bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rheological properties of internal viscosity models with stress symmetry
Authors: Bazúa Enrique R. , Williams Michael C. 
Published: April 2003

AbstractInternal viscosity models (IVM) for dilute‐solution polymer dynamics differ in how they define the deformational force Fd which includes φ, the IV coefficient, and in how they treat polymer rotational velocity Ω. Here, the handling of angular momentum is shown to be crucial. A torque balance in simple shear flow at shear rate G leads to stress symmetry and specification of Ω(G) which differs greatly from the conventional Ω = G/2. This determines the G dependence of viscosity η and normal stress coefficient ζ. There are also implications of a transition in rotational behavior as φ approaches a critical value. Predictions of η(G), ζ(G), and η*(ω) are presented for two versions of Fd: one derived recently by the authors and one being most commonly used at present. Limiting cases for high and low φ, and for high and low G and ω, are discussed. Some differences exist between predictions of the two Fd models, but these are surprisingly minor.
Investigation of the interaction of a polyelectrolyte with low molecular weight electrolytes containing nonidentical counterions by differential refractometry
Authors: Stejskal Jaroslav , Kratochvíl Pavel , Pouchlý Julius 
Published: April 2003

AbstractIf the counterion of a polyelectrolyte is not identical with any of the ions of a low molecular weight electrolyte added to the solution, the system may be regarded as a four‐component system. Relations for the refractive index increments have been derived which allow the determination of the coefficient of selective sorption of the added electrolyte from the refractive index increments of the components independent of the original counterion of the polyelectrolyte. Equilibrium dialysis and differential refractometry were used to study the interaction of KCl, KBr and NaI with poly[‐1(2‐hydroxyethyl)pyridiniumbenzenesulfonate methacrylate] or with an analogous polymer containing a toluenesulfonate counterion in aqueous solutions. The coefficient of selective sorption increases in the series Cl− < Br− < I− from strongly negative to strongly positive values; the specific interaction of these counterions with the macroion increases in the same order.
Nuclear magnetic resonance studies on microstructure of ethylene copolymers. VI. Carbon‐13 spectra of ethylene–vinyl acetate copolymers
Authors: Wu Ting Kai , Ovenall Derick W. , Reddy Gade S. 
Published: April 2003

AbstractThe 22.6‐MHz Fourier‐transform noise‐decoupled 13C (carbon‐13) NMR spectra of several ethylene–vinyl acetate (E–VA) copolymers were obtained. We found that triad information on monomer placement can be deduced from carbonyl resonances, triad and pentad information can be deduced from methine carbon resonances, and triad information is available from the methylene carbon resonances. The random comonomer distributions in E–VA polymerizations were demonstrated up to pentad placements. In addition, the use of model‐compound data in the analysis of copolymer spectra was shown.
Kinetics of polymer crystallization from the melt (calorimetric approach)
Authors: Godovsky Yu. K. , Slonimsky G. L. 
Published: April 2003

AbstractCrystallization kinetics for 12 polymers including polyolefins, polyesters, polyurethanes, polysiloxanes was measured by the evolution of heat in a modified Calvet‐type calorimeter over wide temperature ranges. The results are analyzed in terms of the Avrami equation and a comparison between calorimetric and dilatometric results is carried out. It is concluded that, although in the majority of cases experimental results do not obey the Avrami equation, for some polymers the agreement is rather good. The Avrami parameter obtained, however, depends on the experimental technique. Possible reasons for this disagreement are discussed. Analysis of the calorimetric crystallization rate in the vicinity of the melting point by using the kinetic theory of crystallization shows that the growth is controlled by surface (two‐dimentional) nucleation. Energy parameters for the crystallites were determined and it is shown that the surface energy of the crystallites depends on the molecular structure of the polymer. Temperature dependence of the calorimetric crystallization rate of the polymers for which crystallization rates could be determined above and below the maximum rate are analyzed using a kinetic equation with common approximations for the transport term. The influence of melting conditions on the crystallization rate was studied. The results indicate heterogeneous nucleation in the polymer melt. It is concluded that this may be due both to impurities and to high regularity of macromolecules in the polymer melt.
Electron trapping and luminescence mechanism in thermoluminescence of irradiated polycarbonate
Authors: Hama Yoshimasa , Nishi Kunihiko , Watanabe Kazuo , Shinohara Kenichi 
Published: April 2003

AbstractThermoluminescence of polycarbonate irradiated by electron beams was observed in order to investigate the trapping of electrons and the luminescence mechanism. The thermoluminescence glow curve is composed of three components. The peaks appear at −150°C (α peak), −120°C (β peak), and −30°C (γ peak). The α peak is attributed to recombination of cations with electrons released from trapping sites formed by carbonate groups. The β peak is attributed to small amounts of impurities. The γ peak is perhaps due to untrapping of electrons from the phenoxy anion. The luminescence intensity of the α peak is linearly dependent on the absorbed dose, and that of the β peak is approximately proportional to the cube of the dose. The appearance of these peaks is presumably closely related to local molecular motions.
Electron microscope study of low molecular weight fractions of linear polyethylene
Authors: Kloos F. , Go S. , Mandelkern L. 
Published: April 2003

AbstractElectron microscope studies are reported for crystals of linear polyethylene formed in dilute solution from very sharp low molecular weight fractions. Emphasis is placed on molecular weights in the range of 1.1 × 103 to 15.1 × 103. The dependence of the crystal habit on the crystallization temperature is very similar to that which has been found for the higher molecular weight species. However, the demarcation temperature for the crystallization of the different morphological forms is very molecular weight‐dependent. The conditions under which interfacial dislocation networks form can be clearly defined. The molecular weight must be less than 3000, so that these structures are restricted to very small chain lengths. However, not all crystallization conditions within this allowable molecular weight range yield such dislocations. The formation of interfacial dislocation networks are shown to occur only under very special circumstances. Their occurrence clearly cannot be offered as evidence, as has been done in the past, for a regular, chain‐folded interfacial structure.
Electron spin resonance study of free radicals in the radiation grafting of butadiene to poly(vinyl chloride)
Authors: Hamanoue Kumao , Shimizu M. , Higaki H. , Block Ira , Silverman Joseph 
Published: April 2003

AbstractThe kinetics of the disappearance of propagating butadiene radicals produced in the grafting of butadiene to poly(vinyl chloride) was followed by electron spin resonance measurements. The radical species observed in the temperature range 213–298°K is the conjugated allylic radical:

The reaction conditions were adjusted to provide a highly viscous medium in which the propagation reaction took place. Under these conditions the radicals were stabilized and a precise ESR spectrum was obtained. Arrhenius plots of the second‐order decay rate constants yield an activation energy of 5 kcal/mole. This suggests that the bimolecular termination reaction is controlled by the segmental motion of the grafted side chains.
Further comments on the relation between hydraulic permeation and diffusion
Authors: Paul D. R. 
Published: April 2003

AbstractWe feel that the lengthy comments given here come down to a few simple points. For uniform, homogeneous swollen membranes the internal driving force for transport in hydraulic permeation experiments is a concentration gradient not a pressure gradient. Equation (1) is in error because it neglects the frame of reference term 1/(1 − ν1). Equation (19) shows properly the connection between K0 and the various diffusion coefficients. In the particular case discussed here and previously we see no evidence to say that a viscous flow mechanism is operative since we can explain all of the K0 data in terms of reasonable diffusion coefficients if proper consideration is given to the frame of reference correction. This is not to say that in many other cases a viscous flow mechanism will not be present or even predominate.
Radiothermoluminescence. I. Radiothermoluminescence for investigation of thermal and radiation‐induced crosslinking of rubber mixtures
Authors: Nikolskii V. G. , Zlatkevich L. Yu. , Borisov V. A. , Kaplunov M. Ya. 
Published: April 2003

AbstractPhase heterogeneity of vulcanizates based on cis‐polybutadiene (cis‐Europrene) and SBR (Europrene 1500) blends obtained by radiation, thermal, two‐stage radiation‐thermal, and two‐stage thermal‐radiation processes was investigated by the radiothermoluminescence method. Unvulcanized blends of these polymers are found to be heterogeneous, exhibiting two glass transition temperatures Tg, which coincide with the values for the initial components. Following vulcanization, the difference between the two Tg values for a polyblend decreases. The decrease is more distinct for polyblends crosslinked at high temperatures. When the vulcanization temperature exceeds 140°C and the crosslink density (or 1/Mc) exceeds 5 × 10−5–1 × 10−4 mole/cm3, the glass temperature ranges of the crosslinked blend are practically superimposed. Such crosslinked mixtures should be considered pseudohomogeneous in phase.
Radiothermoluminescence. II. Radiothermoluminescence of polyethylene with different chain conformations
Authors: Nikolskii V. G. , Zlatkevich L. Yu. , Konstantinopolskaya M. B. , Osintseva L. A. , Sokolskiĭ V. A. 
Published: April 2003

AbstractMolecular relaxation processes in the 77–260°K interval and the structure of polyethylene melt‐crystallized under normal and high pressures have been studied. The positions of relaxation transitions and activation energy for molecular relaxation were determined by radiothermoluminescence. The most intense maximum in the glow curve of the sample crystallized under normal pressure is observed in the 200–240°K interval, i.e., in the range of the β transition. In this temperature interval the β relaxation activation energy changes from 15 to 25 kcal/mole. An increase of the pressure under which crystallization takes place results in a substantial decrease of the intensity of the β maximum. This indicates that the β transition of polyethylene is most probably due to the mobility of segments on the chain‐folded lamellar surface. For samples melt‐crystallized under pressure between 5000 and 7000 atm, relaxation transitions were found at 150 and 190°K. Various processes of molecular relaxation appear to be associated with the maxima observed on the polyethylene glow curve.
Thermostimulated depolarization currents and thermoelectret effects in poly(methyl methacrylate)
Authors: Solunov H. , Vassilev T. 
Published: April 2003

AbstractThe electrical dipole relaxation in PMMA has been studied by measuring thermostimulated depolarizing currents. A master curve for the segmental component of the dielectric constant has been constructed. The increment of the dielectric permittivity due to the α‐relaxation has been determined. The distribution function of the relaxation times and the average relaxation times in the region from 70°C up toTg= 105°C have been obtained. A way of describing the electret properties of the polymer is discussed.
Correct measurement of birefringence in a nonuniform medium
Authors: Ong C. , Yoon D. Y. , Stein Richard S. 
Published: April 2003

AbstractThe birefringence of an object is usually obtained from its retardation. For an object of variable refractive index and optic axis orientation, a matrix procedure should be used for relating the retardation to the birefringence. There are many cases in the literature where this correct procedure has not been used. The correct procedure is illustrated for the case of a polymer spherulite.
Preparation of crosslinked polymers with increased modulus by high‐pressure polymerization
Authors: Rackley F. A. , Turner H. S. , Wall W. F. , Haward R. N. 
Published: April 2003

Abstractp‐Divinylbenzene has been polymerized by heating at pressures ranging from atmospheric to 2.5 GN/m2, and the moduli (Young's, shear, and bulk), density, and residual unsaturation of the products have been determined. The results show a marked effect of polymerization pressure upon density and upon the degree of conversion of the second double bond. Linear relations are indicated between modulus and either density or an intermolecular force function based on a 6–12 potential field. These results and others on the densification of polystyrene are discussed and it is concluded that the moduli of the poly‐p‐divinylbenzene samples prepared under these conditions are still at a level largely determined by intermolecular forces.
Small‐angle light scattering and crystallization processes in solid polymer films
Authors: Samuels Robert J. 
Published: April 2003

AbstractInformation, not previously measurable, about the internal crystallization processes occurring within spherulitic films can now be obtained by combining refractive index, birefringence, and small‐angle light‐scattering measurements. The surroundings of a spherulite in a solid film are composed of both the adjacent spherulites and their interstices (boundaries), and it is shown that different crystallization processes can occur in each of these regions. Upon annealing a quenched isotactic polypropylene film, the rate of crystallization within the interstices of the space‐filling spherulites is observed to be greater than the rate of crystallization within the spherulites themselves.
Crystallite size determination of nylon 6 by wallner's method
Authors: Kaji Keisuke , Sakurada Ichiro 
Published: April 2003

AbstractThe crystallite sizes of α and β forms of nylon 6 along the chain axis were determined by Wallner's method. First the shifts of the maximum positions of meridional reflections from their ideal reciprocal‐lattice positions were calculated for the various crystallite sizes. Second, using these relationships, crystallite sizes were estimated from the observed maximum positions of reflections. The estimated values agree well with those from the integral widths of reflections by the method of Hosemann and Wilke.
Solid‐state synthesis of large polymer single crystals
Authors: Baughman R. H. 
Published: April 2003

AbstractCriteria for the solid state synthesis of large, nearly defect‐free, polymer crystals are derived and related to experimental observations. Polydiacetylene single crystals are of principal concern, although the concepts presented can be easily generalized. In particular, a least‐motion criterion is developed whereby the solid‐state reactivity of different diacetylene phases and the most likely polymerization mode of a particular phase can be predicted from a two‐parameter description of the relationship between neighboring monomer molecules. Phase stability criteria are considered for four characteristic free energy diagrams which explain the phase behaviors that have been observed for various polymerizing diacetylenes. Reaction uniqueness criteria are discussed as they relate to monomer site point group symmetry, symmetry relations between mutually reacting monomer molecules, and dimensional changes during polymerization.
Specific interactions of polyelectrolytes with counterions
Authors: Prokopová E. , Stejskal J. 
Published: April 2003

AbstractFree electrophoresis, differential spectral UV analysis, and the determination of the coefficients of selective sorption were used to investigate, in aqueous solutions of halides, the behavior of two polycations, poly[1(2‐hydroxyethyl)pyridinium methacrylate] and poly[1(2‐hydroxyethyl)trimethylammonium methacrylate]: i.e., one species with and the other without a pyridine ring in the side chain. Electrophoretic data were used to estimate the length of the electrophoretic segment and the approximate charge of the polyion in solutions of the individual salts. A comparison of the data showed that the interaction is not due to the presence of the pyridine ring in the side chain and that the order of activity of the halide anions is the same for both types of polymers.
Approximate theory of the viscoelasticity of chain‐molecule solutions not infinitely dilute
Authors: Wang Francis W. , Zimm Bruno H. 
Published: April 2003

AbstractThe theories of viscoelasticity of chain‐molecule solutions, based on the bead‐spring model, have been modified to take into account approximately the effect of interactions among chain molecules. The motion of a given chain molecule has been analyzed in detail while all other chain molecules have been treated as a background of uniformly distributed beads in which the given chain molecule is suspended. The inclusion of intermolecular interactions leads to a hydrodynamic interaction tensor, which after averaging, differs from that of Kirkwood by a concentration‐dependent correction term. The modified theory correctly predicts the transition from the non‐draining to the free‐draining behavior which has been observed in chain‐molecule solutions as their concentrations are increased.
Effect of chain defects on the morphology and thermal behavior of solution‐grown single crystals of syndiotactic polypropylene
Authors: Marchetti A. , Martuscelli E. 
Published: April 2003

AbstractThe morphology of solution‐grown single crystals of syndiotactic polypropylene with different degree of stereoregularity is compared. A sector formation phenomenon, found in some monolayer single crystals, is discussed in terms of possible crystallographic fold planes, growth planes, and gemination planes. A correlation between thermodynamic and morphological properties such as apparent enthalpy of fusion, critical long spacing, critical annealing temperature, and the number of configurational chain defects along the macromolecule has been found. Two endothermic peaks are observed in the DSC thermograms of single‐crystal aggregates of syndiotactic polypropylene. The low‐temperature peak is attributed to melting of crystals or parts of crystals with incorporated chain defects. The high‐temperature peak corresponds to the melting endotherm of more regular crystalline zones. The peak‐area ratio seems to depend on the degree of stereoregularity.
Rapid healing of crazes in ruptured rubber‐toughened plastics
Authors: Takahashi Kiyoshi 
Published: April 2003

AbstractHigh‐speed photographic studies in connection with photodensitometry were performed to study craze healing in ABS/MMA sheets occurring within 5 microseconds to 20 milliseconds after rupture. Observations on various parts of the deformed specimens, particularly at a plastic zone in the vicinity of a crack, show that there are two stages of healing; first, a relatively elastic stage, and second, a relatively viscoelastic stage. Results of the observation also indicate that the rate of healing is influenced by the magnitude of plastic strain to which the specimens were subjected. The healing mechanism near an advancing crack is discussed briefly.
Rheological properties of anisotropic poly(para‐benzamide) solutions
Authors: Papkov S. P. , Kulichikhin V. G. , Kalmykova V. D. , Malkin A. Ya 
Published: April 2003

AbstractA study has been made of the viscous properties of poly(para‐benzamide) (PBA) solutions in dimethyl acetamide, which undergo a transition from an isotopic to an anisotropic (liquid‐crystal) state at a definite concentration C*. The polymer solutions behave in many respects (as regards the concentration and temperature dependence of viscosity, etc.) like solutions of low molecular weight compounds forming a liquid crystal phase, although the transitions are less pronounced in the polymer solutions owing to their polydispersity. It is shown that the viscometric method, being extremely sensitive to C*, is convenient for determining phase diagrams of anisotropic polymer solutions. The values of C* as related to the molecular weight of PBA have been determined, and a general criterion for transition from isotropic to anisotropic solutions established; the latter has the form (CM̄)* ≈ 1.3 × 105 at 20°C. This criterion is in line with the condition for the formation of the liquid‐crystal structure in a dispersion of rodlike particles as proposed by Flory.Generalized concentration dependences of viscosity have been plotted by reducing concentration to C* and viscosity, to the maximum viscosity at the phase transition point. In investigating the flow properties of PBA solutions we revealed the existence of a yield point in the range of low shear stresses, and an intersection of the flow curves of solutions of different concentration at high shear stresses, which excludes a generalized representation of the flow curves in reduced ordinary‐type coordinates.
Dilute solution behavior of polyelectrolytes. Intrinsic viscosity and light scattering studies
Authors: Tan J. S. , Gasper S. P. 
Published: April 2003

AbstractThe conformational character of a random copolymer of ethyl acrylate and acrylic acid (mole ratio 3:1) has been examined by intrinsic viscosity and light scattering in organic and in aqueous media. The unperturbed dimensions of this copolymer in its un‐ionized state in an organic theta solvent are 1.3 to 1.4 times those obtained for the fully ionized polymer in an aqueous theta solvent. The data also suggest that a change in conformation from a swollen random coil to a compact random coil occurs in aqueous media as a function of ionic strength. These results are interpreted in terms of the hydrophobic interaction of the ester groups on the chain.An application of the wormlike chain model shows that viscosity data can be used to predict the light scattering results well with in experimental error.
Relation between the critical point and the precipitation threshold
Authors: Šolc K. 
Published: April 2003

AbstractThe relationship between the critical point and the precipitation threshold is examined in the Flory—Huggins approximation with concentration‐independent interaction parameter χ. Approximate explicit expressions for the difference between the critical point and the threshold can be derived by series expansion of threshold conditions. In the first‐order approximation, the concentration difference depends only on the chainlength averages xw, xz, and xz+1, in the second‐order approximation it depends on xw, xz, xz+1, and xz+2, etc. For polymers of low polydispersity, the second‐order approximation gives a good estimate of the concentration difference; for instance, for polymers with exponential distribution and xw/xn < 1.25, the error is lower than ca. 1%. The approximation is not suitable for polymers with xz+1 ≫ xz (including polymers whose cloud‐point curve exhibits a triple point). Irrespective of the polydispersity of the polymer, the threshold as well as the whole cloud‐point curve depend only on the weight‐average and higher averages, xw, xz, xz+1, …, xz+k, where k → ∞; they are, however, independent of the number average xn.