bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of polyethylene modified with phosphonate side groups. I. Thermal and mechanical properties
Authors: Weiss R. A. , Lenz R. W. , MacKnight W. J.
Published: April 2003

Low‐density polyethylene was modified by the inclusion of phosphonate ester pendent groups by using an oxidative chlorophosphonylation reaction followed by esterification of the polyethylene poly(phosphonyl chloride) with an alcohol. Two different types of phosphonate esters were prepared: dimethyl phosphonate from the reaction with methanol and a phosphonate graft copolymer from the reaction with hydroxy‐terminated poly(ethylene oxide) (PEO). For the latter, oligomers with molecular weights of 350 and 750 were used. For each type of phosphonate, a series of polymers were prepared with pendent group concentrations ranging from 0 to 9.1 substituents per 100 carbon atoms. The modified polymers were characterized by infrared spectroscopy, differential scanning calorimetry, and by measurement of the tensile modulus. Infrared spectroscopy proved to be useful for determining if the polymer modification reaction resulted in entirely phosphonate ester pendent group substitutions or if unesterified phosphonic acid groups were also present. The polymers prepared in this investigation exhibited no infrared absorbances arising from phosphonic acid groups. The presence of phosphonate ester groups resulted in a decrease of crystallinity with increasing phosphonate concentration and with the exception of the polymers containing 9.1 PEO–phosphonate grafts per 100 carbon atoms, the effect of phosphonylation on the melting temperature of the polymers was consistent with Flory's theory for the melting point depression of random copolymers. The tensile modulus measured from a constant uniaxial elongation experiment decreased with increasing phosphonylation. The behavior of all three phosphonate series was identical and could be attributed to the effect of decreasing polymer crystallinity.
Dynamics of chain molecules. Intramolecular diffusion controlled reactions for a pair of terminal reactive groups
Authors: Perico Angelo , Cuniberti Carla
Published: April 2003

The first order intramolecular rate constant for the reaction between the terminal groups of flexible macromolecules is calculated in the partial draining case, following the theory formulated by Wilemski and Fixman for diffusion controlled reactions. Substantial differences with respect to the nondraining and free‐draining limits are evidenced, and it is shown that the rate constant in the partial‐draining case has relevant contributions from all the modes of the bead‐spring chain. The effects of chain flexibility and hydrodynamic interaction in macromolecules of increasing molecular weight are examined. The effective diffusion constant of the end groups increases with both the flexibility and the length of the chain. Numerical results for polystyrene (PS) and polydimethylsiloxane (PDMS) are presented and employed to calculate the relative quantum yield for fluorescence quenching. For highly flexible chains, like PDMS, quenching effects are expected in a range of molecular weight well above the limit of validity of the bead‐spring model. On the contrary, for more rigid polymers, like PS, the quenching can be observed only at molecular weights lower than this limit. The calculated behavior is compared with some experimental results recently obtained by the authors.
Solution grown isotactic polystyrene crystals. II. Kinetics of thermal changes by x‐ray diffraction
Authors: Overbergh N. , Sadler D. M. , Keller A.
Published: April 2003

The present paper is a study of the annealing, melting, and recrystallization behavior of solution grown isotactic polystyrene crystals in order to elucidate changes both in total lamellar thickness and in the thickness of the crystalline “core” as a function of temperature. The lamellar thickness was obtained from x‐ray long spacings and the core thickness from the broadening of appropriate reflections, both assessed by a high sensitivity x‐ray detector system able to produce records within a few minutes during time dependent processes. The x‐ray results were correlated with differential scanning calorimetry (DSC) measurements. On heating, first the usual annealing effects with little net melting were observed, but on increasing the temperature large changes in long spacing, which were reversible with temperature, were seen accompanied by only small changes in crystal core thickness. The second effect was found to be associated with a substantial degree of melting. Even after heating above the temperature where complete melting was indicated by DSC, the recrystallization rate was found to decrease as the melt temperature was increased and to be much faster than on cooling from the usual melts. Strikingly, this recrystallization was accompanied by a decrease in long period with time even under isothermal conditions. It is inferred that the memory of the preceding crystalline stack is preserved throughout the melting range and even beyond this, far into the molten state. This “seeding” effect is intrinsic to the polymer even if its nature cannot be specified. The principal effects in question can then be explained by envisaging that randomly placed lamellas gradually disappear within the stack on melting and successively reappear on crystallization during cooling. These ideas agree well with previous work on reversible long spacing changes in polyethylene (see ref. 9) and are likely to be of wider generality for melting and recrystallization phenomena in systems having stacked lamellar morphologies.
The effect of thermal stress on the thermal expansion coefficient and glass transition temperature of glass fiber–polymer composites
Authors: Kajiyama T. , Yoshinaga T. , Takayanagi M.
Published: April 2003

The thermal expansion coefficients of glass fiber–polymer composites were calculated applying the solid cylindrical model taking into account the interaction effects among the glass fibers. The stress and displacement in the composite model were determined as functions of the thermal stress. It was found theoretically that the deviation of the thermal expansion coefficient from the linear mixture relationship based on volume additivity appeared at around Tg + 20 K upon cooling. The thermal expansion coefficient of the composite was also found to be markedly dependent on the dispersion state of the glass fibers. An expression for the difference in the Tg of the matrix resin in the composite from that in the unloaded resin was obtained on the assumption that the volume change of the matrix resin caused by mixing was compensated by free volume expansion. The experimental results obtained by differential scanning calorimetry (DSC) measurements were found to agree well with the theoretically predicted ones.
Small‐angle light scattering from thin polymer films: Multiple scattering from samples with rodlike morphology
Authors: Lévesque Denis , Prud'homme Robert E.
Published: April 2003

Hartel's theory for multiple scattering has been generalized to the case of small‐angle light scattering (SALS) by polymers having a roadlike morphology. It is shown that multiple scattering tends to make the scattering tends to make the scattering patterns more diffuse and leads to an underestimation of the size of the units (rods) measured from such patterns. The error induced by neglecting multiple scattering has been estimated at 10% for a transmittance of 75% and at 22% for a transmittance of 50%. A correction method based on Hartel's procedure is suggested.
Crystallization of polydioxolan. II. Morphology and melting properties
Authors: Prud'homme Robert E.
Published: April 2003

Polydioxolan samples crystallized between 25 and 35°C present two optical phases when viewed on the polarizing microscope. These phases, termed central and external phases, form a spherulite. It is shown in this paper that the central phase of the two‐phase spherulite melts at about 63°C, and is made of modification III crystals. The external portion of the two‐phase spherulites melts at a lower temperature, around 59°C, and is composed of modification II crystals. Differential scanning calorimeter (DSC) melting curves, photomicrographs, and x‐ray results are presented to prove these assertions.
Influence of chemical modification (bromination) on structure and charge transport in poly(N‐vinylcarbazole)
Authors: Griffiths C. H. , Okumura K. , Van Laeken A.
Published: April 2003

Bromine has been randomly substituted in the 3 or 6 position of the pendant carbazole group of poly(N‐vinylcarbazole) using N‐bromosuccinimide in chlorobenzene solution. X‐ray diffraction indicated that this substitution interferes with the interchain interactions in the amorphous polymer eliminating the unusual degree of chain parallelism and destroying the ability to crystallize. Charge carrier photogeneration and mobility measurements show that holes are still the majority carrier in the bromine‐substituted polymer but both generation and mobility are substantially reduced compared to the unsubstituted polymer. It has not been possible to separate the influence of pendant group electronic structure from that of bulk chain conformation in this modification of the polymer photoconductive properties.
Mechanical behavior of a highly oriented polyethylene rod
Authors: Crissman John M. , Zapas Louis J.
Published: April 2003

Dynamic mechanical and single step stress relaxation data are presented for a highly oriented linear polyethylene rod as produced by a high pressure extrusion technique. The results indicate that both major relaxation processes normally observed in unoriented polyethylene are virtually absent in torsion, whereas they are present in flexure. Stress relaxation in torsion data show a very highly nonlinear behavior when compared to similar data for an unoriented polyethylene rod.
Crystallization and melting of the system isotactic polystyrene + poly(2,6‐dimethyl phenylene oxide)
Authors: Berghmans H. , Overbergh N.
Published: April 2003

From glass transition Tg measurements on isotactic polystyrene (IPS)–poly(2,6‐dimethyl phenylene oxide) (PPO) blends, it was concluded that thoroughly annealed, freeze‐dried samples, or samples evaporated from solution at high temperature, are homogeneous. Without annealing, the freeze‐dried blends show two to three Tg's characteristic of the presence of different phases. The overall crystallization rate of these samples is much higher than that observed with annealed samples. The presence of dissolved PPO in annealed samples reduces the overall crystallization rate and the spherulitic growth rate, compared to IPS. The melting behavior of the blends is influenced by the extent of mixing of both polymers. Without annealing, isothermally crystallized, freeze‐dried blends show the same melting behavior as IPS (i.e., multiple melting). In homogeneous annealed samples the rate of reorganization is strongly reduced and multiple melting only occurs at low scanning rate (e.g., 1°C/min). This behavior is influenced by the crystallization temperature and by the composition of the blends. The addition of PPO has no influence on the relation between melting point and crystallization temperature and the same equilibrium melting point is found by extrapolation.
Longitudinal acoustic mode in polymers. II. Solution of the general composite perturbed elastic rod
Authors: Hsu S. L. , Ford G. W. , Krimm S.
Published: April 2003

The theory of the longitudinal vibrations of a composite rod with perturbing forces at the ends has been generalized by the inclusion of inertial effects at the ends of the rod. The frequencies have been calculated for both symmetric and asymmetric forces and masses. The problem of coupled rods has also been treated, and its relation to the isolated rod is shown. These results should be applicable to the study of longitudinal acoustic modes in long chain molecular systems.
Viscoelastic properties of entangled polymers. II. The interchain–intrachain entanglement model
Authors: Hong S. D. , Hansen D. R. , Williams M. C. , Shen M.
Published: April 2003

Our earlier model of entangled chain dynamics represented the elastic effects at entanglement points as a coupling with the surrounding medium, which was propagated weakly to every other entanglement site on the parent chain. In this way, a great variety of linear viscoelastic phenomena could be successfully predicted, with the only significant deficiency being a quantitative failure in curve fitting the local minimum in dynamic loss modulus G″(ω). Here we introduce the “intrachain entanglement,” or the “internal entanglement,” in which the parent chain entangles directly with itself. Elastic forces between pairs of internal entanglements are assumed to be stronger than those with the medium (“external entanglement”). Predictions of the new model are compared with rheological data on monodisperse polystyrene. Good agreement is obtained between theory and experiment, including G″(ω).
Spectroscopic examination of chain conformation and bonding in poly(phenylene oxide)–polystyrene blends
Authors: Wellinghoff S. T. , Koenig J. L. , Baer E.
Published: April 2003

Ultraviolet and Fourier‐transform infrared spectroscopy are used to characterize the chain conformation of 2,6‐dimethyl poly(phenylene oxide) (2MPPO) in compatible 2MPPO‐polystyrene (PS) blends. Blending with PS increases the intramolecular energy of the 2MPPO. Atactic PS induces a greater distortion from the minimum energy conformation of 2MPPO than isotactic PS. The dispersion interaction between the phenyl ring of PS and the phenylene ring of 2MPPO is found to be quite strong. These large intermolecular forces are thought to supercede the increase in 2MPPO conformational energy and to be responsible for the blend compatibility.
Diffusion of long molecules through solid polyethylene. I. Topological constraints
Authors: Klein J.
Published: April 2003

It is proposed that the mobility of sufficiently long molecules undergoing translational diffusion through solid polyethylene is significantly reduced by tie molecules and fixed entanglements within the interlamellar regions of the matrix. The effect on the diffusion coefficient both of diffusant molecular length and of the host matrix morphology is considered, and a semiquantitative relation between them obtained. This indicates that the mobility of long diffusants is higher in polyethylene which has been cooled slowly from the melt than it is in quenched polyethylene, in marked contrast to the behavior of gaseous and other small diffusants.
Diffusion of long molecules through solid polyethylene. II. Measurements and results
Authors: Klein J. , Briscoe B. J.
Published: April 2003

The diffusion coefficient for two diffusants of the type n‐(CH2)NX is measured, where N ≃ 25, 45 and X is a suitable label; the matrix is linear polyethylene cooled at two widely differing rates from the melt. The measuring technique used is a recently developed one based on infrared microdensitometry. The results indicate that these diffusants diffuse faster in the slowly cooled matrix, in marked contrast to the behavior of gaseous diffusants. They are in agreement with the predictions of the model developed in a previous paper (part I), in which the constraints imposed by interlamellar tie molecules on long diffusants were shown to be important.
On the interrelation between microstructure and physicochemical properties of some polyconjugate systems
Authors: Grigorovskaya V. A. , Basin V. E. , Khakimova D. K. , Lyubchenko L. S. , Cherepanova E. S. , Berlin A. A.
Published: April 2003

Soluble oligoarylenes based on naphthalene and anthracene, and fractions of different molecular weights have been studied by electron microscopy. For the examined samples, a definite interrelation is ascertained between microstructure and physicochemical properties, such as density, x‐ray parameters, heat of solution, electron paramagnetic resonance (EPR) spectra, and dark conductivity. The molecular‐weight distribution of oligoarylenes is shown to decisively influence the degree of packing of macromolecules and their physicochemical properties. This allows interpretation of some anomalous properties of oligoarylenes in comparison with the first members of the corresponding homologous series.
Infrared dichroism of glassy polycarbonate at small strains
Authors: Jansson J‐F. , Yannas I. V.
Published: April 2003

The dichroism of the 889, 1364, and 3063 cm−1 infrared absorption bands of glassy, amorphous polycarbonate has been measured as a function of the strain in the range 0 to 2% at 23°C. The data obtained for these three bands superpose rather well over this strain range. Negligible dichroism is observed up to about 0.6% strain; above this level, the dichroic ratio increases in an approximately linear manner. Independent mechanical data, obtained under comparable conditions of time‐scale and temperature, are cited which show that a transition from approximately linear to marked non‐linear viscoelastic behavior occurs with glassy polycarbonate in the range 0.7 to 1.0% strain. The coincidence on the strain axis of a relatively abrupt increase in optical absorption anisotropy with a distinct change in Young's modulus is discussed in terms of a recent molecular theory of deformation of glassy polymers. It is suggested that the data are consistent with the view that the transition from linear to nonlinear viscoelastic behavior in glassy polycarbonate is marked by the onset of significant rotation around backbone bonds.
Extensional flow‐induced crystallization in polyethylene melt spinning
Authors: Nadkarni V. M. , Schultz J. M.
Published: April 2003

Polyethylene was spun into a heated chamber, with the spin‐line temperature controlled in the range of 90–120°C. Within narrow limits, the stretch rate of the fiber was also controlled. Spin‐line and crystallization onset conditions were characterized. Characteristics of fibers as‐spun were measured via wide‐angle x‐ray scattering (WAXS), density, scanning electron microscopy, and differential scanning calorimetry. Spin‐line data indicate that elongational flow enhances crystallization rate and that time under spin‐line conditions is an important parameter. Analysis of WAXS data shows a typical “b‐axis radial” orientation, the details of which change with spin‐line parameters. This orientation is consistent with growth of lamellar crystals on extended‐chain fibrils (shishkebab model). Other physical data are also consistent with this microstructure. Microcamera x‐ray patterns show a similarity of microstructure generation in spinning and drawing.
Supramolecular structure of a high‐modulus polyaromatic fiber (Kevlar 49)
Authors: Dobb M. G. , Johnson D. J. , Saville B. P.
Published: April 2003

The supramolecular organization of the aromatic polyamide fiber Kevlar 49 has been studied using a combination of electron diffraction and electron microscope dark‐field image techniques. The dark‐field images derived using selected reflections from longitudinal sections exhibit axial banding of two main types having periodicities of 500 and 250 nm. Careful analysis, including tilting experiments, conclusively shows that the supramolecular architecture of these fibers consists of a system of sheets regularly pleated along their long axes and arranged radially.
Phosphorescence studies of relaxation effects in bulk polymers. I. Depolarization measurements of segmental relaxation in poly(methyl acrylate)
Authors: Rutherford H. , Soutar I.
Published: April 2003

This paper reports the first measurements of macromolecular segmental relaxation times by phosphorescence depolarization. Steady‐state phosphorescence polarization experiments were performed on samples of poly(methyl acrylate) incorporating 0.5 wt % copolymerized acenaphthylene or 1‐vinyl naphthalene as phosphorescent probes over the temperature range 77 to 310°K. Depolarization of phosphorescence occurs with the onset of segmental motion of the polymer at ca. 278°K. Motion of either probe is characterized by an activation energy of 195 (±5) kJ mole−1, which is in fair agreement with the mean value of 230 kJ mole−1 estimated for the segmental relaxation of poly(methyl acrylate) by dielectric and mechanical relaxation techniques. Transient depolarization measurements confirm the absence of probe motion below the glass transition temperature. Phosphorescence intensity and triplet state lifetime data are capable of detection of a second transition in the polymer in accord with observations using more conventional techniques.
Yielding of a notched poly(vinyl chloride) sheet
Authors: Narisawa Ikuo , Ishikawa Masaru , Ogawa Hiroyuki
Published: April 2003

The development of plastic deformation around the crack tip of poly(vinyl chloride), a ductile glassy polymer, has been studied in relation to the Dugdale–Barenblatt model of ductile yielding. Three‐dimensional observations reveal that the plastic deformation ahead of the crack tip consists of crazes, shear bands, and their intersections. The formation of the craze is due to a state of plane strain at the immediate vicinity of the crack tip and restricted to early steps of loading. The size and shape of the fully developed plastic zone can be described by the model. The influence of strain hardening beyond the yield point is discussed on the basis of comparison of the plastic zone lengths of poly(vinyl chloride) with those of polycarbonate which always shows shorter lengths than the model predicts.
The crystalline character of atactic poly(p‐biphenyl acrylate) and poly(p‐cyclohexylphenyl acrylate) in their dynamic mechanical response
Authors: Frosini V. , Magagnini P. L. , Newman B. A.
Published: April 2003

Dynamic mechanical properties have been determined in atactic poly(p‐biphenyl acrylate) (PPBA) and poly(p‐cyclohexylphenyl acrylate) (PPCPA) in the temperature range from 80 to 540°K at frequencies in the range 103–104 Hz. The general behavior of the dynamic elastic modulus as a function of temperature shows a transition region from the glassy state at about 390°K for both polymers, a plastic region extending over a temperature interval of about 100°K, and another transition to the melt situated at 540 and 480°K for PPBA and PPCPA, respectively. The experimental data show that the mechanical behavior of both polymers strongly resembles that of crystalline polymers. The loss spectrum of PPBA shows the presence of several important maxima: one corresponding to the melting point, characterized by a very rapid increase of losses with increasing temperature (α′ relaxation), one in the glass‐temperature range, characterized by a rather broad peak (α′ relaxation), and others below Tg, associated with secondary relaxation effects. The analysis of the different transitions and relaxations indicates that some of these processes can be ascribed to motions taking place in the ordered regions of the polymer. PPCPA shows a similar loss pattern; however, owing to the lower melting point the α maximum is partially submerged in the α′ relaxation associated with the melting process. Of particular interest is the γ process in the glassy state of this polymer, caused by the chair–chair transition of the cyclohexyl rings. The limited intensity of this relaxation as compared with that of most polymers containing cyclohexyl side groups, has been interpreted as due to the high ΔF associated with such a transition for cyclohexyl rings linked to phenylene groups. This leads to some interesting conclusions about the conformation of the side groups in PPCPA.
Volume dependence of the elastic equation of state
Authors: Yen L. Y. , Eichinger B. E.
Published: April 2003

The elastic component of the solvent chemical potential in isotropically swollen polymer networks is investigated as a function of the degree of dilation. The experimental method is similar to one employed by Gee, Herbert, and Roberts; the differential solvent vapor sorption by crosslinked and uncrosslinked polymers is measured as a function of solvent activity. Three systems have been investigated: poly(dimethylsiloxane) + benzene, poly(styrene‐co‐butadiene) + benzene, and poly(styrene‐co‐butadiene) + n‐heptane. The same vulcanizate was used for the latter two series of measurements. The qualitative behavior found for all three systems is in general agreement with the results of Gee et al. on natural rubber + benzene. The data suggest that the elastic and mixing free energies are not separable.
Crystal structure of isotactic poly(4‐methyl‐1‐pentene)
Authors: Kusanagi Hiroshi , Takase Minoru , Chatani Yozo , Tadokoro Hiroyuki
Published: April 2003

The crystal structure of isotactic poly(4‐methyl‐1‐pentene) was determined by x‐ray analysis. The unit cell is tetragonal, P4b2, with α = 18.70 Å and c (fiber axis) = 13.68 Å; it contains four molecular chains each consisting of seven monomeric units in the fiber period. The molecular conformation is essentially a (7/2) helix, but deviates slightly from the uniform (7/2) helix. The unusual low density is discussed from the structural point of view.
Effect of hydrogen bonding and ionic aggregation on the melt rheology of an ethylene–methacrylic acid copolymer and its sodium salt
Authors: Earnest T. R. , Macknight W. J.
Published: April 2003

A study has been made of the dynamic and steady shear melt theology of an ethylene‐methacrylic acid copolymer, its methyl ester, and 70% neutralized sodium salt. Measurements were made with a Rheometrics mechanical spectrometer using the eccentric rotating disks and cone‐and‐plate geometries over a temperature range of 120–180°C and frequency range of 10−3 to 102 rad/sec. Correspondence was found between steady shear viscosity and the complex dynamic viscosity for the ester and acid materials. Over the temperature and frequency range studied the time‐temperature superposition principle was applicable to G′ data for each of the derivatives and a supermaster curve could be constructed from the three individual master curves. Time‐temperature superposition was found not applicable to G″ data for the sodium salt. Differences in rheological response between the ester and acid copolymers are explained by differences in Tg. It is suggested that differences in temperature shifts ΔT required to produce G′ superposition between the three derivatives reflect differences in ΔH for interchain interactions. A mechanism for flow of clustered ionomers is consisting of an initiation and a propagation step.
Intrinsic viscosity and friction coefficient of polymer molecules in solution: Porous sphere model
Authors: Mijnlieff P. F. , Wiegel F. W.
Published: April 2003

The intrinsic viscosity [η] and the translational friction coefficient f of polymer molecules in solution are calculated on the basis of the porous sphere model. The only information needed to predict [η] and f is the polymer molecular weight, the radius of gyration in the solvent, and the permeability as a function of position in the “porous sphere.” For systems for which this information is available there is satisfactory agreement between predicated and directly measured values of [η] and f. No adjustment of parameters is required. The influence of solvent quality is more complex than is suggested by the experimentally verified Flory–Fox relation for [η]; the simple form of this relation stems from the fact that two quite large effects of solvent quality approximately compensate each other. The complete flow pattern of the solvent around and through the polymer coil can be calculated. Contrary to what is usually believed the solvent flow in the polymer coil is not “effectively blocked”, even at the center. The connection between the present treatment and the microscopic theory of Kirkwood and Riseman is investigated.
Refined NMR analysis of the phase structure of solution‐crystallized linear polyethylene
Authors: Horii F. , Kitamaru R.
Published: April 2003

Nuclear magnetic resonance (NMR) spectroscopy reveals that solution‐grown polyethylene samples have a unique phase structure independent of molecular weight. The lamellar crystallites are composed of about 85% crystalline material with the noncrystalline overlayer as large as 15%. The molecular motion in the overlayer is comparatively hindered and the liquid‐like component, which is generally recognized in melt‐grown crystals, cannot be produced appreciably, even at 60°C. Such hindered molecular mobility can be understood in terms of a rather restricted conformation of the molecular chains in the noncrystalline overlayer, arising from the special mode of crystallization from dilute solution.
Solubility of nitrogen and ethylene in molten, low‐density polyethylene to 69 atmospheres
Authors: Cheng Y. L. , Bonner D. C.
Published: April 2003

Statistical mechanical correlations of ethylene and nitrogen solubility in molten, low‐density polyethylene at several temperatures and at pressures to 69 atm are presented. The solubilities are taken from data previously published by us and by other workers. The data are modeled with a corresponding‐states solution analysis applicable to mixtures of high‐and low‐density fluids. The model is based on a simple variation of the Flory and Prigogine corresponding‐states theories. Gas sorption data are modeled well within experimental precision.
Elastic deformation in polyethylene crystals subjected to a tensile stress distributed over a fold surface
Authors: Evans J. T. , White J. R.
Published: April 2003

The chain axis tilt which occurs when tensile stress is applied to one face of a thin crystal has been estimated by imitating the strain produced at the interface by means of a regular array of dislocations. The calculation also includes image dislocations introduced to make the crystal boundaries stress free. The tilt is found to be small (<1° and probably ≪1° over most of the crystal) for all strains up to the point where plastic deformation mechanisms prevail. The implications of the results are discussed in the context of the electron image contrast.
Bending contribution to line‐broadening in polymer diffraction
Authors: White J. R.
Published: April 2003

It is proposed that bending of solution‐grown polymer crystals causes the observed diffraction line‐broadening in many cases. Independent estimates and observations of the severity of bending which can be sustained are used to calculate corresponding apparent crystal sizes, where the apparent crystal size is that obtained when it is assumed that broadening is caused by the small crystal size effect only. Bending broadening is found to be of sufficient magnitude to produce the observed broadening reported in the literature. Some of the steps taken so far in the development of line‐broadening analysis for polymer crystals show similarities with the evolution of line‐broadening analysis for graphitic carbons and a brief review of the latter is included.
Mechanics of peeling of rubbery materials. II. Initiation and propagation of peeling
Authors: Igarashi Takashi
Published: April 2003

The peel strength of a joint with flexible materials bonded by an elastic adhesive was evaluated in relation to the fracture mechanism. It was found that initiation and propagation of peeling are governed by different mechanisms. Initiation (the formation of an initial crack) occurs when the maximum stress in the adhesive layer reaches a definite value. In this case, the strength fi in a trousers‐type peeling is given by 2fi = y0σbϵb, where y0 is the half‐thickness of the adhesive layer, σb is the tensile strength, and ϵb is the tensile elongation of the adhesive. On the other hand, propagation is governed by the surface energy of the adhesive. In this case, the peeling strength fs is determined by a balance of energies. For trousers‐type peeling it is given by 2fs = Γ, where Γ is twice the surface energy. These results were verified experimentally.
Properties of aqueous salt solutions of poly(ethylene oxide): Thermodynamic quantities based on viscosity and other measurements
Authors: Boucher E. A. , Hines P. M.
Published: April 2003

A previous study of poly(ethylene oxide) (PEO) in aqueous salt solutions has been extended to incorporate cloud‐point measurements in potassium thiocyanate solutions (salt concentration range 3.3–3.8M where salting out occurs) and, particularly, viscosity measurements. A few osmoticpressure measurements were made and molecular weights (∼2 × 104) from gel‐permeation chromatography (GPC) compared. The theta temperature for PEO in water from cloud points was found to be 369 ± 3°K. An empirical linear relation has been found for sodium and potassium salts between the finite change of theta temperatures with change in ionic strength, δθ/δI, and (v3 − v̄3), the difference between the molar van der Waals volume and the partial molar volume of the salt. Values of the Huggins constant k′ are less than 0.5 for PEO in pure water at 303.2°K, indicating a good solvent, whereas in salt solutions they vary from 0.59 to 1.14 in nontheta solvents. They and other findings are attributed to binding of salt to the polymer and to water structure breaking. Kraemer's constants k″ were also determined: k′ − k″ = 0.5 for PEO in pure water, and for aqueous salt solutions of PEO, k′ − k″ = 0.666 at 298°K. Values of K0(= M−1/2[η]θ) with M = 2 × 104 were found to very with salt type (valence)—mean values of 103 K0/dlg−1 with number of observations in brackets are 1:1, 1.19 (2); 1:2, 1.45 (3); 2:2, 1.75 (3). Unperturbed dimensions 〈r2〉 vary from 11.0 to 12.6 nm from 1:1 to 2:2 salts. Values of the characteristic ratio Cn, the steric parameter σ, and the enthalpy and entropy of dilution parameters χH and χS have also been calculated.
Importance of the metal–polymer interface for the piezoelectricity of polyvinylidene fluoride
Authors: Sussner H. , Dransfeld K.
Published: April 2003

The piezoelectric effect in films of polyvinylidene fluoride (PVF2) is investigated using optical and ultrasonic detection techniques. From the analysis of the vibrational resonance frequencies of a freely suspended film we conclude that the polarization induced in PVF2 is inhomogeneous across the volume of the sample. Poling the foils in a sandwich configuration or using blocking electrodes, we can clearly demonstrate that the piezoelectric effect in PVF2 originates from the positive metal electrode. Monitoring the time dependence of the piezoelectric effect during the poling process, a fast and slow component are observed. Using a blocking electrode, however, the same dynamical poling behavior is found only if the contacting metal electrode is positive. In view of these observations, which clearly demonstrate the importance of the metal–polymer interface for the strong piezoelectricity of PVF2, the existing theoretical models, based on the bulk properties of the polymer, are critically reviewed.
Nature of melt rheological transition in a styrene–butadiene–styrene block copolymer
Authors: Chung Chan I. , Lin Ming I.
Published: April 2003

Our laboratory previously reported the observation of a high temperature, melt rheological transition in a styrene–butadiene–styrene (S:7 × 103 and B:43 × 103) block copolymer from the highly elastic, nonlinear viscous behavior typical of a multiphase structure to linear viscous behavior with insignificant elasticity typical of a single‐phase structure. We have investigated the precise nature of this melt rheological transition in the 7S‐43B‐7S sample by measuring the dynamic viscoelastic properties at more than 11 temperatures, including several in the transition region. A new procedure was developed for accurately measuring the sample temperature in a Weissenberg rheogoniometer. The transition is found to start at about 140°C and proceed over a narrow transition region from 140 to about 150°C. Data at all temperatures superimpose onto a single master curve only at high reduced frequencies. At low reduced frequencies, two characteristic branches of the master curve are formed. The data at temperatures below the transition region superimpose onto the upper branch where the dynamic viscosity η′(ω) is a strong function of ω, whereas the data at temperatures above the transition region superimpose onto the lower branch where η′(ω) is independent of ω. The data at temperatures within the transition region fall between the upper and lower branches, ordered according to their temperature positions. The apparent flow activation energy is found to be constant at about 22.8 kcal/mole below the transition region, but appears to decrease to about 17.4 kcal/mole above the transition region. The narrowness of the rheological transition far above the glass transition temperature of the polystyrene domains and the limiting linear viscoelastic behavior at low frequencies above the transition suggest an accompanying morphological transition rather than a gradual weakening of the polystyrene domains.
Viscoelastic behavior and phase domain formation in Millar interpenetrating polymer networks of polystyrene
Authors: Siegfried D. L. , Manson J. A. , Sperling L. H.
Published: April 2003

Millar‐type interpenetrating polymer networks (IPNs) are composed of two identical networks. In the present case Millar IPNs of polystyrene/polystyrene were prepared where the crosslinker levels of the two networks differed by a factor of 10. Polymer network I contained 0.4% divinylbenzene (DVB) and polymer network II contained 4% DVB, the polymers having the following weight proportions: 75/25, 50/50, and 25/75. A single polystyrene network containing 2.2% DVB was synthesized for comparison with the 50/50 Millar IPN, both containing the same average amount of crosslinker. The creep behavior of the Millar IPNs was found to be dominated by polymer network I, as were the rubbery moduli and swelling behavior in toluene. These results suggested that polymer I domains are more continuous in space and polymer II domains are less continuous. The Donatelli equation predicted polymer II domain sizes of 60 Å to 100 Å for the Millar IPNs. Electron micrographs of specimens containing 1% isoprene in polymer II offered visual evidence for the segregation of polymer II domains from polymer I, and showed that the polymer II domains were, in fact, less continuous. Polymer II domains varied from about 50 to 100 Å in size, as predicted. These results have implications for gelation processes in general.
Some effects of melt‐induced orientation on drawing of polypropylene monofilaments
Authors: Garton A. , Stepaniak R. F. , Carlsson D. J. , Wiles D. M.
Published: April 2003

Morphological changes accompanying the deformation of polypropylene filaments with varying degrees of melt‐induced orientation are examined using wide‐angle x‐ray scattering (WAXS), small‐angle x‐ray scattering (SAXS), and electron microscopy, and their behavior is compared both to completely unoriented film samples and to very highly oriented, hard elastic filaments. Melt‐oriented filaments are shown to deform predominantly by a voiding mechanism at low temperatures (<100°C), and destruction of the lamellas to produce fibrils occurs only after extensive drawing. The bimodal crystal texture of the filaments does not appear to greatly affect the low temperature deformation mechanism. High temperature (>100°C) drawing produces a fibrillar structure containing elongated voids.
On the theory of the excluded‐volume effect of a polyelectrolyte in a 1‐1 electrolyte solution
Authors: Odijk Theo , Houwaart Albert C.
Published: April 2003

An excluded‐volume theory of polyelectrolytes is presented based on the concept of a Kuhn statiscal segment depending on the concentration of added salt. The polyion is viewed as a wormlike chain bearing charges which interact according to a Debye–Hückel potential. It is shown that it is consistent to split up the screened Coulomb potential into two parts: a short‐range interaction giving rise to a so‐called electrostatic persistence length which depends on the Debye–Hückel radius, and a long‐range interaction denoting the excluded‐volume effect. The mean‐square radius of the polyelectrolyte is derived, and this deviates markedly from expressions based on a constant Kuhnsegment length. Furthermore, certain polyelectrolytes exhibit negligible excluded‐volume effects and behave as wormlike chains with a persistence length equal to the sum of the bare persistence length and the electrostatic persistence length. In addition, an expression for the polyion–polyion contribution to the second virial coefficient is obtained.
Temperature dependence of the poisson's ratios in low‐density polyethylene with parallel lamellas morphology
Authors: Richardson I. D. , Ward I. M.
Published: April 2003

Three of the Poisson's ratios have been measured on a low‐density polyethylene (LDPE) sheet with parallel lamellas morphology over the temperature range from +20 to −60°C. The measurements were carried out using a specially constructed lateral extensometer which utilized the Hall effect to detect the very small strains involved. The Poisson's ratios show considerable temperature dependence, and at high temperature the overall deformation approximates to pure shear as previously noted. It is suggested that this relates to the onset of the c‐shear relaxation.
Effects of polar group incorporation on crazing of glassy polymers: Styrene–acrylonitrile copolymer and a dicyano bisphenol polycarbonate
Authors: Kambour R. P. , Gruner C. L.
Published: April 2003

The degree of swelling and attendant reduction in the glass transition temperature have been determined for a 70% styrene–30% acrylonitrile copolymer in a large number of organic liquids. The critical strain ϵc for crazing or cracking has been determined also in air and in each agent. Limited crazing data have been obtained also on a dicyano bisphenol polycarbonate in which the CN groups take the place of the methyl groups in bisphenol A (BPA) polycarbonate. The two resins are compared with polystyrene and BPA polycarbonate, respectively, in terms of crazing resistance, swelling, and other properties. In both systems CN incorporation raises ϵc (air) and reduces susceptibility to liquids of low solubility parameter δ; Tg and shear yield stress are raised in the polycarbonate but not in the styrene system. The volume efficiency of CN in raising ϵc (air) is greater in the polycarbonate system than the styrene system; for the rise in polymer solubility parameter, CN efficiency is apparently reversed. These changes are discussed in terms of the differences in molecular architecture of the two systems. For glassy polymers, ϵc (air) is shown to depend in semiquantitative fashion on polymer Tg, δ, and resistance to shear deformation.
Electrically conductive elastomeric TCNQ complexes
Authors: Ikeno S. , Yokoyama M. , Mikawa H.
Published: April 2003

New elastomeric ionene polymers containing poly(tetramethylene oxide) chain units were synthesized. The electrical conductivities of the salts of these polymers with (the anion radical of tetracyanoquinodimethane) (simple salt) and with neutral TCNQ added (doped salt) were investigated. Each cationic site in the polycationic polymer chain is separated by a long elastic chain unit, and consequently, moieties in the simple salt are expected to be well separated. Unexpectedly, doping with neutral TCNQ caused a marked decrease in the specific resistivity and the activation energy. Although the simple salt is elastic, doping with neutral TCNQ increased the stiffness of the material. The room‐temperature specific resistivity of the doped salts was in the range of 103 to 104 Ω cm. The marked change of electrical and mechanical properties brought about by doping with neutral TCNQ is discussed in terms of a structural model in which phase separation of the ionic part from the nonionic elastic units has been assumed.
Four‐center‐type photopolymerization in the crystalline state. XI. Crystal structure of p‐phenylenediacrylic acid diethyl ester above the crystal transition point
Authors: Nakanishi Hachiro , Ueno Katsuhiko , Sasada Yoshio
Published: April 2003

The crystal structure of p‐phenylenediacrylic acid diethyl ester above the transition point was determined at 70°C by x‐ray diffraction. No significant differences in molecular arrangement are found between the structures of the α2 form (above the transition point) and the α1 form (at room temperature). Since the α1 form is photopolymerized, it is concluded that selective dimerization in the α2 form results not form the crystal structure of the monomer, but from the deterioration of molecular arrangement by the formation of dimer.
Melting and crystallization of poly(vinylidene fluride) under high pressure
Authors: Matsushige Kazumi , Takemura Tetuo
Published: April 2003

Precise melting and crystallization temperatures of extended‐chain and folded‐chain crystals of form I and folded‐chain crystals of form II poly(vinylidene fluoride) under high pressure have been obtained by microdifferential thermal analysis (DTA). Upon heating at pressures above 4000 kg/cm2, the micro‐DTA thermogram of form II crystallized from the melt at atmospheric pressure shows melting of the form II structure and the melting of the folded‐chain and extended‐chain crystals of form I, formed through recrystallization processes. These features were clarified by supplemental methods. The bandwidth seen in electron micrographs of the extended‐chain crystal of form I obtained by crystallization under high pressure was in the range of 1500 to 2000 Å. At atmospheric pressure, the extended‐chain crystal of form I melted at 207°C, approximately 17°C higher than the folded‐chain crystal of form I and 31°C higher than the folded‐chain crystal of form II.
Effect of particle shape at finite concentration on the elastic moduli of filled polymers
Authors: Chow T. S.
Published: April 2003

The elegant approach of Eshelby, developed for dilute dispersions, is generalized to include the interaction of filler with filler. It is then utilized to determine the five elastic moduli of filled polymer containing aligned ellipsoidal particles at finite concentrations φ. The anisotropic particle shape is characterized by an aspect ratio ρ of an ellipsoid. The present theory compares well with available experiments in the literature. The experimentally verified Kerner equation for spherical particles and rule of mixtures for the longitudinal Young's modulus at ρ → ∞ are special cases of our new results.
Effect of particle shape at finite concentration on thermal expansion of filled polymers
Authors: Chow T. S.
Published: April 2003

Relations are derived for the linear and volumetric thermal expansion coefficients of a filled polymer containing aligned ellipsoidal inclusions at finite concentrations. The analysis follows a procedure recently developed for elastic moduli by application of a generalized approach of Eshelby. The well‐known Kerner equation is shown to be a limiting case of the present finding. From data on glass in epoxy resin, we conclude that the volumetric expansion varies only slightly with the aspect ratio of an ellipsoid; however, the longitudinal and transverse, linear, expansions show a strong dependence on the particle shape.
Isotactic poly(pentene‐1): Polymorphism of form I
Authors: Moser M. , Boudeulle M.
Published: April 2003

The polymorphism of isotactic poly(pentene‐1) form I was studied by x‐ray diffraction. Upon quenching from the melt at a temperature below 25°C, the films crystallized in a stable monoclinic form, which we have designated as form I (a = 22.4 ± 0.2 Å, b = 6.49 ± 0.05 Å, c = 21.2 ± 0.2 Å, β = 91 ± 1°). For higher quenching temperatures, a metastable form, form I′, appeared, which transforms to the normal modification upon aging (monoclinic, with: a = 24.3 ± 0.2 Å, b = 6.50 ± 0.05 Å, c = 19.3 ± 0.2 Å, β = 96 ± 2°). Both modifications have a 31 helical conformation. Limited changes in the packing mode could explain this polymorphism.