bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymerization of pyromellitic dianhydride with 3,3′‐diaminobenzidine in aprotic solvents I. Reaction variables
Authors: Johnston Norman J. 
Published: April 2003

AbstractThe solution polymerization of pyromellitic dianhydride with 3,3′‐diaminobenzidine to form poly(amide acid amine) was investigated under a variety of reaction conditions. Polymer viscosity and gel formation were highly affected by changes in the order of monomer addition, the type of process (powder or solution), monomer concentration, monomer stoichiometry, and type of solvent. Minor effects were noted with changes in polymerization temperature and the presence of small amounts of water. A limiting intrinsic viscosity of 1.2–1.5 dl/g was observed, regardless of polymerization conditions. The polymerization had a strong tendency to gel at high concentrations and when monomer molar ratios approached 1:1. The conditions which retarded or promoted the formation of macrogel were well‐defined, and macrogel but not microgel could be prevented. The polymerization was conducted successfully only in aprotic solvents. No imidazopyrrol‐one units were detected in polymer made in polyphosphoric acid at elevated temperatures.
Polymérisation anionique de l'isoprène: Nature de la paire d'ions et stéréospécificité
Authors: Essel Alain , Pham Quang Tho 
Published: April 2003

AbstractWith accumulated HR‐NMR spectra of anionic polyisoprenes, it has been possible to study the influence of the nature of the propagating species on the microstructure of the obtained polymers If free ions are responsible for the propagation, the microstructure (1,4‐: 25%, 1,2‐: 33%, 3,4‐: 42%) does not depend on the nature of the cations. But with contact ion pairs, the different addition modes are governed by the size of the alkali metal counterions. Mechanisms of anionic propagations via diene–cation coordination are proposed.
Effect of low molecular weight compounds on the relaxation behavior of poly(2‐hydroxyethyl methacrylate) in the glassy state and in the transition region from the glassy to the rubberlike state
Authors: Kolařík Jan , Janáček Josef 
Published: April 2003

AbstractThe method of free torsional vibrations was used to determine the temperature dependence of the storage and loss shear modulus of poly(2‐hydroxyethyl methacrylate) samples swollen with ethylene glycol, formamide, n‐propanol, and water. The measurements included the glassy region (starting with temperatures from −130 to −190°C) and the main (α) transition from the glassy to the rubberlike state. At a volume fraction of the low molecular weight compound vd > 0.2, the above systems exhibit, besides the α dispersion, only the secondary (βSW) dispersion, which is generally attributed to the relaxation motions of the hydroxyethyl groups of the side chains interacting with molecules of the diluent. If no separation of the diluent in a second phase occurs at the measurement temperatures, the temperatures of both dispersions decrease with increasing vd and approach the glass transition temperature of the low molecular weight compound. The concentration dependences of the dispersion temperatures were described by an equation derived elsewhere for the concentration dependence of the glass transition temperature. The results indicate that molecules of the diluent contribute significantly to the intensity of the βSW transition and simultaneously affect its limiting temperatures (for vd = 1 and vd = 0). Specific differences among the systems described above appear only at those temperatures where same of the low molecular weight compound separates into a crystalline or glassy phase.
Creep and other tensile properties of rubber cross‐linked by dicumyl peroxide
Authors: Wood Lawrence A. , Bullman George W. 
Published: April 2003

AbstractNatural rubber crosslinked by dicumyl peroxide in amounts up to 25 parts per hundred of rubber (phr) showed a maximum in tensile strength near 1 phr, followed by a steep decrease to a minimum near 5 phr. The ultimate elongation decreased from 870% at 0.5 phr. to about 10% above 10 phr. The modulus increased linearly with increase of crosslinking. The creep rate decreased from 5.6% per decade at 0.5 phr to zero at 5 phr and higher values. Crystallization, with a resultant abrupt increase in creep, was noted in specimens held in the stretched condition for more than one day. Between 5 and 25 phr this system (when crystallization is avoided) appears to function as an ideal elastic network and can be recommended for studies of rubber elasticity since no variation of modulus with time is observed.
Photoelastic studies of polymers and copolymers in the rubbery state
Authors: Morgan R. J. , Treloar L. R. G. 
Published: April 2003

AbstractPhotoelastic investigations have been carried out on a number of polymers in the crosslinked rubbery state. These include cis‐polyisoprene, two polybutadienes of different structural configurations, an ethylene‐propylene terpolymer, and a range of styrene—butadiene copolymers. From the measured values of stress‐optical coefficients, together with calculated values of the optical anisotropies of the monomer units in the chain (based on Denbigh's values of bond polarizabilities), estimates are made of the number of monomer units in the equivalent random link (of the Kuhn‐Grün theory) for the polymeric chains considered. Further, from a study of the temperature dependence of the stress‐optical coefficient, the temperature dependence of the lenght of the equivalent random link, and hence of the statistical length of the chain, is derived. The interpretation of the temperature dependence data is discussed in a semiquantitative manner in terms of internal energy differences between different rotational states.
Crystallization of branched polymers. I. Ethylene–vinyl acetate and ethylene–acrylic acid copolymers
Authors: Kortleve G. , Tuijnman C. A. F. , Vonk C. G. 
Published: April 2003

AbstractThe following quantities were measured on a number of ethylene–vinyl acetate (EVA) and ethylene–acrylic acid (EAA) copolymers: (1) the small‐angle x‐ray scattering invariant, (2) the overall density, and (3) the crystallinity. Assuming a two‐phase structure, the separate values of the densities of the crystalline and amorphous regions can be calculated from these data. Of these, the crystalline density is compared with the value obtained from the lattice constants. A systematic difference is observed which is ascribed to the presence of comonomeric side groups in the crystalline regions. For the EVA and EAA samples, their concentration is at least 0.3 and 0.5 times the overall concentration, respectively. The amorphous densities are found to be higher than the values calculated from completely amorphous copolymers by extrapolation procedures.
Calorimetric investigation of poly(methacrylic acid) and poly(acrylic acid) in aqueous solution
Authors: Crescenzi V. , Quadrifoglio F. , Delben F. 
Published: April 2003

AbstractThe enthalpy of dissociation of poly(acrylic acid) and of poly(methacrylic acid) in water and in 0.5N NaCl at 25°C has been measured over a wide range of degrees of neutralization of the polyelectrolytes. In the case of poly(methacrylic acid) the calorimetric data permit the direct evaluation of the enthalpy of conformational transition of the polymer. For this transition, with the aid of standard free energy data derived from potentiometric titrations, the change in entropy was also estimated. The relative accuracy of the thermodynamic data, and the possibility of deriving therefrom information on the mechanism of transitions of the type, globular coils → expanded coils for partially hydrophobic synthetic polyelectrolytes in aqueous solution are discussed.
Characterization of the structure and organization of β‐form crystals in type III and type IV isotactic polypropylene spherulites
Authors: Samuels Robert J. , Yee Rena Yang 
Published: April 2003

AbstractAnisotropic growth of β‐form crystals of isotactic polypropylene in type III and type IV spherulites has made possible microanalysis of the unit cell structure, optical properties, and crystal arrangement within the spherulites. Micro x‐ray studies of the type III and type IV spherulites show that interspherulitic β‐form crystals have a hexagonal unit cell with dimensions; a = 19.08 Å and c = 6.49 Å. The intrinsic refractive indices of these β‐form crystals are 1.506 along the a axis and 1.536 along the c axis. The organization of the crystals within the spherulites and the optical properties of the spherulites are also quantitatively evaluated. Both the type III and type IV spherulites have the a axis of the crystal radial while the crystals rotate randomly around the type III spherulite radii and periodically around the type IV spherulite radii. The radial refractive index for both the type III and type IV spherulites has the same value of 1.496. The tangential refractive index of the type III spherulite has a constant value of 1.509; it varies periodically between a minimum of 1.496 and a maximum of 1.519 in the type IV spherulite. Microtechniques such as micro x‐ray diffraction, interference microscopy, birefringence, and optical microscopy were required for acquisition of the data.
Polytetrafluoroethylene: Effects of γ‐radiation on fine structure
Authors: Pinkerton D. M. , Thompson K. R. L. 
Published: April 2003

AbstractThe structure of granular polytetrafluoroethylene has been studied by electron microscopy. On the basis of the texture of surfaces resulting from fracture a model of the structure is proposed which suggests that PTFE consists of extended chain crystals with both inter‐ and intra‐lamellar noncrystalline regions. The effects of γ‐radiation on the structure have been investigated by examining the texture of irradiated fracture surfaces and also the texture produced by post‐irradiation fracture. The irradiations have been performed in vacuo and in oxygen. In both atmospheres PTFE undergoes degradation with a concurrent increase in crystallinity. However, the texture of the surfaces of high crystallinity PTFE, prepared by radiation, differs markedly to the texture of fracture surfaces of high crystallinity PTFE prepared by thermal annealing. It is proposed that radiation causes rupture of bonds in the interlamellar (chain fold) and intralamellar regions, resulting in the production of chain ends and interlamellar links. Due to scavenging of the free radicals, interlamellar linking is pobably a minor process with irradiation in oxygen. These chemical changes cause modifications to the extended chain lamellar crystals and consequently alterations to the physical properties of the polymer.
Confined‐growth crystallization of polyethylene
Authors: Mencik Z. , Plummer H. K. , Van Oene H. 
Published: April 2003

AbstractA new typical orientation pattern of polyethylene has been observed in extruded, melt‐drawn composites containing 10% polyethylene and 90% polystyrene. In these composites, the polyethylene phase is dispersed in the polystyrene matrix as thin, long ribbons (width 1000 Å, thickness 500 Å). The b axis of the crystallites is found oriented preferentially along the long dimension of the ribbons, i.e., in the extrusion direction. The a and c axes of the crystallites show no preferred orientation. This texture pattern is attributed to the fact that, in view of the small cross section of the polyethylene phase, crystallization can proceed only along the long axis of the ribbons. Since the b axis is the direction of fastest growth in polyethylene (and the radial direction in a spherulite), most polyethylene unit cells are oriented with their b axes in the long dimension of the ribbons.
Size distribution analysis of polymer latex systems by use of the extrema in the angular light scattering pattern. III. Unpolarized and horizontally polarized scattered light
Authors: Wallace Thomas P. , Scott Wayne B. 
Published: April 2003

AbstractThe extrema in the unpolarized and the horizontally polarized angular scattering patterns are used as a basis for size‐distribution analysis of polymer latex systems composed of single, spherical, optically isotropic particles. The method of analysis is similar to that recently proposed for vertically polarized scattered light and the polarization ratio, where the modal diameter and a distribution width parameter are determined from the experimental angular scattering pattern and prepared theoretical diagrams obtained by Mie theory calculations. The method of analysis, based on all four scattering functions, is illustrated by use of a Dow polystyrene latex sample.
Fracture of tendon collagen
Authors: Yannas I. V. , Huang C. 
Published: April 2003

AbstractA study of rat‐tail tendon fibers, about 200 μ in diameter, by scanning electron microscopy of fractured specimens reveals that these crimped fibers are largely made up of cylindrical units, about 10 μ in diameter. These, in turn, are made up of the well‐known collagen fibrils, ca. 0.1 μ in diameter, which have been observed previously by transmission electron microscopy and small‐angle x‐ray diffraction. Both the 10‐μ and 0.1‐μ cylindrical units were found to be arranged parallel to the macroscopic fiber axis rather than helically about it, as has been often proposed in the past. Significant improvement in resolution of the fracture surfaces was obtained by dehydration of the tendon. Microscopy of undehydrated tendon fibers undergoing solubilization by dilute aqueous acetic acid confirmed the results obtained by fractography.
Theoretical study of a conjugated reaction‐center model of anionic acetylene polymerization
Authors: Kříaž J. 
Published: April 2003

AbstractThe energy of the ground state, charge distribution, and bond orders were calculated by a MO method in the SCF‐CNDO/2 approximation for various configurations of the monomer, dimer, and trimer model of both the associated and dissociated reaction center of an anionic acetylene polymerization. According to the results of these calculations, cooperation of π and σ bonds leads to a charge delocalization which increases with growing chain length and is the reason for kinetic deactivation of the center. Propagation is stopped, probably by a cooperative effect of the kinetic and thermodynamic factors.
Kinetics of thermal decomposition of polymers. II
Authors: Atkinson J. , Maccallum J. R. 
Published: April 2003

AbstractThe rate equations for the thermal decomposition of a polymer by a random scission reaction followed by rapid depolymerization of a constant number of monomer units from both fragments together with rapid evaporation of low molecular weight species are solved by using a different approach from that used by previous workers. The results obtained are more specific and differ slightly from previous treatments.
Novel diffraction effects in the combined wide‐angle and low‐angle X‐ray diffraction patterns of solution‐grown nylon crystals
Authors: Dreyfuss P. , Keller A. , Willmouth F. M. 
Published: April 2003

AbstractIt was shown previously that in sedimented mats of solution‐grown nylon crystals the 001 wide‐angle reflection due to the unit‐cell period along the chain and the low‐angle reflection due to the lamellar periodicity are both along the same azimuth (meridian) in the x‐ray diffraction pattern.1 Presently in photographs which contain both the wide‐angle and low‐angle regions a series of new meridional reflections have been observed between the low‐angle and 001 reflections and between 001 and 002 reflections. This finding implies that, with the large chemical repeat distances in question, diffraction effects at low and wide angles cannot be considered in isolation as is usual in most polymer crystal studies. In particular, the new reflections promise to provide a direct diffraction approach to the structure of the chain‐folded lamellae.
Structure analysis of chain‐folded lamellar polyamide crystals from X‐ray diffraction
Authors: Atkins E. D. T. , Keller A. , Sadler D. M. 
Published: April 2003

AbstractFolded‐chain crystals of certain polyamides present some novel diffraction effects due to the small number of repeat units within the lamellar thickness. X‐ray diffraction evidence is available in the complete range from low to wide angles. This information is interpreted in terms of the structure factor of an individual lamella together with the lattice factor appropriate for the stacking of lamellae. When due account is taken of the lattice factor, whose effect can be detected even at large angles, three features of the lamellar structure can be deduced. First, the evidence is in favor of the straight‐chain stems traversing almost the total thickness of each lamella, implying sharp folds at the lamellar surfaces. Some consequences of this result on the interpretation of data obtained from annealed mats are mentioned. Second, the detailed determination of the stem structure demands that the majority of the folds in nylon 66 lie in the acid group. Third, there are regions of depleted electron density at the lamellar surfaces, though features of the crystal structure are still retained. This indicates the presence of some folds deeper in the crystal than the majority.
Adsorption of polymers at the solution‐solid interface. VI. Polyacids on nylon powder
Authors: Cole D. , Howard G. J. 
Published: April 2003

AbstractThe adsorption of some polyacids, principally poly(acrylic acid), on nylon powder has been studied. In aqueous solutions at low pH the adsorption behavior of poly(acrylic acid) is controlled by adsorbate coil dimensions rather than by electrostatic effects. Less adsorption takes place from methanol solutions but the process is much more rapid than from water. Above a critical value, increase of adsorbate molecular weight leads to a reduced adsorption, the effect being particularly evidenced by aqueous solutions. Model compounds (propionic and glutaric acids) are rapidly adsorbed from both methanol and water, but give low specific absorptions. Adsorption of poly(acrylic acids) and model compounds, is reduced, but not eliminated, by modification of the nylon adsorbent through acetylation or methoxymethylation. The adsorption of poly(acrylic acid) on nylon is not readily reversible; however, partial neutralization will release preadsorbed poly(acrylic acid) from nylon powder. The adsorption behavior of copolymers of acrylic acid with N‐vinylpyrrolidone is reported, as are brief studies on some other homopolyacids. The results are generally interpreted on the basis of sorption of the macromolecules into a swollen, flexible adsorbent.
Anisotropy of mechanical and dielectric relaxation in oriented poly(ethylene terephthalate)
Authors: Davies G. R. , Ward I. M. 
Published: April 2003

AbstractThe anisotropy of the α and β relaxations in oriented poly(ethylene terephthalate) has been studied by dynamic mechanical and dielectric relaxation measurements. The α relaxation shows considerable mechanical anisotropy but gives rise to an isotropic dielectric process. The β relaxation, on the other hand, shows pronounced dielectric anisotropy but very little mechanical anisotropy. The implication of these results with regard to possible interpretations of the relaxations are discussed.
Crystallization kinetics of isotactic polystyrene from isotactic‐atactic polystyrene blends
Authors: Yeh G. S. Y. , Lambert S. L. 
Published: April 2003

AbstractIn an attempt to facilitate a better understanding of the role of noncrystallizable components on the crystallization kinetics, spherulitic growth rates as well as the morphology and melting behavior of isotactic polystyrene in blends with various molecular weight atactic polystyrenes (900 to 1,800,000) over a wide range of concentrations have been studied. The growth rates are uniformly depressed with increasing amounts of atactic diluent. In addition, they are dependent on the molecular weight of the added polystyrene, generally decreasing in the molecular weight ranges between 4800 and 19,800 and between 51,000 and 1,800,000. However, between these two ranges, anomalous growth rates showing a sudden increase are observed, which may be explained by an increase in the entrapment of the noncrystallizable diluent. An explanation based on morphological observations, which showed an increase in coarseness of the spherulites with increasing molecular weight of the added atactic polystyrene, is offered.
Plastic deformation of polypropylene. IV. Wide‐angle x‐ray scattering in the neck region
Authors: Morosoff N. , Peterlin A. 
Published: April 2003

AbstractWide‐angle x‐ray scattering (WAXS) patterns of two polypropylene samples, a quenched sample drawn at 21°C and an annealed sample drawn at 100°C, were investigated in a range of values of draw ratio λ very closely spaced through the neck region. In both cases, a range of small λ where deformation occurred by spherulite deformation was followed by one of higher λ where microfibrils were formed. The contribution to the WAXS pattern of microfibrils could be clearly distinguished from that of deformed spherulites because of the better orientation parallel to the draw direction of the former as compared to the latter. Additionally, for a drawing temperature of 21°C, microfibrils crystallize in the “smectic” phase as compared to the monoclinic phase for the initial sample and deformed spherulites. At this temperature, plastic deformation proceeds through the spherulite deformation mechanism up to λ = 1.4 accompanied by an increase in chain orientation with increasing λ. For λ > 1.4 plastic deformation appears to occur exclusively through microfibril formation. For drawing at 100°C, spherulite deformation is accompanied by very little change in chain orientation up to λ = 2, where microfibril formation begins. For λ > 2 (Td = 100°C) plastic deformation is accompanied by both microfibril formation and some spherulite deformation as reflected by changes in both orientation and crystallite size. At this temperature the lateral crystallite size in the microfibrils is related to the long period according to the “equilibrium crystallite shape” previously found for annealed polypropylene.
Effect of orientation, anisotropy, and water on the relaxation behavior of nylon 6 from 4.2 to 300°K
Authors: Papir Yoram S. , Kapur Sudhir , Rogers Charles E. , Baer Eric 
Published: April 2003

AbstractThe relaxation behavior of nylon 6 from 4.2 to 300°K was investigated as a function of orientation, anisotropy and moisture content by using an inverted free‐oscillating torsion pendulum. Three new relaxations, δ at 53°K, ϵ below 4.2°K, and ζ at 20°K, were discovered. The characteristics of these new relaxations strongly depend on the orientation anisotropy, and concentration of adsorbed water in the specimens. The results suggest that the mechanism of the γ process is associated with the motions of both the polar and methylene units. The mechanism of the β relaxation is postulated to originate with motions of both non‐hydrogen‐bonded polar groups and polymer—water complex units. The behavior of the α peak is consistent with the hypothesis that it originates with the rupture of interchain hydrogen bonding due to the motions of long‐chain segments in the amorphous regions. Finally, the data strongly support the proposition that two types of water, tightly bound and loosely bound, exist in nylon 6.
Time‐dependent elongational viscosity of a solution of elastic dumbbells
Authors: Nicodemo L. , Marrucci G. , Hermans J. J. 
Published: April 2003

AbstractThe elongational viscosity of dilute polymer solutions must always be measured under nonsteady‐state conditions. To predict the time dependence of this viscosity for a polymer solution in which a constant stretching rate is maintained, a simple model is considered in which the polymer molecules are represented by elastic dumbbells. The non‐Hookean elastic force in the dumbbell is determined by the conformational entropy of the chain. Use is made of Peterlin's approximation which replaces the elastic force by a function of the root‐mean‐square end‐to‐end distance. Application to the transient state is straightforward; it can be extended to include the effect of “internal” chain viscosity by means of approximations that are similar to Peterlin's.