bluuebunny/crossref_metadata_2025_split huggingface dataset:
Time dependence of mechanical and transport properties of drawn and annealed linear polyethylene
Authors: Decandia F. , Vittoria V. , Peterlin A. 
Published: April 2003

AbstractLinear polyethylene both as drawn, or drawn and subsequently annealed with free ends, changes its length, density, crystallinity, elastic modulus, sorption, and diffusivity as the sample stands completely unrestrained at room temperature. Most of these changes occur during the first few hours. But they are important on a molecular scale since they suggest strongly that drawn, and drawn and annealed samples are far from equilibrium. As a consequence of the tendency of each mobile tie molecule in the amorphous conformation to retract and to crystallize, the specimen approaches but does not reach complete equilibrium. The transient seems to be caused by slow crystallization of tie molecules which creates crystalline bridges across the amorphous layers.
Random‐coil configurations of aromatic polyesters: Birefringence of poly(triethylene glycol terephthalate) networks in elongation
Authors: Riande E. , Guzman J. 
Published: April 2003

AbstractHydroxyl‐terminatd poly(triethylene glycol terephthalate) was crosslinked with an aromatic triisocyanate. Birefringence–stress–strain experiments, performed on the networks at 70°C, showed an anomalous increase in the modulus and a downturn in the birefringence–strain isotherms at high elongations. These results suggest that crystallinity is not responsible for the non‐Gaussian behavior of the chains at high extension. The same kind of experiments were performed over the range 20–70°C. Values of the optical configuration parameter Δa of the order of 13.3 × 10−24 cm3 with negligible temperature coefficient were found for these networks. The quantities Δa and d In Δa/dT were calculated by means of the rotational isomeric state model. Better agreement between the theoretical and experimental values of these parameters was found for poly(triethylene glycol terephthalate) than for poly(diethylene glycol terephthalate). Since the polarities of the two chains are similar, intermolecular interactions involving terephthaloyl residues may be responsible for the discrepancies observed between theory and experiment for Δa in aromatic polyesters.
The β dielectric relaxation in some methacrylate polymers
Authors: Ribelles J. L. Gomez , Calleja R. Diaz 
Published: April 2003

AbstractDielectric results at frequencies between 6 × 10−4 and 105 Hz are given for the β relaxation region of poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), poly(butyl methacrylate) (PBMA), and poly(isobutyl methacrylate) (PisoBMA). Apparent activation energies and relaxation strengths are calculated, as well as the relaxation time distribution and the form factor of the Fuoss‐Kirkwood equation. It is found that in PMMA, PEMA, and PBMA, the activation energy of the β relaxation is the same, the maxima occurring at the same frequency for the same temperatures, in accordance with the dynamic mechanical results of Heijboer, the dielectric results of Mikhailov, and at variance with data of Tetsutani et al. It is also found that the form factor follows the same temperature dependence. Data on the β relaxation of poly(hydroxyethyl methacrylate) (PHEMA), not previously reported, are also presented, and the displacement toward high temperatures of the β relaxation of PisoBMA and PHEMA is justified.
A comparative study of approaches applied to the permeability of binary composite polymeric materials
Authors: Petropoulos J. H. 
Published: April 2003

AbstractA study has been made of various approaches to the problem of evaluating the permeability of a binary composite polymeric material on the basis of certain fundamental theoretical assumptions. In particular, it is assumed that the component phases form well‐defined microscopic domains and do not interact with each other or with the penetrant. The main characteristics and relative merits of these treatments are considered in detail, and it is shown that considerable information can be obtained about the range of validity and physical significance of certain well‐known formulas, which were previously applied in a largely empirical way. These results indicate specific fields of application (which include filled or semicrystalline polymers, foams, block and graft copolymers, and nonhomogeneous polymer blends) for each of the formulas in question and lead to a deeper understanding of the relation between permeability or analogous properties (such as thermal or electrical conductivity, electrical permittivity, elastic modulus, etc.) and the structural characteristics of composite polymeric (and other) materials.
Linear thermoviscoelasticity and characterization of slightly crystalline EPDM networks
Authors: Scholtens Boudewijn J. R. 
Published: April 2003

AbstractThree EPDM network families with various degrees of chemical crosslinking and slightly crystalline below about 350 K have been characterized by thermoviscoelastic and equilibrium swelling measurements. Between 300 and 450 K the thermoviscoelasticity of these elastomers, whether cured or not, is complex. Important differences from previous results on noncrystalline EPDM networks are their dependence on waiting time and temperature history below 350 K, and an equilibrium modulus for the uncured elastomers. These effects increase with rising ethylene content of the EPDM and are related to the crystallinity in the networks. A previously proposed modified time‐temperature (t‐T) superposition scheme is also applicable to these data, and the resulting frequency shift functions aT are of the usual WLF type. The vertical shift functions for the relaxational components bT are different from those for the equilibrium moduli. Experimental data demonstrate that the absolute values of the relaxational components, i.e., G″ (ω) and H(τ), are not changed by small variations in crystallinity. In addition, larger variations in crystallinity do not affect their frequency dependence, only their absolute values. On the contrary, the equilibrium modulus, and therefore all characteristics containing this as a component, is extremely sensitive to small variations in crystallinity, and hence in temperature. The linear viscoelastic characteristics of these slightly crystalline networks and their deviations from thermoviscoelastically simple behavior are discussed as functions of the ethylene content, temperature, and degree of crosslinking of the elastomer. The data provide evidence for three contributing factors, namely chemical crosslinks, crystallinity, and a more disordered type of crystallinity termed microparacrystallinity.
Temperature‐dependent melt crystallization kinetics of poly(butene‐1): A new approach to the characterization of the crystallization kinetics of semicrystalline polymers
Authors: Icenogle R. D. 
Published: April 2003

AbstractThe experimental measurements necessary to characterize the crystallization kinetics of a semicrystalline polymer are established by adopting a model for the crystallization of the polymer and specifying the range in which thermodynamic variables and other field interactions with the polymer will be varied during processes of interest. The theory for a model of instantaneous heterogeneous nucleation followed by spherulitic growth is developed. To the extent to which this model accurately describes the crystallization, determination of the spherulitic growth rate and nucleation density as a function of temperature then characterizes the temperature‐dependent crystallization kinetics of a polymer. These have been measured for poly(butene‐1), and, with the adoption of a cooling of the polymer at a constant rate as a processing model, a useful description of the melt crystallization kinetics of poly(butene‐1) is given. Literature data for the crystallization rates of linear polyethylene and isotactic polypropylene, poly(butene‐1), and polystyrene and compared.
Interpretation of photon correlation spectroscopy data: A comparison of analysis methods
Authors: Stock R. S. , Ray W. H. 
Published: April 2003

AbstractProperties of solutions and colloidal suspensions such as molecular and particle dynamics, diffusivities, and size distributions may be determined through dynamic light‐scattering experiments. Here a number of methods for predicting the details of the linewidth distribution from photon correlation spectroscopy data are reviewed. Their performance on simulated data (with and without noise added) and experimental data from polystyrene latex standards (including a mixture of two standards) is compared. Methods which do not assume a specific form for the distribution are considered. These include cumulants, histograms, exponential sampling, subdistributions, a non‐negatively constrained histogram, and Provencher's constrained regularization. Constrained regularization was found to be most robust to noise present in the autocorrelation function and therefore most reliable for analyzing experimental data; however, the method sometimes oversmoothed the distribution. For bimodal distributions the histogram method performed well in our testing, especially when the approximate peak locations were known a priori. Two linear least‐squares fitting methods, exponential sampling and the non‐negatively constrained histogram, yield accurate values for the overall mean and standard deviation and can be implemented easily on a microcomputer. The linear subdistribution method, although computationally fast, sometimes was not as accurate as other methods.
Application of the method of brather for the determination of complex dielectric permittivity from measurements of isothermal polarization current
Authors: Ribelles J. L. Gomez , Calleja R. Diaz 
Published: April 2003

AbstractSome years ago, Brather proposed a method for calculation of the real and imaginary parts of the complex dielectric permittivity starting from measurements of isothermal polarization current. This method shows some advantages over the Hamon method, which is normally used. Both methods are applied in this work to the β relaxation of poly(butyl methacrylate). It is concluded that, with the usual accuracy of measurement, a combination of the two methods is advisable; Hamon's method is taken to be a first approximation to that of Brather. Results following the two procedures are compared, and their respective advantages and disadvantages are discussed.
Irradiation of ultrahigh‐molecular‐weight polyethylene
Authors: Shinde A. , Salovey R. 
Published: April 2003

AbstractAn ultrahigh‐molecular‐weight polyethylene material covering a range of crystallinity from 42 to 79% increased in calorimetric crystallinity as a result of chain scission following ionizing irradiation. Carbonyl was formed by a diffusion‐limited reaction of oxygen with long‐lived free radicals. Trans‐vinylene production was linear with radiation dose and was highest for the sample of highest crystallinity but was not sensitive to environment.
Chemiluminescence study of polymer oxidative stability
Authors: Zlatkevich Lev 
Published: April 2003

AbstractThe application of the chemiluminescence technique to the study of polymer oxidative stability is discussed. For the initial stages of oxidation a sigmoidal change in the chemiluminescence intensity with time is justified when the experiment is performed isothermally at high oxygen pressure, whereas at low oxygen pressure and constant heating rate an exponential increase in the chemiluminescence intensity is expected. For advanced stages of oxidation depending on the ratio between the initial and equilibrium levels of hydroperoxides, the intensity of emitted light may either grow or decay until the equilibrium concentration of hydroperoxides is established. Two major parameters of an autocatalytic oxidation (induction time and oxidation rate) can be obtained by carrying out the experiment in an oxygen atmosphere at constant temperature. Alternatively, the extent of oxidation in a certain temperature region can be evaluated when a constant‐heating‐rate experiment is conducted under nitrogen.
Dilute solutions of poly(vinyl alcohol) derived from vinyl trifluoroacetate
Authors: Yamaura Kazuo , Hirata Kohsei , Tamura Satoko , Matsuzawa Shuji 
Published: April 2003

AbstractThe dilute‐solution behavior of poly(vinyl alcohol) (PVAVTFA), derived from vinyl trifluoroacetate, in water‐dimethylsulfoxide (DMSO) mixtures was investigated. With solvent mixtures ranging from 10 to 20 vol % DMSO, the relation between the reduced viscosity ηsp/C and the polymer concentration C was linear for polymer concentrations above 0.2 g/dL, whereas in solutions in mixed solvents of other compositions the dependence was linear for polymer concentrations above 0.1 g/dL. The relation between the intrinsic viscosity [η] obtained for aqueous solutions of PVAVTFA and the molecular weight M estimated from viscosity measurements in solutions of poly(vinyl acetate) (PVAVTFA), obtained by acetylation of PVAVTFA, was given by [η] = 7.34 × 10−4 M0.63. The value of [η] was greatest for the solvent mixture with 10 vol % DMSO and smallest for about 50 vol % DMSO, and Huggins constants k were smallest and greatest for these two cases, respectively. The turbidity of the solutions of low‐molecular‐weight PVAVTFA, was higher than that of high‐molecular‐weight PVAVTFA up to 30 vol % DMSO, and the reverse relation held for 40‐70 vol % DMSO.
Elastic moduli of ultradrawn polyethylene
Authors: Choy C. L. , Leung W. P. 
Published: April 2003

AbstractThe five independent elastic moduli C11, C12, C13, C33, and C44 of oriented high‐density polyethylene with draw ratio λ from 1 to 27 have been determined from −60 to 100°C by an ultrasonic method at 10 MHz. At low temperature the sharp rise in the axial extensional modulus C33 with increasing λ and the slight changes in the other moduli result from chain alignment and the increase in the number of intercrystalline bridges connecting the crystalline blocks. At high temperature (say, 100°C) the transverse extensional modulus C11, as well as the axial (C44) and transverse (C66) shear moduli, also show substantial increases, reflecting the prominent reinforcing effect of stiff crystalline bridges in this temperature region where the amorphous matrix is rubbery. If the crystalline bridges are regarded as the fiber phase, the mechanical behavior can be understood in terms of the Halpin–Tsai equation for aligned short‐fiber composites.
Rheological and DSC changes in poly(vinyl alcohol) gels induced by immersion in water
Authors: Watase M. , Nishinari K. 
Published: April 2003

AbstractPoly(vinyl alcohol) (PVA) gels were prepared by freezing and thawing aqueous solutions at temperatures from −20 to 15°C. The temperature was varied periodically by use of a computer. The endothermic DSC peak was observed for the PVA gels at about 60°C for five specimens of different degrees of saponification (DS). Another endothermic peak was also observed in the range 67–80°C, and this peak shifted to higher temperature with increasing DS. These endothermic peaks shifted to lower temperature on immersion of the PVA gels in water. The dynamic Young's modulus E′ at room temperature was also decreased by immersion of PVA gels in water; E′ decreased monotonically with increasing temperature for PVA gels without immersion in water, while it increased up to a certain temperature and then decreased with increasing temperature for PVA gels in water. The X‐ray diffraction showed a characteristic crystalline pattern for PVA gels of higher DS, and this peak was intensified by stretching the gel.
Differential sorption in viscoelastic fluids
Authors: Durning C. J. 
Published: April 2003

AbstractThe diffusion of organic solvents in concentrated polymer solutions often deviates from the predictions of Fick's second law, especially when the solution is in the glassy state; such behavior is called anomalous or non‐Fickian. This paper analyzes the one‐dimensional sorption of a solvent into a concentrated polymer solution under a small driving force. The treatment includes the effect of an entanglement network on the process as postulated by Thomas and Windle. The deformation of the entanglement network during sorption creates a normal stress on the solvent equivalent to an osmotic pressure. Including the osmotic pressure gradient in the driving force for solvent diffusion leads to a linear, third‐order partial differential equation for solvent concentration distributions. By evaluating the physical constants in the theory for the system methyl acetate/poly(methyl methacrylate) at 30°C the treatment is shown to predict the anomalous characteristics found experimentally.
Short‐branch formation via the roedel mechanism in copolymers of ethylene and vinyl acetate
Authors: Viswanadhan V. N. , Mattice Wayne L. 
Published: April 2003

AbstractA realistic rotational isomeric state model has been used to estimate the relative probabilities of the formation of various types of short branches in ethylene–vinyl acetate copolymers that are rich in ethylene. Butyl is predicted to be the most common short branch in all of the copolymers examined, although it is less common in the copolymers than in low‐density polyethylene. The major factor responsible for the suppression of the R04 backbiting intrachain radical transfer is the increased preference for trans states at the mainchain bonds flanking the attachment site for an isolated acetoxy side chain.
The local structure of blends of polystyrene and poly(2,6‐dimethylphenylene oxide)
Authors: Mitchell G. R. , Windle A. H. 
Published: April 2003

AbstractPolystyrene (PS) and poly(2,6‐dimethylphenylene oxide) (PPO) are miscible over the complete composition range. The addition of 30–40% PPO to PS changes the mechanical behavior of the material from brittle to tough and ductile. The x‐ray scattering curves from unoriented and oriented samples of PS and of PPO are compared with those from a 50/50 blend. The introduction of PPO into PS disrupts microsegregation of phenyl groups into stacks which are a feature of the pure polymer and which may be responsible for formation of sharp shear bands and brittle behavior of PS. The local structure of the blend is significantly different from both PS and PPO.
Miscibility and deformation behavior in some thermoplastic polymer blends containing poly(styrene‐co‐acrylonitrile)
Authors: Mendelson Robert A. 
Published: April 2003

AbstractMiscibility in blends of poly(styrene‐co‐acrylonitrile) (PSAN) with several other polymeric components has been investigated over a range of compositions by means of thermal analysis and transmission electron microscopy. Systems in vestigated were (i) PSAN/polycarbonate (PC), (ii) PSAN/styrene‐maleic anhydride‐methyl methacrylate terpolymer (S/MA/MM), (iii) PSAN/polynorbornene nitrile (PNN), and (iv) PSAN//S/MA/MM//PC. PSAN/PC was demonstrated to be partially miscible in all proportions over the PSAN copolymer composition range 23–70 wt % AN, while the miscibility or lack thereof of PSAN//S/MA/MM depended on the relative AN and MA contents of the PSAN and S/MA/MM, respectively. In contrast, PSAN/PNN was found to be immiscible in all proporations, while the system PSAN//S/MA/MM//PC was shown to be partially miscible. Deformation studies performed on rubber‐modified versions of these blends defined deformation mode and microstructural deformation behavior. Dual extensometer tensile testing yielded relative contributions of crazing and of plastic flow, which correlated both with blend composition and with toughness. TEM observations of deformed specimens indicated a deformation process in the multiphase matrix blends consisting of craze initiation and propagation in the rubber‐containing phase, craze arresting in the ductile second matrix phase, and coordinated extensive deformation of the matrix phases and of the rubber particles, where the ability to support the latter coordinated forms of deformation were observed to increase with increasing proportion of plastically deforming phase.
Dynamic behavior of flexible polymers at a solid/liquid interface
Authors: Pefferkorn E. , Carroy A. , Varoqui R. 
Published: April 2003

AbstractThe mean time spent by a macromolecule at a solid/liquid interface is analyzed in the region of adsorption saturation. The method consists of carrying out preliminary adsorption with radioactively labeled high‐molecular‐weight polyacrylamide and subsequently exposing the surface to a solution of unlabeled polyacrylamide. It was found that, apart from a small fraction of polymers “loosely” attached, the exchange between labeled and unlabeled polymers takes place at the interface at a very slow rate. Furthermore, desorption of surface molecules occurs only in the presence of a solution, and then the rate of desorption increases proportionally to the number of molecules in the solution. A mechanism based on a bimolecular chemical exchange process is proposed.
Conformational analysis of substituted polyacetylenes
Authors: Leclerc Mario , Prud'homme Robert E. 
Published: April 2003

AbstractA conformational analysis of isolated chains of polymethylacetylene (PMA), polypentylacetylene (PPA), and poly(t‐butylacetylene) (PTA) was carried out taking into account interactions between nonbonded atoms and torsional potentials. It was found that the trans configuration of all three polymers is more stable than the cis configuration, the difference in potential energy between the trans and the cis isomers however being very small for PTA, leading to the possibility of observing a trans→ cis isomerization in some solvents. The calculations show that the substituted polyacetylenes are not found in a planar conformation, the larger deviations from planarity being found with the bulkier substituents: PTA > PPA > PMA. A correlation could be established between the UV absorption limit of the samples and the minimum torsional angle of the potential‐energy functions. This relation predicts that the absorption limit is shifted to long wavelengths on increasing the planarity of the molecule. Moreover, UV spectra could be calculated from the potential‐energy functions, and it is shown that the potential‐energy functions of other substituted polyacetylenes can be calculated from their experimental UV spectra.
Quantitative small‐angle light scattering studies of the melting of poly(ethylene terephthalate)
Authors: Tabar R. J. , Leite‐James P , Stein R. S. 
Published: April 2003

AbstractQuantitative Hv small‐angle light‐scattering (SALS) studies of the melting of poly(ethylene terephthalate) (PET) have been performed. The results are compared with those from differential scanning calorimetry (DSC). It is found that fully grown spherulites melt over a temperature range of about 20°C without change in spherulite size, number, or internal disorder. The decrease in Hv SALS intensity is due to a decrease in spherulitic crystallinity over the melting range. The corrected experimental intensities are lower than, but in reasonable agreement with, the theoretically predicted intensities based on the DSC results. Procedures are presented for the quantitative analysis of Hv SALS intensities from spherulitic systems, including the corrections for the experimental, external disorder, and internal disorder effects.