bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular segregation and nucleation of poly(ethylene oxide) crystallized from the melt. I. Calorimetric study
Authors: Cheng Stephen Z. D. , Wunderlich Bernhard 
Published: April 2003

AbstractThermal analysis is used to elucidate the fusion of fractions of poly(ethylene oxide) of from 3500 to 5000000 molecular weight. In addition, the equilibrium and nonequilibrium phase diagrams of binary mixtures of these fractions have been studied. Complete segregation from high‐molecular‐weight polymer is possible up to at leat 20000 molecular weight. This segregation is not governed by the melting/crystallization equilibrium, but rather by molecular nucleation. Over a broader crystallization temperature range three regions can be identified. At low crystallization temperature, solid solutions result, at higher temperature one finds an intermediate type of crystallization, and ultimately one reaches complete, eutectic segregation. This work will be followed by analysis of the kinetics of crystallization.
Molecular segregation and nucleation of poly(ethylene oxide) crystallized from the melt. II. Kinetic study
Authors: Cheng Stephen Z. D. , Wunderlich Bernhard 
Published: April 2003

AbstractA kinetic study of crystallization of fractions of poly(ethylene oxide)s between 3500 and 5,000,000 MW and their mixtures from the melt by differential scanning calorimetry and optical microscopy is reported. For the fractions the crystal growth rate is inversely dependent on the logarithmic molecular weight. Binary mixtures of widely different molecular weights show mixed‐crystal formation at low crystallization temperature described by a single Avrami equation with exponent 3. At higher temperature, increasing segregation takes place despite higher deposition probabilities of the low molecular weight. Two consecutive Avrami equations describe the crystallization. Before the equilibrium melting temperature of the low molecular weight component is reached, complete segregation occurs. This segregation is possible up to at least 20,000 MW. Classical crystallization theory is unable to describe the process. Molecular nucleation seems a viable alternative for the description of crystallization of both fractions and mixtures. Reversibility of crystallization is on a one‐molecule scale and reaches thermodynamic reversibility as the molecular length approaches monomer size.
Equation of state of copolymer melts: The poly(vinyl acetate)–polyethylene pair
Authors: Zoller Paul , Jain R. K. , Simha R. 
Published: April 2003

AbstractThe pressure—volume—temperature properties of a series of copolymers ranging in content from 18 to 40 wt % of vinyl acetate, and up to a maximum pressure of 1800 kg/cm2 are studied. The results for the melt state can be satisfactorily fitted by the scaled equation of state, developed previously and applied to single‐component systems and to mixtures. The dependence of the scaling parameters for the copolymers on composition deviates from that expected for a mixture, where volumes at elevated pressures can be predicted without further recourse to experiment. These differences are discussed in terms of the sequential structure of the copolymer chain and its series of interfaces between the two species.
Effect of doping on thermoluminescence in polymers. I. 9,10‐phenanthrenequinone‐doped polydiancarbonate
Authors: Vanderschueren J. , Linkens A. , Niezette J. 
Published: April 2003

AbstractThe thermoluminescence (TL) and thermally stimulated depolarization currents (TSDC) observed in polycarbonate doped with 9,10‐phenanthrenequinone (PhQ) have been compared in order to test to what extent the TL phenomenon can be correlated with intrinsic relaxation properties of the macromolecular chains. Good qualitative agreement has been found between the two types of curves, showing that the two TL peaks appearing at about 140 and 185 K are attributable to untrapping of electrons induced by the onset of local motions. However, the values and distribution of the activation energies determined by the two techniques differ markedly. The apparent activation energy deduced from TL data presumably reflects the energy level of traps decreased by molecular motions rather than the thermal energy of these relaxations. The primary process responsible for light emission is related to a transition of the n‐π type occurring in PhQ at 420 nm, while the trapping sites are probably formed by carbonate groups of the polymeric matrix. The same trapping mechanism has been postulated for the two TL peaks on the basis of their parallel evolutions as a function of dose and dopant concentration.
Composition dependence of glass transition temperature of sulfonated‐polystrene ionomers
Authors: Mattera Vincent D. , Risen William M. 
Published: April 2003

AbstractThe glass transition temperatures of alkali (Na, K, Rb, Cs) and alkaline‐earth (Ba, Sr, Ca, Mg) ionomers of sulfonated polystyrenes (PSSA) with 3.4, 6.9, 12.7, and 16.7% of the styrene moieties sulfonated are reported. For the alkali‐metal PSSA ionomers, Tg depends on the degree of sulfonation, at least up to 13%, but not strongly on the nature of the cation. For the alkaline‐earth analogs Tg does not depend strongly on either the cation or the degree of sulfonation until the 16.7% level is reached. These and other reported data are discussed in terms of the role of cations in determining morphology.
Dual‐mode analysis of subatomspheric‐pressure CO2 sorption and transport in Kapton H polyimide film
Authors: Uragami T. , Hopfenberg H. B. , Koros W. J. , Yang D. K. , Stannett V. T. , Chern R. T. 
Published: April 2003

AbstractSorption kinetics and equilibria as well as permeabilities and diffusion time lags for CO2 in Kapton polyimide film have been studied at temperatures from 35 to 55°C and pressures up to 0.78 atm. The sorption/desorption cycles indicate that the diffusivity of CO2 increases with increasing local penetrant concentration in the polymer. Both the permeability and time lag decrease with increasing upstream CO2 pressure. All of these results are described well by theoretical expression based on the dual‐mode theory of sorption and transport in glassy polymers.
Demixing and gelation behavior of ternary cellulose acetate solutions
Authors: Reuvers A. J. , Altena F. W. , Smolders C. A. 
Published: April 2003

AbstractThe demixing behavior on cooling of ternary systems of cellulose acetate/solvent/water has been examined for CA concentrations up to 40 wt% CA in several solvents. Cloud points have been measured as a function of cooling rate. The rapid process of liquid—liquid demixing can be discriminated from the slow process of aggregate formation by examining the dependence of the cloud point on the cooling rate and by structure analysis of quenched solutions with scanning electron microscopy. The appearance of aggregate formation depends strongly on the type of solvent. Slow cooling of ternary solutions in which acetone is the solvent leads to aggregate formation long before liquid—liquid demixing occurs.In addition, isothermal sol—gel transitions have been measured for quenched solutions at varying gelation times. It is concluded that gelation is not always preceded by aggregate formation.
Reversible and irreversible variation of the superstructure of highly oriented low‐density polyethylene during heat treatment
Authors: Fronk W. , Wilke W. 
Published: April 2003

AbstractThe small‐angle x‐ray scattering (SAXS) intensity of highly‐oriented, low‐density polyethylene (LDPE) with fixed draw ratio has been investigated during several heating and cooling cycles. Using a three‐dimensional, monoclinic, paracrystalline superlattice to describe the superstructure of the sample, it has been possible to calculate the SAXS patterns completely. A very large irreversible variation of the superstructure during the first heating cycle, and a smaller reversible variation of the average size and distance of the crystallites during subsequent temperature cycles, could be obtained. These results can be explained using the thermodynamic theory of crystallization of polymer multicomponent systems of Kilian.
Small‐angle x‐ray scattering studies of thermally‐induced morphological changes in segmented polyurethane elastomers
Authors: Gibson P. E. , Van Bogart John W. C. , Cooper Stuart L. 
Published: April 2003

AbstractThe effect of temperature on the morphology of a series of polyether and polyester polyurethanes has been studied using small‐angle x‐ray scattering. Scattering curves were obtained in situ at high temperature (90 and 150°C) and also later at room temperature to study the effects of thermal history on the materials. In general, annealing improves the degree of phase separation and increases the hard domain size in the materials studied. Annealing improves the degree of phase separation in more compatible systems to a greater degree than in less compatible systems. Increased interfacial mixing is apparent in the materials studied in situ at high temperatures. Thicker interfacial regions are also present in the annealed material relative to the control.
Ferroelectric switching characteristics of 73/27 copolymer of vinylidene fluoride and trifluoroethylene
Authors: Jimbo Masashi , Fukada Tomohiro , Takeda Hiromi , Suzuki Fuminao , Horino Kaoru , Koyama Kiyohito , Ikeda Susumu , Wada Yasaku 
Published: April 2003

AbstractFerroelectric polarization‐reversal switching of vinylidene fluoride—trifluoroethylene copolymer with 73 mol % of vinylidene fluoride is investigated under a variety of conditions in an attempt to derive detailed information on the polarization reversal of the polymer. The electric‐field dependence of switching time ts obeys an exponential law. The temporal change of switching current density J is presented in the form J/(Ps − P) versus time (P is the polarization, and Ps is its saturation value), which is free of the depolarization‐field effect and discriminates in a straightforward manner between acceleration and deceleration of switching. Effects of the annealing of samples upon ts are observed together with changes in the degree of crystallinity. Effects of space charge distribution upon ts are investigated by applying two successive pulses, positive and negative, with varied intervals tw between the two. The dynamics of space charge redistribution is elucidated from the tw dependence of the ts of the second pulse. The temperature dependence of ts indicates that the switching becomes critically fast as the phase‐transition temperature is approached.
Block copolymers of poly(ethylene terephthalate–polybutylene terephthalate). I. Preparation and crystallization behavior
Authors: Misra A. , Garg S. N. 
Published: April 2003

AbstractBlock copolymers of two crystallizable compounds, poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT), were developed with PET as the major component and the amount of PBT varying from 1.0 to 20.0 wt %. These block copolymers were prepared by end‐group coupling of preformed oligomers. All polymers prepared were of equivalent molecular weight as determined by the intrinsic viscosity method. Thermal properties were determined by differential thermal analysis (DTA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). With increasing PBT content, the block copolymers showed a general decrease in the values of glass transition temperature, melting temperature, initial decomposition temperature, and maximum decomposition temperature. The heat of fusion and heat of crystallization first increased and then decreased slightly. Rates of crystallization were determined by measuring density as a function of time of isothermal crystallization carried out at 95°C. It was found that small amounts of PBT increased the crystallization rate considerably over that of PET. Random copolymers did not show this phenomenon and behaved more like pure PET. The crystallization behavior of block copolymers was analyzed by the Avrami equation and Avrami exponents were determined. Results were explained on the basis that the faster‐crystallizing PBT blocks crystallized first and provided built‐in nucleation sites for the subsequent crystallization of PET, thus resulting in a relatively fast‐crystallizing copolyester.
Infrared and raman spectroscopy of stressed polyethylene
Authors: Wool R. P. , Bretzlaff R. S. , Li B. Y. , Wang C. H. , Boyd R. H. 
Published: April 2003

AbstractPolyethylene films were stressed in uniaxial tension at room temperature while the infrared (FTIR) or Raman spectra were simultaneously measured. The purpose of these experiments was to gain an understanding of the molecular origins of the stress‐induced vibrational frequency shifts Δν and determine the mechanisms of molecular deformation and fracture of PE molecules with stress σ. The PE samples consisted of ultradrawn, high‐density, ultrahigh‐molecular‐weight, solid‐state‐extruded films and the stress was applied parallel to the nearly perfectly oriented orthorhombic crystal c‐axis direction. The experimental frequency shifting coefficients α = (∂ν/∂σ)σ→0 were compared with calculated α values determined from a vibrational analysis of an isolated PE chain using conformational energy minimization methods in which both harmonic and anharmonic (Morse) potential energy functions were used for the CC stretching modes in the valence force field. The following α values were obtained and are compared with theory (anharmonic case in parentheses, in cm−1/GPa): CC symmetric stretch, α(1127) = −5.9 (−5.3); CC asymmetric stretch, α(1059) = −11.2 to −5.7 (−5.8); CH2 rock, α(730/720) = −2.0 to −3.0 (−2.2); CH2 scissors, α(1472/1462) = −1.0 to −1.2 (−1.1); CH2 twist, α(1295) ≃ 0(0.8); CH2 wag, α(1370) undetermined owing to weak bands (−4.6); CH2 stretch α(3000) ≈ 0. The largest negative frequency shifts were observed for the CC stretching modes, in agreement with the calculations using the Morse potential. The harmonic potential for CC stretching resulted in small positive α values for both the CC stretching and CH2 wagging modes, while the other modes were unaffected by this choice of potential. The relative contribution of CC bond stretching and CĈC valence angle bending to the c‐axis strain was about 1:1, in agreement with experiment. The Young's tensile modulus of a PE chain was calculated as Ec = 267 GPa.
Molecular analysis of the crystallization behavior of poly(aryl‐ether‐ether‐ketone)
Authors: Nguyen Huy X. , Ishida Hatsuo 
Published: April 2003

AbstractThe crystallization behavior, via annealing, of PEEK was investigated using FTIR spectroscopy. It was found that predominantly amorphous PEEK (e.g., quenched polymer) follows two distinct mechanisms when it is annealed. One is a lower energy relaxation process that involves the partial rotation of the ether linkages, allowing the molecular chains in the disordered phase to become better packed, and occurs from 50 to 140°C (slightly belowTg). This relaxation process is also observed by dynamic mechanical analyses. The other process is a crystallization that takes place above the glass transition, with its onset characterized by the rotation of the benzophenone linkages nearTg. Isothermal crystallization kinetics data on PEEK can be described by an Avrami equation with an Avrami constantnof about 1.
The physical properties of bisphenol‐A‐based epoxy resins during and after curing
Authors: Choy In‐Chul , Plazek Donald J. 
Published: April 2003

AbstractA series of epoxy resins derived from diglycidyl ethers of bisphenol A with differing initial linear molecular chain lengths have been studied during and after curing with the diamines MDA (4,4′‐methylene dianiline) and DDS (4,4′‐diamino diphenyl sulfone). The properties that were measured during curing were the volume, the fictive temperature Tf, the gel fraction, the viscosity, and the equilibrium compliance. Graphs of Tf as a function the time of curing tc obtained at four curing temperatures between 40 and 100°C have been reduced to a common curve. After curing, creep compliance curves J(t) were determined which characterize the viscoelastic response from the glassy compliance level to a rubbery equilibrium compliance level. The change in properties that occurs during the time‐dependent spontaneous densification below the glass temperature Tg was monitored with repeated measurements of J(t). Time‐scale shift factors as a function of volume contraction obtained during this physical aging below Tg were reduced to a common curve.
Solvent‐induced crystallization. II. Morphology
Authors: Durning C. J. , Rebenfeld L. , Russel W. B. , Weigmann H. D. 
Published: April 2003

AbstractThe Morphology of quenched poly(ethylene terephthalate) (PET) films crystallized by low‐molecular‐weight organic penetrants is studied by scanning electron microscopy. Films with thicknesses from ca. 1 mil (0.0025 cm) to ca. 35 mil (0.1 cm) were exposed to methylene chloride (MeCl2) andN,N‐dimethylformamide (DMF) in the temperature ranges 0–38°C and 22–70°C, respectively. The effects on the surface and internal structures of contact with liquids and saturated vapors were examined. Severe porosity at the surface results from contact with the liquids, but only minor surface roughness appears following contact with vapors. Internal porosity developed in the thinnest films (ca. 1 mil) during crystallization in liquid environments. Here, the internal void fraction is greatest along the film centerline and decreases with increasing crystallization temperature. A mathematical model discussed previously accounts for the observed behavior.
The heat of fusion of poly(4‐methyl pentene‐1)
Authors: Zoller Paul , Starkweather Howard W. , Jones Glover A. 
Published: April 2003

AbstractWe have combined pressure–volume–temperature measurements and high‐temperature x‐ray diffraction to calculate the heat of fusion of the poly(4‐methyl pentene‐1) crystal from the Clapeyron equation. We find ΔHf = 14.8 cal/g, only about half as large as several literature values. The new value of the heat of fusion leads to increased degrees of crystallinity, in agreement with the highly crystalline appearance of the x‐ray patterns of typical samples, in particular oriented fibers. The new entropy of fusion at constant pressure of 2.46 cal/deg per mole of monomer units is significantly lower than the values for polypropylene, polybutene‐1, and polypentene‐1, indicating possible ordering in the melt of this polymer.
Molecular orientation in biaxially oriented sheets of poly(ethylene terephthalate) II. Correlation of orientation averages with measured mechanical compliances
Authors: Bower D. I. , Jarvis D. A. , Lewis E. L. V. , Ward I. M. 
Published: April 2003

AbstractThe aggregate model is extended to examine the relationship between mechanical anisotropy and molecular orientation in one‐way drawn sheets of poly(ethylene terephthalate). It is assumed that both the aggregate and the unit of structure have orthorhombic symmetry. On the basis of a number of detailed assumptions regarding the appropriate application of the model, calculated bounds are obtained for the elastic constants that are in reasonable agreement with the experimental values. The implications of these results with regard to molecular orientation are considered, and it is concluded that both the chain orientation and orientation around the chain axis are important in determining the mechanical anisotropy.
The heat of fusion of polybutene‐1
Authors: Starkweather Jr. Howard W. , Jones Glover A. 
Published: April 2003

AbstractThrough x‐ray diffraction, the changes in the unit‐cell parameters of crystal forms I and II of polybutene‐1 were followed from room temperature to the melting point. These data were combined with the results of other measurements to computer the heats and entropies of fusion by use of the Clapeyron equation.
Gravimetric study of high‐pressure sorption of gases in polymers
Authors: Kamiya Yoshinori , Hirose Takuji , Mizoguchi Keishin , Naito Yasutoshi 
Published: April 2003

AbstractA gravimetric method for determining precisely the solubility of gases in polymers at high pressure is described. The solubilities of N2 and CO2 in low‐density polyethylene (LDPE); CO2 in polycarbonate (PC); and N2, CH4, C2H6, and CO2 in polysulfone (PSUL) have been measured as a function of pressure up to 50 atm. Most of the measured sorption isotherms agreed closely with published data, but reproducible and time‐dependent hysteresis in the sorption of CO2, C2H6, and CH4 in glassy polymers, PC, and PSUL, was observed in this study for the first time. Like the well known conditioning effect of high‐pressure CO2 on the sorption capacity of glassy polymers, these hysteresis phenomena are believed to be due to the plasticizing effect of sorbed gases. On the basis of the current data, the dual‐mode sorption model including the plasticization by sorbed gas is discussed and a primitive equation for the concentration of sorbed gases in a quasiequilibrium state of sorption or desorption is proposed.
The molecular origin of lamellar branching in the α (monoclinic) form of isotactic polypropylene
Authors: Lotz B. , Wittmann J. C. 
Published: April 2003

AbstractThe specific lamellar branching characteristic of isotactic polypropylene (iPP) in its α monoclinic modification, first investigated in detail by Khoury, is analyzed in molecular terms on the basis of the geometrical and structural models of Padden and Keith and of Binsbergen and de Lange, respectively. As suggested by these authors the branching corresponds, structurally, to an homoepitaxy of the daughter lamellae on the lateral (010) faces of the parent lamellae; the epitaxy is favored by a satisfactory interdigitation of the molecular subgroups (methyl side chains) of facing planes and by the near identity of a and c parameters of the α monoclinic unit cell of iPP. On a molecular basis, the branching is initiated on a lateral (010) face made up of chains of a given hand by the deposition of chains of the same hand, whereas the crystal structure of the α modification would call for chains of opposite hand. Favorable interactions of side chains of helices of the same hand is realized only when the helix axes are at a substantial angle (in the present case, 100°) to one another. Related behavior is observed for the packing of α helices in the structure of globular proteins, in which molecular interactions, but no crystallographic interactions, are involved. On the basis of this molecular picture, the widespread occurrence of lamellar branching in the crystallization of the α form of isotactic polypropylene is accounted for, especially for high growth rates. At the same time, the specificity of the branching (only observed for the α crystal modification of this polymer) is explained by stringent geometrical and structural requirements that must be fulfilled at the contact plane.
Poly(p‐benzamide). II. Thermal behavior and crystal transformations
Authors: Takase M. , Ciferri A. , Krigbaum W. R. , Hacker H. 
Published: April 2003

AbstractThe thermal behavior and crystal transformation of poly(p‐benzamide) are reported. Modification I contains both solvent (N,N‐dimethylacetamide) and LiCl in its crystal lattice. Modification II is likely to form a complex crystal with LiCl, whereas crystalline modification III contains neither solvent nor LiCl in its unit cell. The crystal transformation temperature from modification I to II is 214°C, and the crystal–nematic transition temperatures of modification II and III are 475 and 544°C, respectively. Modification III can be obtained from II by heating above 475°C and cooling, or by washing with water. It can also be obtained from modification I by washing with water and annealing.