bluuebunny/crossref_metadata_2025_split huggingface dataset:
Metal‐containing coordination polymers. XI. Crystallization and melting behavior of a semicrystalline polyester and its Mg (II) complexes
Authors: Székely‐Pécsi Zs. , Vancsó‐Szmercsányi I. , Cser F. , Varga J. , Belina K. 
Published: April 2003

AbstractThe effect of metal ion content and thermal history on the crystallization and melting behavior of a semicrystalline low‐molecular‐weight poly(butylene adipate) and its Mg complexes was studied by wide‐angle x‐ray diffractometry and differential scanning calorimetry. Both the polyester and the metal‐containing derivatives are dimorphous, and a β to α transformation takes place as the annealing temperature is increased. The dependence of the degree of crystallinity on the thermal history is more pronounced at higher Mg contents because of the effect of metal ions on the rate of crystallization. Melting of specimens with nonequilibrium structure is accompanied by simultaneous recrystallization processes such as perfection of crystallites and transformation of the crystal forms. The rates of these processes decrease with increasing metal content. The crystallizability is also reduced in the presence of Mg. Above the stoichiometrically equivalent Mg content, an abrupt change in the percentage of crystallinity accompanied by a considerable alteration in the microstructure of the crystalline phase occurs.
Apparatus for infrared measurement of sorption/desorption in strained polymeric films
Authors: Phillips J. C. , Peterlin A. , Waters Paul F. 
Published: April 2003

AbstractA new apparatus has been developed for optical measurement of sorption/desorption in transparent polymer films at a given strain or stress. The technique utilizes a chosen infrared absorption frequency of the diffusing vapor in a spectral region where the film has negligible absorption. From the time dependence of the IR absorption at this frequency the sorption/desorption behavior of the film may be determined at any strain or stress. The simultaneous measurement of mechanical relaxation as a function of the amount of sorbed vapor is also possible. The results presented here show the applicability of the apparatus for determining the transport and mechanical properties of a low‐density polyethylene film in ethyl acetate vapor at 30°C.
Study of the molecular conformation of an aromatic polyamide–hydrazide by intrinsic viscosity
Authors: Bianchi E. , Ciferri A. , Preston J. , Krigbaum W. R. 
Published: April 2003

AbstractThe persistence length of poly(terephthaloyl p‐amino benzhydrazide) (X‐500) in dimethyl sulfoxide (DMSO) has been determined from intrinsic viscosities measured for several whole‐polymer samples. An approximate correction is applied for excluded volume effects, and these corrected values are fitted using the viscosity treatments of Yamakawa and Fujii and of Eizner and Ptitsyn. Both give for the persistence length of X‐500 values in the range 30–35 Å. Revised treatment of our previous light scattering data for the same polymer yields 49 Å for the persistence length. Thus the chain extension of X‐500 falls between those of para‐linked polyamides and those of typical freely coiling macromolecules. Phase diagram studies indicate the solubility of X‐500 in DMSO decreases with rising temperature, and can be increased by the addition of LiCl. No anisotropic phase is found in DMSO at the highest volume fraction of polymer, v2 = 0.19, which can be obtained with 4 g/dl LiCl. The critical concentration of X‐500 needed for the appearance of the anisotropic phase depends upon solvent since Morgan reported an anisotropic phase for this polymer in 100% H2SO4 when v2 ≈ 0.13.
Ultradrawing of high‐molecular‐weight polyethylene cast from solution. II. Influence of initial polymer concentration
Authors: Smith Paul , Lemstra Piet J. , Booij Henk C. 
Published: April 2003

AbstractUltradrawing of films of high‐molecular‐weight polyethylene (M̄w = 1.5 × 106) produced by gelation crystallization from solution is discussed. The influence of the initial polymer volume fraction (ϕ) on the maximum draw ratio (λmax) of the dried films is examined in the temperature region from 90–130°C. The results can be described very well by the relation λmax = λ ϕ−1/2 where λ is the (temperature‐dependent) maximum draw ratio of the melt‐crystallized film. An attempt is made to discuss the marked influence of the initial polymer volume fraction on λmax in terms of the deformation of a network with entanglements acting as semipermanent crosslinks.
Electrostatic fiber spinning from polymer melts. I. Experimental observations on fiber formation and properties
Authors: Larrondo L. , St. John Manley R. 
Published: April 2003

AbstractIt is demonstrated that continuous filaments of rapidly crystallizing polymers, such as polyethylene and polypropylene, can be spun from the melt using an electric field as the only driving force. The molten polymer is fed into a metallic capillary forming a hemispherical drop at the end of the orifice. An electrical field is applied between the capillary and a conducting plate held perpendicular to the axis of the orifice. Above a critical field intensity a fine continuous jet of molten polymer is drawn; rapid crystallization ensues and a continuous fiber is formed. For fibers spun in an uncontrolled thermal environment, corresponding to ambient air temperature, and at electric field intensities of 6 and 7 kV cm−1, the properties are typically those of unoriented or slightly oriented polyolefin fibers, such as would be obtained in a conventional fiber spinning process.
Electrostatic fiber spinning from polymer melts. III. Electrostatic deformation of a pendant drop of polymer melt
Authors: Larrondo L. , St. John Manley R. 
Published: April 2003

AbstractIt has been previously shown that fine jets can be drawn from polymer melts with the aid of an electric field. In an effort to understand the mechanism of jet formation, preliminary experiments have been carried out on the deformation of pendant drops of molten polymers(nylon 12 and polyethylene) subjected to an electric field. The drop deformation was measured as a function of field intensity and frequency, and the results were interpreted in terms of a theory due to Torza et al. It is shown that there is qualitative agreement between the theory and experimental observations. This permits the identification of the parameters influencing the drop deformation and leads to a qualitative picture of the mechanism of deformation.
Negative thermal expansivity of polymer crystals: Planar zig‐zag chain model
Authors: Chen F. C. , Choy C. L. , Wong S. P. , Young K. 
Published: April 2003

AbstractThe thermal expansivity of polymer crystals in the direction parallel to the chain axis α∥ is studied in a planar zig‐zag chain model. Using values of force constants for polyethylene, it was found that α∥ = −1.3 × 10−5 K−1, in good agreement with experimental results. Torsional modes are found to contribute slightly more than half α∥. The expansivity is independent of the mass of the atomic groups on the chain and only weakly dependent on the interchain van der Waals interaction.
Empirical relation for diffusion of gases in hydrocarbon polymers: Interpretation in terms of fractional free volume
Authors: Peterlin A. , McCrackin F. L. 
Published: April 2003

AbstractAn empirical relationship between the diffusion coefficients of gases in three polyethylenes and their diffusion coefficient in natural rubber is given. The diffusion coefficients are given within a relative error of 4.7%. This relationship is interpreted according to the fractional free volume theory. The ratios of the fractional free volumes in the polyethylenes to the fractional free volume in natural rubber are derived.
Small‐angle neutron scattering by two‐component particles: Application to block copolymers
Authors: Ionescu L. , Picot C. , Duval M. , Duplessix R. , Benoit H. , Cotton J. P. 
Published: April 2003

AbstractGeneral equations for small‐angle neutron scattering are derived for block copolymers in dilute solution. The effects of excluded volume and polydispersity are examined. The applicability of the method of variable contrast to such systems is discussed.
Strain birefringence in ethylene‐propylene copolymers
Authors: Llorente M. A. , Mark J. E. 
Published: April 2003

AbstractA series of polymeric networks were prepared by the γ‐radiation crosslinking of two ethylene‐propylene copolymers containing 62 and 69 mol % ethylene units. The elastomeric materials thus obtained were studied in elongation, both swollen and unswollen, over the temperature range −30 to 95°C. The experiments involved measurements of both the elastic force and birefringence, using primarily changes in temperature at constant length (rather than changes in length at constant temperature). There is evidence for crystallization in these networks, as manifested by marked decreases in force and increases in birefringence at relatively low elongations and at temperatures as high as 70°C. As expected, the birefringence and related quantities were found to be more sensitive to crystallization than the force, with the stress‐optical coefficient showing the greatest sensitivity. The results obtained in the elongation‐temperature regions presumably free from effects of network crystallization were used to calculate values of the temperature coefficient of the unperturbed dimensions of the chains, and values of the optical‐configuration parameter. Both are widely used to characterize (spatial) configurations of chain molecules. Values of the former quantity are in very good agreement with those predicted some years ago using a rotational isomeric state model for ethylene‐propylene chains of various chemical and stereochemical compositions. The extension of these theoretical calculations to include the stress‐optical coefficient should provide further information on crystallization in ethylene‐propylene elastomers and the configurational characteristics of these copolymeric chains.
Radiothermoluminescence study of low‐temperature transitions in polyethylene
Authors: Zlatkevich L. Y. , Crabb N. T. 
Published: April 2003

AbstractMolecular relaxation in a series of polyethylene samples has been investigated by radiothermo‐luminescence. Polyethylene structure is discussed in terms of different modes of molecular mobility in different structural regions. Each of the low temperature transitions is assigned to a certain structure region and structural unit(s). The influence of different polyethylene molecular parameters and processing conditions on its structure and mechanical properties is also considered.
SAXS determination of the amorphous surface layer thickness of polymer single crystals
Authors: Varnell W. D. , Harrison I. R. , Kozmiski S. J. 
Published: April 2003

AbstractPolyethylene single crystals were grown from 0.1% solutions in xylene at 80 and 87°C. Oriented mats were made from each preparation and the small‐angle x‐ray scattering (SAXS) profiles obtained. Following treatment of the raw data for main‐beam position and width, background scatter, and the Lorentz factor, five Bragg reflections were resolved. A one‐dimensional lattice was used as a model for the oriented mats of single crystals. This model contains three parameters. An additional parameter Gx was also introduced to demonstrate the general effect of a broadening factor on the model. The effect of each parameter on the calculated diffraction pattern was examined. From this examination it was found that by assuming that the broadening functions are zero we can determine directly from the number of observable peaks the maximum possible thickness of the amorphous surface. Further, we find that the thickness of the amorphous layer must be less than the maximum value calculated if Gx is assigned values greater than zero. A “best‐fit” diffraction pattern was generated in order to estimate how much smaller the surface thickness can be such that one can still resolve five diffraction maxima. The range of amorphous surface thicknesses found from the calculated diffraction profile is 12–20 Å. This is in good agreement with complementary studies performed on the same crystal preparations.
Studies of polylactone/poly(vinyl chloride), polylactone/poly(vinyl fluoride), and polylactone/poly(vinylidene fluoride) blends
Authors: Aubin Madeleine , Prud'homme Robert E. 
Published: April 2003

AbstractIt is shown that polyvalerolactone/poly(vinyl chloride) (PVL/PVC) blends are miscible over all compositions since a single glass transition temperatureTgis observed, intermediate between those of pure PVL and pure PVC. Melting points, enthalpies of fusion and morphologies of PVL/PVC blends are also reported. It is also shown that polyvalerolactone, poly(α‐methyl‐α‐n‐propyl‐β‐propiolactone), poly(α‐methyl‐α‐ethyl‐β‐propiolactone), and poly(caprolactone) are immiscible with poly(vinyl fluoride) and poly(vinylidene fluoride), despite the fact that all these polylactones are miscible with PVC. Differences in electronegativity, in atomic radius, and in molar attraction between the fluoride and the chlorine atoms are probably responsible for this difference in behavior.
Direct observation of phase transitions of polyethylene under high pressure by a PSPC x‐ray system
Authors: Maeda Yoji , Kanetsuna Hisaaki , Nagata Kiyofumi , Matsushige Kazumi , Takemura Tetuo 
Published: April 2003

AbstractA position‐sensitive proportional counter (PSPC) x‐ray measuring system is employed to observe directly phase transition processes of polyethylene at high temperature and high pressure. X‐ray diffraction measurements reveal important new experimental data. First, an irreversible crystal transition from the hexagonal to the orthorhombic structures occurs in the critical region where the hexagonal structure begins to appear at a pressure of 350 MPa. That is, the (100) hexagonal reflection is observed only on cooling at 350 MPa. At pressures above about 400 MPa, however, the hexagonal phase is stable and the phase transitions melt ↔ hexagonal ↔ orthorhombic occur reversibly. Second, during cooling at pressures above 400 MPa, the (100) hexagonal reflection can be observed at temperatures below the hexagonal ↔ orthorhombic transition temperature. This behavior suggests that all the crystal morphologies of polyethylene, from “highly‐extended‐chain” crystals to crystals with a low melting point, are formed by the transitions melt → hexagonal → orthorhombic. Third, in heating at elevated pressures above 500 MPa, a shoulder in the peak intensity versus temperature plot for the (100) hexagonal reflection is observed at a higher temperature than the large maximum which occurs immediately after the crystal transition. This behavior indicates melting in two stages of hexagonal structures with different thermal stabilities, and the shoulder at higher temperature may be due to the fusion of the hexagonal phase annealed either below or above the transition point.
Dielectric relaxation and glass transition temperature of copolymers
Authors: Yagihara Shin , Mashimo Satoru 
Published: April 2003

AbstractDielectric relaxation measurements were made on methyl methacrylate—styrene and methyl methacrylate–p‐chlorostyrene copolymers at temperatures higher than the glass transition temperatureTg. It was found that the temperature dependence of the relaxation time can be described satisfactorily by an expression derived recently for chain motion in amorphous polymers. The temperatureTgobtained from the expression agrees well with that determined by differential thermal analysis.
Phase behavior of some polyamic acid plus ether systems
Authors: Orwoll Robert A. , St. Clair Terry L. , Dobbs Kerwin D. 
Published: April 2003

AbstractPolyamic acids, prepared by reacting 3,3′,4,4′‐benzophenone tetracarboxylic acid dianhydride with 3,3′‐diaminobenzophenone and with 4,4′‐diaminobenzophenone, were dissolved in tetrahydrofuran and in bis(2‐methoxyethyl) ether at concentrations up to 40 wt %. Reversible phase separation was observed when these systems were heated. Evidence cited indicates that all observed phases are isotropic, notwithstanding the fact that a number of aromatic polyamides are mesogenic.
Phase equilibrium study of the ternary system composed of two monodisperse polystyrenes and cyclohexane
Authors: Hashizume J. , Teramoto A. , Fujita H. 
Published: April 2003

AbstractMixtures of two “monodisperse” samples of polystyrene (M1 = 4.53 × 104, M2 = 10.3 × 104; Mw/Mn < 1.01) in cyclohexane were allowed to separate into two phases at different polymer concentrations and temperatures. The compositions in the two phases were measured by gel permeation chromatography, and used to determine isothermal binodals. From the binodal data the critical temperature and concentration were estimated as functions of the composition of the polymer mixture, and the separation factor σ for each polymer component was calculated. In contrast with typical results in the literature, σ was almost independent of molecular weight of the polymer. It is shown by deriving a general expression for σ that theoretical prediction of σ requires accurate knowledge about the Flory–Huggins interaction parameter as a function of the concentrations of individual polymer components.
Spectroscopic study of rigid‐rod polymers. I. Structures of model compounds
Authors: Venkatesh G. M. , Shen D. Y. , Hsu S. L. 
Published: April 2003

AbstractPoly(p‐phenylene benzbisoxazole) and poly(p‐phenylene benzbisthiazole) belong to the class of extended‐chain, rigid‐rod polymers possessing high modulus, high strength, and good thermal and oxidative resistance. Fibers and films of these polymers are processed from anisotropic solutions in strong acids such as methane sulfonic acid or polyphosphoric acid. The electronic absorption and vibrational spectra of the model compounds have been investigated in order to characterize the structures in the solid state and in nonprotonic solvents. The dramatic intensity differences in the spectra obtained have been interpreted by variations in the dihedral angle between the plane of the phenyl group and the plane of the central heterocyclic ring which affect the resonance configuration between the two rings.
Production and properties of fibers spun from nylon 6/lithium chloride mixtures
Authors: Richardson A. , Ward I. M. 
Published: April 2003

AbstractThe possibility of producing high‐modulus nylon 6 fibers by incorporation of lithium chloride (LiCl) in the polymer prior to spinning and drawing has been examined. Samples containing 2% and 4% LiCl (w/w) together with an unsalted control were studied. Particular attention was given to optimizing the spinning process by varying the melt temperature and the draw‐down. The spun fibers were subsequently drawn in a tensile testing machine at 135°C, preliminary studies having established that this was desirable for the production of high‐modulus material. The influence of annealing after drawing was also examined. Drawn fiber moduli in the range 8–9 GPa were obtained, compared with ca. 5–6 GPa for unsalted material. Limited structural studies (birefringence and wide‐angle x‐ray diffraction) suggest that the enhancement of modulus is due to an increase in the stiffening effect of extended molecules in the noncrystalline regions. Dynamic mechanical measurements show that there is reduced chain mobility in the disordered regions of the polymer, suggesting strong polymer‐ion interactions. The salt can be readily removed by washing the fibers in boiling water, with significant reduction in moduli. This militates against commercial application of the salted fibers.
Fourier‐transform infrared study of the reversible interaction of water and a crosslinked epoxy matrix
Authors: Antoon M. K. , Koenig J. L. , Serafini T. 
Published: April 2003

AbstractFourier‐transform infrared spectroscopy is utilized to characterize the interaction of a crosslinked epoxy matrix with sorbed water vapor. The perturbations of the epoxy vibrational spectrum are evidence for weak H bonding between water molecules and polar groups in the resin. The epoxy‐water interactions are reversible.
Effect of interfacial bonding on the strength of adhesion of elastomers. I. Self‐adhesion
Authors: Chang R.‐J. , Gent A. N. 
Published: April 2003

AbstractTwo partially gelled (crosslinked) layers of elastomer were pressed into intimate contact and the gelation reaction was then taken to completion. By varying the extent of initial gelation, the degree of chemical interlinking was varied from zero, when two fully reacted sheets were pressed together, up to a level characteristic of the final density of molecular linking within each layer, when they were brought together before any reaction had occurred. The strength of adhesion between the layers was measured under threshold conditions, i.e., at low rates of peel, at high temperatures, and, in some instances, with the layers swollen with a compatible liquid. Linear relations were obtained between the threshold work of detachment per unit of interfacial area and the amount of chemical interlinking, deduced from the kinetics of molecular linking within each layer. At any degree of interlinking, ranging from zero to the fully interlinked state, the work of detachment was lower for networks composed of shorter molecular chains, in accordance with the Lake–Thomas theory for the threshold strength of elastomer networks. By extrapolation to the fully interlinked state, the strength of adhesion corresponding to cohesive rupture was inferred. These values agreed with measured tear strength for polybutadiene gelled by a free‐radical process. For a sulfur crosslinking system, and for both free‐radical and sulfur crosslinking of poly(ethylene‐co‐propylene), the threshold tear strength of the elastomer was found to be much higher than the extrapolated value from adhesion measurements. This discrepancy is ascribed to roughness of the tear plane in relatively strong elastomers, in contrast to the smooth separation of flat adhering layers. Adhesion of fully crosslinked sheets was generally low, 1–2 J/m2. Higher values, 5–25 J/m2, were found with sulfur crosslinking systems, especially those yielding a high proportion of polysulfidic crosslinks. Interlinking via polysulfide crosslink interchange reactions is suggested in these cases.
Effect of interfacial bonding on the strength of adhesion of elastomers. II. Dissimilar adherends
Authors: Chang R.‐J. , Gent A. N. 
Published: April 2003

AbstractTwo elastomer layers, differing either in initial degree of crosslinking or in chemical reactivity, were bonded together by a free‐radical crosslinking process. The elastomers employed were polybutadiene (BR) and an ethylene‐propylene copolymer (EPR) differing in the efficiency of crosslinking by dicumyl peroxide by a factor of about 20. When a fully crosslinked sheet of either elastomer was pressed into contact with a partially crosslinked sheet of the same elastomer and the crosslinking then taken to completion, the strength of adhesion under threshold conditions was found to be qualitatively in accord with the predictions of a simple theoretical treatment for the degree of interlinking in terms of the corresponding homogeneous crosslinking reaction. Whereas the theory suggests that the effective degree of interlinking will be one‐half of that generated in a homogeneous system, the experimental results were in accord with a figure of about 70%. When a layer of one elastomer was bonded to a layer of the other in a similar way, the strength of adhesion was found to be relatively high when the initial fully crosslinked layer was BR and relatively low when it was EPR. These results were also in qualitative agreement with theoretical predictions for the degree of chemical interlinking developed between layers differing in chemical reactivity. Thus a general correlation appears to hold between the threshold strength of adhesion and the amount of interlinking.