bluuebunny/crossref_metadata_2025 huggingface dataset:
Polymerhomologe ringamide in polycaprolactam
Authors: Rothe M.
Published: April 2003

During the polymerization of ϵ‐caprolactam about 3% of low‐molecular weight cyclic oligomers of caprolactam are formed. Because of their very similar properties and difficult identification (no terminal groups!), authentic preparations of the polymeric ring amides were made as reference substances first. For this purpose several aminocaproic acid residues were linked together step by step according to the methods of the peptide synthesis to chromatographic pure linear oligomers and cyclized in a structure determinating way after transformation into suitable derivatives by means of the Ziegler dilution principle. Ring closure occurred by intramolecular aminolysis of various active peptide esters as well as by a new method with the aid of tetraethylpyrophosphite and by condensation of the peptide chlorides in the presence of tert‐amines. In order to analyze the polycaprolactam extracts, a new paper chromatographic technique was developed with the aid of the test substances. This allows for the separation of all the polymeric ring amides up to the nonamer at least. Thus 5 new ring oligomers, namely the cyclic penta‐ to nonamer (63 ring atoms!), of caprolactam were found in polyamides obtained by polymerization of the caprolactam in the presence of water or also of metallic sodium in the absence of moisture. The percentage of rings of the polymerizate decreases with increasing number of links from the dimer to the nonamer. The preparative separation of the ring amide mixture was carried out according to the following two methods. The isolation of all the rings from the diamide to the pentamide in chromatographic pure from proceeded by fractional molecular distillation in a high vacuum and fractional crystallization; a new method for the isolation of the higher rings used paper chromatography and led, for the first time, to the isolation of the hexa‐ and hepta‐amides from polymerizates. The ring structure of all compounds follows from the elementary analysis, the absence of terminal groups, and the corresponding physical properties (volatility, molecular weight determination, x‐ray spectrum, paper chromatography) with the synthetic products. All ring amides possess considerable stability during heating in the absence of moisture. With the addition of water polymerization takes place, as expected, with the formation of all possible linear and cyclic monomers, oligomers, and polymers. A condensation equilibrium, a reversible splitting from the end of a chain, as well as trans‐amidatings between two parallel chains are discussed as possible formation mechanisms of the ring amides.
Structure and phase state of polymers
Authors: Kargin V. A.
Published: April 2003

In order to determine the structure and phase state of polymers and to define the spacing of molecular groups of atoms of which molecules of the substance under investigation consist, it is necessary to estimate the mutual distribution of macromolecules. The results of a number of investigations carried out by the electron microscope and by direct structural techniques make it possible to obtain such an estimation. In this work the formation of ordered structures in amorphous polymers has been found by investigating solutions of polymers with the electron microscope. The study of thin oriented films of polymers by the above method confirms the possibility of mutual distribution of amorphous polymer chains and of crystallizable polymer chains after destroying the crystals. In investigating thin films of crystallizable polymers by the x‐ray and the electron diffraction techniques at temperatures above and below the crystallization temperatures, a high degree of ordering has been found for the amorphous state of these polymers, too. From the data obtained, the conclusion is to be drawn that a fair mutual ordering of chain molecules can arise even in the amorphous state of polymers. Crystallization of polymers is but the last step in the process of mutual ordering of chain molecules.
Die Bestimmung der thermodynamischen Eigenschaften konzentrierter Polystyrollösungen aus osmotischen Messungen
Authors: Rehage G. , Meys H.
Published: April 2003

Es wird über osmotische Messungen an Lösungen von Polystyrol (PST) in Toluol und Cyclohexan im Temperaturbereich von 0–50°C. bzw. 30–50°C. berichtet. Der Konzentrationsbereich bis ca. 300 g./l (etwa 30 grundmol prozente) konnte durch Messung der Steighöhendifferenz zwischen eweils zwei Lösungen verschiedener Konzentration erfasst werden. σπ/σx wurde als Funktion von T und x ermittelt und hieraus die Aktivität a1 des Lösungsmittels berechnet (π = osmotischer Druck, x = Grundmolenbruch des Polymerisats, T = absolute Temperatur). Die thermodynamische Auswertung erfolgte nach dem Ansatz

(r = Polymerisationsgrad). Die Grössen χI sind empirische Parameter. Sind alle χi = 0, so erhält man die bekannte Beziehung von Huggins und Flory für eine ideal‐athermische hochmolekulare Lösung. Das System PSt‐Toluol befolgt den halbempirischen Huggins‐Ansatz, d.h. χ1 ≠ 0; χ2 = χ3… = 0. Das System ist näherungsweise athermisch. Dagegen sind Lösungen von PST in Cyclohexan endotherm. Dieses System gehorcht der von Tompa erweiterten Huggins‐Gleichung, d.h. χ1 ≠ 0; χ2 ≠ 0; χ3 = χ4… = 0. Es werden grundmolare Zusatzfunktionen G*E, S*E, und H*E eingeführt, die den Unterschied zwischen den gemessenen grundmolaren Zustandsgrössen ΔG*, ΔS*, ΔH* und den entsprechenden Grössen in einer ideal‐athermischen Lösungangeben (G = freie Enthalpie, S = Entropie, H = Enthalpie). ImSystem PSt‐Toluol ist G*E symmetrisch im Grundmolenbruch. Ferner gilt G*E ≈ TS*E > 0. Im System PSt‐Cyclohexan ist G*E > 0, H*E > 0, und S*E < 0. Hier ist der Verlauf der grundmolaren Zusatzfunktionen unsymmetrisch. Aus dem Temperatur‐ und Konzentrationsverlauf der Aktivität resultiert für das System PSt‐Cyclohexan eine Mischungslücke unterhalb 27°C. Das Ergebnis stimmt mit Entmischungsversuchen befriedigend überein. Dies wird als ein Kriterium für die Zuverlässigkeit der osmotischen Messungen angesehen.
Redox systems in the initiation of radical processes and the mechanism of their action
Authors: Dolgoplosk B. A. , Tiniakova E. I.
Published: April 2003

The following redox systems capable of initiating radical polymerizations will be discussed: (1) Systems of the first type, where the reaction leads to the formation of a single radical: (a) Mechanism of action of reversible systems involving dienols and salts of metals of variable valency. (b) Mechanism of the decomposition of hydroperoxides by the action of salts of metals of variable valency in their higher oxidation states. (2) Systems of the second type, where the reaction leads to the formation of two radicals. Mechanism of action and effectiveness of systems involving hydroperoxides, quinol, and sulfite. (3) Systems of the third type, in which the formation of free radicals is not directly linked to the redox process. Mechanism of action of systems involving diazoamino compounds and “polyamine” systems. (4) Crosslinking of unsaturated polymers at low temperatures by the action of redox systems. Transition from crosslinking to destructive processes in presence of oxygen.
The mechanism of vulcanization and the action of accelerators
Authors: Dogadkin B. A.
Published: April 2003

Elementary sulfur which is educed as a result of the reaction between disulfides, peroxides, and H2S does not cause the vulcanization of rubber. Vulcanization as a process of chemical crosslinking formation occurs when this reaction proceeds with radicals formation (light effect, redox systems). Disulfides and sulfenamides cause the effect of vulcanization passing through the stage of hydrogen separation from α‐methylene group, and the formation of polymer radicals. Vulcanizing agent groups join rubber during this process. This is confirmed by isotope exchange of vulcanizate. Conjugated reaction of the linking of sulfur and accelerator to rubber occurs in the presence of mercaptobenzothiazol and sulfur. Intermediate combinations of MBT and sulfur are educed. Monotonous drop of the ability of vulcanizate to exchange with elementary sulfur shows the importance of persulfhydril and polysulfide radicals in reactions of vulcanization.
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

Zur 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

The 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

On 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

The 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

Durch 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

On 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

Durch 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

Results 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

Butadiene 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

On 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

A 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

It 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

The 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

A 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

Previous 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

Free 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

The 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.
The reactivity of cellulose. III. Acid hydrolysis of eucalypt α‐cellulose in the intermediate molecular weight range
Authors: Higgins H. G. , Goldsmith Valerie , McKenzie A. W.
Published: April 2003

An α‐cellulose pulp from Eucalyptus wood was hydrolyzed under homogeneous conditions (mainly 67.5% sulfuric acid at 0 and 20°C.) and under heterogeneous conditions with small weight losses (sulfuric acid solutions of up to 50% concentration for 2 hr. at 50°C. and for periods of up to a week in 21.3% acid at 50°C.). Intrinsic viscosities, [η], of the regenerated samples and the residues, respectively, were determined from measurements in cupriethylenediamine solution. Between weight‐average degrees of polymerization of ca. 310‐70 the apparent rate constants decreased with time of hydrolysis. Comparison of data for homogeneous and heterogeneous conditions confirm the influence of supermolecular factors on the course of hydrolysis of the fiber. Finely ground cellulose is hydrolyzed more rapidly than intact fibers. The concept of a welldefined noncrystalline fiber fraction in which the β‐glucosidie linkages are the only labile bonds and are almost immediately accessible to the hydrolyzing agent is inconsistent with these data. It seems rather that in this material a sharp distinction cannot be drawn between the amorphous and crystalline regions. The observed activation energy for homogeneous hydrolysis, ca. 28 kcal./mole, is in agreement with that determined by other workers under different conditions. The Huggins‐Kraemer equation was followed for heterogeneously hydrolyzed samples, with k′ values of 0.47 for [η] > 2, rising to 0.60‐7 for [ηl] < 1. Regenerated samples gave an average k′ of 0.44 for [η] > 1. Infrared spectra of the hydrolyzed fibers revealed no modification of the cellulose I structure over the whole time series and up to 50% acid in the concentration series. Material regenerated from strong acid solution shows the cellulose II spectrum.
Deuterium isotope effect in inhibited oxidation of butadiene–styrene rubber
Authors: Shelton T. Reid , McDonel E. T.
Published: April 2003

The importance of hydrogen abstraction by peroxy radicals as a mechanism of antioxidant action in rubber has been studied by investigation of a deuterium isotope effect with amine and phenolic inhibitors in the oxidation of butadiene‐styrene rubber. Deuterium was substituted for the active hydrogen of N‐phenyl‐2‐naphthylamine and 2,6‐di‐tert‐butyl‐4‐methylphenol by reacting the antioxidants with methylmagnesium iodide and then with deuterium oxide. The oxidation rates of butadiene–styrene polymer inhibited with 3 parts per hundred of these compounds were measured and compared with the oxidation rates using normal antioxidants. A kinetic isotope effect in the rate of oxidation was observed with both the phenolic inhibitor (kD/kH = 1.3 with not less than 77% substitution) and the amine inhibitor (kD/kH = 1.8 with not less than 60% substitution). The existence of an isotope effect leads to the conclusion that hydrogen donation to a peroxy radical is a controlling step in the mechanism by which these antioxidants function to retard the oxidation of rubber.
Dependence of the ultimate properties of a GR‐S rubber on strain rate and temperature
Authors: Smith Thor L.
Published: April 2003

The tensile properties of an unfilled GR‐S rubber were measured with an Instron tensile tester at strain rates between 0.158 × 10−3 and 0.158 sec.−1 and at fourteen temperatures between −67.8 and 93.3°C. The tensile strength and ultimate strain at the various strain rates and temperatures were superposed to give two composite curves which are functions of a reduced strain rate. From this superposition, the temperature dependence of the ultimate, properties was obtained. The temperature dependence between −53.8 and 71° is essentially the same as obtained by superposing the stress‐strain curves and is given by the Williams, Landel, and Ferry equation. From the composite curves and the temperature function, the tensile strength and the ultimate strain can be predicted at any strain rate and temperature, provided heating and wave propagation effects are negligible. The linear viscoelastic properties were obtained from the initial portions of stress‐strain curves and are represented by a reduced stress‐strain curve.
Specific heat of synthetic high polymers. IX. Poly(ethylene sebacate)
Authors: Wunderlich Bernhard , Dole Malcolm
Published: April 2003

As part of a comprehensive study of the copolymer system poly(ethylene terephthalate‐sebacate), specific heat measurements have been carried out on the annealed polyester, poly(ethylene sebacate), over the temperature range −20 to 140°C. From estimates of densities of completely crystalline and amorphous polymer, the crystallinity at room temperature was calculated to be 57%, and the heat of fusion of completely crystalline polymer to be 30.5 cal. g.−1, a value considerably greater than that calculated by Edgar and Ellery from copolymer data. This discrepancy is attributed to the small crystallite size in their copolymer study. It is shown that the low melting point of the aliphatic polyesters as compared to that of polyethylene is due to the low heat of fusion rather than to a large entropy of fusion as previously supposed. Finally, it is pointed out that in the liquid range, the heat content is closely proportional to volume.
Response of linear high polymers to hydrostatic pressure
Authors: Matsuoka Shiro , Maxwell Bryce
Published: April 2003

The bulk compressibility of linear high polymers has been found to be a function of temperature, pressure, and time. Linear high polymer melts are highly compressible. Addition of pressure causes a structural change in some linear high polymer melts. In the case of amorphous polymers, such as polystyrene, a glassy state response to hydrostatic compression was found at a temperature well above the second‐order transition temperature. In the case of polycrystalline materials, such as polyethylene, pressureinduced crystallization can take place at temperatures above the melting point. In either case, the process requires a higher pressure as temperature is increased. This process is found to be time dependent. There are indications that such structural changes could not take place above a specific temperature limit for any given material, regardless of the amount of pressure. By subjecting a melt of polyethylene to pressure and then cooling, a material that is more dense, more rigid, and more crystalline than the original injection‐molded specimen can be obtained. The effects of the bulk compressibility on the fabrication condition of plastics as well as product properties are discussed.
A new absolute molecular weight method for linear polymers
Authors: Bueche F. , Harding S. W.
Published: April 2003

The measured viscosity for concentrated solutions of linear coiling polymers decreases with increasing rate of shear. By use of a theory previously derived to explain this phenomena, it is possible to determine the absolute molecular weight of the polymer from measurements of this effect. The necessary data required for this determination are readily obtained using a simple cone viscometer. Since the theory requires only a knowledge of the variation of viscosity with shear rate together with the polymer concentration and temperature to compute the molecular weight, the method is easily applied to any polymer of this general type. This shear rate method for determining molecular weights has been checked by measuring M for a large number of samples of polystyrene and polymethyl methacrylate. Satisfactory results are obtained on these polymers. When the method is used as outlined, it gives a value for M which is close to the viscosity average. For very wide molecular weight distributions, the value found is somewhat higher than the weight average. Since the method is only strictly valid for linear polymers, it appears that it may also be used in conjunction with other molecular weight methods to obtain useful information concerning the extent of branching in the molecules.
The denaturation of the proteins of the groundnut (arachis hypogaea) with guanidinium salts, metal salts, and urea
Authors: Williams R. K. , Naismith W. E. F.
Published: April 2003

The denaturation of arachin and conarachin II with urea, guanidinium chloride and thiocyanate, and of arachin with alkali metal thiocyanates and lithium halides has been examined using sedimentation velocity and viscosity techniques. The effect of various anions on the alkaline denaturation of arachin has also been investigated. It was found that with reagents which denature arachin and conarachin II at similar rates, the arachin half molecule was not observed as an intermediate stage in the arachin denaturation with the exception of lithium chloride. The denaturation of arachin with urea and guanidinium chloride was faster at pH 10 than at pH 8. The denaturing power of the alkali metal thiocyanates decreased in the order Li, Na, K, and of lithium halides in the order Lil, LiBr, LiCl. It was found that in the case of denaturation with guanidiniun and alkali metal salts, the cation appeared to be the main denaturant but anions inhibited the denaturation with the exception of the thiocyanate ion which was either noninhibiting or was itself a denaturant. With ionic denaturants in general the nature of both ions was important.
Linear phenol–formaldehyde polymers. Condensation of o‐chlorophenol with formaldehyde
Authors: Burke W. J. , Ruetman S. H.
Published: April 2003

The condensation of o‐chlorophenol with formaldehyde occurred readily at 150°C. in a closed system in the presence of bis(2‐ethoxyethyl) ether as solvent and p‐toluenesulfonic acid as catalyst to form high molecular linear polymers. Use of a high concentration of reactants and a small excess of formaldehyde favored higher molecular weight products. Infrared spectra studies and analytical results on the polymers and their acetyl derivatives indicated that the o‐chlorophenol residues were linked together through ortho and para positions by methylene bridges.
Effect of physical state during the electron irradiation of hydrocarbon polymers. Part I. The influence of physical state on reactions occurring in polyethylene during and following the irradiation
Authors: Lawton Elliott J. , Balwit J. S. , Powell R. S.
Published: April 2003

Measurements of crosslinking, trans‐vinylene formation, and hydrogen evolution have been made on high‐ and low‐density polyethylenes irradiated at temperatures from about −170 to +240°C. Crosslinking produced during irradiation is mainly in the amorphous areas of the polymer; whereas trans‐vinylene unsaturation is produced as readily in the crystalline areas as in the amorphous areas. Radicals are trapped in the crystalline regions. These can react with oxygen to form carbonyl groups, rather than crosslinks. Thus, in Marlex‐50 irradiation in the crystalline state at 25°C. followed by a 7 day storage in air prior to the crosslinking measurements, was only about one‐sixth as effective in producing crosslinks as irradiation in the amorphous state at 150°C. In the low‐density polyethylene where less trapping occurs the factor is about one‐half for the same conditions of irradiation and storage. The lifetime of radicals trapped in Marlex‐50 when stored in oxygen can be thousands of hours compared with a few hours in low density polyethylene. Both the low‐density polyethylene and Marlex‐50 irradiated in the crystalline state at 25°C. (in nitrogen) could be further crosslinked by quickheating them to the amorphous state at 150°C.—delayed carbonyl formation does not occur in this case. Delayed crosslinking resulting from the quick‐heating of irradiated Marlex‐50 gave only about one‐half of the crosslinks for the same irradiation as when irradiated in the amorphous state. Hydrogen evolution as a function of irradiation temperature for Marlex‐50 is discussed; a satisfactory material balance was obtained in which the radiation yield (G value) for total hydrogen produced nearly equaled the sum of G for crosslinking and G for trans‐vinylene formation. Hydrogen yield was found to be nearly constant in the temperature range −170 to +34°C. where crystallinity is also nearly constant, indicating hydrogen production to be nearly independent of temperature. Therefore, the main change in crosslinking yield in the +34 to +150°C. range is considered to be due almost entirely to change in crystallinity. A comparison method for determining relative values of the degree of crosslinking fom the gel measurements is described.
Polymer fractionation. The method of fractionation into summative fractions
Authors: Broda Andrzej , Niwińska Teresa , Połowiński Stefan
Published: April 2003

The correctness of the application of the fraction method into summative fractions for polymer fractionation has been proved. The method of interpretation of the results of fractionation into summative fractions is explained. The basis of this method is the consideration of the function φ(β) which determines the relation between the average degree of polymerization and the weight fraction β of the summative fraction. The whole problem has been limited to the consideration of infinitely small calculated individual fractions. The paper describes the relation between the fractionation results and the selectivity of the polymer separation between the phases of the polymer‐liquid system. A scheme of analysis for systematic errors as well as for determining the exactness of the fractionation method is also given.
Mechanism of vinyl acetate emulsion polymerization
Authors: French David M.
Published: April 2003

The emulsion polymerization of vinyl acetate was investigated with the use of block copolymers of ethylene and propylene oxides (commercially known as Pluronic surfactants) as emulsifying agents. By electron microscopy, the average polymer particle size was determined as a function of conversion of monomer to polymer and as a function of the surfactant concentration. It was found that the number of polymer particles remained constant during the reaction. The polymer surface area per unit volume of completely polymerized emulsion was proportional to the surfactant concentration. In contrast with styrene polymerization, the number of particles varied with the cube of the emulsifier concentration, and the number of particles per unit of surfactant was much less than the number that would have been expected with styrene. It was concluded that the results were consistent with polymerization theory. An expression giving the number of polymer particles produced in the reactions proved to be much simpler than the accepted equation used in the case of water insoluble monomers such as styrene. This simplicity arises from the partial water solubility of vinyl acetate, which enables the monomer to diffuse completely into the polymer particles very early in the reaction. The variation of latex viscosity with polymer particle size was also investigated. At constant solids concentration, the logarithm of the viscosity was proportional to the polymer surface area per unit of latex.
Effect of complexing agents on the persulfate‐bisulfite catalysis of acrylonitrile polymerization
Authors: Campbell Charles H.
Published: April 2003

The effect of a number of iron complexing agents on the persulfate‐bisulfite catalysis of acrylonitrile polymerization was studied. Several complexing agents were found to be effective in retarding suspension polymerization of acrylonitrile with this redox system. A relationship was found betweeen the redox potential of the iron complex and polymerization rate. Evidence was shown that the persulfate‐bisulfite polymerization of acrylonitrile requires the presence of iron or other metal ions.
Dynamic mechanical properties of polyethylene terephthalate
Authors: Kawaguchi T.
Published: April 2003

Dynamic mechanical properties of polyethylene terephthalate have been measured as function of temperature at −70 to +310°C. at 100–200 cycles/sec. by a cantilever vibration method. Two mechanical loss maxima have been distinguished, and effects associated with variations in the degree of crystallinity and orientation and in the water content of the material have been investigated. The main softening region is shown to be influenced by the variations in the degree of crystallinity. Another process, which occurs at low temperature, is affected by changes in the water content of the material. The height of the loss maximum is increased when water is absorbed, although the temperature at which maximum loss occurs remains unchanged. Finally, the low temperature process is compared for members of a series of polyesters. Increasing the distance between the cyclic groups brings about a slight reduction in the temperature of this loss maximum. Interchange of the positions of the magnified image and O groups depresses the loss maximum temperature.