bluuebunny/crossref_metadata_2025_split huggingface dataset:
Über den Reactionsmechanismus des Schwefels in der Polymerisation der Chloroprens und des Thiurams in der Destruktion und Strukturienung der Chloroprenpolymere
Authors: Klebanskii A. L. , Ja. Zukerman N. , Fomina L. P. 
Published: April 2003

AbstractZur Aufklärung des Mechanismus der Reaktion zwischen Chloropren und Schwefel wurden die folgenden Untersuchungen ausgeführt: (1) Die Reaktion einer Lösung von Polychloropren mit Schwefel wurde unter den Bedingungen einer Anregung durch freie Radikale untersucht. Es wurde gefunden, dass Schwefel mit Polychloropren nicht reagiert, während unter Polymerisationsbedingungen die Addition von Schwefel leicht erfolgt. (2) Eine Untersuchung der Polymerisation des Chloroprens an Proben, bei denen die Schwefelmenge variiert wurde (von 0,3 bis 10%), zeigte, dass der Schwefelgehalt des Polymeren proportional zu der ursprünglich vorhandenen Schwefelmenge zunahm. Es wurde gefunden, dass Polymere mit hohem Schwefelgehalt (3–5%) bei niedrigem Polymerisationsumsatz vollständig löslich waren. Dieser Befund weist darauf hin, dass der Schwefel keine Vernetzung hervorruft, sondern dass er vorwiegend linear in den Polymerketten gebunden ist. (3) Es wurde festgestellt, dass der Schwefel vorherrschend in Di‐ und Polysulfidbindungen eingetreten war. Die Anzahl der letzteren steigt mit dem Schwefelgehalt des Polymeren an. (4) Bei der Einwirkung von naszierendem oder katalytisch erregten Wasserstoff wurde ein weitgehender Abbau des Polymeren gefunden, verbunden mit dem Verlust von 80 bis 100% des gebundenen Schwefels und der Bildung niedrigmolekularer Polymerer. Im Verlauf der Reduktion werden die Disulfidbindungen unter Bildung von polymeren Merkaptanen aufgespalten, welche durch Reaktion mit Jod wieder in Disulfide umgewandelt werden; eine Bestätigung dafür bildet die entsprechende Zunahme der Viskositätszhal. Diese Befunde Bestätigen den Copolymerisationsmechanismus, der von Moshell und Nicholls für die Reaktion zwischen Chloropren und Schwefel vorgeschlagen wurde. (5) Der Mechanismus des Abbaus von Polychloroprensulfid durch Tetraäthylthiuramdisulfid (TETD) wurde mittels folgender Modellsysteme für die in solchen Polymeren vorhandenen Hauptstrukturtypen untersucht:
magnified image
Hier ist R CH3CClCHCH2 und R1 CH2CClCHCH2. Der Verlauf der Reaktion über Radikale wurde sichergestellt und es wurde gezeigt, dass die mit den Modellsystemen erhaltenen Ergebnisse den Reaktionen entsprechen, die beim Behandeln der Polychloroprensulfide mit TETD stattfinden. Für den Abbau und die Vernetzung von Chloropren‐Polymeren, die in Gegenwart von Schwefel erhalten wurden, wird ein Reaktionsschema vorgeschlagen.
Donor‐acceptor interactions in cationic polymerization. I. Kinetics
Authors: Veselý K. 
Published: April 2003

AbstractThe monomolecular mechanism of termination generally assumed for cationic polymerization cannot explain our results obtained with AlCl3 and BF3 in ethyl and methyl chloride, where a characteristic dependence of the polymer molecular weight on catalyst concentration has been formed. A catalytic system is considered in which the catalyst is a Lewis acid (A) and the co‐catalyst is correspondingly formed by the base (B). The association (K1) and ionization (K3) equilibria are different for individual catalysts and co‐catalysts. This influences the form of the relation of molecular weights to their respective concentrations. Special attention is paid to the point of equivalency, where the maximnm value of molecular weight is obtained if a decrease in ionization occurs in this point. Extrapolation of the values of 1/Pn for zero concentrations of complex A. B made possible the determination of the transfer with monomer.
Recherches sur le mécanisme de l'accroissement des macromolécules du polytéréphthalate de glycol pendant la polycondensation
Authors: Turska E. , Skwarski T. , Szapiro S. 
Published: April 2003

AbstractOn a effectué la synthbse du polytéréphthalate de glycol à partir de deux monoméres, l'ester diméthylique de l'acide Mréphthalique et éthylène glycol, en présence d'un melange de PbO et Sb2O3 comme catalyseur. Les polymbres obtenus des produits de divers degrés de polymbrisation, qui avaient les valeurs des viscosités intrinsèques de 0,135 jusqu'à 0,727 celles qui correspond aux poids moléculaires de 5000 à 30000 réspectivement. On a separé les Bchantillons polymbriques l'aide d'une méthode de fractionnent déjB publiée. Les courbes intégrales de distribution de masse trades à l'aide du systbme des ordonnbs proposé par Tung, formaient des lignes droites avec le meme coefficient angulaire. De lh on a dérivé une Bquation qui permet de calculer la courbe différentiale de distribution des la viscosiM intrinsèque de 1'échantillon non fractionné. Les courbes diffbrentiales de distribution tracées d'aprbs les résultats expéri‐ mentaux comparcks sont d'accord avec les courbes théoriques d'aprr̀s Flory pour les memes dégrés de polymérisation.
The re‐equilibration of polycaproamide
Authors: Smith S. 
Published: April 2003

AbstractThe polymerization of caprolactam and the depolymerization of polycaproamide at equilibrium lead to an identical mixture of linear polymer, caprolactam and its cyclic oligomers. In this work the depolymerization reaction has been studied. The postulated reaction mechanism is based on hydrolysis and inter‐ and intramolecular segment interchange reactions (acidolysis and aminolysis), according to which the concentrations of water and end groups (—NH2 and —COOH) determine the rate of depolymerization. In an attempt to elucidate the mechanism of depolymerization, the effect of these variables on the rate has been determined. Depolymerizations were carried out at 230, 250, and 270°C. in sealed tubes, using dry polymers of different initial molecular weights, polymers containing various amounts of water up to 30% by weight, and polymers in which the amine end groups had been acetylated to preclude aminolysis. Comparable chemical blocking of the acid end groups could only be partially achieved. The reaction product was analyzed for lactams by boiling water extraction, for caprolactam by a sublimation method, and for end group concentrations by titration. It has been found that: (1) an increase in molecular weight, i.e., a decrease in active end group concentration, causes a decrease in the rate of depolymerization of dry polymer; (2) the equilibrium lactam content as well as the rate of depolymerization are increased by (a) the addition of water and (b) increasing temperature; (3) acetylation causes a decrease in the rate of depolymerization of dry polymer; the lower the molecular weight of the acetylated polymer (i.e., the higher the —COOH concentration), the more rapid is its depolymerization. These results are discussed in terms of the proposed reaction mechanism.
Polythiuroniumverbindungen
Authors: Černý J. , Wichterle O. 
Published: April 2003

AbstractDurch die Reaktion von Thioharnstoff oder N‐Methyl‐Thioharnstoffen mit chlormethylierten Polystyrolen oder chlormethylierten Styrol‐Divinylbenzol‐Copolymeren wurde der völlige Ersatz des Chloratoms durch Isothiuroniumgruppen erreicht. Polythiuroniumverbindungen wurden auch durch die Reaktion von Polyvinylalkohol mit Thioharnstoff in saurer Lösung erhalten; in diesem Fall war der maximale substitutionsgrad ein Drittel der Gesamtmenge der Hydroxylgruppen. Polythiuroniumverbindungen wurden besonders im Hinblick auf die Verwendungsmöglichkeit als Anionenaustauscher untersucht. Von diesem Gesichtspunkt aus waren die Reaktionen, durch welche eine Vernetzung dieses Polyelektrolyten erreicht werden konnte, von besonderem Interesse Vernetzung konnte durch die Reaktion mit Formaldehyd und im Falle der Polyvinyl alkohol‐Derivate auch durch Oxalsäure erreicht werden. Zusätzlich zu dem erwarteten Ergebnis der Vernetzungsreaktion—der Abnahme der Quellung—wurde eine ziemlich überraschende Zunahme der Stabilität vieler oder der meisten Isothiuroniumgruppen festgestellt. Während die linearen oder schwach vernetzten Polythiuroniumverbindungen in alkalischen Medium zu Thiolen gespalten werden, verleiht weitgehende Vernetzung einem Teil der Thiuroniumgruppen eine aussergewöhnliche Stabilität. Dieser Effect kann auf die Fixierung der Thiuroniumgruppen in einer ebenen Anordnung zurückgeführt werden, welche die Bildung des intermediären ortho‐Derivates stört, das durch die Addition des Anions entsteht. Dass der Effekt nicht allein auf die Substitution zurückzuführen ist, zeigt ein Vergleich der Stabilität von Thioharnstoffderivaten, die verschiedene Substituenten tragen. Er kann auch nicht durch sterische Hinderung erklärt werden, da die Austauschfähigkeit für Anionen sogar im Falle der weitestgehenden Vernetzung unbeeinflusst bleibt.
Dégradation du polystyrolène en solution diluée aérée sous l'action des rayons γ
Authors: Durup Jean 
Published: April 2003

AbstractOn étudie par une méthode viscosimétrique la dégradation du polystyrolène en solution chloroformique sous l'action des rayons γ en présence d'air. L'analyse cinétique de la vitesse de dégradation pendant et apres l'irradiation permet d'établir un schéma de dégradation oxydante. Ce mécanisme comporte deux processus parallèles avec deux intermédiaires, l'un a courte durée de vie (radical oxygéné), l'autre relativement stable à température ordinaire (hydroperoxyde). Le résultat de l'irradiation du polystyrolène dans d'autres solvants est discuté à la lumiere de ce mécanisme.
Zur frage der unterscheidung sterischer und induktiver Einflüsse beim Abbau synthetischer polypeptide1
Authors: Heyns K. , Walter W. , Grützmacher H. F. 
Published: April 2003

AbstractDurch Anwendung geeigneter Analysenmethoden kann die Kinetik des Abbaues der inneren und äusseren Peptidbindungen von Polypeptiden unterschieden werden, wenn diese aus den gleichen Aminosäuren aufgebaut sind. Es wurden Polypeptide untersucht, die aus Monoaminomonocarbonsäuren mit verschiedenen aliphatischen und aromatischen Resten am α‐Kohlenstoffatom aufgebaut waren. Bei der sauren Hydrolyse dieser Polypeptide zeigten die Hydrolysenkonstanten der inneren bzw. der äusseren Peptidbindungen jeweils einen charakteristischen Gang in Abhängigkeit von der Substitution, der in der Weise gedeutet werden kann, dass der Abbau der ässeren Peptidbindungen im wesentlichen von induktiven Einflüssen, derjenige der inneren Peptidbindungen aber überwiegend von sterischen Einflüssen beherrscht wird. Bei der Bildung der 2,5‐Oxazoliddione bei der Einwirkung von Phosgen auf in Dioxan suspendierte Aminosäuren sind vorwiegend induktive Einflüsse von Bedeutung für die Reaktionsgeschwindigkeit.
Dielectric losses and polarization of polymers
Authors: Mikhailov G. P. 
Published: April 2003

AbstractResults of research on the dielectric losses and polarization of polymers are presented. In the first and second parts of the paper these behaviors of the polymers are considered for high‐elastic state. The dielectric losses are shown to be of relaxation character since they can be described by the segmental thermal motion of polymolecules. The second part deals with effective dipole moments of elementary chain units of macromolecules of the homologous series of methacrylic acid esters. It is stated that for the polymers under consideration the intramolecular interaction is of considerable significance. The third part of the report supplies data on the dielectric losses and polarization research of the same polymers in the glassy state. In this case the losses of relaxation character, called dipole‐radical, are observed, as they can be described by the thermal motion of separate polar groups or radicals. The application of the method of effective dipole moments for analysis of the experimental date has brought us to the conclusion that it is the intermolecular interaction which is of greater importance for the dipole‐radical losses.
Study of the structures of butadiene polymers produced on initiation by Lewis acids
Authors: Ferington T. E. , Tobolsky A. V. 
Published: April 2003

AbstractButadiene has been polymerized by AlCl3 and related materials at −78°C. The structure of the polymers produced has been studied by infrared analysis. The structure of the soluble polybutadiene was found to be independent of extent of conversion, concentration of catalyst solution, and length of reaction. An insoluble polymer also formed in the system and the amount of this depended on the extent of conversion, being greater at higher conversion whether this was achieved by higher catalyst concentration or longer time. Complexing the AlCl3 with nitroethane or nitrobenzene changed the structure of the polymer slightly, while the use of diethyl ether as a complexer produced no changes. TiCl4, used as the initiator, produced polymers of slightly different structure from those formed with AlCl3, while AlBr3 and BF3·Et2O yielded polymers like those from AlCl3. When the solvent used was varied, the polymer structure also varied. The observed variations were small in all cases.
Polynucleotides. III. The behavior of polyadenylic acid at acid pH's
Authors: Steiner Robert F. , Beers Roland F. 
Published: April 2003

AbstractOn going from alkaline to acid pH's, polyadenylic acid undergoes a marked structural change in the vicinity of pH 6. This change is reflected by a decrease in radius of gyration at low ionic strengths, some increase in molecular weight, and a marked drop in extinction coefficient at 257 mμ. The transition has been shown to result from titration of the adenine group.
Effects of solvent structure in polyvinyl chloride‐solvent systems
Authors: Adelman Robert L. , Klein Isabel M. 
Published: April 2003

AbstractA study was made of the solubility of a high molecular weight polyvinyl chloride in a wide variety of solvents at room temperature. Many powerful solvents and solvent combinations for the polymer were demonstrated. A number of combination of N, N‐disubstituted amides with other classes of solvents, including the cyclic ethers, aliphatic ketones, alkyl‐substituted pyridines, and aromatic hydrocarbons, were found to have synergistic solvent action. The solvent power of many pure and mixed solvents appear to be qualitatively predictable from molecular structure in terms of: (a) the electron donor capacity of the solvent, (b) steric hindrance to approach of the electron donor center of the solvent to the polymer, and (c) effective solvent bulk for keeping the polymer chains well separated. The solubility parameter concept does not appear to be applicable for predicting solvent power in the systems studied.
On the properties of polymers with random stereo‐sequences
Authors: Coleman Bernard D. 
Published: April 2003

AbstractIt is proposed that in most free radical polymerizations of polymers containing asymmetric carbon atoms in the principal chain, the relationships between the stereo‐positions of the substituents on adjacent units are governed by independent Bernoulli trials. An event in which a given substituent has the same stereo‐position as its immediate predecessor is called an “isotactic placement.” The probability, α, of this event may be a function of the temperature of polymerization. The methods of Flory's theory of the melting point of copolymers are used to derive an upper bound for the melting point of a homopolymer with “tacticity,” α. The notation and calculations are then extended to include polymers whose stereo‐sequences are governed by statistics of a more general type than Bernoulli trials. It can happen that the calculated upper bound for the melting point may lie near (or even below) the glass point for the amorphous polymer; when such is the case, the polymer cannot be crystallized by annealing.
Thermodynamic properties of some fused chlorides
Authors: Markov B. F. , Delimarsky J. K. , Panchenko I. D. 
Published: April 2003

AbstractThe stability of complexes and associates formed in compound molten electrolytes can be quantitatively estimated from the excess thermodynamic functions (free enthalpy, entropy, enthalpy). These functions can be most conveniently determined by measuring the electromotive force of chemical cells of the type

where × is halogen. In this way the following systems were experimentally investigated: BeCl2–NaCl; MgCl2–LiCl; MgCl2–NaCl; MgCl2–KCl; MgCl2–RbCl; PbCl2–LiCl; PbCl2–NaCl; PbCl2–KCl; PbCl2–RbCl. The dependence of the excess partial free enthalpy on the mole fraction can be expressed by the equation

where α and β are constants (for example β = 2.4 for PbCl2). In logarithmic coordinates, (ZE; (1—X1)), the experimentally determined data show a linear dependence. A curve‐linear dependence in these coordinates indicates a deviation from an ideal system. According to the magnitude of these deviations, it is possible to judge the stability of the complexes in the melts. The stability of the complexes in the melts regularly increases in the order LiCl, NaCl, KCl, RbCl.
Kinetics of heat inactivation of enzymes in light and heavy water (lysozyme, ribonuclease, and desoxyribonuclease)
Authors: Shugar D. , Gajewska E. 
Published: April 2003

AbstractA study has been made of the kinetics of heat inactivation in light and heavy water, of lysozyme, ribonuclease, and desoxyribonuclease. In all instances, the isotope effect for inactivation (kH/kD) is found to be related to the activation energy and to decrease to approximately unity for low activation energies. For lysozyme at acid and neutral pH and for ribonuclease at acid, neutral, and slightly alkaline pH, the results indicate that hydrogen bonding is not of great importance for enzymatic activity, in agreement with the results of previous studies in ordinary water. For desoxyribonuclease at neutral and alkaline pH, the isotope effect varies from 1.5–5.0 which, in agreement with the high values of the thermodynamic constants for heat inactivation of this enzyme, suggests that the rupture of a considerable number of hydrogen bonds is involved in this process. Although the heat inactivation of this enzyme in the pH range 2.4–3.2 in H2O is partially reversible on cooling (if 50% inactivation is not exceeded), no such reversibility was found in D2O; it is believed that this may be due to a decrease in the pK of the protein carboxyl groups in heavy water. It was also found that the isotope effect decreases with temperature, as is to be expected, the result being a small increase in the activation energy and entropy change for the inactivation process in heavy water. The results are discussed, and it is shown that no general conclusion may be drawn from studies on a single enzyme (or protein), but that the findings must be considered individually in relation to structure, deuterium exchange in solution, titration curve in heavy water, etc. Suggestions for further studies are advanced.
Ringed spherulites in polyethylene
Authors: Keith H. D. , Padden F. J. 
Published: April 2003

AbstractPrevious authors have notes that the concentric dark rings which adorn spherulites of polyethylene under certain conditions of growth are also visible in unpolarized light. This visibility of the rings, moreover, exhibits an angular dependence when observed in phase objects which are not completely resolved by the optical microscope. Some of the light intensity in the image of the rings is considered to be lost by diffraction out of the aperture of the objective, and the experimental observations have been accounted for both qualitatively and quantitatively.
On the oxidation mechanism of rubbers in the presence of inhibitors
Authors: Angert L. G. , Kuzminskiĭ A. S. 
Published: April 2003

AbstractFree oxidation of rubbers represents a chain process which, at moderate temperatures, consists of two stages. The first stage, constant oxidation rate, is characterized predominantly by the development of an unbranched chain reaction leading to the accumulation of an intermediate compound of low stability. The second stage, autocatalytic oxidation, represents a degenerated branched process, resulting from the decomposition of intermediate products. Inhibitors of the secondary aromatic amine type lower the oxidation rate in the first stage and sharply increase its duration. The inhibited process activation energy is 21.3 kcal./mole. In the inhibited oxidation, the major part of the combined oxygen is contained in the aldehyde groups. In contrast to free oxidation, in which crosslinking of the chains is the dominant process, in inhibited oxidation, the process of destruction of polymer molecules is predominant at first. The inhibited rubber oxidation rate depends on the concentration of the inhibitor. This dependence is described by a curve with a minimum. During the process of the oxidation of rubber, some of the inhibitor combines with the molecules of the polymer, and the rest is partially subjected to the action of molecular oxygen. There is an increase in the rate of rubber oxidation, at inhibitor concentrations above a given level, which is attributable to the initiating action of intermediate radical products of inhibitor oxidation. The inhibitors of the secondary amine type do not interact with stable rubber peroxides and with hydrocarbon radicals. It was shown, that the NH bond in the amine molecule is above all responsible for the inhibition effect. It was found that the inhibiting power of amines is a direct function of the mobility of the hydrogen of the NH group. The increase in mobility of this atom is attained by: (1) an increase of the conjugation effect in the inhibitor radical, which results from an increase in the number of aromatic nuclei in the amine molecule; and (2) introduction of electron donor substituents in the position para to the secondary amine in the benzene nucleus. The experimental data obtained and also the contemporary theory of the mechanism of oxidation of low molecular weight hydrocarbons made it possible to suggest a chemical scheme of the rubber oxidation mechanism in the presence of inhibitors of the secondary aromatic amine type.
Effect of composition on the photoelastic behavior of methyl methacrylate–diallyl phthalate (MMA‐DAP) copolymers
Authors: Kawata Kozo 
Published: April 2003

AbstractThe photoelastic behavior of methyl methacrylate‐diallyl phthalate copolymers has been investigated in a wide range of temperature and copolymerization ratio to study the effect of crosslinking. The birefringence was measured under constant stresses. In the relation of the stress‐optical coefficient versus temperature, three different types of behavior, corresponding to the three degrees of crosslinkage are found. The first is that at pure DAP polymer, for which the degree of crosslinkage is too high; the second is seen in several MMA‐DAP copolymers for which the degree is suitable, and the third is shown by pure MMA polymer for which the degree of crosslinking is zero. The first does not come to show perfect entropy elasticity in the higher temperature region. The second group changes to perfect entropy elasticity in the higher temperature region In the third, the coefficient shows a maximum in the higher temperature region and decreases abruptly with increasing temperature above the maximum point. The effect of copolymerization ratio in the glassy region is quite different from that in the higher temperature region.