bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of morphology and degree of crystallinity on the infrared absorption spectra of linear polyethylene
Authors: Okada T. , Mandelkern L. 
Published: April 2003

AbstractThe infrared absorption spectra of selected crystalline and noncrystalline bands were studied in bulk‐crystallized specimens of linear polyethylene which encompassed the extremely wide density range of 0.92–0.99 g./cm.3. The analysis of the data obtained at room temperature yield degrees of crystallinity by infrared methods which are in very good accord with the values deduced from the density measurements. Studies of the infrared spectra as a function of temperature give fusion curves which are in agreement with those obtained by thermodynamic methods. However, in order to obtain these latter results cognizance must be taken of the large negative temperature coefficient of the specific extinction coefficients of the crystalline bands from room temperature to the melting point. The necessary data to account for this phenomena were obtained from studies of the spectra of the n‐paraffin, C94H190, where molecular crystals are formed. Analysis of the two gauche bands, at 1352 and 1303 cm.−1, which are assigned to the noncrystalline regions demonstrate that for bulk‐crystallized samples of lowest densities the intensity ratio at room temperature is identical to that expected from the pure melt at this temperature. The conclusion is thus reached that the noncrystalline regions in these cases and the pure melt are structurally very similar. For samples of higher density, where the crystallite size is comparable to the extended chain length, the intensity ratio of the two gauche bands is altered. This change could reflect a change in the sequential distribution of gauche bonds. This intensity ratio for crystals formed from dilute solution is very similar to that for the high‐density bulk‐crystallized material and indicates a similarity in structure of the noncrystalline regions in the two cases.
Adsorption of iodine from aqueous solutions by samples of tire yarn from regenerated cellulose
Authors: Doppert H. L. 
Published: April 2003

AbstractThe adsorption of iodine by rayon tire yarn samples from aqueous solutions in which the concentration of iodide and triiodide ions is suppressed was studied. Fowler and Guggenheim's model of adsorption on regular localized monolayers appeared to be applicable to the adsorption phenomena considered. It is concluded that adsorption takes place on patches of sites in the cellulose–water gel.
Relaxation spectra of polymer melts from relaxation and steady‐state flow data
Authors: Ajroldi Giuseppe , Garbuglio Carmine , Pezzin Giovanni 
Published: April 2003

AbstractAccurate measurements of stress relaxation after steady‐state flow have been carried out, in the Newtonian flow region, for a polystyrene and a poly(methyl methacrylate) melt, with a cone‐and‐plate rotational rheometer. From the stress relaxation σ(t) versus t curves the relaxation spectra H were calculated by means of the first approximation equation: \documentclass{article}\pagestyle{empty}\begin{document}$ H = - ({1 \mathord{\left/ {\vphantom {1 {\dot \gamma t)d\sigma {{(t)} \mathord{\left/ {\vphantom {{(t)} d}} \right. \kern-\nulldelimiterspace} d}}}} \right. \kern-\nulldelimiterspace} {\dot \gamma t)d\sigma {{(t)} \mathord{\left/ {\vphantom {{(t)} d}} \right. \kern-\nulldelimiterspace} d}}}\ln t $\end{document}. The shear stress–shear rate curves, σ versus \documentclass{article}\pagestyle{empty}\begin{document}$ {\dot \gamma } $\end{document} were also measured, in large ranges of shear rates, for the same melts, and from these data the relaxation spectra H were obtained by means of equations given by Faucher and Ferry. The Faucher equation, \documentclass{article}\pagestyle{empty}\begin{document}$ H = - \dot \gamma ^2 d{\sigma \mathord{\left/ {\vphantom {\sigma d}} \right. \kern-\nulldelimiterspace} d}\dot \gamma ^2 $\end{document}, has been found to give results which compare satisfactorily with those obtained from the first approximation equation. It has been found that the Ferry equation has to be modified for comparable agreement.
Study of crystallization kinetics of trans‐1,4‐polyisoprene
Authors: Fischer E. , Henderson J. F. 
Published: April 2003

AbstractThe concentrations and the growth rates of high‐ and low‐melting type spherulites of trans‐1,4‐polyisoprene were measured in the temperature range 39–49°C. It was shown that above about 40°C., the crystallization rate of trans‐1,4‐polyisoprene is determined primarily by the radial growth rate of high‐melting form (HMF) spherulites, whereas the predominance of the low‐melting form (LMF) crystals below 40°C. can be attributed to the high rate of formation of LMF primary nuclei at lower crystallization temperatures. Temperature‐independent rate parameters were calculated from optical and dilatometric measurements and were found to be in good agreement. Both the change in nucleation habit and spherulite growth rate with temperature can be explained on the basis of a lower end surface free energy of LMF crystals of trans‐1,4‐polyisoprene compared to that of the HMF crystals.
Configurational statistics of polyamide chains
Authors: Flory P. J. , Williams A. D. 
Published: April 2003

AbstractThe statistical mechanical treatment of polymeric chains in terms of the largest eigenvalue of the product of statistical weight matrices for the rotational interactions of skeletal bonds of the repeat unit becomes excessively complicated if the repeat unit spans more than three or four skeletal bonds. Moreover, such treatment is necessarily limited to chains in which the number of repeat units is indefinitely large. Newer methods are readily applicable to chains of any degree of polymerization comprising repeat units of any realizable length. If interdependence of neighboring bond rotations is confined to bond pairs within a given unit, rotations about a pair of bonds belonging to neighboring units being mutually independent, further simplifications may be introduced without sacrifice of rigor. Polyamides, in which rotation about bonds on opposite sides of the amide group are independent, are polymers of this type. Adherence of the amide group to the planar trans conformation favors a more extended configuration of the chain, but this effect is dominated by the smaller steric repulsions affecting rotations about bonds which are first, second, and third neighbors of the amide group. It is for this reason that the characteristic ratio 〈r2〉0〉/nl2 for poly(hexamethylene adipamide), ca. 6.0 according to experimental results of Saunders, is less than the value, 8.0, for polymethylene at 25°C. The characteristic ratios and molecular dipole moments are computed as functions of the degree of polymerization. The poly(εaminocaproamide) chain also is treated.
Transmission electron microscopy of polypropylene lamellae delineated by staining
Authors: Hock Charles W. 
Published: April 2003

AbstractAqueous solutions of phosphotungstic acid were used to stain melt‐crystallized polypropylene which had been oxidized to the leveled‐off stage by boiling in 70% HNO3. Electron microscopy of thin sections of the polymer revealed unstained crystalline lamellae bordered by stained interlamellar layers. The lamella height, which is equivalent to the fold period of the molecules, increased as the crystallization temperature increased. In polypropylene which had crystallized in ice water, and at 125, 145, or 161°C., the heights of the visually delineated lamellae were 80, 105, 158, and 210 A., respectively. Those heights were, in turn, approximately the same as the length of the perpendicularly aligned molecules in the lamellae, which survived the acid etch. The stained interlamellar layers, regardless of the crystallization temperature, were about half the height of the lamellae.
Disorientation of crystallites in highly stretched polyethylene
Authors: Miyasaka Keizo , Makishima Kunio 
Published: April 2003

AbstractCrystallite orientation in polyethylene has been investigated in the high range of stretching. Crystallite disorientation can be observed in samples subjected to various stretching procedures: hot drawing and elongation of oriented fibers at room temperature at constant rate and at constant load. Crystallite disorientation does not take place during elongation but is induced upon removal of the applied stress. The higher the rate of removal of stress the greater is the disorientation. Two mechanisms are postulated for the disorientation: one relating to the irregular residual strain developed in fibrils by high stretching, and the other concerning rotational movement of crystallites caused by amorphous chains terminated on the interfaces. The fibrillation brought about by high stretching is thought to play an important role in the crystallite disorientation.
Isothermal calorimeter for studies of polymer solution processes
Authors: Schreiber H. P. , Waldman M. H. 
Published: April 2003

AbstractA simple differential, isothermal calorimeter has been built to study the thermodynamics of interactions associated with a variety of polymer solution processes. The calorimeter is readily operated at temperatures ranging from ambient to about 200°C., temperature adjustments are rapid, and the apparatus is rugged enough to permit application to commercial process studies. Though less sensitive than microcalorimeters, it represents an attractive combination of satisfactory accuracy, speed, and flexibility of operation. The operation of the calorimeter is demonstrated by measurements of the heat of solution of sodium chloride in water and the heats of solution of various polyolefins in Tetralin and α‐chloronaphthalene. The latter tend to confirm the presence of polymer aggregates in chloronaphthalene solutions below the thermodynamic melting temperature of the polymer.
Application of significant structures theory to amorphous polyethylene
Authors: Stewart Charles W. , Frankenberg C. A. Von 
Published: April 2003

AbstractThe thermodynamic properties of amorphous polyethylene are calculated from a model based on the method of significant structures. The motion of a molecule as a whole is described by the motion of segments, each segment moving independently of all others. It is assumed that on melting, holes appear in the solid lattice and the segments can move into these vacancies, obtaining some gaslike degrees of freedom. The complete frequency distribution for polyethylene is used for the solidlike degrees of freedom, while a corrected classical partition function is used for the gaslike degrees of freedom. The calculated thermodynamic properties are in reasonable agreement with experimentally determined values, assuming each gaslike segment to consist of 20 CH2 groups.
Aromatic poly(amic acids): Fundamental structural studies
Authors: Wallach M. L. 
Published: April 2003

AbstractAromatic poly(amic acids) derived from pyromellitic dianhydride and 4,4′,‐diaminodiphenyl ether were characterized by dilute solution techniques. Number‐average molecular weights M̄n of 13 samples ranged from 13,000 to 55,000 (DP 31–131). Weight‐average molecular weights M̄w of 21 samples ranged from 9,900 to 266,000. The ratio M̄w/M̄n was between 2.2 and 4.8. Heterogeneous polymerization yielded higher molecular weight polymer than homogeneous polymerization. The molecular weight could be varied systematically by control of stoichiometric imbalance. Use of very pure monomers and solvent gave polymers of relatively high number‐average molecular weight (∼50, 000) and the most probable molecular weight distribution M̄w/M̄n = 2. Impure monomers and/or solvent resulted in lower number‐average molecular weight (M̄n ≅ 20,000–30,000) and wider distributions (M̄w/M̄n = 3–5). The Mark‐Houwink relation obtained was [η] = 1.85 × 10−4M̄w0.80 The exponent is characteristic of moderately extended solvated coils. The unperturbed chain dimensions (r02/M)1/2 were 0.848 A., and the steric factor σ was 1.24 which is close to the limiting value of unity for an equivalent chain with free internal rotations. The sedimentation constant–molecular weight relation was S0 = 2.70 × 10−2M̄w0.39. This exponent is consistent with the Mark‐Houwink exponent.
Solubility and diffusion of water in acetal polymers
Authors: Hardy G. F. 
Published: April 2003

AbstractThe rate of water sorption at 25°C. has been determined for a number of polyacetal films differing in structure, density, and orientation induced by extrusion. The equilibrium water uptake was found to be a linear function of density only; no other effect of structure or orientation was detectable. The extrapolated density for zero sorption was 1.51 g./cc., not far from the theoretical crystalline density. The diffusivity of water in unoriented films rose with decreasing density; for linear copolymer, the trend was parallel to that of the area under the dynamic mechanical loss peak associated with long‐range chain motions in the disordered regions (β‐transition). Less pronounced effects of molecular weight and long chain branching on diffusivity were also noted. Films crystallized while an extruded melt was still oriented showed considerable increases in water diffusivity, but no significant changes in the apparent activation energies of permeation (about 6.6 kcal./mole) or diffusion (about 11.5 kcal./mole). On annealing these films, the diffusivity remained almost constant while the sorption coefficient and retraction on remelting decreased.
Configurational enthalpy of polystyrene
Authors: Joshi R. M. , Zwolinski B. J. , O'Reilly J. M. , Karasz F. E. 
Published: April 2003

AbstractRecent precision measurements of the heats of combustion of atactic and isotactic polystyrene permit an unequivocal calculation of the enthalpy difference in the bulk amorphous forms of the two isomers of this polymer. Contributions to this quantity arise mainly from the differences in nonbonded interactions in the two configurations but may also contain terms relating to higher energy conformations and to intermolecular interactions. The thermochemical and NMR data of specific polymers and of simple molecules are discussed in a comparison with model compound calculations. The thermochemical method has potentially important applications in studying molecular interactions in stereoregular polymers.
Energy contents of amorphous polystyrene with different thermal histories
Authors: Bianchi Umberto , Cuniberti Carla , Pedemonte Enrico , Rossi Corrado 
Published: April 2003

AbstractThe Tian‐Calvet microcalorimeter has been used to measure the heat of solution of atactic polystyrene in toluene at 30°C. By using a special technique for polymer sample preparation, it has been possible to measure directly the difference in conformational energy of the polystyrene chain at different temperatures, from 30 to 100°C. and to calculate its contribution to the specific heat.
Dynamic mechanical properties of aromatic, aliphatic, and partially fluorinated epoxy resins
Authors: Dammont F. R. , Kwei T. K. 
Published: April 2003

AbstractThe α, β, and γ transitions at temperatures between −200 and +100°C. of crosslinked aromatic and aliphatic epoxy polymers were determined from damping and shear modulus data, and compared with their fluorine containing analogs. Loci of segmental relaxation are suggested at various temperatures, and similarities between aliphatic and fluorocarbon segments, and polyethylene and polytetrafluoroethylene are discussed. Two systems of structurally similar monomers 2,2,3,3,4,4‐hexafluoropentane diglycidyl ether‐1,5 and 1,4‐butane diglycidyl ether, and 2,2‐bis(4‐glycidyl phenyl ether)hexafluoropropane and 2,2‐bis(4‐glycidyl phenyl ether) propane were polymerized with the aid of two diamine curing agents, namely, ethylenediamine and m‐xylylenediamine. Polymers of the aromatic diepoxides showed transitions with peaks at −56°C. and above +70°C. Three main peaks were registered for the aliphatic and fluorocarbon diepoxides: at −125 and at −100°C., at −56°C., and at 0°C. It is suggested that the Tg is affected by an interdependence of relaxation of all components of the polymer main chain.
Molecular dimensions of polydipropylsiloxamer
Authors: Lee C.‐L. , Emerson F. A. 
Published: April 2003

AbstractThe molecular dimensions of polydipropylsiloxamer were studied by intrinsic viscosity measurements in toluene and in 2‐pentanone. The relationships between the molecualr weight and the intrinsic viscosity were found to be: [η]25°C., toluene = 4.35 × 10−4 M0.58; [η]θ(10°C.), toluene = 1.09 × 10−3 M0.5; [η]θ(76°C.), 2‐pentanone = 8.71 × 10−4 M0.5. This held reasonably well for molecular weights from 25,000 to 3000,000. The root‐mean‐square end‐to‐end length ratio, (r02/M)1/2 as calculated from the constant K, exceeds the free rotation value by approximately 100%. The disparity is greater than that found with polydimethylsiloxamer, indicating a lower degree of flexibility for the polydipropylsiloxamer. This is largely due to the short range steric interaction between near neighboring units of the chain. Gel permeation chromatography was also employed to demonstrate the lower degree of flexibility for polydipropylsiloxamer as compared with polydimethylsiloxamer.
Corresponding state relations for the Newtonian viscosity of polymer solutions. II. Further systems and concentrated solutions
Authors: Simha Robert , Utracki Lechoslaw 
Published: April 2003

AbstractIn earlier work we have indicated a superposition principle for moderately concentrated mixtures (c ≲ 2/[η]) in good and poor solvents. By an examination of data on a number of vinyl polymers and cellulose derivatives in good as well as poor solvents, the validity of this principle is extended to concentrated solutions (c ≲ 50%). The characteristic concentration factor γ is proportional to M over the whole concentration range, with 0.47 ≤ a1 ≤ 1.10 being larger for good than for poor solvents, the result obtained earlier. Significant deviations from this relationship are noted in good solvents for those low molecular weights at which deviations from the usual intrinsic viscosity relationship occur. This may be related to the expansion factor of the polymer coil. On the basis of these results, the concentration and molecular weight dependence of the viscosity in the concentrated solution can be related to each other in terms of the parameter a1 and thus to thermodynamic characteristics. In this manner a bridge between the relatively dilute and concentrated regions is established. Currently used semiempirical expressions are analyzed in terms of these results. For the polystyrene–cyclohexane systems and θ − 9 ≦ T ≦ θ + 3, γ can be identified with the critical concentration for phase separation. Provided an “entanglement” concentration ce exists, in the neighbourhood of which the concentration dependence of the viscosity changes reapidly, γ can alternatively be shown to be proportional to ce, or ce ∝ M. The temperature reduction scheme suggested earlier remains to be investigated.
Dependence of viscosity of concentrated polymer solutions upon molecular weight and concentration
Authors: Onogi Shigeharu , Masuda Toshiro , Miyanaga Nobuyuki , Kimura Yasuo 
Published: April 2003

AbstractMolecular weight M and concentration c dependencies of the zero‐shear viscosity (η) were measured over wide ranges of M and c for concentrated solutions of linear and branched poly(vinyl acetate) as well as of polystyrene under θ conditions. The log η versus log M and log η versus log c curves for a given system can be superposed by the horizontal shift along the abscissa, giving smooth master curves. From the shift factors the ratio of two exponents β and α, which appear in the following equation, can be evaluated: η = K′(cρ)αMβ, where ρ is the density of the solution and K′ is a constant at constant temperature. The evaluated values of β/α for the systems under θ conditions are equal to or very close to 0.50 as was anticipated from the previous work. The above superposition method was also applied to available viscosity data, and it was found that β/α had a good correlation with a in [η] = KMa. This indicates that the individual molecules in concentrated solutions maintain the same individuality as in dilute solutions, and might be a positive support to the packed sphere model proposed previously by the authors. The effect of solvent on the molecular weight and the concentration dependencies of viscosity was also discussed.
Determination of osmotic coefficients in polyelectrolyte solutions by potentionmetric measurements during phase separation
Authors: Shatkay A. , Michaeli I. 
Published: April 2003

AbstractA method of evaluating osmotic coefficients of polyelectrolyte solutions is suggested for systems in which a two‐phase equilibrium is maintained between the polymer solution and a polymer precipitate so that the “polymer” terms Cpdμp in the Gibbs‐Duhem relationship may be neglected. The method is applied to a polybase system, and the osmotic coefficients calculated from the experimental data are discussed in terms of the theory of Alexandrowicz. The results are found to be in line with the above theory but the characteristic parameter ϕp, the fraction of free counterions, is about twice as large as values previously observed in polyacids.
Microstructure of bulk polymers as revealed in ultrathin sections
Authors: Andrews E. H. , Bennett M. W. , Markham A. 
Published: April 2003

AbstractAn improved method is described for obtaining ultrathin sections of soft polymers for examination in the electron microscope. The method involves cooling the specimens in the temperature range 0 to −160°C. during sectioning. The method has proved particularly useful for the study of microstructure in bulk polymers, especially semi‐crystalline materials such as polyethylene. The visibility of some features can be improved by electron staining. Preliminary results obtained on polyethylene and polypropylene are illustrated and discussed.
Mechanical structures in polymer melts. II. Roles of entanglements in viscosity and elastic turbulence
Authors: Busse W. F. 
Published: April 2003

AbstractCurrent theories of polymer flow processes often sacrifice realistic molecular models for simplicity of their mathematical equations. An analysis of what might happen to molecules of more realistic sizes and shapes under shear flow, shows the importance of the rapid Brownian motion of chain segments, the elastic deformations of polymer random coils, and the dissipation of this elastic random coil energy by the relatively slow slippage of the chains past each other at a few entanglements where steric hindrance causes long relaxation times. This makes the energy loss depend on the time at each local deformation, and not on the overall shear rate. At high shear rates this model leads to “cluster flow” and low loss cyclic deformations, rather than the high loss processes of steady‐state shear. This model gives reasonable qualitative explanations for many anomalous flow properties, and it has predicted new effects that have since been observed.