bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solution of water in polymers: The keratin‐water isotherm
Authors: Rosenbaum Shlomo 
Published: June 2010

AbstractThe uptake of water by polar polymers was shown by Simha and Rowen to be described by the Flory‐Huggins solution treatment at high relative vapor pressures. The breakdown at lower vapor pressures is attributed here to the effect of water content on the free volume of the system. By using data for the wool keratin‐water system, similar agreement is obtained for the rest of the isotherm by taking account of the volume changes observed at low vapor pressures. These are shown to set in at a characteristic composition with properties generally associated with a glass transition.
Reaction kinetics in dilute solutions of chain molecules carrying randomly spaced reactive and catalytic chain substituents. I. Estimation of ring closure probabilities from kinetic data and computer simulation
Authors: Goodman Neil , Morawetz Herbert 
Published: June 2010

AbstractAcrylamide was copolymerized with small proportions of monomers containing a p‐nitrophenyl ester group and a small amount of a monomer containing a pyridine residue. The hydrolysis of the ester groups was studied under conditions where the rate of the process was controlled by interaction with pyridine residues attached to the same chain. Variables studied included the mode of attachment of the ester groups to the chain backbone, the concentration of the catalytic pyridine residues in the chain and the fraction of the pyridine present in the unprotonated, catalytically active form. Kinetic data obtained at different pH values gave the same results if the extent of reaction was expressed as a function of the product of the experimental time and the fraction of pyridine residues in the basic form. This proves that the intramolecular process is not controlled by the rate at which cyclic conformations are formed but by their probability. The reaction deviated from first‐order kinetics because the reactive groups had varying spacings from the catalytic groups. Experimental data were in good agreement with the kinetics derived by computer simulation if the probability of group interaction was made inversely proportional to the square of their separation along the chain molecule. Initial apparent first‐order rate constants were about 40% of the value predicted on the basis of a simple theory based on the average extension of the polymer coils.
Spectroscopic study of the n‐π* transition of oriented poly (γ‐benzyl L‐glutamate) in solution
Authors: Hoffman S. J. , Ullman Robert 
Published: June 2010

AbstractCircular dichroism, optical rotation, and ultraviolet absorption studies have been carried out on oriented solutions of poly(γ‐benzyl L‐glutamate). The orientation of the molecules was achieved by use of an electric field parallel to the direction of propagation of the light wave. This was possible because of the design of conducting electrodes which are largely transparent in the ultraviolet. It was accomplished by putting a very thin coating of stannous oxide on optical silica. The results of these measurements show that the magnitude of the circular dichroism and optical rotation decrease substantially in the n‐π* region of the ultraviolet (∼ 2200 Å). The decrease agrees with the calculation of Woody and Tinoco.
Morphology and deformation mechanisms of crystalline polymers
Authors: Stein Richard S. 
Published: June 2010

AbstractCrystalline polymers consist of regions of varying order ranging from perfectly crystalline to random and rubber‐like assemblies of polymer chains. Such structures may thus be represented in terms of statistical parameters characterizing the size and shape of ordered regions, degree of order and orientation of these regions. These parameters may be characterized by such techniques as x‐ray and light scattering. A study of the deformation of such polymers requires the specification of the change in these descriptive parameters with time, temperature, and morphology. The application of a number of optical techniques to this determination is discussed and typical results are presented. A deformation mechanism for crystalline polymers is proposed which is consistent with these observations.
Crack propagation and arrest in polymethylmethacrylate
Authors: Rosenfield A. R. , Mincer P. N. 
Published: June 2010

AbstractBy use of a double‐cantilever‐beam specimen, fast fracture and crack arrest were studied in PMMA. The observation, that the heavily deformed region at the crack tip was confined to a thin wedge of material was confirmed. This result provided support for a onedimensional solid‐mechanics analysis. The computations suggest that the average energy to propagate fast fracture from a sharp crack is only ∼2/3 of that required to initiate it. In addition, the process of very slow crack propagation, leading to arrest, was examined microscopically. At very slow rates the crack was seen to advance in a series of small jumps. The implications of these results with respect to materials development are discussed.
Chain scission and plastic deformation in the strained crystalline polymer
Authors: Peterlin A. 
Published: June 2010

AbstractDepending on temperature and load rate an unoriented polymer solid under sufficiently large applied stress either deforms plastically (high temperature, low rate of loading) or undergoes brittle fracture (low temperature, high rate of loading). The fracture proceeds through the areas of minimum strength, i.e., along the boundaries between adjacent spherulites and between parallel lamellae. Very few chains, i.e., interlamella tie molecules and molecules bridging the crack if a crystal lamella is broken, are ruptured during this process. Hence the number of radicals per cm2 of new surface is small, about 1013/cm2.The plastic deformation gradually transforms the sample into the extremely well oriented fiber structure of much higher elastic modulus and strength but of smaller strain to break. The basic element of the fiber structure is the long and narrow microfibril formed by micronecking of the crystal lamella. The microfibril consists of fully oriented folded chain blocks connected by a great many tie molecules obtained by partial chain unfolding in the micronecks. Their number per amorphous layer increases with the draw ratio and so does the tensile strength of the microfibril.Under load the fiber structure breaks at very small strain. The fracture proceeds through the weakest elements of the structure, i.e., through the boundary between adjacent microfibrils and the amorphous layers between subsequent blocks of the microfibrils. With axial stress the fracture must cut at least one full cross section of the fiber and hence rupture about 1014 intrafibrillar tie molecules per cm2. ESR experiments show long before the final break a much higher number of radicals throughout the whole strained sample upto 1017/cm2. The number of broken chains depends on strain and not on stress. One imagines that at every applied strain one breaks the most strained tie molecules which as a consequence of stress concentration have to carry most of the load. The stress concentration caused by the special morphology of the microfibrils and tie molecules reduces the tensile strength of the polymer far below the theoreticall limit calculated for uniform stress field even if one considers that the number of chains passing through the fracture plane is only a fraction of the maximum number calculated with all macromolecules extended and perfectly aligned.
Chemical structures of surface‐oxidized and grafted polyethylene: Adsorption and wetting studies
Authors: Baszkin Adam , Ter‐Minassian‐Saraga Lisbeth 
Published: June 2010

AbstractSurfaces of thin low‐density polyethylene films are chemically modified either by oxidation or by grafting with maleic acid. The oxidation is performed at constant tempera‐ture by sulfuric acid and potassium chlorate mixtures of variable compositions. Grafting was carried out at constant temperature and time in the solution of maleic anhydride in acetic anhydride in the presence of benzoyl peroxide initiator. Isotherms of calcium adsorption at these surfaces have been established by the use of the radioactive tracer technique. The chemical composition (number of obtained polar sites) of these modified polyethylene surfaces is thus determined. The measurements were conducted at different pH and salt concentrations. Wettability of the modified surfaces is determined by contact angle measurements. It was found that the wettability of these films is directly related to the chemical composition of their surfaces.
Determination of the high frequency viscoelastic properties of polymers using shear mode strip delay lines
Authors: Hunston Donald L. 
Published: June 2010

AbstractA recently developed technique for measuring the high frequency shear mechanical properties of a wide range of samples is discussed. The technique involves the propagation of a shear wave in a thin strip of metal. When a sample coating is applied to the metal, the attenuation of the wave in the strip increases and the velocity decreases slightly. Previously, an expression was developed for the relationship between these changes in the wave and the mechanical properties of the sample; however, a simplified derivation is presented here for the special case where the sample is a liquid. At present the method has been used only at 2 MHz, but it can be adapted to frequencies between 1 MHz and 20 MHz quite easily and with careful work to frequencies outside this range. The sensitivity of the technique makes it possible to measure a range of samples extending from liquids with viscosities of only a few centipoise to deformable solids and in some cases rigid solids.
Solvent effects on the viscosity of moderately concentrated polymer solutions
Authors: Gandhi K. S. , Williams Michael C. 
Published: June 2010

AbstractViscosity ηo and osmotic pressure π were measured for polymer solutions at 25°C, for concentrations up to 30 g/dl. To elucidate the effects of polymer‐solvent interactions of various types, the systems chosen were polystyrene in toluene (good solvent) and decalin (poor solvent), and poly(methylmethacrylate) in chlorobenzene (good) and m‐xylene (poor). The surprising result was the generalization that ηo for poor‐solvent systems increases with concentration faster than for good‐solvent systems, so that eventually ηo becomes far greater with poor solvents. This behavior is enhanced with polar polymers, and is not explainable on the basis of entanglements in the usual sense. It is believed that polymer aggregation occurs in poor solvents, independent of molecular weight effects.Data were correlated with both the powerlaw and the Simha methods. Characteristic shapes of such curves were related to polymer‐solvent effects. Theories for the Huggins constant were found to be inadequate, as was a model proposed earlier (by MCW) for concentrated solutions. The latter was modified by adopting an ad hoc friction constant, which proved successful with good solvents and could be correlated with π to incorporate the poor‐solvent data as well.
Hydrogenation of kraft lignin
Authors: Benigni J. D. , Goldstein I. S. 
Published: June 2010

AbstractA series of high temperature hydrogenolyses‐hydrogenations of kraft lignin in water, organic solvents and aqueous alkali using a variety of catalysts were run. The liquefaction and distillation yields for the resulting products were measured. The products from these reactions were characterized by titration for acidic materials, elemental analyses, catechol content, ultraviolet absorption, and NMR.
ESR study of interactions of γ‐irradiated cellulose I and cellulose II with ammonia, water, and sodium hydroxide solutions
Authors: Hinojosa Oscar , Nakamura Yoshio , Arthur Jett C. 
Published: June 2010

AbstractThe types of long‐lived free radicals formed in predried cellulose I and cellulose II, after irradiation in a nitrogen atmosphere at 25°C by γ‐radiation from 60Co, were resolved by selectively scavenging some of the radicals and then recording the ESR spectra generated. The effects of anhydrous ammonia (both gas and liquid), water, solutions of sodium hydroxide, and temperature of heating on the ESR spectra generated by the irradiated celluloses were recorded. Most of the free radicals formed in the irradiated celluloses are apparently trapped in the amorphous or less ordered regions of the cellulosic structure. About 70% of the radicals formed in irradiated cellulose I and about 90% of the radicals formed in irradiated cellulose II are scavenged by contacting the samples with water. The ESR spectra of the free radicals scavenged by water are almost identical for both irradiated celluloses. Contact of the irradiated celluloses with ammonia (liquid) scavenged most of the trapped free radicals. It also appears likely that the long‐lived free radical sites in the highly ordered regions in both irradiated celluloses are the same. As shown by the effects of orientation of irradiated cellulosic fibers in the magnetic field on the ESR spectra recorded, differences in spectra for the irradiated celluloses are probably related to conformations of the trapped radicals which are dependent on differences in crystal lattice types of cellulose I and II.
Structural characterization of grafted cotton fibers by microscopy
Authors: Goynes Wilton R. , Harris James A. 
Published: June 2010

AbstractThe structure of cotton fibers grafted by radiation induced polymerization with butyl methacrylate and acrylonitrile was investigated by light and electron microscopy. Degree and uniformity of dye uptake was used to indicate uniformity of reaction. The internal structure of the fibers was studied with the transmission electron microscope using ultrathin cross sections and solubility tests. Changes in the fiber surface, and types of damage caused by abrasion were evaluated with the scanning electron microscope. These tests indicated that the grafting procedure had changed the surface as well as the internal fibrillar character of the fibers and the extent of such changes increased with increasing content of graft polymer.
Effect of molecular weight on the crystallization and morphology of poly (ethylene oxide) fractions
Authors: Godovsky Yu. K. , Slonimsky G. L. , Garbar N. M. 
Published: June 2010

AbstractThe temperature dependence of the isothermal growth rate of spherulites and overall crystallization kinetics of different fractions of poly (ethylene oxide) over the range of molecular weight from 300 to 20,000 were studied by calorimetry, dilatometry, and polarized light microscopy, in order to establish the dependence of the kinetic parameters upon molecular weight. The morphology of crystallites was studied by small‐angle x‐ray scattering. In the course of this study it has been established that the growth rates of spherulites and the overall crystallization rates at any fixed supercooling essentially depend upon molecular weight. The minimum in the crystallization rate which occurs at molecular weight 4000 is a consequence of transition from extended‐chain crystallization to folded‐chain crystallization. Small‐angle x‐ray scattering study of the morphological features confirmed this conclusion. This minimum depends very strongly on the degree of supercooling, increasing rather sharply at small supercooling. The temperature and molecular weight dependence of the growth rates of spherulites and the overall crystallization rates has been analyzed by means of the theoretical expression given by Hoffman and Lauritzen. The product of the lateral and basal surface free energies of the crystallites σσe increases with molecular weight and reaches a limiting value at molecular weight 6000. Such behavior is in agreement with morphological transformations.
Growth rate and morphology of polyoxymethylene supermolecular structures
Authors: Pelzbauer Z. , Galeski A. 
Published: June 2010

AbstractThe connection between the growth rate and morphology of supermolecular structures was investigated for polyoxymethylene which was isothermally crystallized from the melt at various temperatures. Optical and electron microscopy showed that below 158°C the crystallization occurred in the spherulite form, while above this temperature hedrites and, sporadically, ovoids were obtained. Although the radial growth rate itself does not exhibit a break around the critical temperature (158°C), a more detailed analysis based on the kinetic theory of crystallization has revealed a sudden drop in the interfacial free energy of the fold surface around this temperature. For the growth model represented by two‐dimensional surface nucleation, which seems the most probable representation, values of 183 and 95.5 erg/cm2 were found for the temperature regions of growth of spherulites and hedrites, respectively. Morphologically, the two types differ by a larger extension of monocrystalline lamellae in hedrites, the mode of their arrangement, and the final external shape. The increasing extension of the lamellae, due to a decrease in the radial growth rate, which can be understood in terms of the segregation theory by Keith and Padden, is probably the reason that at a certain critical size (near 158°C), the hedritic growth becomes stabler than the spherulitic growth. A further investigation will be needed to elucidate the part played by a simultaneous drop in the free energy of the fold surface.
A study of the elongation ratio of deformed spherulites
Authors: Pakula T. , Kryszewski M. 
Published: June 2010

AbstractIn order to describe mathematically small‐angle light scattering in samples containing undeformed spherulites or spherulites deformed by tensile forces we assume a function for the light scattering intensity distribution for Hv patterns. This assumed function is a very good approximation to Stein's equations but has a simpler mathematical form. It is also a good approximation of the distributions experimentally obtained for light scattered from spherulites.By using this function, a new method of calculating the elongation ratio λS of deformed spherulites is elaborated. It consists of measuring the azimuthal angle μmax for which the value of the intensity of light scattered at the vertical angle 0 < θ < π/2 is a maximum.Using this method, the spherulite deformation in PE films was studied. The results are compared with those obtained by Samuels' method.
Anisotropy of the physicochemical properties of single‐textured polymer samples in relation to morphology
Authors: Goffin A. , Dosiere M. , Point J. J. , Gilliot M. 
Published: June 2010

AbstractSingle‐textured samples of high pressure polyethylene were prepared by rolling. The anisotropy of the variations of macroscopic dimensions of these samples produced by thermal expansion or by swelling with solvent allows us to test the classical models. The anisotropy of the expansion coefficients at low temperature for three different samples (respectively annealed at 90, 100, 105°C) show that the structure changes progressively, going from a morphology wherein sample dimensions along the chain axis are stabilized by partially uncoiled molecules to the ideal lamellar structure. The anisotropy of the thermal expansion coefficients at high temperature suggests that there exist distinct phases arranged in layers parallel to the rolling plane, one of which melts on raising the temperature of the sample. A new model explains these results. It describes the samples as composed of two phases: a lamellar one and another without regular structure in the 100 Å range. The anisotropy of the dimensional changes due to the swelling by solvents strongly supports this model. It is shown that swelling at low temperature produces a minimum of expansion perpendicular to the lamellar faces. The fringed fibril model modified by folded chains cannot explain the observed anisotropy. By using the new proposed model a plausible mechanism is proposed to explain the experimental facts. At high temperature, the swelling is due to the dissolution of the lamellar phase and the results obtained are in good agreement with the model.
Thermodynamic limitations on interaction functions and the theta temperatures of polymer solutions
Authors: Kennedy J. W. 
Published: June 2010

AbstractA limiting critical point of a binary solution of a homodisperse polymer of molecular weight M, is any point in a (concentration, Φ, temperature, T)‐plane which is a critical point for a limit M → ∞. At any such point four conditions subsist for a function Φ defined in terms of the free enthalpy of mixing for (polymer) solutions. Because this definition is quite general, the conditions are universal and are not limited by any interpretation of Φ in terms of a particular model. Thus they are to be regarded as thermodynamic constraints on any model which may be applied to polymer solutions over conditions which extend to a critical region. If the limiting critical concentration, ΦL, is zero, then the limiting critical temperature, TL, is identical to the theta temperature, Tθ. If ΦL is not zero, Tθ can be obtained from Φ and is less than TL in a Flory (upper critical) system, or greater than TL in a Rowlinson (lower critical) system. It is concluded that theta temperatures have been seriously misestimated by classical extrapolation procedures.
Mechanism of phosphite stabilizers in polyolefins subjected to ultraviolet irradiation
Authors: Hutson G. V. , Scott G. 
Published: June 2010

AbstractThe effect of thermal‐oxidative processing on the stability to ultraviolet irradiation of high density polyethylene containing a catechol hindered‐phenyl phosphite has been studied by periodic observation of carbonyl index by infrared spectrometry and by recording embrittlement times.Certain of the possible thermal‐oxidative reaction products of catechol hindered‐phenyl phosphite, catechol hindered‐phenyl phosphate and mono‐(σ‐hydroxyphenyl)phosphoric acid have also been studied. The results are consistent with the theory previously developed that the latter or its dehydration product, catechol hydroxy phosphate, is the effective antioxidant produced during processing.
Changes in concentration of some stabilizers during the photooxidation of polypropylene films
Authors: Vink P. 
Published: June 2010

AbstractThe changes in concentration of 2‐hydroxy‐4‐octyloxybenzophenone, Cyasorb UV‐1084, and Tinuvin P during the photooxidation of films of polypropylene, stabilized by these compounds, is determined. The change in concentration of the benzophenone derivative obeys zero‐order kinetics, while that of Cyasorb UV‐1084 tends to be first order. The concentration of both compounds has strongly decreased at the end of the induction period. The concentration of Tinuvin P decreases strongly only after the induction period. The implications of these results for the mechanism of UV stabilization are discussed.
Three‐dimensional anionic polymerization of oligoesteracrylates
Authors: Lipatova T. E. , Shapoval G. S. , Basilevaskaya N. P. , Shevchuk E. S. 
Published: June 2010

AbstractThe mechanism of the formation of soluble and network polymers during the process of anionic polymerization of oligoesteracrylates (OEA) was investigated.It was shown that the network polymer was built from charged branching macromolecules. The anionic polimerization of OEA establishes the equilibrium in the process of electron distribution between functional groups of OEA and equilibrium between soluble and network polymers and residual OEA. Both types of equilibria are determined by the temperature and the ratio of concentration of OEA and catalyst. The equilibrium in the system of network and soluble polymers and residual OEA is established both by the interaction of catalyst with OEA and with “dead” network polymer which may be “vitalized” in this way.