bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effect of heating on polyaniline powders studied by real‐time synchrotron radiation diffraction, mass spectrometry and thermal analysis
Authors: Boyle A. , Penneau J. F. , Geniès E. , Riekel C. 
Published: April 2003

AbstractThe effect of heating on four chemically synthesized polyanilines, three of which were doped by HCI, H2SO4, HCIO4, and one sample which was dedoped, was investigated. The structural variations during thermal decomposition were studied by real‐time synchrotron radiation diffractometry and correlated with mass spectrometry (MS), thermal gravimetry (TG), and differential thermal analysis (DTA). These macroscopic and microscopic techniques were combined in order to shed more light on the role played by the water and the counteranion molecules on the structure of doped polyaniline. Evidence for two H2O fractions was found for HCI‐doped polyaniline. Chain degradation was observed for HCIO4 and H2SO4‐doped polyaniline. The results indicate that intermediate sulphonation of polymer chains occurs in the latter case.
Valence band x‐ray photoelectron spectroscopy of poly(ether ketone) and poly(ether‐ether ketone)
Authors: Cain Stephen R. , Matienzo Luis J. 
Published: April 2003

AbstractPoly(ether ketone) and poly(ether‐ether ketone) are characterized by valence band x‐ray photoelectron spectroscopy. The valence band region appears to be resolved into six regions. Peak assignments were made by comparing the observed spectra with simulations from extended Hückel type band calculations. Results of the band calculations agreed fairly well with the experimental data.
Crystal structure of poly(p‐phenylene) prepared by organometallic technique
Authors: Sasaki S. , Yamamoto T. , Kanbara T. , Morita A. , Yamamoto T. 
Published: April 2003

AbstractThe two‐dimensional crystal structure of poly(p‐phenylene) is investigated by linkedatom Rietveld analysis of the x‐ray diffraction powder profile. Two molecular chains are packed in a rectangular pgg unit cell (a = 0.779 nm; b = 0.551 nm) with a paracrystalline shift distortion along the chain axis. The molecular conformation is not rigidly planar; rotations between adjacent phenyl‐ring planes in a molecule alternate with an angle of about 20°. The setting angle between the mean molecular plane and the a axis is 55.5°.
Crystal and molecular deformation in strained high‐performance polyethylene fibers studied by wide‐angle x‐ray scattering and Raman spectroscopy
Authors: Moonen Joost A. H. M. , Roovers William A. C. , Meier Robert J. , Kip Bert J. 
Published: April 2003

AbstractWide‐angle x‐ray scattering (WAXS) and Raman spectroscopic data show that on both the crystal and molecular levels, a bimodal stress distribution exists in strained high‐performance polyethylene fibers. In part of the crystalline PE the microscopic strain level is high (ca. 70% of macroscopic strain); in the remainder, the microscopic strain level is low (independent of macroscopic strain, ca. 0.4%). During stress relaxation the fraction of highly strained PE decreases with time. WAXS revealed no indication of a change in the a and b unit‐cell dimensions. Furthermore, no indications for stress‐induced formation of monoclinic and/or hexagonal PE and for crystal breaking were found. From the latter it can be deduced that all chains within one crystal are equally strained. The WAXS results are used to calibrate the stress‐induced frequency shifts of Raman bands.
Application of spin trapping to redox‐initiated vinyl polymerization with thiourea as the reductant
Authors: Saha S. K. , Greenslade D. J. 
Published: April 2003

AbstractAn electron spin resonance (ESR) study confirms a free radical mechanism for aqueous vinyl polymerization initiated by three redox systems involving thiourea. The primary radical, NH2C (NH)S., could not be detected by ESR spectroscopy, perhaps because of its large g anisotropy and/or very short relaxation time. Propagating radicals are trapped from methyl‐methacrylate by 2‐methyl‐2‐nitroso propane (MNP) and their structures are found to be the same as those produced by either azo‐bis‐isobutyrnitrile or di‐t‐butyl peroxylate. The latter monomer, however, reacts with MNP in the absence of any initiator, giving different ESR lines.
Thermal and rheological properties of miscible polyethersulfone/polyimide blends
Authors: Liang K. , Grebowicz J. , Valles E. , Karasz F. E. , MacKnight W. J. 
Published: April 2003

AbstractBlends of an aromatic polyethersulfone (commercial name Victrex) and a polyimide (commercial name Matrimid 5218), the condensation product of 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride and 5(6)‐amino‐1‐(4′‐aminophenyl)‐1,3,3′‐trimethylindane, were studied by differential scanning calorimetry, dynamic mechanical analysis, and rheological techniques. The blends appeared to be miscible over the whole range of compositions when cast as films or precipitated from solution in a number of solvents. After annealing above the apparent phase boundary, located aboveTg, the blends were irreversibly phase separated indicating that the observed phase boundary does not represent a true state of equilibrium. Only a narrow “processing window” was found for blends containing up to 20 wt % polyimide. Rheological measurements in this range of compositions indicated that blending polyethersulfone with polyimide increases the complex viscosity and the elastic modulus of the blends. For blends containing more than 10 wt % polyimide, abrupt changes in the rheological properties were observed at temperatures above the phase boundary. These changes may be consistent with the formation of a network structure (due to phase separation and/or crosslinking). Blends containing less than 10 wt % polyimide exhibited stable rheological properties after heating at 320°C for 20 min, indicating the existence of thermodynamic equilibrium.
The mechanism of fatigue failure in a polyethylene copolymer
Authors: Zhou Ying‐Qiu , Brown Norman 
Published: April 2003

AbstractThe fatigue behavior of an ethylene‐hexene copolymer was investigated. The effects of R, frequency, relative times under the maximum and minimum stress, and waveform were measured. The phenomenological aspects were related to the microscopic aspects of the failure process. The maximum stress produces damage by disentangling the molecules in the fibrils of the craze and the minimum stress produces damage by bending the fibrils. The net damage, which is a product of these two damage processes, has been represented by a simple equation which accounts for the phenomenological observations.
Effects of substituent groups of polyimides on sorption and diffusion of gases
Authors: Toi Keio , Ito Tomoyasu , Ikemoto Isao , Kasai Tetsuo 
Published: April 2003

AbstractSorption rate curves of CO2, N2, and He gases below 1 atm were measured for polyimide films prepared from benzophenone tetracarboxylic dianhydride (BTDA) with 3,5‐diaminotoluene trifluoride (DATF), 2,4‐diaminotoluene (DAT), m‐phenylenediamine (MPD), and diaminobenzoic acid (DABA). The molecular structures of these four polyimides differ only in the substituent groups of the diamine structure. These polyimides exhibit dualmode type sorption isotherms for carbon dioxide that are concave to the pressure axis, typical of glassy polymer/gas system. The apparent diffusion coefficients below 1 atm pressure of carbon dioxide for this series of compounds decrease in the order: BTDA‐DATF > BTDA‐DAT > BTDA‐MPD > BTDA‐DABA. A linear relation between the logarithm of the apparent diffusion coefficient and the reciprocal of free volume, calculated by the method of Bondi using density data, is found for these polyimides. However, this tendency is not observed for the other two gases. The activation energies of the apparent diffusion coefficients at 20 cmHg pressure of carbon dioxide increase with increasing cohesive energy density of the polyimides. The energy per mole of free volume elements in a liquidlike structure in each cohesive energy density may be equated to the activation energy and used to calculate the free volume. The values from the activation energy are almost the same as those from Bondi's method.
Orientation and mechanical properties of PBT and its blends with a liquid‐crystalline copolyester
Authors: Ajji A. , Brisson J. , Qu Y. 
Published: April 2003

AbstractBlends of poly (butylene terephthalate) (PBT) and a liquid‐crystalline copolyester (60 mol % poly(p‐hydroxy benzoic acid)/40 mol % polyethylene terephthalate) (LCP) were prepared in the melt state. The investigation of mechanical properties indicated that, for the processing conditions used, neither the addition of up to 30 wt % LCP to PBT nor the cooling history affected significantly the tensile modulus E. For oriented specimens, a marked improvement of E was obtained for all the blends, and increased with the LCP content. This improvement was more marked for slowly cooled samples. X‐ray diffraction was used to quantify the orientation of the crystalline PBT and liquid‐crystalline LCP phases. It was shown that neither the thermal history nor the presence of up to 30 wt % LCP affected the orientation behavior of the PBT crystalline phase. For the LCP phase, measurements were not possible for concentrations lower than 10 wt %, and were more difficult and less precise than for PBT. Nevertheless, it was possible to show that a better orientation was obtained for the slowly cooled samples and for higher concentrations of LCP in the blends. This correlated with the enhancement of mechanical properties observed for the oriented samples.
129Xe NMR as a probe of polymer blends
Authors: Walton J. H. , Miller J. B. , Roland C. M. 
Published: April 2003

AbstractThe miscibility of two‐component polymer blends has been investigated using xenon‐129 (129Xe) nuclear magnetic resonance (NMR) to probe the phase morphology. The chemical shift of 129Xe dissolved in a given polymer is unique, thus heterogeneous blends with large domain sizes exhibit two 129Xe NMR lines. When a single resonance is obtained, the data are consistent with miscibility, yielding an upper bound on the domain size. The temperature dependence of the relative solubilities and chemical shifts of 129Xe dissolved in the pure components may allow a determination of the phase morphology in blends exhibiting a single resonance. The method is used to demonstrate that polychloroprene and 25% epoxidized 1,4‐polyisoprene form a miscible blend.
Sorption and diffusion of gases in a polyimide
Authors: Toi Keio , Ito Tomoyasu , Shirakawa Toshiaki , Ikemoto Isao 
Published: April 2003

AbstractSorption and diffusion of gases (CO2, N2, and He) in a polyimide (PI2080) film were measured by using an apparatus which gives the sorption rate curves from the initial state to the equilibrium state. Nonlinear isotherms observed for CO2 sorption were interpreted successfully in terms of the dual‐mode model for sorption in glassy polymers. Linear isotherms observed for N2 and He seemed to obey Henry's law. Two diffusion coefficients (DI and DE) were obtained using the short‐time method and the long‐time method for a Fickian diffusion model, together with the equilibrium solubility (Ce) from each experiment. The initial sorption rate curves agreed with the calculated curves using DI, however near sorption equilibrium the curves are in accord with the calculated curves using DE. These observations suggest that some relaxation process is superimposed on the diffusion process. The non‐Fickian transport data were correlated successfully with a model that combines time‐dependent diffusion and the Fickian model.
Characteristics and design procedure of hyperbolic dies
Authors: Chen Gao‐Yuan , Cuculo John A. , Tucker Paul A. 
Published: April 2003

AbstractNozzle profiles capable of generating constant extensional strain rates are termed hyperbolic dies. When used in polymer extrusion, they exhibit greater potential in inducing and retaining polymer molecular orientation than conventional capillary dies. Most mathematical expressions found in the literature involve several processing variables in describing and designing such nozzle profiles. This report reveals that a hyperbolic die profile, although rather complicated, can be expressed with equations in terms of two ordinary geometrical parameters—the exit diameter and the hyperbolic length. This finding greatly simplifies the design procedure of hyperbolic dies. The extensional strain rate of a hyperbolic die can be related to the length‐to‐diameter ratio for any given exit diameter. Examples of various types of die profiles are presented and their constant extensional strain‐rate characteristics are discussed.
Dual‐mode sorption of nonionic azo dyes by Nylon 6
Authors: Shibusawa Takao , Chigira Yasuhiro 
Published: April 2003

AbstractSorption isotherms of 2,4‐dinitroaniline and three 4‐amino‐azobenzene derivatives (nonionic dyes with adequate solubility in water) on Nylon 6 (film and fiber) from water were determined at various temperatures. The observed isotherms were curved, not linear. They were very well described in terms of the dual‐mode sorption model, Nernst‐type partitioning, plus Langmuir sorption. The contribution of the Langmuir sorption to the total dye sorption decreased with increasing temperature. The saturation value for the Langmuir sorption increased with the crystallinity of Nylon 6 film, suggesting that the Langmuir sorption is associated with the crystalline phase.
Miscible blends of zinc‐neutralized sulfonated polystyrene and poly(2,6‐dimethyl 1,4‐phenylene oxide)
Authors: Register Richard A. , Bell Theodore R. 
Published: April 2003

AbstractZinc‐neutralized sulfonated polystyrene ionomers (ZnSPS) and poly(2,6‐dimethyl 1,4‐phenylene oxide) homopolymer (PXE) form miscible blends up to at least 7.8 mol % sulfonation, as measured by thermal and mechanical criteria. The addition of an equal weight of PXE raises the glass transition temperature of ZnSPS by 40–50°C. However, this miscibility is not achieved by eradicating the microdomain structure present in ZnSPS, even though the PXE coils are considerably larger than the spacings between ionic aggregates. Small‐angle x‐ray scattering indicates that while the average interaggregate spacing is roughly the same in ZnSPS and its 50/50 blend with PXE at a given sulfonation level, the extent of phase separation is reduced upon PXE addition, indicating that more ionic groups are dispersed in the matrix. Factors influencing miscibility in the ZnSPS/PXE materials and related blends are discussed.
Counterion binding to poly(allylammonium) cation
Authors: Itaya Tomoyuki , Ochiai Hiroshi 
Published: April 2003

AbstractChloride ion activity coefficients in aqueous solutions of poly(allylamine) hydrochloride (PAA · HCl) have been determined both in the absence and the presence of simple salts. Without added salt, the activity coefficient depends on the polymer concentration. With added salt, the binding of added counterions by PAAH+ is evaluated from the release of chloride ion. The extent of interaction between counterions and PAAH+ at a given polymer concentration decreases in the order SO ≫ ClO > NO > Cl− > Br− > I−. This order of counterion selectivity agrees with the previous estimation of potentiometric titrations. The result shows that the hydration of the counterion, as well as its charge, plays an important part in counterion binding to the polyion.
A study of stress distribution in model composites by using finite‐element analysis. I. End effects
Authors: Fan Cun F. , Hsu Shaw L. 
Published: April 2003

AbstractThe stress distribution along a fiber in model polymer composites has been calculated using a finite‐element analysis technique. Earlier experimental studies suggested that the stress distribution for fibers with tapered ends is much more efficient in carrying an external load than is the case for fibers with blunt ends. Both thermal residual (compressive) stress and tensile stress distributions along the reinforcement fiber have been measured with high sensitivity and spatail resolution. For fibers with blunt ends, the measured stress distribution agrees well with the stress distribution expected for an idealized shear‐lag model. For tapered fibers, the stress distribution measured is a constant along the fiber and a critical length was not found. Finite‐element calculations agree well with these experimental data. In addition, the stress distribution in the fiber, i.e., the radial dependence and the relative strain in both the fiber and matrix, was calculated. A detailed description of possible failure modes for the discontinuous fiber composites is provided based mainly on the finite‐element calculation.
Conductivity and the electric modulus in polymers
Authors: Starkweather Howard W. , Avakian Peter 
Published: April 2003

AbstractAt relatively high temperatures and low frequencies the electrical properties of many polymers are dominated by ionic conductivity. In cases where the glass transition is obscured by conductivity, it can be revealed by treating the data in terms of the electric modulus. The magnitude of the activation energy for conductivity (24–67 kcal/mol) for Nylons 6, 66, and 6I, polybutylene terephthalate, and polycarbonate indicates that the transport of charged particles requires the motion of polymer segments.
Water sorption in poly(ammonium sulfopropylbetaines). I. Differential scanning calorimetry
Authors: Galin J. C. , Galin M. 
Published: April 2003

AbstractThe hydration of four amorphous acrylic and methacrylic poly(zwitterions) bearing the ammonium sulfopropylbetaine function as a side‐groups () was studied by differential scanning calorimetry over broad ranges of temperature (150‐400 K) and water content (weight fraction W1< 0.5). Analyses were made of the first‐order transitions and heat capacity of sorbed water, glass transition temperature (Tg) measurements. Nonfreezable bound water, about 7.7 ± 0.9 mol/monomeric unit, behaves as a single phase: Its mobility, fairly similar to that of bulk liquid water in viscoelastic systems at T > 250 K, decreases with temperature in the glassy systems, but never disappears, even at 185 K. The depression of the glass transition temperature of the hydrated polymers obeys Couchman's equation:Tg= ΣiWiΔCpiTgi/ ΣgiWiΔCpi. Freezable bound water, about 6.7 ± 0.9 mole/monomeric unit, shows multipeak melting endotherms in the range 242–272 K. Because of their charged sites, the hydration process of the poly(zwitterions) appears more similar to that of poly(electrolytes) than to that of uncharged hydrophilic polymers. © 1992 John Wiley & Sons, Inc.
Water sorption in poly(ammonium sulfopropylbetaines). II. Sorption isotherms
Authors: Galin J. C. , Galin M. 
Published: April 2003

AbstractWater sorption by four amorphous acrylic and methacrylic poly(zwitterions) bearing ammonium sulfopropylbetaine side groups () was studied at a constant temperature of 23°C and over a broad range of water activity (0.14‐0.90). Whatever the physical state of the hydrated polymer, glassy or viscoelastic, water diffusion is Fickian (average diffusion coefficient D̄s in the range 2‐16 × 10−8 cm2 s−1), and the sorption isotherms may be quantitatively analyzed according to the Guggenheim‐Anderson‐De Boer amended BET equation for multilayer sorption processes. The number of sitebound water molecules per monomeric unit is in the range 1.5–2.0, and apparently there is no great energy difference between direct site binding and indirect binding in the successive solvation layers. The polymer‐water interaction parameter (−0.6 < χ Flory < 0.6) is an increasing function of the water content of the hydrated poly(zwitterions) over the whole composition range (water volume fraction < 0.5), without any clear transition from the glassy to the viscoelastic state. Clustering of water molecules (Zimm‐Lundberg theory) is never observed, even at high water content. Because of the charged structure of their dipolar units, the poly(zwitterions) show a water sorption process similar to that of the corresponding poly(electrolytes) of the tetra‐alkylammonium sulfonate type. © 1992 John Wiley & Sons, Inc.
Dynamic mechanical and gas transport properties of blends and random copolymers of bisphenol‐A polycarbonate and tetramethyl bisphenol‐A polycarbonate
Authors: Kim C. K. , Aguilar‐vega M. , Paul D. R. 
Published: April 2003

AbstractDynamic mechanical and gas transport properties for homogeneous homopolymer blends and random copolymers of bisphenol‐A and tetramethyl bisphenol‐A polycarbonates (PC‐TMPC) were determined. The gas transport measurements were performed at 35°C for the gases He, H2, O2, Ar, N2, CH4, and CO2. The results show that the copolymers have lower permeability, apparent diffusion, and solubility coefficients than the blends. Permeability coefficients for blends follow a semilogarithmic ideal mixing rule while copolymers exhibit negative deviations from this. Specific volume measurements show that the free volume available for gas transport is slightly larger in copolymers than in blends of the same composition. These apparently contradictory results may relate to the differences in local mode chain motions observed for the copolymer and blend series. The γ relaxation processes in PC and TMPC seem to operate independently in the blends (no intermolecular coupling) while there is clear evidence for intramolecular coupling in the copolymers. © 1992 John Wiley & Sons, Inc.
Quasiharmonic treatment of infrared and raman vibrational frequency shifts induced by tensile deformation of polymer chains. II. Application to the polyoxymethylene and isotactic polypropylene single chains and the three‐dimensional orthorhombic polyethylene crystal
Authors: Tashiro Kohji , Minami Shintaro , Wu Gang , Kobayashi Masamichi 
Published: April 2003

AbstractQuasiharmonic equations are derived for stress‐induced vibrational frequency shifts in the infrared and Raman spectra of polymer chains subjected to a tensile stress. The expressions are applied to the helical chains of polyoxymethylene and isotactic polypropylene. Observed frequency shifts can be reproduced well by using reasonable anharmonic force constants. A semiquantitative interpretation is given for the close relationship between stress‐induced vibrational frequency shifts and the deformation mechanism of the polymer chains. Stress‐induced frequency shifts are also calculated for an orthorhombic polyethylene crystal subjected to uniaxial tension along the chain axis or to hydrostatic pressure. The results consistently and reasonably reproduce observed data, not only for the intramolecular vibrational modes but also for the external lattice modes. © 1992 John Wiley & Sons, Inc.
Model filled polymers. IX. Synthesis of uniformly crosslinked polystyrene microbeads
Authors: Ding Zheng‐You , Ma Shenmin , Kriz Dennis , Aklonis J. J. , Salovey R. 
Published: April 2003

AbstractMonodisperse sized crosslinked polystyrene (PS) beads prepared by reaction of styrene (S) and divinylbenzene (DVB), in batch emulsion copolymerization in the absence of emulsifiers, are not uniformly crosslinked, because DVB is more reactive than S. For copolymerization of 1 to 10 mol % DVB and S, within each crosslinked PS microbead, the crosslink density varies by a factor exceeding two and decreases with increased conversion. A semicontinuous copolymerization, involving incremental additions of DVB, produces uniformly crosslinked PS beads. For both copolymerization techniques, Tg correlates well with crosslink density and PS beads are spherical and monodisperse in size. © 1992 John Wiley & Sons, Inc.