bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymerisation höhergliedriger cyclischer imine
Authors: Rentsch Christoph , Lüssi Heinz 
Published: April 2003

AbstractDodecamethylenimin und N‐Methyldodecamethylenimin lassen sich bei Temperaturen oberhalb 200°C polymerisieren. Als Katalysatoren dienen die Salze der Monomeren, LEWIS‐Säuren und Alkylierungsmittel. Zuerst bilden sich Oligomere, welche erst später in höhere Polymere und schließlich in vernetzte Produkte übergehen. Gleichzeitig werden kleine Mengen Ammoniak bzw. Trimethylamin gebildet. Der Vorgang beruht im wesentlichen auf einer Umalkylierung, an der sämtliche Aminogruppen teilnehem. Demzufolge lassen sich die gleichen Polymeren unter ähnlichen Bedingungen auch durch Polykondensation aus Diaminen unter Ammoniakabspaltung herstellen. Andere cyclische Imine mit mehr als 7 Ringgliedern verhalten sich ähnlich. Hexamethylenimin führt infolge der thermodynamischen Stabilität der sich bildenden N‐substituierten 7‐gliedrigen Iminringe nur zur Bildung niedermolekularer Produkte. Das gleiche gilt auch für das N‐Methylhexamethylenimin.
Frictional behavior of the correlated chain
Authors: Horta Arturo 
Published: April 2003

AbstractThe friction coefficient of linear macromolecules is calculated for the correlated chain model using KIRKWOOD's approximation. This model (proposed by SANCHEZ and FRANKENBERG) incorporates a certain long‐range correlation between the segments of a random chain, and contains two parameters: CF, which depends on this correlation (CF = 1 for a random coil and CF = 0 for a fully extended chain), and the radius of gyration RG. In the limit of long chains, the friction coefficient B is a function of these two parameters and the ratio B/6πη0RG (η0 = solvent viscosity) decreases with CF. This means that the correlation between segments has a greater influence on RG than on the equivalent STOKES radius of the macromolecule. These results are used to interpret the influence of excluded volume on B. The validity of the model is ascertained by comparing the theory with the light scattering envelopes and friction coefficients recently reported by MIJNLIEFF et al. for poly(α‐methylstyrene) in good and poor solvents.
Polymerisation of vinyl monomers by transition metal benzyl compounds. Part I. Initial observations
Authors: Ballard D. G. H. , van Lienden P. W. 
Published: April 2003

AbstractA range of stable transition metal alkyl compounds of given formula M(CH2X)4(M = Zr, Ti, Hf) exhibit polymerisation activity in the absence of light towards certain vinyl monomers, e.g., styrene, p‐bromostyrene, methyl methacrylate and ethylene. Rates of polymerisation increase markedly on exposure to light at wavelengths between 450 and 600 nm. It has been established that these polymerisations are probably of the coordinated anionic type. At wavelengths below 450 nm the polymerisation is dominated by a radical process, the radicals being produced by the photolysis of the catalyst (zirconium tetrabenzyl).
Stereocontrol. VII. The relation between instantaneous and final diad and triad fractions in one‐way polymerization mechanism
Authors: Johnson Brian L. , Elias Hans‐Georg 
Published: April 2003

AbstractThe relationships between isotactic and syndiotactic diads and triads resp., on one hand, and the rate constants of the different propagation steps in MARKOV 1st and 2nd order processes have been calculated under the assumption of a steady state condition for the concentration of free radicals. Instantaneous and final diad fractions are equal only if

i and s stand for the formation of an isotactic or a syndiotactic diad at an existing diad A or B. A and B stand for i and s in a MARKOV 1st order process and for ii, is, si, and ss in a MARKOV 2nd order process.
Light scattering of polymethylmethacrylate solutions in binary solvent mixtures. Part 1. In acetone/chloroform mixtures
Authors: Fujishige Shoei , Elias Hans‐Georg 
Published: April 2003

AbstractAn atactic and an isotactic polymethylmethacrylate have been investigated by light scattering measurements at 25°C in acetone/chloroform mixtures. The reciprocal apparent weight average molecular weight (at c → 0) passes through a minimum, the coefficient of preferential adsorption through a maximum with increasing chloroform content of the mixtures. The second virial coefficient is no monotoneous function of the chloroform content.
Free volume theories for penetrant diffusion in polymers
Authors: Machin D. , Rogers C. E. 
Published: April 2003

AbstractFree volume theories for the concentration dependence of organic penetrant diffusion coefficients in rubbery amorphous polymers have been correlated and extended with emphasis given to similarities and mathematical equivalence for small volume fractions of penetrant. The nature of the empirical parameter used in VASENIN's theory has been further clarified by considering the kinetic and thermodynamic aspects of the plasticization effect. Using similar assumptions to those originally used for rubbery polymers, VASENIN's theory is extended to treat solvent diffusion in glassy and semi‐crystalline polymers. A procedure has been developed to extend the applicability of FUJITA's theory over a wider range of polymer‐solvent composition. The general effects of plasticization leading to increase in penetrant diffusion coefficients and decrease in polymeric glass transition temperatures are considered as resulting from the same functional increase in fractional free volume of a mixture with increasing solvent content. It is suggested that the two phenomena should be quantitatively compared for mutual consistency rather than attempting to develop a fully rigorous treatment for either. In this way diffusion data can be predicted from measurements of glass temperature depression or vice versa.
Etude du mécanisme des polymérisations amorcées par les métaux alcalino‐terreux. III. Copolymérisation du butadiène, de l'isoprène et du styrène en millieu non polaire
Authors: Maleki P. , François B. 
Published: April 2003

AbstractNous avons étudié la copolymérisation de trois couples de monomères: butadiène/isoprène, butadiène/styrène et isoprène/styrène; cette copolymérisation est amorcée par des suspensions de calcium, strontium et baryum en milieu toluène. Les paramètres de copolymérisation ont été déterminés dans chaque cas. Les valeurs ainsi obtenues permettent de classer les trois monomères par ordre de réactivité vis‐à‐vis des différentes espèces anioniques en présence. Lorsque le promoteur est constitué par du calcium ou du strontium l'isoprène est moins réactif que le butadiène mais plus que le styrène. En présence du baryum au contraire le styrène est plus réactif que l'isoprène mais moins que le butadiène.
Preparation and polymerization of racemic and optically active tert‐butyl thiirane
Authors: Dumas Philippe , Spassky Nicolas , Sigwalt Pierre 
Published: April 2003

AbstractPreparation and polymerization of tert‐butyl thiirane are described. The racemic monomer was obtained by reaction in aqueous solution of tert‐butyl oxirane and potassium thiocyanate. The levorotatory enantiomer was synthesized from R(−) 3.3‐dimethyl 1.2‐butane diol passing through the intermediate of the cyclic carbonate. Polymerization of the racemic monomer with coordinate type initiators give crystalline, soluble products of high molecular weights and high melting points (close to 205°C). Crystalline, soluble, high molecular weight polymers but of lower melting points (close to 160°C) could also be obtained with the levorotatory enantiomer, either by coordiante or purely anionic initiation. These polymers have high optical activities of positive sign in all the solvents used. NMR measurements show that racemic and optically active crystalline polymers have the same isotactic structure. The differences in melting point and X‐ray diagrams show the existence of several crystalline modifications. These results indicate a strong difference in the behaviour of tert‐butyl thiirane as compared to methyl thiirane.
Carbon‐13 nuclear magnetic resonance spectroscopy of polystyrene and poly‐α‐methylstyrene
Authors: Inoue Yoshio , Nishioka Atsuo , Chûjô Riichirô 
Published: April 2003

AbstractThe carbon‐13 high resolution nuclear magnetic resonance spectra with proton spin decoupling of polystyrene and poly‐α‐methylstyrene were measured. The spectra clearly split corresponding to triad, tetrad, and partially pentad placements, and these peaks were tentatively assigned. By comparison of the triad tacticity of poly‐α‐methylstyrene determined from carbon‐13 spectra with that from proton spectra, it was confirmed that the nuclear OVERHAUSER effect due to proton decoupling has little effect on the relative intensities of the peaks assigned to chemically equivalent carbons except for stereochemical configuration.The stereospecific polymerization mechanisms are discussed on the basis of the microtacticity determined from carbon‐13 spectra. As a result, it is concluded that poly‐α‐methylstyrene polymerized with cationic and anionic catalysts can be described by BERNOULLIAN statistics, while the atactic polystyrene does not obey BERNOULLIAN but first or second order MARKOVIAN statistics.
Die spontane Desaktivierung beim oligomeren α‐Methylstyryl‐Natrium in Tetrahydrofuran
Authors: Schmitt B. J. 
Published: April 2003

AbstractBei der Alterung von oligomerem α‐Methylstyryl‐Na in Tetrahydrofuran (THF) erfolgt eine Hydridabspaltung an der aktiven Endgruppe und ein Protonentransfer vom Lösungsmittel. Der Selbstabbruch kann durch ein einfaches Schema von Simultanreaktionen beschrieben werden.
Experimental verification of effects of conditions of solutional fractionation on molecular weight distribution of the first fraction by atactic polystyrene/methylcyclohexane system
Authors: Kamide Kenji , Sugamiya Ken , Terakawa Toshikazu , Hara Tasuku 
Published: April 2003

AbstractThe solutional fractionations were carried out experimentally on lowering the temperature of solutions of atactic polystyrene in methylcyclohexane. The concentration of the initial solution and the relative amount of the polymer dissolving in the polymer‐lean phase (i.e., the amount of the fraction) were systematically changed. Gel permeation chromatography was applied to determine the molecular weight distribution (MWD) of the first fractions and the original polymer. In addition, polydispersity parameters including the ratio of the weight average molecular weight to the number average molecular weight, Mw/Mn, and the standard deviation, σ′, were calculated from MWD curves. Effects of the fractional conditions on the MWD for the first fractions were compared with those obtained by the computer simulation as well as the experimental results obtained in the case of the precipitational fractionation. The validity of the theoretical conclusions on the solutional fractionation, reached from the computer simulations, was definitely confirmed from the experiments.
Multimerisation: Assoziation und Aggregation. IX. Konzentrationsabhängigkeiten reduzierter Viskositäten bei offenen Assoziationen
Authors: Watterson John Grant , Elias Hans‐Georg 
Published: April 2003

AbstractDie Konzentrationsabhängigkeiten reduzierter Viskositäten werden für Systeme mit offener Assoziation unter folgenden Annahmen theoretisch berechnet: von der Assoziationszahl unabhängige Gleichgewichtskonstanten der Assoziation, gleiche Teilchenform für alle Assoziate, Abwesenheit von thermodynamischen und hydrodynamischen Kreuzwechselwirkungen. Die Kurven πsp/c = f(c) können nach diesen Modellrechungen konvex oder konkav zur c‐Achse gekrümmt sein, Extremwerte aufweisen oder sogar praktisch linear erscheinen. Im letztea Fall liefert die konventionelle Auswertung meist zu hohe scheinbare HUGGINS‐Konstanten. Aus Viskositätsmessungen allein können bei Abwesenheit zusätzlicher Informationen, außer in sehr extremen l'ällen, weder Schlüsse auf die An‐oder Abwesenheit von Assoziationen noch auf einen bestimmten Typ von Assoziation geschlossen werden.
Aggregation and helix—coil transition of poly‐L‐glutamic acid in pyridine—water solution
Authors: Giancotti V. , Quadrifoglio F. , Crescenzi V. 
Published: April 2003

AbstractThe conformational state of poly‐L‐glutamic acid (PLGA) in the mixed solvent pyridine/water has been studied by means of different techniques (ORD, IR, PMR, and viscosity). It has been found that at low water contents PLGA forms aggregates the stability of which depends in a sensitive manner on temperature and solvent composition.At higher water content PLGA undergoes a helix–coil transition.
The syntheses of protected 9‐vinyladenine monomers
Authors: Kaye Howard , Chou Hardy J. 
Published: April 2003

AbstractIn order to develope synthetic approaches to poly‐(9‐vinyladenines) of varying degrees of stereoregularity a series of protected 9‐vinyladenine monomers have been synthesized which are soluble in organic solvents.
Ein iteratives numerisches verfahren zur auswertung von elutionsanalysen an eng verteilten polymeren
Authors: Rauch B. 
Published: April 2003

AbstractEin iteratives Rechenverfahren zur Bestimmung der Molekulargewichtsverteilungsfunktionen aus experimentellen, mit der isothermen Elution ermittelten Daten – speziell für Polymere kleiner Uneinheitlichkeit – wird beschrieben. Hierbei wird die klassisch gewonnene Verteilung als Näherung betrachtet, rechnerisch auf der Basis des Phasengleichgewichts erneut fraktioniert und aus den ermittelten Fraktionen die Zusatzinformation zur Konstruktion einer besseren Näherung gewonnen. Um die Stabilität der Konvergenz des Verfahrens zu zeigen, wurde eine Simulationsrechnung durchgeführt. Schließlich wird das Verfahren an experimentell gewonnenen Daten eines aus zwei gut bekannten, eng verteilten Polystyrolen erzeugten Gemisches demonstriert und diskutiert.
Réactions d'amorçage de la polymérisation anionique de la vinyl‐2 pyridine et leur application à la synthèse de copolymères séquencés de la vinyl‐2 pyridine et du sulfure de propylène I. Copolymères comportant deux séquences
Authors: Gourdenne Albert 
Published: April 2003

AbstractLa réaction d'amorçage de la polymérisation anionique de la vinyl‐2 pyridine par le diphénylméthyl sodium a été étudiée par spectrophotométrie. Le diphénylméthyl sodium ne réagit pas avec les cycles pyridiniques mais, par contre sa conversion est incomplète, la vitesse de propagation étant bien supérieure à la vitesse d'amorçage. La synthèse de copolymères biséquencés linéaires de la vinyl‐2 pyridine et du sulfure de propylène confirme ces résultats.
Untersuchung der basischen Endgruppen bei der mit Aminsalzen initiierten kationischen Lactampolymerisation
Authors: Csürös Zoltán , Rusznák István , Bertalan György , Anna Péter , Kőrösi Jenő 
Published: April 2003

AbstractEntsprechend dem von den Verfassern vorgeschlagenen Kettenwachstumsmechanismus sind bei der mit Aminsalzen initiierten kationischen Lactampolymerisation nicht nur Ammonium‐, sondern auch Amidin‐Endgruppen vorhanden. Es wurde eine Methode zur Bestimmung der beiden basischen Endgruppen nebeneinander ausgearbeitet. Zunächst wird die Gesamtkonzentration aller basischen Endgruppen durch potentiometrische Titration mit Perchlorsäure in nichtwäßrigem Medium bestimmt. In einer anderen Probe werden die Amino‐Endgruppen mit Essigsäureanhydrid acetyliert und die unverändert gebliebenen Amidin‐Endgruppen auf die gleiche Weise titriert.Die Konzentration beider Endgruppen ändert sich im Laufe der Polymerisation in Abhängigkeit von der Temperatur und der Initiatorkonzentration charakteristisch. Die Gesamtbasizität nimmt in jedem Fall auf Grund hydrolytischer Prozesse zu, die durch die Einwirkung des während der Amidinbildung entstandenen Wassers ablaufen. Die Konzentration der Ammonium‐Endgruppen nimmt in jedem Fall in Abhängigkeit von der Temperatur und der Konzentrationen des Initiators ab, die Konzentration der Amidingruppen ändert sich in entgegengesetzter Richtung. Die Änderung der Endgruppenkonzentration ist mit den kinetischen Kurven der Polymerisation und dem vorgeschlagenen Wachstumsmechanismus in gutem Einklang. Beim Auftreten eines Wendepunkts entspricht dieser den Extremwerten der Endgruppenkonzentrationen.
Reactions at low temperature of AlEt3 or ethyl‐aluminum‐chlorides with Me3CCl and addition of ethylene to cationic species
Authors: Priola A. , Cesca S. , Ferraris G. 
Published: April 2003

AbstractReactions between Et3–xAlClx (where x = 0, 1, 2, 3) and Me3CCl, carried out in CH2Cl2, CH3Cl or n‐pentane at −78°C, have been investigated by VPC‐MS analysis of the resulting products. The use of CD2Cl2 and (CD3)3CCl made it possible to confirm the suggested reactions.Under mild conditions and in the presence of ethylene the system EtAlCl2 + Me3CCl yields branched, saturated C6, C8, and C10 hydrocarbons.Conductimetric and NMR observations during the reactions have confirmed the VPC–MS results, which could be interpreted according to an overall cationic mechanism involving the following reactions:

Abstraction of a β‐hydrogen atom from an ethyl group linked to Al and simultaneous formation of ethylene;
repeated addition of ethylene to cationic species;
termination by hydride transfer;
termination by chloride ion abstraction by carbonium ions

.
The chemical shifts and the conformations of linear hydrocarbons
Authors: Ando Isao , Nishioka Atsuo 
Published: April 2003

AbstractThe proton chemical shifts of some hydrocarbons (n‐C9H20, n‐C10H22, n‐C11H24, and n‐C22H46) were calculated assuming the extended chain with one gauche form and predominant contribution of the magnetic anisotropy effect of the C‐C bonds along the chain. It is suggested that the high field peak of the two splitted methylene signals of n‐C22H46 in α‐chloronaphthalene (α‐CINap) solution is assigned to the methylene protons next to the gauche bond in a planar zigzag chain, of which molecular motion is restrained strongly by α‐CINap molecules and the second methylene group next to the terminal methyl group, whereas the low field peak is assigned to other methylene protons, the molecular motion of which is restrained weakly. A small peak at lower field than the two large peaks is assigned to the gauche methylene protons in a planar zigzag chain the molecular motion of which is restrained by α‐CINap molecules.
The configuration of block copolymers of polyisoprene and polystyrene in dilute solution. I. Unperturbed dimensions
Authors: Urwin J. R. , Girolamo M. 
Published: April 2003

AbstractThe unperturbed dimensions of block copolymers of polystyrene and polyisoprene in dilute solution have been determined from measurements made under theta conditions, by application of the FLORY‐FOX theory to viscosity data. In solvents, where theta temperatures preclude direct evaluation, the STOCKMAYER‐FIXMAN method has been applied. The results show that unperturbed dimension determined under theta conditions, whether measured directly or by appropriate extrapolation procedures, vary linearly with composition. Thus the characteristic ratio for the block copolymer may be calculated from homopolymer data according to the relation

where x is the mole fraction and superscripts PS and PI refer to polystyrene and polyisoprene respectively. The steric factor σ = rr obeys a similar relation.Short range interaction parameters have also been determined by application of equations relating osmotic second virial coefficients with the excluded volume and which have been shown to be reasonably successful when applied to homopolymers. Data from viscosity and osmometry methods are compared and discussed.
Hydrogenation of unsaturated polymers with diimide
Authors: Mango L. A. , Lenz R. W. 
Published: April 2003

AbstractWe have studied the homogeneous hydrogenation of a series of unsaturated polymeric substrates with diimide formed from the thermal decomposition of p‐toluenesulfonylhydrazide (TSH) at elevated temperatures (110 to 160°C) and in aromatic solvents. At a TSH/olefin ratio of 2.0, homopolymers of butadiene, polycyclohexadiene, and polyisoprene were quantitatively hydrogenated as were two styrene/butadiene copolymers. Alkyl branching at or near the residual polymer double bond, as in methyl rubber and poly‐2.5‐dimethyl‐2.4‐hexadiene, gave less than 50% hydrogenation. Polychloroprene was not hydrogenated by diimide (conversions less than 10%) which is in agreement with the behavior previously observed for low molecular weight olefins.The unsaturated polymers which were successfully hydrogenated were soluble and, hence, showed no excessive crosslinking. Polycyclohexadiene and polyisoprene, the only samples evaluated for molecular weight changes, exhibited no chain degradation.Some qualitative kinetic data were obtained using per cent conversion vs. time data. Under the conditions of toluene reflux and TSH/olefin ratios of 1.5, the relative rates of hydrogenation for cis, trans and vinyl butadiene units was kcis ≃ ktrans < kvinyl.Byproducts from the diimide generation resulted in the introduction of 0.2 to 1.0% of p‐CH3C6H4SO2‐groups into the polymer based upon 100% of the double bonds originally present.
Polymerization of N‐vinylcarbazole by (3d)‐transition metal oxides
Authors: Biswas Mukul , Mishra Prashant K. 
Published: April 2003

AbstractThe bulk polymerization of N‐Vinylcarbazole (NVC) is carried out using some 3 d‐metal oxides as catalysts and the following order of reactivity is suggested for the various metal oxides studied:

the oxides of copper and cobalt being ineffective. Some kinetic studies are carried out with the NVC/MnO2 system. Endorsed by the observed retardation of the rate in the presence of water and thiophene a cationic mechanism is suggested for the polymerization. The incapability of the oxides of Cu and Co to act as good catalysts is tentatively explained by supposing that they act as oxidizing rather than π‐complexing polymerization catalysts. Stirring does not show any influence on the rate of polymerization.
Über die Wechselwirkung des Katalysators und Cokatalysators mit dem Monomeren und dem Polymeren bei der kationischen Polymerisation des Isobutylens. II. Modellstudium des Polymerisations‐Depolymerisations‐Gleichgewichts im System Triisobutylen/AlBr3/DBr/Heptan
Authors: Kříž Jaroslav , Marek Miroslav 
Published: April 2003

AbstractTriisobutylen unterliegt bei der Reaktion mit AlBr3/DBr neben der Deuterierung einer Skelettisomerisierung und bildet höhere Oligomere. Beide Reaktionen werden durch die Spaltung der Skelettbindungen der intermediären Carboniumionen erklärt. Die Fragmente, die durch diese Spaltung entstehen, können mit weiteren Komponenten des Reaktions‐systems reagieren. Die mögliche Bedeutung dieser Reaktionen für den Mechanismus des Kettenabbruchs und der Kettenübertragung bei der kationischen Polymerisation des Isobutylens wird kurz diskutiert.
Cationic polymerization of 2‐methyl‐1.3‐dioxepane
Authors: Okada Masahiko , Yagi Kazuo , Sumitomo Hiroshi 
Published: April 2003

Abstract2‐Methyl‐1.3‐dioxepane was polymerized in 1.2‐dichloroethane with triethyl oxonium tetrafluoroborate and boron trifluoride as initiators. This polymerization involves a monomer‐polymer equilibrium and the polymer consists of regularly alternating tetrahydrofuran and acetaldehyde units. The thermodynamic parameters for the polymerization were determined from the temperature dependence of the equilibrium monomer concentration as follows: ΔHSS = −2.1 ± 0.3 kcal/mole and ΔS0SS = −8.9 ± 1.3 cal/mole deg. The ceiling temperature for the 1 mole/1. solution is −37°C. The attempted polymerization of 2.2‐dimethyl‐1.3‐dioxepane gave only a crystalline cyclic dimer.