bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic viscoelastic properties of unsintered polytetrafluoroethylene
Authors: Sasuga Tsuneo , Takehisa Masaaki 
Published: April 2003

AbstractThe molecular motion of unsintered polytetrafluoroethylene (PTFE) was studied by dynamic viscoelastic measurements. From results for variously heat treated suspension polymerized (molding powder) PTFE, the following conclusions are drawn. Molding powder, as received, has a high degree of crystallinity according to calorimetric results and lower magnitude of the γ relaxation, but the behavior of the β relaxation suggests that the crystals are disordered more than those of the sintered PTFE. The β relaxation peak for an emulsion polymerized PTFE (fine powder) occurs at a higher temperature and is sharper than that for the molding powder, so that the crystals of the fine powder are better ordered than that for the molding powder. The behavior of the β relaxation for the radiation induced‐polymerized PTFE is affected by polymerization conditions, particularly concentration of emulsifier. It is concluded from the results for the unsintered PTFE polymerized by various methods that the nature of crystalline state is decided during the course of simultaneous polymerization and crystallization.
Molding powder as received has a relatively high magnitude of relaxation between 30°C to 180°C, but with little temperature dependence in this temperature range. This relaxation is diminished by gamma‐ray irradiation. Since the molding powder has a complicated morphology, the relaxation in this temperature range is attributed to inter‐particle friction rather than a relaxation associated with motion on the molecular level.
An improved model for crystalline orientation of spherulitic polymers
Authors: Yoon Do Yeung , Chang Catherina , Stein Richard S. 
Published: April 2003

AbstractA model is proposed to account for the orientation of crystals in spherulites upon deforming a polymer. The model assumes affine deformation of the spherulite accompanied by three processes of crystal reorientation within the spherulite. These are tilting of molecular chains with respect to the plane of the lamellae, characterized by a parameter K, twisting of the lamallae about the spherulite radii described by η, and rotation of the b crystal axis about the c axis characterized by a third parameter, P. Values of these parameters are fitted to measured orientation functions and compared with experimental measurements of the azimuthal variation of the intensities of the 110 and 200 crystal reflections from low‐density polyethylene. Good agreement is found between the experimental and theoretically predicted intensity variation. Time‐dependent experiments under relaxational and vibrational conditions are also treated by the theory.
Crystallization during polymerization of ethylene: Successive events
Authors: Fisa B. , Revol J. F. , Marchessault R. H. 
Published: April 2003

AbstractCrystallization processes occurring during polymer synthesis in a nonsolvent medium are discussed. It is concluded that in the case of heterogeneous polymerization of ethylene the polymer is produced as a supercooled liquid surrounding the catalyst particles. These particles then coalesce until a critical size is reached allowing a high nucleation probability. Thus coalescence coupled with polymerization, leads to crystallization at a relatively uniform particle size. Two less usual polymerization catalyst systems, VCl3 produced by a high‐frequency discharge in VCl4 vapor, and the mixture of TiCl4 and Al(CH3)3 vapors (an apparently homogeneous system) are used to illustrate these concepts for polyethylene.
Rubber networks containing unattached macromolecules. I. Linear viscoelastic properties of the system butyl rubber–polyisobutylene
Authors: Kramer Ole , Greco Roberto , Neira Ramon A. , Ferry John D. 
Published: April 2003

AbstractMixtures of butyl rubber with polyisobutylene (molecular weights 0.055 and 2.3 × 106) up to 50% by weight were crosslinked by sulfur, leaving the polyisobutylene molecules free to reptate in the butyl rubber network. Linear viscoelastic properties were measured in shear creep for periods up to 5 × 105 sec at 25°C and oscillating shear deformations from 0.1 to 3 Hz, at temperatures from 2 to 63°C. Comparison with the properties of a butyl rubber crosslinked without polyisobutylene showed contributions to creep and mechanical loss attributable to the reptating species. Comparison with the properties of polyisobutylene (higher molecular weight) showed that the relaxation times associated with the reptating species in the upper part of the terminal zone are the same for different polyisobutylene contents (25% and 50%) and for 100% polyisobutylene in which no permanent network is present; their contributions to modulus appear to be proportional to the volume fraction of polyisobutylene to a power of about 2/3. The time required in stress relaxation for the portion of the modulus attributable to the reptating species to decay to half its plateau value is, based on the two molecular weights employed, proportional to the polyisobutylene molecular weight to the third power. The magnitude of the associated mechanical loss and its location on the frequency scale can thus be controlled independently.
Evidence of molecular relaxation derived from transient phenomena in poly(vinyl chloride)
Authors: Lupu A. , Bunget I. 
Published: April 2003

AbstractTransient currents in poly(vinyl chloride) (PVC) are recorded after the application of a step‐function electric field for various temperatures. By assuming the Fröhlich rectangular distribution function g(τ) of molecular relaxation times, the limits of relaxation times τ are evaluated. Values of the glass‐transition temperature and activation energies of molecular motion determined from a plot of ln τ against 1/T are in satisfactory agreement with those obtained by other methods. By extrapolation to T = ∞, relaxation times are calculated which are in good agreement with those from dielectric loss measurements.
New apparatus for studies on supermolecular structures of thin polymer films by small‐angle light scattering
Authors: Pakuła T. , Soukup Z. 
Published: April 2003

AbstractThe construction and principle of operation of small‐angle light scattering apparatus for studies of supermolecular structure in thin polymer films is described. The apparatus can be used to study changes in spherulite structure during crystallization and changes in films subjected to steady or sinusoidal strain. Typical results with polyethylene films are given.
Photopolarization and depolarization characteristics of poly(N‐vinyl carbazole)
Authors: Pillai P. K. C. , Ahuja R. C. 
Published: April 2003

AbstractThe photoelectret properties of poly(N‐vinyl carbazole) sandwiched between a conducting glass electrode and an aluminum electrode have been studied. Photoelectret polarization was carried out by simultaneous application of an electric field and ultraviolet illumination. The polarization exhibits a linear dependence on the polarizing voltage, polarization time, and illumination intensity, with saturation effects for large values of these parameters. The depolarization current decay is quite fast, which indicates the absence of deep‐trap levels. The ratio of photoelectret charge to the dark polarization charge is found to be 100, which determines the image contrast if the polymer film is used in persistent internal polarization (PIP) electrophotography.
Conformational analysis of poly(ethylene oxide) and model compounds by nuclear magnetic resonance spectroscopy
Authors: Matsuzaki Kei , Ito Hiroshi 
Published: April 2003

AbstractIn order to determine the conformation of poly(ethylene oxide) (PEO), 13C satellite spectra of PEO, 1,2‐dimethoxyethane (DME), and dioxane were measured at various temperatures in various solvents, and analyzed. Relations between the coupling constants were derived from the linearity between the parameters N = JAB + JA′B and L = JA′B in AA′BB′ spectra of PEO and DME. The vicinal coupling constants for the individual rotational isomers were obtained from the above relations and the temperature dependences of N and L and the enthalpy differences were calculated in each solvent. The gauche rotamer is more stable than the trans isomer by 250–500 cal/mole in all cases examined.
Electrical conductivity of small ions in polyacrylonitrile in the glass–transition region
Authors: Reich S. , Michaeli I. 
Published: April 2003

AbstractThe electrical conductivity process in a new class of ion‐containing polymers—highly concentrated solid solutions of hydrated perchlorate salts in polyacrylonitrile (PAN)—is described (σdc = 10−7−10−2Ω−1cm−1). A low‐ac instrument (70 cps) is used to measure electrical conductivity. We present a cryogenic system in which the temperature dependence of the conductivity is studied (78–340°K). The ionic character of the conductivity process is established. The conductivity both above and below the glass‐transition (Tg) point is thermally activated with an activation energy of 0.7–0.9 e V for the glassy state (ϵg) and 0.12–0.6 eV for the rubber‐like state (ϵr). The systems described exhibit a compensation effect between the pre‐exponential factor for the conductivity in the glassy state σ0g and the difference in activation energy ϵg – ϵr
Elasticity theory. IV. The stress–strain relation
Authors: Eichinger B. E. 
Published: April 2003

AbstractThe stress–strain relation is analyzed in terms of the gyration tensor

where the sum is over all N atomic groups comprising the elastomeric material. All groups are taken for convenience to have the same mass. This tensor is linear in the strain, and furthermore it may be evaluated from a configuration integral. The definition of the strain by use of Sαβ gives new insight into the connection between statistical and continuum mechanics, and further clarifies the significance of “affine deformation.” Stress components are obtained as derivatives of the (Helmholtz) free energy A with respect to the invariants of Sαβ. The first invariant is just the radius of gyration S2 of the network, and the dependence of A on S2 alone provides a basis for analysis of stress–strain isotherms.
Interaction of inorganic salts with polar polymers. I. Physical properties of phenoxy–calcium thiocyanate mixtures
Authors: Hannon M. J. , Wissbrun K. F. 
Published: April 2003

AbstractCalcium thiocyanate is appreciably soluble in “Phenoxy” polymer. Solutions of this salt have significantly different physical properties compared to the pure polymer. The glass‐transition temperature Tg is increased, and the kinetics of the glass transition are affected. The melt viscosity and its temperature dependence are increased. The viscosity changes are predicted from the changes in Tg and thermal expansion coefficients, in contrast to ionomers, in which clustering or domain formation cause viscosity to increase. Mechanical properties of the glassy polymers are also affected by the presence of dissolved salt. The most striking effect is an increased resistance to stress cracking by polar organic liquids. This may be related to the Tg increase, or to changes in solubility parameter, as indicated by insolubility of the salt solutions in solvents for the pure polymer. Increased water sorption and electrical conductivity are also results of salt incorporation.
Mechanisms of fracture in an oriented polystyrene
Authors: Doyle M. J. 
Published: April 2003

AbstractFracture surfaces of an oriented polystyrene (by stretching 150% at 280°F) show many of the same features observed in the fracture of ordinary polystyrene: craze formation followed by quasi‐viscous separation of the craze layer or by quasi‐brittle fracture along the craze boundary. In cleavage fracture along the direction of orientation, advance fractures are initiated in flat areas covered, if at all, by an extremely thin layer of craze: the initiation of the “crazeles” fractures appears to arise from the orientation of the molecules rather than the presence of impurity particles.
Dynamic mechanical properties of plasticized poly(vinyl chloride)
Authors: Nakamura Kunio 
Published: April 2003

AbstractThe complex compliance in extension of gels of poly(vinyl chloride) (PVC) in di(2‐ethylhexyl) phthalate (DOP) and in tricresyl phosphate (TCP) was measured over the frequency range from 0.6 to 0.006 cps and the temperature range from −66 to 65°C: the weight fractions of DOP and TCP in the gels were 0.32, 0.40, 0.49, and 0.59. Measurements were carried out in an apparatus using forced low‐frequency longitudinal osillations. Data for the gels could not be combined by the method of reduced variables, since there were gradual changes with decreasing temperature, attributable to an increase in crystallinity. Application of the reduction method of Ninomiya and Ferry for solutions of crystalline polymers was found to be successful. The apparent melting temperatures (T′m) were obtained from the temperature dependence of the vertical shift factors. An apparent heat of fusion of ca. 120 cal/mole of monomer unit was found. This melting range was in agreement with that of secondary crystallinity in plasticized PVC reported in calorimetric studies by Juijn. With decreasing temperature, two phenomena occurred in the temperature range from Tg + ca. 80°C to Tg: the vitrification of a concentrated amorphous solution and the slight crystallization of the polymeric component. The larger the difference between Tg and T′m the broader the primary dispersion zone on the frequency scale. This broadening effect was explained as due to the difference in dependence of Tg and T′m on plasticizer concentration, without any need to consider any specific interaction between plasticizer and PVC.
Dependence of thermal diffusion effects in liquids on the physical properties of the dispersing phase
Authors: Gaeta F. S. , Di Chiara A. 
Published: April 2003

AbstractA generalization of the radiation‐pressure theory of thermal diffusion in liquids explains the genesis of the forces acting in a condensed phase when heat flows through it. The analytical expressions obtained make it possible to connect such forces originated by the radiation pressure of thermal waves with the transport of matter taking place in solutions or suspensions of particles and also with the ultimate result of this transport, that is, the steady‐state concentrations of the dispersed phase in the hot and in the cold regions of the nonisothermal solution. The form in which the theoretical results are laid down lends itself to direct and unambiguous experimental verification. The confrontation with a few data found in the literature lends support to the theory.
Characterization of macromolecules in liquid solutions by thermal diffusion. II. Dependence of the soret coefficient on the molecular mass of the solute
Authors: Gaeta F. S. , Perna G. , Scala G. 
Published: April 2003

AbstractExperiments have been carried out, in connection with those mentioned in Part I of this series, with the general aim of checking some predictions of the radiation‐pressure theory of thermal diffusion in the case of macromolecular liquid solutions and in particular with the intent of establishing the dependence of the Soret coefficient on molecular mass of the dispersed particles.The results confirm the dependence of Soret coefficient on the shape and on the mass of the particles. The analytical expressions obtained by the radiation‐pressure theory of the phenomenon constitute a satisfactory description of the thermodiffusive behavior of such complex systems. The inner constitution of the particles determines the intensity of the radiation pressures exherted by thermal waves; the molecular cross section determines the total force acting on each particle, while the spatial conformation determines the ratio between mass and cross section and at the same time also the hydrodynamical behavior of a particle within the liquid. All these parameters concur in the phenomenon of thermal diffusion, in the way specified by the radiation‐pressure theory of thermal waves, as proved by our experiments.The possibility of a characterization of macromolecules and supermolecular particles dispersed in a liquid on the basis of their thermodiffusive behavior is demonstrated.
Interaction of inorganic salts with polar polymers. II. Infrared studies of polymer–inorganic nitrate systems
Authors: Wissbrun K. F. , Hannon M. J. 
Published: April 2003

AbstractCertain inorganic nitrate salts are quite soluble in the polymers studied, namely, cellulose acetate, poly(vinyl acetate), poly(vinyl alcohol), poly(methyl methacrylate), and poly(methyl acrylate). Large effects upon the glass‐transition temperature were observed in those systems where the transition could be readily measured. Large shifts in the infrared spectra of both the inorganic nitrate salts and in the polymer carbonyl and ester ether frequencies have been observed. These observations have been interpreted in terms of complex formation between these polymers and salts in the solid state. The proposed structure of the complex explains the nature of the infrared shifts both for the nitrate salts and the polymers as well as explaining the concentration effects observed. Effects of the solvating environment upon the salt and polymer spectra remain unexplained. The large glass‐transition effects are a result of the degree of solubility of the salts in the polymers and the interactions between them. However, the reason why, in some cases, the change in the transition temperature as a function of concentration goes through a maximum is unclear.
Deformational, swelling, and potentiometric behavior of ionized poly(methacrylic acid) gels. II. Experimental results
Authors: Hasa J. , Ilavský M. 
Published: April 2003

AbstractThe deformational, swelling, and potentiometric behavior of poly(methacrylic acid) gels was measured as a function of the degree of crosslinking, ionic strength, and degree of ionization. The comparison of the stress–strain behavior with theoretical relations derived in the preceding part has shown that the relations are valid only if an increase is assumed in the number of monomeric units in the statistical chain segment with increasing degree of neutralization of the gel. This dependence is affected by the salt content in the swelling solution and is also dependent on the activity coefficient of counterions. The pK0 values for an undissociated gel approach pK0 = 5.0 and increase somewhat with degree of neutralization. The swelling equilibria are in qualitative agreement with theoretical assumptions; their quantitative agreement depends on the activity coefficient of counterions.
Crystal structure of optically active poly(isopropylethylene oxide)
Authors: Takahashi Yasuhiro , Tadokoro Hiroyuki , Hirano Tsuneo , Sato Akira , Tsuruta Teiji 
Published: April 2003

AbstractThe crystal structure of optically active poly(isopropylethylene oxide) was analyzed by x‐ray diffraction. Two molecular chains having twofold screw symmetry pass through an orthorhombic unit cell with parameters a = 12.85 Å, b = 7.52 Å, and c (fiber period) = 5.55 Å and space group P212121‐D. The crystal structure was refined by the constrained least‐squares method. The molecular structure consists mainly of ḠTG sequences and is very similar to the (9/4) helical structure in poly(tert‐butylethylene oxide).
Measurement of the Grüneisen number in polystyrene by brillouin light scattering
Authors: Brody Edward M. , Lubell Cathie J. , Beatty Charles L. 
Published: April 2003

AbstractBrillouin light scattering has been used to measure the sound velocities in polystyrene of two different molecular weights. The variation of sound velocity with temperature is related to volumetric expansion of the polymer. Using the thermal expansion data of Fox and Flory we have determined the Grüneisen number, γ, below the glass transition to be 4.4 and 4.3 for low‐ and high‐molecular‐weight polystyrenes, respectively, and 5.1 and 5.6 above the glass transition. These numbers compare reasonably well with the value of 3.9 determined by Wada et al. Our measured values are in good agreement with Barker's “bundle of chains” model.
Crystallinity and the effect of ionizing radiation in polyethylene. III. An experiment on the irradiation‐induced crosslinking in n‐hexatriacontane
Authors: Patel G. N. , Keller A. 
Published: April 2003

AbstractSamples of n‐hexatriacontane irradiated in the crystalline and molten states were compared as regards the GPC chromatograms of the partially crosslinked products. From differences in the elution volumes it could be inferred that there is a greater trend for random linking along the chain in the sample irradiated in the melt as opposed to preference for end‐type linking in the samples irradiated as crystals. In the course of this work the applicability of the GPC technique for detecting short (methyl) branches and for distinguishing between the position of these branches along the chain has also become apparent.
Crystallinity and the effect of ionizing radiation in polyethylene. IV. Effect of segregation of low molecular weight chains on determination of main‐chain scission in linear polyethylene
Authors: Patel G. N. 
Published: April 2003

AbstractDifferent single crystal preparations of polyethylene with (unfractionated) and without (partially fractionated) low molecular weight chains were irradiated at room temperature. G(crosslink) was determined from the gel point. It is shown that in addition to the molecular weight and molecular weight distribution of polymers, G(crosslink) is determined by three more parameters: thickness of crystalline core, amount of amorphous surface layer, and degree of interlamellar contact. Unlike unfractionated polyethylene, partially fractionated polyethylene showed almost 100% gel at about 250 Mrad. To obtain the same amount of gel, unfractionated polyethylene required a much higher dose than that required by partially fractionated polyethylene. Molecular weight distribution of sol fractions of unfractionated and partially fractionated polyethylene was studied by gel permeation chromatography (GPC) and the solubility data analyzed by Charlesby–Pinner plots. It has been shown that the unattainability of 100% gel from unfractionated polyethylene is due to segregation of low molecular weight chains during crystallization which need very high doses for complete gelation.
Crystallinity and the effect of ionizing radiation in polyethylene. VI. Decay of vinyl groups
Authors: Patel G. N. 
Published: April 2003

AbstractFreeze‐dried single crystals of unfractionated Marlex 6009 polyethylene were irradiated at various doses up to 100 Mrad. Analysis of the data of the present work and those of others showed that the decay of vinyl groups can be best described by second‐order kinetics. The decay rate constant is found to increase with decrease in original concentration of vinyl groups. It has been concluded that the increase in the decay rate constant with decrease in initial vinyl concentration is due to a decrease in crystallinity. Some supporting evidence has been presented for this conclusion.
Elastic–inelastic behavior of PET and nylon 66 monofilaments under lateral compression
Authors: Batra Subhash K. , Syed Nuruzzaman 
Published: April 2003

AbstractResults of experiments on short lengths of nylon 66 and PET monofilament specimens, subjected to lateral compressive force between two parallel platens, are described. In the experimental procedure the change in the compressed diameter and the area of contact were determined as a function of the applied force. From these data elastic moduli in lateral compression were estimated. The load–deformation behavior beyond the elastic range exhibited a yield‐like phenomenon. SEM examination of the deformed specimen suggest the possible modes of deformation in the post‐yield behavior. It is inferred that the yield occurs due to concentration of deformation along the maximum shear planes. The deformed specimens also show specific forms of fracture initiation and growth.