bluuebunny/crossref_metadata_2025_split huggingface dataset:
An entanglement model for the dependence of fracture surface energy on molecular weight
Authors: Moon P. C. , Barker R. E. 
Published: April 2003

AbstractOver the last decade, empirical evidence has indicated that the effective surface energy γ associated with the fracture of noncrystalline is a linear function of the reciprocal of the viscosity–average molecular weight: \documentclass{article}\pagestyle{empty}\begin{document}$ \gamma = \gamma _\infty - b\bar M_v ^{ - 1} $\end{document}. For poly(methyl methacrylate), data of J. P. Berry, G. C. Berry and Fox show that gamma; ∼ 0 at about the same value of M̄v that corresponds to the polymer chain‐entanglement length. From this fact, we have developed an entanglement network model for fracture, that bears a resemblance to F. Bueche's entanglement model for the melt viscosity of bulk polymers. Our model allows for the expression of the previously empirical constants, γ∞ and b, in terms of molecular parameters: \documentclass{article}\pagestyle{empty}\begin{document}$ {{\gamma _\infty = \gamma _{\rm s} A_{\rm s} Z_{\rm c} \rho _{\rm c} N_A } \mathord{\left/ {\vphantom {{\gamma _\infty = \gamma _{\rm s} A_{\rm s} Z_{\rm c} \rho _{\rm c} N_A } {\bar M_{\rm s} }}} \right. \kern-\nulldelimiterspace} {\bar M_{\rm s} }} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ b = 2({{\bar M_v } \mathord{\left/ {\vphantom {{\bar M_v } {\bar M_n }}} \right. \kern-\nulldelimiterspace} {\bar M_n }})\gamma _\infty M_{\rm f} $\end{document} where M̄n and M̄f are the number‐average molecular weights of the polymer and of the free chain ends, M̄v is the viscosity‐average molecular weight, γs is the average fracture‐energy per entanglement in the craze volume, As is the average cross‐sectional area of the polymer chain, Zc and ρc are the thickness and density of crazed material on the fracture surface, respectively; M̄s is the average strand molecular weight between entanglements, and NA is AvogadrO's number.
Morphology of injection‐molded polypropylene
Authors: Fitchmun D. R. , Mencik Z. 
Published: April 2003

AbstractA surface zone composed of at least three distinct layers has been detected in injection‐molded polypropylene. The morphology of these layers as determined by optical and scanning electron microscopy forms a continuous picture from the “as‐molded” surface to the core. With the exception of the first layer which is always featureless, the observed morphology is mostly spherulitic. Starting in the second layer, the spherulites decrease steadily in size until they reach a minimum somewhere near the middle of the third layer. After passing this point, they increase in size—rather rapidly—as the boundary between layer 3 and the core is approached. In samples prepared at the shorter fill times, the spherulites continue to decrease in size until they are replaced by the mixed matted straw–flat plate texture. The overall morphological features of this surface zone are explained by using an extension of a model for the crystallization of a quiescent polymer melt. In this model, growth originates from heterogeneous nuclei whose density varies throughout the sample as a function of both a temperature gradient and the induction time. Interpretation of anomalies in the fine structure of the individual layers indicates that shear is influencing the crystalline morphology also.
Environmental stress cracking of polyethylene
Authors: Schonhorn Harold , Frisch H. L. , Albarino R. V. 
Published: April 2003

AbstractModification of the Griffith theory for the presence of liquids has been shown to explain some facets of the environmental stress cracking of polyethylene. In the absence of intercrystalline links and tie molecules, we find that one important factor is the interfacial tension generated between the spherulite boundary and the liquid environment. Judicious incorporation of silanes into polyethylene appear to reduce the tendency to stress cracking by modifying the interfacial tensions between the environment and the polymer.
Crystal structure of nylon 12
Authors: Inoue Kazuo , Hoshino Sadao 
Published: April 2003

AbstractThe crystal structure of nylon 12 prepared by polymerization of dodecalactam has been determined by x‐ray diffraction. Nylon 12 fiber exhibits only the γ form as its stable crystal structure. The unit cell of nylon 12 was determined with the aid of the x‐ray diffraction pattern of a doubly oriented specimen. The unit cell is monoclinic with a = 9.38 Å, b = 32.2 Å (fiber axis), c = 4.87 Å and β = 121.5° and contains four repeating monomer units. The chain is planar zigzag for the most part but is twisted at the position of amide groups, forming hydrogen bonds between neighboring parallel chains. The chain conformation is similar to that of the γ form of nylon 6 proposed by Arimoto. It was deduced from the calculations that there are two chain conformations statistically coexistent according to the direction of twisting. In each conformation, hydrogen bonds are formed between parallel chains to make pleated sheetlike structures. The sheets are nearly parallel to (200) and in the sheet the directions of the neighboring chains are antiparallel, as is the case with nylon 6.
Lower‐frequency infrared spectra and structures of some typical aliphatic polyamides
Authors: Matsubara Ikuo , Magill J. H. 
Published: April 2003

AbstractThe Polarized lower‐frequency infrared spectra (800–33 cm‐1) of nylon 66 (α form), nylon 77 (γ form), and nylon 6 (both α and γ form) have been examined. The spectral changes which occur on complex formation of the polyamides with iodine‐potassium iodide solution and on subsequent iodine desorption have been studied in relation to the changes in the polymer structures. On the basis of these results, most of the stronger bands have been reasonably assigned to the vibrations characteristic of the amide group and the methylene chain of the polyamides, and some new structure–frequency correlations have been established for the polymers.
Small‐angle x‐ray scattering experiments for investigating the validity of the two‐phase model
Authors: Strobl G. R. , Müller N. 
Published: April 2003

AbstractA New method for evaluating SAXS curves of polymer samples with lamellar structure is applied to two typical scattering curves measured with a solution‐crystallized linear polyethylene and a melt‐crystallized branched polyethylene respectively. The method permits a rigorous check of the validity of the two‐phase model and yields, without additional measurement, the volume fractions of the two phases and the difference in their densities. The densities can than be obtained by measuring the overall density of the sample. The results are: ρc = 0.996 g/cm3,ρa = 0.854 g/cm3, wa = 0.20 for the solution‐crystallized sample; ρc = 0.967 g/cm3,ρa = 0.850 g/cm3, wa = 0.36 for the melt‐crystallized sample.
Interpretation of the heat capacity of polymer melts
Authors: Bares Vera , Wunderlich Bernhard 
Published: April 2003

AbstractHeat capacity values for melts of polystyrene, poly(methyl methacrylate), polypropylene, and polyethylene are calculated on the assumption that the total constant‐volume heat capacity Cv is made up of two parts: one associated with molecular vibrations, and one, with holes. Numerical values of both components are given for a wide range of temperatures and compared with experimental data. For poly‐1‐butene insufficient data for complete evaluation are available, so that only the vibrational contribution could be discussed.
Energetics of phase transformations in polyethylene
Authors: Yemni Tarik , McCullough R. L. 
Published: April 2003

AbstractThe molecular mechanisms involved in the orthorhombic‐to‐monoclinic phase transformation in polyethylene were investigated by the computer simulation of a structure–energy map based on empirically justified intermolecular potential functions. Stable packing structures for the orthorhombic and monoclinic form were isolated as relative minima, cohesive energies were determined from the energy minima, specific chain motions involved in the transformation were identified by the minimum energy path connecting the packing minima, and the activation energy for the transformation was determined from the energy barrier along the minimum energy transformation path. The packing structure parameters predicted from the energy map were in excellent agreement with unit cell dimensions observed near 0°K. The activation energy predicted for the transformation is relatively low (∼0.5 kcal/mole of ethylene at 0°K and 0.25 kcal/mole of ethylene near the melting point, 411°K). Monoclinic packing was predicted to be slightly more stable than orthorhombic. Since this result is inconsistent with a large body of observations, we propose that the intramolecular energy of chain folds plays a dominant role in establishing chain‐packing geometry. The inclusion of fold‐transition energetics could give rise to transformation mechanisms which differ in details from those proposed in this work.
Characterization and properties of macromolecules. III. Gel‐permeation chromatography: The effect of temperature upon the elution volume and the efficiency of the separation process
Authors: Cooper A. R. , Bruzzone A. R. 
Published: April 2003

AbstractWe report the first study of the effect of temperature on the elution volume and efficiency of the gel‐permeation chromatographic (GPC) process with the use of porous glass column packings. Monodisperse polystyrenes and narrow fractions of polyisobutenes were used as solutes and 1,2,4‐trichlorobenzene as the eluting solvent. This study has been made possible by the development of a successful method of eliminating the adsorptive properties of the glass surface with hexamethyldisilazane. Previously, without glass treatment, polystyrene would not elute from this system at 150°C. Previous studies dealing with this topic have been limited to the use of polystyrene gel column with ill‐defined temperature–structure behavior. Several measures of polymer dimensions have been correlated with the GPC elution volumes to ascertain which best reduces the data to a common calibration for these linear chains.
Analysis of flow behavior of polyethylenes and polypropylenes with graessley's theory
Authors: Saeda Shigeru 
Published: April 2003

AbstractGraessley's theory of non‐Newtonian behavior of linear polymers is tested with data on polyethylenes and polypropylenes having a wide range of molecular weights and molecular weight distributions, and for a polyethylene fraction. Theoretical flow curves derived by using molecular weight distribution data from column fractionations are in good agreement with experimental curves obtained from a cone‐and‐plate viscometer and an extrusion‐type rheometer, when the distribution is assumed to cut off at a maximum molecular weight. The experimentally obtained relaxation time for entanglement is found to be proportional to the Rouse relaxation time, though the former is about one decade smaller than the latter.
Crystallization kinetics of biaxially stretched natural rubber
Authors: Oono Ryo , Miyasaka Keizo , Ishikawa Kinzo 
Published: April 2003

AbstractThe isothermal crystallization of natural rubber was investigated under biaxial stretching. A marked planar orientation of crystals occurs in such a way that the (010) plane orients parallel to the film plane. The rate of crystallization increases with the biaxial stretching ratio, and the Avrami exponent n decreases. At the highest extension, n becomes less than unity. The equilibrium degree of crystallinity decreases with the stretching ratio. The crystallinity was less than 10% for the highest extension. The melting behavior is similar to that in uniaxial stretching.
Dielectric and ultrasonic studies of the δ‐relaxation of poly(ethyl methacrylate)
Authors: Shimizu Kazuharu , Yano Okimichi , Wada Yasaku , Kawamura Yasuaki 
Published: April 2003

AbstractComplex dielectric constants at frequencies of 110 Hz, 1 kHz, and 10 kHz and complex elastic moduli at 34 kHz and 3 MHz were measured in the temperature region the of δ relaxation of poly(ethyl methacrylate) (PEMA) down to 4°K. The temperatures of the loss maximum correlate well with literature values of the temperatures of mechanical loss maxima and with T1 minima. The activation energy is 2.1 kcal/mole. The energy map for the internal rotation of the ester ethyl group of PEMA was calculated; the activation energy and the energy difference between the two energy minima (0.31 kcal/mole) were found to agree well with those determined from experiment. The strength of dielectric relaxation is interpreted on the basis of 0.11 D as the dipole moment of the ethyl group. The strength of mechanical relaxation obtained in the present study as well as the previously published values are discussed. The volume change arising from the internal rotation of an ethyl group is found to be comparable at low temperatures with the van der Waals volume of the ethyl group and to decrease with increasing temperature.
Diffusion and reaction in polyester melts
Authors: Pell T. M. , Davis T. G. 
Published: April 2003

AbstractAn understanding of the physical and chemical processes involved in the melt polymerization of polyesters in the higher inherent viscosity ranges is of fundamental importance in polyester preparation. For example, the volatile condensation product must diffuse to a polymer–vapor interface before polymerization can take place. Thus, the rate of polymerization of a polyester may be dependent not only upon the chemical kinetics of the polymerization reaction but also upon the diffusion of the condensation product through the polymer melt. The objective of the work presented in this paper was to determine to what degree diffusion or reaction kinetics, or both, limit the melt polycondensation of poly(ethylene terephthalate). Degrees of polymerization in melts between 0.0285 and 0.228 cm in depth at 270°C were measured for various reaction times and were compared with the predictions of mathematical models. The polycondensation rates under these conditions depend upon both the polycondensation rate constant k1 and the diffusivity D of ethylene glycol through the melt. Estimates of the values to these parameters are: k1 = 0.0500 (moles/mole of repeat unit)−1 sec−1; D = 1.66 × 10−4 cm2/sec.
Thermal degradation of cellulose in nitrogen
Authors: Dollimore D. , Holt B. 
Published: April 2003

AbstractThe thermal degradation of four different forms of cellulose in nitrogen has been studied by using a thermobalance. In TG experiments a total weight loss at 900°C was 80% in the cases of film and pulp samples and 83% for two powder forms. The results for the isothermal degradation of the four samples at 270°C are plotted as degree of degradation α against reduced time t/t0.5 and compared with the master plots of Sharp, Brindley, and Achar. The experimental data fit most closely the plot for the Avrami‐Erofeev equation in the form kt = {–ln (1–α)}1/n where n = 2. An activation energy of 144 kJ/mole has been found for the degradation of one of the celluloses from the results of isothermal runs at six different temperatures. It is postulated here that the thermal degradation occurs by random nucleation and nucleus growth in the cellulose fibrils so as to yield a carbon whose microporous structure is a replica of the pore system in the parent cellulose.
Studies of polymer blends. I. Compatibility of poly(vinyl chloride) and poly(ethylene‐co‐vinyl acetate‐co‐sulfur dioxide)
Authors: Hickman James J. , Ikeda Richard M. 
Published: April 2003

AbstractVarious methods of determining polymeric molecular compatibility were applied to blends of poly(vinyl chloride) (PVC) and poly(ethylene‐co‐vinyl acetate‐co‐sulfur dioxide) (E/VA/SO2). In one series, where the E/VA/SO2 had a mole composition of 72.7/18.5/8.8, true compatible blends were demonstrated by phase‐contrast microscopy, torsion pendulum studies, and differential scanning calorimetry experiments for blends containing up to 40% E/VA/SO2. These blends exhibited a single Tg whose compositional variation was found to follow the Fox expression. Experimental densities were slightly greater than predicted on assuming volume additivity. This observation implies better packing and a negative heat of mixing and thus is in harmony with a negative free energy of mixing and the observed molecular compatibility.
Chain‐folding measurements in annealed poly(ethylene terephthalate)
Authors: Mehta R. E. , Bell J. P. 
Published: April 2003

AbstractChain folding in unoriented poly(ethylene terephthalate) (PET) films has been investigated as a function of annealing time and temperature. To meet this objective dynamic mechanical, infrared, and molecular weight measurements were used, together with selective chemical degradation to remove chain folds and amorphous regions. The β dispersion in the dynamic mechanical spectrum of PET is here tentatively associated with motions of methylene and/or carboxyl groups in irregular chain folds; the β dispersion is not found in quenched amorphous polymer, in polymer where amorphous regions and chain folds have been removed, or in highly annealed PET where the irregular folds have regularized. Upon mild crystallization and annealing (30 min at 110°C) of initially amorphous film a large β dispersion appears and then diminishes upon further annealing at 220°C. As the β dispersion diminishes, the infrared regular fold band increases more than the crystallinity band, indicating regularization of folds. The molecular weight of the degraded residue corresponds approximately to typical fold‐period dimensions (∼130 Å), and increases on annealing as expected from lamellar thickening. The degradation process has, by fold removal, reduced the chains in the crystals to a very short, uniform length.
Solution properties of polymers of pyridinium and ammonium methacrylates
Authors: Stejskal Jaroslav , Beneš Milan J. , Kratochvíl Pavel , Peška Jan 
Published: April 2003

AbstractSolution properties of poly[1(2‐hydroxyethyl)pyridiniumbenzene sulfonate methacrylate] and poly[1(2‐hydroxyethyl)trimethylammoniumbenzene sulfonate methacrylate] were studied. Within a certain concentration range of some added low molecular weight electrolytes, phase separation occurs. The dependence of intrinsic viscosity on molecular weight was determined and the steric factor estimated for both polymers. For nonaqueous solvents, an extrapolation of the dependence of the refractive index increment of the polymer on the refractive index increment of the polymer on the refractive index of the solvent leads to an apparent refractive index of the polymer, different from the refractive index determined directly by the immersion method. Some peculiarities of light scattering in solutions with no electrolyte added are mentioned.
Heat capacity of amorphous polyhexene‐1 between 20 and 300°K: Intramolecular vibrational contribution to Cvbelow the glass transition
Authors: Bourdariat J. , Isnard R. , Odin J. 
Published: April 2003

AbstractThe heat capacity of polyhexene‐1 was measured between 20 and 300°K. The apparatus, an adiabatic calorimeter giving results with a random error of 0.2–0.4%, is briefly described. The characterization of the sample by x‐ray diffraction patterns established that it was amorphous at all temperatures. Gold foil was incorporated with the sample to increase the apparent thermal diffusivity and so to decrease the time needed for the measurements. The glass transition temperature was found to be 215.5 ± 1°K. On theCpcurve, no subglass anomaly was detected, unlike the results of experiments described elsewhere. The calculation ofCvis discussed, and an explanation is given for the choice of the number of intramolecular vibrational modes per monomer which are assumed to contribute toCv. A linear continuum model with characteristic temperature θ1= 736°K allows us to fit the experimental curve over a temperature range of 140°K.
A theory for environmental craze yielding of polymers at low temperatures
Authors: Brown Norman 
Published: April 2003

AbstractIt has been recently discovered that polymers craze at low temperatures in the presence of nitrogen or argon. A quantitative theory has been developed which explains (1) the critical temperature above which the phenomenon disappears, (2) the critical stress for nucleating a craze, (3) the effect of strain rate on the yield point and size of crazes, (4) the drop in the load during craze yielding, and (5) the increase in strength of the polymer in N2 or Ar at high strain rates so that the ultimate strength may exceed that in He or vacuum. The crazing action of the gases is described qualitatively at the molecular level.
Annealing effects in poly(vinylidene fluoride) as revealed by specific volume measurements, differential scanning calorimetry, and electron microscopy
Authors: Nakagawa Koichi , Ishida Yoichi 
Published: April 2003

AbstractSpecimens of poly(vinylidene fluoride), crystal form II, annealed at different temperatures between 130 and 180°C were characterized by specific volume measurements, differential scanning calorimetry (DSC), and electron micróscopy. The degree of crystallinity calculated from the specific volume changed only by 15% i.e., from 50% to 65%. On the other hand, the melting behavior changed with annealing conditions. When a specimen was annealed above 170°C, two endothermic peaks appeared on either side of the annealing temperature. Results from DSC measurements made at different heating rates and electron microscopy showed that the two endotherms were caused by a bimodal distribution of lamellar thicknesses. The equilibrium melting point was found to be 210°C from the linear relation of the melting point and the annealing temperature. The equilibrium enthalpy and entropy of fusion were found to be 1.6 keal/mole and 3.3 eu/mole of repeat units by measurement on polymer–diluent mixtures. The surface free energy was found to be 5.1 kcal/mole of lamellar sequences from the plot of melting point versus reciprocal lamellar thickness obtained by electron microscopy. From a plot of enthalpy of fusion versus reciprocal lamellar thickness the surface enthalpy was found to be 20 keal/mole of lamellar sequences. These data lead to the estimate that a chain fold consists of about 30 repeat units.
Shear bands in polycarbonate
Authors: Wu W. , Turner A. P. L. 
Published: April 2003

AbstractLexan polycarbonate specimens in the form of tubes were deformed in torsion. The deformation occurs by the nucleation and growth of discrete shear bands. Shear bands are initially formed at the upper yield point. Development of the bands is accompanied by a drop in the stress to a lower yield point. At the lower yield point the strain inside the bands is approximately 70% and remains constant thereafter. Further deformation occurs by growth of the bands until they cover the entire sample. When the direction of twisting is reversed after the shear bands are formed, the deformed material untwists uniformly, without deformation in the previously undeformed material, and the stress required for untwisting the deformed material is lower than the stress required to propagate the band into undeformed material.
Polymer emissivity
Authors: Gay F. P. 
Published: April 2003

AbstractThe thermal emission characteristics of polypyromellitimides have been examined as a function of temperature by measurement of the power required to maintain steady‐state temperatures in an evacuated system. The emissivity was derived and found to increase with increasing temperature up to a saturation limit of above 0.9 at temperatures above 475°K. The effect is explained as a thermal population of excited infrared transitions. Power emitted is dominated by the most intense bands which are common to absorption and emission spectra.