paracrystalline lattices will then correspond to polymer blends.Special attention is given to the formation of ordered structures from extended (or extruded) binary melts, the segregation parameter ϕAB being high, but where no junctions between A and B components occurs. This corresponds to the so‐called Yudin effect, and a catastrophic deliberation of the excess enthalpy of mixing on elimination of the noncrystallizable component (matrix) leads to an annihilation of the nematic units on annealing, thus showing the influence of the ϕAB parameter on the thermodynamic and morphologic properties of the structon forming component.Finally, something of the nature of ϕAB in phase equilibria during polymerization and its influence on the molecular‐weight distribution of branches during the course of graft copolymerization are considered.
The adsorption of macromolecules on solid/liquid interfaces
Authors: Killmann Erwin , Eisenlauer Josef , Korn Milan 
Published: June 2010

AbstractEllipsometric results obtained from the adsorption of polystyrene, poly(methyl methacrylate) and poly(ethylene glycol) on chrome, gold, and platinum surfaces out of different solutions are reported and the influences of the different interactions are discussed. From the IR spectrometric and calorimetric results for the adsorption of poly(ethylene glycol)s and for low molecular weight model substances, the fractions of adsorbed segments and binding enthalpies are deduced. With the aid of conformation models for the adsorbed macromolecules, the measured values and their dependence upon concentration, molecular weight, and type of polymer, as well as the kind of solvent and the condition of the adsorbent's surface, are discussed. Sedimentation and viscosity measurements and results concerning Aerosil suspensions are discussed and compared with the adsorption data.
Effect of shear on the crystallization kinetics of poly(ethylene oxide) and poly(e‐caprolactone) melts
Authors: Sherwood C. H. , Price F. P. , Stein R. S. 
Published: June 2010

AbstractThe effect of shear on polymer crystallization kinetics has been studied for three materials at several shear rates and degrees of supercooling. Two poly(ethylene oxide) samples, with molecular weights of 72, 200 and 12, 600, and a poly(e‐caprolactone) material, with a molecular weight of 9, 400, were investigated. The apparatus used was a concentric cylinder viscometer, which also functions as a dilatometer, capable of detecting very small volume changes on crystallization. The shear‐rate range of the experiments was 0 to 60 sec−1. Avrami kinetics were used to describe the transformation process and the exponent was found to increase from the quiescent value of 3 to a value greater than 5 with increasing shear rate for all materials studied. The acceleration in the transformation process was associated with a reduction in induction time. The value of induction time at high shear rates did not significantly decrease with increasing shear rate, indicating a saturation effect with shear. This was most pronounced in the low molecular weight samples. The value of induction time for the high molecular weight poly(ethylene oxide) sample, under identical experimental conditions, was substantially less than that of the low molecular weight material in all cases. Nuclei formation measurements were made for the crystallizing melt in a separate instrument. Nuclei formation under shear was very different from quiescent behavior and increased substantially with increasing shear rate. These experimental observations lead to the conclusion that accelerated crystallization is due to increased molecular chain extension and orientation under shear. This orientation greatly enhances the nucleation process, which is thought to be the rate controlling step in the crystalline transformation. This enhancement results in shorter induction times and more rapid crystallization.
The differential scanning dilatometer and phase transitions in liquid crystals
Authors: Armitage D. , Price F. P. 
Published: June 2010

AbstractThe performance of a differential scanning dilatometer is described in terms of the volume changes recorded near the isotropic to cholesteric transition for cholesteryl laurate. The instrument is also applied to a study of crystallization kinetics. The isotropic–nematic phase transition in p‐azoxyanisole was also examined by optical microscopy. An instability in the phase boundary is observed at increasing transformation rates. Size effects on this transition are investigated by absorbing the sample in porous silica. The transition is depressed 0.3°K in a 300 Å diameter pore.
A method for obtaining high modulus polyethylene from the melt: The influence of crystal nucleation
Authors: Keller A. , Odell J. A. 
Published: June 2010

AbstractA method is presented by which polyethylene filaments of exceptionally high modulus (500–1000 kbar) can be prepared from flowing melts. The method relies on the formation of fibrous crystals which are directly flow–induced, but are present in sufficiently small quantities not to block the flow of the melt. If the rest of the still uncrystallized material is induced to crystallize onto these fibers, which then serve as nuclei, under enhanced hydrostatic pressure, the ultrahigh moduli are obtained. In addition to their relevance to mechanical behavior these observations point to some novel aspects of crystal nucleation by fibrous substrates and to the way such nucleation can influence the modulus.
Problems with the popular theory of linear viscoelasticity
Authors: Farris Richard J. 
Published: June 2010

AbstractThe popular theory of linear viscoelasticity based upon representations using distributions of relaxation or retardation times is shown to be a subset of admissible response functions for these materials. The essential missing feature in the popular theory is that it cannot yield a zero energy dissipation rate at short times or high frequencies. Consequently, truly elastic response from an energy point of view cannot be contained in such models of viscoelastic behavior. It is shown that this limitation can be removed if models which include molecular inertial effects are included. It is also shown that the free‐energy functional and the energy‐dissipation functional cannot be uniquely determined from the stress‐strain response and that popular constraints placed on the relaxation functions are overly restrictive and limit otherwise admissible response.
Nucleation and crystal growth in sheared poly(1‐butene) melts
Authors: Wolkowicz Michael D. 
Published: June 2010

AbstractThe nucleation and growth behavior of a poly(1‐butene) melt has been measured as a function of undercooling and shear rate. Experiments were conducted using a parallel‐plate rotary shearing device with polarized light microscopy as the measuring technique. An exponential increase of nuclei with time at constant undercooling and shear rate was found. Growth rates of the crystalline bodies showed no significant change in a shear field. Nucleation and growth rate data were analyzed using expressions of the form I = I0 exp [‐ΔE/RT ‐ UTm/TΔT] G = G0 exp [‐ΔE/RT ‐ UTm/TΔT] where ΔT is the undercooling, Tm is the equilibrium melting temperature, and U contains lateral s̀ and end‐surface s̀e free energies. The value of s̀s̀e calculated from U for crystallization under shear differed from that calculated for the quiescent case by a factor of two. This difference is tentatively explained in terms of an entropy loss in the sheared system.
Some aspects regarding the structure and the mechanism of the PVC synthesis
Authors: Caraculacu A. , Buruiană E. , Robilă Gabriela 
Published: June 2010

AbstractThe behavior of models of PVC‐unsaturated end groups subjected to radical reactions indicates the important role some of these groupings play in the after‐polymerization processes. As a result the respective groups lead to new types of abnormal structures in PVC. The PVC head‐to‐head macroradical is thought to play an essential role in the branching formation and the occurring of the interruption processes leading to labile unsaturated end groups. Based on these results correlated with direct measurements of unsaturated structures in PVC, a reaction mechanism is suggested to explain these phenomena.
Preparation of poly amides via the phosphorylation reaction. I. Wholly aromatic polyamides and polyamide‐hydrazides
Authors: Preston J. , Hofferbert W. L. 
Published: June 2010

AbstractAromatic polyamides of the AB, AA–BB, and ordered copolyamide types plus aromatic hydrazide and amide–hydrazides were prepared via the phosphorylation reaction. The relationship of the molecular weight, as evidenced by the inherent viscosity values obtained, of the several polymers to the structural features and properties of the monomers used and the polymers obtained is discussed in detail. Some salient observations are that poor solubility of the rodlike polymers definitely appears to set limits to obtaining high molecular weight and strongly basic groups, e.g., —CO—NH—NH2, in monomers, prevent the attainment of high molecular weight because such groups coordinate more strongly with the phosphite complex than does the pyridine catalyst in the phosphorylation reaction. Fibers were spun from two aromatic polyamides prepared via the phosphorylation reaction. Excellent tensile properties were achieved for fiber from poly–p–benzamide (PPB) and the polyisophthalamide of 4, 4′‐methylenedianiline despite the relatively low molecular weight of these polymers (?7inh 1.6 and 1.1, respectively). The PPB fiber was spun from both isotropic and anisotropic spinning solutions. Fiber obtained from the anisotropic dope had moderately high tensile strengths (8–12 gpd) and remarkably high initial modulus values (435–745 gpd). These results indicate that polymers made by the phosphorylation route would give fibers with as high tensile properties as polymer made by the diacid chloride‐diamine polycondensation route providing that the inherent viscosities of polymer prepared by the former process could be increased to equal those by the latter process.
The polymerization of phenylacetylene in the presence of ferric acetylacetonate and triethylaluminum
Authors: Nguyen H. X. , Amdur S. , Ehrlich P. , Allendoerfer R. D. 
Published: June 2010

AbstractThe polymerization of phenylacetylene initiated by ferric acetylacetonate and triethylaluminum was studied over the temperature range −30°−70°, in bulk as well as in the presence of diluents, and over a range of catalyst compositions and concentrations. The product consisted of four major fractions: crystalline polymer of molecular weight about 7000 and a very narrow molecular‐weight distribution (MWD), (fraction I); somewhat lower‐molecular‐weight amorphous polymer with a broader MWD (fraction II); linear oligomer (fraction III); and the asymmetric cyclic triphenyl‐benzene (fraction IV). The average degree of polymerization, of fraction I (65–70) is independent of all polymerization variables, that is, temperature from −30° to 70°C, the presence or absence of diluent (tetralin or benzene), and catalyst concentration and composition. The MWD is narrow with M̄w/M̄n equal to 1.05 or less. The results suggest that thermodynamic rather than kinetic factors limit the size of the polymer. A possible mechanism is proposed.
Ultrahigh‐modulus fibers from rigid and semirigid aromatic polyamides
Authors: Alfonso Gian Carlo , Bianchi Estella , Ciferri Alberto , Russo Saverio , Salaris Franco , Valenti Barbara 
Published: June 2010

AbstractIntrinsic viscosity, concentrated‐solution viscosity, and fiber properties of poly(p‐benzamide) (PBA) and the polyterephthalamide of p‐aminobenzhydrazide (X‐500) are presented. PBA yields high‐modulus fibers from solution spinning of anisotropic dopes, and X‐500 yields high‐modulus fibers from isotropic solutions. Both polymers exhibit a wormlike conformation. However, with a low‐molecular‐weight PBA (10,500) an essentially rigid conformation prevails. The viscosity of both polymers goes through a maximum and a minimum on increasing polymer concentration. However, for PBA the maximum and minimum are observed at low shear stress, and for X‐500 the discontinuity is observed only at high shear rate. The initial modulus of low‐molecular‐weight PBA fibers is unaffected by LiCl concentration but increases with polymer concentration of anisotropic dopes. X‐500 (molecular weight, 41,000) is unable to form an anisotropic solution at rest. The initial modulus of X‐500 is unaffected by LiCl but depends slightly on polymer concentration. Both shear and elongational flow contributions appear to be secondary for truly stiff polymers. Orientation is controlled by polymer concentration, and the modulus of low‐molecular‐weight PBA attains the ultrahigh level even for “as‐spun” fibers. On the contrary, control of shear and elongational parameters is shown to be essential, and feasible, in order to match the as‐spun modulus of PBA, with semirigid polymers unable to form anisotropic solutions at rest.
A new technique for molding poly(hema) gels
Authors: Štol M. , Šulc J. , Stoy V. , Raab M. 
Published: June 2010

AbstractA new technique for molding poly(2‐hydroxyethyl methacrylate)—poly(HEMA) is outlined which offers some advantages over existing procedures such as polymerization casting or mechanical processing of polymerized blocks. This technique also extends the possible biomedical applications of this material.
The influence of probe concentration on the determination of tg in polymers by inverse gas chromatography
Authors: Llorente M. A. , Menduiña C. , Horta A. 
Published: June 2010

AbstractRetention volumes are studied as a function of probe concentration in order to establish the optimum conditions to detect the polymer glass‐transition temperature. Poly (cyclohexyl methacrylate) is used as stationary phase and the probes tested are benzene (good solvent), 4‐heptanone (moderate solvent), n‐decane, and n‐dodecane (nonsolvents). At temperatures below Tg, a diffusion limited process (probably bulk penetration of the probe in the glassy polymer) is present over a range of probe concentrations. In the case of benzene, this process persists in up to very large concentrations and is responsible for the difficulties in the determination of Tg encountered previously with such a good solvent. By properly choosing the probe concentration, it is possible to minimize the influence of such a process and to obtain Tg estimates (with all the probes tested, including benzene) which are in quantitative agreement with the value determined by differential scanning calorimetry.
Low‐temperature calorimetry of biological macromolecule solutions
Authors: Andronikashvili E. L. , Mrevlishvili G. M. , Japaridze G. Sh. , Sokhadze V. M. , Tatishvili D. A. 
Published: June 2010

AbstractThe thermal properties of several biopolymeric (DNA, RNAse, Folch‐Pi apoprotein)–water systems have been investigated by low‐temperature adiabatic differential scanning microcalorimetry. Determination of the heat change and temperature of fusion of the water and eutectic mixture allowed resolution of the various water states in native polymer solutions and before and after heat denaturation of the macromolecules.
Calorimetric study on the state of water in microbial cells
Authors: Shinohara A. , Nunomura K. , Fujita T. 
Published: June 2010

AbstractCalorimetric studies were carried out on partly dried yeast cells and some model substances supposed to afford the major binding sites in the yeast cells. The heat of vaporization and thawing as well as the water vapor sorption isotherm of yeast cells suggest that part of the cell water is somewhat bound to dry matter components and loses some of its responses observed when it is in bulk phase. Cell water down to 25% freezes and has the same value of differential heat of vaporization as in the bulk phase (10.5 kcal/mol). The contents of unfreezable water calculated from the heat of thawing obtained with yeast mannan, yeast RNA, bovine serum albumin (BSA), and the whole yeast cells are 43, 35, 30, and 25%, respectively. The calorimetric data obtained for yeast cells and their component molecules indicate that the magnitude of their interaction with water molecules are in the order of mannan, bovine serum albumin (BSA), and the whole yeast cells. The physical properties of water in yeast cells cannot be explained from those bound to their separate components. This may in part be due to some interactions between these molecules that change their binding properties with water molecules in yeast cells.