bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crystallinity and the effect of ionizing radiation in polyethylene. I. Crosslinking and the crystal core
Authors: Patel  , Keller  
Published: April 2003

AbstractAn extensive study has been carried out on the effect of ionizing radiation on polyethylene in the form of solution‐grown single crystals to follow up preceding investigations which had indicated that the radiation‐induced effects along the fold surfaces could be significantly different from those within the crystal interior. In this first part of the series, radiation‐induced crosslinking was investigated in the case of “crystal core” material. This material, obtained by removal of the fold surface by oxidative degradation with ozone, consists of isolated foldfree crystal layers of dicarboxylic acids of uniform length, the length itself depending on the fold length of the starting crystal. This “core material” was irradiated by γ rays and the effect of crosslinking was followed by GPC analysis by recording the development of dimer, trimer, etc., peaks in the chromatograms. For a given dose, the fractional amount of crosslinked material is independent of the chain length. This, together with other effects described, provides unambiguous evidence that crosslinking occurs at the chain ends or, in other words, that there is no crosslinking within the interior of the paraffinoid lattice. Further, no permanent scission was observed to occur within the lattice, at least in amounts detectable by the present molecular weight measurements. The obvious significance of these effects for radiation studies on paraffinoid substances in general, beyond those of the present long‐chain dicarboxylic acids, is discussed prior to utilizing them in the study of chain‐folded polyethylene crystals in the following parts of the series.
Crystallinity and the effect of ionizing radiation in polyethylene. II. Crosslinking in chain‐folded single crystals
Authors: Patel G. N. , Keller A. 
Published: April 2003

AbstractIn order to ascertain whether the crystal core of irradiated polyethylene single crystals is free from crosslinks—as would follow from the results of Part I—the fold surface of irradiated single crystals was shaved off with ozone and the resulting product examined by GPC for molecular weight. It was found that on ozone degradation the entire material, which had been insolubilized by radiation‐induced crosslinking, has become soluble hence became available for the GPC analysis. The chromatograms displayed the same peaked development with degradation as the unirradiated crystals leading eventually to single traverse dicarboxylic acids. This proves the absence of crosslinks within the crystal interior of the material as examined by GPC. The appearance of some additional low molecular weight material, is attributed to scission at the radiation‐induced double bonds due to ozone which eliminates the possibility of the existence of crosslinks within the lattice such as might provide scission sites for ozone. The conclusion could therefore be reached that, to the extent assessable by our GPC test, there are no radiation‐induced crosslinks within the crystal lattice, hence the crosslinks produced must be entirely confined to the fold surface region of the crystals.
Crystallinity and the effect of ionizing radiation in polyethylene. V. Distribution of trans‐vinylene and trans,trans conjugated double bonds in linear polyethylene
Authors: Patel G. N. 
Published: April 2003

AbstractFreeze‐dried chain folded single crystals and the single crystals without amorphous surface layers (crystalline cores) of different thicknesses of linear polyethylene were irradiated with 60Co γ‐rays up to 600 Mrad. Concentration of trans‐vinylene double bonds and conjugated diene produced during irradiation of the crystals was measured by infrared. Concentrations of trans‐vinylene and of the conjugated diene were independent of thickness of crystalline core which suggest that the double bonds wer randomly distributed in the crystalline parts of the crystals. Concentrations of trans‐vinylene and of conjugated double bonds were lower in chain‐folded crystals than in the crystalline cores and this suggests that the folds (amorphous surface layers) are less preferential sites for formation of the double bonds. The zero‐order growth and first‐order decay kinetics of trans‐vinylene double bonds was studied by the equation derived by Dole et al1. The equation is strictly obeyed up to 300 Mrad and the results then deviate. Since there is the decay of trans‐vinylene double bonds and though there are no crosslinks in the crystalline cores, it has been suggested that the decay of the double bond does not result in the crosslinks.
Dielectric and depolarization thermocurrent study of the γ relaxation in polyethylene isophthalamide
Authors: Lacabanne C. , Chatain D. , Guillet J. , Seytre G. , May J. F. 
Published: April 2003

AbstractThe depolarization thermocurrents (DTC) from polyethylene isophthalamide are studied below the glass‐transition temperature. The “entire” DTC spectrum is analyzed in terms of a continuous distribution of relaxation times; the corresponding distribution function is very close to that which fits data deduced from bridge measurements.The complex DTC spectrum can be experimentally resolved into single relaxation time processes. The analysis of each “elementary” DTC peak yields dielectric dispersion and relaxation time which allow one to calculate the frequency variation of the complex dielectric constant. The corresponding Cole–Cole plot is in good agreement with that deduced from studies of the “unresolved” γ relaxation.
Superstructure in segmented polyether–urethanes
Authors: Chang Yeong‐Jen Peter , Wilkes Garth L. 
Published: April 2003

AbstractThe morphology of several series of segmented polyether–urethanes was studied. The “hard” segments contained urethane and urea linkages formed by 4,4′‐dicyclohexylmethane diisocyanate (Hylene W) and selected aliphatic and aromatic monomeric diamines (DA). The “soft” segments were composed of oligomeric poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO), or both PEO and PPO. For studying the composition–morphology relationships, the molecular weight and relative content of PEO, and the relative content of PPO were varied systematically. Different diamines were used as chain extenders. The methods of wide‐angle x‐ray diffraction (WAXD), small‐angle x‐ray scattering (SAXS), polarizing microscopy, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) were employed in the investigation. The effects of PEO content on domain formation were very significant. Calculations based on a highly simplified model indicated that, for two adjacent molecules, if two hard segments are associated with each other, the probability for the association of the next two hard segments varies inversely with the third power of soft segment length. Copolymers composed of both POE and PPO displayed enhanced domain and anisotropic superstructure. The phenomenon was interpreted in terms of polymer incompatibility. The effects on morphology of different DA's as chain extenders were tentatively accounted for by the symmetry, hydrogen bonding, and rigidity of the hard segments as well as their incompatibility with the soft segments. The formation and deformation of superstructure were of particular interest. A model was proposed to account for the formation of the resultant anisotropic structure and mechanical properties.
Dynamics of macromolecular chains. II. Orientation relaxation generated by elementary three‐bond motions and notion of an independent kinetic segment
Authors: Valeur Bernard , Monnerie Lucien , Jarry Jean‐Pierre 
Published: April 2003

AbstractIn the preceding paper, general equations were established for the motions of chains confined to a tetrahedral lattice. In the present paper, bond orientation correlation and autocorrelation functions are explicitly calculated for the case where only three‐bond elementary motions are considered. Effects due to the chain end are analyzed and the relaxation time distribution function is established. The expressions obtained reflect the influence of the chain structure. Finally, to characterize the dynamic behavior of chains in orientation relaxation experiments, the notion of an independent kinetic segment is proposed.
The role of dislocations in the solid‐state polymerization of monomers having conjugated triple bonds: A study of 2,4‐hexadiyne‐1,6‐diol bis(p‐toluene sulfonate)
Authors: Schermann Walter , Wegner Gerhard , Williams John O. , Thomas John M. 
Published: April 2003

AbstractThe crystal structure of the monomer bis(p‐toluene sulfonate) ester of 2,4‐hexadiyne‐1,6‐diol (pT) is conducive from the viewpoint of both the separation distances and molecular configuration, to polymerization, irrespective of whether initiation is thermal, photochemical, or mechanical. The dislocations present in the monomer and polymer structures have been characterized by employing optical microscopic techniques. The slip system (102)[010] is found to be present in both monomer and polymer crystals but the (010)[001] system is found only in the monomer. On this basis a crystal structure for the monomer is proposed based on existing crystallographic information relating to the structure of the polymer. Dislocations are thought, on energetic grounds, to facilitate nucleation of product in the thermal polymerization but have no observable influence on the photoinduced reaction which proceeds homogeneously through the bulk.
Characterization of selectively degraded poly(ethylene terephthalate)
Authors: Duong D. T. , Bell J. P. 
Published: April 2003

AbstractTo investigate the morphology of unoriented poly(ethylene terephthalate) (PET) films and the selective character of the aminolysis of PET, 67% crystalline polymer samples were degraded with 40% aqueous methylamine at room temperature. The aminolyzed PET samples were subjected to gel permeation chromatography (GPC), viscometry, electron microscopy, and small‐angle x‐ray diffraction (SAXD). Weight loss and density crystallinity measurements were also made.After 24 hr of aminolysis, the amorphous regions and chain folds were completely removed. The long molecular chains in the semi‐crystalline polymer were reduced to monodisperse rods having a molecular weight of 1,800. The corresponding lamellar thickness was calculated to be 101 Å, consistent with the x‐ray diffraction and electron microscope (EM) measurements. The EM photographs of “stripped” crystals show the lamellar structure previously found for other selectively degraded polymeric materials. The weight of crystalline debris remaining was consistent with the initial crystallinity. After degradation the crystallinity as determined by density was 96%.
Crystal deformation in aromatic polyesters
Authors: Jakeways R. , Ward I. M. , Wilding M. A. , Hall I. H. , Desborough I. J. , Pass M. G. 
Published: April 2003

AbstractA study has been carried out of the changes in the x‐ray diffraction patterns which occur when oriented fibers or tapes of poly(trimethylene terephthalate) (3GT) and poly‐(tetramethylene terephthalate) (4GT) are subjected to mechanical tensile stress. Although the polymers show very different behavior in detail, in both cases comparatively large reversible lattice strains are observed (∼ several %). The diffraction pattern of 3GT changes monotonically with increasing macroscopic strain, suggesting that the lattice responds immediately to the applied stress, and deforms as though it were a coiled spring. In 4GT, on the other hand, there is no detectable change in the x‐ray diffraction pattern at low macroscopic strains, i.e., low values of the applied stress. At higher stresses, changes in the pattern occur which suggest a definite change in the crystal structure. Finally at the highest values of applied stress, the lattice deformations cease to increase. A preliminary discussion is presented of the relationship of these x‐ray diffraction results to the mechanical stress–strain behavior.
On the refractive indexes and birefringence of nylon 6 yarns as a function of draw ratio and strain
Authors: Gaur H. Angad , De Vries H. 
Published: April 2003

AbstractA systematic study of the dispersion curves of the refractive indexes of nylon 6 yarns was made. The parameters were the draw ratio and strain. The measurements show that the dispersions of the refractive indexes n∥ and n⊥, parallel and perpendicular to the fiber axis, are equal, independently of draw ratio and strain. The average dispersion equals nF − nC = 109 × 10−4. Consequently, the birefringence is, within experimental accuracy, independent of the wavelength. The refractive indexes and the birefringence show a change in trend at 10–12% strain. This point corresponds to the yield strain in the stress–strain diagrams. The inference is that beyond the yield point the overall molecular orientation must increase less strongly with strain than before. An analysis shows that the Lorentz–Lorenz relation holds for the average refractive index n̄ = ⅓ (n∥ + 2n⊥). So the change in n̄ versus draw ratio is mainly due to the change in density. By applying the Lorentz–Lorenz relation to the change of n̄ on straining, a value of Poisson's ratio (μ) could be derived. The average value found for nylon 6 yarns was μ = 0.48, which means that the density hardly changes with strain.
Laser light scattering studies of poly(L‐lysine HBr) in aqueous solutions
Authors: Lee W. I. , Schurr J. M. 
Published: April 2003

AbstractA simple theory for the relaxation of concentration fluctuations in polyelectrolyte solutions is presented, and particular results for the high‐salt and no‐salt limiting cases are discussed.Autocorrelation functions for the fluctuating intensity of scattered light from dilute aqueous solutions of poly(L‐lysine HBr) (PLL‐HBr) with and without added salt have been observed over a wide range of pH. The observed autocorrelation functions are in general very satisfactorily represented by single exponentials except at high pH (>10.5), where considerable aggregation is manifested. Solutions of PLL HBr without added salt exhibit extraordinary behavior, evident at low pH, involving a species with a very slowly decaying autocorrelation function. Though this species is readily annealed to a more ordinary individual free‐molecule form by cycling the pH to 9.5 or higher and back, the resulting molecules are found to require unusually long times to reach internal configuration equilibrium under low pH conditions. Solutions of PLL‐HBr in 0.2M NaBr and 0.1M NaCl are apparently free of similar extraordinary effects and show the normal isothermal helix–coil transition accompanied by a 15–30% rise in the diffusion coefficient to a maximum at pH 10.5, which is interpreted in terms of a change in molecular dimension of an interrupted helix.The predicted K2 dependence of the reciprocal relaxation time and enhancement of the apparent diffusion coefficient of the polyelectrolyte in the absence of salt is confirmed.
Mechanochemical reaction of polymers by ultrasonic irradiation. I. Mechanochemical reaction in mixtures of polystyrene, styrene, and cyclohexanone
Authors: Fujiwara Hideki , Okazaki Kazufumi , Goto Kunio 
Published: April 2003

AbstractMechanical degradation and mechanochemical polymerization in polystyrene–styrene–cyclohexanone mixtures have been studied by ultrasonic irradiation at 60°C. The number of fresh polymer chains after the degradation is 2 × 10−5 mole l−1 hr−1. The rate equations for mechanical scission and mechanochemical polymerization have been deduced. The rate equation for mechanical scission was found to be in agreement with the expression of a previous paper. In addition, the rate equation for mechanochemical polymerization is not essentially different from that for the general radical polymerization in the presence of solvents. The kinetic chain length for polymeric free radicals in the polymerization process has been calculated. The mechanochemical polymerization of styrene was initiated by only one of the two kinds of end radicals after mechanical scission of polystyrene. The molecular weight distributions of the samples after the degradation and the polymerization have been compared and discussed.
Transitions in poly(diethyl siloxane)
Authors: Beatty C. L. , Karasz F. E. 
Published: April 2003

AbstractAn adiabatic heat capacity study of poly(diethylsiloxane) confirms that it has a single glass transition occurring at 130°K, the lowest glass transition reported to date for a high molecular weight polymer. The two previously reported glass transitions are first‐order thermodynamic peaks whose location is dependent upon prior thermal history. Combination of these data with low‐temperature x‐ray diffraction indicates that the transitions in this temperature range are related to a crystal–crystal transformation. A crystal melting transition is observed near 270°K. In addition an anomalous rise in heat capacity near 60°K suggests a sub‐glass transition of unknown origin.
Application of holographic interferometric microscopy to the study of diffusion in the polyvinylpyrrolidone–iodine system
Authors: Cournoyer R. F. , Rhodes M. B. , Siggia S. 
Published: April 2003

AbstractInterferometric studies of the diffusion of molecular iodine into polyvinylpyrrolidone (PVP) are described. The diffusion process is observed by means of a holographic microscope which, with a camera, permits holograms to be recorded during the polymer–iodine interaction. The holograms are subsequently used to produce interferograms that monitor the diffusion process as a function of time. Measurements taken from the interferograms indicate that the diffusion mechanism is not purely Fickian and that the diffusing boundary of iodine is characteristic of case II diffusion. The interferograms yield values for average diffusion coefficients as a function of sample thicknesses that range from 2.32 to 9.53 × 10−10 cm2/sec.
Persistent polarization in poly(vinylidene fluoride). II. Piezoelectricity of poly(vinylidene fluoride) thermoelectrets
Authors: Murayama Naohiro , Oikawa Takao , Katto Takayuki , Nakamura Ken'ichi 
Published: April 2003

AbstractThe piezoelectricity of PVDF thermoelect rets formed with vacuum‐coated aluminum electrodes has been investigated in detail. The piezoelectricity depends on the β‐form crystal structure of PVDF homopolymer and copolymers. However, the piezoelectricity is not attributed to the stress dependence of the spontaneous polarization of β‐form crystals, but rather to the persistent polarization arising from trapped charges. The trapping mechanism is discussed.
Low‐temperature relaxations in styrene–crosslinked polyester networks
Authors: Cook W. D. , Delatycki O. 
Published: April 2003

AbstractTwo low‐temperature dynamic mechanical relaxations have been observed in networks formed by copolymerization of poly(1,2‐propylene fumarate) and poly(1,2‐propylene phthalate fumarate) with styrene. The γ relaxation which occurs around −100°C (1 Hz) is induced by small amounts of water, while the broad γ′ relaxation is reduced in height by the presence of water. Neither xylene nor 1,2‐propylene glycol induced a γ relaxation. The γ relaxation was ascribed to motions involving a fumarate ester group–water complex.
The effect of prior crystallinity on the flow‐induced crystallization of poly(ethylene oxide)
Authors: Theil Michael H. 
Published: April 2003

AbstractAfter flowing in a dilatometer bulb for a small fraction of the duration of the transformation, a relaxed melt of poly(ethylene oxide) (M̄n = (5.9 ± 0.1) × 103) showed marked increases in isothermal crystallization rate. The extent of increase was greater when flow was imposed at modestly later stages rather than at the earliest stage of a crystallization. Kinetic parameters for the flow‐induced crystallizations were obtained via modification of the conventional mathematical treatment of the kinetics of phase change, thereby allowing the analytical resolution of the overall process into flowinduced and quiescent components. Determination of the flow‐induced crystallization parameters required independent determination of the kinetic parameters for quiescent crystallizations at that temperature. The Avrami exponents nf which characterized the flow‐induced portions of the crystallizations were larger for those instances in which flow was imposed at the more advanced stages of the crystallizations, thus indicating a transition in crystallization mechanism. It is suggested that prior crystallinity present at the time of flow contributed to the crystallization by serving as a source of nucleation sites. However, in light of the experimental procedure employed, values of nf approximating 4 that were obtained are not susceptible to mechanistic interpretations now extant.
Infrared spectroscopic evidence of structural defects in the crystalline regions of trans‐1,4‐polychloroprene
Authors: Tabb D. L. , Koenig J. L. , Coleman M. M. 
Published: April 2003

AbstractInfrared spectra have been obtained for the crystalline regions of samples of predominantly trans‐1,4‐polychloroprenes polymerized at −20, 0, and 40°C. Spectral differences among the polychloroprenes are interpreted in terms of the increase in structural irregularities that occur as the polymerization temperature is increased. Results of this study indicate that crystallization occurs with random inclusion of these structural irregularities into the crystalline domains. The conclusion is supported by the spectra of the crystalline regions of a chloroprene copolymer containing known impurities in the form of 2,3‐dichloro‐2‐butenylene units in addition to the normal 2‐chloro‐2‐butenylene units.
Folded chain crystallization of poly(N‐vinylcarbazole)
Authors: Griffiths C. H. 
Published: April 2003

AbstractA study of the morphology of thermally induced crystallization in poly(N‐vinylcarbazole) has shown the formation of folded chain lamellae. Diffraction analysis of multiple and single lamellae indicates a paracrystalline structure with hexagonal symmetry about the chain axis and an interchain spacing of 12.00 Å. No sharp reflections due to chain axis periodicity were observed and the chain axis period was calculated from the crystalline density extrapolated to 100% crystallinity. This gave a chain axis period/monomer unit of 2.16 Å consistent with an isotactic 3/1 screw axis and a basic trigonal structure with a = 12.00 Å and c = 6.47 Å.
ESR evidence for main‐chain scission produced by mechanical fracture of polymers at low temperature
Authors: Sakaguchi Masato , Sohma Junkichi 
Published: April 2003

AbstractESR spectra have been observed from several polymers (polyethylene, polypropylene, polymethylmethacrylate, polytetrafluoroethylene, and polybutadiene) which were mechanically fractured in vacuum at 77°K. The spectra permit identification of the free radicals produced in chain scission. It has been demonstrated for the polymers of the typemagnified imagesuch as polypropylene and poly(methyl methacrylate), that the mechanical fracture produces two different scission radicals in pairs, namely,magnified imageThe results indicate convincingly that microscopic scission of polymer chains is caused by macroscopic destruction of polymeric material. The critical molecular size for mechanical rupture of polyethylene chains was experimentally determined to be a degree of polymerization between 70 and 100. This size agrees fairly well with the value predicted from a theoretical model.