bluuebunny/crossref_metadata_2025_split huggingface dataset:
The use of synchrotron radiation for study of structural changes in polymers during phase transition and deformation
Authors: Forgács P. , Sheromov M. A. , Tolochko B. P. , Mezentsev N. A. , Pindurin V. F. 
Published: April 2003

AbstractAn experimental method using monochromatized synchrotron radiation for a wide‐angle x‐ray scattering study of polymers during phase transition and deformation is described. Results obtained on low‐density and high‐density polyethylenes and on polypropylene are given. Melting processes could be studied conveniently by making exposures during a temperature scan; a few seconds were found sufficient to obtain a diffraction spectrum. This way relatively fast crystallization processes and the structural change accompanying stress relaxation could be followed easily. The crystalline‐amorphous ratio was found to decrease continuously much below the melting temperature measured dilatometrically and by DSC, implying that in the αc‐relaxation transition region of polyethylene and polypropylene a structural change takes place. At the initial state of crystallization the 040 reflection in polypropylene was found to be stronger than the 110 one, while after crystallization has been completed this ratio was inverted. Equatorial spectra made after rapid uniaxial stretching of polypropylene sheet were found to exhibit a slight time dependence demonstrating that orientation went on after stretching had been stopped.
Melting and crystallization of poly(ethylene terephthalate) under pressure
Authors: Siegmann A. , Harget P. J. 
Published: April 2003

AbstractA piston‐cylinder‐type high‐pressure dilatometer has been built and the effect of pressure on melting behavior of poly(ethylene terephthalate) (PET) has been studied. The melting temperature increases but the rate of change of the melting temperature decreases with increasing pressure. Poly(ethylene terephthalate) crystallized from the melt at elevated pressure and temperature was studied by thermal analysis, and wide‐angle and small‐angle x‐ray diffraction and electron microscopy. Chain‐extended PET crystals were observed for the first time and some of their properties are described. A similarity to extended‐chain polyethylene is suggested.
Abrupt dissolution of polydiacetylenes
Authors: Patel G. N. , Khanna Y. P. 
Published: April 2003

AbstractPolydiacetylenes, where R(CH2)3,4OCONHCH2COO(CH2)1,3CH3 dissolve almost instantaneously within a narrow range of temperature (ca. 3°C). The enthalpy of dissolution of these polymers is determined by differential scanning calorimetry to be 25–46kJ/mole of the repeat unit. The abruptness of dissolution is due to breaking of intramolecular H bonds, which appears to be a cooperative phenomenon. Supporting infrared evidence is cited.
Conformational energies of para‐aromatic and aryl‐aliphatic polyamides: Relation to mesogenic character in solution
Authors: Lauprêtre F. , Monnerie L. , Fayolle B. 
Published: April 2003

AbstractPCILO conformational calculations have been carried out on several model compounds of aromatic polyamide oxamides and polyamide hydrazides. The comparison of the entropy of the equilibrium conformations allows a classification of the various constitutive units into “rigid” segments, and “flexible” ones having respectively low or high entropies. From the results, it is possible to predict the mesogenic nature of solutions of a large number of aromatic polyamides, polyamide hydrazides, and polyamide oxamides.
Poling‐time dependence of the field‐induced phase transition and piezoelectric response of poly(vinylidene fluoride) films
Authors: Scheinbeim J. I. , Yoon C. H. , Pae K. D. , Newman B. A. 
Published: April 2003

AbstractWe have examined the poling time dependence of the field‐induced phase transition (from phase II to polar phase II) of biaxially oriented poly(vinylidene fluoride) films by x‐ray methods. These results were compared with the poling‐time dependence of the piezoelectric response (d31 and e31) determined using a piezotron Model U (Toyo Seiki, Tokyo). The piezoelectric response shows an initial rapid increase with poling time followed by a slow increase as the poling time increases. The x‐ray results show that the field‐induced phase transition is time dependent, and occurs first for those crystallites with their a axes perpendicular to the film surface. Crystallites with a in the plane of the film transform at a much slower rate. The data indicate that the poling time dependence of d31 and e31 (and, presumably, film polarization) are dependent on the transition rates.
Longitudinal acoustic mode in linear aliphatic polyesters
Authors: Wang Y. K. , Shu P. H. C. , Stein R. S. , Hsu S. L. , Kanamoto T. 
Published: April 2003

AbstractThe longitudinal acoustic mode has been observed in a series of linear aliphatic polyesters. In some cases, the vibrational frequencies observed do not strictly obey the expected inverse chain‐length relationship. Both the periodicity measured in small‐angle x‐ray diffraction and the chain length deduced from Raman spectroscopy are highly dependent on thermal history.
Diffusion in a multicomponent inhomogeneous multiphase system with moving boundaries. II. Increasing or decreasing volume (swelling or drying)
Authors: Rudolph F. B. 
Published: April 2003

AbstractThe mathematical solution of the following problem is given. Simultaneously with diffusion‐controlled mixing of two phases (e.g., gel formation), a third substance diffuses from one of the two pure phases into the other and through the inhomogeneous mixing phase which expands at a rate proportional to the square root of the time. The phases may change their volumes.
Transient decay studies of photophysical process in aromatic polymers. I. Multiexponential fluorescence decays in copolymers of 1‐vinylnaphthalene and methyl methacrylate
Authors: Phillips D. , Roberts A. J. , Soutar I. 
Published: April 2003

AbstractThe considerable potential of high resolution time‐resolved spectroscopic data for copolymer systems in elucidation of the intramolecular photophysical processes which occur in polymer systems is illustrated. Such information can not be gleaned solely from studies of homopolymers. Kinetic data and time resolved fluorescence spectra of copolymers of 1‐vinylnaphthalene and methyl methacrylate indicate that conventional kinetic schemes are inappropriate for the discription of excimer formation in 1‐vinylnaphthalene polymers. Evidence is presented for the presence of an emitting species in addition to the expected monomeric and excimeric forms. The nature of this third species is discussed and photophysical kinetic schemes are proposed to describe intramolecular excimer formation in such systems. Kinetic data have been derived for the principle deactivation pathways through investigation of the observed fluorescence decays upon the intrachain concentration of aromatic species.
Distortion of crystallites caused by heterogeneous chlorosulfonation of polyethylene
Authors: Bikson B. , Jagur‐Grodzinski J. , Vofsi D. 
Published: April 2003

AbstractThe effect of a heterogeneous chlorosulfonation on the crystalline regions of high‐density polyethylenes are investigated by x‐ray diffraction, differential scanning calorimetry, and infrared spectroscopy. The observed changes and their time dependence are discussed in terms of distortion of the crystallites, which is followed by relaxation processes leading to the elimination of the initially induced imperfections.
Anisotropy of NMR relaxation, and diffusion, of penetrants in stretched cis‐polyisoprene
Authors: von Meerwall E. , Ferguson R. D. 
Published: April 2003

AbstractWe have measured 1H and 19F NMR relaxation times T1, T1ρ, and T2, and diffusion constants, in trace penetrants hexafluorobenzene and n‐hexadecane dissolved in stretched cis‐polyisoprene, as function of temperature, rubber elongation, and angle with respect to the stretch direction. Values of T1 and T2 in the rubber were also measured. At all temperatures (—40 ≤ T ≤ 85°C), T1 in rubber and penetrants is isotropic and independent of elongation; the differences between rubber and penetrants are related to penetrant diffusion. All T2 above—15°C are anisotropic and elongation dependent, and follow a motional narrowing model. For the penetrants, averaging the dipolar interactions implies averaging over a diffusion path; this correctly reproduces the observed much higher T2 anisotropy in the penetrants. Penetrant diffusion rates, however, are essentially isotropic and elongation independent. These effects depend only weakly on the shape of the penetrant molecules.
Five‐line model for the description of radial x‐ray diffractometer scans of nylon 6 yarns
Authors: Heuvel H. M. , Huisman R. 
Published: April 2003

AbstractTypes of nylon 6 yarn which contain large γ crystals cannot be described by a model comprising three Pearson VII curves, as we formerly proposed. Hence, a new extended computer program has been developed containing five Pearson VII lines. Two lines are related to the α phase, two to γ‐phase crystals, and the fifth describes the amorphous contribution. Some physical relations between parameters could be derived and were incorporated into the computer program. This program provides extremely good fits to all equatorial diffractometer scans which can be obtained from nylon 6 yarns, including those containing large γ crystals. The parameter accuracy is quite satisfactory for diffractometer traces with well‐resolved peaks from both α and γ crystals. However, if the traces are poorly resolved or the samples do not contain a sufficient amount of the γ modification, resulting in a lack of detailed information, the parameter accuracy can be rather poor. For those cases special versions of the computer program were developed which contain further empirical interrelations between parameters. With these programs crystal sizes and molecular distances within the crystals of both the α and β modifications can be determined. The method has also been applied to radial scans at various small azimuthal angles with respect to the equator. In that way the relative amounts of the α and γ crystals as well as their orientation factors could be determined. Various aspects of this investigation are illustrated by some examples.
Characterization of Ziegler–Natta catalyst by ESCA
Authors: Furuta Motonobu 
Published: April 2003

AbstractThe surface composition of TiCl3‐based Ziegler—Natta catalysts prepared by various methods was analyzed by ESCA to correlate the total amount of surface titanium with the catalyst activity in propylene polymerization. The ESCA peak ratio (Ti 2P3/2/Cl 2P) of the catalysts was measured to estimate the surface composition. The titanium index defined as the product of the (Ti/Cl peak ratio and surface area) was closely correlated with the catalyst activity in polymerization. This indicates that surface titanium concentration and surface area determine the catalyst activity. It was also found that removal of surface aluminum and chlorine at the catalyst preparation stage results in concentration of titanium at the surface and an increase in surface area.
Dielectric relaxation phenomena in a series of polyhydroxyether copolymers of bisphenol‐A—endcapped polyethylene glycol with epichlorohydrin
Authors: Pochan J. M. , Gruber R. J. , Pochan D. F. 
Published: April 2003

AbstractDielectric relaxation spectra of a series of polyhydroxyether copolymers have been obtained. It has been shown that the systems exhibit very similar relaxation spectra with the α(Tg) process a function of molecular weight. All systems exhibit two secondary relaxations: β (ca. 240 K) and γ (ca. 180 K). These have been assigned as hydroxyl motion and main‐chain motion, respectively. The peak positions are not functions of composition in the ranges studied. The effect of sorbed water on the relaxation spectra is discussed.
Dielectric loss of polyethylene at very low temperatures in the frequency range from 1 kHz to 100 MHz
Authors: Yano Okimichi , Saito Susumu , Sato Yoshio , Takeda Toshifumi , Tanaka Atsushi , Wada Yasaku 
Published: April 2003

AbstractThe dielectric loss of high‐density polyethylene was measured from 1 kHz to 100 MHz with the improved calorimetric method at liquid‐helium temperature for samples with different oxidation times t. Two loss peaks, centered at ca. 4 kHz and at 1 MHz, both increase in height with increasing t. On the bases of these results along with previously reported ones, the low‐frequency and high‐frequency losses are ascribed to the tunneling of protons of OH groups in crystalline and amorphous regions, respectively.
Molecular dynamics and rheological properties of concentrated solutions of rodlike polymers in isotropic and liquid crystalline phases
Authors: Doi Masao 
Published: April 2003

AbstractA molecular theory is presented for the dynamics of rodlike polymers in concentrated solutions. The theory describes the rotational motion of rods in both the isotropic phase and the liquid crystalline phase. Combined with the molecular expression of the stress tensor, it also gives a unified rheological constitutive equation which predicts the nonlinear viscoelasticity in both phases. As an illustrative example, the steady‐state viscosity η at zero‐shear‐rate is calculated. The predicted dependence of η on molecular weight and concentration agrees fairly well with experiments.
Crazing in two polystyrene/polybutadiene block copolymers
Authors: Argon A. S. , Cohen R. E. , Jang B. Z. , Sande J. B. Vander 
Published: April 2003

AbstractCrazing was investigated in two commercial polystyrene/polybutadiene block copolymers made by the Phillips Petroleum Co. and marketed under the trade names of KRO‐1 and KRO‐3 resins. The two block copolymers each with 23% polybutadiene (PB), have radically different microstructure and radically different crazing behavior, leading to strains to fracture of 0.1 and 1.0, respectively. Of these, the KRO‐1 Resin has a phase microstructure that consists of randomly wavy and often interconnected rods of PB of 20 nm diameter surrounded by polystyrene (PS). The microstructure of KRO‐3 Resin consists of lamellae of PB with 20 nm thickness and large aspect ratio which range in packing from regular aligned lamellar domains with randomly varying misorientation in the annealed material, to randomly corrugated and wavy sheets in the as‐received material. Crazes in KRO‐1 Resin have well delineated planar shapes with a conventional, tufty craze matter structure which suggests growth by the now well‐established meniscus instability mechanism proposed by one of us. In KRO‐3 Resin, on the other hand, crazing involves profuse cavitation if the PB lamellae, giving rise to less well delineated zones of cavitational growth dispersed over the volume and suggests a mechanism of craze growth by stable, interfacial cavitational degradation in a process zone ahead of the craze tip. The measured stress and temperature dependences of craze velocities in these two polymers is in partial support of the suggested mechanisms which are also developed in outline.
Measurements of light scattering changes induced by a strong optical field in solutions of tRNA
Authors: Dobek A. 
Published: April 2003

AbstractChanges in light scattering induced by a strong laser beam, as predicted theoretically by Kielich, were measured for unfractionated yeast transfer ribonucleic acid (tRNA) solutions. The vertically polarized electric field of a strong laser pulse (λ = 1060nm) amounted to 4.5 × 103 esu cgs; its duration was 10 nsec. A weak incident laser beam (λ = 630nm) was also polarized vertically and the vertical and horizontal intensity components of the light scattered through 90° at the latter wavelength were measured. These measurements together with previous results from measurements of Rayleigh light scattering and light scattering in a magnetic field permitted evaluation of the tensor of third‐order polarizability (c = 3 × 10−30 esu cgs, c = −373 × 10−30 esu cgs) and the anisotropy of the third‐order polarizability components with its sign (δc = +56 × 10−2, δc = +0.25 × 10−2 for tRNA monomer and aggregate, respectively). The new method described may be useful for studies of macromolecules and macromolecular complexes of biological importance.
Rigid‐backbone polymers. XVIII. Strictly alternating rigid‐flexible polyamides
Authors: Aharoni Shaul M. 
Published: April 2003

AbstractIt is shown that in strictly alternating rigid‐flexible copolyamides with the axial ratio x of their rigid elements between 3 and 3.5, lyotropic liquid crystallinity exists in solutions of 25–40% poiymer. For polymers having 4.0 < x < 4.5, anisotropic solutions appear in the concentration range 15–25%. These axial ratios are substantially smaller than the value of xc = 6.4 predicted by theories for independent rodlike particles, but are in qualitative agreement with recent theoretical calculations taking cognizance of the connection of rodlike elements by flexible residues in the polymer chain. It is further shown that solid solutions of a model compound in an alternating rigid‐flexible polymer may be prepared, provided there exists shape and size similarity between the model compound and the polymeric repeat unit.
Structure and morphology of heavily deformed single crystals of a polydiacetylene. I. Electron microscopy and x‐ray diffraction
Authors: Young R. J. , Read R. T. , Batchelder D. N. , Bloor D. 
Published: April 2003

AbstractThe structure and morphology of heavily deformed single crystals of a diacetylene polymer have been studied using a combination of x‐ray diffraction and electron microscopy. Crystals have been deformed by both rolling and hammering. The crystals remain intact during deformation and can be reduced in thickness by a factor of over 5 in directions perpendicular to their chain axes. It is found that the chain orientation is maintained during both hammering and rolling. A greenish‐colored surface skin develops during both types of deformation but the structure of the interior of the crystals depends upon the type of deformation employed. The interior of the hammered crystals consists of crystal blocks ca. 50 μm thick formed by cleavage perpendicular to the chain direction whereas the rolled crystals tend to be fibrous with no evidence of molecular fracture. The possible deformation mechanisms which have given rise to the different structures have been discussed.
Sorption of organic vapors by polystyrene
Authors: Saeki S. , Holste J. C. , Bonner D. C. 
Published: April 2003

AbstractActivity coefficients of benzene, toluene, cyclohexane, carbon tetrachloride, chloroform, and dichloromethane in binary solutions with polystyrene at 23.5°C have been determined using a piezo‐electric sorption apparatus. The investigated solvent concentration ranges were 15 to 39 wt % for benzene, 14 to 29 wt % for toluene, 15 to 28 wt % for cyclohexane, 26 to 38 wt % for carbon tetrachloride, 24 to 46 wt % for chloroform, and 21 to 41 wt % for dichloromethane. The polystyrene (weight‐averaged) molecular weights were 1.1 × 105 and 6.0 × 105 g/gmole. The weight‐fraction activity coefficients (Ω1 = a1/w1) of cyclohexane, toluene, and carbon tetrachloride in polystyrene solutions determined in this work agree within experimental error with previously published values determined by measurement of vapor pressure lowering and vapor absorption by thin films. We find disagreement, at low solvent concentrations, between our results for benzene and chloroform and previously published results. We have analyzed our results using Flory's version of corresponding‐states polymer solution theory. The theory can account, qualitatively, for the cyclohexane and carbon tetrachloride results. It cannot account for the toluene, benzene, dichloromethane, or chloroform results.
Spectroscopic studies of solutions, suspensions, and precipitates of poly(1,6‐di‐p‐toluene sulfonyloxy‐2,4‐hexadiyne)
Authors: Bloor D. , Batchelder D. N. , Ando D. J. , Read R. T. , Young R. J. 
Published: April 2003

AbstractOptical‐absorption, fluorescence, and Raman spectra for solutions, suspensions, and precipitates of poly(1,6‐di‐p‐toluene sulfonoxy‐2,4‐hexadiyne) in and from nitrobenzene, acetone, and chloroform are presented. These are interpreted in terms of the occurrence of two forms of the polymer chain; a quasicrystalline form with properties close to those of single crystal polymer and a chain‐extended form occurring in solution and colloidal particles, with an absorption energy of about 2.5 eV (20,000 cm−1). No evidence is found for the presence of very short polymer chains in partially polymerized monomer at low conversion. The relationship of these results to those for deformed single crystals is briefly discussed.
Laser Raman spectroscopy of polyacrylamide
Authors: Gupta Manoj K. , Bansil Rama 
Published: April 2003

AbstractThe Raman spectra of polyacrylamide and its covalently crosslinked gel (with N,N′‐methylenebis‐acrylamide as the crosslinking agent) in the region of 200–3600 cm−1 are discussed. The vibrational band assignments for polyacrylamide are made on the basis of a comparison with the spectra of acrylamide, acrylic acid, polyacrylic acid, poly(vinyl alcohol), and other vinyl polymers. The Raman spectra of polyacrylamide in the solid phase and in aqueous solution have similar spectral features. The Raman spectra of gels with low crosslink content and of polyacrylamide in aqueous solution are comparable except that one new band, predominantly due to the residual monomer, appears in the gel phase. An analysis based on polarized Raman, infrared and NMR spectra, model building, and group theoretical calculations suggests a structure dominated by isotactic species.
Heterogeneous reactions of polyethylene. II. Distortion of crystallites due to chlorination
Authors: Bikson B. , Jagur‐Grodzinski J. , Vofsi D. 
Published: April 2003

AbstractThe effect of heterogeneous chlorination of high‐density polyethylene on its crystalline regions was investigated by NMR, x‐ray diffraction, differential scanning calorimetry, and infrared spectroscopy. Crystallites remained inaccessible to attack by chlorine, even after extensive chlorination, however, their perfection was affected by extensive chlorination of the adjacent amorphous regions.
Measurements of infrared frequency shifts in stressed polymers
Authors: Wool R. P. 
Published: April 2003

AbstractA difference‐spectrum method is used to measure vibrational frequency shifts in mechanically stressed polymers. It is shown that the peak‐to‐peak height of the difference‐spectrum intensity profile is a linear function of small frequency shifts with a slope inversely proportional to the band halfwidth for Lorentzian or Gaussian bands. The method is applied to measure frequency shifts in uniaxially stressed ultraoriented isotactic polypropylene films, using a double beam infrared grating dispersion spectrometer with a nonstressed sample in the reference beam. It is shown that frequency shifts can be measured with an accuracy of better than 0.01 cm−1 using the difference‐spectrum method.
Cellulose–hydrazine complexes
Authors: Lee David M. , Blackwell John 
Published: April 2003

AbstractCellulose–hydrazine complexes have been prepared by soaking cellulose fibers in anhydrous hydrazine, and their structures have been investigated by x‐ray diffraction. The unit cells for the complexes formed by native ramie (cellulose I) and by Mercerized ramie and Fortisan (both cellulose II) have different dimensions, but all contain sections of four chains; and the x‐ray patterns suggest significant changes in the chain stagger, as compared with the uncomplexed structures. The differences between the Mercerized ramie and Fortisan complexes may reflect the differences in morphology and crystallinity of these materials. Reconversion to cellulose is effected by soaking in water. For the cellulose II complexes a hydrate intermediate is observed in this process. The hydrate is a two‐chain unit cell and contains approximately one water molecule per glucose residue.