bluuebunny/crossref_metadata_2025_split huggingface dataset:
Velocity of dissolution of polymers. Part II
Authors: Asmussen Frithjof , Ueberreiter Kurt 
Published: April 2003

AbstractPolystyrenes of molecular weight 429 to 973,000 were prepared by fractionation of a pure thermal polymerizate. The velocity of dissolution ⋅ (in cm./sec.) of these fractions in a solvent follows the relation ⋅ = kM−A over a wide range of molecular weight. Only the parameter k is temperature‐dependent and changes with the speed of stirring in the bath. A is constant. ⋅ can be very accurately measured in the molecular weight range from 1000 to 20,000. This offers a new means for determining the molecular weight in a range which otherwise presents difficulties. The swollen surface layer δ increases with the square root of the molecular weight. It increases abnormally above M ≈ 150,000 due to the strong entanglement of large macromolecules. The velocity of dissolution is thereby considerably diminished. The mean mutual diffusion coefficient D is independent of the chain length of the polymer. Its value can be determined from the slope of the ⋅ vs. δ−1 curve and agrees well with those values calculated from the time lag and dissolution formulae data. The assumption that macromolecular coils are the units building up the swollen surface layer can be proven. The average number of coils in a line of the length δ seems not to depend upon molecular weight and is approximately 104 coils. A distinction between two fundamental definitions of the quality of a solvent is necessary. The thermodynamical definition depends upon the value of the second virial coefficient B in the expression for the osmotic pressure. The kinetic definition is simply based on the value of ⋅. High values of these qualities indicate good solvents. However both properties are independent of each other. Whether or not a solvent is suitable from the thermodynamic standpoint depends upon the chemical constitution of the solvent and its interaction with the polymer. Suitability from the kinetic standpoint is related to a small molecular size and viscosity which creates no difficulties for the penetration into the channel system of the polymer.
Shear dependence of the reduced viscosity—concentration slope constant
Authors: Van Oene H. , Cragg L. H. 
Published: April 2003

AbstractThe variation with shear of the concentration dependence of the reduced viscosity was studied in the system polystyrene‐toluene at 20, 40, and 60°C. The slope constant k′ was determined at constant shear stress k′T and at constant shear rate k′D; k′T was found to increase, k′D to decrease, with increasing shear. Alternatively, the concentration dependence was expressed in terms of Peterlin's effective viscosity. For this system the effective viscosity at constant shear stress was independent of shear but the effective viscosity at constant shear rate decreased with shear. The decrease in k′D, and in effective viscosity at constant shear rate with shear are attributed to molecular entanglement and an explanation is proposed for the observed differences in behaviour at constant shear stress and constant shear rate. In appendices a new formula for the calculation of viscosity ratios from the relative flow times is derived, and a procedure is outlined to compute intrinsic viscosities and limiting slope constants that will be free from absorption effects.
Diffusion de la lumière par les solutions de copolymères
Authors: Leng Marc , Benoit Henri 
Published: April 2003

AbstractOn montre comment l'étude de la diffusion de la lumière par un copolymère dans des solvants d'indices différents permet d'obtenir des informations précises sur la masse moléculaire de chacun des constituants, la structure de l'échantillon et sa polydispersité en masse et en composition. Dans une première partie, on analyse du point de vue théorique les données fournies par les mesures de masses moléculaires et de rayons de giration. Dans une deuxième partie, on étudie un copolymère séquencé du type polyméthacrylate de méthyle—polystyrène—polyméthacrylate de méthyle préparé par voie anionique, étude qui permet de caractériser ce produit de façon assez complète. On décrit enfin une série d'expériences qui permettent de mettre en évidence d'une façon très directe, “l'effet de volume.”
The viscosity behavior of linear and branched dextran sulfates
Authors: Pasika W. M. , Cragg L. H. 
Published: April 2003

AbstractLinear and branched samples of potassium dextran sulfate have been prepared without significant degradation from samples of linear and branched dextran having similar intrinsic viscosities. The dilute solution viscosity behavior of these polyelectrolytes has been studied with particular reference to the effect of branching and degree of sulfation. A comparison of the reduced viscosity—concentration curves, in aqueous 0.001N and 0.0005N KCl, of linear and branched potassium dextran sulfate with the same degree of sulfation revealed a significant difference in their viscosity behavior. This difference is attributed to a greater charge density in the nonlinear sample resulting from its branched structure.
Statistical computation of distribution functions of dimensions of macromolecules
Authors: Schatzki T. F. 
Published: April 2003

AbstractRandom walks of 100 steps or less in a three‐dimensional tetrahedral lattice have been generated by means of the ILLIAC computer. Excluded volume has been introduced by forbidding double occupancy of lattice sites. The distribution function of end‐to‐end lengths has been collected and expanded in terms of Hermite polynomials. One finds that the distribution can be expressed as a two‐term expansion, the second term contributing 10% at 100 steps. For walks of a given number of steps and a given end‐to‐end length the spatial distribution of monomer segments has been investigated and compared to the (no excluded volume) expression of James. One finds that the introduction of excluded volume swells the chains and increases the moment of inertia along the major axis.
Fractionnement des polyamides par une méthode en continu
Authors: Duveau N. , Piguet A. 
Published: April 2003

AbstractLes auteurs présentent un procédé rapide de fractionnement des polyamides. Ce procédé est basé sur la mise en continu de la méthode développée par G. B. Taylor [J. Am. Chem. Soc., 69, 638, (1947)], utilisant le partage du polymère entre deux phases liquides phénol—eau M, dont la composition est variable en fonction du temps. A chaque instant, la solution contenue dans la cellule de fractionnement forme deux phases; le mélange M arrive dans la phase inférieure; la phase supérieure s'écoule goutte à goutte dans les tubes d'un collecteur; au cours du temps le volume de la phase inférieure décroǐt, pour s'annuler lorsque tout le polymère est extrait. L'exploitation des fractions se fait par la méthode classique: précipitation, séchage, détermination de la viscosité intrinsèque. Le choix de conditions opératoires appropriées (débit, gradient de composition du mélange M) permet d'obtenir une courbe de répartition correcte, comme il est possible de s'en rendre compte en travaillant sur des échantillons de polydispersité connue (répartition de Flory). La méthode développée pour le polyamide 66 est applicable à d'autres polyamides. La durée d'une opération est de l'ordre de quinze heures.
The morphology and internal structure of poly(ethylene oxide) spherulites
Authors: Price Fraser P. , Kilb Ralph W. 
Published: April 2003

AbstractThe development of spherulites in thin films has been observed. At low supercoolings they develop scalloped edges, with each scallop sector having a branched structure reminiscent of a fern frond. At high supercoolings they develop smooth circular boundaries. An x‐ray diffraction study has been made both of the fronded structures and of the more perfect spherulites formed at higher supercoolings. Only one of the latter types of spherulites was examined. Here it appears that the crystallites have a rotation axis perpendicular to the spherulite radius. This axis is the 4, 0, 1 direction in the crystal which has a monoclinic unit cell. The fronded spherulites, when examined along the radial frond spine, have the same rotation axis of the crystallites, both ±45° to the radius. This double orientation of rotation axis also occurs in material crystallized in a fine capillary, where the spherulite radial direction is presumably along the capillary axis. Low‐angle x‐ray diffraction shows spacings of about 200 A. (sometimes to sixth order) parallel to the spherulite radius for both fronded and perfect spherulites.
A study of the molecular dimensions of fractions of high pressure polyethylene
Authors: Schuurmans H. J. L. 
Published: April 2003

AbstractA sample of high pressure polyethylene was fractionated and subsequently characterized by means of osmometry, light scattering, and viscometry. The molecular weight distributions of the fractions as calculated by means of the numerical approximation method of Beall were compared with those obtained from the osmometry and light‐scattering experiments. Also a comparison was made between the molecular dimensions calculated respectively from light‐scattering data, viscometry, and second virial coefficients. It is shown that an application of current theories to the data gives vastly different values for the molecular dimensions depending on what measurements are taken as a starting point. For calculations on the branching, it appears necessary to take into consideration the difference in the width of the molecular weight distribution of the branched polymer and the linear polymer with which it is compared.
The effect of pressure and temperature on the specific volume of polyethylene
Authors: Matsuoka Shiro 
Published: April 2003

AbstractA spherulitic crystallization process can be divided into three successive stages: the formation of spherulite centers, the growth by means of crystalline fibrils with many branches extending into the melt, and finally crystallization of the intervening regions between these already crystallized fibrils. The three stages were identified with parts of a typical dilatometric isotherm for crystallization from the melt. The last stage of the isotherms was analyzed as crystal growth accompanied by the predetermined nucleation of one‐dimensional character. Isothermal annealing was also studied dilatometrically and was found to be similar in mechanism to the last stage of crystallization from the melt. The influence of the thermal history, including the conditions of crystallization, on the degree of crystallinity were summarized as a kinetic factor, and was distinguished from the thermodynamic consequence of branches on the equilibrium degree of crystallinity. Specific volumes of the crystal (estimated) and the melt were determined at various temperatures and pressures. The relationship between the entropy of fusion and pressure was determined from the volume of fusion by utilizing Clausius‐Clapeyron's equation. The entropy of fusion at atmospheric pressure thus obtained was found in agreement with values obtained elsewhere by other methods. The compressibility of the melt and the true volume of fusion decreased substantially under high pressure, while the entropy of fusion was essentially unchanged. This was ascribed to the change of the melt property from the familiar free‐volume type of behavior to a more solidlike one without an increase in structural order.
Effect of carbon black on chain mobility and structure of synthetic rubbers
Authors: Baccaredda M. , Butta E. 
Published: April 2003

AbstractDynamic mechanical properties of polyisobutylene, butyl rubbers, Paracril, cis‐1,4‐polybutadiene, reinforced with EPC black, were determined in the temperature range −150‐+170°C., in the frequency range 2–20 kcycles/sec. In the amorphous polymers, reinforcement causes an increase of sound velocity at any temperature, while the glass transition point Tg and the thermal coefficient of sound velocity dV/dT remain practically unchanged. Only at high temperatures, near the softening region, are lower values of the damping factor Q−1/dT found for the filled samples, as compared with the corresponding unfilled ones. Addition of reinforcing carbon black to cis‐1,4‐polybutadiene causes an increase of sound velocity at any temperature, and a little shift of the maximum damping point toward lower temperatures. In the reinforced sample, the Q−1 − T curve, in the region of high dissipation, becomes more unsymmetrical, showing a flat region at temperatures just above the maximum. A comparison of the mechanical spectra of the unfilled vulcanized samples of cis‐1,4‐polybutadiene with those of the corresponding filled vulcanized ones (with the same sulfur content and the same heat treatment) shows a shift of the glass transition point and of the maximum damping toward lower temperatures with addition of the filler. The experimental results are discussed and the conclusion is drawn that neither structural changes nor appreciable variations of chain mobility are caused by addition of carbon black in the examined rubbers.
Experimental determination of the elastic modulus of crystalline regions in oriented polymers
Authors: Sakurada Ichiro , Nukushina Yasuhiko , Ito Taisuke 
Published: April 2003

AbstractThe elastic modulus of the crystalline regions in some oriented polymers was determined. An x‐ray diffractometer specially constructed for this purpose was used, and the lattice extension in the direction of the fiber axis was measured under application of a direct load. Usually a meridional reflection was used for the measurement of the lattice extension, but in the case where no strong meridional reflection exists a reflection from planes which are almost perpendicular to the fiber axis of the crystallites was used. The elastic modulus was calculated under the assumption of a simple series model. The values found are as follows: polyvinyl alcohol, 255 × 104 kg./cm.2; polyethylene, 240 × 104 kg./cm.2; polypropylene, 42 × 104 kg./cm.2; polyoxymethylene, 54 × 104 kg./cm.2; cellulose, 137 × 104 kg./cm.2; polyvinylidene chloride, 41.5 × 104 kg./cm.2.
Influence de la température sur le greffage du styrène sur des films de polytetrafluoroéthylène et de poly(chlorure de vinyle) par la méthode radiochimique directe
Authors: Chapiro Adolphe , Matsumoto Akira 
Published: April 2003

AbstractLe greffage radiochimique direct du styrène sur des films de polytetrafluoroéthylène a été étudié à 40 et à 60°C. A 40°C, la réaction présente des caractères cinétiques analogues à ceux que l'on avait observés au cours d'une étude antérieure conduite à 19°C. On trouve en particulier qu'au dessus d'une certaine intensité “critique,” le greffage ne se fait plus dans la masse mais est limité à une zone superficielle du film. La valeur de cette intensité critique est voisine de 6 à 8 rads/sec à 40°C tandis qu'à 19°C, nous avions trouvé une valeur de 1,0 rads/sec. A 60°C, l'intensité critique est supérieure à la plus grande intensité examinée, soit 35,1 rads/sec. Les courbes de conversion obtenues pour des intensités inférieures à la valeur critique mettent en évidence une autoaccélération. En représentant ces courbes en échelles logarithmiques, on obtient des droites dont la pente est 1,5–1,6 à 40°C et 1,0–1,2 à 1,0–1,2 à 60°C. A 19°C, la pente des droites correspondantes était comprise entre 2,5 et 3,2. Cette pente, qui est l'exposant du temps dans la relation C = Ktβ est désignée sous le nom de coefficient d'autoaccélération. Ce coefficient β permet de caractériser le comportement cinétique des différentes réactions autoaccélérées. Le déplacement de l'intensité critique vers les grandes valeurs, lorsque la température s'élève, est interprété par une augmentation de la vitesse de diffusion du monomère et à 60°C, on suppose que cette dernière cesse de contrǒler la cinétique de la réaction dans les conditions expérimentales utilisées. D'un autre cǒté, on pourrait penser que la diminution du coefficient d'autoaccélération β, lorsque la temperature croǐt, est dǔe à une diminution de la contribution de l'effet de gel, en raison de la mobilité accrue des chaǐnes croissantes. Cependant l'exposant α de l'intensité dans la relation V = KIα, qui est égal à 0,5–0,55 à 19°C, passe à 0,68 à 40°C et à 0,70–0,72 à 60°C, ce qui montre que, malgré la forme linéaire des courbes de conversion à 60°C, la réaction n'atteint pas l'état stationnaire. Le greffage radiochimique du styrène sur des films de poly(chlorure de vinyle) a été étudié à 60°C. Contrairement à la réaction étudiée antérieurement à 20°C, cette réaction n'est plus controlée par la vitesse de diffusion du monomère et la cinétique du greffage est “normale.” C'est ainsi que les courbes de conversion sont pratiquement linéaires et que la vitesse de la réaction est proportionnelle à la racine carrée de l'intensité. Une certaine courbure vers l'axe des abscisses persiste sur les courbes de conversion obtenues aux faibles intensités. Elle pourrait, soit résulter d'une diffusion non homogène du monomère, soit d'un phénomène de “protection” radiochimique du poly(chlorure de vinyle) par les noyaux phényliques du styrène greffé.
The dynamic birefringence of high polymers
Authors: Stein Richard S. , Onogi Shigeharu , Keedy Daniel A. 
Published: April 2003

AbstractThe simultaneous measurement of the birefringence and strain of a sample subjected to sinusoidal strain is proposed as a means for elucidating the molecular mechanism of the response of high polymers to mechanical deformation. A linear phenomenological theory is proposed in which strain‐optical coefficient distribution functions are assigned to the elastic and viscous members of a distribution of Maxwell elements. An apparatus has been constructed to determine the dynamic strain‐optical coefficient at frequencies between 0 and 600 cycles/sec. by means of mechanical excitation of vibration at low frequencies and electromagnetic at high frequencies. The dynamic birefringences of polyethylene has been studied at room temperature over this frequency range.
Kinetics of polymerization of vinylidene chloride. IV. Copolymerization of vinylidene chloride and acrylonitrile
Authors: Marker Leon , Sweeting Orville J. , Wepsic James G. 
Published: April 2003

AbstractThe emulsion polymerization of vinylidene chloride is divisible into three stages: (I) a normal emulsion polymerization at a rate dependent on the 0.6 power of both the catalyst and surfactant concentration; (II) at a rate less than half that of I; (III) at a rate which increases in direct proportion to the catalyst concentration and independently of surfactant concentration. A careful examination of stirring rate has shown that the slowdown in stage II probably results from monomer starvation caused by slow diffusion of coalesced droplets, and that recovery in stage III is the result of transfer of monomer at the time of collision between a polymer particle and a monomer droplet. Extension of this work to copolymers of vinylidene chloride and acrylonitrile has shown a similar kinetic effect at high ratios of vinylidene chloride. The rate of polymerization for a system containing 90% vinylidene chloride decreases sharply after 15% conversion. The polymer formed increases in acrylonitrile content with conversion, reaches a maximum, and then decreases during stage III of the reaction. A run containing 70% vinylidene chloride in the charge did not show a slowdown but gave evidence of a maximum in the curve relating conversion and composition. At higher acrylonitrile content, no slowing occurred, and the polymer composition changed monotonically with conversion. Since acrylonitrile is partially soluble in water, the partition coefficient of acrylonitrile between vinylidene chloride and water was determined at concentrations similar to those used in the polymerizations. The partition coefficient decreases with increasing acrylonitrile concentration in the water phase. Apparent reactivity ratios were calculated on the basis of the monomer composition corrected for the water solubility of acrylonitrile and the initial composition of the copolymer. These values are r1 = 0.390 and r2 = 0.585, vinylidene chloride being considered to be the first monomer. The existence of a unique reactivity ratio indicates that the composition of the initial polymer is controlled only by the relative reactivities of the comonomers and the water solubility of acrylonitrile. The polymer formed later is also influenced by the rate of transport of vinylidene chloride to the reaction site. This is confirmed by the conversion curves and the manner in which composition changes with conversion.
Kinetics of the γ‐radiation‐induced polymerization of ethylene
Authors: Wiley Richard H. , Lipscomb N. T. , Johnston F. J. , Guillet J. E. 
Published: April 2003

AbstractStudies of the rates of γ‐radiation‐initiated polymerization of ethylene in the gas phase at 22°C., 40–70 atm. and 380,000 r/hr. have shown that the rate expressions show a good correlation with the relations expected from kinetic considerations if the density is used to express the ethylene concentrations. In this range of temperature and pressure, the density, pressure, and fugacity relations for ethylene differ significantly from those at the elevated pressures which have been used in previous rate studies. Use of fugacities in the rate expression log (rate) = a + b log x, where x = p, f, or d, gives a value of 10.4 for the b term; use of pressure gives a value of 5.0; and use of density gives a value of 2.4. This last value is closest to that predicted (2.0) from a kinetic analysis which takes into consideration an initiation step dependent on monomer concentration and termination by primary radicals. Studies of the liquid‐phase polymerization over the temperature range of 5 to −40°C. give an activation energy of 4.4 ± 1.8/kcal./mole. Infrared analysis of the product indicates that short‐chain branching is much less (0–1.2 vs. 2–3 branches per 100 carbon atoms) than for polyethylenes prepared at higher temperatures. Relations between solution and melt viscosities indicate a high degree of long‐chain branching in the polymer.
Preliminary studies of the effects on crystal structure of introducing aromatic rings into linear polyamides. Polyamides made from p‐xylylenediamine and dicarboxylic acids
Authors: Vogelsong Donald C. 
Published: April 2003

AbstractX‐ray diffraction has been used to study molecular packing in the crystalline regions of fibers of the polyamide made from p‐xylenediamine and sebacic acid, PXD‐10. Many of the diffraction spots are displaced from the layer lines. This has been attributed to the crystallites assuming a preferred orientation of about 5° off the fiber axis. No amount of drawing orients the crystallites parallel to the fiber axis. Unit cell dimensions and indices have been determined from normal fiber photographs. The unit cell is triclinic with the following dimensions: a = 5.74 A., b = 4.87 A., c = 20.6 A.; α = 75°45', β = 55°13', γ = 65°19'. A structure is proposed in which the chains pack together in hydrogen‐bonded sheets. The sheets pack together to form a three‐dimensional lattice. No evidence has been found to indicate a second crystalline phase as is usually found in linear polyamides. Fiber photographs of the polyamides PXD‐6 and PXD‐8 show packing and orientation similar to that found for PXD‐10. Fiber photographs of the polyamides PXD‐7 and PXD‐9 show a different type of triclinic packing Long fiber identity periods, combined with the fact that many of the diffraction spots are displaced from the layer lines for these latter two polyamides, prohibit any quantitative interpretation of the diffraction patterns.