bluuebunny/crossref_metadata_2025_split huggingface dataset:
Texture development in polyethylene II. Unidirectional rolling
Authors: Krause Stephen J. , Hosford W. F. 
Published: April 2003

AbstractThe effect of degree of strain on texture development in high‐density polyethylene has been studied by pole figure analysis for unidirectional rolling. The crystallite orientation distribution in rolling textures has been quantified with an efficient technique which fits three‐parameter, two‐dimensional Gaussian‐type distributions to pole figure intensity data around ideal single crystal orientations. During flat rolling of polyethylene a texture consisting of a strong (100) [001] component and a weak (110) [001] component develops continuously from the lowest true strain of 0.24 (21% reduction) up to the highest true strain of 1.36 (74% reduction). The peak intensity of the Gaussian distributions of both (100) [001] and (110) [001] components increase continuously to the highest strain. The maximum angular breadth of both component distributions, which are roughly perpendicular to the strain direction, remains constant with increasing strain. The minimum angular breadth of both component distributions, which are roughly parallel to the strain direction, decreases continuously owing to gradual alignment of the covalently bonded chain backbone parallel to the strain direction. The development of the (100) [001] component is explained by slip on (100) planes while the weak (110) [001] component is explained by slip on (110) planes. Although the latter component was previously attributed to (110) or (310) relaxation twinning, this seems unlikely because of the lateral constraint during plane strain deformation conditions used in this study.
Comparison of three models for permeation of CO2/CH4 mixtures in poly(phenylene oxide)
Authors: Story Brooks J. , Koros W. J. 
Published: April 2003

AbstractTwo models for the permeability of pure gases have been extended to include binary gas mixtures. The first is an extension of a pure gas permeability model, proposed by Petropoulos, which is based on gradients of chemical potential. This model predicts the permeability of components in a gas mixture solely on the basis of competition for sorption sites within the polymer matrix. The second mixed gas model follows an earlier analysis by Barrer for pure gases which includes the effects of saturation of Langmuir sites on the diffusion as well as the sorption processes responsible for permeation. This generalized “competitive sorption/diffusion” model includes the effect of each gas component on the sorption and diffusion of the other component in the mixture. The flux equations from these two models have been solved numerically to predict the permeability of gas mixtures on the basis of pure gas sorption and transport parameters. Both the mixed gas Petropoulos and competitive sorption/diffusion model predictions are compared with predictions from the earlier simple competitive sorption model based on gradients of concentration. An analysis of all three models is presented for the case of CO2/CH4 permeability in poly(phenylene oxide) (PPO). As expected, the competitive sorption/diffusion model predicts lower permeability than either of the models which consider only competitive sorption effects. The permeability depression of both CO2 and CH4 predicted by the competitive sorption/diffusion model is roughly twice that predicted by the competitive sorption model, whereas the mixed gas Petropoulos model predictions for both gases lie between the other two model predictions. For the PPO/CO2/CH4 system, the methane permeability data lie above the predictions of all three models, whereas CO2 data lie below the predictions of all models. Consequently, the competitive sorption/diffusion model gives the most accurate prediction for CO2, while the simple competitive sorption model is best for methane. The effects of mixed gas sorption, fugacity, and CO2‐induced dilation were considered and do not explain the inaccuracies of any of the models. The relatively small errors in mixed gas permeability predictions using either of the three models are likely to be related to “transport plasticization” of PPO owing to high levels of CO2 sorption and its effect on polymer segmental motions and gas diffusivity.
Treatment of asymmetric SANS data
Authors: Hammouda Boualem 
Published: April 2003

AbstractSmall‐angle neutron scattering (SANS) is a useful technique for investigating the anisotropy of density fluctuations when these have single orientation direction. The commonly used method for treating asymmetric SANS data is to analyze sectors of data parallel and perpendicular to the orientation axis. Other methods based on the use of all the available two‐dimensional (2D) data are discussed. These consist in least‐squares fitting of the 2D data to models that include nonuniform deformations of the sample. An inverse 2D Fourier transform of the raw data has also been used to obtain an asymmetric pair correlation function. A hot stretched partially deuterated homopolymer and a stretched microphase segregated rubbery random copolymer system are used as examples of anisotropic scatterers.
X‐ray diffraction by thermotropic main‐chain polymers with side groups. II. semiflexible polyesters
Authors: Chin Hui H. , Azároff Leonid V. , Saini Agya R. , Lenz Robert W. 
Published: April 2003

AbstractSemiflexible thermotropic aromatic polyesters with lateral groups were aligned magnetically and mechanically in monodomains after separation into high‐molecular‐weight (polymer) and low‐molecular‐weight (oligomer) fractions. Based on the x‐ray intensity distributions recorded for a series of seven different substituents in the arylsulfonyl substituted group, a novel smectic structure was determined for H, F, Cl, OCH3, and CH3 in the para position while a normal nematic alignment prevailed when it contained Br or NO2.
A Study of the dielectric properties of the polymer electrolyte PEO‐LiClO4 over a composition range using time domain spectroscopy
Authors: Gray F. M. , Vincent C. A. , Kent M. 
Published: April 2003

AbstractHigh frequency dielectric measurements in the range 10 MHz to 10 GHz have been performed on poly(ethylene oxide) (PEO) and its complexes with lithium perchlorate using time domain spectroscopy. Measurements were made over a wide polymer‐to‐salt composition range and in the temperature range 50–75°C. All samples were amorphous. A relaxation was observed for PEO and its complexes with LiClO4 in the GHz region and is attributed to the β (αa) relaxation arising from long‐range segmental motion of the polymer or the ion‐polymer complex. Good agreement was found between conductivity values determined by TDS and those quoted in the literature An increase in salt concentration in the polymer increases the distribution of relaxation times which may be explained in terms of increased intermolecular and intramolecular transient crosslinks. The dispersion amplitude (ε−ε) has a maximum value between an O/Li ratio of 20:1 and 12:1 and shows a similar dependence on salt concentration as the conductivity.
XPS studies of charge transfer interactions in some polyphenylacetylene‐electron acceptor systems
Authors: Kang E. T. , Neoh K. G. , Tan K. L. , Tan B. T. G. 
Published: April 2003

AbstractX‐ray photoelectron spectroscopy (XPS) studies have been performed on charge transfer complexes of trans‐polyphenylacetylene (PPA). The acceptors used included halogens, such as I2 and Br2, and organic electron acceptors, such as 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone (DDQ), chloranil, fluoranil, and 7,7,8,8‐tetracyano‐p‐quinodimethane (TCNQ). Incomplete and relatively weak charge transfer interactions were observed in most of the complexes. These help to account for the relatively low conductivity levels observed in most of the PPA complexes when compared with the corresponding complexes of other conjugated polymers. PPA has also been found to interact with molecular oxygen to some extent in solution. In complexes involving O2, Br2, and fluoranil, XPS data suggest that the charge transfer interaction may have proceeded further than the pure formation of molecular charge transfer complexes.
The time of flight static secondary negative ion mass spectra of poly(methylmethacrylate), poly(ethylmethacrylate), and poly(methylmethacrylate‐co‐ethylmethacrylate). Ion structures and quantification
Authors: Lub J. , van Vroonhoven F. C. B. M. , van Leyen D. , Benninghoven A. 
Published: April 2003

AbstractNegative secondary ion mass spectra of poly(methylmethacrylate) (PMMA), poly(ethyl‐methacrylate) (PEMA), and two copolymers of methylmethacrylate (MMA) and ethylmethacrylate (EMA) are presented. The spectra were obtained with a time of flight‐static secondary ion mass spectrometer without charge compensation. The structures of typical ions in the mass range 20–220 amu are given, and the intensities of these ions were used to obtain some quantitative information about the ion formation processes. It is shown that quantification of a simple two‐component system like the copolymers mentioned above is rather straightforward.
The effect of electrolyte‐controlled growth morphology on the charge transport properties of poly(3‐methylthiophene)
Authors: Reynolds John R. , Hsu Shing‐guang , Arnott Howard J. 
Published: April 2003

AbstractPoly(3‐methylthiophene) films were potentiostatically and galvanostatically synthesized on platinum electrodes in acetonitrile using lithium perchlorate, lithium tetrafluoroborate, tetra‐n‐butylammonium perchlorate, and tetra‐n‐butylammonium tetrafluoroborate as supporting electrolytes. Cyclic voltammetric analyses of the polymer films indicate the synthesis is polymerization process dependent. Constant potential syntheses, which resulted in a higher current density and were carried out at higher potentials, yielded polymer films with a higher charge capacity. Chronocoulometric results show that the charge transport rates of the films were electrolyte dependent and that tetra‐n‐butylammonium tetrafluoroborate yielded poly(3‐methyl‐thiophene) with the highest charge transport rate. The charge transport rate was found to be electric field dependent for all cases, suggesting that the films resemble a porous electrode. Scanning electron microscope analyses of the films, prepared under various conditions, indicate that the synthesis method used, and the nature of the electrolyte, strongly influence morphology and charge transport.
Thermodynamics of the glass transition
Authors: Astarita Gianni , Paulaitis M. E. , Wissinger R. G. 
Published: April 2003

AbstractA thermodynamic analysis of the glass transition in polymers is presented, which predicts, with a minimum of assumptions, three of the four inequalities which have consistently been observed experimentally: i.e., that specific heat and isothermal compressibility of the glass are lower than those of the rubber, and that the Prigogine‐Defay ratio is larger than unity. The analysis cannot predict the fact that the thermal expansion coefficient of the glass is also lower than that of the rubber, and indeed the converse situation is not a thermodynamic impossibility.
Comparative study of the phase behavior of liquid‐crystalline components in closely related blends and copolyesters
Authors: Lenz Robert W. , Rao A. Kameswara , Reddy C. Rami , Bafna Sudhir , Bhattacharya Subrata 
Published: April 2003

AbstractPhase behavior of blends of a liquid‐crystalline (LC) polymer with a non‐LC polymer and of a series of copolymers containing mesogenic and nonmesogenic units was studied by thermal, optical, and dynamic mechanical methods. The polymers composing the blends and the copolymers had the same constituent monomers. The blends exhibited phase separation over the whole range of compositions studied as observed by DSC and dynamic mechanical analysis. Two glass transition temperatures (Tg) corresponding to the two components and independence of melting (Tm) and isotropization temperatures (Ti) to changes in composition were observed for the blends. The copolymers did not show phase separation over most of the composition range studied. Only one Tg corresponding to that of the major component could be detected for the copolymers, and the Tg was found to increase with an increase in the amount of nonmesogenic monomer in the copolymers. The difference in phase behavior was explained on the basis of the chemical environment of the constituent units in the blends and in copolymers. Phase inversion in the blends was observed by microscopy when the blends contained 60 mol% or more of the non‐LC polymer.
A light‐scattering study of phase separation kinetics in polystyrene/poly(2‐chlorostyrene) blends
Authors: Takahashi Masato , Kinoshita Satoshi , Nose Takuhei 
Published: April 2003

AbstractThe angular dependence of the intensity of scattered light from polystyrene/poly(2‐chlorostyrene) blends was measured as a function of time in early and late stages of phase separation. The results were discussed in terms of Cahn's theory and scaling law for the late stage. Some distinctive behaviors which had not been found in other polymer blends were observed: the intensity of low‐angle scattering increased significantly during phase separation, possibly because of inhomogeneities in density. In the power laws km α tϕ and Im α tθ for the time (t) evolution of the peak position km and peak heigh Im of the structure function in the late stage; the value of ϕ was around −1, almost independent of composition and temperature; the ratio |θ/ϕ| was less than the theoretical value 3. Possible explanations for these behaviors are discussed in relation to the glass transition.
Investigations of a series of PPDI‐based polyurethane block copolymers. I. General morphology
Authors: Kazmierczak M. E. , Fornes R. E. , Buchanan D. R. , Gilbert R. D. 
Published: April 2003

AbstractThe morphology of a series of segmented polyurethane block copolymers is characterized by x‐ray scattering, differential scanning calorimetry (DSC), density measurements, and tensile studies. The materials contain hard segments formed from paraphenylene diisocyanate (PPDI) and flexible segments formed from poly(oxytetramethylene) (POTM) ranging in molecular weight from 650 to 2000. Four different molecular weight compositions were investigated, with the weight fraction of the hard segment (wh) ranging from 0.14 to 0.33. The microphase structure has been examined using small‐angle x‐ray scattering, and the microphase transition zone thickness is estimated to be on the order of 1 nm. Oriented samples have been characterized with wide‐angle x‐ray scattering, and the flexible segment is shown to undergo stress‐induced crystallization. DSC thermograms show flexible segment melting in the compositions containing the highest two molecular weights of the flexible segments. The hard segment thermal transitions were complex with a broad melting peak that varied with weight fraction and with a high temperature transition attributed to regions with hard segment lengths longer than the bulk of the hard segment component. There is an increase in tensile strength and initial modulus and decrease in elongation with increasing wh. Density data suggest the existence of a multiphase system.
Investigations of a series of PPDI‐based polyurethane block copolymers. II. Annealing effects
Authors: Kazmierczak M. E. , Fornes R. E. , Buchanan D. R. , Gilbert R. D. 
Published: April 2003

AbstractIn a previous study, the morphologies of a group of paraphenylene diisocyanate (PPDI)‐based polyurethane block copolymers were examined. These polyurethanes exhibited a multiphase structure with an interfacial boundary thickness estimated to be on the order of 1 nm and crystallization of the polyoxytetramethylene (POTM) flexible segment. Further studies involving annealing of these polyurethanes are reported here. An annealing time of 4 h was used, and the annealing temperature varied from 125 to 200°C. The samples have been characterized using differential scanning calorimetry (DSC) and with wide‐ and small‐angle x‐ray scattering (WAXS, SAXS) in order to determine the effects of annealing on the microphase structure. Annealing increases the phase separation of the two phases as evidenced by sharper endotherms in DSC thermograms and increased intensities in WAXS diffractometer traces. Annealing also slightly increases the transition zone thickness and long‐period spacing. At the highest annealing temperature in this study, the long‐period spacing increases dramatically due to hard segment domain aggregation.
Miscibility of poly(vinyl chloride) with styrene/acrylonitrile copolymers
Authors: Kim J. H. , Barlow J. W. , Paul D. R. 
Published: April 2003

AbstractPoly(vinyl chloride) (PVC) is shown to be miscible with styrene/acrylonitrile copolymers (SAN) having AN compositions from 11.5 to 26%. Blend samples were prepared using several methods, including solution casting, melt mixing, and precipitation of solutions by a nonsolvent. It is shown that the blend phase behavior is affected by preparation method due to the solvent effect, or Δχ effect, and lower critical solution temperature (LCST) behavior. The intramolecular repulsion between styrene and acrylonitrile units in SAN is shown to be the cause of miscibility using heats of mixing obtained from low‐molecular‐weight analog compounds. An FTIR analysis supplements the above results.
Interplay of rubber network theory with the damping behavior of crosslinked polyurethanes
Authors: Hur T. , Manson J. A. , Sperling L. H. 
Published: April 2003

AbstractNetwork formation (branching) theory was used to examine the relationships between network structure and concomitant sound and vibration damping. For a series of model polyether‐based polyurethane networks with varying stoichiometry and composition, the glass transition temperature Tg, was found to increase with increasing concentration of elastically active network chains, EANCs, as well as the ratio of branch OH group concentration to the total OH group concentration ρ. The values of (tan δ)max, the peak height of tan δ at Tg, linearly decrease with increasing concentration of EANCs, regardless of the ρ values. However, the loss area (LA), equal to the integral of the linear loss modulus‐temperature curve, is independent of the concentration of EANCs and/or ρ. Utilizing group contribution analysis techniques, the value of the main chain ‐O‐ group contribution, LA‐O‐, is 19.1 GPa·K/g, a rather large value. This finding gives insight into why polyether urethanes are preferred for many damping applications.
Short time molecular dynamics simulations: Stressed polyethylene results
Authors: Noid Donald W. , Pfeffer George A. 
Published: April 2003

AbstractThe multiple signal classification method (MUSIC) for frequency estimation is used to compute the spectrum (intensity versus frequency) for stressed polyethylene in a crystal from the time‐dependent structure factor. In this article we demonstrate that MUSIC can accurately determine the frequencies for our model from very short time trajectories and can compute the frequency shifts for various stress perturbations. A preliminary study of the dynamical effects of stress on the fracture of a PE chain showed that at low stress the chain had an irregular period of the end‐to‐end distance (reaction coordinate) oscillation and at higher stress a periodic extension and contraction.
Synthesis and solution properties of comblike poly(mono‐n‐alkyl itaconates). I. Poly(monodecyl itaconate)
Authors: Leon Arturo , Gargallo Ligia , Horta Arturo , Radić Deodato 
Published: April 2003

AbstractThe monoester of itaconic acid with n‐decyl alcohol was prepared and polymerized. The polymer was fractionated and characterized by viscometry, size‐exclusion chromatography (SEC) and light scattering. Some of the common semiempirical relations for flexible and rigid polymers were used in order to obtain the unperturbed dimensions and the conformational parameters. Thermodynamic and dimensional parameters were determined and calculated. The results are compared with those reported previously for similar compounds.
Angular dependence of 1H‐NMR and 2H‐NMR spectra of water absorbed in cellulose film
Authors: Matsumura Kazunori , Hayamizu Kikuko , Yamamoto Osamu 
Published: April 2003

Abstract1H‐NMR and 2H‐NMR spectra of water (H2O and D2O) absorbed in Visking cellulose tubing have been observed as a function of the angle Θ between the film surface and the magnetic field. 1H‐NMR spectra show broad lines, and the chemical shift and the linewidth depend on Θ. From the angular dependence of the chemical shift, the anisotropic volume diamagnetic susceptibilities of the film are determined, i.e., χ∥ in the direction longitudinal to the tubing (stretched direction) is 0.43 ppm, and χ⊥ in the transverse direction is 0.57 ppm. The different values of χ∥ and χ⊥ afford an evidence of the anisotropy of the film. 2H‐NMR spectra of D2O absorbed in the film show quadrupole splitting which also depends on Θ. The angular dependences of the linewidth (1H‐NMR) and the quadrupole splitting (2H‐NMR) indicate that the HH axes of the water molecules have a tendency to orient in the direction longitudinal to the film surface.
Kinetics of structural relaxation of poly(ethylene terephthalate)
Authors: Avramov I. , Avramova N. , Fakirov S. 
Published: April 2003

AbstractThe results of an experimental study of the kinetics of structural relaxation of amorphous poly(ethylene terephthalate) are reported. Samples were prepared by ultraquenching the melt on rotating stainless‐steel discs. Two types of measurements by differential scanning calorimetry were made: (1) the dependence of the “fictive” (or “structural”) temperature Tf(q−) introduced by Tool, on the cooling rate q− and (2) the dependence of the glass transition temperature Tg on the heating rate q+. In this way the value x = 0.47 was obtained for the dimensionless parameter proposed by Narayanaswamy.
Effect of molecular weight distribution on the structure and mechanical properties of ultradrawn, ultrahigh‐molecular‐weight polyethylene cast from solution. I. Thermoluminescence and NMR
Authors: Bao Liu Liang , Murakami Noriko , Sumita Masao , Miyasaka Keizo 
Published: April 2003

AbstractUltradrawing of ultrahigh‐molecular‐weight polyethylene (UHMW‐PE) films produced by gelation/crystallization from solution was investigated using thermoluminescence (TL), DSC, and pulsed NMR. The TL from an x‐irradiated UHMW‐PE gel film is considerably affected by ultradrawing. The TL glow peak is correlated with the αc dispersion of the crystalline phase in the UHMW‐PE gel film. The TL integrated intensity is weak for folded‐chain crystals but strong for extended‐chain crystals. An extra higher TL peak, observed for samples drawn 150x, is related to the appearance of some highly extended tie‐chains in the interfacial region in the process of ultradrawing. On the basis of the above observations, the effects of molecular weight distribution on the morphology of UHMW‐PE gel film are examined. It is concluded that B‐PE (Broad MWD) having a broader MWD has better drawability than N‐PE; but at a given draw ratio, higher modulus and tensile strength are realized for N‐PE (Narrow MWD).