bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spectroscopic studies on the effect of field strength upon the curie transition of a VDF/TrFE copolymer
Authors: Jin Kim Kap , Reynolds Nicholas M. , Ling Hsu Shaw 
Published: April 2003

AbstractInfrared spectroscopic studies of the effects of field strength upon the ferroelectric phase transition behavior of a VDF/TrFE (75/25) copolymer upon heating and cooling in an electric field have revealed new findings. The paraelectric phase in the absence of an electric field resembles the α phase of PVDF with a trace of short trans sequences distributed randomly along the chain axis. The paraelectric phase in a high electric field is very different from that in the absence of an electric field. The paraelectric phase under an electric field has much longer trans sequences. The Curie transition temperature upon heating is a first‐order transition temperature (T↑c) and is dramatically elevated from 120 to 135°C under the field of more than 0.4 MV/cm. Upon cooling, the paraelectric phase in an electric field does not show a clear transition. The field‐induced phase transition and the loss of dipole switchability observed below a cooling temperature of 120°C, and their dependence on time and filed strength when exposed to a cyclic bipolar electric field are discussed. © 1993 John Wiley & Sons, Inc.
Study of terbium(III)–dextran and terbium(III)–α‐methyl glucoside interactions
Authors: De A. Soares Sandra , Rodrigues Judith F. , Alario Adelaide F. 
Published: April 2003

AbstractThe interaction of dextran with terbium(III) was studied in aqueous solution, pH 3.0–6.6, by fluorescence and optical rotatory dispersion. The polysaccharide enhances Tb(III) fluorescence intensity when the system is excited at the 290‐nm hypersensitive transition (7F6 → 5H4). The dextran rotatory power is decreased in the presence of the metal ion. The results indicate that a 38% maximum of the polymer repeat units are coordinated. Complex formation occurs with displacement of water from the cation coordination sphere by hydroxyl groups at the second and third carbon atoms of the pyranoside ring. As the pH increases, a more asymmetric complex is formed. The α‐methyl glucoside, low molecular weight dextran analogue, interacts with Tb(III) less strongly than dextran. Fluorimetric titrations indicated that the order of binding ability to polysaccharide is Tb(III) > Al(III) > Ca (II). © 1993 John Wiley & Sons, Inc.
Miscibility studies on blends of polycarbonate with syndiotactic polymethyl methacrylate
Authors: Kyu Thein , Ko Che‐Chian , Lim Dong‐Soo , Smith Steven D. , Noda Isao 
Published: April 2003

AbstractMiscibility of bisphenol‐A polycarbonate (PC) and syndiotactic polymethyle methacrylate (sPMMA) blends was investigated by differential scanning calorimetry (DSC) and small‐angle light scattering. Cloud‐point measurements indicated the existence of both a lower critical solution temperature and an upper critical solution temperature, forming an immiscibility loop. This immiscibility gap was observed for PC blends with sPMMA of various molecular weights ranging from 8,300 to 55,000. The DSC study on solvent‐cast and coprecipitated PC/sPMMA blends from tetrahydrofuran solutions showed a single glass transition, shifting regularly with composition. The annealing of the 50/50 composition within the immiscibility loop exhibited dual glass transitions, but the system reverted to a single phase upon annealing above the loop. Phase dissolution took place during annealing above the loop, followed by thermoxidative branching (cross‐linking) reaction. Dry pellets of PC and sPMMA were melt mixed above the loop in a Mini‐Max mixer/molder; these molded blends exhibited a single phase. © 1993 John Wiley & Sons, Inc.
Computer simulation of crystallization kinetics and morphology in fiber‐reinforced thermoplastic composites. II. Three‐dimensional case
Authors: Mehl Nathan A. , Rebenfeld Ludwig 
Published: April 2003

AbstractA three‐dimensional computer simulation has been used to predict crystallization kinetics and crystalline morphology in composite materials that are based on crystallizable thermoplastics. Reinforcing fibers in three‐dimensional simulations show similar behavior to those in two‐dimensional simulations; fibers suppress crystallization relative to an unreinforced polymer since they constrain spherulitic growth by an impingement mechanism, and also enhance crystallization by providing added surface nucleation sites. The effects of varying controlling parameters on crystallization kinetics and morphology are qualitatively the same as those observed in the two‐dimensional case. The relative bulk and fiber nucleation denisities, in addition to the fiber volume fraction, fiber diameter, and spherulitic growth rate control the crystallization kinetics and crystalline morphology that develop in reinforced thermoplastic composites. It is more difficult to achieve the transcrystalline morphology in slices of three‐dimensional composites than it is in two‐dimensional composites because nuclei in 3‐D systems are not constrained to positions in or near a 2‐D plane. © 1993 John Wiley & Sons, Inc.
Radiation degradation of poly(methyl methacrylate) in the soft x‐ray region
Authors: Yates Brian W. , Shinozaki Douglas M. 
Published: April 2003

AbstractThe molecular weight distribution change has been measured for the photoresist poly(methyl methacrylate) [PMMA] after in‐vacuo exposure to monochromatic soft x‐rays from the Canadian Synchrotron Radiation Facility [CSRF]. The experimental changes in the mo‐lecular weight distribations derived from gel permeation chromatography [GPC], were compared to a simple Monte Carlo simulation model that assumes random main chain scission. Using this model a scission radiation chemical yield of G(S) = 1.28± 0.10 at room temperature was found to give the best fit at a photon energy of 621 eV. This value is similar to values reported previously in the literature using electron beam and γ‐ray sources, but significantly larger than those reported for fast neutrons, α‐particles, or energetically charged particles. It was found that in this soft x‐ray energy regime, that degradation of PMMA involves primarily a random scission process of the main chain. The results of a least‐squares fit of this soft x‐ray G(S) data and all available literature values from other radiation sources, to the linear energy transfer [LET] dE/dx are discussed. © 1993 John Wiley & Sons, Inc.
Supermolecular morphology of thermoreversible gels formed from homogeneous and heterogeneous solutions
Authors: Prasad A. , Marand H. , Mandelkern L. 
Published: April 2003

AbstractThe supermolecular structures of thermoreversible gels formed from either homogeneous or heterogeneous solutions were examined by scanning electron microscopy. The morphologies of gels of polyethylene and polystyrene of various tacticities were then related to the phase diagram of the polymer–solvent system. We confirmed the morphological findings of Aubert on isotactic polystyrene gels formed either above the binodal or inside the spinodal and extended his study to gels prepared within the metastable region of the phase diagram. For polystyrenes and polyethylene, the morphology of the gels formed inside the coexistence curve differs markedly from that of gels formed outside. Inside the binodal, gels of polyethylene and polystyrenes exhibit remarkable morphological similarities, indicating a common gelation mechanism, namely, liquid‐liquid phase separation. Depending on the concentration, these gels exhibit either an open strut‐like network structure or smooth spherical globules. The former is attributed to gelation inside the spinodal whereas the latter is believed to result from gelation in the metastable region. For crystalline polymers, gels formed inside the coexistence curve subsequently undergo crystallization within their polymer‐rich phase. The morphology of isotactic polystyrene and polyethylene gels formed outside the binodal consists of overlapping lamellar structures, whereas that of atactic and epimerized polystyrene gels is characterized by a sheet‐like structure, differentiating the crystallization‐based mechanism from others. © 1993 John Wiley & Sons, Inc.
The absorption coefficient spectrum and radiation degradation of poly(butene‐1 sulfone) in the soft x‐ray region
Authors: Yates Brian W. , Shinozaki Douglas M. , Kumar Ashok , Meath William J. 
Published: April 2003

AbstractThe interaction of soft x‐rays with poly(butene‐1 sulfone) (PBS) has been examined in detail, using monochromatized synchrotron radiation from the Canadian Synchrotron Radiation Facility (CSRF). The total photoabsorption cross section and neutral fragment yields of poly(butene‐1 sulfone) (PBS) were measured over the photon energy range 20 ≤ hv ≤ 1000 eV. Energy deposition in this energy region results primarily in mass loss due to depolymerization. The chemical byproducts were detected using an in situ mass spectrometer. The experimental absorption data was corrected for spectral contamination of the incident monochromator radiation through the use of calculated photoabsorption cross sections. The calculations incorporated reliable dipole oscillator strength distributions of smaller molecules chemically related to PBS as input, and the results are reliable over the absorption regions away from the edges. The corrections thus applied to the initial experimental data have produced the most reliable spectrum available presently for PBS. The near‐edge extended x‐ray absorption fine structures (NEXAFS) were measured and assigned for the sulfur 2p (L2,3), carbon 1s (K) and oxygen 1s (K) edges. The sulfur 2p edge of PBS was found to be very similar to that found in the photoabsorption spectrum of gaseous SO2, particularly in the continuum region. The two broad peaks in the continuum have been assigned as σ*‐shape resonances caused by a centrifugal potential barrier. Ionization of the valence orbitals of PBS produced a significant increase in the depolymerization reaction, and subsequent neutral yields of sulfur dioxide (SO2) and 1‐butene. © 1993 John Wiley & Sons, Inc.
Melting behavior of poly(ether ether ketone) in its blends with poly(ether imide)
Authors: Chen Hsin‐Lung , Porter Roger S. 
Published: April 2003

AbstractWe detail the melting behavior of poly(ether ether ketone) (PEEK) and investigate its melting behavior in miscible blends with poly(ether imide) (PEI). The determination of the equilibrium melting point (Tm0) of PEEK is discussed by considering its inhomogeneous morphology. Tm0 is obtained by a long extrapolation of a Hoffman–Weeks plot to 384°C. Hindrance of PEEK crystal reorganization induced by PEI during heating is observed over the blend composition investigated (20–75 wt % PEEK). This behavior is correlated with the incorporation of PEI in the interlamellar zones of PEEK crystals. The interaction parameter χ of PEEK/PEI blends is estimated by the equilibrium melting point depression. This gives the interaction density B = −1.2 cal/cm3, and x = −0.40 at 400°C. © 1993 John Wiley & Sons, Inc.
Broadened glass transition in a liquid‐crystalline polymer studied by thermally stimulated currents, AC dielectric, dynamic mechanical, and DSC methods
Authors: Sauer Bryan B. , Dipaolo Nicholas V. , Avakian Peter , Kampert William G. , Starkweather Howard W. 
Published: April 2003

AbstractThermally stimulated currents (TSC), a. c. dielectric, dynamic mechanical (DMTA), and differential scanning calorimetry (DSC) methods were used to study the glass transition in a thermotropic liquid‐crystalline copolyester. All the techniques were consistent in the determination of the main glass transition temperature. Using the high sensitivity of the TSC thermal sampling method, it was shown that cooperative glass transition‐like relax‐ations occur down to 100°C below the main glass transition. DSC was sensitive only to a broadening of the glass transition to about ca. 30°C, so it was concluded that the thermal sampling method is sensing a very small fraction of cooperatively relaxing species which cannot be detected by DSC. Ac dielectric measurements and DMTA also indicated that the glass transition was broad, but difficulties with overlapping transitions prevented quantitative determination of the breadth of the glass transition. The results suggest that the broad glass transition, in this mostly amorphous LCP, is due to chemical heterogeneity of the copolyester chain. Other evidence indicates that the broadening is not due to the oriented nature of the glassy state. Some discussion is presented concerning how the heterogeneous nature of the LCP glass leads to compensation of the Arrhenius curves obtained by the thermal sampling method. © 1993 John Wiley & Sons, Inc.
Further EPR studies of molecular motions in polymer/plasticizer mixtures
Authors: Krishnan P. , Le H. , Lee S. H. , Gelerinter E. 
Published: April 2003

AbstractMolecular motions in mixtures of the side chain polymer—poly(vinyl acetate) and dibuthyl phthalate were studied as a functionof polymer concentration and temperature using the technique of paramagnetic resonance (EPR). When the small spherical probe tempol (TPL) was used, we were able to approximate the observed EPR spectrum with a simulation using a single rotational correlation time τ. The peviously developed Grest–Cohen all‐temperature model matched the Arrhenius polts. The EPR spectra from a cigar‐shaped cholestane (COL) probe could not be adequately matched by single τ simulation when the polymer was at temperatures somewhat above the glass to rubber transition temperature (Tg). Points corresponding to these temperatures were left of the Arrhenius plot and a discontinuity was observed where the gap in the data occurred. As the concentration of plasticizer was increased, we found that the discontinuity became less steep, but the τ at which the gap occurs was always ≈ 10−8. The spectra observed at the temperature region of the gap were approximately 50–50 composites of experimental spectra observed at ± K. In both the TPL and COL cases, there was evidence of the existence of multiple correlation times. Preliminary studies of other polymers, both with and without side chains, also indicated the existence of the gap when COL is used as the probe. © 1993 John Wiley & Sons, Inc.
Short‐range order in noncrystalline polymers examined with spin‐polarized neutrons
Authors: Gabryś Barbara , Schärpf Otto , Peiffer Dennis G. 
Published: April 2003

AbstractThe application of spin‐polarized neutrons with spin polarization analysis to study diffraction patterns from polymers is discussed. The experimental separation of the coherent and incoherent parts of the scattering coupled with the use of the internal standard resulted in the quantitative analysis of the purely coherent scattering from unfunctionalized and functionalized polystyrene in terms of absolute units. This allowed us to model the scattering curves in terms of paracrystallinity. © 1993 John Wiley & Sons, Inc.
Molecular dynamics simulations of the hexagonal structure of crystals with long methylene sequences
Authors: Liang G. L. , Noid D. W. , Sumpter B. G. , Wunderlich B. 
Published: April 2003

AbstractAn unconstrained polymethylene crystal, consisting of 9600 CH2 groups, in which each CH2 is permitted to carry out stretching, bending, and torsional motion, has been studied at various temperatures using molecular dynamics simulations. Information about the atomistic details of the dynamics and structure of these crystals is presented. A significant disorder exists at tempratures well below the melting point. Close to melting, the disordered crystals have about 2% of gauche bonds that are distributed mainly at positions close to the surface of the crystal. The major disorder consists, however, of a collective twisting of the chains leading to a hexagonal crystal structure. The hexagonal structure of the symmetric motifs is caused by a dynamic multidomain arrangement of the chains. © 1993 John Wiley & Sons, Inc.
poly(4,4′‐oxybibenzoate): Polymerization, morphology, transitions, and crystal structures
Authors: Liu J. , Rybnikar F. , East A. J. , Geil P. H. 
Published: April 2003

Abstract4‐Acetoxy 4′‐carboxy biphenyl has been polymerized from solution, the bulk melt, and in constrained thin films, all below the melting point of the monomer as measured by differential scanning calorimetry (DSC). An isothermal sublimation–recrystallization–melting (and chemical change)–polymerization–crystallization process is proposed. From solution and in the thin films, single crystals consisting of ca. 100 Å thick lamellae are observed, with evidence for monomer addition–reaction on the end (top and bottom) surfaces. The bulk samples are fibrous, the “fibers” consisting of whisker‐like single crystals. The polymer is highly heat and radiation (electron beam) resistant, with numerous successive electron diffraction (ED) patterns from the same crystal or sheared sample permitting comparison of the changes in ED patterns with transitions seen by DSC at ca. 350, 530, and 590°C. Phase I (a = 7.8, b = 5.5, c = 10.8 Å), a possible phase II (a = 15.6, b = 3.6 Å c = unknown), and a phase III (a = 9.0, b = 5.2 = √3a, c = 10.8 Å). Phases I and II are seen in samples polymerized at temperatures at and below 310°C; phase III is observed in samples polymerized at and above 350°C and in sheared samples. © 1993 John Wiley & Sons, Inc.
Structural investigations on lewis acid mediated solubilization of poly(p‐phenylenebenzobisthiazole) in an aprotic solvent
Authors: Venkatasubramanian N. , Polk Malcolm B. , Kumar Satish , Gelbaum Leslie T. 
Published: April 2003

AbstractInvestigations on aluminum chloride‐mediated solubilization of poly(p‐phenylenebenzo‐bisthiazole), PBZT, in nitromethane revealed that, in general, dilute solutions of the polymer prepared in nitromethane with a large molar excess of the Lewis acid with respect to PBZT were relatively stable and thus suitable for processing into films and coatings via regeneration with hydroxylic nosolvents while polymer solutions with minimum stoichiometrically required (PBZT:AlCl3 molar ratio 1:4) or marginal molar excess of AlCl3 relative to PBZT tended to gel during handling. Structural studies on polymer–Lewis acid complex solutions were performed using 1H and 27Al NMR. 1H NMR of the protonated structure of the model compound 2,6‐diphenylbenzo [1,2‐d:4,5‐d′] bisthiazole was useful for confirming the 1H NMR assignments of PBZT‐AlCl3 complex solution in CD3NO2. 27Al NMR was particularly useful in probing the different tetrahedrally coordinated environments of the Al nucleus in the polymer solution, pointing to a complexation interaction between the polymer molecule and the Lewis acid and also between the solvent and the Lewis acid. Direct evidence in the solid state for the presence of a reversible electron donor–acceptor complex (EDA complex) was obtained from FTIR spectra of complexed films, isolated and handled in an inert atmosphere. The structural changes upon PBZT complexation caused significant frequencly shifts in both aromatic as well as heteroring stretching modes relative to PBZT itself, and intensity variations indicative of changes in the resonance configuration between the 1,4‐phenylene moiety and the aromatic heterocyclic ring were also observed upon complexation. A preliminary comparison between the pristine PBZT fibers and regenerated PBZT by dilute solution viscometry indicates that the process results, to some extent, in polymer degradation leading to a decrease in the molecular weight of the polymer © 1993 John Wiley & Sons, Inc.
Molecular dynamics simulations of a poly(p‐phenylene) oligomer
Authors: Socci E. P. , Farmer B. L. , Adams W. W. 
Published: April 2003

AbstractWe have studied the conformation and coefficient of thermal expansion in the poly(p‐phenylene) oligomer p‐sexiphenyl (C36H26) by molecular dynamics simulations. Studies of the backbone phenyl–phenyl torsion angle in a simulated p‐sexiphenyl crystal at room temperature indicate the presence of torsional librations of approximately ±20°. Further analysis of the phenyl–phenyl backbone torsion angle in less closely packed regions of the simulated crystal (crystal ends) indicate the presence of 180° phenyl ring flips, in agreement with solid‐state deuterium NMR data on poly(p‐phenylene oligomers). The linear coefficient of thermal expansion was also calculated and found to be negative, in qualitative agreement with experimental data on rigid‐rod compounds. © 1993 John Wiley & Sons, Inc.
Second harmonic generation and optical anisotropy of a spin‐cast polymer film
Authors: Wang C. H. , Guan H. W. 
Published: April 2003

AbstractThe nonlinear susceptibilities (χ(2)33, χ(2)31), and the refractive index anisotropy, of a main chain accordion polymer, BCSC (see the text for the complete chemical formula), have been measured by the techniques of second harmonic generation (SHG) and waveguiding. A large birefringence, which is induced in the BCSC film by the spin‐coating process, is almost removed by electric field poling. Our results demonstrate the fundamental difference between the birefringence associated with quadrupolar orientational order and the dipolar order associated with SHG. © 1993 John Wiley & Sons, Inc.
Radiation‐induced dielectric loss in hydrocarbon polymers
Authors: Mopsik Frederick I. 
Published: April 2003

AbstractThe dielectric loss of several cables insulated with hydrocarbon polymers has been measured over the frequency range of 10−3–104 Hz at 50° after being subjected to neutron doeses of up to 65 Mrad. The loss data show that a new loss process appears upon irradiation and that the frequencies associated with this loss are not those that are characteristic of those found for the unirradiated polymaric relaxations, ruling out main‐chain motions. This loss seems to be related to dose and is probably due to local dipoles that are formed by the irradiation. It is also shown that the dominant behavior is not due to simple ionic conductivity. © 1993 John Wiley & Sons, Inc.
Effect of oligomers and acrylonitrile content on the interfacial adhesion between PC and SAN
Authors: Janarthanan V. , Stein Richard S. , Garrett Paul D. 
Published: April 2003

AbstractThe interfacial fracture toughness between polycarbonate (PC) and poly(styrene‐co‐acrylonitrile) (SAN) bilayers was measured using an asymmetric double cantilever beam geometry. The effects on fracture toughness of oligomer content and copolymer composition were investigated. Results showed that by removing residual oligomers from SAN, the fracture toughness of the PC/SAN interface was increased significantly. To study this effect in more detail, benzonitrile was used as a model oligomer and added in controlled amounts to pure SAN before attaching to PC and annealing. The PC/SAN interfacial fracture toughness in this case decreased monotonically with increasing benzonitrile content presumably due to migration of the small molecule to the interface. Interfacial toughness was also measured for five purified SAN materials with a range of 17–31 wt % acrylonitrile. A maximum in PC/SAN toughness was seen for a 24 % AN material. Evidence of possible chain scission during fracture in purified SAN and PC was observed from x‐ray photoelectron spectroscopy measurements. Optical microscopy showed that a single craze ahead of the crack is a possible failure mode during fracture of the SAN/PC interface. © 1993 John Wiley & Sons, Inc.