bluuebunny/crossref_metadata_2025_split huggingface dataset:
Viscoelastic properties of epoxy‐diamine networks
Authors: Delatycki O. , Shaw J. C. , Williams J. G. 
Published: April 2003

AbstractEight epoxy–diamine networks have been formed, diamines with 2 to 12 methylene groups being used as curing agents. Dynamic mechanical tests revealed four transition regions in the dynamic loss modulus/temperature relationship. Two possible explanations for the relaxation of the glycidyl portion of the structure are proposed. One of the relaxations could be due to the breakdown of hydrogen bonds through the hydroxyl and ether groups. The second could be ascribed to the relaxation of the unbonded glycidyl groups or a second relaxation of the glycidyl groups after the breakdown of the hydrogen bonds.
Measurement of hydrogen isotope transport in poly(vinyl fluoride) films by the permeation‐rate method
Authors: Ziegel K. D. , Frensdorft H. K. , Blair D. E. 
Published: April 2003

AbstractA novel gas‐flow method of measuring the diffusion, solubility, and permeability of gases and vapors in polymer films is described. The specific advantages of this system over the time‐lag technique are discussed. Transport data, including activation energies and enthalpies of solutions, for hydrogen and deuterium in poly(vinyl fluoride) are presented, and the effects of the glass transition and of orientation on the observed transport rates are discussed.
Conformational energy contribution to the heat of solution in polymer–solvent systems. Part I. Theory
Authors: Bianchi Umberto , Cuniberti Carla , Pedemonte Enrico , Rossi Corrado 
Published: April 2003

AbstractThe conformational energy contribution (ΔUconf) to the heat of solution in polymer‐solvent systems is presented and discussed in connection with chain conformational properties. In particular, ΔUconf has been discussed in terms of various possible mechanisms of coil deformation.
Conformational energy contribution to the heat of solution in polymer–solvent systems. Part II. Experimental results
Authors: Bianchi Umberto , Cuniberti Carla , Pedemonte Enrico , Rossi Corrado 
Published: April 2003

AbstractHeats of solution (ΔHexp) in solvents of increasing thermodynamic power have been measured for four polymers: polystyrene (PS), poly(vinyl acetate) (PVAc), polyisobutylene (PIB) and polydimethylsiloxane (PDMS). After subtraction from ΔHexp of an interaction term (calculated by the Hildebrand treatment based on solubility parameters) and the excess volume term, the quantity remaining is interpreted as the conformational energy contribution (ΔUconf) to the heat of solution. ΔUconf appears to correlate well with some basic conformational properties of the chain, such as the sign of the temperature coefficient of unperturbed dimensions derived from solution properties, and shows a monotonic behavior with α, the expansion coefficient of the polymer coil in the final solution. Numerical values of ΔUconf, at least for those cases in which polymer solubility parameters are known with some certainty, are much larger than those evaluated from rubber elasticity experiments (through the experimentally accessible value of the energy component of the force of retraction im simple elongation).
Diffusion in glassy polymers. I
Authors: Kwei T. K. , Zupko H. M. 
Published: April 2003

AbstractSynopsisThe diffusion of six solvents in three crosslinked, glassy epoxy polymers is studied. Case II swelling and Fickian sorption are observed as two simple limiting cases. The mechanism of diffusion changes from one limit to another as the nature of the solvent or the crosslink density of the polymer is altered. With mixed solvents, properly chosen, a superposition of Fickian diffusion and case II swelling is observed.
Dilute solution properties of poly(α‐methylstyrene–ethylene) “regular” sequence copolymers
Authors: Tanzawa Hiroshi , Tanaka Tatsundo , Soda Atsuhiko 
Published: April 2003

Abstract“Regular” sequence copolymers having the structure {[CH2C(CH3)(C6H5)]m(CH2CH2)n}p with relatively small values of m and n were prepared by means of “living” polymerization techniques. The intrinsic viscosities of fractions of these copolymers were obtained in various solvents including a theta solvent. The molecular weights of these fractions were determined by the Archibald ultracentrifugal method. The results show that the intrinsic viscosity–molecular weight relations of the regular sequence copolymers are affected not only by the average composition of the copolymer, but also by the sequence length in the copolymer molecule. It is suggested that the effective conformation of a chain element in the copolymer is not always the same as that in the homopolymer.
Structural and steric isomerism of polypropylenes
Authors: Miyamoto Takeaki , Inagaki Hiroshi 
Published: April 2003

AbstractThe structural and steric isomerism of propylene polymers has been estimated on the basis of solution properties as well as infrared and high‐resolution nuclear magnetic resonance spectra. Three general types of polypropylenes were prepared: polymers prepared with the cationic catalytic system AlCl3–C2H5Cl, stereoblock polymers obtained by successive extraction from a commercial product and isotactic polymers of low molecular weight obtained by thermal degradation of a highly isotactic polymer followed by hydrogenation with Adam's catalyst in dioxane at 40°C. The characterization of all samples was accomplished by equilibrium ultracentrifugation, vapor‐pressure osmometry, viscometry, and gel‐permeation chromatography. It is found that the molecular chain of cationically prepared polymer is somewhat branched owing to structural isomerism during polymerization. Isoamyl acetate is found to be a theta solvent for stereo‐block as well as for atactic and syndiotactic polymers; the theta temperature is determined as the temperature at which the light‐scattering second virial coefficientA2vanishes. A close correlation is found between the theta temperature and stereoisomerism. The absorbances of the 1154 and 974 cm−1bands in the infrared spectra decrease with decreasing molecular weight; in addition to the mere existence of alternating CH2and CH(CH3) groups in the polymer chain, rather long sequences of this type are required for the appearance of these bands. Changes in the absorption band at 997 cm−1show that chains consisting of over ten isotactically connected monomer units can assume a helical conformation. From the high‐resolution NMR spectra of different polypropylenes, including isotactic polymers of low molecular weight, it is found that in estimating the microstructure, account must be taken of the effects of stereoisomerism within tetrads of monomer units on the apparent widths of the methylene proton resonances. If substantial concentrations of several of the possible types of tetrads are present (i.e., if the tactic sequence lengths are quite short), then it is difficult to determine the relative amounts of tactic dyads accurately from the 100 Mcps methylene proton resonances.
Birefringence of native cellulosic fibers. Part II. Spiral structure of cotton
Authors: Iyer K. R. Krishna , Neelakantan P. , Radhakrishnan T. 
Published: April 2003

AbstractInterferometric studies have been made on cotton fibers as well as on twisted nylon filaments. The results so obtained provide strong evidence that the fibrils in the cotton fiber become less inclined to the fiber axis as one proceeds from the surface to the core. Also, studies on twisted nylon filaments by the fiber refractometer and Becke line techniques indicate that the latter, as practiced in this laboratory, does give values of refractive index which are heavily weighted towards the fiber periphery.
Spin lattice relaxation in linear polyethylene
Authors: Crist Buckley , Peterlin A. 
Published: April 2003

AbstractThe proton spin‐lattice relaxation times (T1) of linear polyethylenes (PE) of varying morphology were measured as a function of temperature. The T1 of oriented bulkcrystallized and solution‐crystallized material was isotropic, in disagreement with calculations based on a sample dipole pair model. Motion in the non‐crystalline regions of the samples is shown to be responsible for the T1 minimum occurring around −20°C. The dependence of T1 at the minimum on the long period reinforces the model of an amorphous fraction composed of disordered lamellar surface layers. The temperature of the T1 minimum and the dependence of T1 on the long period imply that the mobility of these amorphous regions is reduced in cold‐drawn and solution‐crystallized samples. This mobility irreversibly increases with annealing. In highly relaxed samples the motion of a small portion of the disordered regions is almost liquidlike, as indicated by the presence of a second shorter T1.
Spherulitic crystallization studies of poly(tetramethyl‐p‐silphenylene)–siloxane (TMPS). Part III
Authors: Magill J. H. 
Published: April 2003

AbstractExtensive studies of the kinetics of spherulitic crystallization have been made on fractionated samples of TMPS. An analysis of these results reveals that a two‐dimensional growth rate mechanism is a more likely mode of growth than a three‐dimensional one. This conclusion is substantiated by experimental evidence from optical microscopy and light scattering from within spherulites. The crystallite end surface energy is found to increase as the molecular weight is raised.
Surface tension of polymer solutions. II. Poly‐isobutylenes in n‐heptane and tetralin
Authors: Gaines George L. 
Published: April 2003

AbstractThe surface tensions of solutions of polyisobutylene fluids in n‐heptane and tetralin have been measured at room temperature. The polyisobutylene samples studied range in molecular weight from 400 to 2800. The results conform closely to the predictions of equations previously developed from a simplified lattice theory calculation.
Polymer chain motion from viscosity and dielectric dispersion measurements
Authors: Bueche F. , Tokcan Güngüur 
Published: April 2003

AbstractShear viscosity and dielectric dispersion measurements have been made on a series of concentrated solutions of poly‐p‐chlorostyrene in toluene, chlorobenzene, and diethylbenzene, as well as on the pure polymer. It is found that the product ηνm/T is nearly temperature‐independent in the present range of measurement (30 ≤ νm ≤ 30 ≤ 104 Hz), where νm is the frequency at which the dielectric loss maximum occurs. For the pure polymer, ηνm (200/T) is 1011.5 poise/sec. This leads to a segmental jump distance of 5 Å. Although the results in this range correspond quite well to the concept of a segmental friction constant determined by the matrix viscosity, deviations appear as the apparent energy of activation for viscous flow decreases below 13 kcal/mole. There is reason to believe that these deviations reflect the increasing importance of bond rotation barriers at low matrix viscosity. It is speculated that the damped torsional oscillator interpretation of f0 proposed by Tobolsky will become valid in systems still more fluid.
Conformation of polyisobutylene in dilute solution subjected to a hydrodynamic shear field
Authors: Cottrell F. R. , Merrill E. W. , Smith K. A. 
Published: April 2003

AbstractA new light‐scattering experiment which allows a direct determination of the conformation of macromolecules deformed in flow is described. Light‐scattering relationships based on the interference function are developed, and results of an experimental study are detailed. The deformed conformation of high molecular weight polyisobutylene was determined in a Couette‐type shear field. Decalin was the solvent. Variables investigated were the shear rate (0 to 600 sec−1), the polymer molecular weight (1.0 × 107 to 1.6 × 107), and the polymer concentration (2.0 × 10−4 to 8.0 × 10−4 g/cc). Conformation variables determined were the orientation of the molecule in the shear field and its maximum and minimum extension ratios in the plane defined by the direction of flow and the direction of the shear rate. The deformation of the macromolecule was found to be markedly discrepant when compared to the dynamic macromolecular models which assume complete coil flexibility, and more closely in agreement with the recent theories of Cerf, developed for nonfree‐draining coils which exhibit a finite internal viscosity.
Melting behavior and morphology of drawn nylon 6
Authors: Arakawa Tamio , Nagatoshi Fumio , Arai Naoki 
Published: April 2003

AbstractThermal analysis has been carried out on drawn nylon 6 filaments annealed at various temperatures between 150 and 210°C and then methoxymethylated to various degrees. It is shown that the melting point inherent to the morphology of drawn nylon 6 can be obtained from samples in which the reorganization of defect crystallites in the course of thermal analysis is prevented by a proper degree of methoxymethylation of amorphous regions. The melting point thus obtained is in linear relation with the reciprocal crystallite size in the direction of fiber axis which has been obtained from small‐angle x‐ray data and crystallinity. The extrapolation and the slope of this linear relation give the equilibrium melting point of nylon 6 as 245°C and an end‐surface free energy of 42 erg/cm2. The results seem to provide strong support for the presence of chain‐fold surfaces in the drawn and annealed polymers.
Thermodynamics of polyether solutions
Authors: Malcolm G. N. , Baird C. E. , Bruce G. R. , Cheyne K. G. , Kershaw R. W. , Pratt M. C. 
Published: April 2003

AbstractMeasurements are reported of the vapor pressures and the heats and volumes of mixing of solutions of poly(ethylene glycol dimethyl ether) in chloroform and in carbon tetrachloride. The measurements have been used to calculate the thermodynamic mixing functions for mixing with zero volume change. These values have been compared with the predictions of the lattice theory of mixtures at three different levels of approximation, viz., the generalized “first approximation” theory of Barker, the “zeroth approximation” theory, and the Flory theory. In the hydrogen‐bonding chloroform solutions the Barker theory is more successful than the other forms of the lattice theory. The results have also been used, in conjunction with those for solutions of poly(propylene glycol dimethyl ether) in the same two solvents, to test the ability of the Barker theory to correlate the properties of related systems. Good correlation is found between the two carbon tetrachloride solutions but not between the chloroform solutions. It is probable that the side‐chain methyl groups in the propylene oxide repeating unit cause the hydrogen‐bonding interaction to be weaker in this polymer than it is in the polymer with the ethylene oxide repeating unit.
Scattering of light from assemblies of oriented rods
Authors: Rhodes M. B. , Stein R. S. 
Published: April 2003

AbstractThe scattering patterns are calculated from anisotropic rods having an arbitrary angle of the polarizability axis with respect to the rod axis. The effect of a distribution of orientation of the rods is explored. This leads to a change in scattering patterns produced by orienting the rods upon stretching the sample. The scattering patterns are affected by the relationship between the refractive indexes of the rods and that of the surroundings. The influence of the optic axis orientation angle changing upon orienting the rods is explored. Theoretical patterns are compared with experimental ones obtained upon stretching polytetrafluoroethylene (PTFE) films.
Volume recovery of glassy poly‐α‐methylstyrene
Authors: Endo Hiroshi , Fujimoto Teruo , Nagasawa Mitsuru 
Published: April 2003

AbstractA method for evaluating the relaxation time as a function of both temperature and volume from volume contraction experiments, as proposed by Kovacs, was experimentally examined by using monodisperse poly‐α‐methylstyrene samples of various molecular weights and blends. It was concluded that his theory can be successfully applied to the present experimental data, though his two different approximations give somewhat different values of the shift factor for the time‐temperature superposition of volume contraction data. A difference was observed between the temperature dependence of the shift factor of monodisperse polymers and that of blends.
Vibrational analysis of molten poly(ethylene glycol)
Authors: Matsuura Hiroatsu , Miyazawa Tatsuo 
Published: April 2003

AbstractThe infrared absorption of poly(ethylene glycol) was measured in the molten state. Characteristic bands of the molten state were identified. Normal vibrations and frequency distributions were treated for various conformation models with CH2CH2O repeat units. The infrared absorption peaks of the molten state closely correspond to the frequency distribution peaks of the TGT conformation with gauche OCH2CH2O groups, although infrared bands due to trans OCH2CH2O groups are also observed. Vibrational assignments of the infrared bands and Raman lines were made on the basis of potential energy distributions.
Tensile yield‐stress behavior of poly(vinyl chloride) and polycarbonate in the glass transition region
Authors: Bauwens J. C. , Bauwens‐Crowet C. , Homès G. 
Published: April 2003

AbstractThe yield‐stress behavior of two glassy polymers is studied through the glass transition region over a wide range of strain rates. For temperatures below the glass transition temperature, the yield stress behavior could be described as a non‐Newtonian flow in agreement with Eyring's theory, if one excepts a narrow range relating to the slowest strain rates. For temperatures above Tg, the yield‐stress behavior is still nonlinear but fits the relations based on the concept of free volume.
A simple, sensitive graphical method of treating thermogravimetric analysis data
Authors: Broido A. 
Published: April 2003

AbstractThermogravimetric Analysis (TGA) is finding increasing utility in investigations of the pyrolysis and combustion behavior of materials. Although a theoretical treatment of the TGA behavior of an idealized reaction is relatively straight‐forward, major complications can be introduced when the reactions are complex, e.g., in the pyrolysis of cellulose, and when experimental imperfections arise. Consequently, a fairly large number of analytical methods have been proposed for obtaining kinetic parameters from TGA curves. Among the proposed methods are several graphical procedures, mostly involving relatively inaccurate tehniques, such as obtaining slopes on a rapidly changing curve. Included among the proposed procedures is one which permits a linear plot of TGA data. The sensitivity with which such a plot can be used to identify and correct for a variety of experimental complications seems to have escaped even the proponents of the techniques. This paper provides an illustration of the use of this graphical procedure in a hypothetical first‐order pyrolysis typical of those occurring in the TGA behavior of cellulose.
Effect of immobilizing adsorption on the diffusion time lag
Authors: Paul D. R. 
Published: April 2003

AbstractA “dual sorption” model has been proposed by Michaels, Vieth, et al. to explain extensive equilibrium sorption data for several gases in some glassy polymers. To explain data on sorption kinetics, it was further postulated that one of the sorption modes immobilizes the gas molecules. Stated mathematically, this model leads to a modified form of Fick's second law. Both normal and desorption time lags for diffusion have been computed here for this model of diffusion in glassy polymers. The computed time lags are shown to be dependent on the boundary concentrations used in permeation. Experimental measurement of these time lags would be a sensitive and critical test to ascertain the validity of this theory.
GPC analysis of degraded annealed single crystals
Authors: Sadler D. M. , Williams T. , Keller A. , Ward I. M. 
Published: April 2003

AbstractAnnealed polyethylene single crystals have been degraded with fuming nitric acid, and the molecular weight distribution of the fragments determined by using a gel‐permeation chromatograph. Peaks due to chain folding were observed in these distributions as for unannealed single crystals. The peaks moved to lower molecular weight with increasing degradation time. Comparison of the lowest molecular weight peak length after a given degradation time with the low‐angle x‐ray periodicity before degradation gave information about a disordered surface layer. The thickness of this layer at early states of degradation was dependent solely on annealing temperature, though changes in the layer must have occurred with annealing time, since there was an increase in reaction rate with annealing time. At higher degradation states, the thickness of the layer was dependent solely on the original low‐angle periodicity. This has been related to the depth at which some folds are buried beneath the lamellar surfaces. The relevance of these observations to the structure of annealed single crystals is discussed.
Statistics of extreme values applied to the brittle fracture of poly(methyl methacrylate) containing polytetrafluoroethylene particles
Authors: Hansen K. E. , Forsman W. C. 
Published: April 2003

AbstractPoly(methyl methacrylate) tensile bars were prepared containing nearly spherical polytetrafluoroethylene particles in concentrations from one to a thousand particles per gauge length of the bars. Particle diameters varied from 0.0035 to 0.018 in. Exhaustive tensile tests were performed at sufficiently high strain rate to assure brittle fracture and the results analyzed statistically by the theory of extreme values as proposed by Epstein. The results suggested that the polytetrafluoroethylene particles themselves did not act as flaws, but that they intensified the stress field on natural flaws which acted as the origin of fracture. Assuming a Laplace distribution as the underlying distribution of tensile strength (not to be confused with observed distribution of tensile strengths) gave predicted fracture statistics in good agreement with experiment.
Effect of molecular weight on the radial growth rates of polymer spherulites
Authors: Devoy C. , Mandelkern L. 
Published: April 2003

AbstractData existing in the literature for the spherulitic growth rate of molecular weight fractions of linear polyethylene, poly‐(tetramethyl‐p‐silphenylene)siloxane, and trans‐1,4‐polyisoprene have been analyzed according to nucleation theory on taking into account the influence of chain length on the free energy of fusion. All three polymers display very similar behavior in that the interfacial free energy reaches an asymptotic value at high molecular weights, decreases as the molecular weight is lowered, and appears to also reach an asymptotic value at low molecular weights. Although the changes in the interfacial energy with molecular weight are quite distinct, the relative change is much less than has been previously reported when a molecular crystal analysis is used. The same general behavior observed points out the dominating influence of the chain‐like character of the molecules in governing the growth rate.
Diffuse interphase layer in microheterogeneous polymer mixtures
Authors: Letz Ján 
Published: April 2003

AbstractThe thickness of the interphase layer as a function of time at 160°C has been determined directly in a microheterogeneous polymer mixture, and the layer thickness between two bonded sheets has also been measured by phase‐contrast microscopy. Two mixtures of polymers, isotatic polypropylene with polyethylene and poly(vinyl chloride) with polyethylene, were prepared by mixing size‐sorted powders in suspension, followed by evaporating the suspension medium and compacting the powdered mixtures. The mutual penetration initially obeyed Fick's second law; then diffusion was retarded and stopped after 15–20 min. An equilibrium state was reached which did not correspond to the classical thermodynamic equilibrium, at which the so‐called equilibrium thickness of the interphase layer for the pair isotactic polypropylene‐polyethylene was about 28,000 Å and for the pair poly(vinyl chloride)‐polyethylene was about 89,600 Å. The equilibrium values can be used as a quantitative criterion for the compatibility of the polymer pairs.