bluuebunny/crossref_metadata_2025_split huggingface dataset:
Griffith fracture of a phenol–formaldehyde polymer
Authors: Nelson B. E. , Turner D. T. 
Published: April 2003

AbstractCast samples of a phenol–formaldehyde polymer with a crack of length defined by a metallic foil inclusion were fractured in tension. The stress at fracture was inversely proportional to the square root of the crack length, in agreement with the Griffith equation for brittle fracture. The behavior did not conform to the Griffith equation with respect to the experimental value of surface free energy, which was several orders of magnitude higher than a theoretically calculated value. However, as the temperature of tensile testing was raised, the experimental value did approach the calculated value. Consistently the appearance of the fracture surface was observed to change from one showing evidence of plastic deformation at room temperature to a featureless appearance, characteristic of brittle fracture, at higher temperatures.
Infrared dichroism of polyethylene crystallized by orientation and pressure in a capillary viscometer
Authors: Miller Philip J. , Jackson John F. , Porter Roger S. 
Published: April 2003

AbstractPolarized infrared absorption spectra have been obtained by Fourier‐transform spectroscopy for several crystalline and noncrystalline absorption bands of polyethylene crystallized by orientation and pressure in capillary viscometer. An analysis of data obtained at room temperature yielded degrees of crystallinity which are in good accord with values obtained from calorimetry and density measurements. The dichroism of the infrared absorption bands for the crystalline region revealed an extreme degree of orientation consistent with previous x‐ray studies and also demonstrated that the degree of orientation is a good or better than that obtained from drawn polyethylene films with extension ratios of 20. Dichroism of bands from the amorphous phases revealed that the noncrystalline chain segments are in a comparatively relaxed state compared with results for drawn films having extension ratios of about 2 to 7. This is 1/10 to 1/3 the extension ratio of drawn polyethylene which shows maximum crystalline orientation. The results also indicated that the ratio of the GTG′ to GG segment conformations in the amorphous regions is larger than that of amorphous portions in unoriented polyethylene. The vinyl endgroups were shown to be highly oriented, while the main bulk of the amorphous polymer was fairly relaxed, i.e., of low orientation. It is concluded that the amorphous polyethylene state is strongly dependent on the nature of the crystalline–amorphous interface.
A constitutive equation for composite systems
Authors: Chen Y. T. 
Published: April 2003

AbstractBy the differential operator representation of constitutive equations for linearly viscoelastic materials, general theoretical expressions are developed for the physical parameters of a composite system in relation to those of the constituents. The interfacial tension between the dispersed phase and continuous matrix is included in the derivation. The results show that it has effect only on the shear parameter but not on the bulk parameter of the composite system. The general expressions developed in this article represent a unified theory for composite systems. The results are shown to reduce to many special cases obtained by other investigators.
Interpretation of fracture surface features in polycarbonate
Authors: Hull D. , Owen T. W. 
Published: April 2003

AbstractThe fracture surface of notched impact specimens of polycarbonate tested in the range 130°C to −196°C have been studied by use of optical microscopy and scanning electron microscopy. The morphological features associated with the initiation and propagation of fracture have been determined and interpreted in terms of the processes which occur in association with fracture, notably crazing. The fracture processes are similar to those observed in poly(methyl methacrylate) and polystyrene. The transition from ductile to brittle fracture is attributed to the case of crazing relative to shear yielding.
Infrared spectroscopic studies of polymer transitions. III. Effects of sodium ion on glass transitions in styrene‐based ionomers
Authors: Ogura Katsuyuki , Sobue Hiroshi , Nakamura Shigeo 
Published: April 2003

AbstractThe glass transition in styrene‐based ionomers was investigated by means of infrared spectroscopy and differential scanning calorimetry (DSC). Transition temperatures were determined from the temperature dependence of the peak absorbances of the 1700 and 1745 cm−1 bands. These transition temperatures agreed with glass transition temperatures (Tg) determined by DSC. With increasing degree of ionization, Tg and the enthalpy ΔH of the residual intermolecular hydrogen bonding increased. The values of Tg obtained were analyzed by the theory of Fox and Loshaek for the effect of crosslinks. It is concluded that sodium ions probably from ionic domains and act as crosslinks to reinforce the residual hydrogen bonding and may increase Tg. The absorbance at 1560 cm−1 (νCOO−) did not change at Tg. This suggests that the glass transition observed here is not due to the onset of the mobility in ionic domains, as has been proposed for ethylene‐based ionomers on the basis of dielectric measurements.
Drag reduction in turbulent flow by polymer additives
Authors: Lumley J. L. 
Published: April 2003

AbstractA brief survey is given of the drag reduction phenomenon, emphasizing the aspects which must be explained by any theory: onset, the existence of intrinsic drag reduction, the Newtonian plug, saturation with increasing concentration, and the maximum drag reduction asymptote. In addition, the polymer properties observed to be favorable are noted. Experimental and theoretical arguments are cited, indicating that sublayer stability arguments are not relevant. Recent evidence is given, linking the onset phenom‐enon to a molecular time scale. The behavior of isolated molecules in flow fields is briefly surveyed, indicating the possibility of large increases in viscosity in relatively rotation free strain rate fields; indirect experimental evidence for such behavior is cited, and it is shown how, by reducing the intensity of the smallest eddies, this can explain the various aspects noted. The maximum drag reduction asymptote is discussed, in connection with recent measurements of turbulent fluctuations in drag reducing flows, and it is shown how both of these may be related to changes in the large eddy structure caused by the polymer induced changes in the small eddies.
Correlations between types of absorbed water molecules and water permeability in swollen polymer membranes
Authors: Chang Y. J. , Chen C. T. , Tobolsky A. V. 
Published: April 2003

AbstractA series of poly(vinyl formal) membranes was synthesized by formalization of poly(vinyl alcohol) membranes. Representative pieces were selected for this study. Some cellulose acetate membranes cast from dioxane were used for comparison. The main experimental techniques employed included water absorption measurements and direct osmosis measurements. Aqueous solutions of sodium chloride at various concentrations were used for the studies of permeation through the membranes by direct osmosis.The plot of water permeability coefficient Pw versus volume fraction Vw of water absorbed in a membrane was interpreted in terms of the effect of two different types of absorbed water molecules. The individual diffusion coefficients were evaluated from asymptotic slopes of the curves. Similar analyses applied satisfactorily to data found in the literature.
Calorimetric study of free‐radical polymerized poly(p‐biphenyl acrylate) and poly(p‐cyclohexylphenyl acrylate)
Authors: Frosini V. , Magagnini P. L. , Newman B. A. 
Published: April 2003

AbstractDSC traces and specific heat data for poly(p‐diphenyl acrylate) (PPBA) and poly(p‐cyclohexylphenyl acrylate) (PPCPA) obtained by radical polymerization are reported. The results indicate the existence of a definite ordered phase and of a reversible firstorder solid–liquid transition in both polymers although x‐ray diffraction studies showed that they are not crystalline in the conventional sense. The extent of the ordered phase present in each polymer is calculated, and the problems involved in such determination by thermal measurements are discussed. On the basis of the experimental results reported here in conjunction with the x‐ray data, models are proposed for the morphology of these polymers.
Free‐radical decay in irradiated PMMA
Authors: Davis L. A. 
Published: April 2003

AbstractData from the literature are analyzed to show that decay of the chain‐end radical of PMMA in the regime of 80–130°C and 1–13000 atm occurs by two mechanisms operating in parallel. These processes are characterized by activation volumes of ca. 70 Å3 (I) and ca. ∼7.5 Å3 (II), suggesting that decay by process I occurs by chain‐end diffusion and decay by process II occurs by unzipping of the polymer radical to the monomer.
Thermally stimulated chemiluminescence in photo‐oxidized poly(ethylene 2,6‐naphthalene dicarboxylate)
Authors: Richards R. R. , Rogowski R. S. 
Published: April 2003

AbstractPoly(ethylene 2,6‐naphthalene dicarboxylate) exhibits thermally stimulated chemiluminescence after exposure to ultraviolet radiation and oxygen. The chemiluminescence spectrum is essentially the same as the fluorescence spectrum of the polymer with a maximum intensity at 430 nm. Upon heating, the decay of the luminescence follows a first‐order law with an activation energy of 26.3 ± 0.3 kcal/mole. A comparison of the ultraviolet absorption spectra of the polymer before and after exposure to ultraviolet light and oxygen indicates that the naphthalene ring is oxidized. Heating the polymer above 80°C causes decomposition of the initial photo‐oxide to produce luminescence.
Optical anisotropy of polyisobutylene: Strain birefringence
Authors: Liberman M. H. , Debolt L. C. , Flory P. J. 
Published: April 2003

AbstractStrain birefringence measurements on crosslinked polyisobutylene (butyl rubber) confirm earlier work of Stein and Tobolsky on the linear polymer indicating the optical anisotropy to be much greater than should have been expected from the structural symmetry of the polyisobutylene (PIB) chain. The configuration–optical anisotropy parameter Δa for PIB at 25°C is 4.1(±0.1) × 10−24 cm3, or about half the value for crosslinked polymethylene, both polymers being undiluted and amorphous. Swelling with cyclohexane, CCl4, and CBrCl3 lowers Δa to values of 3.8, 3.4, and 2.8 × 10−24 cm3, respectively. Contributions from intermolecular correlations in the bulk polymer and from form anisotropy in the diluted systems are small, if not negligible. Temperature coefficients measured isometrically yield d In Δa/dT ≈ 0.2 × 10−3 deg−1. Both Δa and its temperature coefficient are much greater than calculated from rotational isomeric state theory assuming additivity of bond polarizabilities. The disparity (more than tenfold for Δa) cannot be relieved by any rational adjustment of the structural parameters. It is suggested that the severe crowding of groups in the PIB chain may affect the anisotropies of group polarizabilities.
Macromolecular nucleation
Authors: Wunderlich Bernhard , Mehta Aspy 
Published: April 2003

AbstractThe rate‐determining step of crystallization of macromolecules from melt and solution is shown to be molecular nucleation. Molecular nucleation is described by using classical nucleation theory. Good agreement is found between the molecular nucleus size and the critical length of the rejected species. Molecular nucleation has a higher free‐energy barrier than secondary nucleation; it might thus lead initially to independent patches of each molecule on the crystal surface. A possible reason for secondary nucleation on extended surfaces is suggested.
Crystallization of poly(ethylene terephthalate) induced by inorganic compounds. I. Crystallization behavior from the glassy state in a low‐temperature region
Authors: Groeninckx G. , Berghmans H. , Overbergh N. , Smets G. 
Published: April 2003

AbstractThe kinetics of isothermal crystallization from the glassy state at low temperatures and the morphology of poly(ethylene terephthalate) (PET) filled with additives are reported. Talc, kaolin, silicon oxide, and titanium oxide have been used as fillers; they act as effective nucleating agents for PET. The overall rate of crystallization depends on the volume concentration, the size distribution, and the nucleating ability of the additives. An electron microscopic study reveals a transcrystalline morphology at the surface of the filler particles. The occurrence of transcrystallinity is attributed to extensive heterogeneous nucleation induced at the filler surface. From the shape of the crystallization isotherms, it can be concluded that the crystallization mechanism depends on the type of filler.
Studies on amylose and its derivatives. X. Dilute solution conformation of amylose tripropionate
Authors: Cowie J. M. G. , Maconnachie Ann 
Published: April 2003

AbstractSome dilute solution parameters have been measured for linear amylose tripropionate samples in ethyl acetate and tetrahydrofuran. Mark‐Houwink relations for the molecular weight range 104 to 1.5 × 105 have been established, and the exponents are 0.58 and 0.61 in ethyl acetate and tetrahydrofuran, respectively. This indicates that the coil is only slightly expanded in these solvents. A value of 6.21 was calculated for the characteristic ratio C∞ leading to a steric parameter of σ = 2.32. The temperature dependence of the unperturbed dimensions (d In C∞/dT) was found to negative and of the order −4.05 × 10−3°K−1.
Synthesis and dynamic mechanical properties of heterogeneous network polymers from poly(L‐glutamic acid) and poly(oxyethylene glycol)
Authors: Mori Tetsuo , Kuchihara Yutaka , Tanaka Ryuichi , Tanaka Takehide 
Published: April 2003

AbstractHeterogeneous network polymers composed of rigid polypeptide chains and flexible polyether chains were synthesized. That is, poly(L‐glutamic acid) (PLGA) was crosslinked with poly(oxyethylene glycol) (PEG) at various carboxy/hydroxyl mole ratios K. The solubility tests and hydrolysis of heterogeneous network polymers suggest that the crosslinking reaction proceeds by esterification. The dynamic mechanical properties of these polymers(100 Hz, −100–200°C) are greatly influenced by the presence of a trace of water and the weight per cent of PLGA. In addition, some of these polymers show only one maximum in the temperature dispersion of dynamic loss modulus E″ and tan δ, although their shape is rather broad. The x‐ray photographs of these polymers show an amorphous halo or weak Debye‐Sherrer rings. These findings suggest that these polymers are not simple adducts; neverthless PLGA and/or PEG domains exist.
Crystal structure of polyisobutylene
Authors: Tanaka Tamotsu , Chatani Yozo , Tadokoro Hiroyuki 
Published: April 2003

AbstractThe crystal structure of polyisobutylene was determined by x‐ray analysis. The orthorhombic cell, with a = 6.88 Å, b = 11.91 Å, c (fiber axis) = 18.60 Å (space group: P212121 − D), contains two molecular chains each consisting of eight monomeric units in the fiber identity period. The chain conformation is essentially an (8/3) helix, but deviates appreciably from the exact (8/3) helix symmetry. The symmetry of the molecular chain is only a twofold screw axis in exact sense, and a crystallographic asymmetric unit consists of four monomeric units. The torsional angles are

equation image

where M denotes the methyl group. The averaged skeletal CCH2C and CCM2C bond angles are 128° and 110°, respectively. The large CCH2C bond angles may be due to steric respulsion between the adjacent methyl groups, giving intramolecular distances larger than 3.09 Å.
Light scattering and x‐ray characterization of amylose films
Authors: Unbehend John E. , Sarko Anatole 
Published: April 2003

AbstractSmall‐angle light scattering (SALS) in the solid state and x‐ray diffraction were used to investigate the development of anisotropic structure in water‐cast amylose films prepared under various conditions. The conditions investigated were different temperatures and relative humidities maintained during the drying of the films and different aging times and temperatures of the amylose solution prior to the casting of films. As revealed by SALS, the predominant morphology developing in these films was based on rod‐like scattering units of considerable size. At times, a low degree of spherulitic character was also evident in the films. All four experimental conditions affected the development of anisotropic structure, with the aging time and temperature producing the most noticeable effects. Increasing aging time and/or decreasing aging temperature markedly increased the rod‐like morphology of the films. On the other hand, crystallite sizes as measured by x‐ray diffraction remained constant at 24–28 Å, indicating no influence on the part of experimental conditions. These findings are discussed in the light of starch retrogradation.
Mechanical properties of ultra‐oriented polyethylene
Authors: Weeks Norman E. , Porter Roger S. 
Published: April 2003

AbstractSemicrystalline polymers generally exhibit moduli well below their theoretical limit due to chain folding and to lack of crystal alignment. Modulus increases attainable through standard drawing procedures are limited by sample fracture before large draw ratios are reached. Using an Instron capillary rheometer which allowed a draw ratio of > 300, transparent polyethylene strands of unusually high c‐axis orientation have been produced by a combination of pressure and shear. The virtually perfect crystalline orientation and evidence for extended chains confirm that a significant improvement in modulus can be realized by this technique. The dynamic tensile storage modulus was measured by Vibron over the temperature range −160°C to +120°C. Room‐temperature moduli were 7 × 1011 dyne/cm2, higher than any reported values for drawn polyethylene. Values also remained above 1011 dyne/cm2 even at 120°C. The moduli and morphological data have been related by a model consisting of an extended‐chain component in paralled with a conventional drawn morphology. Experimental and calculated moduli are compared and related to available theory.
Diamagnetic susceptibility effects in NMR measurements of the properties of water in polymeric membranes
Authors: Shporer Mordechai , Vega Alexander J. , Frommer Moshe A. 
Published: April 2003

AbstractThe NMR spectra of water adsorbed at various relative humidities on various cellulose ester membranes have been studied. Membranes of cellulose acetate (CA), cellulose triacetate (CTA), and cellulose acetate butyrate (CAB) were investigated. It was found that the resonance peak of a liquid imbibed in or adsorbed on membranes from high relative humidity is very sensitive to the angle between the membrane plane and the direction of the magnetic field, shifting 5–7 ppm to higher fields as the membrane plane is rotated from a perpendicular to a parallel position with respect to the direction of the external magnetic field. This phenomenon was found to be independent of the nature of the polymeric material (namely CA, CTA, or CAB), porosity of the membrane (varying from an “all bulk” dense sheet to an 80% porosity and 0.2 μm average pore size membrane), nature of the magnetic nuclei (H2O or D2O), intensity of the external magnetic field (60 Mcps or 100 Mcps), and nature of the liquid in the membrane (water, methanol, or n‐hexane). It is therefore concluded that the dependence of the position of the resonance peak on the position of the membrane plane with respect to the external magnetic field, is a geometrical phenomenon due to the magnetic “bulk susceptibility” of the medium. Quantitative estimations of the magnitude of the diamagnetic susceptibility effect in a cylindrically rolled sheet are given. These estimates agree well with the experimentally observed “splittings.”
Effect of solvent and carbon black species on the rubber–carbon black interactions studied by pulsed NMR
Authors: Nishi T. 
Published: April 2003

AbstractThe spin–spin relaxation time T2 and the fraction of short T2 component for composites of natural rubber with carbon black prepared under various conditions have been measured by pulsed NMR. Effect of swelling with a solvent (CCl4), carbon black species (SAF, HAF, SRF) with different surface areas, and different initial carbon black loadings (35, 50, 70 phr) have been determined. Molecular motion in the rubber phase not in the immediate vicinity of the carbon black surface increases rapidly with increasing solvent concentration, yet it is still slightly restricted compared to rubber with solvent alone. On the other hand, molecular motion in the immobilized layer around carbon black and the fraction rubber in that layer are not affected by the solvent. This indicates strong restriction of molecular motion of polymers at the surface. For estimation of the thickness of the immobilized layer, the necessity of using an appropriate measure of surface area accessible to polymer molecules is pointed out. The degree of immobilization in the layer and the thickness of the layer do not vary appreciably with the nature of carbon black or the initial loading of carbon black.
Raman scattering in uniaxially oriented samples of planar zigzag poly(vinylidiene fluoride)
Authors: Cessac Gerald L. , Curro John G. 
Published: April 2003

AbstractBand assignments of phase‐I PVF2 have been Revised by using additional data obtained by laser Raman spectra of oriented samples. A set of least‐squares refined force constants was obtained which reproduce the experimental data to an average error in frequencies of 1.3 cm−1. In order to determine the effect of electrical polarization on the spectra, a Gaussian distribution of the dipole axis was assumed. The calculation shows that polarizations of less than 60% will not significantly affect the Raman spectra.
Effect of interference between anisotropic scattering entities on light scattering from polymer films. II. The correlation function approach
Authors: Yoon Do Yeung , Stein Richard S. 
Published: April 2003

AbstractA theory is developed by use of the correlation function approach for calculating both the Hv and Vv intensity of scattered light for a concentrated assembly of spherulities. The scattering becomes a function of the radial and tangential polarizabilities of the spherulite αr and αt, the polarizability αm of the medium, surrounding the spherulites, and the volume fraction ϕs of spherulites. The “effective polarizability of the surroundings” αs, which appeared in previous theories, becomes function of these variables. The theory can explain, for example, why the Vv scattered intensity passes through a maximum during the course of crystallization.
Analysis of fractionation of ethylene–propylene copolymers
Authors: Ogawa Toshio , Inaba Tadami 
Published: April 2003

AbstractAnalysis of the solution fractionation of ethylene–propylene copolymers was carried out by assuming a bivariate normal distribution function for the distribution of molecular weight and chemical composition. It was found that the variation of the molecular weight and composition distributions in fractions was complicated, because two distribution characteristics of the original copolymer affect fractionation to differing extents. The hypothetical cumulative weight distribution curves thus obtained agreed essentially with those obtained experimentally.