bluuebunny/crossref_metadata_2025_split huggingface dataset:
Low‐temperature specific heat of polystyrene and related polymers (1.6° to 4°K)
Authors: Zoller P. , Fehl D. L. , Dillinger J. R. 
Published: April 2003

AbstractThe specific heat of polystyrenes of different origin and molecular weight, of α‐substituted and ortho‐substituted polystyrenes, and of polystyrenes crosslinked with different amounts of divinylbenzene have been measured between 1.6 and 4°K. The specific heat of all samples shows a temperature dependence that can not be explained by assuming a Debye frequency spectrum for the vibrational modes in these polymers. Good agreement is obtained by fitting the data to a superposition of a Debye T3 term and an Einstein specific heat with a characteristic temperature of 15–18°K. This localized frequency mode may have its origin in the one‐dimensional nature of the polymer chain. A simple calculation of the length of a polystyrene chain necessary to obtain these characteristic temperatures shows reasonable agreement with the number of Einstein oscillators observed in the samples.
Nascent polypropylene morphology: Polymer fiber
Authors: Wristers J. 
Published: April 2003

AbstractA new morphological structure has been shown to be a general feature of polyolefin powders. This feature is a fiber approximately 0.5 μ in diameter and is common to a large number of samples of polyethylene, ethylene‐propylene copolymer, polypropylene, polybutene‐1, and poly‐4‐methylpentene‐1 samples. Polymer particles prepared with different catalysts under different conditions are composed of these fibers. The fibers grow from globules formed during the initial phase of polymerization, and their formation at high catalyst efficiency suggests that not all primary catalyst particles have equivalent activities.The fiber structure is one of at least six levels of order prevailing in the polypropylene particle. While the catalyst particle is responsible for some of the distinctive morphological arrangements, polymer morphology is the primary cause for the other structures. The primary catalyst particle is thought to be the determinant for the fiber.
Direct examination of polymerization catalyst by electron scanning microscopy
Authors: Wristers J. 
Published: April 2003

AbstractDirect examination of different polymerization catalysts with an electron scanning microscope is made possible by modification of the inlet port. This represents the first time that polymerization catalysts are thus directly observed at high magnification. The procedure differs from the more tedious and restricted examinations usually performed with electron transmission microscopes. Distinct differences between various catalysts are observed depending on their mode of preparation. These differences account for diverse physical properties of polymers produced with these catalysts.
Fold length of single crystals of polystyrene: A conflict with crystallization theories at high supercoolings
Authors: Jones D. H. , Latham A. J. , Keller A. , Girolamo M. 
Published: April 2003

AbstractThe purpose of the work was to test existing theories of chain folded polymer crystallization over a supercooling range which is much is excess to what could be hitherto realized. This was made possible by the recognition that crystallization of isotactic polystyrene in solution could be conducted over an exceptionally wide range of temperatures in an isothermally controlled manner. The results revealed that the familiar inverse dependence of the fold length on supercooling (the behavior observed and studied in polyethylene) was only displayed at the lowest supercooling; at high supercoolings the fold length reached a constant lowest value unaffected by further lowering of the crystallization temperature. This is in conflict with present theories, which predict a catastrophic upswing in fold length at high supercoolings. It is demonstrated that the observations cannot be made compatible with this prediction by any conceivable adjustment of the numerical parameters. The implications of these findings are discussed.
Diffusion and sorption of gases in poly(ethylene terephthalate)
Authors: Toi Keio 
Published: April 2003

AbstractThe sorption and diffusion of gases in poly(ethylene terephthalate) (PET) films have been measured by using a newly devised apparatus which gives the sorption rate curves from the initial to the equilibrium state. By analysis of sorption data for carbon dioxide in PET film, it was shown that the diffusion rate, as well as the equilibrium solubilities, could be explained by the dual‐mode sorption mechanism proposed by Vieth et al. Constants of their equation were used in the analysis of our experimental results, in which the apparent diffusion coefficients were dependent on pressure. The result showed that the dual‐mode sorption mechanism indeed applies to diffusion. The value of the real diffusivity obtained in amorphous PET was 5.7 × 10−9 (± 8%) cm2/sec in the range of pressure from 0 to 1 atm. It is believed that this apparatus has wide applicability, not only to diffusion of gases in polymers, but also to the measurement of surface properties, and can be used to study the morphology of a variety of polymers.
Structural studies of polyethers. IX. Planar zigzag modification of poly(ethylene oxide)
Authors: Takahashi Yasuhiro , Sumita Isao , Tadokoro Hiroyuki 
Published: April 2003

AbstractA new crystal modification was found in poly(ethylene oxide) stretched about two‐fold after necking at room temperature. An x‐ray diffraction analysis indicated that the planar zigzag molecule passes through a triclinic unit cell with parameters α = 4.71 Å, b = 4.44 Å, c (fiber axis) = 7.12 Å, α = 62.8°, β = 93.2°, and γ = 111.4°. The space group is P1−Ci1. Packing of the molecule is very similar to that of monoclinic polyethylene.
Moiré patterns in the electron image of solution‐grown polymer crystals
Authors: White J. R. 
Published: April 2003

AbstractRelative tilt between two similar thin crystals may result in the formation of a moiré pattern in the electron image. Patterns hitherto interpreted as being parallel moirés or rotation moiré obtained from overlapping solution‐grown polymer crystals are reconsidered, and it is shown that in some cases a tilt model is more acceptable. The general features of tilt moiré patterns predicted for crystals of this kind are discussed and compared with micrographs appearing in the literature. Methods of distinguishing tilt moiré patterns are indicated, though it is admitted that such experiments would be difficult to complete in the time limited by destruction of the crystal structure under the action of the electron beam. Extinction contours may also sometimes be confused with long‐period tilt moiré patterns, and again careful experimentation is required for accurate identification. The model of the structure of solution‐grown polyethylene crystals inferred from a tilt moiré interpretation of many of the electron image fringe patterns found in the literature is consistent with that derived from other sources.
Transient permeation of organic vapors through elastomeric membranes
Authors: Curry J. E. , McKinley M. D. 
Published: April 2003

AbstractThe permeation of benzene and acetone vapors through sulfur‐cured natural rubber was studied by the time‐lag method. The experimental results were analyzed by a method suggested by Meares. The zero concentration diffusion coefficient D0 was obtained by the early‐time method. The Frisch time‐lag equation was utilized to estimate both the solubility coefficient s and the additional parameter b required to define the concentration dependence of the diffusion coefficient: D(c) = D0 exp {bc}. This form of concentration dependence was manifested by the corresponding permeability coefficient values. At low entering penetrant pressure, where the transport coefficients are constant, indirect evidence was obtained that D0 is the mechanistically correct diffusion coefficient. The solubility coefficient values calculated for benzene vapor in natural rubber are in reasonable agreement with published equilibrium sorption data for a similar rubber compound. At higher entering penetrant pressures, average diffusion coefficients obtained at steady state tended to be larger than the corresponding average diffusion coefficients derived from the time lags. This same effect has been detected by other experimental approaches. Permeation experiments designed for this rapid method of analysis appear capable of yielding information consistent with that obtained by more time‐consuming traditional methods.
Cloud‐point curves for polystyrenes of low polydispersity in cyclohexane solution
Authors: Krause Sonja , Stroud Dale E. 
Published: April 2003

AbstractCloud‐point curves and relative volumes of the coexisting phases just below the cloud‐point temperatures were observed for a commercial sample of “monodisperse” polystyrene and one of its fractions. As expected from theoretical considerations, the cloud‐point curve for the more monodisperse sample was flatter near the peak over a greater concentration range than that of the parent sample. Furthermore, the critical point for the fraction appeared to be closer to the peak of the cloud‐point curve than was that of the unfractionated polymer. In addition, it was learned that one type of impurity could be detected with extraordinary sensitivity by means of the cloud‐point curve.
Ultrasonic absorption and dielectric loss in heterophase block copolymers
Authors: Shen M. , Kaniskin V. A. , Biliyar K. , Boyd R. H. 
Published: April 2003

AbstractA styrene–butadiene–styrene block copolymer (SBS) and a plasticized SBS were studied as a function of temperature by an ultrasonic wave propagation technique at 9 MHz. Two absorption maxima were found for each of these polymers, one being attributable to the primary glass transition of the polybutadiene blocks and the other to that of the polystyrene blocks. The SBS was cast from two different solvents, namely benzene and tetrahydrofuran–methyl ethyl ketone. Parallel dielectric loss measurements were also made of the SBS in the frequency range of 50–105Hz. Relaxation temperatures determined from the ultrasonic and dielectric loss maxima over a range of measurement frequencies can be correlated by an Arrhenius‐type equation. The polystyrene loss peak in the ultrasonic data was found to be much weaker than the polybutadiene loss peak. However, these two peaks were of comparable magnitude in dielectric data. This observation was interpreted as being due to the onset of structured–unstructured (heterophase to homogeneous) transitions at sufficiently high temperatures. Ultrasonic data were also compared with low‐frequency dynamic mechanical data (11 Hz) and stress relaxation data (102–105sec) through the use of simple time–temperature superposition principle. Considerable discrepancies were found by using this principle, indicating that the heterophase SBS block copolymer was thermorheologically complex.
Steady‐shear viscosity of polydimethylsiloxanes over the range from the lower to the upper Newtonian region
Authors: Ito Yoshio , Shishido Shunsuke 
Published: April 2003

AbstractThe mechanism of non‐Newtonian behavior for flow from the lower to the upper Newtonian region is explained by a modification of Graessley's theory. In the theory proposed here, a viscosity ηfric, which is based on friction between polymer segments and is almost shear‐independent, is introduced in addition to Graessley's entanglement viscosity ηent, which decreases with increasing shear rate. The theory is applied to previously obtained data on steady flow of polydimethylsiloxanes of different molecular weights. The agreement between calculated and experimental results is good. In polymers with the molecular weight above the critical molecular weight for entanglement Mc, the major contribution to viscosity near zero shear rate is ηent. As the shear rate increases, the flow curve has an inflection where ηfric cannot be disregarded in comparison with ηent. In the upper Newtonian region, ηfric has more influence on the viscosity than ηent. The theory can also explain the experimental results on flow of polymers with molecular weight below Mc, which were shown to be slightly non‐Newtonian in the previous paper.
Ultimate properties of lightly crosslinked polymer networks in the long‐time region
Authors: Janáček J. , Raab M. 
Published: April 2003

AbstractIt was found that the strain‐at‐break plotted against strain rate of poly(2‐hydroxyethyl methacrylate) networks crosslinked to a low degree suggests in the region of low reduced speeds of deformation the presence of a maximum.This effect was related to the secondary maximum in loss compliance, J″, and explained by the long relaxation times of untrapped entanglements.
Depolarization thermocurrents in amorphous polymers
Authors: Lacabanne C. , Chatain D. 
Published: April 2003

AbstractThe depolarization thermocurrent (DTC) method gives the dependence of the dielectric relaxation time on temperature. It has been used for investigations of relaxations obeying an Arrhenius‐like law in crystalline polymers. The analysis of this method shows it is possible to study mechanisms described by the Williams‐Landel‐Ferry (WLF) equation. The critical temperature appearing in the free‐volume theory of Cohen and Turnbull and also in the statistical thermodynamic theory of Adam and Gibbs can then be measured with good accuracy. The thermal coefficient of expansion of the free‐volume and the WLF coefficient for any reference temperature can also be obtained. Since analysis of the experimental DTC spectrum is particularly simple, this method seems to be a very useful tool for examination of relaxation transitions in amorphous polymers. As an example, results obtained for poly(methyl methacrylate) are presented; they are consistent with published data.
High‐resolution gel‐permeation chromatography
Authors: Kato Yoshio , Kido Shiro , Hashimoto Tsutomu 
Published: April 2003

AbstractThe resolution attainable in gel‐permeation chromatography (GPC) was investigated by using columns packed with polystyrene gel particles of about 5 μ diameter and mixtures of two monodisperse poly‐α‐methylstyrene samples studied previously. The resolution of GPC was found comparable to that of the sedimentation velocity method and slightly better than that of precipitation chromatography. Standard polystyrene samples obtained from Pressure Chemical Co. also were measured with the same columns. It was found that weight‐average to number‐average molecular weight ratios (M̄w/M̄n) of these samples with molecular weight in the range 97,000–411,000 are smaller than 1.006. For samples with molecular weight of 10,000–51,000 and 498,000–860,000, M̄w/M̄n is larger than 1.006, and the width of molecular weight distributions of these samples differed. In particular, molecular weight distributions of samples with molecular weights 19,800 and 51,000 were shown to be bimodal. It is therefore concluded that GPC is useful for samples of very narrow molecular weight distribution if high‐resolution columns are used.
Sinusoidal normal stress measurements with the Weissenberg rheogoniometer
Authors: Kajiura Hirokazu , Endo Hiroshi , Nagasawa Mitsura 
Published: April 2003

AbstractIn measuring sinusoidal normal stress difference of concentrated polymer solutions in a Weissenberg rheogoniometer, the resistance to motion of the upper platen due to the sample between the cone and plate should be taken into account. Correction terms are derived. The theoretical predictions of Lodge and others concerning the relationship between oscillatory normal stress difference and oscillatory shear stress are found to agree with experimental data if these corrections are applied.
Phase transition and paracrystalline order in solution‐crystallized solid n‐paraffins
Authors: Phaovibul O. , Čačković H. , Loboda‐Čačković J. , Hosemann R. 
Published: April 2003

AbstractSolution‐crystallized single crystals of various paraffins were investigated at room temperature by nuclear magnetic resonance and by small‐angle and wide‐angle x‐ray scattering. The samples were crystallized from various solvents and annealed 2, 5, 6, and 12°C below the melting point. The NMR spectra are separated into three components (α, β1 and γ) of different chain‐segment mobility. On combining these results with x‐ray measurements and with results on polyethylene, enough information is obtained to propose a model of the paracrystalline superlattice built up by at least 30 paraffin lamellae and to find where the chains of various conformation are located in the structure. The phase transition of C44H90 in the solid state gives further hints for this allocation. For instance, the β1 component of intermediate mobility increases anomalously from 3% before to 10% after the phase transition. The paracrystalline g value of the macrolattice of the orthorhombic phase is 1.5% and the gap between the lamellae is 2.2 Å. At the beginning of the phase transition, the chains incline stepwise to the lamella surface retaining the orthorhombic macrolattice distance P0 = 58 A and enlarging the gap to 8.8 Å without changing the g value of 1.5%. The growing monoclinic phase, on the other hand, has a constant g value of 3.5% from the beginning with Pm = 52 Å and has gaps of only 3 Å between adjacent lamellae. This explains the large β1 (ca. 10%) of these two new phases, because the mobile chain ends consist of approxiamately 1 CH3 and 1 CH2 group on the average. The γ component of highest micro‐Brownian mobility corresponds to the γ component in polyethylene with a line width of ca. 0.07 gauss. Unlike the case of polyethylene it is produced by only a small amount (0.02–0.13) of free CH3 groups per chain. Another fraction of the CH3 groups belongs to the rigid component α of the crystalline phase. They are located where adjacent lamellae touch each other in crystalline‐like order. Because of these contacts, stacks of lamellae about 1000 Å thick scatter coherently, and the long period Po of the orthorhombic phase remains undestroyed by annealing until the monoclinic domains collapse to the smaller period Pm of the monoclinic phase.
Local mode relaxation in polychlorotrifluoroethylene
Authors: Sasabe Hiroyuki 
Published: April 2003

AbstractThe effects of temperature and pressure on the dielectric relaxation time τ, relaxation strength Δε, distribution of relaxation time β, and shape of absorption curve of the local mode relaxation in polychlorotrifluoroethylene are discussed from the viewpoint of intermolecular interaction. Changes of τ and Δε with temperature and pressure are explainable in terms of changes in intermolecular distance. The temperature and pressure dependences of the dielectric retardation spectrum for the local mode relaxation are different from each other.
Relevance of cage recombination in the plastic deformation of polymers
Authors: Davis L. A. , Baughman R. H. , Pampillo C. A. 
Published: April 2003

AbstractFor a polymer in which permanent rupture of individual molecules is the rate‐limiting process for plastic deformation, the kinetics of chain‐end diffusion and secondary radical reactions should be compared with the kinetics of caged radical recombination in the calculation of activation parameters for plastic deformation. If mechanisms of cage escape are slower than those for cage recombination, the activation parameters for plastic deformation will differ from those for the initial bond‐breaking process. For the case of polyethylene deformed in the vicinity of 250°K, the critical thermally activated event appears to involve scission of the polymer molecule near the site of an abstracted hydrogen atom. For this system the dominant cage‐escape mechanism is diffusion, which is faster than either hydrogen abstraction or unzipping to the monomer. However, at low stresses the rate of cage recombination is expected to be higher than the rate of cage escape, so that the activation parameters for deformation should be the sum of those for chain scission and diffusion. The contribution of diffusion (ca. 15 kcal/mole) to the activation energy for deformation (E*, extrapolated to zero stress conditions) is relatively modest. However, the calculated molar activation volume for deformation V* increases by almost an order of magnitude, i.e., from ca. 10 to ca. 76 cm3/mole when diffusion is required. Consideration of experimental values of E* and V* for high molecular weight polyethylene indicates that, in the regime examined, chain scission plus chain‐end diffusion is required to effect plastic deformation.
Negative thermal expansion of a polydiacetylene single crystal
Authors: Baughman R. H. , Turi E. A. 
Published: April 2003

AbstractMacroscopic thermal expansion in the chain direction has been measured for the first time on organic polymeric single crystals. Negative linear thermal expansion coefficients αM are reported and related to chain torsional motion and equilibrium point‐defect formation for a solid‐state polymerized phase of 2,4‐hexadiyne‐1,6‐diol bisphenylurethane (HDU) which contains crystallographically located interstitial dioxane and for a dioxanefree phase obtained by thermal annealing. Data for as‐polymerized single crystals (which are probably of extended chain morphology) between −50 and 100°C give αM = −(1.686 ± 0.039) × 10−5 − (1.35 ± 0.18) × 10−7 t with t in °C. During volatilization of 11.7 ± 1.0 wt‐% interstitial dioxane and a resulting crystal structure change, the as‐polymerized fibers fibrillate and shrink irreversibly by 0.16 ± 0.04%. Although dichroism and diffraction measurements indicate both a high degree of crystallinity and chain alignment for the dioxane‐free phase, the average thermal expansion coefficient, (−3.0 ± 1.0) × 10−6 °C−1 between −50 and 150°C, is about an order of magnitude less than for the as‐polymerized single crystals.
Diffusion into and adsorption of polyethylenimine on porous silica gel
Authors: Hostetler Ronald E. , Swanson John W. 
Published: April 2003

AbstractThe polyethyleneimine (PEI)–water–silica gel absorption system was used as a model system to investigate the relationship between diffusion into the porous structure, adsorption rate, and molecular weight of the polymer. Three silica gels, Porasil A, B, and and C having a range of characteristic porosity were used as adsorbents. Adsorption of PEI on Porasil C, which has the majority of its pores much larger than the dimensions of the adsorbate molecule, increased initially with increased molecular weight but became nearly constant at higher molecular weight. Little increase in adsorption occurred for this silica gel with increased ionic strength or with increased pH between 9.5 and 10.8. In contrast, adsorption increased sharply with increased ionic strength and for the same pH range on Porasil A. Molecular weight dependence was reversed. Adsorption decreased with increased molecular weight on Porasil A. In this case, the molecular size of PEI investigated was the same as the majority of pore apertures in the adsorbent. Solution environments (i.e., pH and ionic strength) that decrease the size of the PEI molecule and its affinity for the anionic silica gel surface, thus enabling it to more readily diffuse into the smaller porous regions of the adsorbent, are the apparent causes of the very large adsorption increase. Electrostatic repulsion between PEI molecules do not appear greatly to affect adsorption. Similar adsorption behavior has been reported in the literature for the PEI–cellulosic fiber adsorption system. Maximum adsorption on Porasil A occurred at pH 10.8, the same maximum generally reported for adsorption of PEI on cellulosic fibers. In this case, the silica gel (Porasil A) was found to have a pore size distribution and specific surface area of the same magnitude as cellulosic fibers prepared in the expanded state.