bluuebunny/crossref_metadata_2025_split huggingface dataset:
Contribution à l'étude des hauts polymeres par la viscosité des couches monomoléculaires
Authors: Jaffe J. , Loutz J. M. 
Published: April 2003

AbstractLes propriétés des couches monomoléculaires constituent un moyen d'investigation qui fournit des renseignements sur la grandeur de la molécule, sur sa morphologie e t parfois sur sa structure. C'est l'application de I'osmométrie superficielle qui conduit à la détermination de la masse nioléculaire de certaines macromolécules. De nombreux exemples montrent m e concordance avec les résultats classiques obtenus par d'autres procédés. Cette méthode a été employée avec succès surtout pour les protéines. En ce qui concerne les macromolécules de synthèse, on observe des résultats qui ne sont pas toujours en accord avec les données obtenues par les techniques hahituelles. En général, ces résultats sont moins concordants pour les macromolécules possédant une faible rigidité. Dans ce travail, nous prenons en considération deux cas: une macromolécule assez rigide, e t deux autres plus ou moins flexibles. Nous proposons m e nouvelle méthode dc détcrmination de la masse moléc:ulaire par la viscosimétrie superficielle. Cette méthotle envisage la transposition de l'équation de Staudinger dans l'espace à deux dimensions.
Neuere bestimmungen des molekulargewichtes und der molekularen konstanten von cellulosenitraten in lösung
Authors: Meyerhoff G. 
Published: April 2003

AbstractEs wurden die Sedimentations‐ und Diffusionskonstanten für zwölf Fraktionen und ein sehr hohes unfraktioniertes Präparat von nitrierter Baumwollcellulose untersucht. Der Stickstoffgehalt aller Präparate lag bei 13,8%. Für die Viskositätszahl in Aceton bei 20°C ergibt sich zum Ultrazentrifugenmolekulargewicht die Beziehung [η] = 2,8 × 10−3 M1.00S.D in cm3 g−1 beim Gradienten 0. Rechnet man die Ultrazentrifugenmessungen von Jullander auf unseren Stickstoffgehalt um und die Messungen von Newman, Loeb, Conrad in Aethylacetat auf Aceton, so zeigen die drei Ultrazentrifugenmessungen untereinander recht gute Uebereinstimmung. Dagegen liegen die Lichtstreuungsmolekulargewichte MLS bei gleicher Viskositätszahl druchweg höher, was vielleicht durch den Eichstandard oder auch durch nicht ganz reine Lösungen erklärt werden kann. Aus [η], M und dem Reibungsfaktor f werden nach Debye‐Bueche‐Peterlin die Knäueldurchmesser berechnet. Da MLS viel grösser als MS.D, ist, lassen sich die Knäuelradien als Funktion des Molekulargewichtes bei den verschiedenen Methoden nicht vergleichen. Jedoch stimmen bei gleicher Viskositätszahl die Knäueldurchmesser (r)1/2 der Lichtstreuung gut mit den berechneten überein. Es ergibt sich für alle Molekulargewichte, dass mit guter Näherung (r2) proportional M1,34 ist, an Stelle von M1,00 beim idealen Knäuel. Das sehr steife Cellulosemolekül zeigt also in Lösung ein nicht‐ideales Verhalten. Die Gleichung (r2) ∼ M gilt nicht, wir finden auch keinen Hinweis darauf, dass sie vielleicht noch als Grenzgesetz für extrem hohe, nicht mehr messbare Molekulargewichte erreicht wird. Es besteht für Cellulosenitrate ein ähnlicher Zusammenhang, wie er früher für Polymethacrylate in Aceton gefunden wurde, nur dass hier die Effekte ausgeprägter sind. Ein Exponent > 1/2 in der Viskositäts‐Molekulargewichtsbeziehung läuft parallel mit einem zweiten Virialkoeffizienten > 0 und einer Zunahme des Kuhn'‐schen statistischen Fadenelementes mit wachsendem Molekulargewicht.
Chemical effects in the irradiation of polymers in the solid state
Authors: Weiss J. 
Published: April 2003

AbstractThe action of ionizing radiations on polymers leads, in general, to degradation and, in certain cases, to some further polymerization (crosslinking). It is known, on general physical grounds, that the energy of the radiation is converted into ionization and excitation of the molecules present in the system. The question arises as to how the radiation‐produced primary species enter into the mechanism of the subsequent chemical processes. It is suggested that electronic processes are of considerable importance in the radiation‐induced reactions of solid polymers; this is discussed with reference to various physical and chemical data on irradiated polymers (radiation‐induced electrical conductivity, paramagnetic resonance, etc.). A unified picture for the mechanism of the action of ionizing radiations is proposed, based on the zone theory of solids.
Molecular distributions in polycondensations involving unlike reactants. II. Linear distributions
Authors: Case L. C. 
Published: April 2003

AbstractA general procedure is developed for the treatment of the molecular distributions arising from linear polycondensations involving more than one monomer. The distributions actually arising are rather complex, and are usually represented by several series. A method is elucidated by which the number average molecular weight may be derived directly and by which normalizing factors for the number and weight fraction distributions may be determined. The general expression for the number fraction of a given species of molecule is found to be a product of several probabilities. The weight fraction distribution and the weight average molecular weight may be derived in a straightforward manner from the number fraction distribution. A number of molecular distributions are worked out in detail. These include reactions of diacids with glycols, reactions of acid anhydrides with glycols, reactions involving asymmetric reactants, and reactions of mixtures of the above types of reactants. Certain polycondensations of interest are treated by the methods of this work. The results are the following: (1) The distribution of AB self‐condensing is identical to the condensation of AA with BB only if all have identical molecular weights and equivalent amounts of AA and BB are used. (2) In the condensation of AA with BB, the more unequal the proportions, the broader the molecular weight distribution. (3) In the above condensation, the greater the difference in molecular weights, the broader the distribution. (4) For all distributions, as M̄N → ∞ M̄W/M̄N → 2. (5) The distributions for anhydrides or unsymmetrical reactants are narrower than for symmetrical reactants, and are different from each other.
Freie radikale in fester phase
Authors: Breitenbach J. W. , Frittum H. 
Published: April 2003

AbstractRadikalbidende Substanzen, in festen Polymeren gelöst, geben unter geeigneten Reaktionsbedingungen freie Radikale, die in den hochpolymeren Substanzen verteilt sind. Bei der Reaktion zwischen Radikal und Polymeren werden Seitengruppen in dieses eingeführt und es tritt auch ein Kettenabbau des Polymeren ein. Bei Raumtemperatur ist die Reaktionsmöglichkeit der Radikale so stark herabgesetzt, dass es gelingt die Radikale durch längere Zeit in dem Polymeren zu konservieren.
Influence of the solvent on the polymerization velocity of trifluorochloroethylene
Authors: Lazár M. 
Published: April 2003

AbstractThe influence of carbon tetrachloride, pentachloroethane, 1,2‐dichloroethane, 1,1,2‐trifluorotrichloroethane, benzene, and 1,3,5‐trimethylbenzene on the velocity of the benzoyl peroxide‐initiated polymerization of trifluorochloroethylene was studied over a wide range of concentrations. Throughout the entire range of variation of concentration of trifluorochloroethylene, there was no simple relation between concentration and velocity of polymerization; the solvents in these systems did not behave merely as diluents. The influence of the solvents on the polymerization velocity of trifluorochloroethylene varies greatly: some solvents behave as an inert medium for example, 1,1,2‐trifluorochlorethane, benzene; other solvents, however, act as inhibitors 1,3,5‐trimethylbenzene. Finally, certain chlorinated hydrocarbons carbon tetrachlorides, pentachloroethane, 1,2‐dichloroethane show a maximum in the reaction velocity at a certain ratio to the monomer. Various possible hypotheses are discussed which could explain the observed anomalous dependence of increased polymerization velocity, on a lowering of the concentration of trifluorochloroethylene.
Chain transfer of polymer in radical polymerization
Authors: Lím D. , Wichterle O. 
Published: April 2003

AbstractChain transfer with polymethylacrylate was determined by measuring chain transfer constants with model substances resembling part of polymer chain with P = 1–3 and extrapolating to higher P. The found value, 5 × 10−5, is much less than expected for an explanation of gel formation in the polymerization of methyl acrylate.
Une méthode nouvelle de synthese de la polyvinylamine
Authors: Hart R. 
Published: April 2003

AbstractLa polyvinylamine a été obtenue par solvolyse des poly‐N‐vinylcarbamates dont la préparation et les propriétés ont été décrites dans une étude antérieure [Bull. soc. chim. Belges, 66, 229 (1957)]. La polyvinylamine peut ainsi être synthétisée à partir de l'acide acrylique:
magnified image
La solvolyse des esters de l'acide poly‐N‐vinylcarbamique peut être effectuée soit en milieu aqueux (hydrolyse acide ou alcaline), soit en milieu anhydre (HBr ou HCl dans l'acide acétique glacial). Une polyvinylamine pratiquement pure est obtenue lorsque le poly‐N‐vinylcarbamate de benzyle est traité par l'acide bromhydrique dans l'acide acétique, a température ordinaire. La structure des polymères ainsi préparés est établie par l'analyse élémentaire, la détermination de la teneur en groupes amines primaires (méthode de Van Slyke), ainsi que par des titrations potentiométriques et conductimétriques. Tous ces résultats sont concordants. LEs courbes viscosimétriques présentent l'allure caractéristique des polyélectrolytes.
Principles of protein structure and their application to synthetic polypeptides and fibrous proteins
Authors: Huggins Maurice L. 
Published: April 2003

AbstractThe principles of protein structure may be stated as follows: (1) Proteins are composed primarily of long polypeptide chain molecules. (2) In natural proteins, only levo orientations are present. (3) The distances between adjacent bonded atoms and the angles between adjacent bonds are approximately the same as in comparable small molecules. (4) Hydrogen bonds are formed wherever possible. (5) Like atomic groups tend to be surrounded by close neighbors in a like manner. (6) Atoms, atomic groups, and molecules tend to pack as closely as possible. These principles, first published by the writer in 1943, have been amply verified by subsequent developments. Their application is illustrated by brief consideration of the structures of silk, polyglycine II, α‐ and β‐polypeptides, α‐ and β‐keratin, and collagen. It is proposed that in α‐keratin the polypeptide helices are grouped (not coiled) into triplets, triple‐triplets or “nonets,” and 27‐chain groups, to give most efficient packing of the side chains. For collagen, a single chain helical molecule is proposed, with hydrogen bonds forming 10‐atom rings and with the residues in groups of three. One residue of each group, it is suggested, is pro, hypro, asp, or glu, with the last two types existing as rings, formed either by condensation or by hydrogen‐bonding.
Some properties of enzymatically produced polynucleotides
Authors: Steiner R. F. , Beers R. F. 
Published: April 2003

AbstractPolymers of adenylic and uridylic acids have been prepared from the monomers by the action of an enzyme isolated from the bacteria M. lysodéikticus. Polyadenylic acid has been found to undergo an interesting structural change in the vicinity of pH 6. This is reflected by a marked contraction of the molecule, as observed by light scattering and sedimentation, and a pronounced drop in ultraviolet extinction at λ = 257 mµ. The structural and optical transitions may be eliminated by formaldehyde treatment or by the addition of calcium ions. By direct titration it has been found that these effects reflect the titration of the adenine group and probably its subsequent electrostatic pairing with a negatively charged phosphate. The molecular interaction of polyadenylic and polyuridylic acids to form a stable complex has also been studied. It has been found that the interaction is blocked by: (1) the binding of a hydrogen ion by the 6‐amino group of adenine, (2) formaldehyde blocking of the 6‐amino group of adenine, and (3) ionization of the hydroxyl group of the pyrimidine ring of uridine.
On the mechanism of the polymerization of ϵ‐caprolactam. I. The polymerization initiated by ϵ‐aminocaproic acid
Authors: Kruissink Ch. A. , van der Want G. M. , Staverman A. J. 
Published: April 2003

AbstractIn this first‐paper of a series of publications on the mechanism of the polymerization of ϵ‐caprolactam (CL), an investigation of the kinetics of the polymerization initiated by ϵ‐aminocaproic acid (ACA) is reported. Experiments were performed at 254°C. for three different initial ratios (ACA/CL)0:0.05, 0.022, and 0.011 mole/mole. The concentration (x) of unconverted CL and that of end groups (c) were determined by extraction with water at room temperature and by potentiometric titration, respectively. The method of kinetic evaluation consists in the direct checking of rate equations making use of the quantities dx/dt and dc/dt which were determined graphically from the curves of x and c versus time. In this way tedious integration procedures are avoided and the testing of rather different mechanisms is much easier. Moreover, it is not necessary to make the assumption of constant rate coefficients which, of course, will seldom apply. Thus the inadequacy of the “polycondensation mechanism” has been proved for every time instant separately, although accidentally the rate constant of the main reaction is fairly constant. In this polycondensation mechanism it is assumed that polymer formation can take place only by polycondensation of ACA, the supply of which is provided for by the reaction of CL with water formed in the process of polycondensation. It turns out that even when the rate of hydrolysis of CL is so high that the polycondensation reaction is rate determining, this latter rate is to small by a factor of 10 or more to account for the rate of CL conversion observed. It is shown that this difficulty can be overcome only by incorporating a third reaction in the mechanism, a reaction which must provide for the main consumption of CL. We have assumed this reaction to be a reversible polyaddition reaction, i.e., a reaction in which CL is added to one of the end groups of the polymer molecules. The rate constant for this reaction derived from the experiments appears to be in good agreement with the value derived from the experiments on the polymerization of CL initiated with water.
Polymerisation radiochimique de l'acrylonitrile quelques observations sur le post‐effet
Authors: Bensasson R. , Bernas A. 
Published: April 2003

AbstractNos expériencea ont porté sur l'irradiation par les rayons γ du 60Co (4 r/mn < I < 400 r/mn) du monomhre acrylonitrile qui donne lieu à un post‐effet très important quand la polymérisation est conduite en milieu précipitant. La rbaction, pendant et aprhs irradiation, a été suivie par dilatométrie et à la température de 20°C, sauf pour les déter‐ minations des énergies d'activation. Les résultats suivants ont été obtenus: Vitesse du post‐effet: La vitesse décroft continument au cows du temps. A 20°C, sa valeur initiale (V0)pp, ne semble pas dépendre du taux de radio‐conversion et paraît équivalente à la vitesse globale de radiopolymérisation. Le taux de post‐polymérisation (AM/M),,, pour un temps donné, augmente avec la quantité de polymhre formé au cours de l'irra‐ diation. Pour un taux de radioconversion donné, et des durées de post‐effet assez longues, (ΔM/M)pp peut s'écrire sous la forme:

L'Bnergie globale d'activation E i de la radiopolymérisation semble varier avec la température:

Si la radiopolymerisation est conduite à. 20°C, et le post‐effet observé à 40, 50, 60°C, l'énergie d'activation relative aux vitesses initiales semble très élée: de l'ordre de 35 kcal/mole. Viscosités des solutions ak polyacrylonitriles (PAN) : Si on compare le comportement dans le diméthylformamide de polyacrylonitriles P1. pour lesquels le post‐effet ne s'est pas développé, et de polyacrylonitriles P2 qui ont subi une post‐poly‐ mbrisation, on constate: (I) que P2 est moins facilement soluble que P1; (2) que P2 correspond à un indice de viscosite limite inferieur à celui de P1 et que la pente de la droite ηsp/c = [η] + [η]Kc est plus grande pour P2 que pour P1. Ces dernibres observa‐ tions sugghrent que la post‐polymérisation conduit tl la formation de chaînes branchés.
A study of diffusion in polymer solutions by the use of the polarization interferometer
Authors: Tsvetkov V. N. , Klenin S. I. 
Published: April 2003

AbstractThe use of the polarization interferometer and the further perfection of the experimental technique makes possible the measurement of diffusion coefficients between solutions whose concentrations differ by less than 10−4 g./cm.3 These circumstances permit the direct measurement of the differential diffusion coefficient, D, corresponding to the given concentration c. The concentration dependence of the diffusion coefficient obtained for fractions of polystyrene in the region of not too small concentrations agrees well with the concentration dependence of the scattering of light in the same samples. In the region of low concentrations, the curve of the dependence D = D(c) has a horizontal section which cannot be described by the formulas usually used. In the region of concentrations, where the dependence D = D(c) may be considered as a rectilinear one, it is shown experimentally that the integral coefficient of diffusion between solutions whose concentrations differ by c1–c2 is equal to the mean of two differential diffusion coefficients, D1 and D2, where D1 = D(c1) and D2 = D(c2). In that region of concentrations, the integral diffusion curve shows a marked asymmetry, which agrees with the concentration dependence of the differential diffusion coefficient. The measurement of the diffusion coefficient D in dilute solutions of fractions of a series of polymers shows that the value of D is inversely proportional to the radii of the high polymer molecules calculated from viscosity and from light scattering data. The value of the empirical constant was determined, which permits the determination of the radius of the molecules from the measured values of the diffusion coefficient.
Polymerization of aromatic and heterocyclic vinyl compounds
Authors: Koton M. M. 
Published: April 2003

AbstractThe polymerization of vinyl derivatives of naphthalene and of the heterocyclic series containing the atoms of nitrogen, oxygen and sulfur has been investigated. It is proved that an increase in the number of condensed rings in the radicals replacing the hydrogen atoms in the ethylene molecule, as well as the introduction of heteroatoms (nitrogen, oxygen, sulfur) into these radicals increase the polymerization ability of the above compounds.
Inhibited thermal polymerization of styrene. Kinetics of copolymerization of quinones with styrene
Authors: Tüdös F. 
Published: April 2003

AbstractIn research on the kinetics of the inhibition of the thermal polymerization of styrene, we came to the conclusion that quinones participate not only in the inhibition reaction but also in the copolymerization. We carried out the derivation of the basic kinetic equations of the process in two ways: (1) Using the usual simplifying assumptions of the theory of copolymerization (Melville‐Watson method) and (2) using the stationary state method. The kinetic equations derived by the second method transform under certain conditions to the corresponding equations of simple inhibition, while the equations from the first method lead to contradictions. On the basis of the kinetic analysis it was found that the inhibition period during copolymerization of the inhibitor does not increase linearly within increasing concentration of the inhibitor, and that on the curve of conversion versus time there is an inflection point if the concentration of inhibitor is higher than a certain value. The curve of initial polymerization velocity against concentration of inhibitor has a minimum at a certain concentration (“inhibition optimum”). Experiments carried out with p‐benzoquinone at 90, 105, 120, and 135°C. completely agree with what has been stated above. At the lower temperatures, except for a slight shortening of the inhibition period, no significant indications of copolymerization are apparent; the course of these experiments is well described by the equation of simple inhibition. At 120 and 135°C. copolymerization occurs to a marked extent and is well characterized by the equations derived by the second method. Finally, from the temperature dependence of the appropriate velocity constants, we determined the activation energy of the inhibition reaction (4.3 kcal./mol.) and the activation energy of copolymerization of quinone (9.4 kcal./mole).
Kritische betrachtungen zur bestimmung der uneinheitlichkeit von polyamiden
Authors: Griehl W. , Lückert H. 
Published: April 2003

AbstractDie von verschiedenen Autoren durch Zerlegen von Nylon 6 in 8 bis 10 Fraktionen erhaltenen differentiellen Verteilungskurven zeigen eine grössere Einheitlichkeit des Polymers, als es der Flory‐Schulz‐Verteilung entspricht. Im System Kresol‐Benzin wurden nach der Zweiphasenmethode sowohl unstabilisierte als auch mit Essigsäure stabilisierte Polykondensate aus ϵ‐Caprolactam in 63 bzw. 33 Fraktionen zerlegt. Die integralen Verteilungskurven sowie die aus den Fraktionierergebnissen berechneten Werte für die Uneinheitlichkeit stimmen innerhalb der dieser Methode eigenen Fehlergrenzen mit der Theorie von Flory‐Schulz in demselben Masse überein, wie die von Taylor für das Polyamid Nylon 6–6 gefundenen Ergebnisse. Trotzdem erscheint ein exakter experimenteller Beweis für die Flory‐Schulz‐Verteilung mit Hilfe von Fraktionierungen weder beim Nylon 6–6 noch beim Nylon 6 möglich zu sein. Die Gründe hierfür wurden ausführlich erörtert und diskutiert. Ein zuverlässiger Beweis kann jedoch dadurch erbracht werden, dass man Endgruppenbestimmungen sowie Viskositätsmessungen an Fraktionen einerseits und nichtfraktionierten Proben andererseits durchführt und damit das Verhältnis M̄v : M̄n bestimmt. Im Bereich mittlerer Molekulargewichte wurde auf diese Weise ein gut mit der Theorie übereinstimmender Wert von 1,82 gefunden. Schliesslich konnte nachgewiesen werden, dass auch über eine längere Zeit kondensierte Produkte ihre Molekulargewichtsverteilung nicht ändern.
Zur kinetik der polyesterbildung durch umesterung
Authors: Griehl W. , Schnock Günther 
Published: April 2003

AbstractNach eingehender Untersuchung der sogenanten Vorkondensation bei der Polyäthylenterephthalatbildung bezüglich des Katalysatoreinflusses, der Reaktionskinetik usw, wird die als Umesterung verlaufende Polyesterbildung studiert. Der Reaktionsverlauf wird durch Viskositätsmessungen verfolgt und es ergibt sich erwartungsgemäss wie bei der “Vorkondensation” eine Reaktion erster Ordnung.