bluuebunny/crossref_metadata_2025_split huggingface dataset:
The hard elasticity of polypropylene and its blends with polyethylene
Authors: Du Qiangguo , Wang Lihui 
Published: April 2003

AbstractHard elastic monofilaments from polypropylene (PP) and its blends with polyethylene (PE) have been studied. Filaments with sharply different degrees of hard elasticity have been obtained by the same melt‐spinning process from three types of PP resin with almost the same isotacticity, molecular weight, and melt index and from blends of one of the PP resin with PE or high‐molecular weight PP (HMPP). With addition of a small amount of HDPE or HMPP to the parent PP resin, the hard elasticity of the filaments is increased significantly. Filaments with high hard elasticity can be prepared from PP resins of blends which show a relatively slow spherulitic growth rate. It is argued that the increased hard elasticity is due to row lamellae in PP fibers containing more adjacent folded chains and fewer tie molecules between lamellae and chain entanglements in the amorphous phase.
A mathematical model for stress‐driven diffusion in polymers
Authors: Cox Robert W. , Cohen Donald S. 
Published: April 2003

AbstractA model for case II diffusion into polymers is presented. The addition of stress terms to the Fickian flux is used to produce the characteristics progressive front. The stress in turn obeys a concentration‐dependent evolution equation. The model equations are analyzed in the limit of small diffusivity for the problem of penetration into a semiinfinite medium. Provided that the coefficient functions obey two monotonicity conditions, the solvent concentration profile is shown to have a steep front that progresses into the medium. The formulas governing the progression of the front are developed. After the front decays away, the long time behavior of the solution is shown to be a similarity solution as in Fickian diffusion. Two techniques for approximating the solvent concentration and the front position are presented. The first approximation method is a series expansion; formulas are given for the initial speed and deceleration of the front. The second approximation method uses a portion of the long time similarity solution to represent the short time solution behind the front.
The effect of morphology on sorption and transport of carbon dioxide in poly(4,4'‐oxydiphenylene pyromellitimide)
Authors: Okamoto Ken‐Ichi , Tanaka Kazuhiro , Yokoshi Osamu , Kita Hidetoshi 
Published: April 2003

AbstractSorption and transport of carbon dioxide were investigated for poly(4,4'‐oxydiphenylene‐pyromellitimide) films (PI‐1, PI‐2, and PI‐3) imidized at 160, 200, and 400°C, respectively, as well as for a chemically identical commercial polyimide film, Kapton‐H. The solubility, permeability, and diffusion coefficients (S, P, and
\[ \overline D \]
, respectively) at 80°C and 20 atm in PI‐3 were 67, 25, and 37%, respectively, as large as those in PI‐2. These significant reductions are attributed to a higher degree of segmental aggregation in PI‐3 caused by a 1.7% increase in the density (d) as compared with PI‐2. The differences in S, P,
\[ \overline D \]
, and d between PI‐3 and Kapton‐H were rather small as compared with those between PI‐3 and PI‐2, suggesting that the in‐plane orientation has a minor effect on the sorption and transport in Kapton‐H as compared with the aggregation. Influence of the morphology on the dual‐mode sorption and transport parameters was also investigated. With increasing density, the Langmuir capacity constant and the diffusion coefficients for the Henry's law and Langmuir populations decreased by higher rates than the Henry's law solubility constant, being contrary to the results reported for a typical semicrystalline glassy polymer, polyethylene terephthalate. This may suggest that the nonaggregated or less‐aggregated regions taking an important part in the sorption and transport are denser for the sample having a higher overall density.
Influence of a neutral surface on polymer molecules in the vicinity of the surface
Authors: Fitzgibbon Denise R. , McCullough R. L. 
Published: April 2003

AbstractMonte Carlo simulations based on the rotational isomeric model are used to investigate the influence of a neutral surface on the structural and thermodynamic descriptors of polymethylene chains on and in the vicinity of the surface. For large chains, the results of the simulations are replicated by a properly scaled distribution based on a random walk with absorbing barriers. Accordingly, the affects noted for the trial polymethylene system may be extended to other molecules.The perturbations in the geometry of the chain were confined to the components of the various descriptors perpendicular to the surface; the radial components were unaffected by the neutral surfaces. The perturbations induced by the neutral surfaces extend to chains whose origins were within about $\[ 10\left\langle {s_x \left( \infty \right)^2 } \right\rangle ^{1/2} \]$, where $\[ \left\langle {s_x \left( \infty \right)^2 } \right\rangle ^{1/2} \]$ is the perpendicular component of the mean square radius of gyration of an unperturbed chain.In contrast, the average bond conformation, the associated internal energy, and the variance of the internal energy distribution are unaffected by a neutral surface. The major thermodynamic effect is manifest through the entropy arising from the reductions in accessible chain configurations due to the neutral barrier.
Chain structure and entanglement
Authors: Wu Souheng 
Published: April 2003

AbstractIt is shown that the entanglement junction may be modeled as a binary hooking contact of Kuhn nodes between two chains. The entanglement behavior is thus determined by chain tortuosity and given by Nv = (1/β)C, where Nv is the number of real or virtual skeletal bonds in an entanglement strand, C∞ is the characteristic ratio, α = 2 is the number of hooks involved at an entanglement junction, and β = 1/3 is the fraction of binary hooking configurations out of all possible configurations at a binary nodal contact. In other words, we have Nv = 3C, which is verified experimentally for 44 polymers, covering a wide variety of skeletal, pendant, and stereoisomeric (tacticity) structures. Since C∞ may be estimated by group additivity, the present equation may be used to predict the entanglement behavior from chemical structure.
Effect of length of side chains on the optical configuration parameter of poly(n‐alkyl acrylate) networks
Authors: Ilavský M. , Saiz E. , Riande E. 
Published: April 2003

AbstractThe effect of the length of side chains on the optical configuration parameter Δa of poly(n‐alkyl acrylate) networks was theoretically studied using the valence optical scheme (VOS). The theoretical calculations suggest that Δa should be negative, and its absolute value should increase as the side‐chain length increases. Moreover, a positive temperature dependence is also predicted. By comparing theoretical and experimental results, it was found that the valence optical scheme gives a good qualitative interpretation of the side‐chain effects on the birefringence of the stretched networks. However, the method fails to give a quantitative description of Δa, presumably because strong intermolecular interactions enhance the polarizability along the chains. The fact that the difference between theoretical and experimental values of Δa decreases with increasing side‐chain length suggests that flexible long chains act as a diluent reducing intermolecular interactions that enhance Δa.
Dielectric properties of bisphenol‐a epoxy resins
Authors: Sheppard Norman F. , Senturia Stephen D. 
Published: April 2003

AbstractThe α‐relaxation process of seven commercial diglycidyl ether of bisphenol‐A (DGEBA) epoxy resins of varying molecular weights, without hardener, was characterized by measuring the frequency and temperature dependence of the complex permittivity, (ϵast;). The temperature dependences of the frequency of maximum dipole loss ƒmax and the ionic conductivity σ are non‐Arrhenius and can be described by the Williams‐Landel‐Ferry (WLF) equation. The frequency dependence of the molecular relaxation process is described by the Kohlrausch‐Williams‐Watts (KWW) relaxation function. The WLF C1 parameter and the KWW β parameter, describing the temperature and frequency dependences, respectively, vary systematically with the molecular weight of the resin. These results are discussed in the context of recent theories of the glass transition.
Diffusion of linear polyisoprene molecules into polyisoprene networks
Authors: Gent A. N. , Kaang S. Y. 
Published: April 2003

AbstractDiffusion and equilibrium absorption of polyisoprene liquids into crosslinked samples of cis‐polyisoprene (natural rubber) have been studied by direct observation of volume swelling. Natural rubber was crosslinked in the form of fine threads, about 40 ± 20 μm in diameter, using a gaseous reaction with SO2 and H2S (the Peachey process). An optical microscope was used to observe the relatively rapid absorption of linear high‐molecular‐weight polyisoprene liquids by these fine threads. From the kinetics of absorption, values of the self‐diffusion coefficient Ds of polyisoprene were estimated. They ranged from 10−16 m2/s to 10−12 m2/s, depending upon molecular weight, and varied with molecular weight approximately as M−2 over the entire range employed, from 1,000 to 60,000 g/mol, i.e., both above and below the entanglement molecular weight. Amounts of polymer absorbed at equilibrium varied widely, depending upon the degree of crosslinking of the host material and the molecular weight of the absorbing liquid. They were in reasonable agreement in all cases with simple swelling theory, with the heat of mixing equated to zero.
Study of ferroelectric transitions of vinylidene fluoride–trifluoroethylene copolymers
Authors: Faria R. M. , Latour M. 
Published: April 2003

AbstractThermally stimulated depolarization (TSD) measurements with superimposed “piezoelectric noise” allow us to identify the ferroelectric‐to‐paraelectric phase transition in vinylidene fluoride–trifluoroethylene (VDF/TrFE) copolymers with different molar ratios. In addition, a new transition which did not change the ferroelectric features of the material has also been detected. Long relaxation processes always accompany these transitions. By the initial‐rise method we calculated the activation energies for these relaxations as 0.73 eV for the ferroelectric‐to‐paraelectric transition and 0.33 eV for the ferroelectric‐to‐ferroelectric one.
Permeation of carbon dioxide through homogeneous and asymmetric polysulfone membranes
Authors: Sada E. , Kumazawa H. , Xu P. 
Published: April 2003

AbstractTo confirm the validity of the working assumption that a thin dense skin layer in an asymmetric membrane can be essentially replaced by a thick homogeneous dense membrane, both homogeneous and asymmetric polysulfone membranes were prepared by solvent casting, and the permeation behavior of carbon dioxide through these two types of membranes was investigated. The pressure dependence of the mean permeability coefficient through an asymmetric polysulfone membrane is apparently very similar to that through a homogeneous dense membrane, following the dual mode mobility model driven by gradients of chemical potential. The dense skin layer in the asymmetric membrane can be simulated approximately by a homogeneous dense membrane from the point of view of gas sorption and diffusion.
Metal‐catalyzed oxidation of poly(α‐methylstyrene) during surface‐enhanced Raman scattering
Authors: Boerio F. J. , Tsai W. H. , Montaudo Giorgio 
Published: April 2003

AbstractSurface‐enhanced Raman scattering (SERS) was used to characterize thin films of poly(α‐methylstyrene) (PMS) spin‐coated onto silver island films supported by glass substrates. At laser powers of a few tens of milliwatts, SERS spectra of thin films of PMS (about 100 Å) were weak, and only the bands near 1010 and 1040 cm−1 were observed. At laser powers of about 100 mW, additional bands characteristic of PMS were observed near 720 and 1610 cm−1. However, oxidative degradation of the PMS films to form graphite‐like substances was also observed at the higher laser powers. When the thickness of the PMS films was increased to several hundred angstroms, degradation of the films was inhibited, but the intensity of the Raman scattering remained constant, indicating that the observed SERS was an interfacial rather than bulk effect. Degradation during SERS experiments was also inhibited by overcoating PMS films with much thicker films of poly(4‐styrene sulfonate) (PSS). Scattering from the PSS overlayers was not observed as long as the thickness of the PMS films was greater than several tens of angstroms, again showing that the SERS was an interfacial effect. Oxidative degradation of the PMS films was also inhibited by adding a few percent of the antioxidant 2,6‐di‐tert‐butyl‐4‐methylphenol to the polymer. Bands related to sulfite contaminants adsorbed onto the silver island films were observed near 640 and 940 cm−1. These bands disappeared when PSS, but not PMS, was spin‐coated onto the SERS substrates, indicating a strong interaction between PSS and silver.
Birefringence, compliance, and viscoelasticity of poly(ethylene terephthalate) fibers
Authors: Northolt M. G. , Roos A. , Kampschreur J. H. 
Published: April 2003

AbstractThe experimental relation between birefringence and dynamic compliance has been determined for a wide range of poly(ethylene terephthalate) fibers. This relation is explained by two complementary versions of the series aggregate model. The classical series aggregate model provides a satisfactory interpretation of the data for the low‐oriented fibers. A model developed earlier for aramid fibers explains the data for the well‐oriented fibers. By monitoring the dynamic compliance during creep and stress relaxation of well‐oriented fibers it is shown that these phenomena are caused by shear relaxation, resulting in a progressive contraction of the chain orientation distribution.
Crystallization oftrans‐1,4‐polyisoprene and of hydrochlorinated segmented block copolymer derivatives from solution
Authors: Corrigan Joseph P. , Zemel Irina S. , Woodward Arthur E. 
Published: April 2003

AbstractCrystallization oftrans‐1,4‐polyisoprene from the mixed solvent pair hexane/2‐pentanone was carried out and the effects on the morphology of seeding and the solvent composition were studied. α‐TPI lamellae obtained by crystallization from a single solvent, hexane, at 20°C and by mixed‐solvent crystallization at 40°C were characterized by DSC, FTIR, and suspension epoxidation/C‐13 NMR. Crystalline stem lengths of 14.5 and 18 and a fold length of 10 monomer units were found. Segmented block copolymers were prepared by reaction of TPI lamellae in acetone suspension with HCl at −7°C. These products were dissolved in 2‐pentanone and precipitated at 0°C. A lamellar morphology, the details of which depend on the TPI block length, was observed by SEM; both preparations showed sharp endotherms; and the FTIR was characteristic of a combination of amorphous TPI, amorphous hydrochlorinated TPI, and of either the β crystalline form or both the α and β forms for TPI depending on the sample.
Studies of poly(vinylidene fluoride)/poly(vinyl pyrrolidone) blends. I. Thermal transitions by differential scanning calorimetry
Authors: Alfonso Giovanni Carlo , Turturro Antonio , Pizzoli Maria , Scandola Mariastella , Ceccorulli Giuseppina 
Published: April 2003

AbstractThermal measurements were carried out to investigate the macrostructure of as‐cast poly(vinylidene fluoride) (PVDF)/poly(vinyl pyrrolidone) (PVP) blends. At high PVP content, above about 70 wt.%, the two components form a homogeneously mixed amorphous phase whose Tg varies with composition. Crystals are formed upon casting mixtures richer in PVDF; these systems exhibit complex thermal behavior that cannot be justified by a simple two‐phase model. DSC measurements above room temperature on semicrystalline blends show, in addition to the melting of PVDF crystals at temperatures that decrease on increasing PVP content, a glass transition at about 80°C, independent of composition. Experimental results strongly support the hypothesis that an interphase, composed of essentially undiluted noncrystalline PVDF, is always associated with the lamellar crystals.
A phenomenological description of large deformations in polymeric glasses (polycarbonate)
Authors: Koenen J. A. , Heise B. , Kilian H.‐G. 
Published: April 2003

AbstractA new description of the quasistatic deformation of polymeric glasses is presented. The stress‐strain energy of a glass is defined to comprise two components: a “solid term,” which controls the low‐strain range of deformation, and a “conformational term” proportional to the first strain invariant. By introducing internal variables in terms of classical irreversible thermodynamics, the stress‐strain behavior and the thermoelastic properties of polycarbonate are fairly well described over the whole range of accessible strains. The necking phenomenon is interpreted as a “constrained strain‐induced phase transition” (“one‐way phase transition”). A new version of a Clapeyron‐Clausius equation is derived. Its application yields a new understanding of the temperature dependence of yielding of cold‐drawn polycarbonate. The typical phenomena of a first‐order transition, discussed in the special form of a “one‐way phase transition,” have been fully identified experimentally (by microscopy, stretching‐microcalorimetry, simple extension, and birefringence). Sharp phase boundaries appear just when the new phase is nucleated. The transition then proceeds under a constant force as demanded by thermodynamics. The stress‐strain behavior is shown to be uniquely dependent on temperature at temperatures below the glass‐transition range. General consequences of the phenomenological treatment are discussed.
A model of environmental craze growth in polymers
Authors: Brown H. R. 
Published: April 2003

AbstractA model of environmental craze growth has been developed based on the customary meniscus (or Rayleigh‐Taylor) instability model of craze propagation but allowing for the possibility that environmental plasticization may cause the active layer of material adjacent to the craze to be of significant thickness with respect to the fibril spacing. Initially, as the active layer thickness increases, the fibril growth rate increases at constant fibril spacing, but eventually the fibril spacing comes to be controlled only by the active layer thickness and not by the surface tension and stress. This model of craze growth has been coupled to a model of stress‐enhanced case II diffusion that is itself based on the Thomas‐Windle model. Two main regimes of craze thickness growth are distinguished. In one the craze growth rate is controlled by the velocity of the diffusion front, the meniscus instability growth rate is assumed to be relatively slow, so that a significant plasticized active layer exists whose thickness assures that the meniscus instability front travels at the same speed as the diffusion front. In the other regime the propagation of the craze front is sufficiently fast that it also forms the diffusion front, so the growth rate is controlled by a combination of the two processes: diffusion and meniscus instability.
Characterization of thermal diffusion in polymer solutions by thermal field‐flow fractionation: Dependence on polymer and solvent parameters
Authors: Schimpf Martin E. , Giddings J. Calvin 
Published: April 2003

AbstractThe thermal diffusion coefficient DT has been obtained for 17 polymer‐solvent combinations, each of them spanning a range of polymer molecular weights, using thermal field‐flow fractionation. The polymers examined include polystyrene, poly(alpha‐methyl)styrene, polymethylmethacrylate, and polysioprene. The solvents include benzene, toluene, ethylbenzene, tetrahydrofuran, methylethylketone, ethylacetate, and cyclohexane. Although DT was confirmed as essentially independent of polymer molecular weight, it was found to vary substantially with the chemical composition of polymer and solvent. The results were used to evaluate several thermal diffusion theories; the agreement with theory was generally found to be unsatisfactory. Attempts were then made to correlate the measured thermal diffusion coefficients with various physicochemical parameters of the polymers and solvent. A good correlation was found in which DT increases with the thermal conductivity difference of the polymer and solvent and varies inversely with the activation energy of viscous flow of the solvent.
Mechanical relaxations in trans‐1,4‐polyisoprene crystals
Authors: Anandakumaran K. , Manley R. St. John 
Published: April 2003

AbstractDynamic mechanical relaxation spectra were obtained for solution‐grown crystals of trans‐1,4‐polyisoprene (TPI) in the α and β form. For single crystal mats three relaxations were observed. The highest temperature relaxation peak was characterized as due to the crystalline regions, whereas the intermediate peak was assigned to the primary amorphous relaxation which originates from the fold regions. The nature of the amorphous regions was elucidated by examining the effect of epoxidation on the lamellar fold surface. For an epoxidized single crystal mat, the intermediate relaxation maximum shifted to a higher temperature which corresponds to the glass transition of the almost completely epoxidized TPI. These results are discussed in terms of the fold structure of the TPI single crystals.
A Flory–Huggins thermodynamic approach for predicting sorption equilibrium in ternary polymer systems
Authors: Campos Agustin , Gavara Rafael , Tejero Roberto , Gomez Clara , Celda Bernardo 
Published: April 2003

AbstractThe Flory–Huggins theory as modified by Pouchlý has been applied to calculate preferential (λ) and total (Y) sorption coefficients for a ternary polymer system. The ternary interaction function (ϕ1ϕ2ϕ3GT(u1, ϕ3)) is described as the product of three independent binary functions. This expression allows prediction of λ and Y from binary interaction parameters χ, χ, g, g, and g12(ϕ10). Three ternary polymer systems are used to check the validity of the expression. Moreover for polymer systems in which the parameters g and/or g are unknown, a procedure to evaluate them has been developed and verified on systems for which sufficient experimental information is available.
Vibrational spectroscopy of the oxidation of polyethylene. I. Fourier self‐deconvolution of the carbonyl absorption
Authors: Maddams W. F. , Parker S. F. 
Published: April 2003

AbstractFourier self‐deconvolution of the carbonyl peak present in the infrared spectrum of oxidized polyethylene has successfully resolved the peak into its components. Three strong bands at 1713, 1719, and 1723 cm−1, together with a number of weaker features, are detected. In agreement with previous work, the 1719 and 1723 cm−1 bands are assigned to saturated ketones and saturated carboxylic acids, respectively. A new band is also observed at 1697 cm−1. The relative amounts of the components differ between high‐density, linear low‐density, and low‐density polyethylene. The 1697 cm−1 band is very dependent on the type of polyethylene; it is strong in high‐density, weak in linear low‐density, and very weak in low‐density polyethylene.