bluuebunny/crossref_metadata_2025_split huggingface dataset:
Piezoelectricity, pyroelectricity, and the electrostriction constant of poly(vinylidene fluoride)
Authors: Nakamura Ken'ichi , Wada Yasaku 
Published: April 2003

AbstractA new device for measuring the electrostriction constant of polymer films is described. Observed values for various polymers except poly(vinylidene fluoride) and poly(methyl methacrylate) agree well with those calculated from the Clausius‐Mosotti equation. Elongational piezoelectricity, the pyroelectric current, and the electrostriction constant are measured for undrawn and roll‐drawn poly(vinylidene fluoride) films. The piezoelectricity and pyroelectric current are attributed to space charges antisymmetrically distributed along thickness direction of the film for two reasons: (1) the polarity coincides between these two phenomena for all specimens, and (2) the piezoelectricity and the electrostriction constant have the same anisotropy for drawn films. Similarity of signs between piezoelectricity and pyroelectric current is observed also in poly(vinyl chloride) films. The electrical behavior of poly(vinylidene fluoride) is interpreted in terms of the ferroelectric nature of the β‐form crystal.
Oscillatory shear measurements on polystyrene melts in the terminal region
Authors: Mills N. J. , Nevin A. 
Published: April 2003

AbstractOscillatory shear measurements have been made on a range of anionic polystyrene melts of molecular weights 1000‐‐500,000. For M < 5000 the polymer chain is too short to act as a Gaussian coil and hence the compliance of the melt is very low. For 10,000 < M < 100,000 the compliance of the melt follows the Rouse model of the elasticity of isolated polymer molecules. It is necessary to use the Ferry, Landel and Williams extension of the Rouse theory for M > 40,000 to allow for the effect of entanglements on the complex modulus. For M > 200,000 the entangelment network dominates the compliance and the Rouse theory is no longer applicable.
Scattering of light by deformed disordered spherulites
Authors: Stein R. S. , Hashimoto T. 
Published: April 2003

AbstractThe change in the light‐scattering patterns upon deforming two‐dimensional disordered spherulites is shown to arise from four effects occurring upon stretching: (1) the change in shape of the spherulite, (2) the change in average orientation of the optic axes of the scattering volume elements, (3) the change in deviation of the optic axis orientation angle from its average value, and (4) the change in the distance over which this deviation is correlated. The effects of these contributions upon the experimental scattering patterns are analyzed.
Morphology of polyethylene crystallized by solution stirring
Authors: Rijke A. M. , Hunter J. T. , Flanagan R. D. 
Published: April 2003

AbstractDilatometric and calorimetric studies have been made of the fusion process of linear polyethylene crystallized by stirring xylene solutions at elevated temperatures. It is shown that the melting point of the crystals increases rapidly from 139.5°C to 145°C in the crystallization temperature range of 100–103°C and levels off to 146 ± 0.5°C, provided that very slow heating rates are employed. Stirrer‐crystallized samples treated with fuming nitric acid show higher crystalline contents. Comparison of their enthalpies of fusion and melting points indicate that higher molecular order along the fiber axis is associated with higher crystallization temperatures. This is in general agreement with corresponding results of other modes of crystallization. The attack of fuming nitric acid on stirrer crystals is characterized by weight‐loss curves similar to those of dilutesolution crystals and bulk polyethylene. The linear molecular weight dependence on time of exposure to nitric acid suggests that the oxidation proceeds mainly from the chain ends at a constant rate for samples stirred in the lower crystallization range, but an increased rate is observed for a sample stirred from xylene at 105°C. It is suggested that the lamellar overgrowths, most evident at low crystallization temperatures, are epitaxially attached to the fiber axis, whereas the smaller crossbandings observed at higher crystallization temperatures are possibly made up of elements of chains that are only partly incorporated in the highly ordered fibrous core.
Ultraviolet photoelectric effects in polyethylene
Authors: Vermeulen L. A. , Wintle H. J. , Nicodemo D. A. 
Published: April 2003

AbstractPhotocurrents developed in polyethylene in the wavelength range 360–180 nm have been measured. The action spectra show features which can be related to the corresponding features in the absorption spectrum, and in addition there is electron injection from the metal electrode at a wavelength determined by the electrode material. The time dependence of the response indicates that a long‐lived space charge is formed in the material.
Photocurrents in simple polymer systems. II
Authors: McGibbon G. , Rostron A. J. , Sharples A. 
Published: April 2003

AbstractLarge photocurrents have been observed in films of some simple polymers (containing no π‐orbitals), of which poly(vinyl fluoride) is a typical example. Not only are the currents large (up to 10−5 A/cm2) but also they are capable of being excited by light in the visible wavelength region where absorption by the polymer is too low to be detectable. The results indicate that the effects are electronic, rather than ionic, in nature.
Analysis of small‐angle x‐ray diffraction from polymers
Authors: Buchanan D. R. 
Published: April 2003

AbstractThe Fourier transform method of Vonk and Kortleve for the analysis of small‐angle x‐ray diffraction (SAXRD) from semicrystalline polymers has been compared with a modified direct method, originally due to Tsvankin. SAXRD data for three melt‐crystallized polyethylene samples have been analyzed in terms of the mean true periodicity, mean crystal length, and mean length of amorphous segments. The two methods of analysis yield substantially equivalent results for all three samples. Calibration curves for the Tsvankin analysis are tabulated, and the relative merits of the two methods of analysis are discussed. With either method, information about the diffracting structure may be deduced that is not available from a simple measurement of the position of the SAXRD maximum. In fact, direct application of the Bragg law to any but the sharpest maximum yields a spacing (the long period) that lacks direct physical significance.
Relationship between compressive yield and tensile behavior in glassy thermoplastics
Authors: Haward R. N. , Murphy B. M. , White E. F. T. 
Published: April 2003

AbstractThe effect of temperature and strain rate on the compressive yield behavior of polystyrene is compared with the effect of the same variables on crazing in tension. The results support the conclusion of other, more extensive work, which shows that crazing involves the same types of molecular processes as those which occur during deformation under compression and shear. An improved method of measuring compressive stress–strain curves is then described, and the compressive yield stress is also compared with an extrapolated tensile yield stress. The difference between the two is in line with concepts which assume a dependence of yield stress on the state of hydrostatic tension (or compression). It can be adequately described by the Mohr‐Coulomb yield criterion. Application of this criterion also enables a theoretical stress strain curve in tension to be derived from other results in compression. Comparison of the tensile stress–strain curve so obtained with those which can be directly measured with other plastics, supports the hypothesis that crazing is favored by a marked decline in engineering stress during tensile elongation (plastic instability).
Effect of water sorption on the dielectric behavior of calcium chondroitin‐4‐sulfate
Authors: Kaufman Leslie J. , Bettelheim F. A. 
Published: April 2003

AbstractThe dielectric properties of calcium chondroitin‐4‐sulfate were studied as a function of frequency, temperature, and water content. The dielectric constant changes very little with water content below “monolayer” coverage, and after that the dielectric constant follows the shape of the adsorption isotherm. The dielectric behavior is discussed as affected by interfacial polarization and by the increase in the rotational freedom of the polymer side chains.
Optical anisotropy of polymer chains and Markov processes. II. Polyoxyethylene
Authors: Lemaire Bernard , Fourche Georges 
Published: April 2003

AbstractA comparative study of the average molecular optical anisotropy 〈γ2〉 of the polyoxyethylene chain, \documentclass{article}\pagestyle{empty}\begin{document}${\rm R} \hbox{---} {\rm O}\rlap{--} ({\rm CH}_2 {\rm CH}_2 {\rm O}\rlap{--} )_n {\rm R}$\end{document} where R = CH3, H and n is the degree of polymerization of the molecule, was carried out for the different internal rotational models considered in Part I of this series. In particular, the results obtained show that the condition of interdependence between internal rotational angles of nearest‐neighboring bonds increases the average molecular optical anisotropy by about 4% (n ≫ 1), compared with the case of independent rotations. This increase is much weaker than in polyethylene chains, for which it is about 20% under analogous conditions.
Orientation effects in biaxially stretched linear polyethylene
Authors: Adams G. C. 
Published: April 2003

AbstractThe literature on polymer morphology contains many studies of structural and orientation changes occurring upon uniaxial stretching of films and fibers, but it has only an occasional reference to such studies on biaxially stretched film. This paper presents data on a structural change due to simultaneous biaxial stretching up to 6 × 6 stretch ratio of quenched linear polyethylene slightly below the melting temperature. At low stretch ratios the b axis of the orthorhombic unit cell orients predominantly in the biaxial plane of stretching or film plane. At higher than 4 × 4 stretch ratio, a second crystal orientation appears which is a (110) orientation in the film plane. Differential scanning calorimetry scans show two melting peaks occurring concurrently with diffraction effects of two crystal orientations. The evidence for two populations of crystals differing in orientation are discussed in the light of current concepts of folded‐chain lamellae and their fragmentation with elongation.
Surface tension of polymer solutions. III. Effect of molecular weight distribution
Authors: Gaines George L. 
Published: April 2003

AbstractThe lattice‐theory equations for the surface tension of polymer solutions based on the parallel‐layer model have been extended to include more than two components. The surface tensions of tetrachloroethylene solutions of some blended polydimethylsiloxane fluids have been measured at room temperature. The results are in nearly quantitative agreement with the theoretical calculations.
Structural origin of the cryogenic relaxations in poly(ethylene terephthalate)
Authors: Armeniades C. D. , Baer Eric 
Published: April 2003

AbstractThe effect of molecular organization (crystallinity, orientation) on the internal friction of poly(ethylene terephthalate) was studied by means of dynamic mechanical measurements at temperatures from 300 to 4.2°K, with a free‐oscillating torsion pendulum at 1 Hz. It was found that crystallinity decreases the intensity of the composite γ relaxation at 210°K and gives rise to an additional loss maximum ε at 26°K. Uniaxial orientation broadens the γ relaxation and gives rise to an additional loss peak δ, at 46°K. The δ and ε losses are dependent on molecular organization, occurring only in samples containing aligned, taut chain segments and crystalline structures, respectively. They have a common activation energy of 4 kcal/mole. All three low‐temperature relaxations in oriented specimens show pronounced directional anisotropy, which, in the γ loss, may be due to the preferred orientation of noncrystalline chain segments, while in the δ and ε losses, may be associated with the direction of defect structures. On the basis of the observed behavior of the δ and ε relaxations it is suggested that they may involve motions of defect structures and may thus participate in stress‐transfer mechanisms at large deformations.
Thermodynamic parameters of polymer‐solvent systems from light‐scattering measurements below the theta temperature
Authors: Scholte Th. G. 
Published: April 2003

AbstractAs is well known, the chemical potentials of polymer and solvent in solution and, hence, the Flory‐Huggins interaction parameter χ can be determined from scattered light intensities from dilute and concentrated solutions of the polymer in the solvent concerned. Preferably, measurements should be performed at temperatures as low as possible, provided the temperature exceeds the cloudpoint for the concentration used. It is shown that the lower the temperature and, consequently the higher the scattered light intensity, the better is the accuracy of the parameters obtained. At each temperature the scattered light intensity shows a maximum at some concentration. Below the theta temperature the ratio of scattered light intensity and concentrations also shows a maximum at some concentration. The values and the concentrations of these maxima for various temperatures enable the maximum of the spinodal to be determined. The spinodal itself can be determined by an extrapolation procedure of the reciprocal scattered light intensities. Measurements have been performed with three narrow‐distribution polystyrene samples in cyclohexane. On the basis of the results, χ, and its dependence on concentration, temperature, and molecular weight can be determined to high accuracy.
Morphology of polyethylene crystallized under the simultaneous influence of pressure and orientation in a capillary viscometer
Authors: Crystal Richard G. , Southern John H. 
Published: April 2003

AbstractThe morphology of high‐density polyethylene crystallized under simultaneous pressure and shear in an Instron capillary viscometer has been examined by scanning electron microscopy, electron microscopy, and selected‐area electron diffraction. Two distinct fibrous morphologies were observed in these unusually transparent strands. The outer sheath was composed of fibers, 3000 Å in diameter, aligned parallel to the extrusion direction and apparently interconnected by a lamellar cross texture. A highly crystalline ribbon texture composed of fine fibers, 200–250 Å in diameter, dominated the inner core. Sharp‐spot electron diffraction patterns obtained from these central ribbons indicated a high degree of c‐axis orientation parallel to the fibers and an extended‐chain crystal structure. The melting behavior of both irradiated and unirradiated strands examined by differential scanning calorimetry was consistent with the formation of two distinct crystalline morphological units.
Glass transition in nylons
Authors: Gordon Gerald A. 
Published: April 2003

AbstractDifferential thermal analysis (DTA) of some commercial nylons has disclosed some anomalous phenomena with respect to the glass transition, generally considered to occur at 40–50°C. On the first heat cycle the transition occurs normally. On cooling, however, no corresponding transition occurs, and on an immediate rerun the transition has disappeared. If another DTA thermogram is made after a few hours, the transition begins to reappear, but at a temperature lower by a few degrees. After about five days rest, the transition is again normal in size and temperature. On annealing at 75°C, the 43°C transition is pushed up to about 92°C. On resting after annealing, transitions appear at both 40 and 92°C. These phenomena are explained in terms of the slow formation of a hydrogen‐bonded network in the amorphous regions of the polymer. It is the disruption of this network that is normally considered to be the glass transition in nylons. The network is slow in re‐forming because of problems involved in matching up potential hydrogen‐bonding sites, which are, of course, distributed at intervals along the polymer chain. The temperature at which the network is disrupted is apparently dependent not so much on the ratio of bonding to nonbonding sites, as on the temperature at which it was formed.
Radiation chemistry of poly(propylene oxide)
Authors: Roberts G. P. , Budzol M. , Dole Malcolm 
Published: April 2003

AbstractAtactic, isotactic, and optically active poly(propylene oxides), PPOx, were irradiated with both γ‐rays and electron beams. Up to a dose of 37 Mrad no change could be detected in the optical activity. G values for hydrogen evolution decreased as compared to polypropylene in about the same ratio as G(H2) of polyoxymethylene decreased as compared to polyethylene. G values for crosslinking and scission, estimated by means of gelation theories of Saito and Inokuti, were found to be greater for isotactic than for atactic PPOx. The behavior of transient infrared and ultraviolet absorption bands is discussed. Intrinsic viscosity data indicate a rapid initial chain degradation whereas CO gas and OH group production is linear with dose. Evidence for the conversion of one type of free radical to another on heating an irradiated sample from 77°K to room temperature is based on the behavior of transient infrared and ultraviolet absorption bands.
Fold surface of polyethylene single crystals as assessed by selective degradation studies. II. Refinements of the nitric acid degradation method
Authors: Keller A. , Udagawa Y. 
Published: April 2003

AbstractDetailed critical examinations of three aspects of nitric acid treatment of polyethylene are reported. (1) The endgroups introduced by the nitric acid are examined. It is concluded that in samples degraded to a single‐crystal traverse stage, carboxyl features only as endgroup, and conversely each chain‐end is terminated by such a group. Consequently, the carboxyl content can be used for quantitative characterization of the cut chain length. The function and position of the nitro group remains unexplained. (2) The morphological selectivity of the nitric acid‐induced degradation is scrutinized. It is concluded that the crystal core is attacked and thinned by the acid; the slowing down of the reaction is principally due to accumulation of reaction products. Accordingly, the usual distinction between a vulnerable amorphous layer and a resistant crystal core is not justified on the basis of such degradation experiments. It follows that meaningful structural information is obtained only when the relevant crystal properties are studied as a function of chain cutting, assessed from the molecular weight distribution (GPC), as opposed to that of degradation time alone. (3) The role of sample consistency and reagent strength has been examined. It is demonstrated that for the reaction to be sufficiently uniform throughout the sample for the results to be meaningful, the reaction rate has to be slow compared to the rate at which the reagent diffuses into the specimen. To realize these conditions, finely dispersed samples and weak reagents were found to be favorable
NMR observations of drawn polymers. VIII. Doubly oriented nylon 66
Authors: Olf Heinz G. 
Published: April 2003

AbstractA wide‐line NMR study of chain segmental motion in nylon 66 has been made on a rolled sheet having “double orientation.” In this sheet the crystallite c axis, i.e., the molecular chain axis, is oriented preferentially along the roll direction, and the crystallographic (010) plane lies predominantly parallel to the roll plane, or the plane of the sheet. The direction of the applied magnetic field with respect to the sheet is characterized by two angles, the polar angle γ subtended by the roll direction and the magnetic field, and an azimuthal angle ϕ. NMR spectra were taken at various values of the angles γ and ϕ and at three temperatures −196°C, 20°C, and 180°C. The second moments of the absorption spectra taken at 180°C were compared with theoretical predictions of second moments based on two models for the high‐temperature segmental motion (called the αc process) in crystalline regions of nylon 66. One model consists of rotational oscillation with amplitudes δ of segments around their axies. The second model is denoted 60° flip‐flop motion and consists of rotational 60°C jumps of the segments around their axes between two equilibrium sites with the possibility that the segments also oscillate with a general amplitudes δ around each site. The experimental results are consistent with fairly large amplitudes δ, in which case both models approach the limiting case of full segment rotation. For this reason the experiments do not allow a distinction between the two models. From the second moments at −196°C and 20°C the decrease in second moment due to the low temperature segmental motion, the γ process, is obtained. This motion occurs in noncrystalline regions of nylon 66 and is found to cause a decrease in second moment which is strongly dependent on the two angles γ and ϕ, implying double orientation of the noncrystalline segments. It is suggested that at low temperatures the noncrystalline segments become immobilized in sites dictated by the crystallite orientation through the extensive hydrogen bonding known to exist in nylon 66.
Self‐oscillation mechanism of necking on extension of polymers
Authors: Andrianova G. P. , Kechekyan A. S. , Kargin V. A. 
Published: April 2003

AbstractA new phenomenon in necking of some polymers, including poly(ethylene terephthalate) (PETP) was detected. It was found that extension of PETP films under certain conditions results in periodic stress oscillations and a periodic change in appearance of the sample. The conditions at which self‐oscillations appear have been determined, and the principal regularities of this regime of deformation are described. The following factors are critical for the appearance of self‐oscillation: speed of straining and compliance of the sample. The self‐oscillation of stress and formation of the periodic transverse bands is attributed to heat dissipation during necking corresponding to local temperature jumps and periodic strong variation of elasticity modulus due to poor heat conductivity of the polymer. Changing the external conditions of heat transfer influences the possibility and development of the effect. The phenomenon is common for various crystallizing polymers, being dependent on physical properties of the polymer and conditions of deformation.
Crystallinity and conformational changes in poly(β‐benzyl L‐aspartate)
Authors: Obata Hiroko , Kanetsuna Hisaaki 
Published: April 2003

AbstractThe crystallinity of poly(β‐benzyl L‐aspartate) is highly variable, in a series of specimens prepared under various conditions: films cast from chloroform solutions at various evaporation rates, films cast comparatively slowly from chloroform–trifluoroacetic acid solutions, films prepared from dichloroacetic acid solution by treatment with ethyl alcohol, precipitates formed from trifluoroacetic acid solution by addition of ether. Film cast slowly from chloroform is in the highly crystalline ω form. In contrast, the conformation of the benzene rings in the ω helix obtained from the α helix by heating is distorted to some extent in comparison with the structure of the highly crystalline ω form. Crystallization and conformational changes from the α to the ω form, and from the ω to the β form upon heating, are correlated with the dispositions of the side chains, the packing of the benzene rings, and the motion of the side chains. The main chain of the α helix is distorted into the ω form when its side chains are in a favorable conformation. The α helix is stable in the disordered conformation, and it is distorted to some extent at high temperature.