bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effect of pressure on the volume and the dielectric relaxation of linear polyethylene
Authors: Sayre John A. , Swanson Stephen R. , Boyd Richard H. 
Published: April 2003

AbstractThe effects of pressure on the α (ca. 70°C, 1 kHz) and γ (ca. −100°C, 1 kHz) relaxations of linear polyethylene were studied dielectrically between 0 and 4 kbar. Equation of state (PVT) data were also determined in the range of interest of these relaxations. The sample was rendered dielectrically active through oxidation (0.8 C0 per 1000 CH2). The α process (which occurs in the crystalline fraction) could be studied over a much wider temperature range than heretofore possible due to the effect of pressure in increasing the melting point. Examination of relaxation strength from 50 to 150°C showed that there must be two crystalline relaxation processes: the well‐known α relaxation plus a competing one. The α relaxation is believed to be due to a chain twist–rotation–translation mechanism that results in rotation–translation of an entire chain in the crystal. The relaxation strength of the α process decreases and therefore indicates the presence of a second (faster and not directly observed) process that increases in intensity with increasing temperature. It is postulated that the second process is due to motion of defects that become more numerous through thermal injection at higher temperatures. Analysis of the relaxation data along with the PVT data allowed the constant volume activation energy for the α relaxation to be determined. It was found to be 19.4 ± 0.5 kcal/mole. The constant volume activation energy is important in modeling calculations of the crystal motions and is significantly smaller than the atmospheric constant pressure activation energy of 24.9 kcal/mole. The effect of pressure on the activation parameters and shape of the γ process was also determined. There has been controversy over whether the γ process occurs only in the amorphous fraction or in both the amorphous and crystalline phases. Since the two phases have quite different compressibilities, increasing the pressure should change the shape of the loss curves (versus frequency and temperature) if the process occurs in both phases. The shape (but not location) of the loss curves was found to be remarkably independent of pressure. This finding strengthens the view that the γ process is entirely amorphous in origin.
An ESR study of polymer‐Cu(II) complexes in poly(vinyl alcohol), polyacrylamide, and poly(vinyl pyrrolidone) films
Authors: Sumita Osao , Fukuda Atsuo , Kuze Eiichi 
Published: April 2003

AbstractOptical and ESR spectra of polymer‐Cu(II) complexes in polymer films have been studied. The dependence on F1 = [Cu2+]/[MU] and F2 = [OH−]/[Cu2+], where [MU] is the molar concentration of monomeric units of the polymer, has been obtained. Optical spectra and potentiometric titration curves in solution have also been studied. There exists a buffer region 0 ≲ F2 ≲ 2. Optical spectra in films are slightly different from those in solutions. At least five different ESR signals, designated as A, B, C or D, and E, have been found in poly(vinyl alcohol)‐Cu(II). These signals appear successively with increasing F2. Assignments are proposed as follows. Signal A (F2 ≈ 0), also found in poly(acrylamide)‐Cu(II) and poly(vinyl pyrrolidone)‐Cu(II), is due to a single Cu(II) coordinated with two water molecules and chelated with two oxygens or nitrogens attached to the polymer. A chain of Cu(II) ions singly and double bridged with OH− ions is responsible for the B signal (F2 ≈ 1). The C and D signals (F2 ≈ 2) appear to be caused, respectively, by a dimeric Cu(II) complex singly or doubly bridged with OH− ions. The E signal (F2 ≈ 7) appears to be due to a monomeric Cu(II) complex, different from that responsible for the A signal.
Crystallization and melting of aqueous gelatin
Authors: Godard P. , Biebuyck J. J. , Daumerie M. , Naveau H. , Mercier J. P. 
Published: April 2003

AbstractGelation and melting of aqueous gelatin were investigated by differential scanning calorimetry. This phenomenon can be analyzed as a conventional crystallization process assuming predetermined primary nucleation and unidirectional growth. The results were interpreted in terms of the fringed micelle model. Calculated values of the diameter of the renatured collagen fibril were found in excellent agreement with those determined previously by electron microscopy.
Thermoluminescence from photoexcited polyethylene terephthalate
Authors: Takai Yoshiaki , Mori Koji , Mizutani Teruyoshi , Ieda Masayuki 
Published: April 2003

AbstractThermoluminescence from polyethylene terephthalate (PET) has been investigated. A correlation was found between thermoluminescence (TL) and thermally stimulated current (TSC). The apparent activation energy was estimated at 0.23–0.50 eV for both TSC and TL from −170 to 0°C. This activation energy presumably indicates the trap depth, which is decreased by molecular motions, since both TSC and TL are quenched efficiently with visible light, but not with infrared light of energy of the magnitude of thermal activation energy. The spectrum of TL glow curves agrees with the photoluminescence spectrum at −185°C, which is composed of an excimer and a monomer fluorescence and also a structured phosphorescence at wavelengths longer than 400 nm.
Fourier transform infrared analysis of the stereoregularity of atactic polystyrene
Authors: Jasse B. , Koenig J. L. 
Published: April 2003

AbstractFourier transform infrared spectroscopy provides a sensitive method allowing one to detect easily changes in the syndiotactic sequence content in polystyrene. The method is based on analysis of the 540‐cm−1 absorption band, which is conformationally sensitive. Results in the solid state and solution are presented. A shift of 2.5 cm−1 of the 540‐cm−1 band towards the high‐frequency side is observed between the solid state and solution.
A model for the adsorption of poly(γ‐benzyl‐L‐glutamate) from solution onto alkali‐halide substrates
Authors: Balik C. M. , Hopfinger A. J. 
Published: April 2003

AbstractThe isothermal adsorption of high‐and low‐molecular‐weight poly(γ‐benzyl‐L‐glutamate) (PBLG) onto (100) alkali‐halide surfaces has been studied with the intent of developing a model for the adsorption process. Data from both the solution and adsorbed phases were correlated in this study. The α‐helical conformation was maintained in solution and on the substrate for all molecular weights investigated. Fourier‐transform infrared spectroscopy proved to be a sensitive technique for conformational analysis of adsorbed PBLG films as thin as 200 Å. High‐molecular‐weight PBLG was adsorbed as an interwoven fibrous mat, homogeneously covering the entire substrate surface. This morphology was independent of the substrate. Adsorption of low‐molecular‐weight PBLG took on a lamellar morphology, often exhibiting epitaxial orientation in the substrate 〈100〉 directions. Quasielastic laser light scattering studies showed that low‐molecular‐weight PBLG had a much higher degree of aggregation in nonpolar solvents than did high‐molecular‐weight PBLG. The proposed adsorption model is essentially a modification of one suggested by Silberberg. It involves segmental adsorption of aggregates, as opposed to single macromolecules of PBLG. The unadsorbed segments of the aggregates form a concentrated interfacial region directly above the substrate. Further interaction and association of PBLG may occur in this region, thus reducing the epitaxial ordering influence of the substrate. Consequently, polymers which do not interact strongly in the concentrated interfacial region, such as polyethylene, are expected to be adsorbed epitaxially, as has been reported.
The thickness of adsorbed polymer layers at a liquid–solid interface as a function of bulk concentration
Authors: Priel Z. , Silberberg A. 
Published: April 2003

AbstractWith a glass apparatus which is capable of measuring the thickness of adsorbed polymer layers with as accuracy of 0.5 nm, determinations on adsorbed polystyrene layers in contact with extremely dilute solutions (ca. 10−7 g/ml) in toluene were performed. Thermodynamic equilibrium was proved to exist between the adsorbed polymer layer and bulk solution. The thicknesses found suggest that a fluid mechanical effect is operative, as has recently been calculated. It was shown that in the very dilute region the thickness of the adsorbed layer is initially a linearly increasing function of concentration, and that regions of (very low) concentrations exist over which a first plateau arises, where the layer is as thin as might be expected from isolated, adsorbed coil analysis. A second much higher plateau arises at concentrations in excess of 10−5 g/ml, which is the plateau usually described.
CO2 sorption in poly(ethylene terephthalate) above and below the glass transition
Authors: Koros W. J. , Paul D. R. 
Published: April 2003

AbstractHigh‐pressure CO2 sorption data in semicrystalline poly(ethylene terephthalate) (PET) are presented for temperatures ranging from 25 to 115°C. The results are described by Henry's law above the glass‐transition temperature of PET, while a dual‐mode sorption model comprised of a Henry's law and a Langmuir isotherm applies in the glassy state. The disappearance of the Langmuir capacity of the polymer above Tg presumably results from the elimination of regions of localized lower density which are frozen into the glass upon quenching from the rubbery state. Exposure of PET to a high CO2 pressure produced a systematic variation in the apparent sorption equilibria. Correlation of the Langmuir capacity of PET with the dilatometric parameters of the polymer provides a useful framework for understanding the origin of the Langmuir sorption mode and for interpreting annealing and conditioning effects in glassy polymers.
Thermally stimulated current from extended‐chain crystals of polyethylene
Authors: Hashimoto Toshimasa , Sakai Tetsuya , Miyata Seizo 
Published: April 2003

AbstractThermally stimulated current (TSC) has been observed in extended‐chain crystals of polyethylene above room temperature. The TSC spectra exhibit two current peaks of opposite polarity. The peaks were separated into separate components by curve fitting. The position of the negative peak, which appears at 123°C, is independent of charging conditions. The positive current increases after γ irradiation or aging of the samples.
Elastic modulus of the crystalline phase of poly(cis 1,4‐isoprene)
Authors: Avitabile G. , Napolitano R. , Riva F. 
Published: April 2003

AbstractThe crystalline elastic modulus of poly(cis 1,4‐isoprene) has been measured by x rays and calculated by molecular mechanics. The experimental modulus is E = (2.3 ± 0.3) × 109N m−2. The calculated modulus is E = (8.8 ± 0.1) × 109N m−2 for chains in S+ cis S−T conformation and E = (6.1 ± 0.1) × 109N m−2 for chains in S+ cis S+T conformation. The modulus calculated for a statistical structure including both conformation is E = (6.7 ± 0.1) × 109N m−2. The experimental modulus is thought to be a lower limit because of partial crystallinity of the sample. The chief mechanism of deformation is rotation around single bonds adjacent to the double bond.
Molecular confirmation and crystal structure of the β form of poly(ethylene oxybenzoate)
Authors: Takahashi Yasuhiro , Kurumizawa Toshimitsu , Kusanagi Hiroshi , Tadokoro Hiroyuki 
Published: April 2003

AbstractThe crystal structure of the β form of poly(ethylene oxybenzoate) was analyzed by x‐ray diffraction. Four nearly extended molecular chains pass through a unit cell with parameters a = 8.19 Å, b = 11.07 Å, c (fiber axis) = 19.05 Å, β = 114.8°, and the space group P21/n‐C. The structural difference between the α and β forms is mainly due to the internal rotation angles for the virtual bond
magnified image
and the CH2CH2 bond. They are essentially in trans confirmation in the β form, while the α form contains cis
magnified image
and gauche (CH2CH2) conformations.
Hydrostatic extrusion of polyoxymethylene
Authors: Coates P. D. , Ward I. M. 
Published: April 2003

AbstractThe hydrostatic extrusion behavior of polyoxymethylene (POM) is described. Extrusions were performed at 164°C for a range of different molecular weight grades. Excellent unflawed lengths of extrudate were obtained with axial Young's moduli, measured at room temperature, reaching values as high as 24 GPa. The extrusion characteristics are discussed in terms of the very strong dependence of the flow stress of POM on strain and strain rate and pressure. In addition to measurements of Young's modulus over a wide temperature range, data for shear modulus and transvers modulus are also presented. A limited amount of other structural measurements is presented.
Mechanical and transport properties of drawn low‐density polyethylene
Authors: Araimo L. , De Candia F. , Vittoria V. , Peterlin A. 
Published: April 2003

AbstractQuenched, quenched and annealed, and slowly cooled branched low‐density polyethylene films were drawn at 25, 40, and 60°. The true draw ratio λL of the volume element was obtained and used to characterize the dependence on plastic deformation of the density, drawing stress, and work of plastic deformation, and the sorption and diffusion of methylene chloride. The effects observed are similar but less drastic than on linear high‐density polyethylene. In particular, the transformation from the original lamellar to the final fibrous structure seems to be fastest for λL between 3 and 4. But the changes of vapor transport clearly indicate that the transformation is not yet complete even at the highest draw ratio λL = 6, just before the sample breaks. Annealing at 90°C of the drawn samples with free ends restores or even increases the transport properties beyond those of the undrawn sample without causing the fibrous structure to revert to the original lamellar structure.
Laser Raman scattering in uniaxially oriented atactic polystyrene
Authors: Jasse B. , Chao R. S. , Koenig J. L. 
Published: April 2003

AbstractRaman polarization measurements of atactic polystyrene (APS) films were recorded after uniaxial stretching. Twelve different polarization directions were observed by varying the direction and polarization of the laser and scattered radiation. The polarization behavior of several vibration modes were shown clearly in the Raman spectra. On the basis of these polarization properties and previous vibrational studies of model compounds of polystyrene as well as of monosubstituted benzene derivatives, a reassignment of some of the vibrational modes of APS is made and discussed.
The structure and properties of oriented fibers of poly(pentamethylene terephthalate). II. Structural analysis of two different crystalline phases by x‐ray crystallography
Authors: Hall I. H. , Rammo N. N. 
Published: April 2003

AbstractOriented fibers of poly(pentamethylene terephthalate) will crystallize in one of two phases. In one phase (designated α), which is preferred in the unstressed fiber at room temperature, the chain is contracted from its chemical repeat length. In the other (designated β), induced by tension, it is nearly fully extended. The structural analysis of both forms is described. The unit cells of both phases are triclinic. The parameters of the α phase are a = 4.7 Å, b = 5.8 Å, c = 24.7 Å, α = 112°, β = 94°, γ = 105°. For the β phase they are a = 5.0 Å, b = 5.8 Å, c = 28.2 Å, α = 126°, β = 74°, γ = 120°. The methylene sequence is all trans in the β phase but, surprisingly, in the α phase, three of its bonds are near the eclipsed conformation. The other surprising feature is the departure from planarity of one of the terephthaloyl residues in the β phase. These, and other features of the structures are compared with those of other chemically similar materials, both monomeric and polymeric.
Structure of glassy polymers. V. Small‐angle x‐ray scattering from polystyrene
Authors: Renninger A. L. , Uhlmann D. R. 
Published: April 2003

AbstractSmall‐angle x‐ray scattering (SAXS) from glassy atactic polystyrene has been measured using a Bonse–Hart system. After correcting for absorption, background, and beam divergence, the scattering has been placed on an absolute basis using a standard silica suspension as a reference.The desmeared absolute intensity decreases strongly with increasing scattering angle over the range between 20 sec and 20 min. At larger angles, the intensity decreases much more slowly with increasing angle and approaches the value expected for density fluctuations frozen‐in at the glass transition. The angular variation of intensity is well described by the scattering from heterogeneities of various sizes and concentrations superimposed on the scattering from thermal density fluctuations. These heterogeneities range in radius from 10 to 4000 Å. The present SAXS results on glassy polystyrene seem inconsistent with the presence of nodular features as representative of the bulk polymer.
Chain mobility of some terephthalic acid polyesters in solution. A 13C spin‐relaxation study
Authors: Komoroski Richard A. 
Published: April 2003

AbstractCarbon‐13 spin‐lattice relaxation times (T1), nuclear Overhauser enhancements (NOE), and resonance linewidths (Δp) have been measured for a series of terephthalic acid polyesters containing ethyl, butyl, hexyl, and isopropyl groups between neighboring terephthalate units. The relaxation parameters of all carbons in the terephthalate groups are independent of the length of the separating alkyl chain. Reduced NOE's are seen for all carbons. The data are interpreted in terms of a log X2distribution of correlation times of constant width, but variable average mobility. The average mobility in the alkyl chain increases with increasing distance from the terephthalate group in a given polymer. For a given position in the chain. mobility increases with increasing chain length. This behavior is consistent with the presence of independently reorienting, highly solvated terephthalate groups.
The heat of fusion of polymer crystals: Polyethylene crystals in suspension
Authors: Harrison I. R. , Runt J. , Stanislow L. J. , Bell D. A. 
Published: April 2003

AbstractRecent experiments have supported the view that polyethylene (PE) single crystals kept in suspension, in a variety of liquids, have different physical properties compared with the same crystals after drying. The present work was undertaken in an attempt to directly measure one of the basic properties of crystals in suspension, namely their percent crystallinity (X). Differential scanning calorimetry was chosen as the primary tool for this investigation. A method has been developed to determine the weight of PE in a suspension of crystals in a nonsolvent. Thus, a determination of X can be made. For suspension crystals, X was found to be at least 88.5%, some 6% larger than that for the corresponding dried or freeze‐dried material. Implications with regard to the fold‐surface structure are discussed. Differences in degree of crystallinity as a function of drying procedure have also been observed.
Far‐infrared studies of ion clustering in ionomers
Authors: Rouse George B. , Risen William M. , Tsatsas Andreas T. , Eisenberg Adi 
Published: April 2003

AbstractThe far‐infrared spectra of polystyrene methacrylic acid/(PSMA) ionomers have been investigated as a function of cation and ion‐site concentration to obtain spectroscopic evidence of domain formation. A far‐infrared band, due to the vibration of a higher‐order cluster, is found at 170 cm−1in Na+‐form PSMA. This band, which is observed in addition to the known cation‐motion bands, is assigned to the vibrations of aggregates involving many cations and anionic sites close together, and the results are discussed in light of ion aggregation models.
Glassy polymer solutions: Morphology of in situ crystallized additives
Authors: Narkis M. , Siegmann A. , Puterman M. , Dibenedetto A. T. 
Published: April 2003

AbstractIn the present work the phenomenon of in situ crystallization of low molecular weight organic compounds from an amorphous polymer was studied. Phase diagrams of tetrachloroxylene and tetrachlorobenzene with polystyrene showing softening, precipitation, and dissolution have been constructed. Three modes of crystallization, namely, needlelike, dendritic, and tiny crystalline particles have been observed depending on cooling rate. Hot stage optical microscopy and electron microscopy have been used to study crystallization, dissolution, and morphology. Softening temperature was determined by the vicat method. Shearing of samples undergoing crystallization has produced oriented samples.
The heating rate dependence of polymer melting points
Authors: Harrison I. R. , Runt J. 
Published: April 2003

AbstractThe melting points (Tm) of small quantities (ca. 0.1 mg) of polyethylene (PE) single crystals in the dried state and in suspension were determined as a function of heating rate. Melting points were also obtained for large amounts (ca. 3 mg) of dried‐down crystals. It has been reported previously that PE crystals of high molecular weight possess a single melting point and this Tm decreases with increasing heating rate. However, all samples in our study show multiple melting behavior. Moreover, suspension samples show little or no variation in the various peak temperatures with heating rate. There is some dependence of Tm on heating rate for small dry samples but the change in Tm is not nearly as great as previously reported. These small changes can be the result of the relatively poor resolution of small dry samples compared to suspension. Differences between the behavior reported here and those of other authors can be explained on the basis of the relative contributions to the various melting endotherms.
Mechanical relaxations in episulfide network polymers
Authors: Charlesworth John M. 
Published: April 2003

AbstractA variety of condensation network polymers have been prepared by the reaction between amine, episulfide, and epoxide monomers. The mechanical relaxations occurring in these systems have been examined using a torsion pendulum and the role of hydrogen bonding in the mechanism of the β relaxation is shown to be insignificant. The chemical reaction between amine and episulfide groups has been investigated by IR spectroscopy and is shown to parallel the reaction between amine and epoxide groups. However, steric and electronic factors are suggested to decrease the extent of reaction when aromatic amines are involved. In the case of networks prepared from blends of episulfide and epoxide monomers, measurements of the gel time, together with the mechanical behavior around the glass transition, indicate that either interpenetrating or two‐phase networks are formed. This is postulated to be a consequence of the high reactivity of the episulfide ring compared to the epoxide ring. The blending of small amounts of episulfide monomer with the epoxide monomer prior to curing may provide an effective method for lowering gel times without reducing the crosslink density and its dependent physical properties.
The elastic potential function of slightly compressible rubberlike materials
Authors: Peng S. T. J. 
Published: April 2003

AbstractIn order to obtain an analytical expression for the stored energy function W of slightly compressible rubberlike materials, two recent results are used to obtain a unified expression

where Γi are a new set of invariants, and H(Γ1,Γ2) is the shear part of the stored energy function which is now assumed to be a separate symmetric function of the modified stretch ratio, λ = λi/I, i.e.,

Various analytical forms of h(λ) are proposed. Also, a straightforward transformation technique is formulated such that one can easily relate the stress‐strain relation in terms of modified stretch ratio λ to the new invariants Γi. Thus, by a combination of the above equations and the transformation technique, one may readily determine the elastic strain energy function of slightly compressible materials from careful measurements of the volume change in multiaxial deformations.