bluuebunny/crossref_metadata_2025_split huggingface dataset:
Morphology of gamma‐irradiated, low‐density, bulk polyethylene
Authors: Besmann Theodore , Greer Raymond 
Published: April 2003

AbstractLow‐density bulk polyethylene was subjected to gamma radiation doses between 0.1 and 100 megarads. Surfaces produced by fracture at liquid nitrogen temperatures were studied using scanning electron microscopy. The unirradiated polyethylene and polymer irradiated to 0.1 megarad had spherical units with a diameter of about 0.15 micron lying on the fracture surface. The units lay along the edges of the lamellae and were formed by the fracture that was, therefore, not entirely brittle. Polyethylene irradiated between 1 megarad and 100 megarads exhibited spherical voids, with a diameter of about 0.1 micron in the fracture surface. The voids have been produced either by the evolution of gas in the polymer during irradiation, the most likely mechanism, or as a function of the fracture mechanism only.
Deformation of oriented polyethylene
Authors: Pope D. P. , Keller A. 
Published: April 2003

AbstractThe deformation of polyethylene in terms of structural processes has been investigated by low‐and wide‐angle x‐ray diffraction in the case of low‐density and, to a lesser extent, high‐density polyethylene. The samples possessed a range of simple textures which enabled the deformation processes to be identified. The results are interpreted in terms of a model of stacks of lamellae which have axes along the original draw direction and which deform by lamellar slip, chain slip, and lamellar separation. In most cases these processes accounted for the macroscopic strain but in some cases discrepancies were observed which could be accounted for by inhomogeneous deformation or by the effects of a distribution of lamellar thicknesses. Attempts were made to identify fibrillar slip, without success. The relative contributions of the various deformation processes are examined as a function of temperature and sample treatment by defining a compliance constant for each process. Below room temperature, the results are consistent with expectations based on the α and β mechanical relaxations, whereas the unusual effects at high temperatures are attributed to gradual melting. The compliance constants are also found to depend on the annealing temperature of the sample, and are used to predict the mechanical anisotropy. The volume changes accompanying lamellar separation are examined. They were less than expected in low‐density polyethylene, but satisfactory agreement was obtained in high‐density polyethylene. A general relation is suggested between volume changes and the lateral development of the lamellae. Hence in narrow lamellae the interlamellar layer can contract laterally whereas the greater constraints imposed by wide lamellae lead to void formation. Other effects examined include the reversibility of the processes which is most marked in the case of chain slip and which is explained by the presence of restoring forces in the amorphous regions including the fold surface. Finally, the differences between low‐ and highdensity polyethylene are highlighted, emphasizing the part played in the deformation by the amorphous component.
Heat capacity of fluoropolymers
Authors: Lee W. K. , Choy C. L. 
Published: April 2003

AbstractThe heat capacities of poly(vinyl fluoride), poly(vinylidene fluoride), and polytrifluoroethylene have been measured between 80 and 340°K. The results can be expressed as the sum of two terms: the optical contribution calculated from the vibrational band assignments in the literature and the acoustical contribution calculated according to the Tarasov continuum model. Combining our data with those for polyethylene and polytetrafluoroethylene, it is concluded that the force constant for one‐dimensional intrachain interaction is approximately constant for all polymers with carbon backbones. The force constant for three‐dimensional interchain interaction is one order of magnitude smaller than the one‐dimensional force constant, and decreases when the hydrogen atoms in polyethylene are replaced by fluorine atoms. The thermodynamic functions for the three polymers have been evaluated. Glass transitions at 228°K and 305°K have been found in poly(vinylidene fluoride) and polytrifluoroethylene, respectively.
Crystallization and melting of polyethylene under high pressure. II. Effect of pressure on melting behavior of various types of crystals
Authors: Maeda Yoji , Kanetsuna Hisaaki 
Published: April 2003

AbstractThe effect of pressure on the melting point and volume of fusion of polyethylene was studied by high‐pressure dilatometry. Starting materials were crystallized slowly from the melt under pressures of 1500, 3500, 5130 kg/cm2, and 1 atm. It has been shown that the unusual behavior observed at pressures above 4000 kg/cm2 is due to crystallization and melting of two kinds of extended‐chain crystals differing in thermal stability. These are designated as ordinary extended‐chain and highly extended‐chain crystals, respectively. The relation between pressure P and melting temperature Tm of folded‐chain, ordinary extended‐chain, and highly extended‐chain polyethylene was determined precisely. At pressures up to about 3000 kg/cm2, plots of P against Tm for the crystal forms have almost the same curvature and then become parallel. But at pressures above 4000 kg/cm2, ordinary extended‐chain crystals show a linear increase of Tm with a constant slope of about 70 atm/deg. Curve for the highly extended‐chain crystals changes in slope from 70 to 50 atm/deg at pressures between 3500 and 4300 kg/cm2, and then show a sharp increase of Tm with increasing pressure. Experiments show that the meltingpoint curve of the highly extended‐chain crystals overlaps that of the ordinary extended‐chain crystals at pressures below 4000 kg/cm2. Annealing experiments with folded‐chain and ordinary extended‐chain crystals have been made under high pressure. It is suggested that the formation of highly extended‐chain crystals occurs stepwise through the formation and reorganization of ordinary extended‐chain crystals from the original folded‐chain crystals by a mechanism of partial melting and recrystallization at pressures above 4000 kg/cm2.
Theory of the epitaxial crystallization of polymers on alkali halide substrates. II. Polyoxymethylene and polythiomethylene
Authors: Mauritz K. A. , Hopfinger A. J. 
Published: April 2003

AbstractThe epitactic behavior of a single chain of polyoxymethylene and of polythiomethylene on alkali halide substrates has been simulated by computing the coulombic, induced dipolar, and dispersion–repulsive potential energies as a function of polymer–substrate geometry. Inspection of the total potential energy surface for a polyoxymethylene chain in a 9/5 helix reveals a favorable alignment in which the chain is parallel to the substrate surface ((001) cleavage plane) with specific positioning along rows of positive charge. This preferential orientation has been found to be independent of lattice matching between the substrate and deposited phase. An identical mode of orientation is predicted for a polyoxymethylene chain and a polythiomethylene chain, both in the 2/1 cis‐planar conformation. The theoretical results for polyoxymethylene are in agreement with available experimental evidence, whereas the outcomes of the calculations performed on polythiomethylene should be considered predictive study to be complemented by a future experimental investigation.
Matrix ENDOR of polyenyl radicals in polymers
Authors: Helbert John N. , Wagner Burkhard E. , Poindexter Edward H. , Kevan Larry 
Published: April 2003

AbstractEPR and matrix ENDOR spectra have been examined for polyenyl radicals in γ‐irradiated PVF, PVF2, PVC, and PMMA polymers. Proton matrix ENDOR is observed for all four polymers, and fluorine matrix ENDOR for PVF and PVF2. By line shape analysis of the ENDOR spectra obtained under comparable conditions, delocalization diameters for the unpaired electron of the polyenyl radical in each polymer are obtained. These diameters indicate extensive delocalization over 5–7 carbon double bonds for the polyenyl radicals investigated. It is suggested that these conjugated and crosslinked radiation products account for the observed nondevelopment of electron beam resist PMMA material at high radiation charge densities.
The distribution of stereochemical configurations in polystyrene as observed with 13C NMR
Authors: Randall James C. 
Published: April 2003

Abstract13C NMR configurational assignments are made for an amorphous polystyrene sample examined at 25.2 MHz and 120°C. The assignments are based strictly on a one‐parameter Bernoullian fit that was in satisfactory agreement with the nine observed methylene relative intensities. The methylene regions of the 13C NMR spectra of a polystyrene were examined before and after hydrogenation of the side‐chain phenyl substituents. It was concluded that ring current effects have influenced the 13C methylene chemical shifts substantially and are limited largely to contributions from adjacent phenyl substituents. In addition, aromatic substituent parameters are reported that can be used in conjunction with the Grant and Paul parameters for calculating chemical shifts in aromatic hydrocarbons and polymers. Finally, it is concluded that free‐radical and n‐butyllithium‐prepared polystyrenes have essentially atactic structures with meso additions favored over racemic additions by approximately 55/45.
Temperature dependence among the grant and Paul parameters as derived from 13C NMR polymer spectra
Authors: Randall James C. 
Published: April 2003

AbstractImprovements in the 13C NMR Grant and Paul parameters as applied to polymers have been obtained by noting that the “corrective terms” can be temperature‐sensitive. A corresponding temperature sensitivity was not observed for the primary parameters, α through ϵ. Results are given for a hydrogenated polybutadiene and six different ethylene–1‐olefin copolymers where the standard deviation between calculated and observed chemical shifts has been improved from 1.04 to 0.30 ppm. Since the “corrective terms” in the Grant and Paul empirical analyses of chemical shifts reflect the conformational character of polymers, it is shown that values for these terms can best be obtained directly from the system under study.
Basic modes of three‐dimensional polymer crystal associations: Interlocked single crystals and crystal halves
Authors: Lotz B. , Kovacs A. J. , Wittmann J. C. 
Published: April 2003

AbstractTridimensional associations of lamellar polymer single crystals, grown from dilute solutions, are described as derived from their sedimentation patterns. These associations include interlocked crystals and decorating crystal halves. The origin of these crystals and their mutual orientation are discussed and tentatively interpreted by specific interactions between the fold surface and the crystallizing chains.
Approximate relations among compliance functions of linear viscoelasticity for amorphous polymers
Authors: Riande Evaristo , Markovitz Hershel 
Published: April 2003

AbstractIn the glass–rubber transition region of viscoelastic behavior of amorphous polymers, it is found that

is a good first approximation. Here J(t) is the value of the shear creep compliance at time t and J″(1/t) is the value of the shear loss compliance at an angular frequency of 1/t. Previous approximations related the creep compliance to the storage compliance. When J(t) is proportional to tm, where m is a positive constant, J″(1/t) is within 30% of J(t) for m > 0.6. Over the entire range,

is a better approximation than either of the other two. The relaxation modulus G(t) is hardly ever a good approximation for the loss modulus G″(1/t).
Electrospray mass spectroscopy of macromolecule degradation in the electrospray
Authors: Teer Dan , Dole Malcolm 
Published: April 2003

AbstractAs previously shown, by electrospraying dilute polystyrene (PS) solutions gas phase macroions can be produced. Degradation of the PS in the electrospray was tested by collecting the electrosprayed PS and measuring its number‐average molecular weight osmotically. About 10% degradation was observed when using negative voltages, but the degradation was considerably reduced when the electrospray occurred in the presence of SF6 gas. No degradation was apparent in the case of positive sprays. A quantitative analysis of the results was made difficult by a small less of PS in the nitrogen gas stream and by diffusion of lighter ions to the vertical wall of the spray chamber. The latter effect did not occur at the highest spray voltage used, −24 kV.
A theoretical analysis of the effect of solvent on the Kerr constant of dilute polymer solutions
Authors: Fortelný I. 
Published: April 2003

AbstractA new model in which solvent molecules are regarded as discrete particles is used for investigating the influence of solvent orientation near a polymer chain and of the anisotropy of the internal electric field on the Kerr effect in a polymer solution. The relation derived for the Kerr constant consists of two parts containing nine terms each in the general case (the physical meaning of the terms is briefly discussed). Relations for the above effect in a nonpolar isotropic solvent, and explicit calculations of the Kerr constant for a simple model of a rigid polymer molecule are given.
Orientation of crystallites in lightly crosslinked isotactic polypropylene crystallized from the melt under uniaxial compression
Authors: Kitamaru R. , Hyon S.‐H. 
Published: April 2003

AbstractA lightly crosslinked polymer film was made from isotactic polypropylene by gammaray irradiation in an acetylene atmosphere. When the crosslinked polymer film was crystallized from the melt under uniaxial compression, a unique alignment of crystallites is found. The (040) crystal plane is preferentially oriented parallel to the film surface at relatively low degrees of compression, and the (110) and (130) crystal planes are oriented parallel to the film surface at higher degrees of compression. The origin of these orientations, analogous to that previously found in a lightly crosslinked polyethylene, is discussed.
Measured and calculated solubility of polymers in mixed solvents: Monotony and cosolvency
Authors: Wolf B. A. , Blaum G. 
Published: April 2003

AbstractBy a study of two ternary systems, 4‐heptanon–1‐chlorobutane–poly(methyl methacrylate) and 2‐butanol–1‐chlorobutane–poly(methyl methacrylate), differing only in one component of the mixed solvent, two types of demixing behavior are demonstrated: i.e., a monotone change with composition of the mixed solvent (monotony), of which the first system is a good example, and the synergistic behavior (cosolvency) exhibited by the second system. The situation can be seen most clearly from the binodal edges (precipitation thresholds as a function of solvent composition) which were constructed from various types of sections through the binodal surface of the systems.In order to compare experimental results with theoretical calculations, we first characterized the binary subsystems. The polymer solutions, representing conventional (endothermal) theta systems, were investigated by light scattering and cloud point measurements. For the cosolvent 2‐butanol–1‐chlorobutane the necessary thermodynamic information was accessible from vapor pressure measurements. Applying the Prigogine–Patterson theory to the polymer solutions and using the single‐liquid approximation of Scott for the ternary systems yielded theoretical binodal edges in good agreement with experiment except for the branch belonging to mixed solvents rich in 2‐butanol. This finding is explained by an abnormal amplification of preferential solvation effects due to the existence of an association equilibrium of the alcohol via hydrogen bonds.
Tensile properties of ultradrawn polyethylene
Authors: Capiati Numa J. , Porter Roger S. 
Published: April 2003

AbstractHigh‐density polyethylene filaments prepared by a solid‐state deformation in an Instron capillary rheometer show unusually high crystal orientation, chain extension, axial modulus, and ultimate tensile strength. The Young's modulus and ultimate tensile strength have been determined from stress–strain curves. Gripping of this high modulus polyethylene has been a problem heretofore, but the measurement of ultimate tensile strength has now been made feasible by a special gripping procedure. Tensile moduli show an increase with sample preparation temperature and pressure. Values as high as 6.7 × 1011 dyne/cm2 are obtained from samples extruded at 134°C and 2400 atm and tested at a strain rate of 3.3 × 10−4 sec−1. The effect of strain rate and frequency on modulus has also been evaluated by a combination of stress–strain data and dynamic tension plus sonic measurements over nine decades of time.
Crystalline isomeric polyester block copolymers. Scanning calorimetry and density measurements
Authors: O'malley James J. 
Published: April 2003

AbstractA series of isomeric polyester block copolymers were synthesized by coupling hydroxyl‐terminated poly(hexamethylenesebacate) (HMS) and poly(2‐methyl‐2‐ethyl‐1,3‐propylene sebacate) (MEPS) with hexamethylene diisocyanate. Poly(HMS) is crystalline, whereas poly(MEPS) is amorphous. All of the block copolymers, including one containing only 28% HMS were found to crystallize. DSC, density, and optical microscopy were used to measure the thermal transition temperatures and the degree of crystallinity. The data indicate that block copolymerization causes a small depression in the melting point and that the degree of crystallinity of the HMS block in the copolymer is more a function of molecular weight than it is of copolymer composition. Crystallization appears to be the major driving force for phase separation in this isomeric copolymer system.
On the transition from paraffinic to polymeric behavior: Mechanical properties
Authors: Crissman J. M. 
Published: April 2003

AbstractAn attempt has been made to determine what influence chain folds may have on the α and γ mechanical loss peaks in linear polyethylene. In so doing, one long‐chain n‐paraffin (C94H190) and two low molecular weight polyethylene fractions have been examined with mechanical relaxation, differential scanning calorimetry (DSC), and low‐angle x‐ray diffraction techniques. The data suggest that chain folds play a prominent role in both the α and γ processes but that other factors such as polydispersity and/or branching are also important.
Quantitative structural characterization of the melting behavior of isotactic polypropylene
Authors: Samuels Robert J. 
Published: April 2003

AbstractThe melting behavior of restrained isotactic polypropylene fibers is examined quantitatively in terms of the influence the anisotropic structural state of the polymer has on the observed properties. Two endotherm peaks are observed to occur in some of the samples. The formation and location of the multiple peaks are determined by the orientation of the noncrystalline chains, and is independent of the fabrication path used to achieve that orientation. Above a certain minimum orientation of the noncrystalline chains, multiple endotherm peak formation occurs. The high‐temperature endotherm (T2M) extrapolates to an ultimate melting point for fully oriented noncrystalline chains of 220°C, while the lower‐temperature endotherm (T1M) extrapolates to an ultimate melting point of 185°C. Noncrystalline chain orientation influences the endotherm temperature through its changing configurational entropy. It is shown quantitatively that the noncrystalline polymer must be considered as plastically deformed, since rubber elasticity theory is not followed as predicted. The melting behavior of isothermally crystallized samples are also reported to further elucidate the nature of the observed endotherms.
Calorimetric study of mixtures of butyl methacrylate oligomers with methanol
Authors: Pouchlý J. , Máša Z. , Biroš J. , Živný A. , Trekoval J. 
Published: April 2003

AbstractHeats of mixing of methanol with butyl isobutyrate and with oligomers of butyl methacrylate (monomer to tetramer) having a butoxyl group on one chain end have been measured. To discuss the effect of hydrogen bonding on the heat values, it is appropriate to correlate the heat per mole of binding sites with the binding site fraction. This dependence can be described by a single curve for all oligomers studied, in contrast to the results obtained in a previous paper for the same oligomers with chloroform. This fact suggests that the binding parameters for methanol are not influenced by the degree of polymerization.
Radical formation during tensile deformation of highly drawn crystalline poly[p‐(2‐hydroxyethoxy)benzoic acid] fibers
Authors: Nagamura Toshihiko , Fukitani Kazunori , Takayanagi Motowo 
Published: April 2003

AbstractThe micromechanism of tensile deformation of poly[p‐(2‐hydroxyethoxy)benzoic acid] fibers is discussed on the basis of a detailed esr study of radical formation. The concentration of primary phenoxy radicals, which were detected during deformation at room temperature as a direct indicator of main‐chain rupture, was determined by extrapolating the radical decay curves at various strains to zero time. The relation between the initial radical concentration and the strain is well expressed by the cumulative normal distribution curve. By use of this relation and a model of fiber structure, the distribution of the contour length of tie chains was determined. No radicals were detected during a second stretching cycle until the maximum strain in the first run was exceeded. The deformation model which includes alternating crystalline and amorphous regions connected by tie chains, a distribution of contour lengths of tie chains, and a phase transformation of molecular chains in the crystalline region accounted fairly well for the observed stress–strain behavior of monofilaments in first and second stretching cycles. The comparison between the observed and the calculated radical concentration suggests that statistical factors and other deformation mechanisms have to be taken into account.
Excluded volume study of a sulfonate‐containing polyelectrolyte in salt solutions
Authors: Tan J. S. , Gasper S. P. 
Published: April 2003

AbstractChain characteristics of a linear sulfonate‐containing homopolymer, sodium poly(3‐methacryloyloxypropane‐1‐sulfonate), in aqueous salt solutions (ionic strength, Cs = 0.01N to 5N NaCl) have been investigated by light scattering and intrinsic viscosity. The molecular weight (M̄w)–viscosity relation can be well described by the Mark–Houwink and the Stockmayer–Fixman equations. The coil is highly expanded even in the most concentrated NaCl solution (6N), and no 1:1 electrolyte was found to precipitate this polymer.A linear relation was observed between the viscosity expansion factor, α3η, and (M̄w/Cs)1/2. Examination of the data in terms of theories for excluded volume and hydrodynamic interaction suggests that the coil experiences dominant hydrodynamic interaction, corresponding to a nondraining coil, and the second virial coefficient and coil expansion at high Cs can be correlated by the Flory–Krigbaum–Orofino equation. Results for this polymer are compared with those for other polyelectrolytes, and are discussed in terms of chain structure, flexibility, and hydrophobicity.