bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular conformations in polyethylene after recrystallization or annealing at high pressures
Authors: Olley R. H. , Bassett D. C. 
Published: April 2003

AbstractInformation on molecular conformations inside polyethylene lamellas following high pressure treatments is obtained by comparing observed and predicted length distributions of nitrated samples. Three types of conformation are inferred. The commonest is that molecules are folded with chain ends included in lamellas, except that ends are not turned in by less than ∼600 Å from a surface. This situation accounts in detail for the previously observed agreement between the number fracture‐surface distribution of crystal thicknesses and the gel permeation chromatography (GPC) weight distribution following nitration. The second conformation, found especially for samples of low polydispersity, is also of folded molecules but with chain ends excluded from lamellas. This particular case justifies rigorously the initial assumption of folding. Finally there are examples where the molecular length distribution is substantially lower than the crystal thickness distribution, implying that molecular length is not the upper limit of crystal thickness and that molecules can be fully extended inside lamellas.
The fatigue process in highly oriented nylon 6 fibers
Authors: Narisawa Ikuo , Ishikawa Masaru , Ogawa Hiroyuki 
Published: April 2003

AbstractThe micromechanism of the fatigue process in highly oriented nylon 6 fibers is discussed on the basis of changes in mechanical and structural properties during fatiguing. Experimental results show that the fatigue process can be divided into two stages. The characteristic features in the initial period are increases in breaking strength, long period, and molecular orientation, and a reduction in dye penetration. In the second period, after about 500 cycles, breaking strength and orientation decrease slightly, and the long period, permanent strain, and dye penetration increase with duration of fatiguing. It is demonstrated that the structural changes mainly occur in the amorphous regions of the fiber structure. The structural and mechanical changes in the initial period lead to the conclusion that the initial cyclic strain causes strain hardening caused by extended tie chains which do not rupture. A combination of load bearing by tie chains and sliding motion of the fibrillar elements can explain the progressive degradation of the fiber during the second stage of fatiguing.
Segmental orientation in blends of poly(ϵ‐caprolactone) with poly(vinyl chloride) and nitrocellulose
Authors: Hubbell Douglas S. , Cooper Stuart L. 
Published: April 2003

AbstractBinary blends of polycaprolactone (PCL) with poly(vinyl chloride) (PVC) and nitrocellulose (NC) have been shown to be compatible over a wide range of composition. In this study, segmental orientation was determined by dynamic, differential infrared dichroism for each component in the PVC and NC blends with PCL. In compatible amorphous blends, PCL orientation behavior was essentially the same as for the orientation of NC or the isotactic segments of PVC. Syndiotactic PVC segments showed higher orientations, reflecting the greater intrachain stiffness of the microcrystalline PVC phase. PCL segments in the blends where the PCL component was semicrystalline were found to exhibit orientation characteristics which were quite different from the orientation of the nitrocellulose and PVC components of the blends. By assuming that the NC orientation represented the response of the amorphous PCL, the orientation of the crystalline PCL was determined for a NC blend using a simple model of additive dichroism response. In PVC blends, a similar analysis using the amorphous‐component response of PVC was made. In both cases the results from the dichroism model showed fair agreement with the PCL unit cell C‐axis orientation from independent dichroism calculations.
A fiber composite model of highly oriented polyethylene
Authors: Barham P. J. , Arridge R. G. C. 
Published: April 2003

AbstractA fiber composite model of highly drawn polyethylene is presented. Quantitative predictions and calculations are made using shear‐lag theory. The drawing process is shown to occur in two stages, a neck and a postneck taper. It is shown that there is an empirical linear relationship, with a high correlation, between the parameter x in shear‐lag theory (which involves the aspect ratio of the reinforcing elements and the square root of the ratio of matrix shear modulus to the Young's modulus of the reinforcing elements) and the 3/2 power of the taper draw ratio. It is concluded that crystalline fibrils (the reinforcing elements) deform homogeneously during the secondary, taper drawing process. The increase in aspect ratio resulting from this homogeneous deformation is held to be responsible for the increase in tensile modulus owing to the increased efficiency of the fibrils as reinforcing elements. The model is also used to explain the self‐hardening process exhibited by these fibers and, using measurements of density of hardened fibers, to predict that immediately after the neck the aspect (length to diameter) ratio of the crystalline reinforcing elements is ca. 2 and that the shear modulus of the matrix material in as‐drawn fibers is ∼103N/m2 and does not change significantly during the taper‐drawing process.
Light scattering studies of mixtures and fractions of linear polyethylene
Authors: Mandelkern L. , Go S. , Peiffer D. , Stein R. S. 
Published: April 2003

AbstractPrevious work on the small‐angle light scattering of polyethylene films, to determine the supermolecular structure, has been continued. One of the main efforts has been the study of a binary mixture whose low molecular weight component forms well defined spherulites and whose high molecular weight component yields a poorly defined rod‐like morphology. The addition of the high molecular weight fraction causes a progressive deterioration of the initial spherulitic morphology; a relatively small amount of the high molecular weight species causes a major decrease in the spherulitic size. However, there are no indications of any spherulitic structures when the weight fraction of the high molecular weight species is 0.5 or greater. The isothermal crystallization of a fraction M = 6.6 × 105 was also studied. Spherulites were formed at low crystallization temperatures while at the higher crystallization temperatures the morphology became nondistinct. Preliminary studies with solvents indicate that high molecular fractions, which do not form spherulites when crystallized in the pure state, do so when crystallized from highly swollen solutions.
Light scattering from epoxy‐elastomer resins: A study of statistical methods in heterogeneity analysis
Authors: Boisserie C. , Marchessault R. H. 
Published: April 2003

AbstractThe solid‐state light scattering from ABE (acrylonitrile butadiene epoxy) copolymers was studied as a function of rubber content by measuring the intensity distribution of scattered light under Vv polarization conditions. The range of heterogeneity has been quantified by the Debye–Bueche statistical treatment and by comparison with simulated scattering envelopes. The data indicate that below a critical rubber concentration of 20% the rubbery phase precipitates as spherical domains of nearly constant size. Phase inversion occurs at a rubber concentration of 20% and is accompanied by a maximum in polydispersity of the dispersed phase. Beyond this concentration, epoxidic domains are imbedded in a rubber and epoxy matrix. As a result of comparison of Debye–Bueche parameters with simulated values of these, it is concluded that the correlation distance is very sensitive to the presence of a small number of large particles.
A fourier transform infrared spectroscopic investigation of polyethylene single crystals. I. Methylene wagging mode
Authors: Painter P. C. , Havens J. , Hart W. W. , Koenig J. L. 
Published: April 2003

AbstractThe application of the spectral subtraction routine to the determination of the morphology of polyethylene single crystals is discussed in detail. An analysis of the CH2 methylene wagging mode is presented. A band at 1346 cm−1 is observed to be unique to polyethylene single crystals. The assignment of this band to a regular, tight fold structure is discussed.
Conformational study of isotactic poly[(S)‐5‐methyl‐1‐heptene] and poly[(S)‐2‐methylbutyl vinyl ether] by IR spectroscopy
Authors: Benedetti Enzo , Chiellini Emo 
Published: April 2003

AbstractInfrared (IR) investigation of structurally analogous optically active polymers such as poly[(S)‐5‐methyl‐1‐heptene (1)] and poly[(S)‐2‐methylbutyl vinyl ether (2)] was carried out in the solid state, in the molten state, and in solution. Vibrational data are in accordance with the existence of helical conformations in solution and in the molten state for both polymers, confirming the previous suggestions based on optical rotation measurements. In particular, an accurate examination of the spectral region between 850 and 700 cm−1, where characteristic absorptions of the sec‐butyl group occur, enables us to assign the medium intensity band at 827 cm−1 (present in both polymers in the solid state) to the GTTG−T conformation of the side chains.
Effect of molecular orientation on the swelling of nylon 6
Authors: Inoue K. , Hoshino S. 
Published: April 2003

AbstractThe effect of molecular orientation on the linear swelling of nylon 6 caused by absorption of water was studied using two kinds of oriented films, melt drawn and cold drawn. The molecular orientation causes anisotropy in swelling at all humidities such that the swelling is larger in the orientation direction than in the directions perpendicular to it. The large contribution of crystalline orientation to this phenomenon was expected for the melt drawn film which has practically no amorphous orientation. An analysis with a two‐phase morphological model reveals that the distance between the crystallites is a prominent factor controlling the degree of linear swelling, and that the anisotropy of swelling arises from the change in the distribution of crystallites due to orientation. By comparing the result for the melt drawn film with that for the cold drawn film, which has considerable amorphous orientation, it was proven that molecular orientation in the amorphous phase where swelling actually occurs does not depend so much on the degree of swelling as on the distribution of crystallites.
Configurational properties of aromatic polyesters: Dipole moments of poly(diethylene terephthalate) chains
Authors: Riande E. 
Published: April 2003

AbstractDielectric constants have been determined for a fraction of poly(diethylene terephthalate) in benzene at several temperatures. The data indicate that the dipole moment ratio 〈μ2〉/Nm2 is somewhat higher than that of poly(ethylene oxide), and its temperature coefficient is in the vicinity of zero. Both the dipole ratio and its temperature coefficient are in very good agreement with those predicted by the rotational isomeric state theory. Using this theory, the unperturbed dimensions of poly(diethylene terephthalate) were calculated and it was found that (〈r2〉/M)∞ = 0.80 Å2 (g mol wt)−1, a value intermediate between those of poly(ethylene oxide) (0.57) and poly(ethylene terephthalate) (1.05).
Dimensional changes in ultradrawn polyethylene
Authors: Capiati Numa J. , Porter Roger S. 
Published: April 2003

AbstractSamples of ultradrawn high density polyethylene were studied by thermomechanical analysis. The purpose was to study the dimensional changes in polyethylene morphologies of extreme orientation. Dimensional changes were measured from −140 to +70°C with a precision of better than 1%. A negative thermal expansion coefficient was observed along the length (c axis) of the fibers containing the polyethylene morphologies of extreme orientation. A change in negative coefficient is observed between −35 and −45°C. The sign and magnitude of the expansion coefficient confirm, along with other evidence, the existence of extended chain structures in these morphologies. A series‐parallel model has been developed for the ultradrawn polyethylenes to describe the dimensional changes with temperature.
Unperturbed dimensions of random and alternating styrene/n‐alkyl methacrylate copolymers
Authors: Podešva J. , Bohdanecký M. , Kratochvíl P. , Samay G. 
Published: April 2003

AbstractThe steric factors σ of homopolymers of ethyl, n‐butyl, and n‐octyl methacrylate, of equimolar random and alternating copolymers of these monomers with styrene, and of polystyrene, were determined by measuring intrinsic viscosities in a good solvent (butanone, 25°C) and extrapolating the data thus obtained to zero molecular weight of the polymer. For all comonomeric pairs under investigation, the σ2 of an equimolar random copolymer and, particularly, of an alternating copolymer, is higher than the arithmetic mean (σ + σ)/2 of the σ2 values of the parent homopolymers. The positive deviation from the linear dependence of σ2 on the copolymer composition, expressed as an increment of σ2, is proportional to the mole fraction of alternating dyads in the copolymer chain with in the limits of experimental error. The effect of copolymer microstructure on the unperturbed dimensions of the chains has been compared for equimolar copolymers of styrene with methyl, ethyl, n‐butyl, and n‐octyl methacrylate by using a relative increment ξ defined as the ratio of σ2 of the alternating copolymer to (σ + σ)/2. The dependence of ξ on the number of carbon atoms in the alcohol substituent of the methacrylate component of the copolymer seems to exhibit a maximum for ethyl methacrylate.
Stress‐induced diffusion of macromolecules
Authors: Tirrell Matthew , Malone Michael F. 
Published: April 2003

AbstractA framework for analysis of stress‐induced diffusion is presented. Diffusion of macromolecules is considered to be driven by gradients of entropic potential arising from distortion of the molecular conformation by deformation, as well as by gradients of concentration of individual molecular weight species. Resulting concentration profiles in circular capillary flow have been calculated for a system containing a single macromolecular species. Significant variations in concentration with capillary radius are predicted at full development. Estimates of the dynamics of development of these profiles indicate that the length to diameter ratios needed to see a measurable effect are proportional to the Peclet number, which may be quite large for macromolecular fluids depending on the geometry and flow velocity of the system. This effect may have implications in the rheology, chromatography, and technological uses of macromolecular fluids.
Power law relationship between yield stress and shear modulus for glassy polymers
Authors: Kitagawa M. 
Published: April 2003

AbstractThe published data on the yielding of glassy polymers under a variety of testing conditions reveal that the yield stress increases with the elastic modulus. However, fundamental understanding of the interrelation has not yet been established. In this paper, a power law relation between the shear yield stress τy and the shear modulus G is presented: T0τy/Tτy0 = (T0G/TG0)n, where T is the absolute temperature, T0. is reference temperature, and τy0 and G0 are, respectively, the shear yield stress and the shear modules at T0. The exponent n takes a value 1.63 for amorphous polymers without exception, whereas it is about 0.8–0.9 for crystalline polymers. The exponent 1.63 for amorphous polymers is in good agreement with the value derived from the approximation of the Bowden–Raha dislocation analog. This law may enable us to investigate a model for the yielding of glassy polymers.
Investigation of heterogeneities in solid polyethylene by small angle neutron scattering
Authors: Ullman Robert , Summerfield George C. , King John S. 
Published: April 2003

AbstractSmall angle neutron scattering was applied to the investigation of heterogeneities in solid poly‐ethylene. The heterogeneities arise from the contrast between amorphous and crystalline regions and also from the presence of a small fraction of voids. The method is easily put on an absolute basis by calibration with an incoherent scatterer, in this case, cyclohexane.
Texture and molecular chain mobility in cold‐deformed linear polyethylene
Authors: Arai Hidehiko , Hayakawa Naohiro , Tamura Naoyuki , Kuriyama Isamu 
Published: April 2003

AbstractThe fine texture and molecular motion in rolled (draw ratios λ = 2, λ = 5), cold‐drawn (λ = 6), and hot‐drawn (λ = 6), linear polyethylene (Sholex 6050) films were studied by small‐angle x‐ray scattering, wide‐line nuclear magnetic resonance (NMR), and dynamic viscoelastic measurements. NMR spectra of the rolled (λ = 5) and cold‐drawn samples show a small narrow component at room temperature. For these cold‐deformed samples, a gradual decrease in the second moment is observed well below the α relaxation temperature and a new relaxation appears in the same temperature region in the logarithmic decrement versus temperature. This relaxation is absent in the original and hot‐drawn samples. It is concluded that the new relaxation arises from molecular motion in intermediate regions where molecular chains are less mobile than in the amorphous state.
Étude par rayons X de copolymères téléchéliques butadiène acide méthacrylique
Authors: Moudden A. , Levelut A. M. , Pineri M. 
Published: April 2003

AbstractThe telechelic polybutadiene–methacrylic acid copolymer (Hycar CTB) containing 2 mole percent acid and neutralized (5–100%) by alkali ions, Na+, K+, and Cs+, has been studied by small‐angle x‐ray scattering. Salt groups form clusters, and the average value of the radii of gyration is approximately 8 Å; this value seems to be independent of the nature of the cation and the degree of neutralization. The existence of a low‐angle maximum in the scattering intensity gives evidence of a mean distance of 80 Å between clusters in the fully neutralized sample. This distance increases slightly with a decreasing degree of neutralization. A more precise analysis of the small‐angle scattering curve gives further information on the cluster structure: the ionic groups may form small bilayer disks while the polymer chains maintain a regular distance of 80 Å between the disks.
Green's function analysis of the vibrational spectra of polymer chains. I. Several approaches to the problem
Authors: Kozyrenko V. N. , Kumpanenko I. V. , Mikhailov I. D. 
Published: April 2003

AbstractVarious methods of solving the dynamical equation for defect polymers are discussed. It is shown that the Green's function (GF) can be conveniently used to reduce the order of the characteristic equation to the number of the degrees of freedom of a repeat unit in the case when the perturbation caused by each of the defects is localized within it. In the general case, the order of the reduced determinant depends on the range of the interaction forces between the defect unit and the regular chain.For a polymer chain containing one or two defect units, the Green's function method allows us to obtain the exact solution of the dynamical equation, while for a high concentration of randomly distributed defect units various approximation methods can be used. As a possible approach to the solution of the latter problem we suggest using either one of the versions of the perturbation theory (the dilute limit, the coherent potential approximation) or the cluster approximation.
Quasielastic scattering of neutrons from freely jointed polymer chains in dilute solutions
Authors: Akcasu A. Ziya , Higgins Julia S. 
Published: April 2003

AbstractStarting with Kirkwood's Fokker–Planck equation for the polymer configuration‐space distribution function and using the Zwanzig–Mori projection operator technique we have calculated the scattering law S(q,w) for a freely jointed model polymer chain in a dilute solution. When memory effects are neglected, the theory predicts a Lorentzian for S(q,w) with a halfwidth Ω(q), which we have determined as a function of the momentum transfer q for all values of q. The results are compared with recent neutron scattering experiments on deuterated polytetrahydrofuran and polystyrene in dilute solution in CS2. It is found that the observed q dependence of Ω(q) is represented satisfactorily by the present theory with a bond length b of about 6.3 Å for polystyrene and 3.8 Å for polytetrahydrofuran, and a friction coefficient ζ = 4πη0b where η0 is the viscosity of the solvent.
Deformation mechanisms of constrained polymer chains. II. Deformation energetics of tie molecules
Authors: McCullough R. L. , Eisenstein A. J. , Weikart D. F. 
Published: April 2003

AbstractEnergy‐deformation characteristics for the primary T, S, and U conformational units of tie molecules were obtained from the analysis of data generated from a constrained minimization algorithm. Energy‐deformation profiles (covering the range from compact equilibrium defect structures to the fully extended chain) are reported for the S0 and S1 members of the Sλ family and for the U00 member of the Umn family. Estimates of the energy content V0 and the elastic modulus E were obtained from the computed energy‐deformation data in the vicinity of the equilibrium Structure—S0 → {60°, 180°, −60°}, V = 1.7 kcal/mole, E = 60 kcal/cm3 [250 × 1010 dyn/cm2];S1 → {60°, 180°, 180°, 180°, −60°}: V = 1.7 kcal/mole, E = 25 kcal/cm3 [100 × 1010 dyn/cm2]; and U00 → {60°, 180°, 60°, 180°, 60°}: V = 2.7 kcal/mole, E = 80 kcal/cm3 [340 × 1010 dyn/cm2]. Although the elastic modulus of the U00 unit is comparable to the elastic modulus of the fully extended chain, the highenergy content of this unit (V0 = 2.7 Kcal/mole) prohibits a significant population and thereby mitigates an appreciable reinforcing effect from this rigid unit. A model for a surrogate force constant is introduced to generalize the results from this study to any member of the Sλ or Umn family as well as any combination of Sλ and Umn units. This generalization provides a basis for estimating the deformation characteristics of tie molecules comprised of various populations of these primary conformational building blocks.
Low‐temperature relaxations in styrene‐crosslinked polyester networks. III. Influence of water concentration and chemical structure on the γ relaxation
Authors: Cook Wayne D. , Delatycki O. 
Published: April 2003

AbstractThe intensity of the water‐induced γ relaxation (see ref. 1) in crosslinked polyester networks in creases rapidly at low water concentrations (0 to 0.5% by weight). At higher water concentrations (0.5 to 3.0%) the intensity of the γ relaxation approaches a constant value. The shift of the relaxation peak to lower temperatures shows a similar pattern of behavior. These results have been related to the fraction of water involved in the relaxation and the changing nature of the relaxation sites with the increase in water concentration. The important role that fumarate units play in the γ relaxation has also been confirmed; however, the chemical nature of the relaxing unit appears to be more complex than was originally considered. Two models are proposed for this behavior.
ESR study of pressure and temperature dependence of free‐radical decay in poly(vinyl chloride)
Authors: Szöcs F. , Klimová M. 
Published: April 2003

AbstractGamma‐irradiated poly(vinyl chloride) was annealed at various temperatures (80 to 140°C) and pressures (0.1 to 800 MN m−2). Rate constants and activation volumes of free‐radical decay were determined from the changes of the electron spin resonance (ESR) spectra before and after annealing. The pressure and temperature dependence of the rate constant is compared with the pressure and temperature dependence of the mechanical relaxation parameters. The correlation between the kinetics of radical reactions and the kinetics of the molecular motions in the α‐relaxation region is discussed.