bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical absorption spectrum of PMMA via laser calorimetry
Authors: Avakian P. , Hsu W. Y. , Meakin P. , Snyder H. L. 
Published: April 2003

AbstractThe optical absorption spectrum of poly(methyl methacrylate) (PMMA) has been obtained in the wavelength range 570–780 nm via laser calorimetry (employing a dye laser source). Because of the low thermal conductivity of PMMA, the complete solution to the heat conduction equation (carried out numerically) was required in the analysis of the data. At the wavelength of minimum absorption (near 647 nm), the absorption coefficient had the value 153 dB/km.
Preoriented poly(ethylene terephthalate) yarns: Influence of the gauche‐trans transformation on crystallization
Authors: Galli R. , Canetti M. , Sadocco P. , Seves A. , Vicini L. 
Published: April 2003

AbstractEffects of macromolecular orientation on the crystallization of preoriented poly(ethylene terephthalate) filaments were studied. Infrared spectrophotometry and differential scanning calorimetry analyses showed that macromolecular segments in the trans conformation begin to crystallize below the glass transition temperature. Since filaments prepared by stretching at room temperature have different degrees of orientation, it is possible to evidence correlations between crystallization from an anisotropic matrix and the resulting morphology.
Local composition effect in poly(dimethyl siloxane) solutions: A comparison of two models
Authors: Cánovas A. , Rubio R. G. , Renuncio J. A. R. 
Published: April 2003

AbstractTwo polymer solution models have been used to analyze poly(dimethyl siloxane) (PDMS) + alkane and PDMS + ketone systems. The free‐volume and nonrandom interaction contributions are studied separately in order to compare the expressions for the local site fractions used in the two models. Predictions of the reduced residual chemical potential and excess volumes are discussed and compared with those found in the literature for these systems.
Densification effect on physical properties of atactic polystyrene
Authors: Destruel P. , Ai Bui , Hoang‐Thê‐Giam  
Published: April 2003

AbstractAtactic polystyrene has been densified under hydrostatic pressure, up to 2 kbar, at about 180°C. Dielectric measurements were made on densified and nondensified polystyrene samples by using the thermally stimulated depolarization current (TSDC) and the absorption and resorption current methods. The dielectric loss is modified by the densification. This effect can be explained in terms of the free‐volume reduction and the internal stress induced in the material during densification.
Vapor‐pressure osmometry and inverse gas chromatography in the analysis of thermodynamic properties of polymer solutions
Authors: Fernández‐Berridi M. J. , Eguiazábal J. I. , Elorza J. M. , Iruin J. J. 
Published: April 2003

AbstractThe primary objective of this work is to check the utility of vapor‐pressure osmometry as an experimental technique in obtaining thermodynamic data on polymer/solvent systems. The second objective is to obtain experimental values for the exchange energy parameters ΔP, X, and ζ of the theory of Sanchez and Lacombe. With respect to the first objective, solvent activities of polyiso‐butylene/benzene mixtures have been measured at several concentrations up to 600 g/kg of the solvent and at two temperatures. From the activities, it is possible to determine free energies, entropies, and enthalpies and their concentration dependence. Satisfactory agreement has been found between the results obtained and data provided by other techniques such as membrane osmometry and the Cahn electrobalance. These and other data obtained by inverse gas chromatography for the same mixture in the range 35–200°C have been used in calculating the exchange energy parameter of the lattice fluid theory at different concentrations and temperatures.
Nonhomogeneous state of stress, strain, and swelling in amorphous polymer networks
Authors: Erman Burak 
Published: April 2003

AbstractThe total free energy of an amorphous, crosslinked polymer is given as ΔA = ΔAmix + ΔAel, where ΔAmix indicates the free energy of mixing of the crosslinked polymer and the solvent to which the network is exposed throughout the deformation process; ΔAel indicates the elastic free energy of the network as a function of strain, including the effect of dilation with the solvent. The explicit forms of the mixing and the elastic free energies are obtained from the molecular theory of rubber elasticity. Recent developments in this field allow accurate representation of the behavior of swollen networks under strain. Expressions for the stress in terms of strain and swelling ratio are obtained from the free energy. Formulation of boundary‐value problems are discussed. Bending of a cuboid subject to the action of a swelling agent is analyzed as an example. Material parameters are chosen for a crosslinked amorphous network. The distribution of stresses, strains, and solvent in the bent cuboid are calculated numerically. The magnitude of moments applied at the two ends are calculated for different degrees of flexure. Results are compared with those obtained for the same network in the dry state.
Drawing by solid‐state coextrusion of blends of atactic and isotactic polystyrene with poly(2,6‐dimethyl‐1,4‐phenylene oxide)
Authors: Wang Li‐Hui , Porter Roger S. 
Published: April 2003

AbstractAtactic polystyrene (aPS)/poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) and isotactic polystyrene (iPS)/PPO compatible blends of varied composition were subjected to solid‐state coextrusion. The efficiency of drawing, orientation, and crystallinity development were studied as a function of composition and draw ratio. The efficiency of drawing, as measured by elastic recovery, is high for coextrusion at temperatures ≲40°C above the glass transition temperature of the particular blend. The maximum attainable draw ratio for the blends decreased with increasing PPO concentration; the highest blend draw ratio attained was 6.5 for 25 wt % PPO. The orientation on drawing, as measured by birefringence, increased with draw but decreased with increasing PPO component at the same draw ratio. When PPO was <50% in iPS/PPO blends, iPS crystallized on draw. The morphology of drawn blends was studied by electron microscopy and wide‐angle x‐ray scattering.
Some electrophysical properties of polyphthalocyanines under the action of high pressure and shear deformation
Authors: Zhorin V. A. , Beshenko S. I. , Makarova L. I. , Sherle A. I. , Berlin Yu. A. , Enikolopian N. S. 
Published: April 2003

AbstractThe effect of high pressure or the combined action of high pressure and shear deformation on the conductivity G and capacitance C of metal‐free polyphthalocyanines (PPhCs), differing in macromolecular size, order, and degree of crosslinking, has been studied. It has been found that both G and C increase with compression. A similar phenomenon is observed under the combined action of high pressure and shear deformation on PPhC, but in this case the critical pressure needed for change in G is lower than that observed in uniaxial compression experiments. Spectroscopic investigations show that the effects of pressure and deformation on the electrophysical properties of samples under load is not connected with changes in the chemical structure of PPhC, but appear to be due to the change in the average distance between the regions of continuous conjugation. The sizes of such regions may be increased by preliminary thermal treatment.
Ionic conductivity of hybrid films composed of polyacrylonitrile, ethylene carbonate, and LiClO4
Authors: Watanabe Masayoshi , Kanba Motoi , Nagaoka Katsuro , Shinohara Isao 
Published: April 2003

AbstractThe electrical conductivity of hybrid films consisting of polyacrylonitrile (PAN), ethylene carbonate (EC), and LiClO4 was investigated. In these films, EC and LiClO4 are found to be molecularly dispersed in PAN, forming solid solutions over a wide composition range. The ionic character of the electrical conductivity is demonstrated. The conductivity is not correlated with the content of LiClO4 or of PAN, but primarily with the mole ratio [EC]/[LiClO4] in the films. An increase in the [EC]/[LiClO4] ratio enhances the conductivity. When the ratio is about 2, the conductivity attains 10−4–10−5 S cm−1 at 25°C. This change in conductivity results from a change in carrier mobility. PAN makes the films solid without decreasing the carrier mobility. In the hybrid films, the carrier mobility and the macroscopic viscosity are not related by Walden's rule. The high conductivity is due to regions in the film characterized by a low microscopic viscosity. This is determined by the mole ratio [EC]/[LiClO4] and largely controls the carrier mobility.
Radiation chemistry of linear low‐density polyethylene. I. Gel formation and unsaturation effects
Authors: Basheer Rafil , Dole Malcolm 
Published: April 2003

AbstractQuenched and annealed samples of linear low‐density polyethylene (LLDPE) were irradiated with 60Co γ rays in vacuo at room temperature. The data follow rather accurately Charlesby's equation s = k/r, where s is the soluble fraction, r the dose, and k a constant from which G(X), the G‐value for crosslinks, was calculated. Crosslinking in the LLDPE is about twice as extensive at equal doses as in LHDPE. Production of vinylene unsaturation was approximately the same in the two types of polyethylene.
Temperature effects in the environmental stress cracking of polyethylene
Authors: Shanahan M. E. R. , Debski M. , Bomo F. , Schultz J. 
Published: April 2003

AbstractAn already existing model describing three types of behavior in the environmental stress cracking (ESC) of polyethylene (PE) subjected to uniaxial tensile loading at 25°C has been extended to cover the temperature range 25‐50°C. Three effects have been observed and are found to be qualitatively consistent with the model. The transition between “pure” ESC (zone 1) and liquid‐flow‐controlled behavior (zone 2) occurs at shorter times for higher temperatures—an effect mainly due to reduced liquid viscosity. “Pure” ESC is less temperature dependent than failure occurring without the liquid playing a significant role (zone 3). This has been attributed to a compensation of reduced mechanical resistance of the polymer at higher temperatures, by reduced stress concentrations at the crack tip due to local absorption of the liquid. The transition time between zones 2 and 3 increases with temperature. Although it is surprising at first sight, this effect is shown to be compatible with the ESC model.
Solid‐state coextrusion of poly(ethylene terephthalate). I. Drawing of amorphous PET
Authors: Pereira Jose R. C. , Porter Roger S. 
Published: April 2003

AbstractFilms of uniaxially oriented poly(ethylene terephthalate) (PET), Mv = 81,000, have been drawn by solid‐state coextrusion in the range 40–100°C surrounded by polyethylene. This is well below the PET melting temperature and in some cases below its glass transition temperature. Properties of the extrudates, such as degree of crystallinity, mechanical and thermal properties, were investigated as a function of coextrusion temperature and draw ratio (EDR ≤ 4.4). The results show that the percent crystallinity depends strongly on draw ratio, whereas its sensitivity to extrusion temperature is limited only to the highest draw ratio (4.4). On the other hand, Young's modulus was sensitive to both extrusion temperature and draw ratio, exhibiting a maximum at EDR = 4.4 and Text = 65°C. Above this temperature, moduli decrease apparently because of increased chain mobility, resulting in dissipation of chain orientation. Furthermore, changes in yield and tensile strength followed the changes in mechanical properties, suggesting that they are dominated by the same factors. The cold‐crystallization temperature TCC also revealed information about the morphological changes occurring during the extrusion drawing. For samples of EDR = 4.4, TCC increased with extrusion temperature, suggesting again dissipation of orientation by thermal motions. On the other hand, TCC decreases with EDR, and a ΔTCC as high as 73°C was found. Conventional drawing of amorphous PET has been widely reported. To our knowledge this is the first time oriented PET has been prepared using the advantages of solid‐state coextrusion.
Solid‐state coextrusion of poly(ethylene terephthalate). II. Drawing of semicrystalline PET
Authors: Pereira Jose R. C. , Porter Roger S. 
Published: April 2003

AbstractThe drawing of semicrystalline (33 and 50%) poly(ethylene terephthalate) (PET) films has been studied by solid‐state coextrusion. Because of its brittleness and opacity, isotropic and semicrystalline PET film is of little practical use. Early attempts to cold‐draw crystalline films led to fracture in contrast to deformation of amorphous PET. However, we have succeeded in systematically preparing films with extrusion draw ratios ≤4.4 from semicrystalline PET. In many cases, the properties of the drawn extrudates, as a function of extrusion temperature Text and extrusion draw ratio EDR, were similar to those prepared from amorphous PET. However, some remarkable differences have also been found. In the case of coextrudates prepared from isotropic 50% crystalline PET, we found that the larger the deformation, the lower the apparent resulting crystallinity. In the extreme, a 34% reduction in crystallinity after deformation was observed. For the coextrudates drawn from initially 33% crystalline PET, slightly different behavior occurred. For Text ≤ 90°C, all extrudates showed crystallinities lower than the original isotropic film, with a minimum at EDR = 3; for Text ≥ 110°C, crystallinities were slightly greater than in the original film and increased with EDR. Qualitative measurements of heats of fusion were in agreement with density gradient results for PET crystallinity. In contrast is our previous finding that extrudates from initially amorphous PET always increase in crystallinity with EDR, because of stress‐induced crystallization. The results now suggest that in the Text range investigated, the initial spherulitic structure is at least in part destroyed on drawing. In addition, the percent crystallinity is revealed to be dependent on Text, with lower values at lower temperatures. Mechanical tests show that the extrudates are similar or sometimes higher in tensile modulus when compared to amorphous PET drawn under the same conditions.
The dependence of dielectric response of an elastomer on hydrostatic pressure
Authors: Pae K. D. , Questad D. L. 
Published: April 2003

AbstractDielectric methods have been employed to study the high‐pressure behavior of a polyurethane elastomer (Solithane 113) in the vicinity of its α transition. The α‐loss peak is shifted to higher temperatures and broadened somewhat with the application of hydrostatic pressure up to 6.4 kbars. The slope ofTαvs.P, ordTα/dP, obtained at low frequencies was found to be equal todTg/dPobtained by a volumetric method. Moreover, it attained a nonzero limiting value at high pressures for each frequency tested (3—30,000 Hz) and the limiting value itself increased with increasing frequency from 10.5°C/kbar at 3 Hz to 18°C/kbar at 30,000 Hz. The activation enthalpy ΔH* was found to be nearly constant over the pressure range tested, but the activation volume ΔV* decreased with increasing pressure. The relationdTα/dP=T(ΔV*/ΔH*) was shown to hold for the elastomer.
Rheological studies of moderately concentrated polystyrene solutions in the vicinity of the θ temperature. II. Shear‐rate dependence for different thermodynamic conditions
Authors: Ballauff M. , Krämer H. , Wolf B. A. 
Published: April 2003

AbstractThe viscosity data of moderately concentrated polystyrene solutions in trans‐decalin (TD) (θ solvent, θ temperature 21°C) and toluene (TL) (good solvent) reported in Part I are discussed in terms of Graessley's entanglement theory. Under good solvent conditions, Graessley's master curve provides an excellent fit up to high shear rates, whereas in the vicinity of the θ conditions the data have to be modified by a parameter ηfric introduced by Ito and Shishido. The characteristic time of mechanical response to flow of chains approximately given by the shift factor τ0 is found in good solvents to be on the order of the Rouse relaxation time. In poor solvents, close to demixing, τ0 tends to much higher values, indicating a reduced chain mobility. The influence of temperature on the viscosity decreases with increasing shear. The resulting apparent energy of activation of flow shows very small or even negative values at high shear rates. This behavior can be explained by the modified Graessley theory, however, in a quite natural way.
Studies on dilute solutions of rodlike macroions. II. Electrostatic effects
Authors: Cotts P. Metzger , Berry G. C. 
Published: April 2003

AbstractA group of rodlike polymers soluble only in strong protic acids was studied using light scattering and viscosity techniques. These include poly(1,4‐phenylene benzobisoxazole), poly(1,4‐phenylene benzobisthiazole) and poly(1,4‐phenylene terephthalamide). The solution properties were dependent on the ionic strength of the acid used as solvent. In a low ionic strength acid such as chlorosulfonic acid, the polymer solutions exhibited decreased unpolarized scattering, an extremely small translational diffusion coefficient, and high viscosity. All of these effects could be eliminated by the addition of a salt such as lithium chlorosulfonate, which increased the ionic strength of the solvent. The effects were attributed to a pseudo ordering of the polymer solvent system caused by electrostatic repulsions between protonated polymer chains effective over large distances (ca. 100 Å) in the low ionic strength solvent. This type of ordering is distinct from actual anisotropic phase formation, which occurs at higher concentrations in these systems. Analysis of data at infinite dilution gave a persistence length of at least 45 nm for poly(1,4‐phenylene terephthalamide), larger than previous experimental results, but in accord with recent rotational isomeric state calculations and similar to experimental data for poly(p‐benzamide).
Thermoluminescence from extended‐chain crystals of polyethylene
Authors: Hashimoto Toshimasa , Ogita Kiyoshi , Umemoto Susumu , Sakai Tetsuya 
Published: April 2003

AbstractThermoluminescence (TL) has been observed in γ‐irradiated extended‐chain crystals of polyethylene above room temperature. The TL curve, which exhibits four peaks at 50, 90, 120, and 140°C, is different from that given by folded‐chain crystals, in both shape and intensity. In particular, a shape, strong glow peak is observed at 140°C, corresponding to the melting temperature of the extended chain crystals. These results are discussed in relation to independent measurements by differential scanning calorimetry and electron spin resonance.
Retardation of spherulitic growth rate in the crystallization of isotactic polystyrene due to the presence of nucleant
Authors: Kennedy M. A. , Turturro G. , Brown G. R. , St‐Pierre L. E. 
Published: April 2003

AbstractAlthough the rate of heterogeneous nucleation of crystallization in isotactic polystyrene, as studied by photomicroscopy, is markedly increased by addition of fine‐particle silica, the rate of subsequent radial growth of spherulites formed is diminished. The latter observation is rationalized on the basis of a modified Hoffman–Lauritzen treatment wherein the nucleant is depicted as a quasicrosslink which impedes the transport of polymer segments.
Polymer single crystals of poly(4‐hydroxybenzoate). II. A contribution to crystal structure and polymorphism
Authors: Lieser G. 
Published: April 2003

AbstractElectron diffraction has been used to investigate the structure of a wide range of as‐polymerized crystals of poly(4‐hydroxybenzoate) [systematic name: poly(1,4‐oxybenzoyl)]. The chemical composition and the degree of polymerization (DP) have been varied and some samples have been thermally treated. At room temperature two crystalline modifications with orthorhombic unit cells coexist. The chains adopt a 21 helical conformation in both forms, but there are differences for oligomer and polymer crystals. Oligomers of low DP have an extended chain‐conformation, whereas in polymers a shortening of the repeat distance along the chain is observed as a function of both the DP and the crystallization conditions. From the most extensive data sets we have derived the lattice parameters a = 7.52, b = 5.70, and c = 12.49 Å for polymer crystals of phase I, and the subcell parameters for oligomer crystals of phase II a = 3.77, b = 11.06, and c = 12.89 Å. Both phases contain two chains per unit cell. In addition to modifications I and II several defect structures exist the unit cells of which contain more than two chains. At temperatures which depend on the degree of polymerization, a phase transition to a third modification takes place. The large difference between the densities of phase III as compared to both phase I and II suggests that torsional degrees of freedom exist in phase III which allow a certain mobility of the phenyl and ester groups. This mobility enables the end groups of adjacent layers in interlamellar regions of oligomer crystals to undergo transesterification reactions and therefore to increase the molecular weight of the samples.
Study of molecular deformation mechanisms in the glassy state. I. Temperature effect on stress‐birefringence and strain‐birefringence responses of poly(methyl methacrylate)
Authors: Hong Su‐Don , Chung Shirley Y. , Fedors Robert F. , Moacanin Jovan 
Published: April 2003

AbstractIn order to gain better understanding of the molecular deformation processes occurring in poly‐(methyl methacrylate), a series of studies was carried out in uniaxial tension on the simultaneous stress and birefringence response in both constant‐strain‐rate and stress relaxation experiments. The former covered the temperature range −120 to 75°C and the latter 0 to 90°C. Three deformation mechanisms, i.e., (i) change in intermolecular distance, (ii) distortion of the conformation of the COOCH3 group from its thermal equilibrium state, and (iii) orientation of main‐chain segments, are invoked to interpret the experimental results. It is concluded that, in the temperature range from −120 to 75°C and possibly at higher temperatures as well, the polymer chains deform in the small‐strain region by an orientation of those chain segments having lower potential‐energy barriers to conformational changes and straining those chain segments having higher potential‐energy barriers. Subsequent chain orientation of the already strained segments occur in the higher strain regions. Changes in intermolecular distances occur over the entire temperature range from −120 to 90°C, but their magnitude decreases gradually as the temperature increases from −40 to 40°C and then decreases sharply for temperatures above 40°C. Strain‐induced distortion of the conformation of the COOCH3 group may involve only rotation of the OCH3 group around the CO bond rather than rotation of the entire ester group itself.
The effect of dye sorption on electromechanical properties in sodium poly(L‐glutamate)
Authors: Ando Yutaka , Kawabata Naruto , Nishida Kenzo 
Published: April 2003

AbstractPiezoelectric constant, Young's elastic modulus, and dielectric constant of undyed and dyed films of poly(L‐glutamate) were measured at 10 Hz over the temperature range −120 to 120°C. The temperature of the maximum in −d″14 shifts toward higher temperature up to 0.6 mg/g polymer of dye uptake and then shifts toward lower temperature by further dye sorption. The variation of the piezoelectric modulus was interpreted by the change of mobility of impurity ions in the sample.