bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanical relaxations and moduli of oriented nylon 66 and nylon 6
Authors: Leung W. P. , Ho K. H. , Choy C. L. 
Published: April 2003

AbstractThe mechanical relaxations of dry and wet nylon 66 and nylon 6 with draw ratios λ = 1–3 have been studied from −180 to 160°C and in the frequency range of 1 Hz to 10 MHz. The five independent elastic moduli C11, C12, C13, C33, and C44 have also been determined by an ultrasonic method at 10 MHz. Wide‐angle x‐ray diffraction and birefringence measurements reveal that the crystalline orientation rises sharply at low λ and becomes saturated near λ = 3; the amorphous orientation function increases continuously, reaching values of 0.3–0.5 at λ = 3. The alignment of molecular chains and the presence of taut tie molecules in the amorphous regions lead to a lowering of segmental mobility, thereby reducing the magnitude and increasing the peak temperature and activation energy of the α relaxation. Water absorption weakens the interchain bonding and so gives rise to effects opposite to those of drawing. At low temperature, the development of mechanical anisotropy is largely determined by the overall chain orientation, with the c‐shear mechanism contributing a small additional effect. However, above the α relaxation, where the amorphous region is rubbery, the stiffening effect of taut tie molecules becomes dominant and leads to increases in all moduli.
On the ordered structure of poly(butylene terephthalate) in polyester blends
Authors: Desper C. Richard , Kimura M. , Porter Roger S. 
Published: April 2003

AbstractSome unusual x‐ray diffraction results have been obtained corresponding to an ordered structure in binary blends of a poly(butylene terephthalate) (PBT) with a polyarylate. The polyarylate is a noncrystallizable copolyester of bisphenol‐A with a 50–50 mix of terephthaloylisophthaloyl units. The two polyesters have been previously found by us to be compatible in their mutual amorphous phase. The x‐ray data are shown to be consistent with a nematic order for the PBT in the blends.
Crystallization in stretched and unstretched EPDM elastomers
Authors: Scholtens B. J. R. , Riande E. , Mark J. E. 
Published: April 2003

AbstractElastomeric networks were prepared from ethylene‐propylene‐diene (DPDM) terpolymers containing 5‐ethylidene‐2‐norbornene as the diene monomer incorporated to facilitate crosslinking. Such materials, although highly elastomeric, show some crystallinity over much of the compositional range and thus an understanding of their mechanical properties requires characterization of this crystallinity in both the stretched and unstretched states. The properties and techniques used in the present investigation for this purpose were differential scanning calorimetry, stress‐strain isotherms (at various extension rates), stress‐temperature coefficients, birefringence and stress‐optical coefficients, polarized light microscopy, small‐angle light scattering, and wide‐angle x‐ray scattering. Correlations of the various types of results obtained are used to elucidate the dependence of EPDM network crystallization on composition, strain, and temperature. It was found to be particularly important to use a wide variety of techniques to provide a reliable characterization of the poorly developed crystallinity present in typical EPDM elastomers.
Surface orientation of polypropylene. II. Determination for uniaxially and biaxially oriented films using internal reflection spectroscopy
Authors: Mirabella Francis M. 
Published: April 2003

AbstractThe major objective of this work was to develop a simple and rapid technique to quantitatively measure the macromolecular chain orientation in polypropylene surfaces. A previously described experimental design employing attenuated total reflection spectroscopy near the critical angle was applied. The infrared dichroism of the 841‐ and 809‐cm−1 bands of polypropylene was used to quantitatively determine a fractional orientation function of the macromolecular chains along the three major film axes (machine direction, transverse direction, and thickness or normal direction). The surface orientation of a set of polypropylene films uniaxially extended from 0 to 500% was determined using this technique. The variation of surface orientation, bulk crystallinity, and thickness with extension of these uniaxially extended films were compared. The surface orientation of an unoriented and several biaxially oriented polypropylene films was compared to the bulk orientation determined by a similar transmission infrared dichroism method. It was found that surface and bulk orientation were generally similar. It was shown that rather small orientations could be measured by the surface orientation method and that it was applicable to multilayer films and very thick samples, where the transmission method fails.
Thermodynamic and conformational properties of partially butyralized poly(vinyl alcohol) in aqueous solution
Authors: Shiomi Tomoo , Imai Kiyokazu , Watanabe Chiyoji , Miya Masamitsu 
Published: April 2003

AbstractPhase separation behavior has been studied in aqueous solutions of partially butyralized poly(vinyl alcohol) (BuPVA) with various degrees of butyralization xBu and various molecular weights. It is found that these systems exhibit both upper and lower critical solution temperatures. The theta temperatures θLCST, evaluated by means of Shultz–Flory plots, are found to be 25.1, 23.3, and 14.4°C for BuPVAs with xBu of 7.5, 9.9, and 12.7 mol %, respectively. The unperturbed dimension 〈R2〉0/M is evaluated as ca. 1.2 × 10−16 Å2 in the above range of xBu from viscosity measurement at θLCST. Properties of the BuPVA solutions are compared with those of other PVA copolymers.
Configurational studies on amylose. I. Scattering functions
Authors: Yamaguchi Saburo , Hayashi Hisao , Hamada Fumiyuki , Nakajima Akio 
Published: April 2003

AbstractScattering functions for amylose chains have been calculated as a statistical mechanical average over eligible configurations based on the rotational isomeric state approximation. Main emphasis has been placed on an intermediate‐angle range (0.1 < h = (4π/γ)sinθ < 1.0 Å−1) where the scattering function is sensitive to local chain configurations. In order to avoid overestimation of the regularity of chain configurations, the rotational isomeric states for each glycosidic bond have been defined by a set of discrete torsion angles at intervals of 5°. Pair correlation functions for atoms separated by sequences shorter than 31 glucose units are evaluated by the Monte Carlo method, while the interference for longer sequences is calculated by a series expansion in the even moments of the chain. All carbons and all skeletal oxygens are treated as point scatterers in order to incorporate all the interferences between atoms in unit pairs in the calculations. The calculated scattering function shows appreciable oscillation at intermediate angles, reflecting the characteristic helical tendency of the configurations. The Debye function is found to be inadequate in the intermediate‐angle region owing to the non‐Gaussian character of the distribution function and to breakdown of the assumption that the mean‐square distance between a pair of atoms is proportional to the number of bonds between them, because of the bulkiness of the glucose unit.
Optical absorption of perdeuterated PMMA and influence of water
Authors: Avakian P. , Hsu W. Y. , Meakin P. , Snyder H. L. 
Published: April 2003

AbstractThe optical absorption coefficient of perdeuterated poly(methyl methacrylate) has been obtained by laser calorimetry at 568.2, 647.1, 676.4, and 752.5 nm. The lowest value of 18 dB/km is obtained at 647.1 nm. The dramatic effect of water uptake by the polymer on the total optical attenuation spectrum in the wavelength range 500–1000 nm has been investigated.
Isobaric thermal behavior of glasses during uniform cooling and heating. III. Predictions from the multiparameter KAHR model
Authors: Ramos A. R. , Hutchinson J. M. , Kovacs A. J. 
Published: April 2003

AbstractThe behavior of the multiparameter KAHR model (put forward by Kovacs, Aklonis, Hutchinson, and Ramos) has been investigated using a single‐box retardation spectrum to describe the kinetics of volume and enthalpy recovery of glasses in three‐step thermal cycles involving colling, isothermal annealing, and subsequent reheating. It has been shown that during the heating stage, the system may display up to three peaks in the expansion coefficient and the specific heat. The shifts of the peak temperatures Tp with respect to each of the four experimental variables Yi defining the thermal history are analyzed systematically in terms of a set of reduced variables, scaled by two of the material constants of the system. These shifts, from which the various partial derivatives (∂Tp/∂Yi)j≠i are estimated, are determined for five values of another material parameter x, which characterizes the relative contributions (O ≤ x ≤ 1) of temperature and structure to the retardation times. the results show that the upper peak is always small and is insensitive to the characteristics of the spectrum and to the value of x, while the relevant peak temperature depens only slightly on the cooling and heating rates. On the Other hand, the magnitude and the shifts of the main peak depend on all the experimental variables and the material constants in a rather complex manner. It is shown, however, that in limiting situations, involving fast heating of well‐stabilized glasses, the shifts of the relevant peak temperature T̂all reduce to a linear function of x−1. since this relationship is rather insensitive to the shape of the spectrum, the experimental determination of any one of the nonzero partial derivatives of T̂ provides a simple means for an independent estimate of the value of the important material constant x. Finally, the shifts of the upper and main peaks relative to each other will be analyzed in terms of the pertinent experimental variables and compared with actual data reported in the literature for polymer glasses.
The effect of crystallinity and crosslinking on the depression of the glass transition temperature in nylon 6 by water
Authors: Jin X. , Ellis T. S. , Karasz F. E. 
Published: April 2003

AbstractThe influence of crystallinity and crosslinking on the depression of the glass transition temperature in nylon 6 by water has been investigated by dynamic mechanical methods. Radiation crosslinking by high‐energy electrons was effective in preventing morphological changes during the measurement of the incremental change in heat capacity (ΔCp) at Tg, which was performed by differential scanning calorimetry. The experimentally determined value of ΔCp, when normalized to account for the crystalline phase, was found to deviate from a linear two‐phase relation and was reduced further than would be expected based on this model. It is proposed that nylon 6 is best described by a three‐phase model which consists of a crystalline domain, a wholly amorphous domain, and an “intercrystalline” region. The importance of this in explaining the relatively large depression of Tg by small quantities of water is illustrated by applying equations derived to account for the compositional dependence of Tg in polymerdiluent mixtures, based on a classical thermodynamic interpretation of the glass transition phenomenon.
The influence of strain deformation on the solubility of ethyl acetate vapor in poly(vinylidene fluoride)
Authors: Phillips J. C. , Peterlin A. , Waters P. F. 
Published: April 2003

AbstractThe degree to which a polymer film develops plastic flow depends largely on the total strain ϵ and the elongation time th. The magnitude and the time dependence of the elastic component ϵe of the total deformation are controlling factors, respectively, in the solubility and diffusion processes. The plastic deformation ϵpl seems not to contribute to the transport properties. The nonlinearity in solubility due to ϵ may be conveniently handled. In this study, the solubility of ethyl acetate vapor in poly(vinylidene fluoride) was determined as a function of pressure and total elongation at 30°C. These results suggest that the strain magnitude and time de pendence of the component deformations play important roles in transport behavior.
High‐temperature fourier transform infrared study of polystyrene/poly(vinyl methyl ether) blends
Authors: Garcia Dana 
Published: April 2003

AbstractFourier transform infrared (FTIR) studies of polystyrene (PS)/poly(vinyl methyl ether) (PVME) miscible blends as a function of temperature are presented. Below the lower critical solution temperature (LCST) little change is observed in the interaction spectrum obtained via digital subtraction techniques. Once above the LCST, the magnitude of the interaction spectrum decreases as a result of the phase separation process. Comparison of the behavior of the ether CO stretching band in the reference PVME and in the blends has yielded a lower limit estimate for the interaction energy of about 0.15 kcal/mol.
Regression rates of polymers during burning of their volatile degradation products
Authors: Jellinek H. H. G. , Juznic K. 
Published: April 2003

AbstractRegression rates as functions of air flow rates and oxygen content of the oxidant gas as well as the distance of the polymer surface from the top of the reaction vessel have been investigated for poly(methyl methacrylate), poly(α‐methyl‐styrene), a polymide, and isotactic polypropylene. The results are discussed from the standpoint of reaction kinetics, considering regression rates and energies of activation for diffusion and degradation.
Lamellar diffusion during heat treatment in meltcrystallized low‐density polyethylene
Authors: Rueda D. R. , Martinez‐Salazar J. , Calleja F. J. Baltá 
Published: April 2003

AbstractThe annealing behavior of low‐density melt‐crystallized polyethylene is discussed in terms of an unprecedented lamellar diffusion mechanism. For this purpose a combined small‐angle x‐ray diffraction (SAXS) and differential scanning calorimetry (DSC) study has been carried out. The presence of an initial double‐lamellar population is directly evidenced by electron microscopy of freeze‐cut and stained sections. The intercalation of thinner lamellae within the dominant wide‐lamella population gives rise to an x‐ray periodicity of 220 Å (structure I). The independent stacking of thinner lamellae within the material contributes to a second periodicity at 110 Å (structure II). During annealing at successively higher temperatures TA, the low‐molecular‐weight components from the thin lamellae progressively diffuse out of the double population, reinforcing the stacks of thinner lamellae. At the melting temperature of the thinner crystals a complete segregation of these lamellae takes place, and a new periodicity (structure III) corresponding to stacks of collapsed thick lamellae emerges. The periodicity of structure III increases further with TA. The thin lamellae of structure II can be extracted by a solvent, removing the corresponding SAXS peak and DSC maxima. The partial removal of thin lamellae from structure I by means of solvent extraction concurrently yields a decrease of the SAXS period. The present results suggest that molecular segregation of a low‐molecular‐weight fraction, contributing to the population of thinner lamellae, occurs during annealing.
Piezoelectric properties and molecular motion of poly(β‐hydroxybutyrate) films
Authors: Ando Yutaka , Fukada Eiichi 
Published: April 2003

AbstractPiezoelectric, elastic, and dielectric properties of films of poly(β‐hydroxybutyrate) (PHB), an optically active natural polymer, were measured as functions of frequency and temperature. In mechanical properties, three relaxation processes were observed at 10 Hz: the α dispersion at 130°C, the β dispersion at room temperature, and the γ dispersion at −120°C. It was concluded from x‐ray diffraction and the thermal expansion coefficient that the α dispersion can be ascribed to thermal molecular motions in the crystalline phase, that the β dispersion is the primary dispersion due to the glass transition, and that the γ dispersion is related to local molecular motion of the main chains in the amorphous phase. Piezoelectric relaxations were also observed in these relaxation regions. It is proposed that the high‐temperature process is due to ionic dc conduction. The piezoelectric relaxation at room temperature is ascribed to the increase of piezoelectric activity in the oriented noncrystalline phase, in which the sign of the piezoelectric modulus is opposite to that in the oriented crystalline phase.
Dependence of the elastomeric properties of bimodal networks on the lengths and amounts of the short chains
Authors: Mark J. E. , Tang M.‐Y. 
Published: April 2003

AbstractBimodal elastomeric networks were synthesized by tetrafunctionally end‐linking very short and relatively long hydroxyl‐terminated chains of poly(dimethylsiloxane). Decrease in the molecular weight of the short chains (from 880 to 660 to 460 g mol−1) generally results in significant increases in ultimate strength and energy for rupture. Decrease in the number of short chains, however, causes these two quantities to go through a maximum. Too many short chains gives essentially a brittle thermoset, and this precludes any upturn in the modulus from the limited extensibility of the short chains. Having too few short chains makes their limited extensibility irrelevant since the entire macroscopic deformation can then be taken up by the long chains present in the network.
Longitudinal acoustic mode in polymers. VII. Surface structure from swelling studies of freeze‐dried polyethylene single crystals
Authors: Chang Chih , Krimm S. 
Published: April 2003

AbstractRaman longitudinal acoustic mode (LAM) spectra have been obtained from freeze‐dried polyethylene single‐crystal samples swollen in decalin. The changes in ν(LAM) have been studied as a function of molecular weight, temperature of crystallization, and temperature of measurement. These data, together with knowledge of how terminal “defects” influence ν(LAM) of the trans stems, lead to the conclusion that surface folds and cilia are the components responding to the swelling agent. The analysis also shows what the relative effects of these structures are as a function of molecular weight and crystallization temperature. This study indicates that cilia are primarily responsible for the large increases in x‐ray long period observed for swollen single‐crystal mats.
Interpretation of anomalous sorption kinetics in polymer‐penetrant systems in terms of a time‐dependent solubility coefficient
Authors: Petropoulos J. H. 
Published: April 2003

AbstractA formulation of the molecular relaxation model of anomalous diffusion in polymers, in terms of a time‐dependent solubility coefficient, which was previously introduced and studied by us, is discussed here in greater detail. A full account of the methods of application of the treatment is given and the prediction of typical absorption and desorption kinetic features characteristic of glassy polymer‐good swelling agent systems, including Case II absorption, is demonstrated.
A quantitative electron microscopic study of the crystallite structure of molecular weight fractions of linear polyethylene
Authors: Voigt‐Martin I. G. , Mandelkern L. 
Published: April 2003

AbstractUtilizing thin‐section techniques, transmission electron microscope studies were performed on a series of bulk‐crystalized fractions of linear polyethylene covering the range M = 5 × 103−6 × 106. The crystallization conditions were varied from long‐time isothermal to rapid quenching. Quantitative analysis could be carried out on such samples crystallized under controlled conditions. The crystallite thickness distributions and long periods are presented in terms of histograms. From these data the degree of crystallinity can be calculated and was found to compare favorably with that from other methods. The amorphous thickness increases significantly with molecular weight for all modes of crystallization. On the other hand, the crystallite thickness is essentially independent of molecular weight for very rapid crystallization, and shows a complex dependence on chain length for isothermal crystallization. The tilt angle, the angle of inclination of the chain axis with the lamellar basal plane, has also been determined. There is a tendency for this angle to increase with decreasing crystallization temperature. This observation can be related to the crystallization mechanisms.
Molecular aggregation and mechanical properties of Kapton H
Authors: Kochi Masakatsu , Shimada Hiromichi , Kambe Hirotaro 
Published: April 2003

AbstractMolecular aggregation of Kapton H (KH) was investigated by small‐angle x‐ray scattering (SAXS). Superstructure parameters were estimated using a one‐dimensional model, taking into account that the SAXS from KH is anisotropic out of the film plane. The results show that KH has a two‐phase structure with a volume ratio of the ordered to the less‐ordered phase of about 1:1. The β dispersion in dynamic mechanical properties is reasonably ascribed to oscillations of p‐phenylene groups in the main chain.
Birefringence of amorphous polyoxides: Stress‐optical behavior of poly(3‐methyltetrahydrofuran)
Authors: Saiz Enrique , Tarazona María P. , Riande Evaristo , Guzmán Julio 
Published: April 2003

AbstractThe stress‐optical behavior of an unswollen elastomeric network of poly(3‐methyltetrahydrofuran) was measured for elongation ratios a in the range 1.182–1.549, at several temperatures between 20 and 60°C. No evidence of strain‐induced crystallization was found; moreover, the dependence of birefringence Δn on true stress f/A was linear in the interval of α investigated. Values of Δa ranged from 2.4 to 2.8 in units of 10−24 cm3, in the temperature range studied, with a temperature coefficient 3.1 × 10−3 K−1. Theoretical calculations carried out with the rotational‐isomeric‐state model gave values of Δa noticeably smaller than the experimental results; however, a small increase in the backbone valence angles θ improved the theoretical result of Δa without worsening that of the dipole ratio. Analysis of the Δa results seems to corroborate the conclusion obtained through the study of dipole moments concerning the preference for nucleophilic attack on the less hindered α carbon in the monomer. Theoretical and experimental values of the temperature coefficient of Δa were in clear disagreement; a qualitative explanation for this discrepancy is discussed.
Analysis of the longitudinal acoustic mode in linear aliphatic polyesters
Authors: Chang Chih , Wang Y. K. , Waldman D. A. , Hsu S. L. 
Published: April 2003

AbstractTwo intense modes are observed in the low‐frequency Raman spectra of as‐grown and annealed linear aliphatic polyester single crystals. Our experimental data in conjunction with theoretical normal mode calculations of several model oligomers reveal the two bands observed to be vibrations of the longitudinal acoustic mode type. The unbalanced mass units associated with the ester groups couple the transverse and longitudinal motions, giving rise to the multiple modes.