bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mapping the phase diagram of an aromatic polyamide blend using infrared spectroscopy
Authors: Bhagwagar Dorab E. , Painter Paul C. , Coleman Michael M. , Krizan Timothy D. 
Published: April 2003

AbstractThe results of an infrared study of poly (meta‐phenylene adipamide)‐poly (ethylene oxide) blends are reported. This is the first time, to the authors' knowledge, that infrared spectroscopy has been used to experimentally map the phase diagram of a polymer blend. The results are compared with theoretical phase diagrams calculated from a recently described association model.
A study of crystalline transitions in a thermoplastic polyimide
Authors: Gautreaux C. R. , Pratt J. R. , St. Clair T. L. 
Published: April 2003

AbstractA new polyimide derived from 4,4′‐isophthaloyldiphthalic anhydride (IDPA) and 1,3‐bis(4‐aminophenoxy‐4′‐benzoyl)benzene (1,3‐BABB) having semicrystalline behavior was prepared at NASA Langley Research Center in 1987. The crystalline transitions of this thermoplastic polyimide have been studied. The differential scanning calorimetry (DSC) pattern of partially imidized film exhibited two distinct crystalline melt endotherms. For this study each crystalline phase was isolated and enhanced by controlled thermal treatment. A film containing approximately 50% of both phases and an amorphous film were also prepared. Evaluations of these films were performed by DSC, wide‐angle x‐ray scattering (WAXS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Three distinct crystalline morphologies; ellipsoid, cubic, and needlelike embedded in an amorphous matrix were observed as a function of various cure conditions by SEM.
A 13C NMR study of the effect of γ‐irradiation on the chain dynamics of poly(ethylene oxide)
Authors: Schilling Frederic C. , Tonelli Alan E. , Cholli Ashok L. 
Published: April 2003

AbstractA comparison of solid‐state 13C nuclear magnetic resonance (NMR) spectra of virgin and vacuum γ‐irradiated poly (ethylene oxide) (PEO) evidences marked differences. The unirradiated PEO shows a well‐resolved amorphous resonance and a weak, broad envelope of crystalline resonances, while the irradiated PEO presents well‐resolved resonances for both the crystalline and amorphous carbons. Upon recrystallization from the melt both PEO samples yield solid‐state 13C NMR spectra that are closely similar to that of the virgin, unheated sample. Observation of both melt‐recrystallized samples at −60°C yields similar spectra with well‐resolved crystalline resonances. Crosslinking is the predominant chemical change occurring during the γ‐irradiation of PEO under vacuum and produces a change in the motional character of the crystalline phase. This change is not the result of a reduction in crystallinity as evidenced by differential scanning calorimetry (DSC) observations. The most probable explanation is that the crosslinks are concentrated at the surface of the crystalline lamellae with a resultant change in the low frequency molecular motions of the crystalline chains. This motional change shifts the T1pH such that the crystalline carbon nuclei can now be cross‐polarized at room temperature and the resonance linewidth is reduced. Following melting and recrystallization the motional characteristics of the irradiated PEO are nearly identical to those of the unirradiated sample, probably as a result of a redistribution of the crosslinks throughout the amorphous phase during recrystallization.
Crystallization and melting of cold‐crystallized poly(phenylene sulfide)
Authors: Chung Jerry Sengshiu , Cebe Peggy 
Published: April 2003

AbstractIn this study, we report the melting behavior of poly(phenylene sulfide), PPS, which has been cold‐crystallized from the rubbery amorphous state. We find that the crystallization kinetics are faster for cold‐crystallized PPS than for melt‐crystallized material, due to formation during quenching of a short‐range ordered, but noncrystalline, structure. We observe that the endothermic response of cold‐crystallized PPS at a large undercooling consists of a low temperature endotherm, followed by an exothermic region, and by the main higher melting endotherm. The lower melting peak temperature of cold‐crystallized PPS increases as the crystallization temperature increases, but the main upper melting peak temperature remains almost the same. The size of the exothermic region is strongly related to the degree of undercooling, and must be taken into account in order properly to determine the degree of crystallinity of the material prior to the scan. When the crystallization time is varied, we see a systematic decrease in the size of the main endotherm, and an increase in size of the lower melting endotherm. This suggests that a portion of the main endothermic response is due to reorganization during the scan. Annealing will not only increase the degree of crystallinity but also improve the crystal perfection; therefore the ability of an annealed sample to reorganize decreases as the annealing time increases. However, an additional third melting peak is seen when a cold‐crystallized sample is annealed at high temperature for a sufficiently long residence time. The existence of the third melting peak suggests that more than one kind of distribution of crystal perfection may occur when PPS has been cold‐crystallized and subsequently annealed.
The absorption coefficient spectrum of poly(methyl methacrylate) in the soft X‐ray region
Authors: Yates B. W. , Shinozaki D. M. , Kumar Ashok , Meath William J. 
Published: April 2003

AbstractThe total photoabsorption cross section for poly(methyl methacrylate) (PMMA) is measured experimentally, using synchrotron radiation, over the photon energy range 40 < E < 1000 eV. The experiments utilize nominally monochromatic radiation from a grazing incidence grating monochromator (the “Grasshopper” at the Canadian Synchrotron Radiation Facility) on the storage ring “Aladdin” at the University of Wisconsin. The raw experimental data are corrected for the spectral contamination of the incident radiation from the monochromator by utilizing a calculated photoabsorption spectrum for PMMA. The calculations are carried out using the “mixture” rule and reliable dipole oscillator strength distributions for smaller molecules related to PMMA.
Relative molecular weight distributions of cis‐polybenzoxazole/polyphosphoric acid rodlike liquid crystalline polymer solutions from dilute solution rheometry
Authors: Shaffer Edward O. , Carriere Craig J. , Bubeck Robert A. 
Published: April 2003

AbstractThe molecular weight for a dilute solution of cis‐polybenzoxazole (PBO) in polyphosphoric acid (PPA) was determined by fitting the rheological data with a semiempirical polydisperse hybrid theory. The hybrid theory models a semiflexible rigid rod as an elastic cylinder. The cylinder has both a rotational relaxation spectrum given by an ideal rigid rod and an internal bending relaxation spectrum spaced in accord with the relaxation time spectra of a flexible coil with fully developed hydrodynamic interactions. The model was fitted to rheological data collected for a 0.05 weight percent solution with intrinsic velocity (one‐point determination) of 320 ± 10 cc/g. The model predicts a number‐average molecular weight near 12800 ± 400 g/mol with a polydispersity index of 2.5 ± 0.1. By using the Yamakawa‐Yoshizaki equation the intrinsic viscosity is calculated for the model molecular weight distribution as 310 cc/g.
Properties of sulfonated poly(butylene terephthalate)
Authors: Gorda K. R. , Peiffer D. G. 
Published: April 2003

AbstractThe synthesis, morphology, and mechanical properties of sulfonated poly(butylene terephthalate) (PBT) and its unsulfonated analogs were studied. The morphology of these copolymers crystallized from the melt were examined by a combination of wide‐angle x‐ray scattering (WAXS), polarized light microscopy, and small‐angle light scattering (SALS). Stress‐strain measurements are correlated with the morphological results. Spherulitic morphology, with a maltese cross at 45°C with respect to the crossed polars, is formed at low sulfonate levels (≤ 5.0 mol %). At a higher ion content, the maltese cross rotates 45° to form a cross pattern. At still higher sulfonate contents, typically 13 mol %, the light scattering pattern disappears completely. Microscopic and WAXS examination of these functionalized PBT copolymers confirms that the crystallinity level decreases with increasing ion content and is eliminated completely at the higher sulfonation level. The spherulite radius, however, remains invariant until the highest functionalization level. On the contrary, the morphology and properties of the unsulfonated isophthalate copolymer analogs remain relatively constant over the entire composition range examined. In several compositions clearly inferior properties are noted compared with the ion‐containing copolymers.
Conductivity and dielectric properties of the monomer and polymer of the bis(p‐toluene sulfonate) of 2,4‐hexadiyne‐1,6‐diol
Authors: Pingsheng He , Chune Li , Jianbang Peng 
Published: April 2003

AbstractThe electrical conductivity of single crystals of the bis(p‐toluene sulfonate) of 2,4‐hexadiyne‐1,6‐diol (TS) and its polymer (PTS) was measured in a temperature range 77–373 K (to 353 K for TS), dielectric properties were measured from 123 to 283 K. Anomalies of the conductivity and the real part of the complex dielectric permittivity of TS and PTS along the molecular stacking direction at the temperature corresponding to the low‐temperature phase transitions were observed. The dependence of phase transitions on the polymerization conversion of the monomer TS was examined. The phase diagram of the TS‐PTS mixed system was constructed.
Generalized composite degradation kinetics for polymeric systems under isothermal and nonisothermal conditions
Authors: Nam Jae‐Do , Seferis James C. 
Published: April 2003

AbstractA composite degradation methodology is extended to the conversion‐dependence function in order to explain the importance of multiple reaction mechanisms which might be considered to be involved in degradation processes. Based on two elementary reaction mechanisms, a specific form of the model equation is derived, which is capable of describing various types of degradation behavior showing sigmoidal rate as well as deceleratory rate. The conversion‐dependence function is derived to be independent of the Arrhenius‐type reaction constant or temperature, and thus the kinetic parameters are determined by analytic methods that have been developed for isothermal and dynamic‐heating experiments without any modification or additional assumptions. The developed model equation is tested by predicting the isothermal master curve of polyether‐ether‐ketone (PEEK), which is used as a model system in this study. The activation energies of the model system are analyzed using comparable methods for isothermal and dynamic experiments, which compare favorably in terms of the activation energy as a function of conversion. The resulting model equation, based on the kinetic parameters determined by isothermal experiments, can accurately predict both isothermal and dynamic‐heating thermogravimetry utilizing the same constants and identical reaction mechanisms without additional assumption.
Positron annihilation in irradiated and unirradiated polyethylenes
Authors: Suzuki T. , Oki Y. , Numajiri M. , Miura T. , Kondo K. , Ito Y. 
Published: April 2003

AbstractPositron lifetimes were measured for four kinds of polyethylene samples and were resolved into four components. The temperature dependence of the two longlived components was examined in detail. In agreement with other results, the longest lived component could be reasonably assigned to ortho‐positronium located in amorphous regions. This component was shown to be sensitive to the defects in high‐density polyethylene introducted in the course of its production. Both the intensity and the lifetime of the second longest lived component were structure insensitive, i.e., they did not change even on passing through the melting point. This component has been tentatively assigned to a positronium compound state. The effect of gamma‐ray irradiation was also examined. Although the intensity (I4) of the longest lived component was reduced by the irradiation, correlation between I4 and the free radical concentration was poor, and the reduction in I4 caused by the irradiation is considered to be due to structure change and not to chemical reasons.
Influence of concentration on the activation energy for diffusion in polymer‐solvent systems
Authors: Zielinski John M. , Duda J. L. 
Published: April 2003

AbstractThe self‐diffusion of benzene, toluene, and ethylbenzene in polystyrene have been analyzed using the Vrentas/Duda free‐volume diffusion model. Diffusion coefficient predictions suggest an exponential concentration dependence of the activation energy required to overcome attractive forces, E. Without the use of any diffusion data approximating E as zero over the entire concentration range yields self‐diffusion coefficient predictions which are in good agreement with experimental data. © 1992 John Wiley & Sons, Inc.
Brillouin scattering study of a polymer hydrogel
Authors: Vanderwal J. , Sidebottom D. , Walton D. , Johari G. P. 
Published: April 2003

AbstractBrillouin light‐scattering measurements of H2O imbibed in hydrogels of poly(2‐hydroxyethyl methacrylate) of two cross‐linking densities have been made at 294 K. Increase in the amount of water imbibed in 19‐30 Å size pores of the cross‐linked network causes the velocity of sound to decrease monotonically from a value, which differs for the two pure polymers, to a limiting value for pure water. The absorption coefficient reaches a maximum at about 30% water content and then decreases toward that for pure water. The velocity and absorption coefficient of both pure polymer and hydrogel containing 32% water were measured from 110 to 300 K. The former decreases and the latter increases with increasing temperature, and both show a change in the slope at about 160 K for the hydrogel, which agrees with the calorimetric glass transition temperature of the hydrogel. The effect of the water on the velocity and absorption coefficient of the polymer increases with temperature. © 1992 John Wiley & Sons, Inc.
Surface‐enhanced Raman scattering study of polymer on metals. III. Chemisorbed polybenzimidazole and its corrosion‐inhibiting properties at high temperature
Authors: Xue Gi , Dong Jian , Wu Peiyi 
Published: April 2003

AbstractChemisorption of polybenzimidazole on silver and copper etched with nitric acid has been observed by surface‐enhanced Raman scattering (SERS). The polymer is found to react chemically with silver, forming a complexed film on the surface. The SERS spectra show that polybenzimidazole film inhibits oxidation of the metal at high temperature, unlike chemisorbed benzimidazole, benzotriazole, and poly(4‐vinyl pyridine). © 1992 John Wiley & Sons, Inc.
Kinetics of orientation of a side‐chain liquid–crystal polymer as measured by a high‐temperature SQUID‐magnetometer
Authors: Fuhrmann K. , Dries Th. , Fischer E. W. , Ballauff M. 
Published: April 2003

AbstractA superconducting quantum interference device (SQUID) magnetometer suitable for measurements of the magnetic susceptibility up to 600 K has been used to follow the kinetics of realignment in the nematic phase of a side‐chain liquid–crystal polymer. Experiments are performed using monodomain and polydomain samples. Results obtained in monodomain samples are in quantitative agreement with the prediction of the continuum theory up to an angle of approximately 60°. Experiments conducted at higher starting angles give clear indication of backflow effects. Data obtained from experiments on polydomain samples have been compared with model calculations using the data on the monodomain samples. This comparison leads to the conclusion that in this case backflow effects play an important role, too. All results show that SQUID magnetometry allows monitoring of the kinetics of realignment with highest precision. © 1992 John Wiley & Sons, Inc.
The dependence of slow crack growth in a polyethylene copolymer on test temperature and morphology
Authors: Lu X. , Mcghie A. , Brown N. 
Published: April 2003

AbstractThe slow crack growth resistance was measured in an ethylene‐octene copolymer as a function of the morphological changes produced by varying the thermal history. Morphology was varied by annealing the quenched state at temperatures between 86°C and the melting point. The slow crack growth behavior was measured by the lifetime of a notched tensile specimen under a constant load. In general, the lifetime exhibited a maximum at a critical value of the annealing temperature. This critical annealing temperature decreased with a decrease in the temperature at which the lifetime was measured. The former result is understandable in terms of the increase in crystal strength as the annealing temperature is increased and the decrease in the number of tie molecules when more material is melted as the annealing temperature increases. The latter result depends on the relationship between crystal size and the effect of testing temperature. Differential scanning calorimetry data played a key part in analyzing the results. © 1992 John Wiley & Sons, Inc.
Activation parameters associated with the β relaxation of poly(cyclohexyl acrylate)
Authors: Díaz‐Calleja Ricardo , Riande Evaristo , Román Julio San 
Published: April 2003

AbstractThe interpretation of the mechanical and dielectric β relaxations of poly(cyclohexyl acrylate) by the coupling scheme suggests that the dielectric relaxation process is more complex than the mechanical one, contrary to what occurs in the glass–rubber relaxation. The distribution of activation energies for the dielectric process, obtained from isochronal and isothermal loss curves, increases with temperature and frequencies. The determination of the distribution of the activation‐free energy indicates a distribution of the activation entropy for both the mechanical and dielectric β process, suggesting that a distribution of preexponential factors in the Arrhenius equation also exists. © 1992 John Wiley & Sons, Inc.
The effect of lattice compressibility on the thermodynamics of gas sorption in polymers
Authors: Barbari T. A. , Conforti R. M. 
Published: April 2003

AbstractA compressible lattice model with holes, the glassy polymer lattice sorption model (GPLSM), was used to model the sorption of carbon dioxide, methane, and ethylene in glassy polycarbonate and carbon dioxide in glassy tetramethyl polycarbonate. For glassy polymers, an incompressible lattice model, such as the Flory–Huggins theory, requires concentration‐dependent and physically unrealistic values for the lattice site volumes in order to satisfy lattice incompressibility. Rather than forcing lattice incompressibility, GPLSM was used and reasonable parameter values were obtained. The effect of conditioning on gas sorption in glassy polymers was analyzed quantitatively with GPLSM. The Henry's law constant decreases significantly upon gas conditioning, reflecting changes in the polymer matrix at infinite dilution. Treating the Henry's law constant as a hypothetical vapor pressure at infinite dilution, gas molecules in the conditioned polymer are less “volatile” than those in the unconditioned polymer. Flory–Huggins theory was used to model the sorption of carbon dioxide, methane, and ethylene in silicone rubber. Above the glass transition temperature, the criterion of lattice incompressibility for Flory‐Huggins theory was satisfied with physically realistic and constant values for the lattice site volumes. © 1992 John Wiley & Sons, Inc.
Direct imaging of smectic B phase of poly(p‐xylylene)
Authors: Zhang Weiping , Thomas Edwin L. 
Published: April 2003

AbstractSingle crystals of poly(p‐xylylene) were grown in dilute α‐methylnaphthalene solution and studied by bright‐field and high‐resolution electron microscopy (HREM). The crystallization process was discussed in terms of the dependence of crystal form on crystallization conditions. A 0.15 nm resolution was achieved from high‐resolution images of a frozen liquid crystalline phase. High‐temperature electron diffraction patterns confirmed the existence of the liquid‐crystalline phase in agreement with previous work of Lieser. The HREM images show the molecular packing in the smectic B phase. © 1992 John Wiley & Sons, Inc.
Energy‐consuming micromechanisms in the fracture of glassy polymers. I. Chain scission in polystyrene
Authors: Mohammadi N. , Yoo J. N. , Klein A. , Sperling L. H. 
Published: April 2003

AbstractThe number of chain scissions per unit area that occur during the fracture of partially annealed latex films from Mn ≃ 180,000 g/mol polystyrene particles of about 275 Å radius were measured and correlated to annealing times. A curve with four regimes was found. At short annealing times the curve is nearly flat, in what is called the chain pull‐out regime. In the second regime, the number of chains broken per unit area increases with a 0.8 power of annealing time as entanglement of the diffusing polymer chains increases in neighboring host particles. This is in good agreement with Wool's theory which predicts a 0.75 power dependence. Then, after reaching a peak, the number of scissions decreases in the third regime, indicating a change in fracture mechanism. The number of chain scissions increases again in the fourth regime, as final healing of the film interface takes place. Fracture surface analysis reveals a rough surface for short annealing times and a smooth surface for longer annealing times. The number of polymer chain scissions per unit area of fracture surface showed no dependence on initial molecular weights for t ≫ τr where t and τr are annealing and relaxation times, respectively. The number of chain bridges crossing a unit area of interface was suggested as the basic molecular property. © 1992 John Wiley & Sons, Inc.
Chain orientation and anisotropies in optical and dielectric properties in thin films of stiff polyimides
Authors: Boese D. , Lee H. , Yoon D. Y. , Swalen J. D. , Rabolt J. F. 
Published: April 2003

AbstractThin films of poly(p‐phenylene biphenyltetracarboximide) (BPDA‐PDA), prepared by thermal imidization of the precursor poly(amic acid) on substrates, have been investigated by optical waveguide, ultraviolet‐visible (UV‐VIS), infrared (IR), and dielectric spectroscopies. The polyimide films exhibit an extraordinarily large anisotropy in the refractive indices with the in‐plane index n∥ = 1.806 and the out‐of‐plane index n⊥ = 1.589 at 1064 nm wavelength. No discernible effect of the film thickness on this optical anisotropy is found between films of ca. 2.1 and ca. 7.8 μm thickness. This large birefringence is attributed to the preferential orientation of the biphenyltetracarboximide moieties with their planes parallel to the film surface, coupled with the strong preference of BPDA‐PDA chains to align along the film plane. The frequency dispersion of the in‐plane refractive index n∥ is consistent with the results calculated by the Lorentz–Lorenz equation from the UV‐visible spectrum exhibiting several absorption bands in the 170–500 nm region. The contribution from the IR absorption in the range 7000–400 cm,−1 computed by the Spitzer‐Kleinmann dispersion relations from the measured spectra, adds ca. 0.046 to the in‐plane refractive index n∥. Tilt‐angle–dependent polarized IR results indicate nearly the same increase for the out‐of‐plane index n⊥. Application of the Maxwell relation then leads to the out‐of‐plane dielectric constant ε⊥ ≃ 2.7 at 1.2 × 1013 Hz, as compared with the measured value of ca. 3.0 at 106 Hz. Assuming this small difference to remain the same for the in‐plane dielectric constants ε∥, we obtain a very large anisotropy in the dielectric properties of these polyimide films with the estimated in‐plane dielectric constant ε∥ ≃ 3.4 at 1.2 × 1013 Hz, and ε∥ ≃ 3.7 at 106 Hz. © 1992 John Wiley & Sons, Inc.