bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comment on the concentration and temperature dependences of the translational diffusion coefficient of flexible‐coil macromolecules in solution: Poly(2‐vinyl pyridine) in tetrahydrofuran
Authors: Van Den Berg J. W. A. , Jamieson A. M. 
Published: April 2003

AbstractConcentration‐dependence coefficients kDϕ of the mutual diffusion coefficient of poly(2‐vinyl pyridine) in tetrahydrofuran in the temperature range 15–55°C are compared with predictions of recent theories of macromolecular diffusion. In this temperature range a change in local conformation of the polymer occurs. The accompanying changes in chain solvation and coil hydrodynamics result in a sizable decrease in the hydrodynamic interaction parameter X defined by Akcasu. The formulation of theory appropriate for comparison with frame‐indifferent experimental diffusivities is discussed. We find that current theories predict qualitatively, but not quantitatively, the change in temperature dependence of kDϕ that occurs at the conformational transition. The discrepancies closely parallel those reported in recent independent comparisons of theoretical kDϕ versus experimental data for flexible‐coil molecules. No theory can adequately predict kDϕ over a wide range of X.
Strength of interaction and penetration of infrared radiation for polymer films in internal reflection spectroscopy
Authors: Mirabella Francis M. 
Published: April 2003

AbstractThe strength of interaction of infrared radiation with relatively thick polymer films was systematically studied by internal reflection spectroscopy. The so‐called “effective thickness” was used as a measure of the strength of interaction. The experimental and theoretical effective thickness were compared, and it was found that the theoretically predicted effective thickness can be approached or achieved experimentally with film samples routinely encountered in the polymer industry when moderate attention is paid to surface preparation and clamping force on the film in the internal reflection sample holder. A series of curves for various types of film samples was developed and found to be useful in predicting the spectral contrast for KRS‐5 and germanium internal reflection elements. These data were collected for infrared radiation polarized parallel and perpendicular to the plane of incidence and for unpolarized radiation. The data for unpolarized radiation was checked for the effects of the inherent polarization of the Fourier‐Transform Infrared Spectrometer used by comparing it to the arithmetic mean of the data for parallel and perpendicular polarization. These data were in good agreement and this indicated that the inherent polarization of the instrument introduced only minor errors into the data collected with unpolarized radiation. The concept of the “sampling depth” was established where the sampling depth ds was defined as the depth normal to the surface sampled. The sampling depth was found to be on the order of three times the value of dp, the depth of penetration, at 45° for polypropylene and polystyrene on KRS‐5 and was observed to exceed the effective thickness values at the same conditions. The value of the electric field amplitude was observed to fall to 5% of its value at the surface at ds.
Birefringence and glass transition temperatures of poly(diethylene glycol terephthalate) networks
Authors: Riande E. , Guzmán J. , Llorente M. A. 
Published: April 2003

AbstractA series of polymer networks were prepared by trifunctionally endlinking poly(diethylene glycol terephthalate). The elastomeric properties of these materials were studied at constant temperature using experiments that involve both the elastic force and birefringence. Whereas the stress‐strain isotherms show an anomalous increase in the modulus at very high elongation ratios, a downturn appears in the birefringence‐strain isotherms at the same extensibilities. These results suggest that the upturn that appears in the force should be attributed to maximum chain extensibility rather than to strain‐induced crystallization. A variety of additional thermoelastic experiments were carried out on these networks, to elucidate the dependence of the glass transition temperature on strain. It was found that for the elongation ratios at which the networks exhibit Gaussian behavior, the free‐volume effects on the glass transition temperature Tg (decreasing Tg with increasing free volume) offset the conformational effects (increasing Tg with decreasing entropy). However, the contrary occurs in the region where the stress increases anomalously with increasing strain.
A theoretical investigation of chain packing and electronic band structure of the rigid‐rod polymer trans‐poly(p‐phenylene benzobisthiazole) in the crystalline state
Authors: Bhaumik D. , Mark J. E. 
Published: April 2003

AbstractThe extended Hückel method was employed to calculate electronic band structures in trans‐poly(p‐phenylene benzobisthiazole) (trans‐PBT) in an attempt to elucidate the packing and electronic properties of these chains in the crystalline state. The unit‐cell energies thus calculated indicate that the most stable arrangement for trans‐PBT corresponds to the chains in planar configurations, at an interplanar spacing of 3.5 Å, and shifted axially by 3.0 Å relative to one another. These calculated results are in good agreement with experimental results obtained on the polymer and on relevant model compounds. No discernible dispersion of the energy bands perpendicular to the planes is observed, indicating that the neighboring chains are electronically noninteractive, as was found earlier for trans‐polyacetylene and polyethylene. Similarly, the band gap of 1.69 eV in the axial direction for one of a pair of chains was nearly the same as that, 1.73 eV, calculated previously for an isolated trans‐PBT chain. These values are in the range 1.4–1.9 eV reported for trans‐polyacetylene, which has been extensively studied because of its promise as a semiconductor.
Shear‐induced coalescence in two‐phase polymeric systems. I. Determination from small‐angle neutron scattering measurements
Authors: Roland C. M. , Böuhm G. G. A. 
Published: April 2003

AbstractIt has been found that flow‐induced coalescence occurs at a very rapid rate during the mixing of polymeric fluids. Furthermore, the rheological properties of the dispersed and continuous phases, as well as the nature of the flow field used in their blending, can greatly influence this coalescence. The significance of these findings is that in the development of a mixing scheme to obtain a desired morphology with minimum expenditure of time or energy, attention is usually focused only on the particle breakup aspects of the blending process. The competing coalescence can, however, be accelerated by the same conditions often employed to facilitate particle breakup (e.g., higher shear rates, reduced dispersed‐phase viscosity).A better understanding of the mechanism for coalescence of viscoelastic fluids is clearly required. In this manner optimal blending of immiscible polymers can be achieved with respect to both the nature of the final material and the ease with which it is obtained.
The hexagonal phase and melt of low‐molecular‐weight polyethylene
Authors: Asahi Takanao 
Published: April 2003

AbstractPhase diagrams of low‐molecular‐weight polyethylene (M = 1000, 2000, 6500, 16,000) and polyethylene (M ≈ 1,000) after fuming nitric acid treatment have been determined from 20 to 300°C up to pressures of about 10 kbar. The fractions with molecular weights 1000 and 2000 do not exhibit the hexagonal phase, but the others do. Effects of molecular weight and fuming nitric acid treatment on the phase diagrams are discussed in terms of the entropy of the melt.
Linear thermoviscoelasticity and characterization of noncrystalline EPDM rubber networks
Authors: Scholtens Boudewijn J. R. 
Published: April 2003

AbstractAn experimental study has been made to specify how the time‐temperature superposition and the linear viscoelastic characteristics vary with the degree of crosslinking for a broad class of noncrystalline peroxide‐cured EPDM networks. A new, very sensitive method is applied to determine the horizontal and vertical shift functions in an independent way. All uncrosslinked samples are thermoelasticoviscously simple with horizontal shift functions aT of the WLF type and vertical shift functions almost independent of temperature, in agreement with recent theoretical understanding. Upon crosslinking, these materials become thermoviscoelastically complex networks, but superposition can still be accomplished by assuming different temperature dependences for the relaxational strength and the equilibrium modulus. The aT functions can be taken independent of the degree of crosslinking. The vertical shift functions bT for the relaxational strength vary with the degree of crosslinking between theoretical predictions for uncrosslinked and perfectly crosslinked EPDM networks. The equilibrium moduli of the lightly cured networks decreases with increasing temperature, which is ascribed to the presence of interchain associations between ethylene sequences in the trans state. Upon further crosslinking, these effects gradually vanish and eventually the networks can be described as viscoelastically simple with an energy elastic contribution due to the ethylene trans‐gauche transitions. The linear viscoelastic characteristics, namely the storage and loss moduli and compliances and phase‐angle master curves and the relaxation and retardation spectra are discussed as a function of the degree of crosslinking. A sol/gel analysis and equilibrium swelling measurements complete the experimental characterization of three familes of five EPDM networks each.
Self‐diffusion in polymer‐solvent‐solvent systems
Authors: Vrentas J. S. , Duda J. L. , Ling H.‐C. 
Published: April 2003

AbstractThe ternary self‐diffusion data of Ferguson and von Meerwall are analyzed using a generalized form of the free‐volume theory of diffusion proposed by Vrentas and Duda. It is shown that the predicative capabilities of this form of the theory are satisfactory and comparable to those of the Fujita version. The lack of significant differences in the predictive capabilities of the two theories for the two ternary systems studied is explained in terms of the properties of the materials utilized. The data of Ferguson and von Meerwall are consistent with the hypothesis that the size of a polymer jumping unit is a fixed property of the polymer and that the jumping units for sufficiently large n‐paraffins are smaller than the entire solvent molecule.
Complex formation between enantiomeric polyesters
Authors: Grenier Daniel , Prud'homme Robert E. 
Published: April 2003

AbstractIn this study, three different polymers were blended: a racemic PMEPL (PMEPL‐RAC) which consists of a random distribution of repeat units of R or S configurations, an isotactic PMEPL made of repeat units of S configuration [PMEPL‐S(−)], and a second isotactic PMEPL made of repeat units of R configuration [PMEPL‐R(+)]. The acronym PMEPL stands for poly[α‐methyl‐α‐ethyl‐βpropiolactone]. The racemic PMEPL is optically inactive but the isotactic PMEPLs are optically active. In the first part of this study, an equimolar mixture of PMEPL‐S(−) and PMEPL‐R(+) was made. This racemate mixture leads to the formation of stereocomplex between the two polymers which has a melting point roughly 40°C higher than those of the isotactic polymers. The racemate morphology is composed of large spherulites. In the second part of this study, binary blends of PMEPL‐S(−) and PMEPL‐R(+) were prepared with an excess of one of the isotactic PMEPLs. The stereocomplex is preferentially formed between the isotactic polymers and this complex controls almost entirely the morphology of the sample. The enthalpy of fusion of the stereocomplex in the binary blends can be predicted. however, the excess isotactic polymer is trapped between the lamellae of the spherulites of the stereocomplex and its crystallization is hindered by the high viscosity of the partially crystallized medium. In the third part of this study, ternary blends were prepared. It is shown that PMEPL‐RAC does not from a complex with the isotactic polymers. The PMEPL‐S(−)/PMEPL‐R(+) stereocomplex is again preferentially formed and it controls the morphology of the sample. It decreases the degree of crystallinity of both the excess isotactic polymer and the PMEPL‐RAC. This control of the morphology is effective even in samples in which the sterocomplex accounts for only 3% of the total weight of the blend.
Study of ordered structures of syndiotactic poly(methyl methacrylate) in solution and in the solid state
Authors: Spěváček J. , Schneider B. , Dybal J. , Štokr J. , Baldrian J. , Pelzbauer Z. 
Published: April 2003

AbstractFrom analysis of infrared spectra it was found that in syndiotactic (s) poly(methyl methacrylate) (PMMA) in solution, long s sequences contain an increased population of diads with a skeletal conformation tt (in the staggered approximation). Self‐aggregation of s‐PMMA in solution leads to a further increase of the fraction of long s sequences in the extended chain conformation, and to an ordering of easter groups. When solid s‐PMMA is isolated from a solution in which it exists in the aggregated state, these characteristics are preserved in the solid. The polymer appears partially crystalline by x‐ray scattering, and it exhibits fibrillar morphology under the electron microscope. Ordered structures of s‐PMMA melt at temperatures about 150°C, while the presence of residual solvent decreases the temperature of melting. Solid s‐PMMA obtained from solutions in which aggregation of the polymer does not take place, like s‐PMMA which did not come into contact with solvent, contains a higher proportion of syndiotactic diads with a skeletal conformation tg; these samples are amorphous and morphologically structureless. Analogies between the structure of ordered s‐PMMA and the structure of the PMMA stereocomplex are also discussed.
Viscometric behavior of mesomorphic ethyl cellulose solution in chloroform
Authors: Suto Shinichi 
Published: April 2003

AbstractA simple modification of the viscometer used to determine the viscosity of concentrated solutions is described which permits the ready measurement of viscosity versus shear rate behavior above room temperature. Basic experimental viscometry was performed on the ethyl cellulose–chloroform system using a B‐type (Brookfield‐like) rotating‐cylinder viscometer. Data are compared with theoretical predictions. The flow curves exhibit yield stress at low shear rate. The yield stress is dependent on concentration and temperature. The viscosity versus concentration curves show typical mesomorphic behavior. The concentration dependences of viscosity and yield stress are similar. The critical concentration increases with temperature. In the single‐phase region (isotropic or anisotropic state) the viscosity decreases with temperature and the apparent activation energy (Ea) for flow is positive, but in the biphasic range the viscosity increases with temperature andEais negative. The experimental results for the critical concentration appear to agree with Flory's theory of rodlike molecules when the ratio of persistence length to diameter of the chain is taken as the aspect ratio.
Fourier‐transform infrared studies of polypropylene during mechanical deformation
Authors: Lee Y‐L. , Bretzlaff R. S. , Wool R. P. 
Published: April 2003

AbstractQuantitative Fourier‐transform infrared (FTIR) measurements of frequency shifts Δν and absorbance profile asymmetry are reported for various polypropylene samples as a function of uniaxial stress σ. Generally, it was found that the frequency shift coefficient αχ, defined by Δν = αχσ, depended on stress rate \documentclass{article}\pagestyle{empty}\begin{document}$\dot \sigma$\end{document}, draw ratio, λ, molecular orientation f, tensile modulus E, and annealing conditions. With annealing, αχ decreased with increasing shrinkage in the case of highly oriented isotactic PP. The αχ values for the “helix bands” were less affected than those for the “liquid bands.” With increasing \documentclass{article}\pagestyle{empty}\begin{document}$\dot \sigma$\end{document}, generally αχ increased to an apparent asymptotic limit. With increasing λ, f, or E, αχ also increased from αχ ≃ 0 for λ = 1 (spherulitic) to maximum values for highly oriented isotactic PP. The observed variations in αχ can be interpreted in terms of the changes in the peak position and shape of the nonuniform molecular stress distribution. Analogous behavior with x‐ray diffraction peaks obtained for polymers under stress is discussed.
Anisotropic swelling of doubly oriented nylon‐11 with a lamellar structure
Authors: Dosiere M. , Point J. J. 
Published: April 2003

AbstractRolled smaples of nylon‐11 annealed in formic acid (90%) at 80°C remain doubly oriented and have the same allotropic form as filter mats of single crystals. the basal planes of the crystals are parallel to (00l) planes. the long spacing is larger than in filter mats. Experimental swelling results obtained on such samples are discussed on the basis of two extreme models, the lamellar and the switchboard models. The long spacing dy and the length of the sample (along 0Y) change reversibly by the same proportion during swelling. Insertion of solvent between lamellae is invoked to explain such changes of dimension. As linear swelling ratios computed from macroscopic dimensions and SAXS measurements can reach 100%, lamellar crystals are only bonded by a few chains. The large increase of the SAXS intensity observed when annealed doubly oriented samples of nylon‐11 are wetted with allylic alcohol cannot be explained on the basis of the switchboard model but only with a three‐phase lamellar model. These three phases are the crystalline phase, the fold region, and a dilute solution of polymer in the swelling agent.
Hard‐segment polymorphism in MDI/diol‐based polyurethane elastomers
Authors: Blackwell John , Lee Chun Dong 
Published: April 2003

AbstractX‐ray analyses of methylene‐bis(4)phenyl isocynate(MDI)/diol/poly(tetramethylene adipate) polyurethane elastomers prepared using hexanediol (HDO), butanediol (BDO), and propanediol (PDO) point to the development of a second crystalline structure in the hard segments as a result of thermal elongation and annealing. The HDO polymer crystallizes initially in the fully extended conformation, but a second crystal structure, a contracted form, develops with stretching and annealing at 130°C. In contrast, the BDO and PDO polymers crystallize initially in contracted conformation, but fully extended forms develop as a result of elongation and annealing. Only a contracted conformation has been seen so far in hard segments prepared using ethylene glycol (EDO) as the chain extender. These results correlate very well with DSC data for the same polymers. The development of the new crystal structures is accompanied by the appearance of new hard‐segment melting peaks in the DSC traces. For the HDO polymer, the new peak for the contracted form appears at a higher temperature than that for the original extended form; for the BDO and PDO polymers the new peaks for the extended forms appear at lower temperatures than those for the contracted forms. Only a single peak is seen for the EDO polymer, for which only one crystal structure has been detected for the hard segments. These results indicate that the development of polymorphic crystal structures must be taken into account in interpreting the multiple melting phenomena seen for the hard domains in polyurethane elastomers.
Microstructural rearrangement during heat treatment of drawn nylon 66 fiber
Authors: Elad J. , Schultz J. M. 
Published: April 2003

AbstractMelt‐spun nylon 66 fibers were drawn and subsequently heat treated isothermally and quenched. The heat‐treated fibers were then examined by wide‐and small‐angle x‐ray scattering (WAXS and SAXS), by differential scanning calorimetry (DSC), and by static mechanical testing. These measurements allow one to follow microstructural changes taking place during the course of the heat treatment. WAXS results show that as the treatment progresses, the crystallites become both more perfect and more disoriented with respect to the fiber axis. SAXS results show crystallite thickening. DSC results show that the melting point increases, goes through a maximum, and then decreases as the heat treatment progresses. The tensile modulus decreases with time to an asymptotic level. The changes in crystallite perfection and thickness occur more rapidly than do the changes in crystallite orientation, modulus, and melting point. A model is proposed whereby the two time frames are related to intracrystalline and intercrystalline processes, respectively.
Thermal expansion and Grüneisen parameters of isotropic and oriented polyethylene
Authors: White G. K. , Choy C. L. 
Published: April 2003

AbstractThe linear thermal expansion coefficients α of three isotropic samples (crystallinity v = 0.42‐0.8) and one oriented sample (v = 0.8, draw ratio 11) of polyethylene have been measured between 2 and 100 K. Together with our previous measurements at high temperatures, these data provide general patterns for the crystallinity and orientation dependence over a wide temperature range. α varies only slightly with crystallinity from 50 to 120 K, but at higher and lower temperatures, it increases significantly with decreasing crystallinity. The increase at high temperature arises from segmental motion in the amorphous regions, while the large increase near 5 K is similar to that observed in many glasses. The tranverse expansion coefficient of the oriented sample is 40‐100% higher than the values for isotropic polyethylene, but the axial expansion coefficient is much smaller and is negative over the entire temperature range. The values of these coefficients are quite close to those for the polyethylene crystal, a feature readily understood in terms of existing models. However, as a result of the much larger elastic anisotropy of the crystal, the Grüneisen parameters (especially the axial Grüneisen parameters) of these two types of polyethylene have rather different values.
Strain birefringence studies on poly(vinyl acetate) networks
Authors: Riande E. , Saiz E. , Mark J. E. 
Published: April 2003

AbstractAtactic poly(vinyl acetate) prepared in a free‐radical polymerization was crosslinked by means of benzoyl peroxide. The resulting elastomeric networks were studied in elongation, both unswollen and swollen with triethylbenzene, over the range 0–90°C. The most important experimental results obtained were values of the network birefringence, which is negative, as was recently also found to be the case for networks of atactic poly(methyl acrylate).Calculations carried out to interpret the birefringence were based on Monte Carlo simulations of the atactic structure, and on the rotational isomeric‐state theory of chain configurations. The agreement between theory and experiment was very good, in fact much better than has usually been observed for other polymers studied to date.
An equation for diffusion in shrinking or swelling bodies
Authors: Viollaz Pascual E. , Suarez Constantino 
Published: April 2003

AbstractThe differential equation that describes the mass balance of a solvent which diffuses in a shrinking or swelling body is transformed in order to fix the domain of integration and a numerical solution is given. The numerical results obtained differ significantly from the solution of the equation without volume change commonly used in literature. Hence, the new equation could affect substantially the fields of drying, dyeing ion exchange, diffusion in polymers, and solid‐liquid extraction.