bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetic studies of structure formation during anionic adiabatic polymerization of ε‐caprolactam
Authors: Frunze T. M. , Shleifman R. B. , Belavtseva E. M. , Genin Ya. V. , Volkova T. V. , Kotel'nikov V. A. , Radchenko L. G. , Davtyan S. P. , Kuraschev V. V. , Tsvankin D. Ya. 
Published: April 2003

AbstractThe kinetics of crystallization and structure formation of polycaproamide (PCA) during anionic adiabatic polymerization of ε‐caprolactam was studied. The adiabatic crystallization was shown to comprise three successive stages. In the first stage PCA forms dendritelike structures, the space between which is filled with the monomer. In the second stage rather rapid crystallization proceeds to give large loose spherulites. The dendritic structures serve as nuclei for development of spherulites. In the third stage slow secondary crystallization occurs. It is accomplished by crystallization of the residual amorphous substance located both in the dendritic nucleus and throughout the volume of the spherulites. This process is followed by the partial disappearance of the dendritic nuclei and by thickening of lamellae, which results in a substantial densification of initial structures and appearance of fine spherulites. As a result, a fine spherulitic structure with 50% crystallinity is formed.
Spherulite morphology in liquid crystals of polybenzylglutamates. Optical rotatory power and effect of magnetic field
Authors: Patel Dahyabhai L. , Dupré Donald B. 
Published: April 2003

AbstractThe stepwise growth and emergence of spherulitic structures as isolated entities from lyotropic solutions of polybenzylglutamate liquid crystals is described. Spherulites that form ringed internal structures indicative of a cholesteric organization of macromolecules have large optical rotatory powers. The sense of the rotation is solvent dependent. The morphology of the spherulite is distorted in the presence of a magnetic field. The pitch of the cumulative twist of “onion‐shell” molecular layers was measured as a function of field strength and found to follow the theoretical form shown previously to hold for continuous‐phase polypeptide liquid crystals.
Piezoelectric relaxation in poly(γ‐methyl‐L‐glutamate) at high temperature
Authors: Furukawa Takeo , Ogiwara Kiyoshi , Fukada Eiichi 
Published: April 2003

AbstractPiezoelectric relaxation has been studied on elongated poly(γ‐methyl‐L‐glutamate) films with the α‐helical molecular conformation. Relaxation processes are observed near 0 and 100°C. Each process has a dual character composed of relaxational and retardational frequency dependences. The low‐temperature process is ascribed to thermal motion of side chains. The high‐temperature process, discussed in relation to the dielectric relaxation, is attributed to the ionic dc conduction connected with the two‐phase structure of crystalline regions and the electrode polarization.
Internal field of polymer crystals: Polarizability tensor of the methylene group from the birefringence of paraffin crystal
Authors: Pietralla M. 
Published: April 2003

AbstractUsing the concept of a point dipole lattice, it is shown that the internal field of induced dipoles can be calculated for crystals comprised of simple chain molecules. The only structure which must be taken into account accurately is that of the chain molecule itself. From the calculations, reliable values of the polarizability tensor of the CH2 unit are deduced from the birefringence of the paraffin crystal. In addition, it is shown that birefringence measurements provide a method for demonstrating the consistency of polarizability data so that no detailed structural information is needed. For the CH2 unit, it is found by both methods that α∥ − α⟂ = − 0.63 with respect to the chain direction [the units of polarizability α are 10−24 cm3 (cgs)]. The most probable anisotropies for the bond polarizabilities are α − α = 0.30, α − α = − 0.62.
Vibrational spectroscopic studies on modifications of poly(trans‐alkenylene)s. I. The orthorhombic modification of poly(trans‐pentenylene) and poly(trans‐heptenylene)
Authors: Holland‐Moritz K. , Van Werden K. 
Published: April 2003

AbstractExperimental results of vibrational spectroscopic studies on the orthorhombic modification of poly(trans‐pentenylene) and poly(trans‐heptenylene) are discussed on the basis of a normal coordinate analysis for an isolated chain model.
Structure of native and regenerated cellulose as revealed by proton NMR analysis
Authors: Hirai Asako , Horii Fumitaka , Kitamaru Ryozo 
Published: April 2003

AbstractDifferences in fiber structure between cotton and cuprammonium rayon are studied by a refined broad‐line proton NMR analysis of samples swollen with deuterated dimethyl sulfoxide, which has no effect on the spectra but enhances differences in molecular mobility between crystalline and noncrystalline regions. The spectra obtained are decomposed into four components: broad, medium, narrow, and extremely narrow. These components are identified as contributions, respectively, from crystalline and rigid noncrystalline (frozen glassy) material, a noncrystalline glassy component exhibiting local segmental motion, a noncrystalline rubbery component exhibiting liquidlike molecular motion, and protons included in DMSO‐d6 as an impurity. The mass fraction of the narrow component in cotton was about 0.01, whereas it was as high as 0.18 in cuprammonium rayon. It is concluded that even in the swollen state, native cellulose is devoid of a liquidlike mobile component, but regenerated cellulose contains a considerable amount of a noncrystalline component involving liquidlike segmental motion of molecules.
Thermal conductivity and heat capacity of liquid and glassy poly(vinyl acetate) under pressure
Authors: Sandberg O. , Bäckström G. 
Published: April 2003

AbstractThe dependence of thermal conductivity λ and heat capacity per unit volume pcp on temperature and pressure for poly(vinyl acetate) has been measured by a transient hot‐wire probe technique. The measurements were made under pressures up to 0.5 GPa over a temperature range of 270–470 K. The temperature coefficient of thermal conductivity (∂ lnλ/∂T)p was found to increase with pressure for both the liquid and the glassy state. The change in heat capacity per unit volume in the region of the glass‐transition temperature was found to decrease with increasing pressure. The Ehrenfest relation does not explain the variation of the pressure coefficient of the glass‐transition temperature.
Tear strength and tensile strength of model filled elastomers
Authors: Dreyfuss P. , Gent A. N. , Williams J. R. 
Published: April 2003

AbstractMeasurements have been made of the tear strength, tensile strength, and energy dissipated during stretching for model filled elastomers consisting of polybutadiene with glass beads incorporated. The glass beads were pretreated with various silanes, some of which could, in principle, form covalent bonds with the polybutadiene matrix during free‐radical crosslinking of the latter and some of which could not. The tear strength of the elastomer was increased by the addition of glass beads, by about 25% for the largest beads, having a mean diameter of 150μm. This effect is attributed to increased roughness of the tear path. The breaking elongation in tension was reduced by the addition of glass beads but the breaking stress was only seriously reduced for the least‐well‐adhering beads. The stored strain energy density at break was reduced in all cases. This is attributed to large glass beads acting as fracture nuclei in tension. Calculated sizes of a Griffith crack, 150–300 μm, are consistent with this hypothesis. Strain energy dissipated due to dewetting was found to be in the range 4–13% of the input energy, depending upon the degree of interfacial adhesion, in addition to about 10% dissipated in the unfilled material. The maximum value observed is in reasonable agreement with theoretical predictions.
Study of the thermal effects in the necking of polymers with the use of an infrared camera
Authors: Maher J. W. , Haward R. N. , Hay J. N. 
Published: April 2003

AbstractWhen a polymer specimen yields under tension by the process of cold‐drawing, heat is generated in the necking region. This beating effect has been studied in polycarbonate, polyethylene, polypropylene, and PVC with the use of a thermovision system which produces a real time thermal image of the necking specimen. In this way it was possible to observe the temperature distribution over the surface of the neck and to show that at least 85% of the mechanical work done on the specimen during necking was converted into heat. A semiempirical equation relating the maximum temperature to the drawing rate has been derived.
Structural evolution of an ABA poly(styrene‐b‐isoprene) block copolymer with temperature
Authors: Widmaier J. M. , Meyer G. C. 
Published: April 2003

AbstractThe structural evolution with temperature of an anionically synthesized ABA poly(styrene‐b‐isoprene) (SIS) lamellar block copolymer (total molecular weight 45,000; isoprene content 38% by weight) was studied by melt‐rheological measurements, electron microscopy, and x‐ray and light diffraction. Above 225°C, the dynamic viscosity was found to be independent of frequency up to a critical frequency. The variation of the elastic modulus confirmed the occurence of a transition between 215 and 225°C. For the temperature range considered, all results superimposed well on a two‐branch master curve. It was concluded that above 225°C, our SIS behaves like a Newtonian material, whereas for lower temperatures and/or higher frequencies classical non‐Newtonian behavior is found. The melt‐rheological properties were explained by microscopy and diffraction investigations, which allowed us to follow morphological changes as the temperature was raised. It was found that the two‐phase lamellar structure is progressively destroyed, and the transition temperature of 225°C corresponds to the temperature above which complete mixing occurs.
Light scattering in multicomponent solutions—A general equation
Authors: Procházka Ondřej , Kratochvíl Pavel 
Published: April 2003

AbstractA general equation for light scattering in multicomponent solutions is derived and applied to some important systems. The equation is compared with one published earlier by Casassa and Eisenberg [Adv. Protein Chem., 19, 287 (1964)], and the difference between them is explained.
Star‐shaped block copolymers. III. Surface and interfacial properties
Authors: Huynh‐Ba‐Gia  , Jérôme R. , Teyssié Ph. 
Published: April 2003

AbstractSurface and interfacial activities of A(B)2 star‐shaped block copolymers, where B is a polyoxirane block and A a polydiene or polyvinyl block, have been measured at 20°C. The surface tension of organic solvents is only slightly lowered by these copolymers, whereas a significant surface activity is noted in water. Interfacial tensions are dependent on both the nature of the organic solvent (aliphatic or aromatic hydrocarbons) and the molecular parameters of the copolymers; 50% polyoxirane seems to be the composition of maximum surface activity. The role played by the molecular architecture [A‐B or A(B)2] of the copolymers is demonstrated. The same limiting interfacial tension is obtained on increasing the concentration of diblock [A‐B] or star‐shaped block [A(B)2] copolymer. The limiting value is, however, attained at significantly lower concentration with the star‐shaped copolymers. Their ability to fill the interface is accordingly higher.
Light scattering from polymer films having optically anisotropic rodlike texture. III. Inter‐rod interference
Authors: Hashimoto Takeji , Ebisu Satoshi , Kawai Hiromichi 
Published: April 2003

AbstractEffects of interparticle interference on depolarized light scattering from polymer films having nonspherulitic (rodlike, disklike, or fibrous) crystalline superstructures are explored, both theoretically and experimentally. Discrepancies between the observed “rodlike scattering” and the predicted scattering based on “single‐rod” theory are pointed out and accounted for in terms of various types of aggregation models for polymeric solids and solutions.
Orientation distribution functions for uniaxially oriented polymers
Authors: Bower D. I. 
Published: April 2003

AbstractMost methods of studying molecular orientation in polymers can give only limited information about the distribution of molecular orientations, and this is particularly true of methods for studying the noncrystalline material. It is shown, however, that if the mean values P2 and P4 of the second‐order and fourth‐order Legendre polynomials in cosθ can be determined for the chains in a uniaxially oriented polymer, where ‐ is the angle between the chain axis and the drawing or extrusion direction, some qualitative statements about the form of the distribution can be made with complete certainty for some, but not all, sets of values of P2 and P4. It is shown in addition, that if the distribution is fairly smooth a good estimate of its general form can also be obtained, and that a knowledge of P6 and higher‐order means will not improve this estimate appreciably unless they are known with great accuracy.
Formation and characterization of polydiacetylene monolayer fibers
Authors: Day David R. , Lando Jerome B. 
Published: April 2003

AbstractMonolayers of certain surface‐active diacetylene compounds were polymerized at the gas—water interface and collapsed to self‐supporting fibers. The monolayer fibers were found to have an unusual morphology in that while the polymeric backbones have a random orientation, the hydrocarbon side chains are all perpendicular to the fiber axis. The fiber d spacings determined from x‐ray diffraction agree well with electron diffraction data from unperturbed polymeric monolayers. Tensile tests of the monolayer fibers indicate average strength and high modulus.
Negative thermal expansion in oriented crystalline polymers
Authors: Choy C. L. , Chen F. C. , Young K. 
Published: April 2003

AbstractMeasurements on the thermal expansivity α∥ and α⟂ (along and normal to the draw direction, respectively) have been carried out for a series of oriented polymers with widely different crystallinities (0.36–0.81) and draw ratios (1–20) and over large temperature ranges covering the major amorphous transitions in each case. While α⟂ increases with temperature, α∥ tends to decrease sharply above the transition temperature. For highly crystalline polymers, α∥ decreases to values typical of polymer crystals (−1 × 10−5 K−1) and this can be attributed to the constraining effect of the crystalline bridges connecting the crystalline blocks. However, for polymers of lower crystallinity, α∥ may become an order of magnitude more negative and this remarkable phenomenon is attributed to the rubber–elastic contraction of taut tie‐moleucles. Since taut tie‐molecules and bridges have drastically different effects on α∥ at high temperatures, this allows a rough determination of their relative fractions.
Conformational properties of polar polymers. II. Poly(vinylidene chloride)
Authors: Boyd Richard H. , Kesner Laya 
Published: April 2003

AbstractA recently developed polarization model for representing polar bond effects in conformational energy calculations is applied to poly(vinylidene chloride) (PVDC). The geometries and conformational energies of a number of conformers of 2,2,4,4,6,6‐hexachloroheptane were calculated. The geometries were found to be similar to the hydrocarbon analog polyisobutylene (PIB) in that steric crowding results in the usual T, G, G′ states being split into + or − distortions of the torsional angles away from the traditional values. Only distortions of the same sign occur in the same pair of bonds interior to CCl2 groups. Distortions of G states towards eclipsed were found to be much more stable than those away. The interior skeletal valence angle is also distorted to an unusually large value, ca. 121°. The calculated dipole moments were used to infer a group moment for CCl2 of 1.56 D. The calculated conformational energies were fitted by linear combinations of interaction parameters representing the stabilities of G+, G− bonds (relative to T+, T−) and the interactions between bonds across intervening CCl2 groups. These parameters were used in statistical mechanical calculations of the characteristic and dipole‐moment ratios. In order to make comparison with experiment, the dipole‐moment/repeat unit of a 90% (by weight) PVDC copolymer with PVC was measured and found to be 1.42 ± 0.05 D. From this, the dipole‐moment ratio for PVDC homopolymer is inferred to be ca. 0.8. The characteristic and dipole‐moment ratios calculated from the interaction parameter set were somewhat too high but adjustment of the gauche energies downward brings the calculated ratios into agreement with experiment. The same statistical model along with energy parameters previously calculated also gives agreement with experiment for the characteristic ratio of PIB. The calculated geometries are in agreement with the conformation in the crystal being (T+G′+T−G−).
Concentration dependence of the distribution coefficient for macromolecules in porous media
Authors: Anderson John L. , Brannon Judeth H. 
Published: April 2003

AbstractPartitioning of macromolecules between pore and bulk solutions directly affects both equilibrium and transport processes such as exclusion chromatography and movement of solutes through porous media. Because of interactions between macromolecules and the pore wall, the variation of the macromolecule activity with concentration is different inside the pore than in bulk solution. This difference causes a concentration dependence of the distribution coefficient, as reported in experiments involving exclusion chromatography. In order to explain this effect, we develop a model for a concentration‐dependent distribution which explicitly accounts for a coupling between pore–macromolecule and macromolecule–macromolecule interactions. Predictions using this model are reported for the case of rigid spherical macromolecules in both cylindrical and slit pores, including both steric (hard sphere–hard wall) and long‐range (screened electrostatic) interactions. An important result is the existence of a general correlation between the first order concentration effect and measurable properties of the macromolecule and porous medium.
Relaxation of shear and normal stresses in step‐shear deformation of a polystyrene solution. Comparison with the predictions of the Doi–Edwards theory
Authors: Osaki Kunihiro , Kimura Shinichi , Kurata Michio 
Published: April 2003

AbstractThe shear stress σ, two components of birefringence, and extinction angle were measured for a concentrated polystyrene solution in step‐shear deformation of magnitude of shear 0.3 ≤ γ ≤ 4.0. The stress‐optical coefficient did not depend on either γ or time. The first and the second normal‐stress differences v1 and v2 were evaluated with the use of the stress‐optical law. Over a certain range of long times, σ could be factored as σ = γh(γ)G(t) and the quantity h(γ) agreed with the prediction of the Doi–Edwards theory based on the de Gennes tube model of entangled polymer chains. At short times the effect of γ on σ/γ was smaller than at long times. The relaxation spectrum became approximately independent of γ at the short‐time end of the rubbery plateau region. The ratios v1/σ and v2/v1 were independent of time and were in quantitative agreement with those predicted by the Doi–Edwards theory: v1/σ was equal to γ, v2/v1 was negative, and |v2/v1| decreased with increasing γ.
Network models of concentrated polymer solutions derived from the yamamoto network theory
Authors: Fuller G. G. , Leal L. G. 
Published: April 2003

AbstractSeveral choices of the functions describing the creation and destruction processes of entanglement junctions in the Yamamoto network theory of concentrated polymer solutions have been examined. These choices are simple functions of the extension of the network segments bridging the entanglement points and it is demonstrated that the moments of the distribution function describing the network conformation can be solved for analytically. This has been done for a wide range of two‐dimensional flows, both for the steady state and transient start‐up and relaxation problems. The macroscopic stress tensor and flow birefringence are calculated and a variety of nonlinear effects are predicted and discussed.
Ordering phenomena in thin polystyrene films
Authors: Cohen Y. , Reich S. 
Published: April 2003

AbstractOrdering of polystyrene (PS) molecules in thin films collapsed from toluene solutions onto a glass substrate by dip coating is studied in relation to the polymer molecular weight and its distribution. The degree of ordering of chain elements is deduced from measurements of film birefringence, between the normal and parallel directions to the film surface, as a function of film thickness. A technique has been developed for measuring this birefringence by monitoring the intensity of laser light passing through the film, as a function of the angle of incidence. Films of monodisperse low‐molecular‐weight PS exhibit high ordering very close to the substrate, but this ordering decays within 1 μm from the glass surface. Films of monodisperse high‐molecular‐weight PS, on the other hand, exhibit a much smaller, but very long‐range degree of order. In a blend of PS of these two molecular weights, as well as in a polydisperse sample, these effects appear in tandem. The long‐range ordering effect, evident in the 100,000 molecular weight polystyrene films, is much smaller in magnitude in lower‐molecular‐weight films, reflecting probably the importance of chain entanglements.
Carbon‐13 NMR linewidths of polyethylenes and related polymers
Authors: Dechter J. J. , Komoroski R. A. , Axelson D. E. , Mandelkern L. 
Published: April 2003

AbstractThe carbon‐13 NMR linewidth (proton decoupled) of linear and branched polyethylenes crystallized so as to yield different supermolecular structures, as well as a polyethylene oxide sample, have been studied in detail. The purpose has been to assess the different molecular contributions to the linewidth in the completely amorphous polymer as well as in the amorphous regions of the semicrystalline state. These studies on a number of different structures were complemented by both proton‐decoupled and dipolar‐decoupled magic‐angle spinning experiments on a particular sample, as well as frequency dependence studies. It is found that the abnormally broad resonance lines previously reported for the molten polymer can be significantly reduced by adopting appropriate methods of sample preparation and magnetic‐field homogenization at each temperature. Relatively narrow lines result which can be interpreted in a conventional manner. In the semicrystalline state, the resonance lines are relatively broad and are shown to be morphology dependent. Specific contributions and their temperature dependence are discussed.