bluuebunny/crossref_metadata_2025_split huggingface dataset:
The spherulitic structure of crystalline polymers. Part III. Geometrical factors in spherulitic growth and the fine‐structure
Authors: Keller A. , Waring J. R. S. 
Published: April 2003

AbstractThe spherulites are built of distinct fibrillar units and their fine‐structure presents two problems: the arrangement of these units and their internal structure. In the present paper the first has been treated in greater detail. Based on direct observations, and on earlier works on nonpolymeric spherulites, a regular periodic branching mechanism of the fibrillar units is proposed, where, in the case of maximum regularity, the position of each branch with respect to the preceding one is defined by one constant branching period and one constant angle in the two‐dimensional case, and by one constant branching period, two constant angles, and a constant direction of rotation in the three‐dimensional case. The various stages of such a spherulitic growth were directly observed in suitable samples. It is shown that this mechanism can lead to helices, to be referred to as “large‐scale helices,” which produce the previously observed zigzag extinction effects. The effects of the thickness of the crystallizing layer is followed, and possible connections between these effects and more general problems of crystal growth are indicated. Investigations of the fine‐structure of the fibrils indicate a closely coiled rope‐like arrangement in samples suitable for these observations. These are on a size of 400 A. and upward, sometimes reaching the limit of the optical microscopic resolution dependent on the preparation. They will be referred to as “small‐scale helices.” These units appear to be built of and connected by much smaller fibrils which themselves possess a periodicity of 100–200 A. or less. The possible reasons for coiling and its relation to the perpendicular orientation found in Part II are discussed, and it is suggested that branching could be a possible consequence of the coiling structures. The conclusion is reached that, as far as the morphology is concerned, crystallization in polymers represents a special case of the formation of crystalline aggregates in viscous media.
The tensile strength of elastomers
Authors: Taylor G. R. , Darin S. R. 
Published: April 2003

AbstractThe tensile strength of decamethylene dismethylazodicarboxylate vulcanizates of GR‐S, 50°C. polybutadiene, 5°C. polybutadiene, and natural rubber has been determined as a function of temperature and/or the degree of crosslinking. A theory of tensile strength of amorphous polymers which adequately describes the effect of the degree of crosslinking on strength is proposed. The theoretical expression for the strength of amorphous materials is then modified to include the effect of crystallization. The complete expression for the tensile strength of crystallizable elastomers, which includes amorphous elastomers as a special case, is:

where ω0 = 1 − (1 + δ2λ3)−1/2, fc = volume fraction crystallinity, M = primary molecular weight, Mc = molecular weight per crosslink in the uncrystallized polymer, λ = extension ratio at break, and δ, K = parameters. The theory is shown to be good for GR‐S and semiquantitatively correct for a crystallizable polymer, 5°C. polybutadiene.
Determination of crystallinity in polyethylene by X‐ray diffractometer
Authors: Aggarwal S. L. , Tilley G. P. 
Published: April 2003

AbstractA convenient and rapid x‐ray diffraction method is described for the determination of per cent crystallinity in polyethylene, using a scanning goniometer with Geiger tube and scaler counter. Results are presented on per cent crystallinities of a number of polyethylenes and on samples made by quenching polyethylene melt at different temperatures in the range of 20–102°C. The samples of polyethylene studied were found to have 65‐71% crystallinity. The temperature at which plyethylene melt is quenched has no appreciable effect on the crystalline content.
Contribution à l'étude de la cellulose sèche et mouillée à l'Aide de la diffraction des rayons X par la ramie
Authors: Antzenberger Paulette , Fournet Gérard , Rogué Jean 
Published: April 2003

AbstractA partir du diagramme équatorial complet de diffusion des rayons X par la ramie sèche et mouillée, nous avons cherché non pas à préciser un modèle idéal de structure cristalline mais plutôt à obtenir des renseignements sur la structure réelle des fibres. Comme la cellulose contient plusieurs sortes d'atomes, nous avons considéré la fonction de répartition des densités électroniques et non celle des centres d'atomes. Cette fonction peut s'obtenir directement à partir des données de photométrie des diagrammes équatoriaux. Par ailleurs, G. Fournet a développé une méthode permettant d'obtenir cette fonction à partir du modèle de Meyer et Misch. Nous exposons la comparaison de la courbe synthétique avec les deux courbes expérimentales et montrons que l'accord est meilleur dans le cas de la ramie mouillée. Nous pensonsque dans le plan perpendiculaire à l'axe de fibre la cellulose sèche est assez homogène en densité électronique mais très perturbée à petite distance (distorsions locales de la maille) tandis que la ramie mouillée, plus hétérogène à cause des zones gonflées présente des zones cristallines presque parfaites de l'ordre de 100 Å.
Swelling and absorption by cellulose acetate in binary solvent‐hexane mixtures
Authors: Moore W. R. , Russell J. 
Published: April 2003

AbstractPreferential absorption and swelling by cellulose acetate in binary solvent‐type liquid/hexane mixtures has been studied at 25°C. Secondary cellulose acetate, of acetic acid yield 53.7%, was used in fibrous form and as film. Triacetate, prepared by nondegradative acetylation of the secondary, was also used. Factors affecting preferential absorption by the fibrous secondary acetate seem to include the activity of the solvent‐type liquid and its chemical type, the swelling power of the mixture, and steric effects. Preferential absorption of ketones and esters other than methyl formate appears to be independent of both acetyl content and structure. Absorption of methyl formate, acetic acid, and heterocyclic bases by the triacetate is less, at all concentrations, than by the secondary acetate. At low concentrations cresols and chlorinated hydrocarbons are absorbed to a smaller extent by the triacetate but at higher concentrations the reverse is the case, such variations in absorption being ascribed to steric effects and to the elimination of hydroxyl groups on complete esterification. Absorption by the secondary acetate films also suggests steric effects. Comparison of the measured weight of films with that estimated from the change in composition of the mixture following absorption, assuming no hexane to be absorbed, Suggests that this assumption is true at low concentrations. At higher concentrations, leading to high degrees of swelling or to gelatinization, the mixture seems to be imbided. There is no general relationship between swelling and the δ value of the solvent‐type liquid but δ values for the mixtures just causing complete solution of the acetates are not very different when the mixtures involve solvents of similar chemicals type.
Phase equilibria in ternary systems involving a polymer and two polar solvents
Authors: Newman S. , Krigbaum W. R. 
Published: April 2003

AbstractA recent treatment of phase equilibria in nonpolar ternary systems is modified to permit application to the interesting case of a polymer and two polar liquids which may associate. The deviations from ideality exhibited by associated liquids are incorporated with the pair interaction free energy in the X parameter for the liquid pair. Hence, the expressions for the chemical potentials remain unaltered, but the X parameters for the polar liquid pair are concentration dependent; furthermore, the relation X12 = (V1/V2)X21, no longer applies. The equation deduced allows theoretical description of the phase equilibria in polar ternary systems provided sufficient information is available to characterize the binary polar liquid mixture. The predictions arising from the modified theory are tested using data obtained from phase composition analysis of the two ternary systems: nitrocellulose‐ethanol‐water and nitrocellulose‐diethylene glycol‐water. The isotherms obtained for the former system provide excellent confirmation of the theoretical predictions. Although for the second system studied the polymer‐solvent interaction parameters appear to be concentration dependent; nevertheless, application of theory yields values for the difference (lX − X) over the concentration range of interest. The (lX − X) differences deduced from the data for both ternary systems yield values for the nitrocellulose‐water interaction parameter which stand in good agreement with the value directly deduced from the sorption isotherm for that binary system, thus providing further confirmation of the theoretical treatment.
Rupture of rubber. III. Determination of tear properties
Authors: Greensmith H. W. , Thomas A. G. 
Published: April 2003

AbstractA method of investigating the tear behavior of rubber vulcanizates is described. The method, based on the tear criterion of Rivlin and Thomas, involves the determination of the energy required to propagate a tear and its dependence on the rate of propagation. The type of test‐piece employed and the methods of measuring the energy and rate of tear propagation are described and discussed. Two principal types of tearing, indicative of different tear processes, are described. Experimental results for natural rubber and GR‐S gum vulcanizates, obtained over a wide range of temperature and rate of propagation, are given to illustrate the method. The results indicate that the nature of the tear process and the resistance to tearing, as represented by the energy required to propagate a tear, can change appreciably with the rate of propagation and the temperature. The significance of these changes is discussed.
The structure of neoprene. VIII. Effect of polymerization temperature on polymer properties
Authors: Maynard J. T. , Mochel W. E. 
Published: April 2003

AbstractThe chemical and physical properties of polychloroprenes made at temperatures ranging from −60 to +200°C. are discussed in the light of knowledge of structure gained from analysis of their crystallization behavior and infrared absorption spectra. The properties of polychloroprenes made below 0°C. are shown to be dominated by the preponderance of trans‐2‐chloro‐2‐butenylene units in their structure, e.g., they are highly crystalline and relatively unreactive. Polychloroprenes made at 10–90°C. show typical elastomeric properties and the chemical reactivity expected from the presence of a higher proportion of the allylic chloride units that result from 1,2‐polymerization. Polychloroprenes made at temperatures over 100°C. contain an even higher proportion of 1,2‐units and hence are unstable chemically. They are generally obtained as crosslinked gels. Chloroprene polymers made by ionic initiation are found to be chemically unstable, low molecular gums or resins. Their structure remains to be elucidated.
Polyvinyl alcohol gelling systems. I. Congo red and related dyes
Authors: Dittmar C. , Priest W. J. 
Published: April 2003

AbstractAzo dyes of the Congo Red type are known to be amount the most effective gelling agents for polyvinyl alcohol. It has been shown by means of measurements of dilute solution viscosities that all of the dyes effective as gelling agents associate strongly with polyvinyl alcohol, as well as other hydroxylated water‐soluble polymers. This association is not, however, a sufficient condition for the promotion of gelation. Measurements of gel properties of aqueous systems consisting of polyvinyl alcohol and Congo Red or other related dyes have been made. From these measurements it has been possible to draw some conclusions pertaining to the nature of the crosslinks which contribute to the gel structure.
Crystallization in natural rubber. IV. Temperature dependence
Authors: Gent A. N. 
Published: April 2003

AbstractExperiments are described in which the temperature dependence of crystallization in natural rubber, unvulcanized and vulcanized by a peroxide, was investigated dilatometrically over the temperature range −37 to 0°C. Avrami type time functions describe the progress of crystallization to a first approximation. The numerical parameters indicate the growth of spherical crystal structures from nuclei which appear randomly at a constant rate in a purified rubber. It is shown that classical nucleation theory describes the temperature dependence to a first approximation. The retardation of crystallization caused by the introduction of crosslinks is ascribed partly to a reduction in chain segment mobility and partly to the prohibition of crystal nucleus formation around each crosslink. Crystal nucleation appears to be promoted in plantation smoked sheet rubber by the nonrubber constituents at temperatures below 0°C.
Studies on the mechanism of mastication of rubber. IX. Scission of squalene molecule with benzoate free radical
Authors: Imoto Minoru , Kiriyama Shigeru 
Published: April 2003

AbstractSqualene was treated with benzoyl peroxide and isoprene‐dialcohol dibenzoate was isolated. It is now proved for the first time that the molecule of polyisoprene was decomposed by a free radical and the location of the scission was the CH2CH2 linkage.
Formation of spherulitic structure in polyhexamethylene adipamide (66 nylon). I. Structure and optical properties of spherulites at room temperature
Authors: Barriault R. J. , Gronholz L. F. 
Published: April 2003

AbstractIt is found in studies with the polarizing microscope that 66 nylon spherulites form readily at temperatures near the melting point and grow until they are stopped by the presence of other spherulites. They possess a radially positive birefringence of approximately 0.01. X‐ray diffraction studies confirm conclusions, drawn from the birefringence results, that the polymer chains are oriented approximately in the tangential plane and that the hydrogen bonds are oriented approximately along the radii. Spherulites are composed of the same type of crystallites as nonspherulitic, crystalline regions of the polymer. The formation of the “transcrystalline” region on the surface of the polymer in the temperature range where spherulites form has been observed at the interface between nylon and a wide variety of other substances. This is taken as evidence that spherulite nuclei form more readily on the surface than inside of the polymer. It is decided, on the basis of x‐ray melting point studies, that the true thermodynamic melting point of 66 nylon must be higher than the normally accepted fusion temperature. From the shapes of interfaces between spherulites, it is concluded that the radial growth rate is constant for any isotherm.
The relationship between the dielectric constant and water‐vapor accessibility of cellulose
Authors: Kane Daniel E. 
Published: April 2003

AbstractThe relationship between the water‐vapor accessibility of cellulose and its dielectric constant at 10,000 cycles per second and 30°C. has been examined. Six different celluloses were studied. These included a cotton linters, a hydrolyzed cellulose, two regenerated celluloses, and two bleached wood pulps. In the accessibility range between 35 and 85%, the relationship appears to be very nearly linear. The maximum deviation of the experimental dielectric constant values from the least squares regression line is 0.1. Extrapolation of this relationship indicates that the dielectric constant of accessible cellulose is about 9, while that of inaccessible cellulose is about 4. The dielectric constant of the cellulose can then be thought of as that of a two‐component system, one component the accessible fraction and the other the inaccessible fraction. A slight increase in the dielectric constant of cellulose was brought about by drying the cellulose by a solvent replacement method rather than from water. This increase could be explained by density changes in the cellulose.
Vinyl esters of perfluoro acids
Authors: Reid Thomas S. , Codding Donald W. , Bovey Frank A. 
Published: April 2003

AbstractA series of seven vinyl esters of perfluoro acids has been prepared by the mercury catalyzed reaction of the acids with acetylene. Certain physical properties of the monomers are given. Homopolymers gave clear, flexible films with the exception of vinyl caprylate and caprate, which formed waxy films. Copolymerization of vinyl perfluorobutyrate proceeded readily with vinyl acetate and methyl methacrylate, but less readily with styrene, maleic anhydride, and acrylonitrile.
Base accelerated degradation of polyvinyl chloride
Authors: Campbell John E. , Rauscher William H. 
Published: April 2003

AbstractThe degradation at 150°C. of polyvinyl chloride in the presence of base is studied by means of ultraviolet, visible, and infrared spectra. The reaction of polyvinyl chloridebase systems at 150°C. is viewed as a base accelerated dehydrochlorination of polyvinyl chloride proceeding through initiation, propagation, and termination phases. Polyene units with sixteen double bonds in conjugation are considered to be the most probable component of polyene structures contributing to the longest wave length absorption maxima recorded at 550 mμu. Dichroism to polarized light is observed in a plasticized, oriented, base degraded polyvinyl chloride film. This dichroism is considered a confirmation of the assigned polyene structure. The infrared spectra obtained reveal the development, as the reaction progresses, of conjugated carbon‐carbon double bonds, conjugated carbonyl groups, bonded hydroxyl groups such as from hydroperoxides and/or alcohols, and the eventual formation of carboxyl groups. The mechanism of the oxidative degradation at 150°C. is attributed to the attack, after dehydrohalogenation, by molecular oxygen at the olefinic double bonds to form peroxide radicals which by radical chain transfer yield hydroperoxides that degrade to carbonyl containing products.
Monomer reactivity ratios in a model unsaturated polyester system
Authors: Gordon Manfred , Grieveson Brian M. , McMillan Ian D. 
Published: April 2003

AbstractMonomer reactivity ratios for the system polyethylene fumarate/methyl methacrylate have been determined. The experimental methods used in measuring these ratios for simple linear systems had to be severely modified. While the technique evolved does not give results of great accuracy, the ratios obtained are in agreement with those expected from consideration of the radicals involved. Ethylene fumarate polymers have been characterized in several different ways, and it was shown that, although prepared from maleic anhydride, substantial conversion to the isomeric fumarate form had occurred.
Organopolysiloxanes containing group IV organometallic substituents in the side chains
Authors: Seyferth Dietmar , Rochow Eugene G. 
Published: April 2003

AbstractIn an attempt to increase the intermolecular attraction between polyorganosiloxane chains and rings, polar groups have been introduced into methyl groups attached to the silicon atoms. To avoid the usual weakening of the CSi bond by negative polar substituents, positive substituents of the type (CH3)3M (where M is Si, Ge, or Sn) were employed in this study. Cyclic trimers and extended linear polymers were prepared, both from the pure polar‐substituted monomers and from mixtures of these monomers with octamethyltetrasiloxane. Intermolecular attraction was estimated by measuring viscositities and activation energies of viscous flow. The preparations also were compared in these respects with pure dimethylsiloxanes and with neopentylsiloxanes. The results show that intermolecular attraction is increased by the positive polar substitutents, and that the CSi bond is rendered more stable toward OH− attack by such positive substituents than by negative. More detailed analysis indicates that the effects of the groups on the viscosity of the polymers depends on: (1) the dipole attraction of the polar groups, (2) the bulk or steric effect of the enlarged group, and (3) the effect of the metal M upon the ease of rotation of the methyl groups (the characteristically free intramolecular motion of silicon polymers). The trends of these effects oppose each other in the CSiGeSn series, and so limit the observed increase of viscosity.
Disulfide interchange in polysulfide polymers
Authors: Bertozzi E. R. , Davis F. O. , Fettes E. M. 
Published: April 2003

AbstractA study has been made on the effect of thiols and disulfides on lowering the molecular weight of polysulfide polymers. It was shown that in the presence of aqueous sodium disulfide there is an interchange of chain segments. This effect is observable if a simple organic disulfide is present in the system, resulting in a lower molecular weight. Co‐polymers can be prepared by heating together in the presence of sodium disulfide, aqueous dispersions of two different polysulfide polymers. When thiols are present in the system, interchange of disulfide groups occurs in the absence of sodium disulfide. The results show that disulfide/disulfide redistribution and thiol/disulfide interchange take place in polysulfide polymers. The occurrence of these same reactions has recently been recognized by workers in the biochemical field. A literature survey of thiol/disulfide reactions showed that results formerly attributed to oxidation/reduction reactions could be also explained by an interchange mechanism.
The incorporation of aroyloxy radicals in polymer molecules
Authors: Dannley Ralph L. , Kay Edward L. 
Published: April 2003

AbstractInitiation of the bulk polymerization of samples of 2‐vinylpyridine with N‐nitroso‐N‐phenyl‐m‐bromobenzamide and N‐nitroso‐p‐bromoacetanilide gave polymers containing 0.06% and 0.52% bromine, respectively. Therefore, the aroyloxy radical is only about one‐eight as reactive as the aryl radical for incorporation in a polymer molecule. This is a rough comparison, for there is no data upon which to base an estimate of the influence of the halogen substituent upon the reactivity of the parent free radicals. The purification of the polymers included an ether extraction of an acid solution of the substances to insure removal of all initiator fragments not attached to the polymer molecules. The presence of aroyloxy radicals in the polymers does not give assurance, however, that they were introduced in the step of chain initiation or even in the original polymerization process. For example, treatment of polystyrene with p‐chlorobenzoyl peroxide was found to introduce 0.60% chlorine which through saponification proved to be a minimum of 96% chlorobenzoyloxy groups. Therefore, it seems highly probable that, when nitrosoamides are used as catalysts, aryl radicals may serve exclusively as chain initiators while a much smaller quantity of aroyloxy groups are incorporated by other mechanisms.
A comparison of the propagation of longitudinal waves in rods of viscoelastic materials
Authors: Lee E. H. , Morrison J. A. 
Published: April 2003

AbstractThe stress and velocity distributions associated with the propagation of an impulsively applied velocity and stress along rods of viscoelastic materials are presented. Various viscoelastic materials are considered of complexity up to that represented by a four element model which exhibits a combination of instantaneous elastic response, delayed elastic response, and permanent viscous flow. The solutions are compared to determine under what circumstances the mathematically simpler solutions comprise an adequate approximation to the more complicated ones, to provide a guide to the choice of analysis in treating such dynamic stress analysis problems in viscoelastic bodies.