bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dielectric relaxation in ethylene–methacrylic acid copolymers and their salts
Authors: Phillips P. J. , Macknight W. J. 
Published: April 2003

AbstractDielectric relaxation data have been obtained for two ethylene–methacrylic acid copolymers (containing about 4 mole‐% methacrylic acid units and about 8 mole‐% methacrylic acid units, respectively) and the lithium, sodium, and calcium salts prepared by partial neutralization of the polyacids. The frequency range employed was from 50 Hz to 10 kHz and the temperature range was from −130°C to 100°C. Attention is focused on three dielectric loss regions labeled β, β and α in order of increasing temperature. The β′ process (−10°C at 100 Hz in the salts only) correlates with a mechanical loss process previously reported and is attributed to microbrownian motion taking place in an amorphous hydrocarbon phase. The β′ process (20°C at 100 Hz) has also been observed mechanically and is attributed to the same mechanism as the β process. The higher temperature of this relaxation compared to the β relaxation is attributed to the presence of acid groups which form crosslinks composed of interchain hydrogen bonds. The α process (>50°C at 100 Hz in the salts only) correlates with dielectric and NMR data previously reported for a sodium salt and is assigned to motions within ionic domains formed by the clustering of salt groups.
NMR study of molecular motion in oriented long‐chain alkanes. I. Theoretical part
Authors: Olf H. G. , Peterlin A. 
Published: April 2003

AbstractSeveral molecular mechanisms, proposed in the literature for the low‐ and high‐temperature relaxation processes in linear polyethylene and commonly referred to as γ and α processes, are examined, and their effect on the second moment of the broad line NMR absorption is predicted quantitatively. The following models for the α process are discussed: rotational oscillation of the long chain molecules around their axes, general two‐site models where the chain performs thermally activated rotational jumps through an angle τ between two equilibrium positions, a particular two‐site model (τ = 180°) denoted as flip‐flop motion, and the kink model. For the γ process, the following molecular mechanism are considered: the kink model, a vacancy with a chain end, the crankshaft mechanism. The decrease of the second moment caused by these motions is considered. Characteristic differences between the motional models are predicted with respect to the anisotropy of the decrease in second moment in a uniaxially oriented sample and/or the magnitude of the overall decrease. These differences allow an experimental distinction between the different models.
NMR study of molecular motion in oriented long‐chain alkanes. II. Oriented mats of polyethylene single crystals
Authors: Olf H. G. , Peterlin A. 
Published: April 2003

AbstractMeasurements of the NMR second moment of a uniaxially oriented sample of polyethylene single crystals in the range of temperatures from −196°C to 130°C and its dependence on the alignment angle γ between the orientation axis (preferential direction of the molecular chains) and the NMR magnetic field are presented. The experimental results are discussed mainly with respect to the high temperature relaxation, called the α process, in polyethylene. They are compared to theoretical predictions made for a number of mechanisms of molecular motion in Part I of this work. Only one of the mechanisms considered is found to be in quantitative agreement with experiment, the mechanism here referred to as flip‐flop motion. This consists of thermally activated rotational jumps of the crystalline chain segment between folds around its axis between two equilibrium sites in the lattice. Each rotational jump through 180° is accompanied by a shift of the molecule along its axis by one CH2 group. The discussion of the low‐temperature relaxation of polyethylene, the γ process, is based partly on the above measurements and partly on measurements of second moments for unoriented polyethylene samples varying widely in morphology and noncrystalline content. The decrease of the second moment observed with these samples between −196°C and 20°C is taken as a measure of the intensity of the γ process. A linear correlation is found between the decrease in the second moment, designated ΔS, and the noncrystalline content, 1 − αm; this can be represented by ΔS = 1.4 + 22.1(1 − αm). It is shown that neither the crankshaft mechanism not the kink mechanism is able to account quantitatively for this result. The model of a chain end moving in a vacancy fails to adequately describe the angle dependence of ΔS in oriented polyethylene single crystals. The “sandwich model” of a polyethylene single crystal, in which the crystalline core is covered by noncrystalline surface layers, is in better agreement with observations.
Phase‐distribution chromatography (PDC) of polystyrene
Authors: Casper R. H. , Schulz G. V. 
Published: April 2003

AbstractA chromatographic technique is described where the stationary phase is a layer of a very high molecular polystyrene fraction (M = 107) on glass beads (ballotines). The mobile phase is cyclohexane passing the column at a constant temperature below the theta‐temperature. A polystyrene sample of sufficiently low molecular weight (M ≤ 106) injected as a small plug at the top of the column is fractionated because the distribution between the mobile and the stationary phase depends on the molecular weight. Since the large molecules preferentially remain in the stationary phase, the smaller molecules leave the column first. The fractionation effect is inverse to that found in GPC experiments. The separation efficiency is rather good and can be described by a simple thermodynamic theory.
Internal motion in organosilicon polymers. II. Dimethylpolysilazanes crosslinked through silicon
Authors: Model F. S. , Rochow E. G. 
Published: April 2003

AbstractAn investigation of the internal motion in organosilicon polymers by wideline nuclear magnetic resonance has been extended to a pair of dimethylpolysilazanes crosslinked through trifunctional silicon. The data suggest that there is considerable internal motion in all silazanes at 77°K. Evidence is presented for the presence of C3 rotation of the methyl groups, as well as rotation or torsional oscillation of the Si(CH3)2 groups about the polymer backbone. Upon warming the NMR line is seen to narrow, and this is associated with the onset of additional motion, including chain translation and chain flexing or bending. Crosslinking through silicon increases the barrier to chain translation while decreasing the barrier to chain flexing or bending.
Scattering of light by disordered spherulites
Authors: Stein R. S. , Chu W. 
Published: April 2003

AbstractThe scattering of light by a two‐dimensional spherulite of radius R is calculated when there is disorder of optic axis orientation with respect to the radius. Special cases are considered when (1) the disorder occurs in the radial direction only, (2) the disorder occurs in the angular direction only, (3) there is combined radial and angular disorder, and (4) the optic axis makes a constant angle with the radius but there is disorder in the twist angle about the axis. In all of these calculations, a correlation function for disorder is defined and the scattering pattern depends on the ratio of the associated correlation distance to the size of the spherulite. With decreasing correlation distance, the azimuthal dependence of the scattering becomes less and there is a change in the variation of scattered intensity with scattering angles in a manner dependent upon the type of disorder.
ESR and electrical conduction in polypropiolamide
Authors: Michel R. E. , Chapman F. W. 
Published: April 2003

AbstractESR and electrical conductivity measurements have been made on a recently prepared polymer, polypropiolamide. The polymer was obtained as a fine powder which exhibited a nearly Lorentzian line with a width between derivative maxima of 5.2 ± 0.1 gauss and a g value of 2.0036 ± 0.0005. The signal intensity increased with increasing molecular weight. The signal was retained in a dilute solution in formic acid with a slight narrowing of the line. Permanent changes were produced in the spectra at room temperature by heat treatments of the polymer at temperatures up to 800°K. The changes were similar for samples sealed in tubes containing air, dry nitrogen gas and a vacuum of 3 × 10−5 mm of Hg. Spectra obtained at temperatures up to 500°K showed no dependence on the presence or absence of oxygen in the ambient atmosphere. The deresistance of pressed pellets of the polymer was measured in the temperature range 450°K to 525°K, and the results were described by the relation R = R0cE/kT. The activation energy E had a value of 1.2 ± 0.2 ev and the resistivity at 500°K was approximately 1013 ohm‐em. The ESR signal is attributed to an intrinsic property of the polymer which is associated with a conjugated bond system along the polymer backbone. Neither the activation energy nor the magnitude of the resistivity suggest that the delocalized electrons associated with the conjugated bond system have produced unusual electrical characteristics in the polymer.
Methods of description of orientation in polymers
Authors: Roe Ryong‐Joon 
Published: April 2003

AbstractThe nonrandom orientational distribution of structural units, such as crystallites and chain segments, prevailing in an anisotropic bulk polymer sample can be represented fully by an orientation distribution function. Measurements of fluorescence polarization and wide‐line NMR are, in principle, capable of yielding information on the moments of the distribution function up to the fourth order. This work presents the method of analysis required to determine these moments. For this purpose, the distribution function is expanded in a series of generalized spherical harmonies. The method is an extension of a similar technique previously proposed for analysis of x‐ray diffraction data for determination of a complete crystallite orientation distribution function.
Study of molecular orientation in poly(ethylene terephthalate) fibers by fluorescence polarization
Authors: McGraw Gary E. 
Published: April 2003

AbstractMolecular orientation in poly(ethylene terephthalate) (PET) fibers was studied by polarized fluorescence. The observed amorphous orientation of the spun as fiber was not random but uniaxial along the fiber axis. This orientation increased with draw ratio up to about 2 and then remained fairly constant. The amorphous regions of PET fibers were disoriented when the fibers were heated while unconstrained. The fluorescence data obtained were correlated with shrinkage measurements. Fluorescence data indicated that spin drawing had more effect upon orientation than subsequent drawing of the fiber, whereas birefringence data indicated the opposite. The reason for this behavior is discussed.
Dependence on strain rate of the nucleation of cracks in polystyrene at 293°K
Authors: Murray J. , Hull D. 
Published: April 2003

AbstractThe processes associated with the deformation and fracture of polystyrene tested in uniaxial tension have been studied over a range of strain rates from 1.4 × 10−2 to 4.3 × 10−7 sec−1 and at constant stresses between 4.1 and 2.9 kg/mm2. The effect of strain rate on the surface craze distribution prior to fracture, the fracture stress, the mechanism of nucleation of cracks, and the nature of fracture surfaces associated with slow and fast crack propagation have been determined. The changes in fracture surface appearance have been studied using optical and stereoscan microscopy. The observations are consistent with the model presented in a previous paper. Fracture is preceded by craze formation, cavitation in the craze, coalescence of cavities to form large planar cavities which propagate slowly until a critical stage is reached at which fast crack propagation occurs. The effect of changes of strain rate and material variables on these processes is discussed.
Studies on biaxial stretching of polypropylene film. IV. Overall orientation during one‐step biaxial stretching and its application to the estimation of the principal refractive indices of isotactic polypropylene
Authors: Masuko Toru , Tanaka Hiroshi , Okajima Saburo 
Published: April 2003

AbstractPolypropylene film was biaxially stretched in one step in air at 140°C or 152°C, and the deformation was studied optically. A linear relation held between Δnss and vA−½ for vA > 10, at both temperatures, where Δnss is the birefringence with respect to the normal to the film and vA is the degree of stretching expressed as the factor by which the area of the film is increased. Extrapolation of data in this linear region yielded a value of 20 × 10−3 for −Δnss at infinite vA. Since it is presumed that the polypropylene molecules lie completely parallel to the film surface when the film is stretched infinitely, −Δnss at vA−½ = 0 must be just half Δn°, the intrinsic birefringence in the case of completely parallel orientation. Thus, Δn° must be 40 × 10−3. This value was obtained experimentally in uniaxial stretching when the birefringence with respect to the direction of drawing was extrapolated to infinite extension. Similar relations held between np, the average of the refractive indices in the two stretching directions, and vA, and between nss, the index normal to the film, and vA. By similar extrapolations, (1/2)(n′γ + n′β) and n′β = n*α′ were estimated, and thence nα′ was obtained. Here, n′α and n′β are the refractive indices along the c axis (molecular chain axis) and b axis. All these optical parameters refer to a density of 0.900 g/cm3. Hence by applying a density correction to those values, the principal refractive indices and the intrinsic birefringence of polypropylene crystal were evaluated as follows: nα = 1.5522, nβ = n*α = 1.5106 and Δnc° = 4.16 × 10−3, where n*α is the refractive index prependicular to the b and c axes of the crystal.
Superposition of dynamic mechanical properties in the glassy state
Authors: Cuddihy Edward F. , Moacanin Jovan 
Published: April 2003

AbstractSuperposition of the loss tangent curves could be achieved for the β‐transition of a series of homologous epoxy resins. It was found that both a vertical and horizontal shift were necessary to achieve superposition when the curves were plotted as the logarithm of the loss tangent versus reciprocal absolute temperature. Resins from the diglycidyl ether of bisphenol A (DGEBA) were prepared with five different curing agents and their loss tangent curves measured on a free‐oscillation torsion pendulum (ca. 1 cps). The β transition is caused by DGEBA, which was found via molecular models to contain a mobile group. The intensity of the loss for three of the resins was found to be proportional to the concentration of DGEBA, molecular models revealing that no additional mobile groups were introduced by these curatives. The remaining two curing agents introduced mobile groups into their systems and for these two, no separate transitions were identified but the intensity of the DGEBA β transition was increased. This may be caused by a coupling of the DGEBA mobile groups through the flexibility of the curative‐introduced mobile groups.
Measurement of the optical activity of some stereoregular vinyl polymers in the crystalline state
Authors: Bonsignori O. , Lorenzi G. P. 
Published: April 2003

AbstractThe general problems presented by the determination of the optical activity of polymers in the crystalline state are considered. The necessity of using unoriented samples, if the polarimetric data are to be compared with analogous data measured in solution, is emphasized. The optical activity in the crystalline state of a number of stereoregular vinyl polymers has been measured by employing either suspensions of fine powders or thin plates with no detectable orientation. The results of optical rotatory dispersion studies in the crystalline state suggest that, at least in the case of the poly‐α‐olefins investigated, the same chromophores are responsible for the optical activity in the crystalline state and in solution.
Transcrystallinity and x‐ray diffraction in trans‐1,4‐polyisoprene
Authors: Lovering Edward G. 
Published: April 2003

AbstractMiddle range fractions of mimusops balata, a natural trans‐1,4‐polyisoprene, exhibit transcrystallinity when crystallized in the 35–40°C range. The presence of transcrystallinity was established by x‐ray diffraction and optical microscopy. Diffraction peak intensities change due to transcrystallinity, suggesting x‐rays be used to detect transcrystallinity and that caution be exercised in using x‐ray diffraction techniques to determine the phases present in bulk material and in calculating the degree of crystallinity. The tendency toward transcrystallinity may depend upon molecular weight.
Mechanical and optical properties of an anelastic polymer at intermediate strain rates and large strains
Authors: Weiss R. T. , Goldsmith Werner , Chase K. 
Published: April 2003

AbstractThe mechanical and optical properties of a polyester–styrene copolymer have been investigated by means of drop tests at strain rates from 38 to 113 sec−1 for strains less than 50%. Over this range of rates, the optical behavior was found to be linear with strain and independent of strain rate while the elastic–plastic mechanical behavior was only slightly dependent on strain rate. Comparison with the results of similar experiments at lower strain rates achieved by means of an Instron tester reveals that both mechanical and optical properties vary significantly with strain rate. The variation of flow stress with strain rate was found to obey a power law.
A theory of the influence of branching on the crystallinity of bulk polyethylene
Authors: Des Cloizeaux J. 
Published: April 2003

AbstractThe temperature dependence of the crystallinity of bulk polyethylene is calculated in terms of branching (methyl or ethyl side groups on the chain). In the model, the chains are approximately parallel and they pass through alternating amorphous and crystalline layers forming a periodic structure. The crystalinity and the thicknesses of the layers are determined by minimization of the free energy. The theory shows that the temperature at which the polymer begins to crystallize is lower than the melting point of pure polyethylene and that the thicknesses of the layers becomes smaller as the temperature decreases.
Raman spectra of poly(ethylene glycols) in solution
Authors: Koenig J. L. , Angood A. C. 
Published: April 2003

AbstractRaman spectra have been obtained from poly(ethylene glycol) (PEG) in the solid and molten phases and in aqueous and chloroform solutions. Several new lines are observed or resolved in the Raman spectrum of the solid state as a result of using a high‐power argon‐ion laser as a source. The Raman spectra of the molten polymer and the chloroform solutions are indicative of a disordered structure, since additional Raman lines appear as a result of the additional rotational isomers. The Raman spectrum of the aqueous solution shows that considerably less structural change occurs upon dissolution in water.
Gel‐permeation chromatography: Examination of universal calibration procedures for polydimethylsiloxane in a poor solvent
Authors: Dawkins J. V. , Maddock J. W. , Coupe D. 
Published: April 2003

AbstractVarious procedures for universal calibration in gel‐permeation chromatography with polystyrene gels are examined for polystyrene and polydimethylsiloxane fractions. For o‐dichlorobenzene at 138°C, experimental intrinsic viscosity–molecular weight data show that the Mark‐Houwink exponents are 0.70 and 0.57 for polystyrene and polydimethylsiloxane, respectively. In principle, this difference permits a distinction between the various polymer size parameters proposed for universal calibration. An interpretation of the experimental polydimethylsiloxane calibration for o‐dichlorobenzene at 138°C requires a consideration of errors in average molecular weights and errors arising from the use of average molecular weight instead of peak molecular weight. When calibration procedures utilizing hydrodynamic volume and unperturbed dimensions are examined, the difference between them is comparable with experimental error. If the Flory‐Fox viscosity expression is employed, the perturbed end‐to‐end distance (or radius of gyration) and the hydrodynamic volume give equivalent universal calibrations. The experimental data are sufficiently accurate to show that the perturbed dimension determined with the Ptitsyn‐Eizner relation does not give an adequate universal calibration.
Thermodynamic study of deformation of crosslinked ethylene–propylene copolymer
Authors: Romanov A. , Pollák V. 
Published: April 2003

AbstractThe thermodynamics of deformation of ethylene–propylene copolymer crosslinked by dicumyl peroxide with addition of sulfur or maleic anhydride has been studied. Both the entropic (fS) and energetic (fU) components have been studied at elongations α up to 65%. It was found that the course of fU/f, where f is equilibrium stress, in dependence on α agrees with the determined difference in both chemical and physical bonds.
A light‐scattering photometer for use at elevated pressures
Authors: Schulz G. V. , Lechner M. 
Published: April 2003

AbstractA new light scattering photometer has been designed in order to perform light‐scattering measurements at various temperatures and under pressures of 1–1000 atm. Since the scattering angle is constant (90°C), the dimensions of the dissolved molecules are determined by measuring the intensity at different wavelengths. The method of measurement, the calibration of the instrument, and the treatment of data are described. By a series of test measurements on polystyrene in trans‐decalin solutions it is shown that one obtains reliable results and finds considerable effects of pressure on the radius of gyration and the fundamental thermodynamic properties of the system.