bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study of the viscoelastic behavior and molecular weight distribution of polyisobutylene
Authors: Van Holde Kensal E. , Williams J. W. 
Published: April 2003

AbstractA study is made of the behavior under constant shear stress of several carefully characterized samples of polyisobutylene. The materials used are whole polymers and fractions obtained from these by dractional precipitation. As a first step in the characterization, the intrinsic viscosity of each is determined. It is shown that the samples cover a molecular weight range from 1 × 105 to 1 × 106. To provide a more detailed characterization, sedimentation equilibrium experiments are performed with several of the polyisobutylenes. These experiments yield values of several average molecular weights for each polymer, from which data an approximation to the molecular weight distribution can be made. It is pointed out that the whole polymers of isobutylene are very polydisperse. The viscosity‐average molecular weights calculated from these experiments are in good agreement with the results of the intrinsic viscosity measurements. The viscoelastic behavior of some of these polymers is then studied by means of creep and recovery experiments. The melt viscosity is determined in two ways, from flow during creep and from the amount of nonrecoverable deformation after elastic recovery. The elastic recovery of the polyisobutylene samples is analyzed in some detail. A method for the reduction of data taken at several temperatures to a standard temperature, previously used for dynamic‐mechanical properties and stress relaxation data, is shown to be applicable to elastic recovery data. Furthermore, the results of creep and recovery experiments can be superimposed in favorable cases. The steady‐state elastic compliance is evaluated, and errors in its determination discussed. The results would seem to indicate that this quantity depends, at least in part, upon the degree of polydispersity of the polymer. This dependence appears to mask any direct variation with average molecular weight. Finally, it is shown that an average retardation time is directly proportional to the melt viscosity of the polymer.
Quantum‐mechanical discussion of the gas‐phase formation of quinonedimethide monomers
Authors: Hush N. S. 
Published: April 2003

AbstractThe formation of quinonedimethide monomers by pyrolysis of the corresponding dimethyl hydrocarbons has been described by Szwarc in a number of publications. Under certain conditions, the monomers so produced may polymerize to high molecular weight products which are of considerable interest. Some dimethylated hydrocarbons do not, however, appear to from monomers under these conditions, and the products of pyrolysis vary considerably with hydrocarbons of different structure. In this communication, the energetics of the various reactions leading to formation of radicals, quinonedimethide monomers, and products of their dimerization or disproportionation are briefly discussed theoretically. The kinetics of the most probable reaction sequences are discussed in the light of the energetic data, and it is shown that a number of features of results so far obtained can be understood in terms of this preliminary treatment. It is hoped that this approach will prove useful as a guide to the types of reactions to be expected for aromatic hydrocarbons of differing π‐electron structure.
Thermal degradation of vinyl polymers in solution. I. Degradation of polystyrene in naphthalene solution
Authors: Jellinek H. H. G. , Turner K. J. 
Published: April 2003

AbstractThe thermal degradation of polystyrene has been studied in naphthalene solutions in high vacuum. The rates of loss of weight have been determined over a range of temperatures from 350 to 380°C., and the energy of activation has been derived. Also the decrease in intrinsic viscosity with time and the loss of weight as function of polymer concentration have been investigated. The mechanism of degradation in naphthalene solution is similar to that of the thermal bulk degradation; it consists of an initial random chain scission process due to weak links, followed by a reverse polymerization process with chain end initiation.
X‐ray small angle scattering of ramie and rayons
Authors: Heikens D. , Hermans P. H. , Van Velden P. F. , Weidinger A. 
Published: April 2003

AbstractThe small angle scattering of ramie and of 25 highly oriented rayon samples of widely different prehistory has been examined in both the air‐dry and the water‐swollen condition with monochromatic radiation in a vacuum camera. All intensity curves are given. For some rayons the curves show distinct maxima or inflection points in either the swollen or the dry condition which seem to be indicative of the existence of a maximum of relatively low intensity superimposed on a normally descending small angle intensity curve. The Bragg spacing corresponding to these maxima lies close to 80 A. for the swollen and to 50 A. for the dry fibers. Other specimens either do not show these superimposed maxima or show only faint indications of their occurrence. The existence of maxima (particularly pronounced in Fortisan, Fiber G, Super Cordura, and Celanese K 36) seems to demonstrate that in some rayons a part of the fiber substance has a micellar structure of unexpectedly high regularity and with average interparticle distances given by the Bragg spacings indicated. The intensity curves of those swollen specimens which did not exhibit a maximum, when evaluated by the Guinier method for dilute systems, assuming parallel cylinders as the basic structure, yield figures between 35–55 A. for the diameter of the cylinders. Evaluation of the intensity curves according to an approximation suggested by Kratky (based on the picture of closely packed lamellae) points to the existence of a preferred spacing of the same order of magnitude (∼40 A.) for the dry and of ∼60 A. for the swollen fibers. No clear correlation between small angle scattering features and other known properties of the rayons has been detected.
A simple and inexpensive osmometer. The molecular weight of 1:3 vinyltoluene‐styrene copolymer fractions
Authors: Mock Richard A. , Marshall Charles A. , Floria V. Deane , Sanders John W. 
Published: April 2003

AbstractA simple and inexpensive instrument for measuring the osmotic pressure of polymer solutions has been designed. It consists of two 1‐mm. I. D. Pyrex capillary tubes sealed into a flanged Pyrex sleeve, which is ground to fit snugly into a 19 × 60 mm. roundbased Alundum Thimble of medium porosity. A regenerated cellulose membrane is cast over the Alundum thimble, and the entire assembly is sealed in a test tube containing the polymer solution to be examined. This osmometer offers several unique advantages over others in current use. Its low cost and compact size permit inexpensive simultaneous measurement of many polymer solutions.A 1:3 copolymer of vinyltoluene and styrene monomers was separated into 24 cuts by fractional precipitation. On the basis of viscosity data these cuts were combined into 14 fractions. They were in the order of decreasing molecular weight, and infrared analysis indicated a uniform distribution of the ring methyl groups among the fractions. These two observations demonstrate that introduction of methyl groups into the benzene rings of a polystyrene molecule does not influence the polymer solubility appreciably.Osmotic molecular weights obtained with the Alundum thimble instruments and experimental limiting viscosity numbers gave values of 2.69 × 10−4 and 0.622 for K and α respectively in the Flory‐Staudinger relation [η] = KMα. These results compare favorably with reported values for polystyrene samples prepared under similar conditions.
The general theory of irreversible processes in solutions of macromolecules
Authors: Kirkwood John G. 
Published: April 2003

AbstractThe general theory of irreversible processes in solutions of macromolecules, previously formulated by the author, is reviewed. The theory is based upon the Oseen method for determining the perturbation in the hydrodynamic flow pattern produced by the frictional forces exerted by the macromolecule on the solvent, and on a generalized theory of Brownian motion in molecular configuration space. Applications of theory to viscoelastic behavior, flow birefringence, and the Kerr effect, and to dielectric dispersion are presented in outline.
Etude de la validité des lois fondamentales de la diffusion brownienne de translation et de rotation, de la viscosité et de la sedimentation des particules rigides de petites dimensions, en solution infiniment diluée
Authors: Donnet J. B. 
Published: April 2003

AbstractNous avons groupé dans cet article les principaux résultats d'un travail, dont le principe consiste à mesurer au microscope électronique les dimensions des particules colloïdales rigides utilisées comme modèles, puis à calculer à partir des dimensions la viscosité intrinsèque [η], les constantes de diffusion de translation Δ et de rotation D ainsi que la constante de sédimentation s. Ces paramètres calculés à l'aide des théories fondamentales sont ensuite comparés aux valeurs expérimentales mesurées par les techniques correspondantes et la comparaison des deux groupes de résultats doit permettre de juger de la validité des théories mises en jeu. Dans le calcul des valeurs théoriques nous avons tenu compte de la polydispersité et nous indiquons comment nous avons calculé les valeurs moyennes apparentes de \documentclass{article}\pagestyle{empty}\begin{document}$[\bar \eta ], {\rm \bar \Delta}, {\rm \bar D} $\end{document}. Les mesures de viscosité, de diffusion de translation et de sédimentation effectuées sur un sol de V2O5 donnent des résultats dont la comparaison avec les valeurs théoriques calculées à partir des dimensions n'est guère possible de manière quantitative en raison de l'imprécision de celles‐ci. Mais l'utilisation simultanée des valeurs expérimentales de [η], Δ, s, nous conduit à la conclusion que le sol de V2O5 se comporte comme un sol monodispersé d'ellipsoïdes de révolution rigides de 1692 Å de longueur et de 44 Å de diamètre, or 40,3% des particules de sol étudié ont pour dimensions 1607 Å de longueur et une section rectangulaire de 100 sur 50 Å. La détermination de D par birefringence d'écoulement conduit à un désaccord considérable avec la valeur calculée de D̄ et ce désaccord semble dǔ à la présence dans le solvant d'acides vanadiques qui perturbent l'orientation des bǎtonnets. L'étude d'un sol de virus de la mosaïque du tabac a donné un bon accord entre la valeur calculée D̄ = 205 c.g.s. ± 20% et la valeur mesurée D = 260 c.g.s. ± 20% ce qui constitue la première vérification expérimentale de la théorie de Peterlin et Stuart. Cette étude a permis de calculer l'indice de réfraction de la particule de V.M.T., on trouve n1 = 1,58, n2 = 1,59, ce qui corrobore les valeurs trouvées par d'autres employant des méthodes indirectes. Enfin l'étude d'un sol aqueux de noir de carbone a permis d'observer un accord convenable entre \documentclass{article}\pagestyle{empty}\begin{document}$ \bar \Delta $\end{document} calculé = 1,10 · 10−7 c.g.s. ± 15% et Δ mesuré = 1,37 · 10−7 c.g.s. ± 10%, ce qui montre la validité de la loi de Stokes pour des sphères dont le diamètre est de l'ordre de 1 à 200 Å. Ce sol présente d'autre part de l'effet électro‐visqueux et la constante d'Einstein K = 2,5 est trouvée égale à K = 7,8 ± 0,5. On donne quelques résultats concernant l'étude de l'effet électro‐visqueux de ce sol.
Thermodynamic properties of polystyrene solutions
Authors: Bawn C. E. H. , Wajid M. A. 
Published: April 2003

AbstractMeasurements have been made of the osmotic pressure of polystyrene fractions in toluene and methyl ethyl ketone at 25, 50, and 55°. The results can be accurately represented by the equation:

The virial coefficients have been evaluated and it is shown in agreement with theory that A2αM−ε where ε = 0.15 or 0.33 according to method of derivation of A2. The results are compared, and shown to be in general agreement with other reported measurements. The heat of dilution of polystyrene in toluene and methyl ethyl ketone was determined from measurements of the temperature coefficient of the osmotic pressure. In the concentration range 3 to 9 × 10−3 g./cc. ΔH/ϕ where ϕ2 is the volume fraction of polymer was approximately zero in toluene and −20 ± 5 cal./mole in methyl ethyl ketone. In part III vapor pressure measurement of polystyrene fractions in acetone, chloroform, and propyl acetate solutions are summarized and the heat of dilution in these solvents derived. The results are discussed in relation to existing theories of the free energy and entropy of dilution of polymers and it is shown that the results cannot be explained in terms of theories based on the lattice model of solutions.
Solution properties of polystyrene prepared under high pressure
Authors: Trementozzi Q. A. , Buchdahl R. 
Published: April 2003

AbstractThe molecular weight, the size, and the second virial coefficient have been determined for a series of styrene polymers prepared under high pressure (0 to 4000 atmospheres) using light scattering techniques. The intrinsic viscosity–molecular weight relationship, the size–molecular weight relationship, and the magnitude of the second virial coefficient reveal no significant differences when compared to similar data of regular polystyrene. Structural differences due to the method of polymerization do not exist to the extent that they can be revealed by such measurements.
Effect of salts on the interaction of nucleic acid particles
Authors: Conway B. E. , Butler J. A. V. 
Published: April 2003

AbstractThe finding of Pouyet and Sadron that, at extreme dilutions of thymonucleic acid, the specific viscosity at low shear rates is either unaffected or only slightly affected by salts is confirmed with two samples prepared in different ways. The specific viscosity in these solutions increases considerably above the limiting value at very low concentrations and is then markedly sensitive to the presence of salts even at very small concentrations of the latter. The rapid increase of the specific viscosity with increasing concentration must be due to increasing interaction between the particles, and as these interactions are sensitive to small salt concentrations they must be electrostatic in nature. It is suggested that they arise from the Debye‐Hückel forces between the particles and their counter ions. When no added salt is present the counter ions can only complete their ion atmospheres by interacting with two of the polyelectrolyte particles and this will give rise to interactions between the particles, which will be greatly reduced by even small concentrations of added electrolytes. Interactions of this type will vary in strength according to the distances of the interacting charges and may be so weak that the shearing stresses can over come them. This will produce the high shear dependence observed in solutions of this kind. The differences between the behaviour of deoxyribonucleic acid and various synthetic polyelectrolytes which have been studied may arise from the fact that in the former the charges are carried by the “backbone” of the fiber and in the latter on side chains which are capable of rotation.
The preparation and properties of some gelatin fractions
Authors: Stainsby G. , Saunders P. R. , Ward A. G. 
Published: April 2003

AbstractA method for fractionating gelatin based on the solubility behavior of gelatin/detergent complexes is described. The method is practical and convenient both for determining molecular weight distributions and for preparing gelatin fractions. It is shown that fractions of equal reduced viscosity, and hence molecular weight, derived from gelatins of similar isoelectric points may still differ in important respects, thus confirming the conclusions of Pouradier and Venet, who prepared fractions by a different method of fractionation. It is established that the rigidity of gels formed from the gelatin fractions is independent of molecular weight, at least at 5.5 g./100 ml. concentration. There is some indication that, for the lowest molecular weight fraction, a slight variation of rigidity with molecular weight is occurring. Some other structural feature, at present unidentified, must be associated with the mechanism of gel formation.
Ultracentrifuge studies with a synthetic boundary cell. I. General applications
Authors: Schachman H. K. , Harrington W. F. 
Published: April 2003

AbstractThis report presents some general applications of a new type of ultracentrifuge cell, called a synthetic boundary cell, in which a sharp, stable boundary is obtained by layering one solution over another more dense solution while the ultracentrifuge is in operation. Since such a boundary between a solvent and a dilute solution of a low molecular weight solute can be formed in the center of the cell, the complications encountered at the meniscus in conventional ultracentrifugation by the high diffusion and low sedimentation rate of the solute are obviated. By this technique the sedimentation velocity method has been extended to substances with molecular weights as low as 350. Sedimentation constants of a number of low molecular weight materials such as fraction A of insulin (molecular weight 3000), vitamin B12 (molecular weight about 1500), β‐dextrin (molecular weight 1134), and sucrose (molecular weight 342) have been determined. The cell has also been used to form a boundary between solutions of two different concentrations of the same macromolecule and differential sedimentation constants have been obtained. The relationship between these differential sedimentation constants and those obtained for either of the two solutions when studied alone is discussed. Application of the cell to the determination of hydrodynamic volumes of sedimenting components is described. Measurements are made of the backward flow of solvent by the use of an indicator boundary formed by layering a virus solution over another virus solution containing an additional component, such as sucrose or a protein, which acts as an indicator. In addition, the cell was used in a preliminary investigation of some fundamental problems in ultracentrifugation such as the sedimentation of slowly sedimenting materials in the presence of more rapidly sedimenting components, the analysis of equilibrium systems such as insulin and chymotrypsin, and the role of convection.
Ultracentrifugation of bacterial viruses
Authors: Putnam Frank W. 
Published: April 2003

AbstractThe bacteriophages (bacterial viruses) are the largest biologically active agents having known dimensions and particle morphology which have been prepared in a homogeneous state. Because all the bacteriophages have an appendage or “tail”, they offer an interesting system for study in the analytical ultracentrifuge in comparison of the results of direct and indirect methods for estimation of particle size and shape. The sedimentation behavior of phages T5, T6, and T7, all differing in size and morphology, has thus been investigated. Although, under certain conditions, the three viruses sediment with a single sharp boundary, T6 appears to undergo aggregation to form a dimer at neutral pH. The sedimentation rate of the phages is little affected by concentration and is uninfluenced by the centrifugal field, thus indicating the absence of interaction or of particle orientation due to the peculiar morphology. A comparison of estimates of the particle size and weight based on molecular‐kinetic constants, electron micrograph dimensions, and unit infectivity yields a good correlation among the results of the direct and indirect physical methods for the quasispherical particle of T7, satisfactory agreement for the large tadpole‐shaped particle of T6, but considerable discrepancy for the sperm‐shaped particle of T5. It is suggested that the dimensions of T5 based on early electron micrographs are in error. Despite their large size and unusual shape the bacteriophages are amenable to physicochemical study, and each type is as uniform in molecular‐kinetic properties as are molecular proteins.
New types of membranes for osmotic pressure measurements
Authors: Immergut E. H. , Rollin S. , Salkind A. , Mark H. 
Published: April 2003

AbstractSemipermeable membranes used for osmotic pressure measurements are usually made from collodion or from regenerated cellulose or from other cellulosic materials. Such membranes are readily attacked by corrosive solvents, they are easily oxidized, and they can be used for only a few hours at high temperatures. To overcome these difficulties new noncellulosic membranes have been developed. The preparation of a polyvinyl butyral membrane and of a Kel‐F (polychlorotrifluoroethylene)membrane is described. The data for typical osmotic pressure measurements using the new membranes are presented. The Kel‐F membrane can be used for measurements in all common organic solvents as well as for solutions of cellulose in solvents such as cupriethylene diamine and cuprammonium hydroxide. It is also suitable for high‐temperature osmotic pressure measurements.
The synthesis of block copolymers in a flow system
Authors: Hicks J. A. , Melville H. W. 
Published: April 2003

AbstractA selected monomer containing a photosensitizer flows along a capillary at a defined rate into a suitable receiver. Very high concentrations of free radicals (up to 10−4mole/l.) are produced at a selected point by focusing into it a large proportion of the radiation from a capillary are lamp. These polymer radicals grow to a chain length determined by the time spent subsequently in the capillary and it has been demonstrated by a utilization of the theory of the nonstationary phase in chain reactions that most of the radicals can be introduced into a second monomer contained in the receiver. That their continued growth in the new environment leads to the synthesis of block copolymer has been proved by examination of the ultraviolet spectra of the products.
A new method for the determination of the rate of initiation in radical polymerizations
Authors: Bevington J. C. , Bradbury J. H. , Burnett G. M. 
Published: April 2003

AbstractIn a radical polymerization in which initiation is solely by the addition of an initiator fragment to a monomer molecule, there must be in the polymer one combined initiator fragment for each kinetic chain; analysis of the polymer therefore can lead to a determination of the kinetic chain length. The rate of initiation is equal to the over‐all rate of polymerization divided by the kinetic chain length, and so it can be calculated. This new method for calculating rates of initiation is not subject to the uncertainties associated with older methods. Analysis for initiator fragments can be performed accurately if the initiator is labeled with a radioactive isotope; in the work described here C14‐α,α′‐azo‐bis‐isobutyronitrile was used. An essential requirement is that the polymer molecules of low molecular weight must not be lost during precipitation of the polymer. Tests are described showing that loss of low molecular weight materials is negligible in most cases and that even when the average molecular weight of the polymer is low and there is an appreciable loss a correction can be made. A correction can also be made for the consumption of initiator during the reaction. The results presented in this paper refer to the copolymerization of butyl acrylate and styrene in benzene solution at 60°. It is shown that for a given monomer mixture the rate of initiation is proportional to the concentration of initiator, and that for each initiator molecule decomposed approximately one reaction chain is started.