bluuebunny/crossref_metadata_2025_split huggingface dataset:
Viscoelasticity of oriented poly(ethylene terephthalate)
Authors: Murayama Takayuki , Dumbleton John H. , Williams Malcolm L. 
Published: April 2003

AbstractTime–temperature superposition can be successfully applied to both the stress relaxation and dynamic mechanical properties of oriented PET fibers. Two curves result; one is the time dependence of the modulus at constant temperature, while the other is the shift, log aT, of this curve along the time scale as a function of temperature. This temperature dependence is less than that for both unoriented PET and typical amorphous polymers above Tg. It is about the same as that for oriented nylon 66 and unoriented glassy poly(methyl methacrylate). The isothermal modulus has the same time dependence as that of the unoriented PET; however, it is a factor of 3.3 larger. The modulus curve is almost identical in both shape and magnitude with that of oriented nylon 66. However, a temperature of 82°C. is required to place the viscoelastic dispersion region of PET at the same time scale as nylon 66 at 25°C. This temperature increase is the major difference in viscoelasticity between these two oriented polymers.
Phase equilibria in polymer–liquid–liquid systems
Authors: Suh K. W. , Liou D. W. 
Published: April 2003

AbstractThe phase equilibria in polymer–liquid 1–liquid 2 ternary systems have been calculated on the basis of the Flory‐Huggins theory of polymer solutions. A new approximation method based on the “cluster” concept has been introduced for mixed solvents comprising a solvent and a nonsolvent. This concept has been verified with polystyrene–solvent–methanol systems.
Melting of polycaprolactam
Authors: Liberti F. N. , Wunderlich Bernhard 
Published: April 2003

AbstractHighly crystalline polycaprolactam was prepared by zone polymerization of ε‐caprolactam. Folded‐chain crystallized and annealed, melt‐crystallized, and solution‐crystallized polycaprolactam was produced from commercial polycaprolactam. All samples were characterized by x‐ray diffraction, electron microscopy, density measurement, and heat of fusion measurement. The determination of the time‐dependent melting by DTA and scanning calorimetry revealed that all the different morphologies show different melting behavior. Zone‐polymerized polycaprolactam superheats, and the other morphologies reorganize on heating to different degrees. Densities and heat of fusion vary in the same manner—from highest to lowest—in the order: zone‐polymerized, solution‐crystallized, annealed, and melt‐crystallized. An estimate of heat of fusion, equilibrium melting point, and surface free energy was obtained from the melting points.
Some rheological properties of molten polypropylene
Authors: Adamse J. W. C. , Janeschitz‐Kriegl H. , Den Otter J. L. , Wales J. L. S. 
Published: April 2003

AbstractThe following measurements were carried out on the melts of two samples of polypropylene, one with a narrow and one with a broad molecular weight distribution: viscosity in steady shear flow, dynamic storage and loss moduli, total normal thrust in cone‐and‐plate apparatus, and flow birefringence. The validity of various theoretical interrelations between the measured quantities is checked. The influence of molecular weight distribution is qualitatively discussed.
NMR studies of polymer solutions. III. Conformational transition study of oligomeric polyethylene in mixed solvents
Authors: Liu Kang‐Jen 
Published: April 2003

AbstractThe intramolecular structure of oligomeric polyethylene (PE) in solvent mixtures of α‐chloronaphthalene and carbon tetrachloride, α‐chloronaphthalene and deuterated octane, and α‐chloronaphthalene and deuterated hexadecane was studied at 35°C. by a high‐resolution nuclear magnetic resonance technique. It was clearly shown that the n‐alkanes show no detectable selective solvent absorption in these systems. The conformational structure (Pp), which was formed in “bulky” aromatic solvents when the chain length was greater than 16, was significantly destroyed by the presence of carbon tetrachloride, octane, or hexadecane in the above‐mentioned solvent mixtures. Therefore, the “bulky” aromatic solvents, such as α‐chloronaphthalene and 9‐chloroanthracene, can be classified as Pp‐structure‐promoting solvents, in which the PE remains in the Pp conformation. In contrast, carbon tetrachloride and linear alkanes are Pm‐structure‐promoting solvents, in which the PE does not exhibit any Pp structure but is in the disordered Pm conformation. It is speculated that the Pp structure is caused by a “chain‐fold” mechanism.
Viscoelastic properties of 1,2‐polybutadiene—comparison with natural rubber and other elastomers
Authors: Sanders James F. , Ferry John D. , Valentine Robert H. 
Published: April 2003

AbstractViscoelastic properties of uncrosslinked 1,2‐polybutadiene (91.5% vinyl, 7.0% cis, 1.5% trans, number‐average molecular weight 99,000) were studied by dynamic shear measurements between 0.15 and 600 cps (torsion pendulum and Fitzgerald transducer) and shear creep measurements over time periods up to 3.7 × 104 sec., in the temperature rang from 5 to 50°C. More limited dynamic measurements were made on a sample of unvulcanized natural rubber with number‐average molecular weight 350,000 at frequencies from 0.4 to 400 cps and temperatures from 13 to 48°C. All data were reduced to 25°C. by shift factors calculated from equations of the WLF form with the following coefficients: 1,2‐polybutadiene, c1 = 6.23, c2 = 72.5; natural rubber, c1 = 5.94, c2 = 151.6. In the transition zone, the relative positions of the loss tangent curves on the logarithmic frequency scale for these and other rubbers (1,4‐polybutadiene with 50% trans configuration; styrene–butadiene rubber with 23.5% styrene content; and polyisobutylene) provided relative measures of local segment mobility. At 25°C., these ranged over a factor of 3700 with 1,2‐polybutadiene and polyisobutylene the lowest and 1,4‐polybutadiene the highest. When the frequency scale of each rubber was reduced to a temperature 100°C. above its glass transition temperature, however, the loss tangent curves for all except polyisobutylene were nearly coincident; the latter still showed a lower mobility by a factor of about 1/800. The terminal relaxation time and steady‐state compliance for the 1,2‐polybutadiene calculated from the Rouse theory were larger than those observed experimentally. The level of compliance corresponding to the entanglement network of 1,2‐polybutadiene, JeN, was calculated by integration over the loss compliance, J″, to be 1.62 × 10−7 cm.2/dyne; integration over G″ to obtain the corresponding modulus gave reasonable agreement. From such JeN, values, the average number of chain atoms between entanglement points, jZe, was estimated as follows: 1,2‐polybutadiene, 132; natural rubber, 360; 1,4‐polybutadiene, 110; styrene–butadiene rubber, 186; polyisobutylene, 320. Values of jZe were also estimated from the minimum in the loss tangent and compared with those reported from the molecular weight dependence of viscosity. The three sources were in generally good agreement.
Vibrational analysis of chain folding in polyethylene crystals
Authors: Tasumi M. , Krimm S. 
Published: April 2003

AbstractThe vibration frequencies of a polyethylene crystal lattice have been computed for various structures in which a fully deuterated chain is mixed with a normal chain. Intermolecular potential functions previously developed by the authors were used in the calculation. It is shown that such structures make it possible to distinguish experimentally between chain folding in the (110) plane and folding parallel to the (100) plane. Calculations have also been done for a regular polymer of (CH2CD2). Such a structure would permit the determination of the parity of the number of methylene groups in the fold.
Quantitative characterization of deformation in drawn polypropylene films
Authors: Samuels Robert J. 
Published: April 2003

AbstractThe submicroscopic morphology of uniaxially deformed isotactic polypropylene films has been examined by small‐angle light scattering (SALS), electron microscopy, optical microscopy, small‐angle x‐ray scattering (SAXS), wide‐angle x‐ray diffraction, birefringence, sonic modulus, and density methods. Several new interpretations and extensions of existing theories are developed and verified experimentally as follows. (1) The Vv SALS pattern is shown to be a new tool for the identification of the sign of the birefringence of spherulites too small to be seen in the optical microscope. The theoretical dependence of the Vv SALS pattern is developed and verified experimentally with patterns from isotactic polypropylene, polyethylene, Penton, nylon 6,6, poly(ethylene terephthalate), and nylon 6,10. (2) Intraspherulitic lamellar behavior during deformation can be identified from the SAXS pattern. This includes quantitative evaluation of the long spacing between lamellae and their average orientation. (3) The two‐phase sonic modulus theory is valid over the wide range of deformations, crystallinities, processing temperatures, and molecular weights used in this study. The deformation of isotactic polypropylene films drawn at 110 and 135°C. has been characterized quantitatively in terms of an integrated picture of mass movement on all morphological levels: the molecular, the interlamellar, and the spherulitic. At both temperatures, the spherulites deform affinely with extension, whereas the deformation mechanisms within the spherulite depend on the location of the radii with respect to the applied load. During spherulite deformation, lamellar orientation and separation processes predominate, whereas at high extensions, fibrillation occurs and crystal cleavage processes predominate. The noncrystalline region orients throughout the draw region. At 135°C. non‐orienting relaxation processes appear in the noncrystalline region which retard the rate of molecular orientation with extension.
Temperature dependence of photoelastic properties of crosslinked amorphous polyethylenes
Authors: Saunders D. W. , Lightfoot D. R. , Parsons D. A. 
Published: April 2003

AbstractCrosslinked samples of polyethylene were prepared by electron irradiation of both high‐ and low‐density polymers in the crystalline state. A further crosslinked sample was obtained by curing a high‐density polyethylene by reaction with dicumyl peroxide at 180°C. The stress–strain–birefringenece relations were obtained on specimens cut from these samples at temperatures between 130 and 250°C. All samples showed a substantial decrease in stress‐optical coefficient with increasing degree of crosslinking and with increasing temperature. The stress‐optical properties at each temperature were extrapolated to zero degree of crosslinking to give quantities characteristic of the Gaussian network. Comparison of these properties with the theory of networks of rotational isomeric chains with both independent and interdependent rotation allows estimates to be obtained for (1) the trans–gauche energy differences in rotation around skeletal bonds and (2) the difference in principal optical polarizabilities for the CH2 group in the elastomeric state. This latter quantity is shown to be more nearly given by Denbigh's than by Bunn and Daubeny's bond polarizability values.
Dielectric relaxations and electrical conductivities of poly(alkyl methacrylates) under high pressure
Authors: Sasabe Hiroyuki , Saito Shogo 
Published: April 2003

AbstractDielectric properties of four methacrylate polymers (methyl, ethyl, n‐butyl and n‐octyl) were studied in the frequency range 0.0001 cps–300 kcps at temperatures above and below the glass transition temperature and at various pressures up to 2500 atm. At temperatures well above Tg a single relaxation peak (α′ peak) was observed in the case of the higher n‐alkyl methacrylates. However, this peak was split into two peaks, α and β, with decrease in temperature or increase in pressure. The molecular motions corresponding to the α and the β relaxation processes are the micro‐Brownian motions of amorphous main chains and of flexible side chains, respectively. From the temperature and the pressure dependence of the average dielectric relaxation time of these polymers the single relaxation process (the α′ process) was attributed to the micro‐Brownian motion of the main chain coupled with that of the side chain. The effects of temperature and pressure on the d.c. conductivity of these polymers were also studied.
Fast passage dispersion signals in inhomogeneously broadened electron spin resonance spectra: Application to the measurement of the spin‐lattice relaxation times of free radicals derived from esters and salts of poly(methacrylic acid)
Authors: Bullock A. T. , Griffiths W. E. 
Published: April 2003

AbstractThe shape of the first derivative of the dispersion mode of an inhomogeneously broadened electron spin resonance spectrum changes markedly on saturation. This behavior provides a convenient and rapid technique for estimating the spin latice relaxation time of the paramagnetic species involved. The technique is described together with the relevant theory. Values for the relaxation times of free radicals derived from poly(methyl methacrylate) and from poly(sodium methacrylate) have been obtained by this method and are found to be in good agreement with those obtained by the progressive saturation technique. A series of salts of polymethacrylic acid have been γ‐irradiated, and the spin lattice relaxation times of the resulting trapped radicals were determined at 77 and 299°K. For a given polymer the relaxation times show little variation with temperature. This is attributed to a broad distribution of correlation times.
Sedimentation transport method for determination of molecular weight distributions
Authors: Kotaka Tadao , Donkai Nobuo 
Published: April 2003

AbstractThe sedimentation of the system polystyrene‐cyclohexane at the Flory temperature has been studied with emphasis on the effects of pressure as well as concentration. The relation between the molecular weight M and the limiting sedimentation coefficient s00, is found to be s00 = 1.50 × 10−15 M1/2 (sec.) The concentration dependence parameter ks has the form, ks = k′M1/2 = k″s00 with k′ = 4.5–5.5 × 10−4. However, a rather unexpected dependence of ks on the rotor speed is also found. A procedure is proposed for deducing solute molecular weight distributions from boundary spreading data in sedimentation transport experiments, a so‐called “single concentration” method, requiring only one sedimentation run. Application to several polystyrenes (in cyclohexane at 35°C) with narrow, broad, and very broad distributions demonstrates the feasibility of the procedure. Comparisons are made with data from elution chromatography and gel permeation chromatography. The GPC method predicts somewhat broader distributions than those obtained by the other two methods.
Tensile strength of rubbers
Authors: Tobolsky A. V. , Lyons P. F. 
Published: April 2003

AbstractA current theory of the tensile strength of rubbers invokes large‐scale crosslink interchange at room temperature to explain the high tensile strengths of networks crosslinked with weak linkages. This mechanical lability of certain crosslinks has been assumed from their known thermal lability at higher temperatures. Relaxation of stress experiments at various elongations have been performed at room temperature on networks crosslinked with both weak and strong linkages. Our purpose was to detect mechanically induced crosslink slippage. We have found no evidence of any mechanical lability of weak crosslinks at room temperature. A hypothesis is presented which explains the high tensile strengths of rubbers crosslinked with weak linkages as resulting from an internally relaxed network formed by the thermal lability of the crosslinks at the vulcanization temperature. This theory is shown to be consistent with some previously unexplained experimental results.
Variation of crystallite orientation with degree of crystallinity: Isotactic polystyrene
Authors: Krigbaum W. R. , Maruno Shigeo 
Published: April 2003

AbstractThe orientation of the crystallographic c axis (chain axis) was followed by x‐ray diffraction during the crystallization of four samples of isotactic polystyrene differing in elongation ratio. The crystallite orientation can be expressed by 〈cos2 χc〉, where χc is the angle between the c axis and the stretching direction. The degrees of crystallinity w were estimated from the diffraction data by using density for calibration. It was found that 〈cos2 χc〉 decreases in a linear manner with crystallinity, the rate of decrease being very small when the elongation ratio α is 5, but becoming progressively larger as α is decreased toward unity. A qualitative measure suggests that amorphous orientation decreases during crystallization at a rate which is nearly independent of α. The variation of 〈cos2 χc〉 with w is therefore governed by the orientation of the statistical chain segments prior to crystallization. If the elongation ratio is small, the supply of well oriented statistical segments is limited, and 〈cos2 χc〉 will decrease at a rapid rate during crystallization. A treatment due to Krigbaum and Roe permits evaluation of the ratio, ν/N, where ν and N are the average numbers of statistical segments in the crystallization nucleus of critical size, and in a network chain, respectively. Our polystyrene samples were not crosslinked, so chain entanglements must serve as junction points. Values of ν could not be obtained, since N was unknown. However, the (ν/N) ratio for isotactic polystyrene decreases slowly with α, and the values agree reasonably well with those obtained in a previous study of oriented polychloroprene networks. After nearly complete crystallization (ω ca. 0.30), the long period spacing measured by low angle diffraction was approximately 135 Å, and varied only slightly with elongation ratio in the range α = 1 to 5. It therefore appears that chain folded lamellae are present in both drawn and undrawn samples of isotactic polystyrene.
Dynamic mechanical properties of cross‐linked rubbers. V. An approximate analysis of the modulus contributions of trapped and untrapped entanglements
Authors: Mancke Ralph G. , Dickie Ray A. , Ferry John D. 
Published: April 2003

AbstractUsing the criterion that a coupling entanglement in a polymer network is trapped if all four strands radiating from it terminate in chemical cross‐links (an approximation to a more rigorous treatment of Langley), an equation is derived relating the equilibrium modulus to the magnitude of the compliance in the frequency region where all coupling entanglements, whether trapped or not, contribute to the elasticity. The latter value is estimated from the storage compliance at the frequency where the storage compliance of the uncross‐linked polymer corresponds to the entanglement compliance derived from integration over the loss compliance. The theory agrees rather well with data on vulcanizates of natural rubber. For 1,4‐polybutadiene and styrene–butadiene rubbers, the agreement is somewhat less satisfactory, but the results support the hypothesis that the low‐frequency losses observed in lightly cross‐linked rubbers are due to relaxation of untrapped entanglements.
Bubble formation in vulcanized rubbers
Authors: Denecour R. L. , Gent A. N. 
Published: April 2003

AbstractA theoretical treatment is given for the formation of visible holes in an elastic solid. It differs from previous treatments of bubble formation in liquids by neglecting the problem of hole nucleation altogether. Instead, a small spherical hole is assumed to be present initially. The inflation of such a hole by a dissolved gas is then considered. A critical internal pressure is deduced, at which the hypothetical hole would become infinitely large. This pressure is given by 5G/2; where G is the shear modulus of the rubber. Some model experiments are described in which swollen rubber vulcanizates were rapidly heated to bring the dissolved liquid into a superheated conditions. The temperatures of rapid bubble formation were determined for a number of vulcanizates having different degrees of crosslinking and hence different values of shear modulus, and for different swelling liquids. The results are shown to be in reasonably good quantitative agreement with the theoretical predictions.
Viscosity and normal stresses in branched polydisperse polymers
Authors: Graessley William W. , Prentice James S. 
Published: April 2003

AbstractThe steady‐flow behavior of five samples of branched poly(vinyl acetate) has been studied with the Weissenberg rheogoniometer. The branching densities and molecular weight distributions were known from an analysis of the polymerization kinetics. Measurements were made on concentrated diethyl phthalate solutions (0.170 and 0.225 g/ml) at temperatures of 30 and 70°C. The viscosities of all solutions at zero shear rate were less than of solutions of linear poly(vinyl acetate) with the same weight‐average molecular weight. The amount of decrease was in excellent agreement with Bueche's theory of melt viscosity in branched systems. The viscosity versus shear rate curves were surprisingly independent of molecular weight distribution, the data from all samples being superimposable on the same master curve. Relaxation times derived independently from the viscosity behavior and the normal stress data were of similar magnitude and always close to the Rouse relaxation time of each solution.
Analysis of the random configuration of the polycarbonate of diphenylol‐2,2′‐propane
Authors: Williams A. D. , Flory P. J. 
Published: April 2003

AbstractThe structure of the polycarbonate chain has been analyzed from the point of view of the spatial configurations it may assume. The carbonate group is certainly planar, and the trans,trans configuration probably is strongly preferred. Rotations about the aryloxygen bonds are subject to symmetric, twofold potentials. It follows that the molecule can be treated as a freely rotating chain consisting of a succession of virtual bonds 7.0 Å in length, joined at angles of ca. 112°. Calculations carried out on this basis yield 〈r2〉0/M = 0.85 Å2/g‐mole wt for the unperturbed random coil, in excellent agreement with the experimental results of Berry, Nomura, and Mayhan. The effect of occurrence of some of the carbonate groups in cis, trans configurations is investigated using more elaborate methods.
Polarization of fluorescent light from a uniaxially oriented rubber
Authors: Stein R. S. 
Published: April 2003

AbstractThe polarization of fluorescence from a polymer characterizes two segment orientation functions, fs(2) and fs(4). These may be calculated as a function of elongation using the kinetic theory of rubber elasticity. Three cases are considered: (a) the transition moment direction lies parallel to the segment axis and does not change its orientation during the lifetime of the excited state, (b) the transition moment direction lies at an angle γ to the segment axis, and (c) the transition moment changes its orientation during the lifetime of the excited state.
Poly(1,2‐dimethyl‐5‐vinylpyridinium methyl sulfate). III. Adsorption on a crystalline silica
Authors: Shyluk W. P. 
Published: April 2003

AbstractWith low‐shear mixing, a portion of a high molecular weight poly(DMVPMS) is immediately adsorbed, and fairly stable aggregates are formed by the polymer bridging mechanism. The adsorption equilibrium is not established after several weeks because of a very slow liberation of the partly covered surface that is trapped within the aggregates. At a high ionic strength, or when the polymer is degraded to a low molecular weight, the adsorption equilibrium is quickly established because of a weaker bridging in the aggregates. It is proposed that poly(DMVPMS) adsorbs from water in a flattened conformation by an ion exchange mechanism. The saturation level increases and then becomes constant as the ionic strength is increased. Simple electrolytes show a specific effect on the adsorption of poly(DMVPMS) that is analogous to their effect on the interaction of other colloidal particles.