bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of inorganic salts on the properties of aqueous poly(ethylene oxide) solutions
Authors: Boucher E. A. , Hines P. M. 
Published: April 2003

AbstractCloud‐point curves have been determined for aqueous solutions of poly(ethylene oxide) (PEO) at several concentrations for a variety of inorganic salts (sulfates, carbonates, nitrates, and chlorides). From these, theta conditions have been determined. The resulting dependences of the critical temperature θ (mostly between 300 and 360°K) on the molar concentrations (or ionic strengths) of the salts in solution cannot wholly be summarized in sequences of ion effects. The major findings are that sulfates and carbonates are much more effective in reducing θ than the chlorides and nitrates at the same concentrations. The trends found depend on salt concentration, i.e., certain plots of the data cross over, but they broadly agree with those found for comparable systems by other workers. Exceptional are the chlorides of Group II and LiCl which show minima when θ is plotted against molar salt concentration. While interpretations based on solvent structure‐breaking are not adequate, there are similarities in behavior with the structure‐breaking attributes of the ions based on independent studies (infrared). The results are briefly discussed in terms of current postulates: a more detailed discussion will accompany further experimental studies on these systems.
The theory of phase transition kinetics with growth site impingement. II. Heterogeneous nucleation
Authors: Tobin Marvin C. 
Published: April 2003

AbstractThe kinetics of phase transformation are treated for heterogeneous nucleation, where all nuclei are simultaneously initiated, and where initiation follows first‐order kinetcs. The phase transformation curves are sigmoid. For simultaneous initiation in two dimensions, a(t)/(1 − a(t)) ∝ t2. For first‐order initiation, we have, approximately, a(t)/(1 − a(t)) ∝ t2.85, and v(t)/(1 − v(t)) ∝ t3.74.
Interpenetration of polystyrene chains in bulk polymer
Authors: Worsfold D. J. 
Published: April 2003

AbstractPolystyrenes lightly substituted with either tertiary amine groups or nitrophenol groups have been allowed to interact in concentrated t‐butylbenzene solution and in bulk polymer. Above the glass transition temperature a temperature dependent equilibrium is achieved in the bulk polymer between the two substituents and the amine salt of the phenol. The degree of association found is considerably greater in the bulk polymer than in solution. The results show that much interpenetration of the polymer occurs, and the results are discussed in terms of models of the bulk amorphous state of the polymer.
Relation between preferential solvation and intrinsic viscosity of polymers in solvent mixtures
Authors: Dondos A. , Benoît H. 
Published: April 2003

AbstractPreferential solvation and intrinsic viscosity measurements are reported for three systems: polystyrene + benzene + methanol, polystyrene + carbon tetrachloride + methanol, and poly(2‐vinylpyridine) + ethanol + cyclohexane. Plots of the coefficient of preferential solvation λ′ as a function of variation of the segment density Δρ for a given ternary system, give a single curve for a large range of molecular weight and solvent mixture composition. This correlation between λ′ and Δρ is verified in previously published data.
Phase‐separation phenomena in solutions of poly(2,6‐dimethyl‐1,4‐phenylene oxide). I. Thermodynamic parameters of solutions in toluene
Authors: Koenhen D. M. , Smolders C. A. 
Published: April 2003

AbstractNew experimental data have been collected on thermodynamic properties of solutions of poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) in toluene. The Flory–Huggins interaction parameters g have been determined from light scattering measurements. These values are in agreement with values obtained by osmotic measurements at low concentrations and they allow the calculation of a melting point curve which fits the experimental melting points. No liquid–liquid phase separation can be calculated, as was concluded in a preceding paper. Spinodals could not be detected by light scattering or DSC‐measurements. This also indicates that liquid–liquid phase separation does not occur. The phase separation on cooling of a PPO‐toluene solution is thus believed to be a crystallization phenomenon.
Broad‐line NMR and dynamic mechanical behavior of some aromatic polyesters
Authors: Frosini V. , Levita G. , Landis J. , Woodward A. E. 
Published: April 2003

AbstractThe dynamic mechanical properties of four aromatic polyesters were measured at temperatures in the 78–540°K region at 103–104 cps. The polymers studied were: poly(1,3 phenylene isophthalate), poly(1,4 phenylene terephthalate), poly(4,4′ diphenylene isophthalate), and poly(4,4′ diphenylene terephthalate). All four polymers had β loss peaks at about 280°K. Distinct β* mechanical processes were found for the two terephthalate esters. Broad‐line nuclear magnetic resonance measurements were carried out in the 150–440°K temperature range on the four polyesters mentioned above in addition to poly(4,4′ diphenylene 4,4′ biphenyl dicarboxylate). A change in NMR second moment takes place in the 190–330°K region, the magnitude of which is dependent on the polymer structure. The results are compared with those found for a series of aromatic polyamides and are discussed in terms of possible motional processes.
Crystallization during polymerization of diphenylsilylene by a chemical transport reaction
Authors: Lee Chung Jen , Wunderlich Bernhard 
Published: April 2003

AbstractCrystallization during polymerization of polydiphenylsilylene has been accomplished. Best results are obtained by initial thermal polymerization to the amorphous macromolecule. The macromolecules are then decomposed and repolymerized by sublimation. Macroscopic extended‐chain single crystals are produced. The polymer crystals, once molten, will not recrystallize. Their initial characterization is described using infrared, Raman, ultraviolet, and nuclear magnetic resonance spectroscopy. X‐ray and thermal analysis data are also given.
Self‐hardening of highly oriented polyethylene
Authors: Arridge R. G. C. , Barham P. J. , Keller A. 
Published: April 2003

AbstractUltra‐oriented polyethylene fibers obtained by drawing to approximately 30 times their original length have a Young's modulus of approximately 800 kbar. Such fibers, if unconstrained, contract on heating to a length near the original. We have studied the forces causing this contractile behavior by monitoring the stress in the fiber while maintaining it at constant length. In the course of this we observed a complex sequence of both reversible and irreversible behavior. In the reversible case we observed first energy and then entropy elastic behavior. The most significant feature observed is that at sufficiently high temperature the fiber stress relaxes to an unmeasurably low value. A fiber allowed to relax in this way possesses a much lower room temperature tensile modulus (ca. 80 kbar) immediately after relaxation but, remarkably, this modulus increases to approach the initial high value over a period of a few hours when the fiber is stored either clamped or unclamped at room temperature. High x‐ray orientation is preserved throughout the storage period but the density which dropped during the stress decay rose again in the course of the spontaneous stiffening. None of the stress relaxed fibers displays large‐scale contractile behavior on subsequent heating.A phenomenological composite model is proposed which involves stiff microfibrils of short length—surrounded by a matrix present as a minority component. The softening of this matrix on heating and its subsequent stiffening on storage, involving a certain amount of melting and recrystallization, respectively, could then be responsible for the observed variations in the macroscopic tensile properties using simple fiber composite theories. The fibers are likely to be of extended‐chain type produced by the initial drawing while the matrix may consist of a combination of oriented amorphous material (tie chains), randomly oriented chains, and transverse lamellar overgrowth present in varying proportions in the different stages of sample treatment. The wider implications, fundamental and practical, of this remarkable self‐hardening process are indicated.
Diffusion in polymer–solvent systems. II. A predictive theory for the dependence of diffusion coefficients on temperature, concentration, and molecular weight
Authors: Vrentas J. S. , Duda J. L. 
Published: April 2003

AbstractA new free‐volume theory is combined with the thermodynamic theory of Flory and the entanglement theory of Bueche to provide a means of predicting the temperature, concentration, and molecular weight dependence of mutual‐diffusion coefficients in amorphous polymer–solvent systems. The predictions of the theory are compared with actual data for the ethylbenzene–polystyrene system.
Brillouin scattering and hypersonic relaxation in amorphous polymers
Authors: Patterson G. D. 
Published: April 2003

AbstractMechanical relaxation at hypersonic frequencies is measured using Brillouin spectroscopy for polyisobutylene, atactic polypropylene, polydimethyl siloxane, and polyvinyl acetate. The temperatures of maximum loss determined in the gigahertz range are compared to the published transitions maps for the above polymers. It is found that the hypersonic relaxation data fall on an extrapolation of the secondary main chain glass–rubber relaxation line above the region where the primary and secondary lines merge.
Polyelectrolytes near the rod limit
Authors: Odijk Theo 
Published: April 2003

AbstractThe problem of a polyelectrolyte near the rod limit is formulated incorporating both the short‐range stiffness of the backbone (the “wormlike chain”) and the electrostatic interaction between segments taken as a Debye–Húckel potential. By the use of a physically valid approximation an expression is derived for the mean‐square extension length of a short polyelectrolyte chain. Some remarks are made on the relationship between the electrostatic interaction and the usual excluded‐volume problem for polymer solutions.
Chemical origin of thermally stimulated discharge currents in polyacrylonitrile
Authors: Stupp S. I. , Carr S. H. 
Published: April 2003

AbstractThermally stimulated discharge has been used in the past to diagnose and estimate the magnitude of electrical polarization in polymers. Nevertheless, molecular characterization of operative phenomena by this technique alone is often a difficult task. In the present work, infrared attenuated total reflection spectroscopy has been used to investigate the origin of thermally stimulated discharge currents near 200°C in externally unpolarized films of polyacrylonitrile (PAN). Spectroscopic analysis of thermally degraded films reveals some unsaturation of the PAN backbone and possibly the generation of cyanide ions. Opposite surfaces in a solvent‐cast film give different spectra, indicating a gradient in chemical degradation products across the film thickness. Data suggest that nonuniform generation of charged species and unsaturated bonds gives rise to internal potentials in PAN. The origin of thermally stimulated currents in PAN near 200°C is thus believed to be associated with the onset of chemical degradation.
Eutectic solidification of the quasi binary system of isotactic polypropylene and pentaerythrityl tetrabromide
Authors: Smith P. , Pennings A. J. 
Published: April 2003

AbstractThis paper reports of a study on eutectic solidification of the quasi binary system of unfractionated isotactic polypropylene and the dentritic growing diluent pentacrythrityl tetrabromide. This system was characterized by a eutectic‐type experimental phase diagram with a eutectic composition of 68% (w/w) of polypropylene. The eutectic temperature was found to depend on kinetics, and was established by differential scanning calorimetry to be 122 and 102°C at a cooling rate of 0.5 and 32°C/min, respectively. A remarkeable nucleating effect of the primary diluent crystals was observed in the solidification of diluted polypropylene solutions. Here the eutectic horizontal was located at a temperature which was 15°C higher than in the eutectic solutions exceeding the temperature at which the pure polymer crystallized from the melt by 8°C. The eutectic microstructures produced were found to depend on the rate of solidification, which was varied by pulling the polypropylene solutions through a fixed temperature gradient of 3°C/mm at different speeds ranging from 0.2 to 80 mm/hr. At rates lower than 3 mm/hr the polymer and the diluent crystallized simultaneously from the eutectic solution in a uncoupled mode of growth, forming a coarse structure of diluent crystals and isotactic polypropylene spherulites with dimensions of about 0.1 mm. At higher speeds the simultaneous crystallization of the macromolecules and solvent molecules proceeded in a co‐operative manner with a nonplanar growth front. A rodlike eutectic microstructure was produced, in which diluent rods, lined up in the growth direction, were dispersed in a polypropylene matrix. The lateral dimension λ1 of these rods were found to depend on the growth rate R in the following way: λ12 R = 10−9 mm3/sec, and ranged from 0.3 to 1.0 μm. This was in accord with values calculated by using the current theory of rod eutectic growth of Jackson and Hunt.
Electrical conductivity of crystallizable polyphenylacetylene
Authors: Holob G. M. , Ehrlich P. 
Published: April 2003

AbstractThe dc conductivity of crystallizable poly(phenylacetylene), made in the presence of ferric acetylacetonate and triethylaluminum, and its dependence on time, temperature, pressure, and crystallinity was determined. A decrease in conductivity upon annealing is probably attributable to an irreversible conformational transformation of the polymer. There is also a reversible decrease in conductivity upon compression which, under some conditions, corresponds to a volume of activation as high as 70 cm3/mole. Upon complexing with iodine the conductivity is increased by several orders of magnitude and activation energies and volumes are greatly reduced, even at iodine concentrations as low as 1.6 mole % iodine per monomer unit. Although an identification of unpaired spins with the charge carriers is probably not justified, defect states, whose presence is demonstrated by electron spin resonance, may play a major role in the charge transport process. The strong reversible decrease of the conductivity with an increase in pressure is plausible, if intermolecular charge transport is the rate‐controlling step, an interpretation consistent with the large increase in conductivity upon complexing with small amounts of iodine.
D2‐m‐carborane siloxanes. V. Structure–property relationships
Authors: Peters E. N. , Kawakami J. H. , Kwiatkowski G. T. , Hedaya E. , Joesten B. L. , McNeil D. W. , Owens D. A. 
Published: April 2003

AbstractD2‐m‐decacarborane dimethylsiloxane has unusual thermal stability and resistance towards reversion, however, this material exhibits a crystalline phase, Tm at 68°C. To obtain an elastomeric material, this crystallinity is disrupted by replacing 30 to 50% of the m‐carborane with p‐carborane moieties or by the incorporation of phenyl moieties on the polymer backbone. The latter approach is preferred since improved thermo‐oxidative stability accompanies this modification. Correlation of the glass transition temperature and thermo‐oxidative stability with the polymer structure are presented.
Conformational transition of the copolymer of maleic acid and styrene in aqueous solution. II
Authors: Okuda Toshihiko , Ohno Nobumichi , Nitta Katsutoshi , Sugai Shintaro 
Published: April 2003

AbstractThe temperature dependence of the conformational transition from a compact to expanded‐coil form of the alternating copolymer of maleic acid with styrene in aqueous 0.03M NaCl solution was studied at 15 to 40°C by pH titration, optical titration, and calorimetric measurements. The pH titration curve scarcely changed with temperature. The degree of dissociation of primary carboxyl groups in the copolymer at the midpoint of the conformational transition, determined by the optical titration, was almost independent of temperature. The standard enthalpy change of the transition at 25°C estimated from the calorimetric data was 0.363 kcal/mole, which may mean that the difference between the standard free energy changes of the transition at 20°C and 40°C does not exceed experimental error. The enthalpy change agrees well with the heat of transfer of benzene from the hydrophobic to the aqueous medium, and thus the compact form of the copolymer is considered to be stabilized by the hydrophobic interaction between the phenyl residues in the interior of the molecule.
The solubility of nitrogen in polyethylene above the crystalline melting point at high pressure
Authors: Atkinson E. B. 
Published: April 2003

AbstractA simple method of measuring the solubility of gases in polymers at elevated temperatures and high gas pressures is described by direct weighing of the sample after cooling to ambient temperatures. Changes in gas content during cooling which would cause errors are largely prevented by nucleating bubbles throughout the samples immediately prior to cooling, with the effect of making the internal partial pressure of gas equal to the external pressure while the polymer is soft and thus preventing gas flux to or from the sample. Results are given for the solubility of nitrogen in branched polyethylene in the temperature range 130–190°C at gas pressures up to 1,030 bar. A kink in the solubility isotherm at temperatures just above the normal crystalline melting point is believed to be caused by a pressure shift of the melting point. Comparison of the results with previous work by Lundberg et al. suggests a systematic error in the latter which reduced the apparent solubility at higher pressures.
Photoconduction in poly(ethylene terephthalate). I. Mechanisms of carrier generation
Authors: Takai Yoshiaki , Osawa Toshifumi , Mizutani Teruyoshi , Ieda Masayuki 
Published: April 2003

AbstractMechanisms of photocarrier generation in poly(ethylene terephthalate) (PET) have been investigated. In the wavelength range of λ ≦320 nm, the photocurrent spectra correspond closely with the optical absorption spectra of PET and the assignment of the absorption peaks revealed that photocarriers are generated through ππ* excitations. In the wavelength range from 320 to 400 nm, photocarriers are injected from metal electrodes. The threshold energies for Al and Cu electrodes are 2.87 and 2.94 eV, respectively, indicating the presence of surface states. The simplified model gives the density of the surface states as 1.7 × 1014 cm−2 eV−1.
X‐ray diffraction and infrared studies on annealed highly syndiotactic poly(vinyl chloride)
Authors: Baker C. , Maddams W. F. , Preedy J. E. 
Published: April 2003

AbstractX‐ray diffraction scans and infrared absorption spectra for the C‐CI stretching region were obtained for a highly syndiotactic poly(vinyl chloride) (PVC) sample made by the urea clathrate method. When the polymer was annealed at a series of increasing temperatures up to 180°C, x‐ray diffraction measurements showed that the crystallinity increases steadily with annealing temperature. Even at 50°C an increase above the original value of 63% was detectable and by 180°C it had reached 70% with a further increase to 78% after cooling to ambient temperature. There is a concurrent significant increase in the lateral crystallite dimensions. However, the infrared spectrum did not change, in agreement with the recent prediction of Moore and Krimm that there is no observable band splitting from interchain interaction in crystalline regions, thus indicating that these C‐CI bands cannot be used as a measure of crystallinity. The results from computer curve fitting of the spectra suggest that at least 85% of the polymer consists of long planar syndiotactic sequences and there is therefore substantial order along the chain direction. A mechanism for the increase in crystallinity on annealing, involving the lateral ordering of these regular chains, is discussed. Furthermore, as the temperature is raised some amorphous material is converted to a nematic phase, and this may crystallize during the subsequent cooling.
Origin of double melting peaks in drawn nylon 6 yarns
Authors: Todoki Minoru , Kawaguchi Tatsuro 
Published: April 2003

AbstractThe differential scanning calorimetry (DSC) melting curves of drawn nylon 6 were studied from the standpoint of reorganization of the crystals during the heating process. A new method was presented to obtain the DSC curve associated with the growth and melting of the original crystals, and that with the recrystallization and final melting process, separately. The results obtained show that, in the case of a heating rate of 10°C/min, the original crystals in the sample start perfecting themselves at temperatures far below their initial melting temperature and melt out below 222°C, recrystallization starts at about 210°C, and the newly emerged crystals melt out at 228°C. The superposition of two such constructed DSC curves reproduces the observed DSC curve well. Therefore, the double melting peaks of the sample are considered to be the result of superposition of three processes which occur successively during heating; perfection of the original crystals, melting of the perfected crystals concurrently with recrystallization, and melting of the recrystallized crystals.
The effect of density on the properties of high molecular weight polyethylenes
Authors: Trainor A. , Haward R. N. , Hay J. N. 
Published: April 2003

AbstractUltrahigh molecular weight polyethylene has been crystallized at various pressures (0–330 MN m−2) to material of a wide range of specific gravities (0.928–0.967). Tensile measurements illustrate that the properties of these materials are dependent on specific gravity (sg), in that the yield stress increases linearly with sg. Low sg (0.928–0.944) materials exhibit higher yields stress than low molecular weight materials of the same sg but the opposite is true for higher sg material. Low sg material also extends uniformly after yielding while above a sg of 0.944 necking becomes more marked. Orientation hardening is observed with all these materials above 200% extension and is more marked than with low molecular weight polymers. Differential scanning calorimetry (DSC) analysis of the pressure crystallized materials indicate that in the range 200–400 MN m−2 two phases are present, i.e., chain‐folded and chain‐extended lamellas. Increasing or decreasing the pressure changes the crystalline component to chain‐extended or chain‐folded morphologies, respectively. The reorganization of the crystalline components on drawing is discussed.
Polymer–monomer binary mixtures. I. Eutectic and epitaxial crystallization in poly(ϵ‐caprolactone)–trioxane mixtures
Authors: Wittamann J. C. , Manley R. St. John 
Published: April 2003

AbstractBinary mixtures of a linear polyester (poly(ϵ‐caprolactone)) and a crystallizable monomer (trioxane) have been investigated by means of differential scanning calorimetry and optical and electron microscopy. The phase diagram indicates the existence of a eutectic at a temperature TmE = 314°K and for a polymer volume fraction ϕ2E = 0.70, values close to those predicated by the Flory–Huggins theory (using χ = 0.3). Microscopic studies reveal unusual morphologies: (1) In hypoeutectic mixtures, at room temperature, the solvent crystallizes as highly ramified or branched needles. When the remaining melt reaches the eutectic composition, transcrystallization of the polymer is induced by the epitaxial deposition (as established by electron diffraction) of polycaprolactone on the existing trioxane crystals, and leads to highly ordered structures. (2) In hypereutectic mixtures a predominantly spherulitic texture is observed. Blends of trioxane and several other linear polyesters are found to exhibit similar behavior.