bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal behavior of α nylon‐12
Authors: Ishikawa Toshihiko , Nagai Susumu , Kasai Nobutami 
Published: April 2003

AbstractThe thermal behavior of α nylon‐12 film cast from a phenol‐ethanol mixture has been studied by differential scanning calorimetry. Polymorphism has been analyzed by x‐ray diffraction. The γ form exhibits a single endothermic melting peak in the thermogram, whereas the α form exhibits double peaks. Samples with mixed α and γ forms show double peaks at the same positions and the area ratio changes in accordance with the amounts of the two forms. The appearance of the γ peak, even for the α sample, is explained by recrystallization to the γ form after melting of the α form. The melting point of α nylon‐12 is ca. 173°C, which is lower by 6–7° than that of the γ form. Once the α or γ sample has been melted and then cooled, its heating thermogram shows a small peak before the appearance of the main peak. The small peak seems to be due to incomplete and/or smaller crystallites formed during cooling. Heat treatment below the melting point of α nylon‐12 is effective in transforming the α form to the γ form, probably via a melt‐recrystallization process.
Structure of polyethylene solid solutions from vibrational spectroscopy and thermal analysis
Authors: Shu P. H. C. , Burchell D. J. , Hsu S. L. 
Published: April 2003

AbstractSolid solutions of two low‐molecular‐weight polyethylene fractions, formed by rapid quenching from the melt, were studied by differential scanning calorimetry, low‐frequency Raman spectroscopy, and Fourier‐transform infrared spectroscopy. Two kinds of defects exist in these solid solutions; namely, a disruption of chain extension and the presence of monoclinic packing. The distribution of fully extended chain‐segment lengths and the intensity of the 717 cm−1 infrared band, characteristic of the monoclinic phase, are found to be composition dependent. Our spectroscopic studies of the solid solutions support the model first proposed by Ott and Slagle.
Dilute solution and rheological characterization of branched poly(2,2′‐oxydiethylene trans‐1,4‐cyclohexanedicarboxylate)
Authors: Fisher L. W. , Pearson G. H. , Yacobucci P. D. 
Published: April 2003

AbstractThe addition of small amounts of polyfunctional agents can substantially alter the melt and the solid‐state properties of polymers. A practical characterization scheme is necessary for control of polymer preparation and for process analysis. Trifunctionally branched samples of poly(2,2′‐oxydiethylene trans‐1,4‐cyclohexanedicarboxylate) have been prepared as representative of polycondensation polymers. The Drott‐Mendelson procedure was applied to the dilute solution data from gel permeation chromatography and intrinsic viscosity to yield the true molecular weight distributions and the average branching frequency. The melt zero‐shear‐rate viscosity of a branched sample was less than that of a linear sample of equal weight‐average molecular weight, in good agreement with Bueche's theory. The melt elasticity, as measured by the terminal relaxation time, was equal to that of the equivalent linear polymer at constant weight‐average molecular weight.
Small‐angle x‐ray scattering study of ionomer deformation
Authors: Roche E. J. , Stein R. S. , Russell T. P. , Macknight W. J. 
Published: April 2003

AbstractThe small‐angle x‐ray scattering (SAXS) pattern from a cesium salt of a 6.1 mole % ethylenemethacrylic acid (E‐MAA) copolymer is shown to become azimuthally dependent on sample elongation. SAXS was measured using the Oak Ridge National Laboratory (ORNL) spectrometer with pinhole collimation and a two‐dimensional position‐sensitive detector. The sample was quenched prior to deformation to avoid crystallization of the ethylene unit which would complicate the interpretation of scattering. The observed SAXS patterns are interpreted in terms of several proposed models for the structure of ionomers. A model in which ionic aggregates are arranged on a paracrystalline lattice is found to be largely in disagreement with the results for undeformed and deformed samples. Spherical and lamellar models incorporating local structure around a central ionic core are capable of predicting the observed SAXS for the undeformed sample. A model of ellipsoidal deformation of the spherical shell‐core model fails to predict the correct azimuthal dependence of scattering. However, a deformation scheme involving rotation of the lamellar model is more satisfactory.
Use of electron microscopy to obtain quantitative information about the melting behavior of branched polyethylene
Authors: Voigt‐Martin I. G. 
Published: April 2003

AbstractThe melting behavior of low‐density polyethylene was studied by electron microscopy. The experimental techniques and method of evaluation chosen were such as to deliver quantitative numerical data. The values which could be derived from suitably prepared histograms were the minimum, maximum, average, and most probable values of the crystal thickness d and long‐spacing L. All these values were in good agreement with small‐angle x‐ray scattering results. The histograms also show the distribution functions for d and L, so that effects leading to changes in the average values can be observed in detail. The results provide further support for a model of melting and crystallization proposed in a previous paper.
Study of crystal texture in pvc gels by x‐ray diffraction and infrared dichroism
Authors: Guerrero S. J. , Keller A. , Soni P. L. , Geil P. H. 
Published: April 2003

AbstractAn enquiry is presented into the nature and origin of thermoreversible gelation of poly(vinyl chloride) (PVC). In line with a previous paper it is demonstrated by direct x‐ray diffraction evidence that the origin of the gelation is crystallization, and that this crystallinity can be conspicuously apparent even for the usual technological polymer. In addition some unusual diffraction effects become apparent such as do not obviously follow from existing notions of the PVC structure. Combined infrared dichroism and x‐ray studies revealed that these new effects are attributable to a two‐component nature of the crystallinity where the components are distinguished by their orientation behavior, lateral extension, and possibly morphology of the crystallites. Some of the crystals orient with their a axes (type A crystals) and some with their c axes (type B crystals) along the stretch direction. Other more complex orientability differences are also manifest during film formation. Crystals B are smaller, and are believed to correspond to the network forming junctions, hence to fringed micellar crystals. Crystals A have a less evident connection with the network and are hypothesized to be of lamellar character, the behavior of which is closely simulated by lamellar crystal additives (stabilizer crystals). High‐temperature x‐ray work revealed no melting of crystals even in the temperature range where endotherms appear in the thermograms.
Oriented polymers from solution. III. NMR of polyethylene/polypropylene blends
Authors: McBrierty V. J. , Douglass D. C. , Barham P. J. 
Published: April 2003

AbstractT1, T2, and T1ρ measurements are reported for a blended fiber of polyethylene and polypropylene prepared by the “surface growth” technique. The data support the view that the fiber contains mixed crystalline regions of each pure component that may weakly interact via spin diffusion. A tentative model is proposed for the blended fiber.
Sequence distribution in ethylene‐propylene copolymers. I. Relations between multads and between multads and the 13C NMR spectrum
Authors: Smith Wendell V. 
Published: April 2003

AbstractThe theoretical relations between 13C NMR line intensities and monad, dyad, and triad populations are given. In some cases only approximations are possible. The relations between monads and dyads also between dyads and triads are given. Some necessary relations between line intensities are given which provide a basis for making corrections for differing Overhauser enhancements. Included in the discussion are three lines which have not previously been discussed.
Viscoelastic, dielectric, and piezoelectric behavior of solid amylose
Authors: Nishinari Katsuyoshi , Fukada Eiichi 
Published: April 2003

AbstractComplex elastic, dielectric, and piezoelectric properties were measured on amylose films as a function of temperature and moisture content at 10 Hz. The real part of the complex Young's modulus of films containing a small amount of moisture was larger than that of a dry film. Peaks in the imaginary parts of these complex response functions were observed at about −80°C. The height of these peaks decreased when the specimen absorbed a little moisture. The activation energy for this peak as determined from an Arrhenius plot of the dielectric frequency dispersion was about 9.5 kcal/mole. This peak was ascribed to methylol rotation. The real part of piezoelectric e constant was shifted downwards when the specimen absorbed moisture. This was attributed to the instantaneous response in the case of a step function excitation. The structure of amylose was thought to be stabilized by moisture absorption, probably due to hydrogen bonding. The mechanism of methylol rotation was examined by dielectric measurements.
Studies of molecular aggregation of a polybenzimidazole in solution by fluorescence spectroscopy
Authors: Kojima Takakazu 
Published: April 2003

AbstractA purified, well characterized sample of polybenzimidazole (PBI) has been studied by fluorescence spectroscopy in order to obtain information concerning molecular aggregation in solution. Fluorescence and excitation spectra of PBI and a model compound have been measured in N,N‐dimethylacetamide (DMA) and in formic acid (FA). The major emission band for PBI solutions is attributed an excited 1Lb state, which consists of 0‐0 and 0‐1 vibrational energy bands. Concentration quenching is attributed to reabsorption of the emitted light, and self‐quenching due to the formation of molecular aggregates. Therefore, the extent of molecular aggregation in solution is estimated from the self‐quenching constant. In the course of the investigation, a new fluorescence band was found for the PBI‐DMA solution; its intensity increased markedly due to overlapping of polymer coils. The formation of polyelectrolytes in PBI‐FA solutions was confirmed by viscometry. The major fluorescence band was found to originate from the excited 1Lb state and to shift to longer wavelengths upon addition of lithium bromide.
High‐pressure phases in polymers. V. Crystallization studies of synthetic cis‐polyisoprene
Authors: Edwards B. C. , Phillips P. J. , Sorenson D. 
Published: April 2003

AbstractThe effects of elevated pressure on the morphology and crystallization kinetics of cis‐polyisoprenes containing 2–2.5% trans units have been determined. Lamellar growth rates of both α and β crystals are enhanced by elevated pressure. The degree of enhancement of α‐crystal rates is much greater resulting in an effective suppression of β growth. Differences in lamellar growth rates between these polymers and cis‐polyisoprene result from different preexponent values. Hedritic or axialitic growth, presumably due to low‐molecular‐weight fractions, is observed in shish‐kebabs present in strained films. The high‐pressure hexagonal phase cannot be grown in these polymers.
Environmental stress cracking of polyethylene: Analysis of the three zones of behavior and determination of crack‐front dimensions
Authors: Shanahan M. E. R. , Schultz J. 
Published: April 2003

AbstractPrevious work has shown that in the environmental stress cracking (ESC) of polyethylene, there are three major zones of behavior depending on the applied stress and the nature of the liquid environment. These three zones correspond to “pure” ESC (zone 1), ESC controlled by the speed of penetration of the liquid within a growing crack (zone 2), and behavior as in the absence of liquid (zone 3). Analysis of the transitions between zones has shown that, in the present case, a given liquid will either be capable of giving rise to all three types of behavior depending on the stress applied, or will be totally inactive. A related analysis has enabled the order of magnitude of the dimensions of the crack tip to be estimated and this has been found to be in the range of a micron.
Proton NMR studies of a polybenzimidazole in solution
Authors: Kojima Takakazu 
Published: April 2003

AbstractMolecular aggregation of poly(4,4′‐diphenyl ether‐5,5′‐bibenzimidazole)(PBI) in solution has been studied by high resolution proton NMR. PBI and model compounds have been synthesized, purified, and characterized. Proton resonances in the NMR spectrum of PBI are assigned by comparison with the proton resonances of the model compounds. Spectra are studied by total line‐shape analysis, assuming each absorption curve to be Lorentzian. For PBI in N,N‐dimethylacetamide (DMAc), the resonance due to the proton of a hydroxyl group formed by proton exchange between the imino group of PBI and the carbonyl group of DMAc is observed. The activation energy for the proton exchange, obtained from Arrhenius plots of the temperature dependence of the chemical shifts of the hydroxyl proton and the imino proton, was found to increase in the order corresponding to dissociation energy of the NH···OC hydrogen bond. The chemical shifts in the NMR spectra of PBI‐DMAc solutions on the addition of LiCl are strongly dependent on the polymer‐salt ratio; and thereby the coordination position of LiCl to PBI is tentatively identified, assuming a pseudocontact LiCl‐induced shift. The dependence of the chemical shifts of protons in PBI on the dielectric constant of the solvent is demonstrated by using polar solvents of varying dielectric constant, such as N‐methylpyrrolidone, dimethylsulfoxide, and formic acid. The viscosity of the PBI‐DMAc solutions is reported at various temperatures and concentrations of LiCl. The results from viscometry are explicable in terms of the NMR observations.
Solution behavior of ionomers. I. Metal sulfonate ionomers in mixed solvents
Authors: Lundberg R. D. , Makowski H. S. 
Published: April 2003

AbstractThe solution behavior of metal sulfonate‐containing ionomers has been investigated in various mixed solvent systems. Ionomers, such as lightly sulfonated polystyrene (sodium salt) and sulfonated ethylene‐propylene‐diene terpolymer (metal salts) are generally insoluble in typical hydrocarbon solvents, but readily dissolve when small amounts of alcohols or other polar cosolvents are present. At relatively low polymer concentration these ionomers display unusually high thickening behavior in nonpolar solvents when compared with nonionic polymers because of association of the metal sulfonate groups. The addition of modest levels of polar cosolvent markedly decreases the solution viscosity and gives rise to viscosity‐temperature relationships different from those of conventional polymer solutions. For example, such solutions can display vicosities which increase, are relatively constant, or display maxima or minima over broad temperature ranges. These observations are interpreted as arising from a temperature‐dependent preferential interaction of the cosolvent with the sulfonate groups. While these ionomers can be regarded as polyelectrolytes of low charge density, they do not display the typical “polyelectrolyte” behavior often observed in aqueous solutions. This anomalous behavior is attributed to the fact that the metal sulfonate groups are largely un‐ionized in solvents of low dielectric constant. Therefore, the solution behavior is dominated by ion pair interactions rather than free ions.
Crosslinking chemistry and network structure in organic coatings. I. Cure of melamine formaldehyde/acrylic copolymer films
Authors: Bauer D. R. , Dickie R. A. 
Published: April 2003

AbstractCrosslinking chemistry and network formation in hydroxy and carboxy functional acrylic copolymer resins cured with representative melamine‐formaldehyde crosslinking agents have been studied by infrared spectroscopy. Network formation in these systems is dominated by two reactions, the condensation of the hydroxy (or carboxy) functionality of the acrylic resin with melamine alkoxy groups to form acrylic‐melamine crosslinks, and the condensation of melamine hydroxy groups to form melamine‐melamine crosslinks. The extents of these reactions have been studied as functions of acrylic resin composition, melamine type and concentration, and cure time and temperature. For melamines with just methoxy functionality, the extent of formation of acrylic‐melamine crosslinks increased steadily with cure temperature. For melamines with substantial hydroxy functionality, the extent of formation of acrylic‐melamine crosslinks increased rapidly then leveled off with increasing cure temperature. The formation of melamine‐melamine crosslinks increased slowly with increasing cure temperature. From these data and a statistical model, effective crosslink densities were calculated. The crosslink densities correlated well with solvent resistance.
Crosslinking chemistry and network structure in organic coatings. II. Effect of catalysts on cure of melamine formaldehyde/acrylic copolymer films
Authors: Bauer D. R. , Dickie R. A. 
Published: April 2003

AbstractIn a previous paper, the extents of reaction of various functional groups in different acrylic copolymer melamine‐formaldehyde crosslinked formulations were measured by infrared spectroscopy. From these data and a statistical model, various network structure parameters could be calculated. One of these, effective crosslink density, was found to correlate well with film solvent resistance. In this paper the effects of the addition of strong acid catalysts on cure chemistry and network structure are determined. Both solvent‐based and water‐based formulations have been studied. In the solvent‐based formulations studied, the addition of acid catalysts greatly enhanced the crosslinking reactions at low temperatures and dramatically lowered the cure temperature. Acid catalysts also lowered the cure temperature of a water‐based formulation based on a high (180°C) cure temperature melamine. In contrast, the addition of acid catalysts had a negligible effect on the cure chemistry of a water‐based formulation crosslinked with a low (130°C) cure temperature melamine. For this case the rate limiting process was found to be the rate of removal of neutralizing amine from the film. Cure temperatures in this system could only be lowered by replacing the amine used with a more volatile amine.
Equilibria of extended‐chain polymers exhibiting crystalline and liquid‐crystalline phases
Authors: Balbi C. , Bianchi E. , Ciferri A. , Tealdi A. , Krigbaum W. R. 
Published: April 2003

AbstractThe phase diagram of poly(p‐benzamide) (PBA) in N,N‐dimethylacetamide/LiCl solutions was determined for two PBA samples having weight‐average molecular weights of about 10,000. The various equilibria were studied using analytical, viscometric, and optical microscope measurements. The phase diagram at 25°C, taking as variables the concentration of polymer (Cp) and LiCl (Cs), involves several equilibria which can be summarized as follows: solid ↔ isotropic solution when 0.75 ≤ Cs ≤ 2 g/dl, solid ↔ anisotropic solution when 2 ≤ Cs ≤ 4 g/dl, isotropic solution ↔ anisotropic solution when 2 ≤ Cs ≤ 4 g/dl, and Cp > 6 g/dl, and dilute isotropic solution ↔ gel when Cs > 4 g/dl. In the Cp range in which the isotropic and anisotropic phases coexist, enrichment of the high‐molecular‐weight component of the polymer in the anisotropic phase becomes more marked as the volume fraction of the latter phase is decreased. The two PBA samples exhibit noticeable differences in solubility, absolute viscosity, and in their viscosity‐concentration behavior. The location of the maximum in the latter dependence does not necessarily coincide with the first appearance of the anisotropic phase. In the absence of a flow field, anisotropic solutions exhibit an irreversible increase in viscosity. Inclusion of the equilibria involving the crystalline state furnishes insight into some of the common observations for extended‐chain polymers. A diagram illustrates the superposition of the solubility curves for a crystalline polymer and the liquid‐crystal regions. This indicates that, for the high melting crystalline polymers, the crystalline phase should be stable relative to the concentrated anisotropic phase of the wide biphasic region.
A constitutive equation derived from the model of doi and edwards for concentrated polymer solutions and polymer melts
Authors: Doi Masao 
Published: April 2003

AbstractIn deriving a constitutive equation from a molecular model of polymers in concentrated solutions and melts, Doi and Edwards used a mathematical approximation, the “independent alignment approximation,” which has recently been shown to produce significant error in the particular case of stress relaxation following a double‐step strain in opposite direction. In the present paper, in order to examine the approximation in general cases, we derive a new constitutive equation without using the independent alignment approximation. The new equation is a nonlinear integro‐differential equation and is solved numerically for several cases, i.e., steady shear and elongational flows, and the transient flows after the start of shear and elongation. It is found that, in the cases examined here, the new constitutive equation gives nearly the same results as the old one: the rheological functions calculated from the two theories differ no more than 30%. This substantiates the expectation that the independent alignment approximation does not produce drastic error as long as the flow direction is not reversed.
Effect of solvent power on the adsorption of polystyrene onto a metal surface
Authors: Kawaguchi Masami , Takahashi Akira 
Published: April 2003

AbstractThe adsorption of linear polystyrenes from cyclohexane solutions onto a chrome plate of 35 (the theta temperature), 40, and 45°C was studied by ellipsometry. The adsorbance decreases with increasing temperature, while the extension of the adsorbed polymer layer increases. The adsorbance is almost independent of the molecular weight at these temperatures. The slope of a double logarithmic plot of extension versus molecular weight is 0.5 at the theta temperature, whereas at the higher temperatures the slope is a little larger. Both the adsorbance and the extension of the adsorbed layer change reversibly over a cycle of temperature change, indicating that a reversible conformational change has occurred. The expansion factor αt of the adsorbed layer is compared with the theoretical predictions of Hoeve and of Jones and Richmond. The expansion factor αt according to Hoeve's theory, was smaller than the measured value, whereas the expansion calculated by the Jones–Richmond theory is much larger than the measured value. It is concluded that the tail portions of adsorbed chains predominantly govern the extension of the adsorbed layer.
Transport properties of annealed, drawn low‐density polyethylene (LDPE)
Authors: De Candia F. , Russo R. , Vittoria V. , Peterlin A. 
Published: April 2003

AbstractThe specific concentration ca of methylene chloride, the zero‐concentration diffusion coefficient D0, and the concentration coefficient γD of the diffusivity in drawn and annealed LDPE were measured. The influence of the drawing rate, of annealing with the ends of the sample free and fixed and the effects of time of standing at room temperature after annealing were investigated. The observed transport properties are in good agreement with the microfibrillar model of fibrous structure, its relaxation during annealing, and the slow crystallization of relaxed tie‐molecules upon standing at room temperature.