bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular aggregation of solid aromatic polymers. I. Small‐angle x‐ray scattering from aromatic polyimide film
Authors: Isoda Satoru , Shimada Hiromichi , Kochi Masakatsu , Kambe Hirotaro 
Published: April 2003

AbstractMolecular aggregation in a commercial polyimide film, Du Pont Kapton, was investigated by small‐angle x‐ray scattering (SAXS). From the analysis of the desmeared SAXS curve, it is concluded that aggregation in the Kapton film can be elucidated in terms of a two‐phase structure having electron density fluctuations within the phases. For comparison with the molecular aggregation in Kapton, molecular aggregation in polyimides synthesized in our laboratory was also investigated. It was found in this case that molecular aggregation is controlled by the initial imidization temperature. Molecular aggregation of polyamic acid and polyimide cyclized at a low temperature gives amorphous structures. On the other hand, molecular aggregation of polyimide cyclized at high temperatures gives two‐phase structures like that of Kapton film. The SAXS curve for a polyimide having the two‐phase structure shows a peak due to interference between ordered regions. The two‐phase structure of the polyimide can be explained in terms of a one‐dimensional model. The more ordered phase is produced at the higher initial imidization temperature. The relative density difference between two phases is only a few percent for polyimide films cyclized at high temperatures. This result shows that the two‐phase structure of aromatic polyimide differs essentially from that of ordinary crystalline polymers.
DTA and x‐ray studies on extended‐chain crystals of polyethylene under high pressure
Authors: Maeda Yoji , Kanetsuna Hisaaki , Tagashira Katsuharu , Takemura Tetuo 
Published: April 2003

AbstractThe relation between the thermal behavior of extended‐chain crystals (ECCs) of polyethylene and the phase transitions, i.e., orthorhombic ↔ hexagonal ↔ melt, of polyethylene at high pressures above about 400 MPa has been studied by high‐pressure differential thermal analysis (DTA), and with a high‐pressure and high‐temperature x‐ray diffraction apparatus equipped with a position‐sensitive proportional counter measuring system. The original sample used in this study consists mainly of two kinds of ECC, which we designate as “ordinary extended‐chain” crystals (OECCs) and “highly‐extended‐chain” crystals (HECCs). Experimental results at pressures below 300 MPa substantiate the results previously reported: i.e., the phase diagram indicating the relation between the melting temperatures and pressure for the OECCs and HECCs can be determined for pressures up to 500 MPa.In heating at pressures above about 500 MPa, the peak intensity of the (100) reflection of the hexagonal structure decreases in two stages with increasing temperature. The phenomenon corresponds to the thermal behavior determined by high‐pressure DTA in which two small endothermic peaks can be observed at temperatures above that of the crystal transition evidenced by the strong peak. This phenomenon suggests melting in two stages of hexagonal structures with different thermal stabilities, and that the change at higher temperature may be due to fusion of the hexagonal phase annealed either below or above the transition temperature.
Column fractionation of acrylonitrile‐styrene copolymers
Authors: Ogawa Toshio , Sakai Masakazu 
Published: April 2003

AbstractAn acrylonitrile‐styrene copolymer having 51.4 wt % acrylonitrile content was fractionated using dimethylformamide and a toluene–n‐propanol mixture as solvent and nonsolvent, respectively. From characterization of the fractions, it is shown that the copolymer was fractionated principally in accordance with composition. The weight distribution curve of the copolymer was expressed as a function of both molecular weight and chemical composition on a two‐dimensional contour map. The same plotting technique was applied to a copolymer having nearly the azeotropic composition.
NMR study of the demixing process in concentrated polyisobutylene solutions
Authors: Cohen‐Addad J. P. , Roby C. 
Published: April 2003

AbstractA study of the magnetic resonance linewidths of the polymer protons of the polyisobutylene toluene system is presented as a function of concentration c and temperature T. Two distinct regions are observed in the linewidth versus concentration or temperature curves. A phase diagram is constructed, one region of which exhibits characteristic NMR properties supposed to reflect microphase separation of polymer and solvent. The demixing curve derived from NMR measurements is expressed by c = 11.3(267–T). The θ temperature of this system is 260 K.
Craze initiation in poly(methyl methacrylate) under biaxial stress
Authors: Kawagoe M. , Kitagawa M. 
Published: April 2003

AbstractCriteria for craze initiation in poly(methyl methacrylate) have been investigated under various combined loadings including biaxial tension and torsion‐compression at 65°C in air and at room temperature in a crazing agent, kerosene. Environmental crazes are observed even under torsion‐compression loading when air crazing does not occur, and the stress locus for environmental crazing is very different from that for air crazing. A theoretical model analogous to the Cottrell model in crystal plasticity is proposed. Theoretical crazing loci derived from the model are compared with the experimental results.
Morphology of oriented linear polyethylene: A study by Raman spectroscopy
Authors: Capaccio G. , Wilding M. A. , Ward I. M. 
Published: April 2003

AbstractMeasurements have been made of the low‐frequency Raman longitudinal acoustic mode (LAM) vibration in oriented linear polyethylenes. The oriented samples were prepared by tensile drawing of both slow‐cooled and quenched sheets, and included ultrahigh‐modulus materials from draw ratios up to 30. A LAM line is observed clearly in samples of low and intermediate molecular weight up to draw ratios of ca. 15. In all these cases the Raman spectrum has been used to calculate the whole distribution of crystal sizes. This procedure leads to values of the number‐average and weight‐average crystal size which are in good agreement with crystal size determinations by x‐ray diffractometry and gel permeation chromatography on etched samples. At higher draw ratios the peak intensity of the LAM line is diminished. This can be attributed to a change in the distribution of crystal thicknesses, consistent with data from x‐ray diffraction and nitric acid etching. Effects due to initial morphology, sample molecular weight, and draw temperature have also been examined.
Carbon‐13 NMR of poly(vinyl acetate) and ethylene–vinyl acetate copolymer
Authors: Sung H. N. , Noggle J. H. 
Published: April 2003

AbstractCarbon‐13 nuclear magnetic resonance spectra of atactic poly(vinyl acetate) and ethylene–vinyl acetate copolymers are reported and analyzed. Carbon spectra at 22.6 and 62.9 MHz together with use of shift reagents have permitted a more complete assignment than previously reported; in some cases the published assignments are found to be in error.
Stress–strain behavior of randomly crosslinked polydimethylsiloxane networks
Authors: Gottlieb M. , Macosko C. W. , Lepsch T. C. 
Published: April 2003

AbstractThe stress–strain behavior of randomly crosslinked polydimethylsiloxane (PDMS) networks was studied. The small‐strain data obtained agreed well with available data on radiation‐crosslinked PDMS networks. It was found that both the suppression of junction fluctuation and trapped entanglements have to be considered in order to account for the discrepancy between experimental data and the phantom‐network theory. With the addition of a constant trapped entanglement term, Flory's recent network model describes correctly the behavior of our networks under tonsion and compression. The values of the parameters used in fitting the data are within the range suggested by Flory for typical rubber networks. Edwards' “potential pipe” theory did not correlate our data over the entire range of strain variation.
Structure and properties of charge‐mosaic membranes from modified polyethylene. I. Preparation and characterization
Authors: Gajek Ryszard , Trochimczuk Witold 
Published: April 2003

AbstractCharge‐mosaic membranes (CMMs) were prepared by modification of polyethylene (PE) with poly(styrene‐co‐divinylbenzene) or poly(vinylpyridine‐co‐divinylbenzene) and by selective insertion of cation and anion exchange groups in these copolymers. Changes of divinylbenzene content in the monomer mixture gave rise to differences in transport properties mainly through the change in water content. The CMMs were characterized by physico‐chemical properties of control membranes, i.e., they contained only one type of modified PE. Values were similar to those obtained from measurements carried out for CMMs. Diffusion coefficients determined in 0.1/0.02N NaCl solutions were in the range (1.5‐–5.7) × 10−7 cm2s−1. These values indicate that transport of salt through these CMM's occurs by a typical mechanism for such membranes.
Random‐coil configurations of the polyformals. VI. Dipole moments of the stereochemically variable polymer prepared from 4‐methyl‐1,3‐dioxolane
Authors: Riande E. , Garcia M. , Mark J. E. 
Published: April 2003

AbstractMean‐square dipole moments 〈μ2〉0 for the (atactic) poly(4‐methyl‐1,3‐dioxolane) chain [CH2OCH(CH3)CH2O] were determined from dielectric‐constant measurements carried out on two fractions dissolved in benzene. Simple examination of the chain structure leads to the predictions that this polymer should have a significantly larger value of 〈μ2〉0 than poly(1,3‐dioxolane) itself, but that 〈μ2〉0 should be nearly independent of stereochemical structure. The first expectation is confirmed by the experimental results obtained, and the second by calculated results based on rotational isomeric state theory.
A structure with an irregular layer lattice in poly(γ‐methyl L‐glutamate‐co‐γ‐benzyl L‐glutamate) film
Authors: Watanabe Junji , Gehani Ramesh , Uematsu Ichitaro 
Published: April 2003

AbstractTwo types of films showing different characteristic x‐ray equatorial patterns were prepared from chloroform and N,N‐dimethylformamide solutions of poly(γ‐methyl L‐glutamate‐co‐γ‐benzyl L‐glutamate). In the film cast from chloroform solution, the x‐ray pattern on the equator consisted of a remarkable mixture of sharp and diffuse reflections, with the sharp reflections corresponding to integral values of 1/3k. On the other hand, in the film cast from N,N‐dimethylformamide solution, a well‐defined x‐ray pattern was observed. An explanation for this characteristic pattern of chloroform‐cast film was made on the basis of a structural model wherein stacking faults or dislocations are incorporated into the ordered structure characteristic of N,N‐dimethylformamide‐cast film. Two domains divided by a stacking fault are mutually displaced along the (100) crystal planes, but the shape and size of the unit cell is everywhere the same. The intensity distribution of x‐ray diffraction was calculated as a function of the probability of a stacking fault occurring in a regular sequence of (100) planes. The best correspondence with observation was obtained with a stacking fault in every three layers, on the average.
Epitaxial crystallization of aliphatic polyesters on trioxane and various aromatic hydrocarbons
Authors: Wittmann J. C. , Lotz B. 
Published: April 2003

AbstractLinear polyesters of the diacid‐dialcohol type are observed to crystallize epitaxially onto substrate crystals of trioxane, condensed aromatic hydrocarbons, and linear polyphenyls. In line with results previously reported for PE, lattice matching requirements for epitaxy lead to a change in the polymer contact plane on the different substrates. The highly oriented, sometimes single‐crystal‐like polymer films are formed of stacks of lamellae seen edge on which appear well suited to investigations of the lamellar structure.
Small‐angle X‐ray scattering of isotactic poly(4‐methyl‐1‐pentene)
Authors: Tanigami Tetsuya , Miyasaka Keizo 
Published: April 2003

AbstractAlthough the crystalline phase of poly(4‐methyl‐1‐pentene) (P4MP) is less dense than the amorphous phase, the density difference is very small at room temperature. This makes it difficult to study the fine structure of P4MP by small‐angle x‐ray scattering (SAXS). It has therefore not been clear whether a so‐called superlattice, or long‐spacing structure, is formed in P4MP as in other synthetic polymers. However, it is found that raising the temperature increases the density difference sufficiently to make SAXS study feasible, and the existence of the long‐spacing structure of P4MP is indicated. Annealing studies reveal two characteristic temperatures of 170 and 200°C: above 170°C the long‐spacing structure is formed with an abrupt increase of crystallinity, and at 200°C the structure is further developed.
Dual‐mode sorption and transport of sulfur dioxide in kapton polyimide
Authors: Felder R. M. , Patton C. J. , Koros W. J. 
Published: April 2003

AbstractThe kinetics and equilibria of SO2 sorption in Kapton polyimide film have been studied at temperatures from 25 to 55°C and equilibrium sorption pressures up to 0.76 atm. The data are described well by the dual‐mode model of sorption and transport in glassy polymers. The assumption of “partial immobilization” is required to correlate the transport data: the mobility of the Langmuir component of the sorbed population relative to the Henry's‐law component is close to zero at 25°C, and increases to roughly 5% of the Henry's‐law component mobility at 55°C. The heat of sorption is anomalously low, suggesting the presence of residual solvent in the film, a suggestion confirmed by annealing studies. However, the study also shows that partial removal of the residual has a relatively minor effect on the measured SO2 sorption level and transport rates at 55°C.
Effect of disorder in the twist angle on light scattering by a three‐dimensional spherulite
Authors: Matsuo Masaru , Ihara Kumi 
Published: April 2003

AbstractLight scattering patterns are calculated for imperfect three‐dimensional spherulites with fluctuations in the twist angle. The fluctuations are described in terms of a parameter characterizing the distance correlation function. Cases are considered in which (i) the principal axis of the scattering element makes a constant angle with the radius but there is disorder in the twist angle about the axis, and (ii) there is combined twist disorder and orientation disorder of the scattering elements. Calculations suggest that the disorder in the twist angle may lead to a decrease in the higher‐order variation of scattered intensity with scattering angle and deviation from the four‐leaf‐clover‐type scattering characteristic of a perfect spherulite at lower scattering angles. On the other hand, disorder in orientation has little effect on the scattering pattern.
The nature of the nonlinear anelasticity of glassy polymers
Authors: Boyd R. H. , Robertsson M. E. , Jansson J. F. 
Published: April 2003

AbstractNonlinearity in stress‐strain behavior under conditions where the strain is completely recoverable is often observed in glassy amorphous polymers. In the present work a suggestion is made that the nonlinearity is often associated with a secondary (β) relaxation process. By means of a model calculation it is shown that the onset of stress saturation of the relaxed or equilibrium compliance associated with localized group motion is a reasonable explanation for the phenomenon. The effect of stress on relaxation times is predicted to have some contribution but to be less important than the effect on the relaxed compliance.
Concentrated solution viscosities of polymeric associates
Authors: Worsfold D. J. 
Published: April 2003

AbstractReasons have been advanced why in some cases concentrated‐polymer‐solution viscosity measurements are not a suitable method for determining the degree of association of groups attached to polymer chains. These are based on the finite lifetimes of associates compared with the finite lifetimes of the entanglements, which are the major contributors to concentrated‐polymer‐solution viscosities. The validity of these reasons has been checked in a system where the degree of association of polymer chains can be measured spectroscopically. It was found that the viscosity of these solutions was considerably less than that calculated by the concentrated‐solution viscosity equation for solutions of polymers of the average molecular weight expected from the spectroscopically found degree of association.
Wide‐angle neutron scattering studies of mixed crystals of polyethylene and deuteropolyethylene
Authors: Wignall G. D. , Mandelkern L. , Edwards C. , Glotin M. 
Published: April 2003

AbstractWide‐angle neutron scattering studies have been made of a series of mixed crystal blends of polyethylene and deuterated polyethylene in the range 0.68 ≤ K = 4πλ−1 sinθ ≤ 2.02 Å−1. Recent calculations by Stamm have shown that regularly folded subunits of small numbers (two to ten) of stems should produce an observable modulation of the diffuse scattering pattern of such mixtures in this K range. For both melt‐ and solution‐crystallized blends, no extra signal was observed above the background scattering level. The data are used to place an upper limit (of about four) on the number of stems that could be regularly folded in the (100) and (010) planes for these materials.
Melt rheology of ion‐containing polymers. I. Effect of ionic content in a model polyesterionomer
Authors: Connelly R. W. , McConkey R. C. , Noonan J. M. , Pearson G. H. 
Published: April 2003

AbstractThe effects of copolymerizing small amounts of an ionic moiety (0–7 mol %) into the backbone of a polycondensation polymer have been investigated by a combination of linear viscoelastic, steady‐shear, and extensional testing. At a constant viscosity in dilute solution, both the zero‐shear‐rate viscosity and the maximum relaxation time in the melt increase monotonically with an increase in the ionic character. These effects are present after the data are normalized to remove the increase in the glass transition temperature Tg with increased ionic content. Large‐strain, steady‐shear flow experiments showed that the viscoelastic memory of the melt is affected by ionic content. An increase in ion content causes a decrease in the effect of strain on the memory function. This effect is not apparent in extensional flow experiments, which indicate that the ionic content does not affect the response if the tests are conducted at a constant temperature above Tg.
Improved calorimetric procedure for monitoring the approach to thermodynamic equilibrium in glassy polymers
Authors: Lagasse R. R. 
Published: April 2003

AbstractTechniques for measuring the enthalpy change during isothermal aging of polymer glasses are discussed. Critical analysis of conventional scanning calorimetry reveals that its accuracy may be suspect under certain circumstances due to the thermal lag inherent in a temperature scanning experiment. An additional problem is that the conventional technique is restricted to certain kinds of paths for reaching the aging temperature. It is proposed that both problems can be overcome by analyzing the output of a scanning calorimeter not only during steady heating but also during the transients at the beginning and end of a heating scan. This data analysis method represents an extension of a method used previously by others in accurate measurements of the much larger heat of fusion of crystalline polymers. Practical feasibility of the improved technique is demonstrated by preliminary measurements of enthalpy relaxation during aging of well‐characterized polystyrene at 80°C. In particular, the initial departure from equilibrium of a glass prepared by 5°C/min cooling from the liquid state is found to be 6.9 ± 0.6 J/g. This measured value agrees with a value calculated on the basis of the glass transition temperature corresponding to 5°C/min cooling and heat‐capacity data from the literature.
Studies of tensile failure in oriented polymeric fibers by quantitative fractography
Authors: Lamb George E. R. 
Published: April 2003

AbstractFor some fibers, such as the nylon monofilaments studied here, quantitative information may be obtained from scanning electron micrographs of fracture surfaces. On these surfaces the segment of the cross section that supports the load at the instant of rupture is seen distinctly, and its area can be measured. Normalizing breaking load by this area provides a breaking stress characteristic of the final supporting segment. “Ultimate” breaking stresses calculated in this way indicate (i) For notched filaments, the ultimate breaking stress is almost constant with notch depth and also with strain rate. (ii) For un‐notched filaments, there is an increase of breaking load with strain rate, due in part to the extent of the slow cleavage that precedes failure; however, the ultimate breaking stress increases as rate of strain decreases. These two findings are incompatible with mechanisms of failure based on growth of microcracks by heat‐ and stress‐activated chain breakage. A possible explanation involves rearrangement of microfibrils within the fiber which alters their strength distribution. (iii) The apparent strength reduction on wetting nylon filaments in water is due to a faster rate of growth of the slow‐cleavage area; the ultimate breaking stress is unchanged, except at high rates of strain.
Investigation of local order in unreacted DGEBA epoxy resin monomers by light scattering
Authors: Stevens G. C. , Champion J. V. , Liddell P. 
Published: April 2003

AbstractThe existence of local order in two epoxy resins of the diglycidyl ether of bisphenol‐A (DGEBA) type has been investigated using Rayleigh scattering and Brillouin spectroscopy. The resins differ in their molecular weight distributions and their relative concentrations of epoxide and hydroxyl groups. The complementary use of both techniques in elucidating the thermal behavior of local order is illustrated, and the use of the latter technique to study thermal acoustic phonons and hypersonic relaxation is discussed. Both techniques independently show that molecular aggregates exist in each resin system. The scattering‐envelope dissymmetry shows that the resin with the high epoxide/hydroxyl group ratio contains aggregates up to 20 nm in size, and the low‐ratio resin exhibits sizes up to 70 nm. These aggregates are thermally unstable in the temperature range studied (293–443 K). Dissolution in chloroform shows that these aggregates are reduced in size and that further structural changes occur which are dependent on solvent concentration. Aggregate volume fractions were determined for a range of aggregate size. Brillouin spectroscopy indicated that both resins exhibit hypersonic relaxation in the temperature range studied. The complex longitudinal moduli of the resins were superimposable under a WLF temperature transformation comparable to the difference in their static glass transition temperatures. Molecular aggregate size, number, and stability are related to the epoxide/hydroxyl ratio of the resins and the degree of intermolecular hydrogen bonding.
Reduced‐variable mechanical characterization of styrene‐butadiene rubber with varying crosslink density, temperature, and finite strain states
Authors: Arenz R. J. , Landel R. F. 
Published: April 2003

AbstractA single master logarithmic stress relaxation curve of reduced modulus as a function of reduced time is established for a styrene‐butadiene rubber (SBR) system, accounting for the effects of crosslinking density, temperature, and time. The results from recent tests involving uniaxial and various biaxial strain states at finite strain levels may be represented by a unique strain‐energy function W of the Valanis‐Landel separable symmetric type,

where the λi are principal extension ratios. These two representations demonstrate that the mechanical response of whole families of elastomeric materials may be predicted once a single member of the family is fully characterized.