bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rheological technique for determining the order–disorder transition of block copolymers
Authors: Han Chang Dae , Kim Jinhwan 
Published: April 2003

AbstractA rheological technique is proposed for determining the thermally induced order–disorder transition of block copolymers. In the present investigation, a cone‐and‐plate rheometer was used to measure dynamic storage and loss moduli, G′(ω) and G″(ω), as a function of angular frequency ω of a commercial grade polystyrene‐block‐polyisoprene‐block‐polystyrene (SIS) tri‐block copolymer (KRATON D‐1107, Shell Development Company) in the temperature range from 140 to 240°C. For comparison purposes, dynamic viscoelastic properties of a commercial grade low‐density polyethylene (LDPE) were also determined in the temperature range from 160 to 238°C. We have found that log G′ versus log G″ plots for the LDPE show no temperature dependence, whereas log G′ versus log G″ plots for the SIS block copolymer do show systematic temperature dependence in the temperature range 140–230°C. This observation leads us to conclude that the order–disorder transition of the SIS block copolymer takes place gradually as the temperature is raised from 140 to 230°C. This conclusion is in good agreement with that drawn from the study of Roe (Ref. 33), who employed the same block copolymer using small‐angle x‐ray scattering. It is not possible to reach such a conclusion using log G′(ω) versus log ω, log G″(ω) versus log ω, or log η′(ω) versus log ω plots in which η′ is the dynamic viscosity. We have demonstrated further that the use of frequency‐temperature superposition is inappropriate for investigating the rheological behavior of block copolymer in the temperature range over which a thermally induced transition from an ordered structure to a disordered homogeneous phase occurs. We therefore suggest that when using information on dynamic viscoelastic properties, log G′ versus log G″ plots be used for determining the thermally induced order–disorder transition of block copolymers.
Studies of craze fibril deformation during fatigue in polystyrene
Authors: Brown Hugh R. , Kramer Edward J. , Bubeck Robert A. 
Published: April 2003

AbstractSmall‐angle scattering of synchrotron x‐ray radiation has been used to study the effects of fatigue on craze fibril microstructure. The results obtained during unloading and reloading during a single cycle have been compared with those predicted by a model of sinusoidally bent fibrils. In addition the total displacement of the craze boundaries was found from the change in the invariant on unloading. The mean fibril diameter D was measured at the maximum tensile strain in each cycle. Over 250 cycles, D increased by at least a factor of 2 from an initial value of 6.5 nm, with most of this change happening in the first few cycles. The increase in D must occur by fibril coalescence, a mechanism that requires that the material in craze fibrils have considerable molecular mobility, even at room temperature, 70°C below the glass transition temperature.
Thermal diffusivity of polymer films by the flash radiometry method
Authors: Choy C. L. , Leung W. P. , Ng Y. K. 
Published: April 2003

AbstractWe have developed a flash radiometry technique for the determination of the thermal diffusivity of polymer films that consists of flashing a laser pulse on the front surface of the sample and monitoring the thermal radiation from the rear surface as a function of time using an infrared detector. This method is applicable to polymer films of thickness 14–250 μm in the wide temperature range between 150 and 500 K. We have performed measurements on four polymers, including polycarbonate, polyimide, polyvinylidene fluoride, and polyethylene terephthalate. The temperature dependence of the thermal conductivity of polycarbonate can be understood by considering the phonon mean free path, and the crystallinity and orientation dependence of the thermal conductivity of polyethylene terephthalate can be explained in terms of the two‐phase model proposed by Choy and Young.
Solution properties and chain conformation characteristics of cellulose tricarbanilate
Authors: Daňhelka Jaroslav , Netopilíak Miloš , Bohdanecký Miloslav 
Published: April 2003

AbstractFractions of two cellulose tricarbanilate samples were characterized by light‐scattering (weight‐average molecular weight, second virial coefficient, mean‐square radius of gyration), gel permeation chromatography (polydispersity index), and viscometry (intrinsic viscosity) in tetrahydrofuran and acetone. The intrinsic viscosity data were analyzed in terms of the theory developed for the continuous wormlike cylinder model, and the chain parameters (Kuhn statistical segment length λ−1, chain diameter d, and shift factor ML) were evaluated. The molecular‐weight dependence of the mean‐square radius of gyration in tetrahydrofuran was calculated for the Kratky—Porod chain model and compared with the experimental results. Data on the intrinsic viscosity and radii of gyration for other solvents at temperatures from 0 to 100°C were analyzed in the same way, and the effects of solvent and temperature on the statistical segment length were evaluated. Polymer—solvent interaction parameters were estimated from the second virial coefficients.
Thermoluminescence and chain‐fold morphology in low‐density polyethylene
Authors: Markiewicz A. , Fleming R. J. 
Published: April 2003

AbstractFurther thermoluminescence data are presented supporting our earlier suggestion that the electron traps associated with the three peaks in the thermoluminescence glow curve of a low‐density polyethylene sample from which absorbed air has been removed are formed by the polymer chains themselves in the chain‐fold regions of the samples. These traps are shown to be sensitive to heating of the sample to temperature around its melting point; in particular, the lowest temperature peak disappears if the sample is held at 90°C in vacuum for 5 min. If the sample is maintained in vacuum at room temperature after such treatment, its modified glow curve remains unchanged for a period of at least 7 days; however, if the sample is exposed to air, nitrogen, or argon after such treatment, its gas‐free glow curve begins to change within 3 days, evolving toward a three‐peak form with the same peak temperatures but with relative intensities different from those observed before heating began. This suggests that the gas molecules “lubricate” the polymer chains, which then begin to move toward new equilibrium configurations. Immersion in n‐hexane at room temperature has little effect on the luminescence centers but disables the electron traps. Immersion in fuming nitric acid at room temperature for 2 days appears to destroy the electron traps permanently, as would be expected if the chain folds are digested by the acid; its effect on the luminescence centers is still to be determined.
Electron spin resonance and UV absorption of irradiated poly(vinyl alcohol)
Authors: Rao B. Sanjeeva , Murthy M. Ramakrishna 
Published: April 2003

AbstractElectron spin resonance (ESR) of γ‐irradiated poly(vinyl alcohol) (PVA) at room temperature has been used to identify the radiation damage products. The ESR spectrum is analyzed by using least‐squares fits between observed and calculated spectra, assuming various free radical species. The best theoretical fit, together with UV absorption data, enabled the assignment of the observed ESR spectrum. The existence of carbonyl macrofree radicals, probably with aldehyde functional groups, is proposed in irradiated PVA.
Stress‐optical properties of poly(oxypropylene) networks
Authors: Andrady Anthony L. , Llorente Miguel A. , Saiz Enrique 
Published: April 2003

AbstractStrain birefringence of poly(oxypropylene) was studied using several poly(oxypropylene) model networks of different crosslink densities. Most of the measurements were carried out in elongation, in both the unswollen and the swollen states, over the temperature range 10–70°C. The optical configuration parameter was found to be Δa = (4.33 ± 0.09) × 10−24 cm3 at 25°C with a very small temperature coefficient. Theoretical calculations based on rotational isomeric state theory were employed to interpret the experimental data. The results indicate the intermolecular correlations to be low for this polymer, and, contrary to other systems, the stress‐optical coefficient C decreased with increasing average molecular weight between crosslinks. This fact was attributed to the end‐group effect introduced by the crosslinking agent.
Viscometry and light scattering on moderately concentrated solutions of poly(vinyl chloride)
Authors: Lin Y. C. , Beeson J. J. , Berry G. C. 
Published: April 2003

AbstractModerately concentrated solutions (0.015–0.10 g/mL) of poly(vinyl chloride) have been studied in three different solvents by light scattering and viscometry. It is concluded that intermolecular association occurs in all solutions studied, including data over the temperature interval 25–110°C. The data can be interpreted in terms of a model with loci of association holding chains together in an aggregate that has an overall configuration similar to that of a randomly branched polymer.
Ultrasonic measurements of the elastic moduli of ultradrawn polyoxymethylene
Authors: Leung W. P. , Choy C. L. , Nakagawa K. , Konaka T. 
Published: April 2003

AbstractWe have employed an ultrasonic method to measure from −40 to 60°C the five independent elastic moduli C11, C13, C33, C44, and C66 of polyoxymethylene with draw ratio λ from 1 to 26 prepared by continuous drawing under microwave heating. The elastic moduli are controlled by three major factors: molecular orientation in the crystalline regions, fraction of noncrystalline taut tie molecules, and void content. The steep rise in the axial extensional modulus C33 and axial Young's modulus E0 with increasing draw ratio results from the alignment of chains in the crystalline blocks and an increase in the number of disordered taut tie molecules. Below the γ relaxation (located at 0°C at our measurement frequency of 10 MHz), these two factors also give rise to a slight decrease in the transverse extensional modulus C11, Young's modulus E90 and shear modulus C66. At high temperature where the amorphous regions have very low modulus, the stiffening effect of taut tie molecules becomes dominant, leading to an increase in all moduli as λ increases from 1 to 10. At higher λ the void fraction increases appreciably, causing small decreases in E90, C11, and C66 at all temperatures.
Photoelastic properties of polybutadiene rubbers
Authors: Mohsin M. A. , Treloar L. R. G. 
Published: April 2003

AbstractTwo polybutadiene polymers were used in this investigation, one with 98% cis‐1,4 units and the other with an approximately equibinary mixture of cis and trans units. A range of cross‐linking densities were obtained using dicumyl peroxide as a vulcanizing agent. The experiments involved measurement of both the elastic force and birefringence (using the changes in length at constant temperature) over the temperature range −10−20°C. The force‐extension curves for both rubbers were similar in form. Both showed a strong upward deviation from the Gaussian statistical theory at high extensions, especially at lower temperature in which the extension to break increases. As expected, the experimental data on both polymers showed the stress‐optical coefficient to be substantially independent of the degree of cross‐linking. On the other hand, the values of the stress‐optical coefficient were found to increase slightly with a decrease in temperature. This effect is a result of the temperature dependence of the stress as indicated by the statistical theory.
Effects of initial morphology and molecular weight on the deformability of poly(ethylene terephthalate)
Authors: Ito Masayoshi , Tanaka Koji , Kanamoto Tetsuo 
Published: April 2003

AbstractSolution‐grown crystal (SGC) mats and solution‐cast (SC) films of poly(ethylene terephthalate) (PET) were drawn by solid‐state coextrusion followed by tensile drawing of the coextrudates. Drawabilities and properties of the drawn films, such as mechanical and thermal properties, were investigated as functions of molecular weight, initial morphology, and drawing conditions. The initial morphology and molecular weight have a marked effect on the drawability and tensile properties of the resultant drawn films. The attainable maximum draw ratio increases with increasing molecular weight, and the highest draw ratio of 11.5 can be achieved by two‐stage drawing of SC films prepared from pellets with an intrinsic viscosity of 1.43 dl/g. Such highly drawn films exhibit a tensile modulus of 17.5 GPa and strength at break of 400 MPa. These values are comparable to those obtained in conventional spinning of standard grade PET. At a given draw ratio, the tensile strength of the drawn films increases with increasing molecular weight, but the molecular weight dependence is not so marked in the tensile modulus as in the tensile strength. At a given molecular weight, the drawability of SGC mats is lower than that for SC films; however, the efficiency of drawing is higher for the former than for the latter. The difference may arise from the difference in crystallinity and/or crystal perfection of predrawn samples.
Proton NMR relaxation and molecular motion of long‐chain cyclic paraffins in the solid state
Authors: Takenaka Masami , Yamanobe Takeshi , Komoto Tadashi , Ando Isao , Sato Hisaya , Sato Kazuo 
Published: April 2003

AbstractTemperature‐dependent measurements have been made on the proton NMR relaxations and proton linewidths of the cyclic paraffins (c‐C24H48, c‐C28H56, and c‐C128H256) in the solid state. It is found that in c‐C24H48 and c‐C128H256 there exist two transitions, one due to the melting process and the other due to a rapid transition between trans and gauche conformers in a compact structure that consists of two parallel trans zigzag straight chains bridged at both ends in the crystalline state. In c‐C28H56 there exists only the transition due to melting. Proton NMR relaxations have also been measured for c‐C40H80 and c‐C160H320 at room temperature, in addition to those for c‐C24H48, c‐C28H56, and c‐C128H256. It is found that the extent of molecular motion decreases as the chain length increases.
An experimental study of dilute polyelectrolyte solutions in strong flows
Authors: Dunlap P. N. , Wang C.‐H. , Leal L. G. 
Published: April 2003

AbstractFlow‐induced changes in the conformation of polymer molecules in dilute polyelectrolyte solutions were studied, using birefringence techniques, as a function of molecular weight and added salt concentration in laminar, two‐dimensional extensional flows produced in four‐ and two‐roll mills. Overshoots in the flow birefringence during startup of simple‐shear flow are presented. Of particular interest is the so‐called coil‐stretch transition. It is shown that the electrostatic expansion of the polyelectrolyte has a dramatic effect on the onset shear rate for the coil‐stretch transition and also on the shape of the flow birefringence versus shear rate curves during the stretching process. A reasonable description of the coil‐stretch transition and its dependence on equilibrium configuration is obtained theoretically using a charged dumbbell model with conformation‐dependent bead friction. Being dependent on the longest relaxation time of the polymer, and therefore not too sensitive to intramolecular details, the dumbbell model can be applied in two ways: either using a charge force to expand its rest state or reducingN, the number of Kuhn segments, in proportion to the increase in relaxation time of the expanded polyelectrolyte.
Stability of the interface between two dynamic phases in capillary flow of linear polymer melts
Authors: McLeish T. C. B. 
Published: April 2003

AbstractResults of previous work1 on a theoretical explanation of the “spurt effect” in polymer melt flow are extended. A modified Doi—Edwards liquid is shown to support axisymmetric traveling waves on an interface between high and low shear‐rate phases in capillary flow. The stability of these perturbations is found to be governed by normal stress effects and may be related to certain types of melt fracture. Observed effects of varying the capillary length are explained qualitatively.
Gas sorption and transport in miscible blends of tetramethyl bisphenol‐A polycarbonate and polystyrene
Authors: Muruganandam N. , Paul D. R. 
Published: April 2003

AbstractThe permeability coefficients for He, O2, N2, CH4, and CO2 in miscible blends of polystyrene (PS) and tetramethyl bisphenol‐A polycarbonate (TMPC) at 35°C and 1 atm driving pressure are reported. Sorption isotherms for CO2 and CH4 are also presented. The isotherms were fitted to the dual sorption model. The Langmuir capacity factor was found to follow an earlier correlation based on unrelaxed volume. For each gas, the permeability was found to go through a minimum when plotted against blend composition. This behavior is primarily the result of the volume change on mixing observed for this system. The attractive interaction between TMPC and PS is relatively strong as indicated by density and solubility data. The value of the binary interaction parameter was found to be of the same magnitude as that for poly(phenylene oxide) (PPO)‐polystyrene (PS) blends. Considering the similarity of structure between PPO and TMPC, it is concluded that similar phenyl‐phenyl interactions and conformational changes on blending may prevail in TMPC/PS blends.
Properties of poly(ethylene terephthalate) extrudate prepared by hyperbolic convergent flow and high pressure
Authors: Ihm Dae Woo , Cuculo John A. 
Published: April 2003

AbstractThe structure and properties of poly(ethylene terephthalate) segments prepared by high‐pressure extrusion in a pseudohyperbolic die were examined. The translucent segments showed relatively high levels of orientation, crystallinity, and modulus. Higher melting point, larger crystal size, and higher loss modulus peak temperature (Tg) were observed for these segments as compared with those prepared earlier in our laboratory using the conventional 90° conical die. This seems to indicate that a hyperbolic profile is very effective in producing and maintaining a highly aligned chain network in a flowing melt.
Heat capacities and entropies of liquid polyfluoroethylenes and polychloroethylenes
Authors: Loufakis Kyriakos , Wunderlich Bernhard 
Published: April 2003

AbstractThrough new measurements and from literature data, the heat capacity of all liquid polyfluoroethylenes could be established as:

above 480 k, and as

below 480 K in J/(K mol), where NF is the mole fraction of F atoms. In connection with previously established heat capacities of the solid polymers, enthalpies, entropies, and residual entropies of the glassy state at 0 K were computed. Data for liquid polychloroethylenes are much less complete, and the thermodynamic functions could only be established for liquid poly(vinyl chloride) and compared with the data for solid poly(vinyl chloride), poly(vinylidene chloride), and polychlorotrifluoroethylene.
Spherulitic morphology in polyethylene and isotactic polystyrene: Influence of diffusion of segregated species
Authors: Keith H. D. , Padden F. J. 
Published: April 2003

AbstractMorphological consequences of a localized diffusion of segregated species at crystal growth fronts have been studied in two specific contexts: (1) variation of texture in spherulites grown in unfractionated polyethylene over a range of crystallization temperatures mostly in regime II, and (2) development of elongated lamellar habits in spherulites of a polymer (isotactic polystyrene) whose native crystal habit is regularly polygonal. In relation to (1) it is shown that, as crystallization temperature is varied, there is a correlation between mean thickness of stacks of lamellae and an averaged diffusion range of segregated molecules of lower molecular weight. It is noted that lamellar organization appears to be significantly different in polyethylene fractions. In relation to (2) it is shown that principal contributors to the evolution of spherulitic texture from hedritic precursors are fragmentation of lamellae by screw dislocations and radially biased growth under the influence of concentration gradients of segregated species.
A study of spontaneous rubber/metal adhesion. I. The rolling cylinder test
Authors: Zaghzi N. , Carre A. , Shanahan M. E. R. , Papirer E. , Schultz J. 
Published: April 2003

AbstractThe spontaneous adhesion of vulcanized filled elastomers to steel has been studied using a rolling cylinder test. Owing to the relatively high degree of crosslinking, heavy cylinders are required to ensure good contact with the hard rubber track. This in turn invokes compression within the bulk of the rubber. A consequence is that hysteresis losses are associated not only with the adhesion phenomenon but also with the compression deformation of the system. Theoretical and experimental analyses have led to the conclusion that the two effects may be treated as additive. Both hysteresis losses can be related to the WLF superposition principle.
Molecular orientation in liquid fibers of nematic polymers
Authors: Capasso R. , Roviello A. , Sirigu A. , Iannelli P. 
Published: April 2003

AbstractThe degree of macroscopic orientation of molten fibrous samples of nematic semiflexible polymers has been investigated by x‐ray diffraction. Melting of highly oriented fibers is followed by a partial loss of macroscopic orientation but does not produce collapse of the fiber. The residual orientational order remains unaltered for a considerable time. The degree of orientational order depends on the temperature and undergoes odd‐even fluctuations according to the parity of the number of carbon atoms contained in the flexible part of the monomer unit. Extrapolation of the order parameter to the isotropization temperature leads to a value of about 0.63 for even‐type polymers and to about 0.47 for odd‐type polymers. An intermediate value is found for a copolymer containing equal amounts of even and odd monomer units along the polymer chain.
Thermotropic rigid‐chain copolymers: X‐ray investigations of the structure
Authors: Sauer T. H. , Wendorff J. H. , Zimmermann H. J. 
Published: April 2003

AbstractThe structure of a rigid rodlike random copolyester, consisting mainly of p‐hydroxybenzoic acid, hydroquinone, and carbonyl units, was investigated by means of wide‐angle x‐ray scattering. The lateral order of the chain molecules was found to be short‐range in the nematic melt, in close agreement with the spatial order in the melt of flexible chain molecules. The packing density was found to be surprisingly large in the anisotropic melt. The low‐temperature solid state consists of two phases, namely a frozen‐in nematic and a three‐dimensionally ordered crystal phase. Quenched samples were found to have a degree of crystallinity of about 25%, whereas well‐annealed samples may display a degree of crystallinity of up to 70%. The ordered phase apparently displays an orthorhombic unit cell. Its dimensions indicate that a cocrystallization of the comonomers has taken place. On the basis of the observations that the lattice dimensions change continuously as a function of annealing parameters and taking into account the fact that the transition enthalpy, entropy, and volume are smaller by at least one order of magnitude in comparison to those found for crystals of flexible chains, we arrived at the conclusion that the polymer displays a rotationally disordered crystalline state.