bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solid‐state extrusion of chain‐extended polyethylene
Authors: Chuah Hoe Hin , Porter Roger S. 
Published: April 2003

AbstractBillets of chain‐extended polyethylene were prepared from Alathon 7050 (Mw 59,000, Mn 19,000) in an Instron capillary rheometer by crystallization at a constant pressure of 460 MPa, at a series of teimperatures from 198 to 221°C corresponding to varying degrees of undercooling. This gives chain‐extended morphologies with a range of crystallinites and lamellar thicknesses. The billets were then solid‐state extruded at 100°C through a conical die with 20° entrance angle up to an extrusion draw ration 23.4. Thermal behavior was studied with differential scanning calorimetry. The orientation function measured by wide‐angle x‐ray diffraction showed higher orientation function measured by wide‐angle x‐ray diffraction showed higher orientation at equivalent draw ratio when the initial billets were crystallized at lower temperatures. Drawing efficiency, defined as the ratio of molecular draw ratio (from shrinkage) to extrusion draw ratio correspondingly increases, reaching a maximum of 0.71 in our solid‐state extrusion. These studies show that highly chain‐extended polyethylene, i.e., with few chain entanglements, draws poorly. Drawability was improved by increasing chain entanglements by lowering the crystallization temperature. Electron micrographs of fracture surface replicas of extrudates revealed the coexistence of undeformed, tilted, partially drawn lamellae and fibrillar structure consistent with the cahange of morphologies in Peterlin's model of plastic deformation.
The sectioning of randomly branched filamentous structures
Authors: Sellen D. B. 
Published: April 2003

AbstractA theorectical analysis is given of the two‐dimensional picture observed when a three‐dimensional randomly branched fibrous structure is sectioned. The model adopted consists of randomly oriented, interconnected straight rods having either the same length or a defined distribution of lengths. Expressions are derived for the total number of fragments observed and their total apparant length per unit area projected in the plane of the section, together with the distribution function of the projectd lengths. However, the expression derived for the total projected length per unit area, one‐fourth πtρl, where t is the section thickness and ρl the fiber length per unit volume in the three‐dimensional stucture, is, however, independent of the above model. The theory is discussed in terms of electron microscopy which has been carried out by other workers on agarose gels.
Low‐temperature dielectric relaxation in poly(4,4′‐oxydiphenylene pyromellitimide)
Authors: Iida K. , Nakamura S. , Sawa G. , Waki M. , Ieda M. 
Published: April 2003

AbstractThe effect of end groups on the low‐temperature dielectric relaxation in poly(4,4′‐oxydiphenylene pyromellitimide) has been studied using three kinds of samples with different content of anhydride end groups. The magnitude of the dielectric loss peak, designated here the V peak, which appears near −40°C at 1 kHz, depends on the content of anhydride end groups. If a sample with few anhydride end groups is allowed to absorb water, a loss peak appears near the temperature region of the V peak, but it disappears after subsequent heating. In contrast, a sample having a larger amount of anhydride end groups exhibits a large V peak which remains even after further heating. We conclude that the Oportion of the anhydride end groups is responsible for the V peak, though there may be an additional contribution from absorbed water.
Dielectric relaxation studies of some linear crosslinked and branched polymers
Authors: Aras Leyla , Baysal Bahattin M. 
Published: April 2003

AbstractDielectric loss measurements are reported for polystyrene, crosslinked polystyrene, polyacrylamide, branched polyacrylamide, and poly(methyl methacrylate) at 1 and 10 kHz f over the temperature range −85 to +100°C. Crosslinking and branching have a pronounced effect on the dielectric relaxation spectra of polymers. The methods of preparation of these polymers and their viscosity molecular weight data are also reported.
Miscibility of poly(vinyl chloride) with ethyl acrylate 4‐vinyl pyridine copolymers
Authors: Clas S.‐D. , Eisenberg A. 
Published: April 2003

AbstractBlends (50:50, w:w) of poly(vinyl chloride) (PVC) and poly(ethyl acrylate‐co‐4‐vinyl pyridine) (PEA–4‐VP) of different 4‐VP contents (2–14 mol %) were prepared. These were found to be partially miscible as evidenced by the presence of a single, through broad, tangent δ peak obtained from torsion pendulum experiments. Several possible types of interactions which might exist between PVC and PEA‐4‐VP, such as ion‐dipole, crosslinking, charge transfer, hydrogen bonding, and dipole–dipole interactions, were explored. From ultraviolet, conductance, infrared, and solubility studies, it was shown that hydrogen bonding or dipole–dipole (or possibly a combination of the two) interactions were the most likely in this system. These interactions have been suggested previously for other systems by various investigators.
Continuous measurement of dynamic tensile mechanical properties in polymer solids over a wide range of frequencies. III. Effect of absorbed water on nylon 6 at 23°c
Authors: Yokouchi Mitsuru 
Published: April 2003

AbstractThe dynamic tensile mechanical properties (E′, E″, and tanδ) of nylon 6 have been studied over the frequency range 10−25−102 Hz and water content up to 12.6 wt % at a constant temperature of 23°C. From the dispersion maps in the coordinates of frequency and water content, the relaxation behavior can be classified into three regions of water content: (A) dry to 2 wt %, (B) 2‐5 wt % and (C) 5 wt % to wet. For region B, it is found that the logarithmic frequency shift Δ logfα/Δx of the α dispersion per 1 wt % change of water content is 1.7. Taking into consideration that the change of glass transition temperature per 1 wt % change of water content Δ Tg/Δx is 3.7°C (according to Kettle), we find Δ logfα/ΔTg = 0.5. For regions A and C, such an evaluation cannot be made. The effect of absorbed water on the dynamic mechanical properties at 23°C is discussed in terms of two kinds of processes: (a) formation of water‐amide hydrogen bonds with free amide groups and (b) scission of amide‐amide hydrogen bonds.
Properties and chain flexibility of poly(dl‐isobornyl methacrylate)
Authors: Hadjichristidis Nikos , Mays Jimmy , Ferry William , Fetters L. J. 
Published: April 2003

AbstractThe glass transition temperature and characteristic ratio of poly(dl‐isobornyl methacrylate) have been determined. The results indicate that in the case of certain polymethacrylates the chain flexibility depends mostly on the bulkiness of the side group, while the glass transition temperatures depend mostly on side‐group rigidity.
Kinetics of photoinitiated free‐radical polymerization
Authors: Shultz A. R. , Joshi M. G. 
Published: April 2003

AbstractAnalytical expressions describing the kinetics of photoinitiated free‐radical polymerization are derived for a variety of conditions. The effect of the exponential attenuation of intensity of light in the direction of incidence in the system is carefully accounted for in each case. An attempt is made to include the depletion of initiator due to its photolysis in the kinetic scheme. The marked difference between the polymerization kinetics in well‐stirred and unstirred systems is shown by comparing them under limiting conditions. The variation of this difference with the optical density of the system is illustrated graphically. The influence of light absorption by components other than the photoinitiator (e.g., solvent, monomer) is examined. The order of the polymerization reaction with respect to initiator as determined by conventional kinetic experiments depends on the amount of light absorbed by components of the system other than the photoinitiator.
Phase segregation kinetics in segmented linear polyurethanes: Relations between equilibrium time and chain mobility and between equilibrium degree of segregation and interaction parameter
Authors: Camberlin Yves , Pascault Jean Pierre 
Published: April 2003

AbstractThe kinetics of phase segregation of segmented linear polyurethanes, from a homogeneous single‐phase system into a two‐phase one, have been studied by measuring the heat capacity change at the glass transition of the soft phase. The extent of phase segregation at equilibrium is a linear function of the Flory–Huggins interaction parameter χ. For χ lower than about 3, no segregation can take place. This value, higher than expected theoretically, indicates forced compatibility due to chemical links between soft and hard blocks of the segmented polyurethanes. The time required to attain equilibrium is not a function of thermodynamic parameters but of the chain mobility. A linear relation is proposed between the logarithm of equilibrium time and the viscosity of the pure soft phase.
High‐resolution electron microscopy of polyethylene and paraffin crystals: Stability in the electron beam
Authors: Giorgio S. , Kern R. 
Published: April 2003

AbstractUncollapsed polyethylene pyramids (200–1500 Å) in length are irradiated with the electron beam of a 100‐kV transmission electron microscope. Their high stability is remarkable compared to the stability of 1–10 μm crystals collapsed on the substrate, usually taken as a reference. Therefore, the maximum magnifications (300,000–750,000 X) of the microscope can be used and high‐resolution images can be obtained. No lattice defects can be detected in the images of PE pyramids. Irradiation with Dc > 800 C/m2 induces the orthorhombic → hexagonal transition, and slight lattice distortions appear in the high‐resolution image of the hexagonal phase. For an irradiation dose Dc ≈ 2400 C/M2, the diffraction pattern disappears. Normal C36 orthorhombic and monoclinic paraffins have the same stability as orthorhombic PE and high‐resolution patterns are obtained. These exceptional stabilities are discussed in detail. From the diffraction pattern of these uncollapsed pyramids, the fold surfaces of PE pyramids have been indexed as the {111} and paracrystalline distortions in the orthorhombic PE have been measured at low irradiation dose. Along the a and b axes g is ca. 5% and along the chain axis c it is ca. 17%; these values agree with the previous x‐ray determinations of PE crystallized from the melt. The large difference between these two distortion factors may be interpreted in terms of packing.
The dynamics of mechanical relaxation in polyisobutylene
Authors: Hill R. M. , Dissado L. A. 
Published: April 2003

AbstractThe published data on the mechanical response of a set of samples prepared from a single batch of polyisobutylene have been examined and three relaxation/retardation processes have been characterized in the temperature region above the glass transition temperature. It is shown that the time/frequency dependences can be explained in terms of the cooperative theory of relaxation/retardation. It is also shown that the values of the fractional power‐law indices of relaxation/retardation, which are a characteristic feature of the cooperative approach, are independent of the technique used in their observation.
X‐ray scattering from amorphous acrylate and methacrylate polymers: Evidence of local order
Authors: Miller Robert L. , Boyer Raymond F. , Heijboer J. 
Published: April 2003

AbstractX‐ray scattering patterns from amorphous polymers frequently contain halos corresponding to distances significantly greater than that of van der Waals packing of carbon atoms. Regularities in the positions of such halos as a function of pendant group size have been reported, primarily for the “crystallizable” comb polymers. This work concerns n‐alkyl acrylate, n‐alkyl methacrylate, and cycloalkyl methacrylate polymers with small alkyl groups: regularities in halo position with alkyl group size are seen, but the behavior with size is quantitatively different from that of the comb polymers. A case is made for the existence of a moderate amount of intersegmental order as the normal condition in the condensed amorphous state. The behavior of poly(methyl methacrylate) is anomalous and studies on it may not be used to generalize about the structure of the amorphous state.
Interactions of a sulfonated ionomer with surfactant in nonaqueous media
Authors: Peiffer D. G. , Lundberg R. D. 
Published: April 2003

AbstractThe viscometric behavior of dilute solutions of the sodium salt of sulfonated polystyrene (0–6 mol % sulfonation level), with and without surfactant, is investigated to determine the extent of interaction as the structure of the solvent surfactant, and polymer concentration is varied. Reduced viscosity measurements confirm that formation of a polymer–surfactant complex in a relatively polar solvent is controlled to a large extent by charge–charge and hydrophobic forces. The magnitude of these specific interactions is dependent upon the relative polarity of the solvent medium. In a polar solvent, such as dimethylsulfoxide, the hydrophobic forces are strong enough to prevent expansion of the polymer chain at all surfactant concentrations studied. However, in a less polar medium (as in dimethylformamide) the hydrophobic forces are weaker and cannot prevent some chain expansion. It is interesting to note that in this solvent the polystyrene–cationic surfactant complex exhibits a polyelectrolyte effect. Finally, in a lower‐polarity medium (cyclohexanone) where the hydrophobic forces are weak, solution behavior is dominated by the interaction of the surfactant with the intramolecular sulfonate ion‐pair aggregates.
EXAFS analysis of the structure of ionomer microdomains
Authors: Yarusso D. J. , Ding Y. S. , Pan H. K. , Cooper S. L. 
Published: April 2003

AbstractExtended x‐ray absorption fine‐structure (EXAFS) measurements were used to determine the near‐neighbor environment of the neutralizing cation in several ionomer system. The observed structure is compared to that existing in analogous low‐molecular‐weight crystalline salts. A wide variety in the degree of local order was observed between different systems even though all exhibit similar small‐angle x‐ray scattering curves indicating the existence of ionic microdomains.
Analysis of the hysteresis curve of ferroelectric polymers by a phenomenological relaxation theory
Authors: Jimbo Masashi , Kobayashi Shin'ichi , Horino Kaoru , Ikeda Susumu , Wada Yasaku 
Published: April 2003

AbstractA simple relaxation theory for the displacement versus electric field hysteresis of ferroelectric polymers is developed in which the relaxation time is assumed to be a function of electric field, as has been experimentally evidenced by polarization‐reversal switching. The theory gives an analytical expression for the hysteresis curve. The coercive field Ec predicted by the theory agrees well with data on Ec as a function of temperature for poly(vinylidene fluoride) from −60 to 20°C and with data on Ec as a function of frequency for vinylidene fluoride/trifluoroethylene copolymer (73/27 molar ratio) at 20°C over the range 0.01–0.7 Hz.
High‐temperature aging of Halar film. II. Analysis of melting behavior
Authors: Khanna Y. P. , Turi E. A. , Sibilia J. P. 
Published: April 2003

AbstractMelting behavior of an experimental Halar film, a predominantly alternating 1:1 copolymer of ethylene (E) and chlorotrifluoroethylene (CTFE), has been studied. Differential scanning calorimetry (DSC) reveals single or double melting peaks, depending upon the thermal history. The lower‐temperature melting peak Tm1 is produced only by the thermal treatment and shows a strong dependence on annealing time and temperature. On the basis of the DSC and x‐ray data it can be suggested that Tm1 represents the melting of relatively small crystallites formed upon annealing. The higher‐temperature melting peak Tm2 is always shown at 238°C. (Note: the specification for commercial Halar product is 240°C. The slightly lower melting temperature reported in this study is probably due to the fact that we are dealing with an experimental melt‐processed material.) On the basis of the heating rate study we propose that Halar crystallizes with stable crystals (Tm2 = 238°C) regardless of the crystallization conditions, i.e., quenching, slow cooling, or even annealing. Crystals of Halar have a heat of fusion of approximately 35 cal/g or 146 kJ/kg. Detailed analysis of the melting behavior of Halar is presented.
Comparison of two models for local chain motion
Authors: Lin Y.‐Y. , Jones A. A. , Stockmayer W. H. 
Published: April 2003

AbstractA connection is presented between the Jones–Stockmayer solution to the three‐bond‐jump equation for local motion and the new correlation function developed by Hall and Helfand. Both correlation functions are based on a diffusional picture for cooperative local motions which allows for the development of a relationship between them. Numerical fits of the Hall–Helfand function to the Jones–Stockmayer function are also given for both the time and frequency domain; these numerical fits are consistent with the analyses of NMR data by both models. The fits and the analyses set a likely range for converting the correlation time of the three‐bond jump to the correlation time for the cooperative transitions in the Hall–Helfand model.
Thermally induced cholesteric‐isotropic transition in lyotropic polypeptide liquid crystals
Authors: Subramanian R. , DuPré D. B. 
Published: April 2003

AbstractThe thermally induced cholesteric to isotropic transition of lyotropic polybenzylglutamate liquid crystals in six solvent combinations was examined optically. The solvents chosen for study support both low and high pitch values, positive and negative pitch temperature coefficients, and polypeptide denaturation. The biphasic zone below the clearing temperature is broad and solvent dependent. Unusual large‐scale phase separations and solution morphologies occur in some solvents. No evidence was found for pretransitional chiral orientational ordering near the clearing point in the high‐temperature isotropic phase.
Evidence for clustering inN‐butyl methacrylate ionomers as shown by thermally stimulated currents
Authors: Vanderschueren J. , Aras L. , Boonen C. , Niezette J. , Corapci M. 
Published: April 2003

AbstractThe relaxation behavior ofn‐butyl methacrylate/methacrylic acid (MAA) copolymers (12 mol % MAA) and their alkaline salts (K, Li) with various degrees of neutralization was investigated from 77 to 400 K by means of thermally stimulated depolarization and polarization methods. For degrees of neutralization higher than 50%, the experimental results were found to be consistent with the existence of complex heterophase structures involving significant widening of the distribution function of relaxation times in the glass transition region, splitting of the side‐chain transition in several discrete relaxation components, and formation of ionic cluster giving rise to their own relaxation process. By systematically studying the influence of polarization conditions, it was also shown that the appearance and stability of such clusters are markedly dependent on the thermal and electrical history of the samples and that the clustering relaxation is closely related to the ionic conductivity via space‐change formation.
Comments on “some evidence against the existence of the liquid–liquid transition. III. The evaluation of the TLL event by differential scanning calorimetry”
Authors: Boyer Raymond F. 
Published: April 2003

AbstractThe volatile‐component evaporation mechanism proposed by Chen et al. to explain molecular‐weight‐dependent endothermic peaks found at temperatures above Tg in anionically prepared polystyrenes (PSs) on first heating in open DSC pans is inconsistent with several bodies of literature data which were overlooked, including similar data with closed DSC pans. Moreover, this mechanism appears deficient in explaining details of the dependence of the endothermic peak temperature on M̄n both below and above the entanglement molecular weight Mc, with a sharp increase in slope at Mc. The original fusion–flow mechanism of Stadnicki et al. is compatible with all other known literature data including results on thermal PS and PMMA fractions. Hot‐stage microscope examination of powdered anionic PSs supports the Stadnicki mechanism from M̄n = 1900 to at least M̄n = 350,000. Addition of small amounts (ca. 1 wt %) of benzene or ethylbenzene to PS results in open‐pan DSC traces without endothermic peaks but with an endothermic slope change indicating gradual loss of diluent at decreasing rate as the temperature is increased from below Tg up through the TLL region.
Rebuttal to “comments on ‘some evidence against the existence of the liquid–liquid transition. III. The evaluation of the TLL event by differential scanning calorimetry’ ”
Authors: Chen J. , Kow C. , Fetters L. J. , Plazek D. J. 
Published: April 2003

AbstractIt is proposed here that readily observable viscous deformation is the common underlying phenomenon which is reflected in several kinds of evidence advanced for the existence of a liquid–liquid transition TLL. These include flow temperature Tf measurements, microscope hotstage coalescence, and differential scanning calorimetry (DSC) measurements. A DSC peak observed at Tg in high‐molecular‐weight bulk‐polymerized poly(methyl methacrylate) is discussed in terms of the presence of conformations of low entropy.
A pulsed NMR study of the effects of initial morphology on the structure of extrusion‐drawn poly(ethylene terephthalate)
Authors: Ito Masayoshi , Kanamoto Tetsuo , Tanaka Koji , Porter Roger S. 
Published: April 2003

AbstractProton spin–spin relaxation times and the Weibull coefficient have been measured as functions of temperature for poly(ethylene terephthalate) (PET) drawn at 50°C in both the amorphous and the semicrystalline (50%) states. Two relaxation times T2a (long) and T2c (short) are observed for all samples. They are ascribed, respectively, to the relaxation of the amorphous and of the crystalline components including highly strained noncrystalline segments. Effects of initial morphology are found for chain mobility in the noncrystalline regions and for the crystal perfection, evaluated from T2a and the Weibull coefficient μc of the T2c‐component, respectively. For all draw ratios, T2a for extrudates prepared from the semicrystalline polymer (C‐50) is short compared to that for preparations from the amorphous (A‐50) polymer. In the A‐50 samples, the perfection of stress‐induced crystals increase with increasing draw ratio. In the C‐50 samples, the crystal orientation increases, whereas the perfection decreases with increasing draw ratio. To improve the crystal perfection, annealing at higher temperature or longer time is required for C‐50 as compared with A‐50. The value of μc correlates well with the change in crystal perfection during deformation and annealing.