bluuebunny/crossref_metadata_2025_split huggingface dataset:
Morphology and thermodynamic properties of solution‐grown single crystals of trans‐1,4‐polybutadiene
Authors: Marchetti A. , Martuscelli E. 
Published: April 2003

AbstractThe morphology and thermal behavior of trans‐1,4‐polybutadiene single crystals prepared from dilute solutions in n‐heptane have been investigated by electron microscopy, wide‐angle and low‐angle x‐ray diffraction, and differential scanning calorimetry. The thickness of the single crystals of trans‐1,4‐PBD is much greater, for the same undercooling, than that of other linear polymers. From the calorimetric study, convincing evidence of the presence, in the single crystals, of crystalline blocks of form 1 with two different thermodynamic stabilities is obtained and the relative amounts are calculated. From thermodynamic considerations we find a value of 75°C for the equilibrium transition temperature between forms 1 and 2, 139°C for the equilibrium melting temperature of form 2, and 31.2 erg/cm2 for the fold‐surface free energy of modification 2.
High‐pressure phases in polymers. III. The nature of the high‐pressure phase in cis‐polyisoprene
Authors: Phillips P. J. , Edwards B. C. 
Published: April 2003

AbstractThe morphology and growth of the disordered hexagonal phase which crystallizes in films of cis‐polyisoprene at pressures in excess of 3 kbar is discussed. A two‐stage growth process is proposed consisting of nucleation and crystallization followed by a pressure‐enhanced thickening process. The phase is metastable and is replaced by normal spherulitic growth at long times. It transforms into lamellar sheafs with higher than usual lamellar thicknesses when pressure is lowered at constant temperature.
Crystal structure of poly(m‐phenylene isophthalamide)
Authors: Kakida Hideto , Chatani Yozo , Tadokoro Hiroyuki 
Published: April 2003

AbstractThe crystal structure of poly(m‐phenyulene isophthalamide) was determined by x‐ray analysis. The triclinic cell, with a = 5.27 Å, b = 5.25 Å, c (fiber axis) = 11.3 Å, α = 111.5°, β = 111.4° and γ = 88.0° and space group P1, contains one monomeric unit. The crystal density is 1.47 g/cc. The molecules in the crystal are contracted by 1 Å per monomeric unit from the fully extended conformation, and the planes of the benzene rings and adjacent amide groups make angles of about 30°. The crystal is composed of molecular chains connected by NH···O hydrogen bonds along the a and b axes forming a “jungle gym” network structure. The low tensile modulus of this polymer as compared with that of poly(p‐phenylene terephthalamide) is attributed to the contracted molecular conformation.
Ion recombination luminescence in polymer glasses induced by electron irradiation. I. High‐vinyl polybutadiene
Authors: Böhm Georg G. A. 
Published: April 2003

AbstractThe luminescence of 1,2‐polybutadiene was measured during and following irradiation with 1.4‐MeV electrons at 90 °K. Measured under isothermal conditions, the light intensity at first increases sharply on start‐up of irradiation, and then reaches a plateau after several seconds. The equilibrium value was found to be linearly dependent on the dose rate employed. The postirradiation luminescence decay measured at 90°K follows second‐order kinetics.The light emitted by the irradiated sample during warm‐up to room temperature is characterized by the appearance of four intensity maxima at 118, 168, 223, and 261 °K. The first three peaks are attributable to the onset of local motion, whereas the peak at 223 °K is caused by the long‐range motion occurring at the glass‐to‐rubber transition. A preirradiation of the polymer in vacuo causes an increase in these four peaks as well as the formation of a new maximum at 143 °K.Intermittent exposure of the irradiated sample to light of wavelengths λ > 450 nm causes the isothermal luminescence decay to be interrupted by a burst of light emitted by the sample during and shortly following the light exposure. This treatment also results in considerably reduced intensity maxima during warm‐up to room temperature. An interpretation of the findings reported is given on the basis of reactions involving primary and secondary transient species produced during irradiation and on the molecular parameters of the polybutadiene.
Thermal–mechanical studies on a heterocyclic polymer (BBB). I. Tensile creep and recovery
Authors: Berry G. C. 
Published: April 2003

AbstractCreep and recovery measurements have been used to study the thermal–mechanical properties of polybisbenzimidazobenzophenanthroline‐dione (BBB) over the temperature interval 30–500°C (in vacuo). The creep measurements were augmented by x‐ray diffraction, isothermal contraction, and solubility measurements. It is found that extensive intermolecular association giving a supramolecular structure with (nearly) planar polymeric repeat units stacked in a “graphite‐like” array dominates the properties of BBB, and that this structure is maintained at temperatures as high as 500°C. The principal mode of creep gives rise to fully recoverable Andrade creep for which the strain depends on the cube‐root of time.
A dielectric study of the amorphous fraction in oriented nylon 610
Authors: Yemni Tarik , Boyd Richard H. 
Published: April 2003

AbstractSince some dielectric loss peaks can be assigned to amorphous phase motions, it would appear that dielectric measurements should be a good probe to study the effects of macroscopic plastic deformation on the structure of the amorphous phase. We report here results of measurements of dielectric constant and loss in nylon 610 measured both parallel (∥) to and perpendicular (⊥) to the extrusion direction in specimens prepared by extrusion through a die at 160°. It is found that the intensity of the (∥) loss was nearly zero and the (⊥) loss intensity was greatly reduced compared to unoriented material. The other relaxation parameters (loss width and location) were largely unaffected. Since the amide dipole is nearly perpendicular to the chain axis and alternates in direction in the extended conformation, a considerable degree of chain alignment parallel to the draw direction is indicated. These results therefore show considerable permanent amorphous phase orientation even though the deformation was carried out 100° above its glass temperature.
A Raman study of the phase transition in crystalline trans‐1,4‐polybutadiene
Authors: Hsu S. L. , Krimm S. 
Published: April 2003

AbstractRaman spectroscopy has been used to analyze the characteristics of the crystal–crystal phase transition of trans‐1,4‐polybutadiene. The low‐ and high‐temperature structures were found to coexist at the transition. The Raman spectra obtained at high temperature can be understood on the basis of the change in chain conformation associated with the phase transition.
Carbon dioxide sorption and transport in polycarbonate
Authors: Koros W. J. , Paul D. R. , Rocha A. A. 
Published: April 2003

AbstractThe solubility, permeability, and diffusion time lag for carbon dioxide in polycarbonate are reported at 35°C for pressures ranging from 1 atm to 23 atm. The solubility data are very well described by the dual sorption mechanism model, Henry's law plus Langmuir adsorption, proposed for glassy polymers. Both the permeability and time lag decrease with increased CO2 pressure. These observations are not consistent with the proposal that CO2 sorbed by the Langmuir contribution is totally immobilized; however, all of the results are entirely consistent with an extension of this proposal which considers partial immobilization. The data have been quantitatively analyzed in terms of this partial immobilization model, and the results suggest for polycarbonate at 35°C that the CC2 sorbed by the Langmuir portion of the isotherm behaves as if it has only about 10% of the mobility of the gas sorbed by the Henry's law part of the isotherm. The results have also been interpreted in terms of a concentration‐dependent diffusion coefficient which is shown to be mathematically equivalent to the partial immobilization model. The latter model was also formulated in thermodynamic terms, whereby fugacity was used rather than pressure, and diffusion coefficients were defined in terms of chemical potential gradients rather than concentration, but the consequences of these changes proved to be minor and no better. The significance of these observations and their interpretation is discussed.
The effect of strain rate on craze yielding, shear yielding, and brittle fracture of polymers at 77°K
Authors: Imai Yasufumi , Brown Norman 
Published: April 2003

AbstractThe tensile strength of poly(methyl methacrylate) (PMMA), polycarbonate (PC), polychlorotrifluoroethylene, and polysulfone was measured in liquid nitrogen over the strain rate range of 2 × 10−4 to 660 min−1. These polymers deformed by crazing which was induced by the liquid nitrogen. The stress versus log strain rate curve was sigmoidal in that its slope increased and then decreased with strain rate. Above a critical strain rate of about 200 min−1, which varied somewhat with the polymer, crazing was not observed with the optical microscope; the behavior became brittle, and the tensile strength became constant. The nonlinear behavior of stress versus log strain rate at low strain rates was associated with a decrease in activation volume with increasing strain rate whereas the nonlinear behavior at high strain rates was associated with an increase in density and decrease in length of the crazes with strain rate. The strain rate effect was the basis for calculating the diffusion coefficient of nitrogen into the polymers at 77°K.The shear deformation mode of PC was measured under compression and under tension. The compressive strength versus log strain rate was linear throughout the entire range giving a compression shear activation volume of 360 Å3. The shear tensile strength of PC varied only slightly with strain rate when compared to the compressive strength. The brittle fracture stress of PMMA, in the absence of crazing, in compression and in tension, did not vary with strain rate.
Conformational and packing stability of crystalline polymers. VI. Stable chain packing of polyethylene
Authors: Tai Kazuo , Kobayashi Masamichi , Tadokoro Hiroyuki 
Published: April 2003

AbstractThe stable packings of polyethylene chains were investigated by intermolecular potential energy calculations based on various chain‐assembly models. The structures of the two crystal modifications of polyethylene (i.e., orthorhombic and the monoclinic), together with their cell constants and the setting angles, were well reproduced. The packing modes of polymethylene chains found in various alkane derivatives were also explained by the energy minima of the chain‐assembly models. In these calculations, several sets of potential functions were tried and three sets of functions were found to reproduce conformations of single polymer chains, the cell constants of polyethylene at low temperature, and those at room temperature.
Temperature‐induced reversible changes in long spacing in oriented polyethylene
Authors: Pope D. P. , Keller A. 
Published: April 2003

AbstractThe possible explanations for the temperature‐induced reversible changes in long spacing in polymers are reviewed. The observation of particularly large changes in certain irradiated samples of oriented low‐density polyethylene is reported. By combining these results with those obtained by DSC and other means it is concluded that the spacing changes are caused by partial melting of small lamellae within the lamellar stacks which alters the mean periodicity. The requirement of an irregular lattice explains why the effect is observed primarily in bulk samples and especially in materials which contain intrinsic irregularities.
Optical and swelling properties of macroscopic “single crystals” of an S–B–S copolymer. I. Samples possessing a lamellar morphology
Authors: Folkes M. J. , Keller A. 
Published: April 2003

AbstractSamples of an S–B–S three block copolymer exhibiting a lamellar morphology have been prepared, in which the macrolattice formed from the segregated amorphous is uniformly oriented throughout the sample volume. The associated optical anisotropy has been studied in the unswollen state and in the presence of preferential solvents for the polybutadiene phase. The results obtained are consistent with form birefringence being the dominant contribution to the observed birefringence. There is a small contribution from a slight molecular orientation, corresponding to polystyrene chains perpendicular to the lamellar surfaces. The form birefringence is appropriately modified when the sample is in the swollen state by molecular orientation produced in the polybutadiene, due to the anisotropic dimensional changes in the sample. The implication of the results as regards the nature of the polybutadiene phase is also discussed.
Optical and swelling properties of macroscopic “single crystals” of an S–B–S copolymer. II. Samples possessing a cylindrical morphology
Authors: Folkes M. J. , Keller A. , Odell J. A. 
Published: April 2003

AbstractA study is reported of the anisotropic swelling behavior of “single crystal” samples of an S–B–S two‐phase copolymer, Kraton K102, on imbibing a selective swelling agent. This material consists of a hexagonal array of polystyrene cylinders in a matrix of polybutadiene. Initially the material expands reversibly, perpendicular to the cylinders. Low‐angle x‐ray studies show that this corresponds to expansion of the hexagonal lattice and indicates lateral expansion of the matrix material. Birefringence changes can be broadly ascribed to the changes in form birefringence.Subsequently, irreversible expansion occurs along the rod direction. x‐ray diffraction studies combined with electron microscopy indicate a transformation of the cylindrical microstructure into a more complex arrangement. This often appears to be an arrangement of spheres, packed on a hexagonal or square lattice, but this cannot completely account for the x‐ray results. Some micrographs suggest the existence of a more complex network of the polystyrene microphase units.
Electron donor–acceptor properties of thin polymer films on silicon. II. Tetrafluoroethylene polymerized by RF glow discharge techniques
Authors: Anderson H. R. , Fowkes F. M. , Hielscher F. H. 
Published: April 2003

AbstractMetal–insulator–semiconductor (MIS) techniques were used to show that 86–210 nm thick plasma‐polymerized tetrafluoroethylene films on silicon stored only negative charge (electron acceptors). This property persisted at a reduced level when a 7 nm thick inner layer of hydrolyzed γ‐aminopropyltriethoxysilane was combined with an outer layer of plasma‐polymerized tetrafluoroethylene. The dispersion force contribution to the surface energy, γds, for the fluorocarbon films was found to be 6 mJ/m2(erg/cm2) which is comparable with the lowest values found in the literature. X‐ray photoelectron spectroscopy (XPS) revealed a substantial content of CF3groups in the fluorocarbon films. This finding coupled with the reported effects of noncrystallinity, crosslinking, and branching on the surface energies of fluorocarbon systems were used to explain the low surface energy and electrophilicity of the plasma‐deposited poly(tetrafluoroethylene)s.
Fracture toughness predictions in polycarbonate
Authors: Gerberich W. W. , Martin G. C. 
Published: April 2003

AbstractThe concepts of fracture mechanics have been used to analyze the fracture toughness of polycarbonate in terms of the polymer relaxation properties. By considering the temperature rise at the tip of a growing crack; a model is proposed which describes the viscoelastic energy loss in the fracture process. The model was used to predict the fracture toughness of polycarbonate as a function of test temperature.
A raman spectroscopic determination of the interlamellar forces in crystalline n‐alkanes and of the limiting elastic modulus Ec of polyethylene
Authors: Strobl G. R. , Eckel R. 
Published: April 2003

AbstractA simple treatment based on continuum mechanics shows that weak interlamellar forces in crystalline n‐alkanes should result in a characteristic upward shift of the frequencies of the longitudinal acoustical (LA) modes, which is independent of the chain length and decreases inversely with the mode order. A raman spectroscopic determination of the LA mode frequencies of a series of different n‐alkanes confirms the theoretical conclusion and permits a derivation of a force constant characteristic of the interlamellar forces. The discussion results in a new formula valid for the LA mode frequencies of the orthorhombic n‐alkanes in the acoustical limit and yields a new determination of the limiting elastic modulus Ec of crystalline polyethylene. The value obtained, Ec = 2.9 × 1012 dyne/cm2, is markedly smaller than the value derived by Schaufele and Shimanouchi neglecting the influence of the interlamellar forces on the LA mode frequencies.
Osmotic coefficient of a polyelectrolyte solution with a mixture of monovalent counterions
Authors: Dolar D. , Škerjanc J. 
Published: April 2003

AbstractAn analytical solution of the Poisson‐Boltzmann equation is presented for the cell model of a polyelectrolyte solution with two species of monovalent counterions of different size. On this basis the osmotic coefficient is calculated as a function of the mole fraction of counterions and their radii. It is shown that the degree of binding of the smaller ion species increases as its mole fraction decreases.
The relationship between the physical structure and the mechanical properties of polycarbonate
Authors: Morgan Roger J. , O'Neal James E. 
Published: April 2003

AbstractThe room‐temperature tensile mechanical properties and fracture topographies of polycarbonate are reported as a function of strain rate, sample preparation, and thermal history above and below Tg. The bulk physical structural changes produced by various thermal treatments were monitored by density, yield stress, and differential scanning calorimetry observations. Ordered regions do not form in bulk polycarbonate at or below 145°C. The changes produced in the mechanical properties of polycarbonate on annealing below Tg, relative to a quenched or 145°C equilibrium‐state glass, are caused by liquidlike packing changes in free volume. In room‐temperature tensile a 125°C–6 day annealed glass exhibits transitional behavior from shear free volume, such as quenched and 145°C equilibrium‐state glasses, this transition occurs at higher strain rates. Polycarbonate embrittles as a result of the cessation of shear yielding and reversion to a crazing failure mode with a corresponding decrease in molecular flow and energy to failure.Density measurements indicate that ordered regions do start to grow immediately above 145°C in bulk polycarbonate. This phenomenon allows precrystalline and/or crystalline entities to grow below the bulk Tg in thin films and on the free surfaces of thick films where mobility restrictions are less severe than in the bulk. From bright‐field transmission electron micrographs of thin films and carbon–platinum surface replicas of etched thick films it is suggested that the observed spherical precrystalline structures are aggregates of 50–60 Å ordered molecular do mains.
Enthalpy relaxation of rigid poly(vinyl chloride)
Authors: Straff R. , Uhlmann D. R. 
Published: April 2003

AbstractThe changes which take place on annealing rigid PVC in the vicinity of the glass transition have been followed by differential scanning calorimetry. The changes appear as an increase in the glass‐transition temperature and a decrease in the enthalpy with time of annealing. For annealing at 75°C, the enthalpy after 50–100 hr approaches the value characteristic of the equilibrium liquid state. The results obtained for annealing at 65°C and 75°C are in accord with those expected for the relaxation of an amorphous material, and are at variance with those expected on the basis of crystallization taking place on annealing. The enthalpy relaxation process is characterized by a distribution of activation energies centered about 18.8 kcal mole−1, and seems to reflect a multiplicity of molecular processes.
Spectrum of light scattered from viscoelastic gels
Authors: Munch J. P. , Candau S. , Duplessix R. , Picot C. , Herz J. , Benoit H. 
Published: April 2003

AbstractSpectra of polarized light scattered from model networks of polystyrene swollen by benzene have been measured by optical mixing spectroscopy. Various series of networks of different functionalities and different lengths of the elastic chain elements have been investigated. A theoretical expression for the characteristic time constant of fluctuations has been derived from rubber elasticity theory. An analysis of the experimental results within the framework of this theory allows determination of the frictional constants of the gels.
Phase equilibrium and glass‐transition temperatures in plasticized amorphous bisphenol‐A polycarbonate
Authors: Onu A. , Legras R. , Mercier J. P. 
Published: April 2003

AbstractGlass‐transition temperatures and phase separation have been studied in amorphous bisphenol‐A polycarbonate plasticized with pentaerythritol tetranonanoate (PETN), trimellitic acid, tridecyloctyl ester (TMDO), and tritolyl phosphate. (TTP). Phase separations occur with partially compatible plasticizers like PETN or TMDO. With PETN, for compositions situated in the miscibility gap, the system is composed of a pure plasticizer phase and of a plasticized polymeric phase characterized by a transition temperature of 110°C. In the case of TMDO and additional phase separation occurs below 55°C and two plasticized polycarbonate phases are observed. In compositions falling in the region where the could point curve crosses the glass‐transition diagram the phase separation may be delayed by quick cooling. TTP is completely compatible with polycarbonate and the variation of the glass‐transition temperature follows a Gordon and Taylor equation.
Glass transitions of ethyl acrylate‐based ionomers
Authors: Matsuura H. , Eisenberg A. 
Published: April 2003

AbstractThe glass‐transition temperatures of a series of copolymers of ethyl acrylate and acrylic acid neutralized with various cations were investigated. It was found that a plot of Tg as a function of ion content, for every type of ion investigated here, gives an unusual sigmoidal curve, which can be correlated with the onset of the failure of time–temperature superposition in viscoelastic studies, as will be shown in a future publication. Also, all of the Tg versus concentration curves for the various counterions can be superposed if the plots are made against cq/a, where c is the metal acrylate content, q the cation charge, and a the distance between centers of charge. Furthermore, in one region of water content, a linear relation is obtained between the glass transition and the water content (in weight‐%) independent of the ion concentration over wide ranges of ion content. Finally, above an ion concentration of 12 mole‐%, the rate of change in Tg per water molecule per ion pair at constant ion content, (∂Tg/∂n)c is linear but with different slopes above and below two water molecules per ion pair.