bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rough‐surface crystallization: Some applications to poly(ethylene oxide)
Authors: Sadler D. M. 
Published: April 2003

AbstractA model incorporating a rough (disordered) crystal growth surface is capable of treating many of the observations and measurements on the crystal growth of short chains of poly(ethylene oxide) from the melt. A simple preliminary treatment if presented which aims primarily to analyze the growth rate data within one growth “branch,” i.e., for a regime in which crystal thickness is approximately constant. Under these conditions the growth rate is approximately linear with crystallization temperature, as expected for rough growth surfaces, but not for smooth (faceted) ones. Simulation results are included which are in agreement with a simple equation and with experiment. The analysis enables the growth rates for different branches to be compared in a systematic way. A very steep decrease in growth rate with increasing crystal thickness is clearly illustrated, together with some influence of molecular weight. The general trend for chain folding can be seen as a consequence of this steep decrease. Parallel work on systems in which crystal thicknesses vary continuously with crystallization temperature led to the realization that “rounding off” will occur at the crystal perimeter and that this will give rise to an entropic barrier for the crystal advance. This argument is presented in the context of extended‐chain and once‐folded crystallization, from which it is clear that growth rates should be much lower as crystal thicknesses increase, and for folded‐chain as compared with extended‐chain crystals. Different morphologies are interpreted in terms of changes in surface structure which are probably due to kinetic as well as equilibrium effects.
Wetting properties of polyacetylene films
Authors: Schonhorn H. , Baker G. L. , Bates F. S. 
Published: April 2003

AbstractThe wetting characteristics of free‐standing polyacetylene films were determined by using a standard series of wetting liquids. As‐prepared films of cis‐polyacetylene were found to contain a significant polar contribution to the surface free energy, which became nearly entirely dispersive upon thermal isomerization to the trans form. Both isomeric forms are characterized by a critical surface tension of wetting γc ≈ 51 mN/m, which is considerably higher than that normally obtained from organic polymers. These results have been interpreted with respect to surface oxidation and tested by examining an oxidized film.
Crystallization behavior of poly(3,3‐bisethoxymethyl oxetane) and poly(3,3‐bisazidomethyl oxetane)
Authors: Hardenstine K. E. , Henderson G. V. S. , Sperling L. H. , Murphy C. J. , Manser G. E. 
Published: April 2003

AbstractTwo crystal modifications have been found for poly(3,3‐bisethoxymethyl oxetane) [poly‐ (BEMO)] by wide‐angle x‐ray powder diffraction and differential scanning calorimetry, while only one modification has been found for poly(3,3‐bisazidomethyl oxetane) [poly(BAMO)]. Melting temperatures for the two polymers were nearly the same, varying from about 70 to about 90°C depending on the thermal treatment; higher crystallization temperatures resulted in higher melting temperatures. The equilibrium melting temperature T was found to be 125 and 128°C for poly(BEMO) and poly(BAMO), respectively, by using the Hoffman‐Weeks extrapolation procedure. Measurement of the melting‐point depression of Poly(BEMO) and poly(BAMO) in dibutyl phthalate yielded enthalpy of fusion values of 2.25 and 12.8 kcal/mol, respectively. The percent crystallinity for poly(BEMO) and poly(BAMO), respectively, was calculated to be 55‐60 and 13‐30% based on DSC and x‐ray analysis.
The superposition of small deformations on large deformations: Measurements of the incremental relaxation modulus for a polyisobutylene solution
Authors: McKenna G. B. , Zapas L. J. 
Published: April 2003

AbstractThe incremental relaxation modulus ΔG(t) for a concentrated solution of polyisobutylene has been determined from step‐shear experiments in which a small deformation Δγ was superimposed on a large deformation γ1; ΔG(t) was found to decrease with increasing γ1 and to increase with the time te after the imposition of the large deformation. It was also observed that the “apparent relaxation specturm” associated with δG(t) narrows and shifts to shorter times when compared to the spectrum associated with the linear viscoelastic relaxation modulus G(t). The results are well described by the nonlinear constitutive equation of the BKZ elastic fluid theory.
Study of spin–lattice relaxation and local motion in dissolved poly[2,2‐propanediylbis(3,5‐dimethyl‐4, hydroxyphenyl)carbonate]
Authors: Roy Ajoy K. , Jones Alan Anthony 
Published: April 2003

AbstractProton and carbon‐13 spin–lattice relaxation times are reported for 10‐wt % solutions of tetramethyl bisphenol‐A polycarbonate. The relaxation times for both nuclei were measured at two Larmor frequencies and as a function of temperature. These relaxation times are interpreted in terms of three motions: segmental motion, restricted rotational diffusion, and backbone methyl‐group rotation. The Hall–Helfand correlation function is used to describe the segmental motion. Internal rotation is described by the usual Woessner approach and restricted anisotropic rotational diffusion by the Gronski approach. As demonstrated by its higher activation energy, correlated segmental motion appears to be slower than the unsubstituted polycarbonate of BPA. In addition, the single‐transition processes seem to be still less important than correlated backbone transitions. Phenylene‐group rotation is described in terms of restricted rotational diffusion instead of complete anisotropic rotation. The time scale for backbone methyl‐group rotation is comparable to that in BPA, a fact indicative of weaker cooperativity between this motion and the other motions. Rotation of the methyl group attached to the phenylene ring is too fast to significantly contribute to relaxation except by partially averaging the dipole–dipole interactions. The higher activation energies for segmental motion observed in solution for this methyl‐substituted polycarbonate relative to the unsubstituted polycarbonate parallel a significant increase in the glass transition temperature observed for the substituted material. The restricted pheylene‐group rotation in solution is also parallelled by a large upward shift of the low‐temperature loss peak in the glassy polymer.
The role of molecular diffusion in the adhesion of EPDM and EPR elastomers
Authors: Ellul M. D. , Gent A. N. 
Published: April 2003

AbstractAdhesion of lightly crosslinked sheets of EPDM (ethylene–propylene–diene terpolymer) to themselves and to a Mylar substrate has been investigated over wide ranges of peel rate and test temperature. The effect of incorporating ethylene–propylene copolymer (EPR) before crosslinking, to yield a loose macromolecular network containing dissolved linear EPR macromolecules, was also studied. The self‐adhesion of these materials was found to be much greater than their adhesion to Mylar, over a wide range of effective peel rates. This is attributed to interdiffusion of EPR and EPDM molecular strands. At extremely low peel rates the enhancement of adhesion was smaller, probably because of back‐diffusion, and at high rates, the strength of adhesion became high in all cases. These results are compared to those obtained previously for polyisobutylene‐co‐ isoprene networks containing linear polyisobutylene molecules. The enhancement of self‐adhesion at intermediate rates of peel was considerably greater for the EPDM‐based materials, probably because of a lower degree of crosslinking and a greater tendency to form molecular entanglements.
A SAXS study of a single crack and craze in plasticized polystyrene
Authors: Brown H. R. , Mills P. J. , Kramer E. J. 
Published: April 2003

AbstractSmall‐angle x‐ray scattering (SAXS) was used to study the structure along a single craze that had broken down to form a crack along part of its length. This study was made possible by use of radiation from the synchrotron source CHESS which is sufficiently intense to permit examination of just a single craze. The total scattering from the craze was in excellent agreement with that expected from a knowledge of its dimensions and fibril volume fraction and width. This fact adds confidence to the interpretation of the scattering pattern of the craze as part diffraction, part reflection, and demonstrates that SAXS is a technique that may be used to measure craze volume within a sample. The craze was shown to grow in width by surface drawing with a constant structure, and then the fibrils broke to form a crack. The broken fibrils contracted and their diameters increased but they appeared to stay parallel with a constant fibril‐axis radial distribution function.
The structure of MDI/BDO‐based polyurethanes: Diffraction studies on model compounds and oriented thin films
Authors: Briber Robert M. , Thomas Edwin L. 
Published: April 2003

AbstractPolyurethanes based on MDI/BDO are known to crystallize in three distinct forms. Two of these crystal structures, type II and type III, have been characterized by electron and x‐ray diffraction experiments on model compounds and oriented thin films of a 77% hard‐segment polyurethane elastomer. The model compounds were of the form BDO(MDI/BDO)n with n = 1, 2, 3. Results from the model compounds indicate that the MDI/BDO repeat crystallizes in the type‐II structure, which has a contracted conformation with a monomer repeat length of 1.70 nm. MDI/BDO‐based polyurethanes also exhibit the type‐II structure under quiescent crystallization conditions. Studies of oriented thin films of an MDI/BDO‐based polyurethane indicate that a change in crystal form occurs on stretching to the fully extended monomer conformation. This crystal form is termed type III and has a monomer repeat length of 1.92 nm.
Thermal and mechanical properties of short‐segment block copolyesters and copolyether–esters
Authors: Castles Janis L. , Vallance Michael A. , McKenna J. Michael , Cooper Stuart L. 
Published: April 2003

AbstractThe effects of chain structure and processing variables on the microstructure and linear viscoelastic behavior of a series of copolyether–ester block polymers are described. In addition, the random copolyester analogs of the hard block are examined. The ester segments are composed of two isomers, poly(tetramethylene terephthalate) (PTMT) and poly(tetramethylene isophthalate) (PTMI), which possess significantly different crystallization kinetics. The ratio of PTMT to PTMI in the series has been systematically varied to alter the crystallizability without changing the chemical composition. The results of differential scanning calorimetry, wide‐angle x‐ray diffraction, and dynamic mechanical characterization are presented. Copolymerization of a second ester shortens the average sequence length of the first ester, resulting in melting‐point depression for crystals of the first polyester and substantial lowering of the dynamic mechanical storage modulus above the glass transition of the intercrystalline phase. The melting‐point depression may be predicted by using Flory's model for random copolymers, but the calculated heats of fusion are significantly lower than those obtained from diluent melting‐point depression.
Relation of internal rotational isomerism barriers to the flow activation energy of entangled polymer melts in the high‐temperature Arrhenius region
Authors: Ngai K. L. , Plazek D. J. 
Published: April 2003

AbstractA strong correlation between internal rotational isomerism barriers and the flow activation energy of entangled polymer melts in the high‐temperature Arrhenius region is observed. This correlation is predicted by a coupling model but is not expected by any other model that we are aware of.
Polymerization of furil in the solid state by reaction with AsF5 at the solid–gas interface
Authors: Burzynski Ryszard , Prasad Paras N. 
Published: April 2003

AbstractSolid‐state polymerization of furil, induced by reaction with AsF5 at the solid–gas interface, has been investigated by means of vibrational analysis of the reactant and the product. Infrared spectra are consistent with the mode of Polymerization which involves an α,α′ linkage and subsequent loss of hydrogen atoms. The C/H elemental analysis suggests that the polymer consists of around six or seven monomeric units. The reaction product is found to be unstable at high temperatures; a prolonged annealing at this temperature leads to a different structure, possibly, by the opening of the furan rings. The x‐ray powder diffraction study shows that the polymeric furil is crystalline, with a lattice similar to that of the monomer, but contains a considerable amount of disorder.
Spectroscopic studies of polymerized surfactants: 1,2‐bis(10,12‐tricosadiynoyl)‐sn‐glycero‐3‐phosphocholine
Authors: Schoen Paul E. , Yager Paul 
Published: April 2003

AbstractSpectroscopic studies have been performed on aqueous dispersions of the surfactant 1,2‐bis(10,12‐tricosadiynoyl)‐sn‐glycero‐3‐phosphocholine before and after polymerization with ul‐traviolet light. Monomers of this lipid can, under certain conditions, convert from the expected spherical liposomal form to a unique phase consisting of hollow tubules. To determine the molecular conformation of these structures we have used Raman and infrared spectroscopies to probe the structure of the hydrocarbon chains and head groups of the lipids, and used absorption spectroscopy and resonance enhanced Raman scattering of the colored polymer to monitor the length and structure of the diacetylenic polymer backbone. Unusual CH stretch‐ing Raman bands imply that the hydrocarbon chain packing in the monomeric bilayers is different from that observed in other phosphatidylcholines, and that a distrubance in alkyl chain packing occurs on polymerization. Depending on irradiation conditions and the dispersal state of the lipid the polymer chains may be of at least three different colors, from which distinct resonance Raman spectra are obtained. The effective bond conjugation lengths range from quite short in the yellow polymer produced in sonicated vesicles to extremely long in a blue component seen in polymerized tubules.
Cyclization of methacrylate–functional silane on particulate clay
Authors: Ishida Hatsuo , Miller James D. 
Published: April 2003

AbstractPhysically absorbed γ‐methacryloxypropyltrimethoxysilane (γ‐MPS) deposited from aqueous alcohol on particulate clay exists as low‐molecular‐weight cyclic, caged polysilsesquioxanes. These structures are incapable of forming high‐molecular‐weight chains or networks because of this internal cyclization tendency. The behavior is extremely different from that found in bulk solutions or when organofunctional silanes are adsorbed on low‐surface‐area glass or metal substrates. Fourier‐transform infrared spectroscopy and gel permeation chromatography were used to characterize the silane species deposited in bulk and on the surface of particulate clay. The cyclization tendency is postulated from analysis of the behavior of hydrolyzed γ‐methacryloxypropyltrimethoxysilane upon cocondensation with other organofunctional silanes and under variable cure conditions.
Application of a new structural theory to polymers. I. Uniaxial stress in crosslinked rubbers
Authors: Lee Michael C. H. , Williams Michael C. 
Published: April 2003

AbstractA continuum rheological theory, endowed with generalized structural significance, has recently been developed. Based on nonequilibrium thermodynamics, it relates stress σ, strain rate \documentclass{article}\pagestyle{empty}\begin{document}$\dot \varepsilon$\end{document} and temperature in terms of material evolution through a series of structural states. The theory has previously had success in dealing with crystalline metals and surface physics, and here it is applied to crosslinked rubbery polymers in the nominally amorphous condition. Structure is believed to be related to interchain associations, chain entanglements, chain ends, and other defects in the hypothetical ideal network which by itself would lead to neo‐Hookean predictions in uniaxial deformation, σnH ∝ λ2 — λ−1, where λ is the stretch ratio. Predictions are made for σ(λ) in both tension and compression and shown to be more compatible with data than either σnH(λ) or the Mooney—Rivlin expression σMR(λ). Only two parameters are required, moduli Go (reflecting initial structure) and Gs (the steady‐state condition), and rate effects are incorporated through Go(\documentclass{article}\pagestyle{empty}\begin{document}$\dot \varepsilon$\end{document}) and Gs(\documentclass{article}\pagestyle{empty}\begin{document}$\dot \varepsilon$\end{document}). The phenomena of yielding and stress softening in cyclic tensile loading are also predicted, suggesting advantages to this approach relative to conventional viscoelastic continuum models.
Structure of iodide ion arrays in iodinated nylon 6 and the chain orientation induced by iodine in nylon 6 films
Authors: Murthy N. S. , Szollosi A. B. , Sibilia J. P. , Krimm S. 
Published: April 2003

AbstractTwo species of iodide ions (I3− and I5−) are found in iodine—nylon 6 complexes. Orientation of I5− arrays (most likely I2/I3− complex) along the polymer chain and I3− ions perpendicular to the chain axis in uniaxially drawn films and in films with planar orientation suggests that there is and intrinsic relation between the direction of iodide ion arrays and nylon 6 chains. When an unoriented film of nylon 6 in the amorphous or the α crystalline form is treated with an aqueous solution of iodine—potassium iodide, the I3− species in the resulting iodine—nylon complex lie in planes parallel to the surface of the film, and I2/I3− units are oriented normal to the surface of the film. The γ form obtained by desorbing the iodine from this complex shows considerable uniaxial rientation with the nylon chains oriented perpendicular to the plane of the film; this orientation is maintained during the γ to α transition. It is proposed that the iodine‐induced orientation of the nylon 6 chains is due to the nucleating effects of the iodide ion species as the iodine diffuses unidirectionally into the film.
Tube relaxation: A quantitative molecular model for the viscoelastic plateau of entangled polymeric media
Authors: Viovy Jean Louis 
Published: April 2003

AbstractThe relaxation of an entangled polymeric medium in the viscoelastic plateau is investigated theoretically by using the slip‐link representation of topological constraints. In addition to the chain retraction process introduced by Daoudi and investigated theoretically by Doi, we show that two processes contribute significantly to the relaxation: The first, “equilibration across slip‐links,” is a longitudinal reequilibration between parts of the chain which have been differently extended or compressed, depending on their initial orientation relatively to the strain tensor. The second, “tube relaxation,” is a mean‐field representation of the loss of topological constraints on one chain due to the retraction of the others. Closed analytical expressions for the stress accounting for these three processes are derived and compared with previous theories: the relaxation should be much more progressive than previously predicted, and the terminal time for retraction is reduced significantly by tube relaxation.
An x‐ray diffraction study of nonlinear polyethylene. I. Room‐temperature observations
Authors: Vonk C. G. , Pijpers A. P. 
Published: April 2003

AbstractIn this investigation on samples of high‐ and low‐density polyethylene and ethylene‐vinyl acetate copolymers, crystallinities ϕW and crystalline densities ρcW were obtained with the aid of wide‐angle x‐ray scattering (WAXS) methods. From small‐angle x‐ray scattering (SAXS) the following characteristics were obtained either directly or by combination with the WAXS data: values, or limiting values, of the crystallinity ϕS; crystal densities ρcS; thicknesses of the diffuse boundary layer; number‐average thicknesses of the crystalline and amorphous layers; and both number and weight averages of the long periods. It was shown that a discrepancy between ϕS and ϕW cannot be attributed to the occurrence of large amorphous regions outside the regular stacks of lamellae; the data were reconciled by assuming that the WAXS crystallinities pertain to the cores of the crystalline lamellae, whereas part of the diffuse boundary layers is comprised in the values of ϕS. The ρcW and ρcS data of the nonlinear samples show systematic differences, which were attributed to partial incorporation of side groups in the crystalline regions at a concentration estimated to be of the order of 20–40% of the overall concentration. With increasing side‐group concentration, the thickness of the core of the crystalline lamellae was found to approach the average length of the linear chain segments between side groups. On the basis of these observations a scheme for the crystallization of nonlinear polyethylene is proposed according to which a number of side groups is encapsulated by the growing crystal. The data can be explained by assuming that all chains, offered at a crystal face where growth takes place, crystallize directly, irrespective of whether the crystallizing stem carries a side group. Further crystallization would then proceed by chain folding at both ends of the first stem, until a noncrystallizable unit is met. In this scheme, allowance is made for about half the stems in the crystals to be connected by folds; this is required in view of the “overcrowding” effect. Finally, the effect of cooling rate and molecular weight on the thicknesses of the crystalline and amorphous layers is discussed, and differences between the amorphous densities of high‐and low‐density polyethylene are noted.
Stability of the γ form and the development of the α form in nylon 6
Authors: Murthy N. S. , Aharoni S. M. , Szollosi A. B. 
Published: April 2003

AbstractThe structure of nylon 6 fibers is analyzed by x‐ray diffraction. Our results suggest that only two forms of nylon 6, α and γ, along with lattice distortion and crystallite size, are sufficient to explain the whole range of crystalline structures observed in nylon 6. The γ phase is the preferred initial form in a number of nylon 6 samples. The lattice distortion of the γ form along the chain axis varies from 0.8 to 2.4%, depending on the processing conditions. Upon annealing nylon 6 fibers, the α form is produced primarily by γ‐to‐α conversion in high‐orientation fibers, while additional α form can also crystallize from the amorphous phase in low‐orientation fibers. Finally, we show that α crystallites are favored during conditioning of poorly crystallized fibers in a humid atmosphere, and therefore fibers with α as the major crystalline form are produced upon drawing these conditioned fibers. Fibers drawn without lag time contain primarily the γ phase.
Visual data mining
Authors: Wegman Edward J. 
Published: April 2003

AbstractData mining strategies are usually applied to opportunistically collected data and frequently focus on the discovery of structure such as clusters, bumps, trends, periodicities, associations and correlations, quantization and granularity, and other structures for which a visual data analysis is very appropriate and quite likely to yield insight. However, data mining strategies are often applied to massive data sets where visualization may not be very successful because of the limits of both screen resolution, human visual system resolution as well as the limits of available computational resources. In this paper I suggest some strategies for overcoming such limitations and illustrate visual data mining with some examples of successful attacks on high‐dimensional and large data sets. Copyright © 2003 John Wiley & Sons, Ltd.