bluuebunny/crossref_metadata_2025_split huggingface dataset:
Icosahedral carboranes, 20. Polymerization and crosslinking mechanism of poly(m‐carboranylene‐siloxane)s
Authors: Dietrich Heinz. J. , Alexander R. P. , Heying Theodore L. , Kwasnik Herbert , Obenland Clayton O. , Schroeder Hansjürgen A. 
Published: April 2003

AbstractThe FeCl3 catalyzed bulk polymerization of a 1,7‐bis(methoxysilyl)‐1,7‐dicarba‐closo‐dodecaborane (12) (m‐carborane) (2) and a dichlorosilane resulting in a poly(m‐carboranylene‐siloxane) raw gum (1b, DEXSIL 200®) was found to occur in three distinct parts: First, the low temperature polymerization stage which includes end group exchange and the subsequent formation of poly(oxydimethylsilanediyl)s, second, the high temperature polymerization stage in which equilibration between the carboborane containing monomers and the polysiloxane occurs to produce polymeric material approximating 1b in composition, and third, the foaming stage in which the polymer chains are crosslinked to provide insoluble raw gum.
Studies on intramolecular association of salt groups in polymers following their binding with a metachromatic dye
Authors: Guhaniyogi Suhas C. , Mandal Broja M. 
Published: April 2003

AbstractIntramolecular association in dilute solution between carboxylate groups present at the ends of a polymer molecule was studied with reference to the effect of solvent and chain length of the polymers. The interaction was followed from the spectral change of a cationic metachromatic dye, pinacyanol (1), bound to the carboxylic groups of α,ω‐poly(butadiene dicarboxylic acid)s and α,ω‐poly(styrene dicarboxylic acid)s. It was found, as expected, that the extent of association decreases with the increase in polymer chain length and the increase in solvent polarity. Evidence was presented for the fact that in case of short chain polymeric dicarboxylic acids in benzene bis‐dye salt formation occurs to a considerable extent, even if less than 50% of the carboxylic groups are converted to the dye salt.
The effect of chain length on the solid‐state polymerization of N‐alkylmaleimides
Authors: O'Donnell James H. , Sothman Robert D. 
Published: April 2003

AbstractN‐alkylmaleimides from the N‐methyl to the N‐octadecyl derivative were polymerized in the solid state by γ‐radiation. Polymerization during irradiation generally showed sigmoidal conversion curves with high rates and complete conversion 10°C below the melting point. Post‐irradiation rates were lower and showed the typical approach to a “limiting” conversion. The polymerization rates increased with temperature and radiation dose and with the length of the alkyl chain. N‐methylmaleimide had a high rate of in‐source polymerization which was attributed to the volatility of the monomer.
Cristallisation de poly(oxyéthylène)s segmentés
Authors: Galin Jean‐Claude , Spegt Pierre , Suzuki Sunichi , Skoulios Antoine 
Published: April 2003

AbstractOn a étudié par analyse enthalpique différentielle, dilatométrie et diffraction des rayons X aux petits angles deux séries homologues de poly(oxyéthylène)s segmentés, comportant de 1 à 4 segments et obtenus par condensation de deux α,ω‐dihydroxy poly(oxyéthylène)s de masse moléculaire 2750 et 10600 respectivement sur du diisocyanate‐2,4 de toluène.On a montré que la structure de ces polymères est lamellaire, comme pour les poly(oxyéthylène)s ordinaires. Que le taux de cristallinité et la température de fusion diminuent sensiblement à mesure que le degré de condensation augmente. Que l'épaisseur des lamelles des polymères bisegmentés varie beaucoup, et de manière discontinue, avec la température de Cristallisation, comme pour les poly(oxyéthylène)s faiblement polydispersés, ordinaires. Et qu'en revanche cette épaisseur varie peu, ou pas du tout, avec la température de Cristallisation pour les polymères tri‐ et tétrasegmentés.On a conclu que ce comportement est dǔ au blocage structural exercé par les fonctions diuréthane lors du processus de recuit. Exclues des domaines cristallins, ces fonctions jouent le měme rǒle que les extrémités des chaǐnes des poly(oxyéthylène)s ordinaries.
Persistent problems and recent progress in the field of cationic polymerization
Authors: Sigwalt Pierre 
Published: April 2003

AbstractSome of the most important unsolved problems of cationic polymerizations are reviewed together with the most significant progress made recently.In the field of initiation reactions, there are more and more data showing that initiation of ethylenic monomers by Friedel Crafts catalysts does not always necessitate a coinitiator. The different hypotheses already put forward to explain these “direct initiations” are discussed and a new mechanism is proposed. The mechanisms of termination and transfer reactions are also examined.Concerning the mechanisms of propagation reactions, the difficulties in determining the concentration of active centers are outlined. Some progress was made by using stable carbocations as initiators, but some discrepancies between the results are discussed (existence of apparently negative activation energies). The different types of active species in equilibrium are examined, together with the nature of the non dissociated species. The differences between the propagation rate constants over free ions, measured in systems initiated by high energy radiations or more classical cationic initiators, are also discussed.
Electric field effects and electroinitiation in cationic polymerizations
Authors: Giusti Paolo 
Published: April 2003

AbstractThe results obtained by various authors in the study of cationic polymerizations carried out in the presence of an electric field of high strength, that we propose to call “electro‐influenced polymerizations”, are shortly reviewed.The most relevant results obtained in the author's laboratories, for the “electroinfluenced” cationic polymerization of anethole, isobutyl vinyl ether and cyclohexyl vinyl ether with constant or periodically reversed field polarity are illustrated.The analogies between these results and those obtained from studies on electroinitiated cationic polymerizations of various vinyl monomers with tetraalkylammonium perchlorates, tetraalkylammonium iodides or tetraalkylammonium triiodides are emphasized.On the basis of these analogies, we interpret the increase of the polymerization rate which is observed in some cases when a d.c. field is applied to a cationically polymerizing system as being due to electrodic processes, namely the anodic generation of new active centres through electrolysis of the counterions. This new interpretation can be formalized in a mathematical model which fits most of the experimental results so far obtained for electro‐influenced cationic polymerizations initiated by iodine.
Organometallic polymers, 28 Condensation polymerization of cobalticinium salts
Authors: Pittman C. U. , Ayers O. E. , Suryanarayanan B. , McManus S. P. , Sheats J. E. 
Published: April 2003

AbstractIonic polyesters of fairly low molecular weights were prepared by melt phase polytransesterification of 1,1′‐bis(carbethoxy)cobalticinium hexafluorophosphate (1a) and diols such as 1,10‐decanediol and 1,4‐bis(hydroxymethyl)benzene. Attempts to prepare polyamides by melt condensation from alkylene diammonium salts of 1,1′‐bis(carboxy)cobalticinium hexafluorophosphate 5a–d resulted in extensive decomposition, and pure polyamides could not be obtained. The polyesters were characterized by analyses, IR spectroscopy, gel permeation chromatography, and differential scanning calorimetry.
Chain transfer reaction of azoisobutyronitrile during polymerization of methyl methacrylate at 60°C
Authors: Ayrey Geoffrey , Haynes Alan C. 
Published: April 2003

AbstractThe kinetics of methyl methacrylate polymerization initiated by 14C labelled 2,2′‐azoisobutyronitrile at 60°C was re‐examined and the chain transfer constant of the initiator, CI, calculated to be approximately 2.10−2.
Hemicelluloses fractionation
Authors: Uglea C. V. 
Published: April 2003

AbstractThe solution properties of the hemicelluloses obtained from Phragmites communis and Arundo donax were investigated. The presented experimental data led to the conclusion that the molecular weight distribution of hemicelluloses depends on the studied product. The parallel existence of the chemical inhomogeneity and the molecular weight distribution determine the bimodal aspect of differential distribution curves obtained by fractionation.
Enzymes immobilisées, 6. Préparation d'invertase et de glucose oxydase immobilisées sur les vanacryls
Authors: Brown Erich , Joyeau Roger 
Published: April 2003

AbstractDe nouveaux polyaldéhydes, le vanacryl et les convanacryls (polyméthacrylate de vanilline et copolymères d'alcool allylique et de méthacrylate de vanilline, respectivement) ont été utilisés comme supports pour immobiliser l'invertase et la glucose oxydase. Les paramètres de la réaction d'immobilisation et les propriétés de l'enzyme immobilisée (activité en fonction du pH, km apparent, stabilité au cours du temps, utilisation intermittente et utilisation en continu sur colonne) ont été étudiées.
High 1,4‐cis‐polybutadiene by uranium catalysts, 2. Bulk and solution crystallization of polymers
Authors: De Chirico Aurelio , Lanzani Primo C. , Raggi Ernestina , Bruzzone Mario 
Published: April 2003

AbstractBulk isothermal crystallization kinetics of some highly tactic 1,4‐cis‐polybutadienes obtained with a new catalyst based on uranium derivatives were dilatometrically measured over a crystallization temperature (Tc) range from −30 to 0°C.The corresponding experimental melting temperatures (T) of uranium polybutadiene range from 3 to 12,5°C. A relationship between the isothermal bulk half‐crystallization time (t1/2) at −10°C and the molecular weight (MW) has been obtained.High MW fractions crystallize faster than low MW fractions as previously reported for 1,4‐cis‐polyisoprene. Uranium polybutadiene has been fractionated by crystallization. by cooling and stirring a dilute toluene solution. Under the same experimental conditions + rubber does not crystallize.
Decomposition, initiation, and chain transfer mechanism of dibenzoyldisulfane
Authors: Kondo Shuji , Tsuda Kazuichi 
Published: April 2003

AbstractIn order to understand the decomposition, initiation, and chain transfer mechanism of dibenzoyldisulfane (2), it was thermally and photochemically decomposed in cyclohexene Mechanistic proposals are made based on the primary reaction products. A comparison of the decomposition of 2 with that of benzoyl peroxide was also made, and it was found that the reaction mechanisms are different.
Untersuchungen zur friesschen verschiebung an hydroxybenzylphenol‐derivaten
Authors: Evers Heinz , Niemann Wilhelm , Böhmer Volker , Kämmerer Hermann 
Published: April 2003

AbstractAn den Acetaten 2a–c, 3b, 4b und 4d von sechs Hydroxybenzylphenol‐Derivaten wurde die Friessche Verschiebung mit AlCl3 als Katalysator in Nitrobenzol bei Temperaturen zwischen 40 und 70°C durchgeführt. Neben den zu erwartenden Hauptprodukten der Friesschen Verschiebung konnte durch Säulenchromatographie eine Reihe von Zwischen‐ und Nebenprodukten isoliert werden. Daraus ging hervor, daß wahrscheinlich eine teilweise Verseifung der Acetate als Nebenreaktion stattfindet. Eine Wanderung der Acetylgruppe an den benachbarten Phenolbaustein des gleichen Moleküls konnte nicht beobachtet werden. Sämtliche Verbindungen, einschließlich der Ausgangsprodukte, wurden durch ihre IR‐ und 1H‐NMR‐Spektren charakterisiert.
Untersuchungen von polymeren im massenspektrometer, 4. Abbaureaktionen von polybenzylen
Authors: Lenz Robert W. , Lüderwald Ingo , Montaudo Giorgio , Przybylski Michael , Ringsdorf Helmut 
Published: April 2003

AbstractDie Abbaureaktionen von unsubstituierten Poly(1,4‐phenylenmethylen)en (A) (Polybenzylen), Poly[(2,5‐dimethyl‐1,4‐phenylen)methylen] [Poly(2,5‐dimethylbenzyl)] (B), Poly[(2,3,5,6‐tetramethyl‐1,4‐phenylen)methylen] [Poly(2,3,5,6‐tetramethylbenzyl)] (C) und Poly(1,4‐phenylenäthyliden) [Poly(α‐methylbenzyl)] (D) wurden durch direkte Pyrolyse im Massenspektrometer untersucht. Die Massenpyrogramme von unter verschiedenen Reaktionsbedingungen dargestellten Polybenzylen wurden verglichen, mit dem Ziel, direkt Informationen über Strukturunterschiede wie Kettenverzweigung und unterschiedliche Verknüpfung der Benzyleinheiten zu erhalten; hierbei konnten in einem Falle auf höhere Kettenverzweigung deutende Bruchstücke nachgewiesen werden.Der thermische Abbau der unsubstituierten Polybenzyle und des Poly(2,5‐dimethylben‐zy1)s verläuft uberwiegend unter Disproportionierung und Übertragung von Wasserstoff der Methylengruppen. Es werden bei diesen Polymeren monomere und oligomere Pyroly‐sebruchstücke mit gesättigten (Phenyl‐, Alkyl‐) und ungesättigten (Chinonmethid‐) Endgruppen gefunden, während beim Poly(α‐methylbenzyl) auch Bruchstiicke mit Vinyl‐End‐gruppen auftreten.Das Abbauverhalten des Poly(2,3,5,6‐tetramethylbenzyl)s unterscheidet sich aufgrund der sterischen Spannung durch die Kernsubstituenten erheblich von den anderen Polybenzylen; neben geringerer thermischer Stabilität werden Hinweise auf einen unterschiedlichen Abbaumechanismus gefunden.Die elektronenstoßinduzierte Fragmentierung der ionisierten Pyrolysebruchstucke verläuft überwiegend unter “α‐Benzyl‐”, “β‐Benzyl”‐, “Alkylspaltung” und ortho‐ Umlagerung.
Photolysis of poly(methyl acrylate) in solution
Authors: Grassie Norman , Davis Thomas I. 
Published: April 2003

AbstractSolutions of poly(methyl acrylate) in methyl acetate, chloroform, methylene dichloride and benzene have been irradiated by 2 537 Å radiation and changes in number average molecular weight measured. The effect of time of irradiation, solvent, polymer concentration and the presence of radical initiator have been investigated and it is concluded that the scission results from random absorption of radiation directly by the polymer without direct participation by the solvent which acts only as an optical filter.
Untersuchungen zum oxidativen Abbau nativer Cellulose, 2. Einfluß der Alkalibehandlung auf die Viskositäts‐Molekulargewichts‐Beziehungen
Authors: Palma A. , Schulz G. V. 
Published: April 2003

AbstractUm die Kinetik des oxidativen Abbaus nativer Cellulose viskosimetrisch verfolgen zu können, müssen neue [η]‐M‐Eichbeziehungen aufgestellt werden, da die Behandlung der Cellulose mit konzentriertem Alkali den Staudingerindex [η] erniedrigt, ohne das Molekulargewicht M zu verändern. Es wurden zwei Reihen oxidativ abgebauter, verschieden lange mit Alkali vorbehandelter Cellulosen hergestellt und an diesen die Konstanten der Kuhn‐Mark‐Houwink‐Gleichung für die Cellulosenitrate in Aceton und die Cellulosen in Cuoxam (Cu(NH3)4(OH)2) durch Vergleich mit Lichtstreuungsmessungen bestimmt.
Modélisation de l'homopolymérisation radicalaire à l'aide de la théorie des chaînes de Markov
Authors: Pflugfelder Bernard , Manzato Franck 
Published: April 2003

AbstractA l'aide des concepts de la théorie des chaînes de Markov il a été possible de construire un modèle d'homopolymérisation. Ce modèle dépend de six paramètres et décrit une homopolymérisation en masse en y incluant les mécanismes de terminaison des chaînes (couplage et disproportion) ainsi que le transfert sur monomère.Cette modélisation, suivant les valeurs des paramètres, est capable de représenter des polymérisations pouvant avoir des indices de polydispersité supérieurs à deux, et saffranchit ainsi des contraintes habituelles.
The application of the molecular probes gas‐chromatographic technique to the study of polypropylene transitions
Authors: Galassi Silvana , Audisio Guido 
Published: April 2003

AbstractBy means of molecular probes gas‐chromatographic technique we have investigated the first and second order transitions of three stereoisomeric polypropylenes: isotactic, syndiotactic, atactic. The choice of the molecular probe for the detection of the first order transition is not particularly difficult. For the 2nd order transition one must choose a molecular probe which, at the transition temperature range, has a appropriate solvent action on the polymer, used as stationary phase: thus, at low temperatures and for hydrocarbon polymers, a suitable molecular probe is a solvent for the polymer and, at high temperatures, a molecular probe is one with limited solvent action and with no specific interactions with the polymer.
Ring‐Opening polymerization of cycloolefins with catalysts derived from ruthenium and iridium
Authors: Porri Lido , Rossi Renzo , Diversi Pietro , Lucherini Antonio 
Published: April 2003

AbstractAn investigation was carried out on the polymerization of norbornene, cyclopentene and cyclooctene by the following iridium and ruthenium compounds: chlorobis(cyclooctene)iridium (1), carbonylchlorobis(cyclooctene)iridium (2), trifluoroacetatobis(cyclooctene)iridium (3), chloroiridic(IV) acid (4), dichloro(2,7‐dimethylocta‐2,6‐diene‐1,8‐diyl)‐ruthenium (5a), and bis(trifluoroacetato)‐(2,7‐dimethylocta‐2,6‐diene‐1,8‐diyl)ruthenium (5b). All the above catalysts were found to be very active for the polymerization of norbornene via ring‐opening. Iridium catalysts were practically inactive for the polymerization of cyclopentene and cyclooctene, but gave copolymers of norbornene with cyclopentene and cyclooctene via ring‐opening. The ruthenium catalysts displayed no activity for the polymerization of cyclopentene and cyclooctene, but it was found that after treatment with H2 they became active for the polymerization of cyclopentene. The results obtained from the reaction of norbornene and aliphatic olefins suggest that the above catalysts act by metathesis. The particular features of these catalysts were examined.
Synthesis and viscosity behavior of poly(γ‐p‐biphenylmethyl‐L‐glutamate) in benzene/dichloroacetic acid mixtures, a comparison with poly(γ‐benzyl‐L‐glutamate)
Authors: Feijen Jan , Sederel Wim L. , de Groot Klaas , de Visser Anthonie C. , Bantjes Adriaan 
Published: April 2003

AbstractThe synthesis of poly(γ‐p‐biphenylmethyl‐L‐glutamate), PBPLG, (poly{L‐imino‐1‐[2‐(4‐biphenylylmethoxycarbonyl)ethyl]‐2‐oxoethylene}), (1d) is described. The viscosity behavior of this polymer in benzene/dichloroacetic acid mixtures (c=0,2.10—3—1,4.10—3 g/cm3) at 25°CC is investigated. The results are compared with measurements on poly(γ‐benzyl‐L‐glutamate), PBLG, (poly[L‐imino‐1‐(2‐benzyloxycarbonylethyl)‐2‐oxoethylene]), (1c) under the same conditions. A transition from a rigid hydrogen bonded helix to a random solvated coil occurs in two stages for both: PBPLG (first stage 0—55%, second stage 55—100% dichloroacetic acid) and PBLG (first stage 0—70%, second stage 70—100% dichloroacetic acid).Therefore, the introduction of a p‐phenyl substituent in PBLG leads to a less stable helix in benzene/dichloroacetic acid mixtures.The stability and viscosity behavior of PBLG in benzene/dichloroacetic acid mixtures (c=0,2.10—3—1,4.10—3g/cm3) is quite similar to the behavior of PBLG in m‐cresol/dichloroacetic acid mixtures (c=1,0.10—3—4,0.10—3 g/cm3).
Polymerisationskinetische und konduktometrische messungen an polystyrylionenpaaren in einem größeren temperaturbereich
Authors: Schmitt B. J. , Schulz G. V. 
Published: April 2003

AbstractMessungen der Bruttogeschwindigkeitskonstante von Polystyryl‐Natrium in 3‐Methyltetrahydrofuran (3‐Me‐THF) in Abhängigkeit von der Konzentration der “lebenden” Kettenenden und der Natriumionen ergeben, daß die Monomeraddition wie in anderen polaren Lösungsmitteln nach einem Mehrwegmechanismus erfolgt. Der Übergang vom Kontakt‐ zum solvatgetrennten Ionenpaar wird in einem Temperaturbereich von — 110 bis +85°CC mit Hilfe kinetischer Messungen im Strömungsrohr und durch Leitf ähigkeitsmessungen verfolgt. Analog zu entsprechenden Untersuchungen in Tetrahydrofuran kann dabei die Polymerisation über jeweils eine Art von Ionenpaaren fast vollständig isoliert beobachtet werden. Die thermodynamischen und kinetischen Parameter der Polymerisation werden mitgeteilt.
Modellrechnungen zur Lösungsmittel‐ und Polymerenabhängigkeit der thermodynamischen Eigenschaften von Polymerlösungen
Authors: Lechner Manfred D. 
Published: April 2003

AbstractUmfangreiche Messungen an Polymerlösungen haben gezeigt, daß eine deutliche Korrelation zwischen chemischem Potential, Entropie und Enthalpie besteht. Es wurden verschiedene Modelle (quasi‐chemische Näherung, Theorie der 1‐2 Kopplung, Theorem der übereinstimmenden Zustände u. a.) durchgerechnet und mit den experimentellen Werten verglichen. Hierbei ergab sich, daß das Theorem der übereinstimmenden Zustände den breitesten Anwendungsbereich hat, wohingegen die anderen Theorien für spezielle Probleme brauchbare Resultate liefern.
Der Ablauf der Rekristallisation in verstreckten Polyäthylenfilmen
Authors: Cayrol Bertrand , Kubát Josef , Petermann Jürgen 
Published: April 2003

AbstractDas Gefüge und die Orientierungen von kalt‐ und warmverstreckten Polyäthylenfilmen werden in Abhängigkeit von der Temperzeit mittels Transmissionselektronenmikroskopie untersucht. Die Kristallitlänge (Dimension senkrecht zur Molekülrichtung) wächst stetig von ca. 100 Å direkt nach der Kaltverformung auf 3000 Å nach einer Temperzeit von 8 Wochen bei 122°C an. Die Orientierung der Filme ändert sich während des Temperns von einer Fasertextur über eine b‐Textur zu einer (110)‐Textur. In warmverstreckten Filmen ist die Kristallitlänge nach der Verformung ca. 500 Å und wächst dann mit ähnlicher Geschwindigkeit wie bei kaltverstreckten Filmen. Im Unterschied zu den kaltverstreckten Filmen tritt die b‐Textur direkt nach der Verformung auf und geht in eine (110)‐Textur über. Diese Beobachtungen werden mit Hilfe der Rekristallisation gedeutet.
Studies on hydrolysis reaction of model substances of cellulose in the presence of polymer catalysts, 1. Hydrolysis reaction of dextrin in the presence of poly(vinylalcohol‐co‐vinylsulfonic acid)
Authors: Arai Kenichiro , Ise Norio 
Published: April 2003

AbstractThe hydrolysis of dextrin was studied in the presence of poly(vinyl alcohol‐co‐vinylsulfonic acid). The reaction was slightly accelerated by the copolymer in comparison with sulfuric acid. Mixtures of poly(vinyl alcohol) and poly(vinylsulfonic acid) retarded the reaction. Although the reaction rates tended to increase with decreasing molecular weight of the substrate, the reaction rates in the presence of the copolymer were always larger than in the case of sulfuric acid at the same molecular weight of the substrate. Both the enthalpy and entropy of activation in the presence of the copolymer were smaller than those for sulfuric acid or ethanesulfonic acid; the acceleration observed was due to the decrease of ΔH≠ as was noted earlier for a variety of reactions in the presence of polyelectrolytes. All of these activation parameters satisfied well the isokinetic relationship, indicating that the reaction mechanism was not changed by the presence of the copolymer.
Kinetics of 1,3,5‐trioxacycloheptane formation in the electro‐initiated copolymerization of 1,3‐dioxolane with trioxane
Authors: Mengoli Giuliano , Furlanetto Ferdinando 
Published: April 2003

AbstractThe kinetics of 1,3,5‐trioxacycloheptane (1,3,5‐trioxepane) formation in the electroinitiated copolymerization of 1,3‐dioxolane with trioxane was investigated, using 1,2‐dichloroethane as solvent and tetrabutylammonium perchlorate as background electrolyte. It was found that at temperatures between 50 and 70°C 1,3,5‐trioxepane is the main product of 1,3‐dioxolane/trioxane interaction till it reaches an equilibrium concentration in the system and that afterwards 1,3,5‐trioxepane can take part itself in the copolymerization which involves 1,3‐dioxolane and trioxane.1,3,5‐Trioxepane formation with respect to the copolymerization process, was unfavoured by decreasing temperature and increasing trioxane concentration, whereas it seemed largely independent from solvent and catalyst nature.