bluuebunny/crossref_metadata_2025_split huggingface dataset:
The fine structure of polytetrafluoroethylene
Authors: Bunn C. W. , Cobbold A. J. , Palmer R. P. 
Published: April 2003

AbstractElectron micrographs of highly crystalline PTFE crystallized by slow cooling from temperatures not far above the melting point show well‐marked bands, often with striations perpendicular to the bands; optical evidence shows that the chain molecules are parallel to the striations. The structure is in marked contrast to the spherulitic structure of most polymers; it appears that in PTFE the molecules are straight and parallel for much greater distances than in other polymers, and it is suggested that the width of the bands is a measure of molecular length. The unusual structure is attributed to the unusual stiffness of the fluorocarbon chain; the molecules in the liquid are straighter and less tangled than in other polymer melts. Heating to 500°C., followed by slow cooling, gives a modified structure approaching the spherulitic type found in other polymers; it is suggested that this is due to increased molecular tangling in the melt at higher temperatures. One type of polymer shows bands of remarkably uniform thickness, suggesting unexpected uniformity of molecular length. PTFE wax made by thermal or radiation degradation of the high polymer shows well‐defined spiral growth steps due to dislocations; the step heights suggest an unexpected uniformity of molecular length.
Solvation of polyvinyl alcohol in solvent–nonsolvent mixtures
Authors: Levi D. W. , Scherer P. C. , Hunter W. L. , Washimi K. 
Published: April 2003

AbstractThe sorption of solvent and nonsolvent by polyvinyl alcohol from water–acetone and water–n‐propanol mixtures was measured by using the dipping refractometer to follow changes in concentration of the liquid phase. Beyond about 15% acetone no selective sorption was observed. The values calculated for n‐propanol and water sorbed are a function of the n‐propanol concentration of the equilibrium solvent.
Degradation of addition polymers by ultrasonic waves. III. Experimental
Authors: Mostafa M. A. K. 
Published: April 2003

AbstractThe degradation of an addition polymer sample (polystyrene) has been studied. In conformity with theory, the process of degradation does not proceed below a limiting chain length. A rate constant has been derived. The experimental size distributions of the polystyrene at different stages of the degradation have been determined and compared with their corresponding theoretical distributions. The experimental values of the number of broken links at the early stages of degradation have been determined photometrically and compared with their corresponding theoretical values as derived from the theory of ultrasonic degradation. Satisfactory agreement has been found between experiment and theory for the main features of the degradation.
Structure and mechanism of dehydrochlorination of polyvinyl chloride
Authors: Baum B. , Wartman L. H. 
Published: April 2003

AbstractPolyvinyl chloride when heated loses HCl, presumably by a “zipper” mechanism. The loss of each molecule of HCl from the polymer results in the formation of a double bond, which activates adjacent chlorine and causes the decomposition reaction to propagate along the resin chain. Virgin and degraded resins were subjected to ozonization in order to ascertain the type and location of the labile structures responsible for initiating the “zipper” HCl loss. The molecular weight decrease and formation of carbonyl structures (detected by infrared) produced by ozone indicate that unsaturated chain ends are primarily responsible for HCl loss. Tertiary chloride chain branches contribute to a lesser degree in the initial stages but become more important as dehydrochlorination proceeds. Stability measurements on simple prototypes of structures presumed to be present in polyvinyl chloride provide additional information which is in essential agreement with this mechanism.
Diffusion‐controlled stress relaxation in polymers. II. Stress relaxation in swollen polymers
Authors: Fujita Hiroshi , Kishimoto Akira 
Published: April 2003

AbstractStress relaxation in the systems PVAc (polyvinyl acetate)‐water, PVAc‐methanol, PMA (polymethyl acrylate)‐water, and PMA‐methanol was measured at several temperatures above the glass‐transition points of the pure polymers in ranges of sufficiently low concentrations of diluents. It was found that the time‐concentration superposition principle as proposed by Ferry is applied successfully to these data to obtain master relaxation curves of the pure polymers at fixed temperatures. The master relaxation curves so obtained at different temperatures were further superposed with each other by horizontal shift along the log time axis, in agreement with the time‐temperature superposition principle. The concentration shift factor ac as a function of diluent concentration C at fixed temperature was well interpreted in terms of the modified Doolittle's free volume equation for the viscosity of supercooled systems on the assumption that the fractional free volume of the system increases linearly with C. The proportionality coefficient, β, of this linear relation provides a measure of the plasticizing effect of a given diluent on a given polymer. It was found that β is practically independent of temperature at sufficiently small C and is larger for water than for methanol in both polymers studied. On the basis of Doolittle's viscosity equation modified to account for the concentration effect, it is shown that the glass‐transition temperature Tg of a given polymer‐diluent pair decreases with C in a linear fashion in the range of small C. The value of β can also be calculated from the slope of this linear relation. Values of β determined in terms of this procedure from literature data on a variety of polymer‐diluent pairs are given in a tabular form. For a given polymer the β values generally become smaller as the size of diluent molecule is increased, but no unique relation can be obtained between the two quantities. Equilibrium sorption and integral sorption processes were studied on the four pairs of polymer and diluent mentioned above, not only to obtain data needed for analyzing the present stress‐relaxation data but also to find information which will serve a study described in Part III of this series which is concerned with diffusion‐controlled stress‐relaxation in amorphous linear polymers. Some correlation (though not definite) appears to exist between the diffusion coefficient D (at zero concentration) and the plasticizing parameter β for a given polymer. This may be expected because both D and β are quantities depending on the frequency at which polymer segments jump cooperatively in the presence of a low molecular weight diluent.
An evaluation of molecular weight distribution in high pressure polyethylene
Authors: Mussa I.V. C. 
Published: April 2003

AbstractA particular kind of plot has been used, yielding graphs tending toward straight lines, to compare the fractionation and viscometry data of eight high pressure polyethylene samples with the distribution formula deduced by Beasley. These graphs are equivalent, except for an additive constant in the abscissas, to the log‐log plots of intrinsic viscosity versus molecular weights. In this way an evaluation of the distribution parameters defined by Beasley can be obtained for all the investigated samples. By means of these parameters and the absolute determination of the (number‐)average molecular weight of a single sample, an evaluation of all the molecular weights and of their distribution in the given samples has been proposed. Within the limits of experimental uncertainty of the measurements of high pressure polyethylene in diluted solutions, these results are in some agreement with the experimental findings of other authors.
Polymerization of p‐isopropenylstyrene
Authors: Dreyfuss P. , Notley N. T. 
Published: April 2003

Abstractp‐Isopropenylstyrene was synthesized and its polymerization characteristics are essentially the same as those of divinylbenzene. A soluble prepolymer can be separated from polymerization in a solvent having chain transfer properties but polymerization in bulk or in an inert solvent gives crosslinked infusible polymer.
Thermodynamic properties of dilute solutions of cellulose derivatives
Authors: Moore W. R. , Tidswell B. M. 
Published: April 2003

AbstractHeats and entropies of dilution of dilute solutions (concentration range 0.2–1.0 g./100 ml.) of cellulose acetate, ethyl cellulose, and cellulose nitrate, of similar degrees of substitution and polymerization, in a number of representative solvents, have been obtained from temperature coefficients of osmotic pressure. In some cases, degradation of polymer at the higher temperature used seems possible and an attempt is made to allow for this in the estimation of values of ΔH̄1 and ΔS̄1. Heats of dilution for the cellulose acetate and ethyl cellulose systems are generally endothermal, those for the cellulose nitrate systems being exothermal. Entropies of dilution are less than those obtained for comparable systems containing less polar and more flexible polymers. Those for the cellulose nitrate systems do not differ much from “ideal” values. The value of ΔH̄1/ϕ22, where ϕ2 is the volume fraction of polymer calculated from the density of the bare polymer, for each cellulose acetate system and most of the ethyl cellulose systems seems to be effectively independent of concentration. Values for the cellulose nitrate systems seems to be effectively independent of concentration. Values for the cellulose nitrate systems become less negative as the concentration increases. Values of ΔH̄1 for the cellulose acetate and ethyl cellulose systems are generally in the order to be expected from the solubility parameters of the solvents and polymers. ΔS̄1/ϕ22 may vary with concentration in a manner rather similar to that suggested by simpler lattice theories. These results are tentatively interpreted in terms of solvation of polymer and possible endothermal mixing of solvated polymer and solvent. Although values of the entropy contribution to the interaction parameter χ1 for the cellulose acetate and ethyl cellulose systems are not always inagreement with the predictions of simpler lattice theories it is possible, if solvation, segment size, and chain stiffness are allowed for, that the thermodynamic properties of dilute solutions of cellulose derivatives may be at least qualitatively interpreted in terms of such theories.
Behavior of human serum albumin in acid solution: Light scattering study
Authors: Sedláe K B. , Štokrová Š. 
Published: April 2003

AbstractThe behavior of human serum albumin in acid solutions containing chloride ions and in citrate and acetate buffers of pH 1 to 5 has been investigated by the method of light scattering. The reduced intensity of the scattered light was found to increase with decreasing pH: this change is most marked in acetate buffers, somewhat less marked in citrate, less again in the presence of higher concentrations of sodium chloride, and least in solutions of low ionic strength and in water. The phenomenon cannot be ascribed to the presence of lipoid substances alone: the possibility of complex formation must also be taken into account.
The charge and deformation of protein molecules
Authors: Pasynskii A. G. 
Published: April 2003

AbstractThe density of like‐charged groups distributed along the molecules of proteins is much lower than in molecules of polyelectrolytes. From this it follows that the degree of deformation of the protein molecules resulting from the charge is much less. In buffered solutions—if the correction for hydration (measured by the compressibility method) is taken into account—the shape of gelatin particles (as measured by viscosity) practically does not depend on the pH, while in unbuffered solutions it varies roughly in proportion to the fourth to fifth root of the number of charges. For molecules of serum albumin and egg albumin the deformation is proportional to the 25th to 30th root of the number of charges, i.e., completely negligible. This comparison also shows that the deformation of the threadlike molecules of gelatin occurs much more easily than with the firmly molecules of the globular proteins. For globular proteins the following expression has been derived

where E is the modulus of elasticity, n the number of charges inthe molecule, m the relative elongation of the molecule, a0, b0, and S the semi‐axes and surface of the ellipsoidal molecule and κ the reciprocal thickness of the ionic atmosphere. A value of E = 10–40 kg./mm.2 was calculated according to this relation for the molecules of these globular proteins (for soft rubber E = 0.14 kg./mm.2, for polyamides 70–80 kg./mm.2, for ebonite 50–80 kg./mm.2, etc.). These results for the first time quantitatively characterize the high rigidity of the molecules of globular proteins.
Propriétés diélectriques du bromure de polyvinyle en solution
Authors: Kryszewski Marian , Marchal Jean 
Published: April 2003

AbstractLe bromure de polyvinyle a été préparé par photopolymérisation et la masse moléculaire des fractions a été mesurée par diffusion de la lumière. Nous avons étudié l'absorption diélectrique pour comparer les variations des composantes du pouvoir inducteur spécifique de ce polyère en solution dans deux solvants en fonction de la fréquence du champ électrique comprise entre 1 et 32 MHz et de la température. Une étude analogue a été faite sur le chlorure de polyvinyle. Nous avons interprété les temps de relaxation et les énergies d'activation de ces deux polymères.
Zum verhalten von makromolekülen in lösung
Authors: Elias H.‐G. , Patat F. 
Published: April 2003

AbstractDie an 15 Polyvinylacetat‐Fraktionen in Butanon bei 25°C. durch Lichtstreuungs‐, Sedimentations‐, Diffusions‐, Osmose und Viskositäts‐Messungen gefundenen Beziehungen

(h = Fadenendenabstand) werden anhand der hydrodynamischen Theorien von Kirkwood‐Riseman, Kuhn‐Kuhn, Debye‐Bueche, Peterlin und Fox‐Flory diskutiert. Die experimentell bestimmten Fadenenden‐Abstände stimmen mit den aus Viskosität und Molekulargewicht nach den Theorien von Kuhn‐Kuhn, Peterlin und Fox‐Flory ausgezeichnet, nach Kirkwood‐Riseman noch innerhalb 10% überein, bei den nach Debye‐Bueche berechneten traten grössere Abweichungen auf. Die aus Sedimentation und Diffusion nach Kuhn‐Kuhn berechneten Fadenenden‐Abstände decken sich mit den experimentell aus Streulicht‐Messungen gefundenen, bei allen anderen Theorien treten mehr oder minder starke Abweichungen auf. Die gleichzeitige Gültigkeit von (1) und (2) wird durch einen mit dem Molekulargewicht abnehmenden hydrodynamischen Radius gedeutet. Die Unstimmigkeiten bei den einzelnen Theorien werden im Lichte dieser Anschauung diskutiert.
Polymer fractionation into summative fractions
Authors: Broda Andrzej , Gawronska Barbara , Niwinska Teresa , Połowinski Stefan 
Published: April 2003

AbstractThe problem of the systematic error of fractionation methods and its dependence on the selectivity of polymer separation are discussed. Comparisons of the results of a theoretical analysis and of an experimental fractionation by means of summative and of successive methods of fractionation are presented. For the purpose of comparing the polydispersity of polymers, the application of the method of fractionation into summative fractions alone is sufficient, since the results of this method depend only on the selectivity.
A thermistor ebulliometer for high molecular weight measurements
Authors: Lehrle R. S. , Majury T. G. 
Published: April 2003

AbstractMolecular weight studies on polyamides have necessitated the construction of an ebulliometer of greater sensitivity than any so far described. This has been achieved by the use of thermistors as the temperature‐sensitive elements; they are incorporated in a bridge circuit whose output is amplified and fed to a pen‐recorder. This apparatus affords a differential temperature sensitivity of better than 0.02 mdeg. Difficulties caused by some lack of reproducibility in readings taken at this sensitivity have been overcome by a design which enables repeated readings of the elevation of the boiling point of a given solution to be taken consecutively. This is achieved by mounting the thermistors in a tube which can be raised or lowered through a gland at the top of the ebulliometer. In the lowered position, one thermistor is at the temperature of the solution and the other at the temperature of the vapor as in normal practice; in the raised position both thermistors are at the temperature of the vapor. This arrangement enables the thermistors to be “zeroed” in the vapor phase after each determination of elevation so that difficulties such as those caused by overall drift can be eliminated. The design also enables the effects of superheating and the temperature gradient in the ebulliometer column to be examined. The instrument has been calibrated with substances of known molecular weight; assessment of the results indicates that values of molecular weights can be obtained having a probable error of less than 3%. Examples of preliminary work on the application of the apparatus to a study of N‐substituted polyamides are given.
Polymer association. IV. Hydrogen bonding and melt viscosities in copolymers of styrene with methacrylic acid
Authors: Longworth Ruskin , Morawetz Herbert 
Published: April 2003

AbstractMelt viscosities of styrene homopolymers and copolymers with 1.5 to 23 mole‐% methacrylic acid were measured with a parallel plate plastometer. Apparent viscosities were found to drop off sharply with increasing rate of shear in the range 10−4 to 10−1 sec.−1. An increasing concentration of carboxyl groups led to a pronounced increase in the melt viscosity and the activation energy for viscous flow. Infrared spectra of the copolymers were recorded while the samples were subjected to various thermal cycles. Equilibrium in the dimerization of carboxyl groups was established very rapidly above about 100°C., but the equilibrium was effectively frozen at lower temperatures. Samples as originally prepared by precipitation from dilute solution were further removed from equilibrium than samples quenched from high temperatures. The results are discussed in terms of the rate process theory of viscosity.
Kinetic effects of salts on vinyl polymerization in non‐aqueous systems
Authors: Bamford C. H. , Jenkins A. D. , Johnston R. 
Published: April 2003

AbstractThe polymerization of vinyl monomers in non‐aqueous solvents, such as N,N‐dimethylformamide, is influenced by a variety of inorganic salts, and both the cationic and anionic components of the salt may be active in this respect. Cations derived from metals possessing several valency states may terminate the kinetic chains by a one‐electron transfer process, e.g., with styrene

equation image

The kinetics of the polymerization of several monomers in the presence of ferric chloride have been worked out, and the absolute rate constants for the termination reactions calculated. Their magnitude is briefly discussed in terms of the structure of the radicals. It is pointed out that these reactions provide a very useful method of determining rates of initiation. Even cations such as lithium, which have only a single valency state, may have an effect on the kinetics of polymerization, for example in the case of acrylonitrile. This arises from association between the metal ions and the radicals which modifies the reactivity of the latter. The associated anions may also interact with radicals in a similar manner. This effect is particularly marked with chloride ions and acrylonitrile, and leads to an increase in the rate of propagation and chain transfer with electron accepting reagents such as carbon tetrabromide.
Polycondensations in the formation of catechin tannins and of lignin
Authors: Freudenberg K. 
Published: April 2003

AbstractCatechin tannins are formed by the action of protons on catechins, by condensation of the carbon atom from the ether bridge in the 2‐position with one of the phenyl rings of the next molecule. As the molecule is bi‐ or polyfunctional, the reaction can proceed further until it ceases, on account of the low solubility of the reaction product. Lignin is formed by dehydrogenation of p‐hydroxy‐cinnamic alcohols. The radicals produced stabilize themselves by combining, giving various types of dimeric products. These, too, are phenols and by virtue of further dehydrogenation, are subjected to a mixed condensation and, in part, to polymerization. In both cases, a highly irregular polymer molecule is formed from a single basic substance.
On the viscometry of poly‐6‐caproamide
Authors: Rybnikář F. 
Published: April 2003

AbstractIn the viscometric evaluation of poly‐6‐caproamide (6‐PA), the following effects were studied in detail: influence of water in tricresol, influence of molecular weight, and influence of temperature. The water present in the tricresol lowers the measured value of [η] proportionately to the water content. The value of K in the Huggins equation ηsp/c = [η] + K[η]2C remains constant within the limits of experimental errors. The value of K in the Huggins equation was found to be influenced significantly by molecular weight. For low values of [η], the constant K increases manyfold. The constant K was, therefore, replaced by a function which takes account of the increase of K due to the molecular weight:

where K1 = 0.26, K2 = 285.5, and x = 1.48. At higher temperatures, the measured value of [η] decreases, and the constant K in the Huggins equation remains constant within the limits of experimental error. The following equation was used to give the dependence of the viscosity of 6‐PA on temperature:

where the constant a is independent of [η], while b is a function of [η].
Effect of structure on polymerizability: Olefin polysulfone formation
Authors: Cook R. E. , Dainton F. S. , Ivin K. J. 
Published: April 2003

AbstractPolymerizability in the thermodynamic sense is measured by the free energy of polymerization. The effect of structure on polymerizability can be measured in two ways: (1) we may compare standard free energies (which are directly related to equilibrium monomer concentrations) at a given temperature; or (2) we may compare the temperatures at which the actual free energy changes are zero for a chosen monomer concentration. These temperatures are termed “ceiling temperatures” Tc and have been determined for the 1:1 copolymerization of sulfur dioxide S. with a wide variety of unsaturated compounds M, under the standard conditions [M] [S] = 27 mole2.1−2(binary mixture, mole fraction of M approximately 0.09). The polymers have the general formula
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Tc was determined by extrapolating the photochemical rate‐temperature relation to zero rate. In the straight chain 1‐olefin series Tc falls from ethylene (gt;135°) to propylene 90°, to butene‐1 64°, and thereafter remains approximately constant with increasing chain length. With 2‐olefins there is a progressive decrease from butene 34°, to pentene 8°, to heptene −38°. Branching invariably lowers Tc and the effect is greatest when the branching is at the double bond: thus isobutene 4°, 3‐methylbutene‐1 36°, 4,4‐dimethylpentene‐1 14°. 2‐Ethyl substitution of a 1‐olefin, or 2, 3 or 4 substitution of a 2‐olefin results in inability to react at any temperature down to −80°. Cyclic olefins have Tc considerably higher than the corresponding 2‐olefins: cyclopentene 102°, cyclohexene 24°. A number of allyl compounds have also been investigated. Tc is related to the heat and entropy of polymerization by the relation Tc = Delta;H/ΔS and in eight cases values of ΔH and ΔS have been obtained. A change of structure mainly affects ΔH. Estimated equilibrium monomer concentrations in polysulfone formation and in vinyl polymerization at 25°C. are summarized.