bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractThis 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

AbstractThe 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

AbstractDynamic 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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractThe 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

AbstractNuclear 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

AbstractStatistical 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

AbstractThe 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

AbstractIt 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

AbstractThe 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

AbstractA 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

AbstractThe 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

AbstractOur 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

AbstractMillar‐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

AbstractMorphological 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

AbstractAn 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

AbstractThree 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

AbstractThe 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.