bluuebunny/crossref_metadata_2025_split huggingface dataset:
The crystalline core of the row structures in isotactic polystyrene. I. Nucleation and growth
Authors: Petermann J. , Miles M. , Gleiter H. 
Published: April 2003

AbstractThe nucleation and growth of the crystalline core in the row structures of isotactic polystyrene were investigated by transmission electron microscopy. The number of core crystals, nucleated at a specific temperature, depends on the external strain. Their length was found to increase with time if the sample is kept at the straining temperature. If a strained sample is cooled to room temperature and subsequently reheated, no further growth of the core crystals is observed. Obstacles in the path of growth were circumvented by local changes of the growing direction. Melt‐soluble noncrystallizable molecules are rejected by the growing core into the surrounding melt. The observations suggest a growth mechanism of the cores based on the successive self‐induced alignment of molecules at the tip of the growing cores.
A comparison of the rheological properties of polytetrafluoroethylene below its melting point with certain low‐molecular smectic states
Authors: Starkweather Howard W. 
Published: April 2003

AbstractPolytetrafluoroethylene (PTFE) was extruded from a capillary rheometer at temperatures between the first‐order transition at 30°C and the melting point. Both PTFE at 50–300°C and various smectic states of certain low‐molecular benzylidene anilines obey the following relationship between the shear stress τ and the apparent shear rate $ \dot \gamma :{\rm }\tau = K\dot \gamma ^{{1 \mathord{\left/ {\vphantom {1 4}} \right. \kern-\nulldelimiterspace} 4}} $. The apparent viscosities for the two classes of substances are similar even though their molecular weights differ by a factor of about 104. Both have characteristic shear planes which are parallel to the polymer chains in PTFE and normal to the long axes of the benzylidene aniline molecules. The melting process in virgin PTFE begins near 300°C. Above this temperature, the shear stress at constant shear rate increases and the rheological exponent rises from 0.25 toward 0.5 at the final melting point.
Solution crystallization of nylon 6
Authors: Kyotani Mutsumasa 
Published: April 2003

AbstractElectron microscopy and x‐ray diffraction data have been obtained on nylon 6 which has been crystallized from solutions in 1,6‐hexanediol and 1,2,6‐hexanetriol. Lamellar single crystals and spherulites of the γ form are obtained by crystallization from 1,2,6‐hexanetriol. The morphology of the single crystals is different from that obtained from glycerine solutions. The spherulites of the γ form are composed of larger lamellae. Sheaflike crystals of the α form are obtained from both solvents. α‐form and γ‐form crystals both grow from 1,2,6‐hexanetriol at appropriate crystallization temperatures. α‐form crystals alone are obtained from 1,6‐hexanediol solution at every crystallization temperature. The long periods measured by small‐angle x‐ray diffraction for the solution‐grown crystals are in the range 56 to 66 Å. The melting behavior of the solution‐grown crystals is examined and discussed. Effects of solvent on growth of the two crystalline forms from solution are investigated.
Quiescent and strain‐induced crystallization of poly(p‐phenylene terephthalamide) from sulfuric acid solution
Authors: Takahashi Toshisada , Iwamoto Hiroaki , Inoue Kazuyuki , Tsujimoto Ishio 
Published: April 2003

AbstractQuiescent and strain‐induced crystallization of poly(p‐phenylene terephthalamide) (PPTA) from sulfuric acid solution has been studied. Negative spherulites (SA‐PPTA spherulites) are formed from hot concentrated solutions by cooling. The spherulite consists of radiating fibrous lamellae several hundred angstroms wide. The electron diffraction pattern indicates that PPTA molecules are oriented perpendicular to the long axes of the fibrous lamellae and that the [010] or [110] direction of the modification I crystal and [010] direction of the modification II crystal are parallel to the long axes of the fibrous lamellae. The width of the lamellae is much smaller than the chain length of the starting PPTA. It appears that hydrolysis of PPTA during melting crystallization determines the chain length, i.e., the width of the fibrous lamella. Stacked, lamellar structures like “row structures” are formed under shear. The longer axes of the fibrous lamellae are oriented perpendicular to the shear direction. It is confirmed by electron diffraction studies that the PPTA molecules are oriented parallel to the shear direction. Well‐developed fibrils with the PPTA molecules oriented to the fibril axis, are formed by adding the SA‐PPTA spherulites to water with vigorous stirring.
Simulation of the brownian motion of macromolecular chains. I. Local motions and chain conformations
Authors: Gény F. , Monnerie L. 
Published: April 2003

AbstractChains confined to a tetrahedral lattice can be considered as models for aliphatic polyethers and polyethylene. The deformations of such chains are analyzed by computer simulation using the Monte Carlo method. The elementary motions that are taken into consideration are three‐bond and four‐bond motions. The local mobility is analyzed in terms of conformational characteristics and compared with some NMR relaxation data.
Hydrodynamic interaction effects on intrinsic viscosity of perturbed chains: Experimental results for polystyrene
Authors: Cuniberti C. , Perico A. , Musi L. 
Published: April 2003

AbstractExperimental measurements of intrinsic viscosity and radii of gyration of monodisperse samples of polystyrene of molecular weights 2.33 X 105, 4.11 X 105, 6.70 X 105, and 2.3 X 106 dissolved in the homologous series of 1‐chloroparaffins from butane to undecane are reported. The dependence of the viscosity expansion coefficient αη on the expansion factor αs for the radius of gyration is discussed in the light of the results obtained by an expansion of the Fixman theory for perturbed chains to include partial draining. These results give support to the finite chain effect on the hydrodynamics of expanded coils in the usual range of molecular weight. The exponent a in the relation α3η = αas depends on molecular weight and agrees with recent nondraining theoretical calculation for exceedingly high polymers.
Comparison of polarized fluorescence with polarized raman and infrared dichroism measures of orientation in uniaxially drawn poly(ethylene terephthalate)
Authors: Nobbs J. H. , Bower D. I. , Ward I. M. 
Published: April 2003

AbstractIn a number of previous papers the results of studies of molecular orientation in poly(ethylene terephthalate) (PET) by means of refractive index measurements and infrared, Raman and fluorescence spectroscopy have been presented. The present paper attempts to correlate the results of these studies and, in particular, to explain the observation that the fluorescent molecules appear to be more highly oriented than the polymer chains. Of the two explanations considered, that which assumes that the fluorescent molecules align themselves preferentially parallel to those segments of polymer chain in which the glycol residues are in the trans conformation is the more successful. It is also shown that the development of orientation in PET can be described well in terms of a simple modification of the rubber‐network model even for large deformations.
Application of the padé approximant method to excluded volume effects in polymer chains
Authors: Tanaka G. 
Published: April 2003

AbstractClosed formulas for the expansion factor α and the h function appearing in the second virial coefficient are derived by the Padé approximant method, using the first two or three series coefficients. The equations for α agree well with experimental results for small z, the excluded volume parameter. The equation for h agrees well with data over the entire accessible range of z.
Dynamic mechanical and crystal‐strain measurements on ultrahigh modulus oriented polyoxymethylene: A revised value for the true crystal modulus
Authors: Brew B. , Clements J. , Davies G. R. , Jakeways R. , Ward I. M. 
Published: April 2003

AbstractDynamic mechanical measurements on ultrahigh modulus polyoxymethylene have been undertaken over the temperature range −150 to 20°C. Measurements of the longitudinal crystal modulus have also been made by studying changes in the (009) reflection with load, over a similar range of temperatures. The dynamic Young's modulus at 5 Hz reaches a value at low temperatures of 64.5 GPa for the most highly oriented sample. The crystal modulus at low temperatures is 105 GPa, which is almost twice the previously reported room‐temperature value.
Characteristics of solid‐state extruded polyethylene
Authors: Kolbeck A. G. , Uhlmann D. R. 
Published: April 2003

AbstractThis paper describes the properties of solid‐state extruded polyethylene as a function of two primary processing variables, extrusion temperature, and area reduction. The polymer was extruded in sheet form, giving a material having an orthotropic mode of orientation. Property data are presented for melting temperature and heat of fusion; sonic modulus, yield stress, and elongation at fracture; small‐angle x‐ray scattering; optical absorption coefficient; and morphology for material etched by ion bombardment at liquid nitrogen temperature. Combining the present results with data previously reported in the literature, it is found that over the temperature range of about 90–120°C, where polyethylene can be successfully extruded to large area reductions, many properties of the extrudates show a surprisingly small dependence on extrusion temperature. A notable exception to this behavior is the elastic modulus, which increases significantly with increasing extrusion temperatures. In contrast to extrusion temperature, area reduction is found to have a major effect on nearly all properties of solid‐state extruded polyethylene. In most cases, the form of this dependence is such that the properties change rapidly at small area reductions and much more slowly at large reductions.
Statistical mechanical model for diffusion of simple penetrants in polymers. I. Theory
Authors: Pace R. J. , Datyner A. 
Published: April 2003

AbstractFollowing Di Benedetto it is proposed that noncrystalline polymer regions possess an approximate semicrystalline order with chain bundles that are locally parallel along distances of several nanometers. Packing with on‐average four nearest neighbors is assumed. A spherical molecule may move through such a substrate in two distinct ways: (a) along the axis of a “tube” formed by locally parallel chains or (b) perpendicular to this axis by two polymer chains separating sufficiently to permit passage of the molecule. The first process is relatively fast, generally requires little activation energy, and determines the effective jump length in diffusion. The second is responsible for the activation energy of diffusion, which is taken as the minimum energy necessary to produce a symmetrical chain separation which allows transfer of a molecule. This is calculated as a function of the penetrant diameter d and parameters Γ and β which characterize the interchain cohesion and chain stiffness, respectively. Γ is estimated from the polymer density and cohesive energy density by suitably linearizing a relation given by Di Benedetto for the potential between two polymer chains approximated as infinite strings of Lennard‐Jones force centers. β is shown to be approximately obtainable from the polymer chain backbone geometry and bond rotation potentials. An expression for the diffusion coefficient D is developed which contains only one disposable parameter, the effective jump length.
Statistical mechanical model for diffusion of simple penetrants in polymers. III. Applications—vinyl and related polymers
Authors: Pace R. J. , Datyner A. 
Published: April 2003

AbstractThe theory developed in Part I of this series is modified to accommodate polymers that possess closely spaced, bulky side groups on the chains. The side groups give rise to free space between the chain “cores,” which reduces the chain separation required for penetrant motion transverse to the local chain axis. The theory is then identical to that of Part I, except that penetrant diameters minus a constant factor are employed in place of the normal diameters. In most of the cases studied the reduction factor for a given polymer may be estimated with reasonable precision from chain geometry data. This diameter‐reduction effect is the likely explanation of the apparent proportionality between the activation energy of diffusion and the square of the penetrant diameter reported earlier for vinyl polymers. The data quoted here and in Part II are analyzed to give a semitheoretical correlation between the effective jump length L̄ and ΔE, the activation energy of diffusion. This correlation appears to be equally valid for glassy and rubbery noncrystalline polymers.
High strength elastic polypropylene
Authors: Samuels Robert Joel 
Published: April 2003

AbstractThe transformation of a spun isotactic polypropylene fiber into a high strength elastic fiber has been followed structurally. By examining each stage of the transformation separately, it has been possible to identify the different structural mechanisms that occur as the process proceeds. The recognition of the important role the noncrystalline polymer plays in the process is a particularly significant result of the study.
Strain dependence of the vibrational modes of a diacetylene crystal
Authors: Batchelder D. N. , Bloor D. 
Published: April 2003

AbstractResonance Raman spectroscopy has been used to measure the strain dependence of four high‐frequency vibrational modes in a single crystal of toluene sulfonate diacetylene polymer. The 0.62‐μm thick crystal was stretched elastically to 4% strain before fracture occurred. This was equivalent to an ultimate tensile strength of 2.0 × 109 N m−2. The strain dependence of the vibrational modes has been interpreted using a simple point mass and anharmonic spring constant model. A Fermi resonance was observed for two vibrational modes which are degenerate at 2.1% strain and a 1464 cm−1 frequency.
An investigation of the coupling agent/matrix interface of fiberglass reinforced plastics by fourier transform infrared spectroscopy
Authors: Ishida Hatsuo , Koenig Jack L. 
Published: April 2003

AbstractThe mechanical performances of fiberglass reinforced plastics (FRP) are quite different when the glass fibers are treated with vinyl (VS) and methacryl (γ‐MPS) functional silane coupling agents. We have studied the structural basis for this difference on the molecular level using Fourier transform infrared spectroscopy (FT‐IR). A high‐surface‐area silica powder is used to study the coupling agent/matrix interface. Both VS and γ‐MPS can react with styrene at the interface. However, when E‐glass fiber is used as a substrate, only γ‐MPS polymerizes in the coupling agent interphase which consists of many layers of coupling agent molecules while the major portion of the VS does not polymerize in the interphase. The effect of glass surfaces, with and without a coupling agent, on the curing of the polyester resin has also been studied. Silane coupling agents participate in the curing of the polyester resin while untreated E‐glass fiber surfaces inhibit the polymerization resulting in different structures from the bulk matrix.
A permanganic etchant for polyolefines
Authors: Olley R. H. , Hodge A. M. , Bassett D. C. 
Published: April 2003

AbstractA permanganic etchant has been developed which reveals lamellar and other fine detail in surfaces of at least three crystalline polyolefines, viz., polyethylene (of both high and low density), isotactic polypropylene, and isotactic poly(4‐methylpentene‐1). In typical treatments of high‐density polyethylene ca. 2 μm of material is removed with defective regions suffering preferential attack. The etchant also discriminates between lamellar orientations, eating deeper where side surfaces of laminae are exposed than on fold surfaces, and between different polymers, attacking isotactic polypropylene more strongly than polyethylene. Comparison with other techniques authenticates the detail exposed and samples appear to be otherwise unaltered by their treatment. Besides normal imaging, it is also possible to use etched samples for transmission diffraction studies in the electron microscope. The method has very considerable application for revealing lamellar details in crystalline polyolefines (which can be chosen to be representative or selective according to the nature of the surface used). Examples are given of a wide variety of melt‐crystallized morphologies for the three polymers cited and also of lamellae in a drawn polyethylene sample. It is pointed out that permanganic etching is complementary to the technique of chlorosulfonation used to stain polyethylene in a similar way as bright field microscopy is to dark field.
Solution behavior of [(ethylene‐co‐vinyl alcohol)‐g‐ethylene oxide] graft copolymers
Authors: Endo Ryuichi , Goto Akihiko , Okano Hiroshi , Arai Hidehiko 
Published: April 2003

AbstractThe solution behavior of hydrophobic‐hydrophilic water‐soluble graft copolymers consisting of poly[(ethylene‐co‐vinyl alcohol)‐g‐ethylene oxide] was investigated by high‐resolution NMR spectroscopy and measurements of solution viscosity in tetrahydrofuran, water, and mixtures thereof at various temperatures. A graft copolymer with a backbone containing 2.7 mole% vinyl alcohol exists in an intramolecular phase‐separated conformation in aqueous solution, independent of the temperature. Graft copolymers with backbones containing 20.3 mol% vinyl alcohol exhibit an intramolecular mixed‐phase conformation in which the mobility of chains in the hydrophobic region depends on temperature. The temperature dependence of the intrinsic viscosity in water shows a maximum near 50°C.
Application of gel permeation chromatography to polyelectrolytes: Salt rejection mechanism and molecular‐weight distribution
Authors: Domard A. , Rinaudo M. , Rochas C. 
Published: April 2003

AbstractGel permeation chromatography (GPC) of polyelectrolytes in dimethylformamide (DMF) is studied. Three methods of monitoring elution (conductimetry, viscosimetry, refractometry) are used to investigate the molecular‐weight distribution and, independently, the chemical composition expressed in terms of the ionic charge density as a function of the chain length in two copolymers of acrylonitrile and sodium methallylsulfonate. The distribution on the gel of the neutral salt NaNO3 added to the DMF and used for elution is discussed in terms of Donnan exclusion; in addition, it is concluded that to obtain the correct molecular‐weight distribution, GPC measurements must be performed with an eluent containing a neutral salt at a concentration at least 5 × 10−2M to prevent electrostatic exclusion. The main difficulty in reaching rigorous conclusions comes from the dependence of the calibration curve on the salt composition of the eluent owing to interactions—dependent on the quality of the solvent—between the polystyrenes used as standards and the porous silica gel. Nevertheless, this perturbation is small and the agreement between the average molecular weights obtained by GPC and by direct determination is good and indicates that the universal calibration proposed for neutral polymers is also valid for polyelectrolytes.
Rigid backbone polymers. I. Polyisocyanides
Authors: Aharoni Shaul M. 
Published: April 2003

AbstractConcentrated solutions of poly(n‐octyl isocyanide) exhibit a mesomorphic structure, most probably nematic in nature. Poly(n‐butyl isocyanide) and poly(benzyl isocyanide), of the molecular weights at our disposal, failed to show similar behavior. Upon acidification poly(n‐butyl isocyanide) does not change, but the other two polymers turn essentially black. Infrared and proton NMR clearly demonstrate that upon acidification, poly(n‐butyl isocyanide) and poly(benzyl isocyanide) are protonated on the nitrogen atom. This process is reversible. Carbon‐13 NMR and x‐ray patterns indicate that no chemical rearrangement or conformational changes take place upon acidification. This conclusion is supported by infrared studies and by inference from the poor electrical conductivity of the solid acidified polymers.
Melting behavior of ultrahigh modulus linear polyethylene
Authors: Clements J. , Capaccio G. , Ward I. M. 
Published: April 2003

AbstractThe differential‐scanning calorimetry (DSC) behavior of drawn linear polyethylene (LPE) has been investigated as a function of draw ratio and molecular weight. All the samples examined showed a dependence of the melting temperature on heating rate, an effect generally known as superheating. The magnitude of this effect, as well as the maximum melting temperatures, increased markedly at high draw ratio and high molecular weight. The highest melting temperature recorded was 145°C for a tape of draw ratio 25 and weight‐average molecular weight of 312,000. The results were first considered in terms of the information which might be provided regarding crystal thickness. It was concluded that the DSC data are consistent with previous wide‐angle x‐ray diffraction results in confirming that an extended chain morphology similar to that observed in pressure crystallized LPE is not present in these samples. Secondly, the superheating effects were examined in the light of the possible configurational constraints on the amorphous regions of drawn polymers, along the lines proposed by Zachmann. It is possible to understand the effects of draw ratio and molecular weight very well on this basis, in a manner consistent with previous structural results on these materials.
Rheo‐optical studies on the deformation mechanism of semicrystalline polymers. IV. On the nature of alpha mechanical dispersion of low density polyethylene in relation to the mechanism of spherulite deformation
Authors: Suehiro Shoji , Yamada Takeshi , Inagaki Hajime , Kyu Thein , Nomura Shunji , Kawai Hiromichi 
Published: April 2003

AbstractThe dynamic mechanical and birefringence behavior of three kinds of test specimens, prepared from a low‐density polyethylene by different heat treatments, was investigated over the frequency range 0.008 to 4.3 Hz at various temperatures from 20 to 80°C. Reduction of both kinds of data to the common reference temperature of 50°C revealed rather broad frequency dispersions, corresponding to the α dispersion, with activation energies for the mechanical and optical relaxation processes of around 25 kcal/mole for all specimens. An annealed specimen was further investigated by dynamic x‐ray diffraction to determine the dispersions of crystal orientation and of lattice deformation. The mechanical and birefringence dispersions are associated with the dispersion of crystal orientation and with the relatively elastic nature of the lattice deformation. Thus, the mechanical dispersion could be assigned to an α1 mechanism arising from rotation of crystallites within the spherulites, i.e., a type of grain‐boundary phenomena, but not to an α2 mechanism resulting from a crystal disordering transition or premelting. Combining dynamic birefringence with dynamic crystal orientation, the mechanical α dispersion is further discussed in terms of dynamic orientation behavior of noncrystalline chain segments in order to elucidate the nature of the grain‐boundary phenomena in detail in relation to the dynamic deformation mechanism of the spherulitic crystalline texture, i.e., reorientation of “crystal grains” within orienting lamellae due to intralamellar shearing resulting from the paracrystalline nature of the lamellae. A mechanical model characterizing the grain‐boundary relaxation in association with the reorientation of the crystal grain is also proposed.