bluuebunny/crossref_metadata_2025_split huggingface dataset:
Säulenchromatographische trennungen von nukleosid/nukleotid‐ und nukleosid/dinukleosidphosphatgemischen an nukleosidgelen
Authors: Schott Herbert , Greber Gerd 
Published: April 2003

AbstractDie säulenchromatographische Trennung von Nukleosiden, Mononukleotiden und Dinukleosidphosphaten an Polymergelen mit kovalent eingebauten Nukleosidresten wurde untersucht.In Wasser treten Nukleoside so stark mit den Nukleosidgelen in Wechselwirkung, daß eine quantitative Trennung der Nukleoside von Mononukleotiden und Dinukleosidphosphaten möglich ist. Dagegen werden in einer wäßrigen Pufferlösung Nukleoside und Dinukleosidphosphate gemeinsam eluiert, so daß eine Trennung der Mononukleotide von Nukleosiden und Dinukleosidphosphaten gelingt.
Säulenchromatographische trennung von mono‐, di‐und trinukleotidgemischen an nukleosidgelen
Authors: Schott Herbert , Greber Gerd 
Published: April 2003

AbstractMit Hilfe von Nukleosidgelen war es in wäßrigem Milieu möglich, nicht nur Gemische von Mono‐, Di‐ und Trinukleotiden, sondern auch Gemische dieser drei Spezies untereinander zu trennen. Die Trennergebnisse zeigen, daß die Stärke der Retardierung von Nukleotiden an Nukleosidgelen mit steigendem Purinanteil ansteigt. Daher erfolgt die Basenpaarung zwischen den am Gel gebundenen Nukleosidresten und den gelösten Nukleotiden vorwiegend über den Stapeleffekt. Aus diesem Grund können auch Basenpaare entgegen dem Sinne von WATSON und CRICK gebildet werden.
Üuber die kationische polymerisation von äthylensulfid, initiiert durch SO3
Authors: Han M. J. , Jaacks V. 
Published: April 2003

AbstractSO3 verursacht eine heftige Polymerisation von Äthylensulfid in wasserfreien, inerten organischen Lösungsmitteln. Die kinetischen Daten, die chemische Analyse der Endgruppen und die IR‐spektroskopische Untersuchung des Polymerisats sprechen gegen eine Cokatalyse und für einen direkten zwitterionischen Initiierungsschritt unter Bildung von
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Die kationischen aktiven Zentren werden rasch durch Reaktion mit den Sulfidgruppen des Oligomeren unter Bildung nicht wachstumsfähiger, acyclischer Sulfoniumionen desaktiviert; dadurch bleiben die kinetischen Kettenlängen klein, und es entsteht ein verzweigtes oder vernetztes, unlösliches Produkt.
Polymerization of N‐CARBOXY‐α‐amino acid anhydride by organometallic compounds III. Mechanism of asymmetric selective polymerization of n‐carboxy alanine anhydride by organoaluminum catalysts
Authors: Makino Tetsuya , Inoue Shohei , Tsuruta Teiji 
Published: April 2003

AbstractCopolymerizations of D‐ and L‐N carboxy alanine anhydride by Al(C2H5)3 and (i‐C4H9)2AlN(C2H5)2 were studied in order to elucidate the mechanism of stereospecific polymerization of the N‐carboxy‐α‐amino acid anhydride (NCA) with the two organoaluminum compounds.The enantiomer involved in higher concentration in the starting monomers was polymerized preferentially in the propagation step by these catalysts. The mechanism of the asymmetric selective polymerization was concluded to be the growing chain end control, neither the enantiomorphic catalyst sites control nor the control by the helical conformation of the growing polymer chains.It was found in Al(C2H5)3 initiated polymerization system that almost perfect stereoselective reaction took place at an early stage of the polymerization; that is, about five mole of the NCA initially reacted with one mole of Al(C2H5)3 and the amounts of L‐ and D‐enantiomer of the NCA reacted were always equal independently of enantiomer ratio in the starting NCA.
On the mechanism of polymerization of methyl substituted 7‐oxabicyclo‐[2.2.1]‐heptanes
Authors: Kops Jørgen , Spanggaard Hans 
Published: April 2003

AbstractThe polymerization of endo‐ and exo‐2‐methyl‐7‐oxabicyclo‐[2.2.1]‐heptane with phosphorus pentafluoride catalyst in methylene dichloride and nitrobenzene has been found to proceed with increasing yield and molecular weight with decreasing temperature in the range +25°C to −30°C, but at −78°C there was no polymerization. The ring‐opening appears to proceed exclusively through nucleophilic attack at C‐1 in the alkyloxonium ion, leading to only one type of structural unit in each type of polymer. The polymers of the exo‐2‐methyl isomer are completely soluble in THF, whilst those of the endo‐2‐methyl isomer are insoluble. The solubility appears to be connected with flexibility of the chain molecule associated with the possibility for interconversion between different chair conformations for the cyclohexane ring‐structures.By ring‐closure of 2.6‐dimethylcyclohexane‐(1.4)‐diol two isomers have been prepared and identified. The endo,exo‐2.6‐dimethyl‐7‐oxabicyclo‐[2.2.1]‐heptane gives insoluble, highly crystalline polymers with phosphorus pentafluoride catalyst in methylene dichloride. The failure of the corresponding exo,exo‐2.6‐dimethyl isomer to polymerize under identical conditions is explained by conformational analysis.
A study of the nature of the active centres in anionic polymerization
Authors: Polyakov D. K. , Baranova N. I. , Gantmakher A. R. , Medvedev S. S. 
Published: April 2003

AbstractThe electron absorption spectra and the electrical conductivity of two systems: 1.1‐diphenylalkyllithium/tetrahydrofuran and the dilithium compound of 9.10‐dialkyl‐9.10‐dihydroanthracene/tetrahydrofuran were studied. The investigations were carried out over a wide range of concentrations of the organolithium compounds, covering both the region of predominant ion pairs and that of high relative free ion content, according to conductometric data. It is shown for both systems studied that the electron absorption spectrum remains practically unchanged when passing from ion pair to free ions.
Kinetic studies on the reaction of formaldehyde with diphenyl sulfide. Formaldehyde resins. 99
Authors: Kunieda Norio , Suzuki Akira , Kinoshita Masayoshi , Imoto Minoru 
Published: April 2003

AbstractKinetic studies on the acid‐catalyzed reaction of formaldehyde with diphenyl sulfide (DPS) were carried out in acetic acid in the presence of sulfuric acid. The rate of the initial stage of the reaction was found to be in agreement with the following equation.

The relative rates of diphenyl sulfide and its homologous compounds in the reaction with formaldehyde gave a good correlation with BROWN‐OKAMOTO's σ⊕ values and a large ρ value. The polar effects of substituents of the substituted diphenyl sulfides on the rates were found to be considerably large. From these results a plausible mechanism of the reaction has been deduced.
Studies on homologous series of oligomeric antioxidants derived from p‐cresol/formaldehyde condensates. II. Evaluation in polystyrene
Authors: Huglin M. B. , Knight G. J. , Wright W. W. 
Published: April 2003

AbstractThe effectiveness of compounds of the type
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as antioxidants in polystyrene has been examined and the results compared with those for some commercial high mol. wt. antioxidants. Effectiveness was found to depend not only on mol. wt., but also on molecular structure, concentration, and temperature of use.
Syntheses and reactions of functional polymers. LXIV. Reactions of phenyl polystyryliodonium salts
Authors: Yamada Yorinobu , Okawara Makoto 
Published: April 2003

AbstractPhenyl polystyryliodonium salts, containing bisulfate, thiocyanate, bromide, or trifluoroacetate as counter anion, were allowed to decompose in dimethylformamide and dioxane at 100°C. The bisulfate and thiocyanate anion preferentially, and trifluoroacetate anion selectively attacks the unsubstituted phenyl ring to give polystyrene derivatives with two components and polyiodostyrene, respectively. On the contrary, the bromide anion preferentially attacks the phenyl ring of the polystyrene side. This result was explained on the basis of the co‐operative charge transfer bonding between the aromatic ring of the iodonium salt and its adjacent aromatic ring through bromide anion. These nucleophilic substitution reactions on the polymer are investigated and compared with their model reactions.
Redox polymerisation. Kinetics of the reaction initiated by the malonic acid/Mn3⊕ system
Authors: Devi N. Ganga , Mahadevan V. 
Published: April 2003

AbstractKinetics of vinyl polymerisation initiated by the redox system malonic acid/Mn3⊕ have been investigated in the temperature range of 5‐15°C in sulphuric acid and perchloric acid media for acrylonitrile and methyl methacrylate. A mechanism involving the formation of a complex between Mn3⊕ and malonic acid whose decomposition yields the initiating free radical with the polymerisation being terminated by mutual interaction of growing radicals has been suggested.
Thermal copolymerizations of vinyl sulfides with some weak acceptor monomers
Authors: Inoue Hiroshi , Otsu Takayuki 
Published: April 2003

AbstractThermal copolymerizations of vinyl sulfides (VS) with some weak electron‐accepting monomers were studied on the basis of donor‐acceptor interaction. VS were thermally polymerized in the presence of diethyl fumarate, dimethyl maleate, acrylonitrile (AN) methyl methacrylate (MMA), methyl acrylate, and ethyl acrylate (EA) in the absence of radical initiators to yield copolymers. The monomer/copolymer composition curves for these copolymerizations were quite similar to those produced from polymerizations initiated by α.α′‐azobisisobutyronitrile, indicating that the propagating species are free radicals. Similar conclusions were obtained from experiments with the inhibitor benzoquinone, and from the small observed solvent effect, but no proof for the occurrence of cationic or anionic polymerization was obtained.Although the existence of a 1 : 1 donor/acceptor complex in AN/VS system was spectroscopically confirmed, such interaction was appreciably weak, in comparison to that of maleic anhydride/VS. In the systems MMA/VS and EA/VS no interaction was observed. Accordingly, the intiating radical species in AN/VS system might be considered to be formed through donor/acceptor interaction. It was also found that alternative copolymers were obtained from thermal copolymerization of AN with VS in the presence of zinc chloride. The initiation mechanism for these thermal copolymerization is discussed.
Electroinitiated cationic polymerization of ethyl and i‐butyl vinyl ethers
Authors: Mengoli Giuliano , Vidotto Graziano 
Published: April 2003

AbstractThe electroinitiated cationic polymerization of ethyl and i‐butyl vinyl ethers has been studied under various experimental conditions using NaB(C6H5)4 as background electrolyte.Differring from other electrolytes with higher oxidation potentials, the NaB(C6H5)4 allows appreciable current intensities and the polymerizations can occur at moderate rates.The monomer to polymer conversion presents a slightly sigmoidal shape as a function of the quantity of electricity and at a fixed quantity of electricity is independent from the current intensities.The molecular weights of the polymers are substantially controlled by chain transfer to monomers and solvents: the relative chain transfer constants are reported.The reaction temperature affects remarkably the molecular weights while the influence of dielectric constant of the reaction medium is negligible.An interpretation is given of the effect of NaB(C6H5)4 electrolyte on the initiation mechanism and on the resulting conditions of polymerization.
Studies in polymerisation of vinyl acetate. II.
Authors: Potnis S. P. , Deshpande A. M. 
Published: April 2003

AbstractThe effect of increase in temperature on various constants such as overall rate constant (K), the quotient of the rate constant of propagation and the square root of the constant of termination (Kp/Kt1/2), rate constant for initiation (KI), transfer constants due to the monomer and initiator (CM), (CI), respectively, and chain transfer constant due to solvent (CS) has been studied in detail by the polymerisation of vinyl acetate in bulk as well as in glacial acetic acid at 65°C with benzoyl peroxide and at 50 and 60°C with azobisisobutyronitrile as initiators. A comparative study of the results obtained has been made.
Polyreaktionen in orientierten systemen. II.. Polymerisation von 4‐vinylpyridinium‐salzen in micellar geordneten lösungen
Authors: Mielke I. , Ringsdorf H. 
Published: April 2003

AbstractDie Kinetik der „spontanen”︁ Polymerisation von 4‐Vinylpyridiniumperchlorat in Wasser zeigt, daß oberhalb einer „kritischen”︁ Konzentration ein Wechsel des Polymerisationsmechanismus eintritt entsprechend einer Änderung in der Struktur des sich bildenden Polymeren. Untersuchungen der Viskosität und der Oberflächenspannung an Modellsubstanzen zeigen, daß dieses Phänomen der Bildung von Micellen und der darin ablaufenden Polymerisation zuzuschreiben ist. Der alkalische Abbau der Polymeren wurde untersucht.
Polyhydrochinonsulfone. VI. Darstellung eines redoxharzes auf der basis von (2‐vinylsulfonyl)‐naphthohydrochinon‐(1.4)
Authors: Manecke Georg , Rühl Christian‐Steffen , Wehr Gregor 
Published: April 2003

Abstract(1.4‐Diacetoxy)‐(2‐vinyl‐sulfonyl)‐naphthalin wurde dargestellt. Durch Copolymerisation des Monomeren mit Styrol und p‐Divinylbenzol und anschließende Sulfonierung und Verseifung des Polymeren wurde ein Redoxharz erhalten, dessen Austausch‐ und Redoxkapazität bestimmt wurde.
Anionic polymerization of cyclic sulfides initiated by metal complexes of aromatic nitriles and ketones
Authors: Panayotov Ivan M. , Berlinova Iliyana V. 
Published: April 2003

AbstractThe capacity of metal complexes of aromatic nitriles and ketones to initiate the polymerization of ethylene sulfide, propylene sulfide and styrene sulfide is studied by means of spectral and chemical methods. The results indicate that the polymerization of styrene sulfide initiated by anion‐radicals of the used nitriles and ketones proceeds via electron transfer from the initiator to the monomer, while ethylene sulfide polymerizes by way of valence bond formation between the initiator and the monomer. The polymerization of propylene sulfide is a multistage reaction linked with the formation of propylene and initiator species. The polymerization of all three monomers initiated by aromatic nitrile dianions proceeds by electron transfer.
Vergleich der zahl aktiver zentren und einiger kinetischer konstanten bei der polymerisation von äthylen, propylen und buten‐1 mit ZIEGLER‐NATTA‐katalysatoren. 11. Mitt. Zur polymerisation mit metallorganischen mischkatalysatoren
Authors: Jung K. A. , Schnecko H. 
Published: April 2003

AbstractFür die drei Olefine, Äthylen, Propylen und Buten‐1, werden mit dem Katalysatorsystem TiCl3/Al(C2H5)2Cl in Abhängigkeit von der Polymerisationszeit gemessen: der Polymerisationsverlauf, die Zahl der Metall‐Polymer‐Bindungen (über Endgruppenbestimmung nach Abbruch mit tritiiertem Alkohol) und die Viskosität der gebildeten Polymeren. Aus diesen Daten lassen sich die Polymerisationsgeschwindigkeit, die Konzentration an aktiven Zentren, die Uneinheitlichkeit sowie weitere Reaktionskonstanten bestimmen. Die Ergebnisse werden diskutiert; sie lassen den Schluß zu, daß sich ein im Ausgangszustand gleiches Katalysatorsystem monomerspezifisch verhält und verändert.
The effect of ionizing radiation on the thermal properties of an ethylene/propylene copolymer
Authors: Melia T. P. , Salpadoru N. , Wilkinson J. 
Published: April 2003

AbstractThe results of heat of fusion measurements on an ethylene/propylene copolymer (containing 27 mole‐% propylene), which had been subjected to different doses of gamma radiation (0–620 Mrad) at 298°K are described. The dependence of both the enthalpy and entropy of fusion on radiation dose is similar to that observed previously with isotactic polypropylene.
The addition halogenation of polyalkenamers. I. Synthesis and properties of the homologous series of poly(1.2‐dihaloalkamer)s
Authors: Dall'Asta G. , Meneghini P. , Gennaro U. 
Published: April 2003

AbstractThe addition chlorination and bromination of a series of polyalkenamesr

where n varies from 2 to 10, yield a homologous series of poly(1.2‐dihaloalkamer)s

Substitution halogenation is completely avoided by operating in methylene chloride solution. Experimental features of the halogenations are examined. No appreciable degradation of the polymers accompanies the halogenation reaction. Some physical properties of poly‐(1.2‐dihaloalkamer)s are reported and compared with those of chlorinated polyethylenes. Many of the polymers exhibit X‐ray crystallinity by well oriented fibre spectra and first order transition at DTA analysis.
Relation between pH and viscosity of some poly(alkylvinylpyridine N‐oxides) in aqueous solution
Authors: Holt Paul , Tamami Bahman 
Published: April 2003

AbstractThe variation with pH of the viscosities of aqueous solutions of the following polyvinylpyridine oxide derivatives has been studied, viz. atactic poly(2‐vinylpyridine 1‐oxide), poly(2‐methyl‐6‐vinylpyridine 1‐oxide), poly(3‐methyl‐2‐vinylpyridine 1‐oxide), poly(5‐ethyl‐2‐vinylpyridine 1‐oxide), poly(4‐vinylpyridine 1‐oxide), poly(3‐methyl‐4‐vinylpyridine 1‐oxide) and poly(2‐methyl‐5‐vinylpyridine 1‐oxide), and mainly isotactic poly(5‐ethyl‐2‐vinylpyridine 1‐oxide).When the vinyl group is in the 3 or 4 position, viscosity is maximal between pH 6 and 10, probably because polymer chains are cross‐linked by water molecules attached to N‐oxide groups. Poly(methyl‐2‐vinylpyridine 1‐oxides) give a pH/viscosity curve that is roughly the inverse of this with a minimal viscosity within this pH range. These polymers probably take up a tightly packed conformation near neutrality due to bonding between N‐oxide and α‐H of the polyvinyl chain. More than one conformation is possible and an attempt has been made to interpret the positions of the viscosity peaks in terms of the possible conformations.
Zur verzögernden wirkung aromatischer aldehyde auf die radikalische polymerisation von vinylverbindungen
Authors: Kämmerer Hermann , Mück Karl‐Friedrich , Janz Birgit 
Published: April 2003

AbstractDie Einwirkung einer Reihe aromatischer Aldehyde auf die mit α.α‐′Azobisisobuttersäurenitril gestarteten Polymerisationen von Styrol und Methacrylsäuremethylester wurde untersucht (a) durch Vergleich der Polymerausbeuten; (b) durch quantitative Analyse der UV‐Spektren der gereinigten Polymeren und (c) durch Vergleich ihrer M̄n‐ und M̄n‐Werte. Bei der Styrolpolymerisation zeigen 4‐Phenyl‐benzaldehyd und Indol‐3‐aldehyd keine Einwirkung. 4‐Phenylazo‐benzaldehyd, Benzaldehyd, Anthracen‐9‐aldehyd und m‐(2.4‐Dinitrophenoxy)‐benzaldehyd verzögern die Polymerisation. Bis auf Benzaldehyd wird hierbei ihr kovalenter Einbau in das Polystyrol nachgewiesen. Für 4‐Phenylazo‐benzaldehyd konnte eine scheinbare Übertragungskonstante bestimmt werden. Bei der Polymerisation von Methacrylsäuremethylester wird entweder inhibierende, verzögernde oder keine Einwirkung der Aldehyde beobachtet; sie werden sämtlich nicht eingebaut. Jedoch zeigen die Molekulargewichte der Polymethacrylsäuremethylester eine Erniedrigung, die bisher nicht erklärt werden kann.
Application de la chromatographie sur gel à l'étude des polyéthylènes ramifiés
Authors: Prechner Roland , Panaris René , Benoit Henri 
Published: April 2003

AbstractL'utilisation conjointe de la chromatographie sur gel et des mesures viscosimétriques permet de définir un indice moyen de ramification. La comparaison de cet indice avec celui obtenu en associant la chromatographie sur gel et les mesures directes de masse moléculaire permet d'apprécier l'hétérogénéité en degrés de ramification d'un échantillon donné. La méthode est appliquée à quelques échantillons commerciaux de polyéthylène haute pression.
Study of radical polymerization by means of ESR. I. Homogeneous polymerization of styrene
Authors: Bresler S. E. , Kazbekov E. N. , Fomichev V. N. , Shadrin V. N. 
Published: April 2003

AbstractAn extremely sensitive instrument for ESR measurements in liquid media was developed on the basis of a new principle of registration of the ESR signals. By means of this device the spectrum of macroradicals of polymerizing styrene was recorded, and the stationary concentration of growing chains was measured quantitatively. Thus the first direct data for the chain propagation constant of the radical polymerization of styrene were obtained.
Morphology of epitaxially crystallized poly‐γ‐benzyl‐L‐glutamate
Authors: Rybnikar F. , Geil P. H. 
Published: April 2003

AbstractEpitaxial crystallization of poly‐γ‐benzyl‐L‐glutamate (PBLG) on 001 alkali halide single crystal surfaces results in block and row structures that are qualitatively similar for various solvents and crystals used. There is a definite tendency in the first stages of epitaxial crystallization to align the α‐helical molecules along the 〈110〉 substrate direction. We propose that the epitaxial structures are built up of straight, non‐folded α‐helical molecules associated side‐by‐side and, in the case of low M̄w fractions, also end‐to‐end. The epitaxial crystallization of PBLG was observed only in the vicinity of the precipitation point. The orienting and attracting forces coming from the crystal substrate have a long range character and are of at least two kinds. The decoration effect of PBLG epitaxial structures could be used for substrate surface structure characterization.
Untersuchungen über die γ‐struktur in unverstrecktem und verstrecktem 6‐polyamid
Authors: Illers K. H. , Haberkorn H. , Simák P. 
Published: April 2003

AbstractDie in der monoklinen α‐Struktur kristallisierten Bereiche des unverstreckten und verstreckten 6‐Polyamids wandeln sich bei der Behandlung mit wäßriger Jod‐Alkalijodid‐Lösung in die γ‐Struktur um. Diese γ‐Struktur wird röntgenographisch, IR‐spektroskopisch und kalorimetrisch eingehend untersucht.Verglichen mit der bei schneller Abkühlung aus der Schmelze oder bei der Kaltkristallisation entstehenden γ*‐Struktur hat die γ‐Struktur eine gute Ordnung, die sich durch Tempern noch erheblich verbessern läßt. Die gut geordnete γ‐Struktur besitzt keine hexagonale, sondern eine monokline oder orthorhombische Elementarzelle und eine Kristalldichte von 1,190 g/cm3. Sie ist im Gegensatz zur γ*‐Struktur thermisch sehr stabil und geht beim Erwärmen unmittelbar in die Schmelze über. Proben mit γ‐ und solche mit γ*‐Struktur zeigen denselben Zusammenhang zwischen Schmelzwärme und spezifischem Volumen und besitzen einen übereinstimmenden Wert für die Dichte der amorphen Bereiche (1,090g/cm3), der mit dem der Dichte einer völlig amorphen Probe übereinstimmt. Die Schmelzwärme des γ‐Kristalls beträgt 51 cal/g. Die in den Röntgendiagrammen und IR‐Spektren vorhandenen Unterschiede zwischen Proben mit γ‐ und γ*‐Struktur werden diskutiert.
Copolymères séquencés poly(oxyéthylène)/poly(oxyéthylène‐oxyadipoyl) à charnières uréthane
Authors: Galin Monique , Galin Jean Claude 
Published: April 2003

AbstractNous avons étudié la cinétique de la réaction du bis(4‐isocyanatophényl)méthane (MDI) et du l‐méthyl‐2.4‐diisocyanatobenzène (2.4‐TDI) sur le poly(oxyéthylène) (POE, M̄n = 2750) et le poly(oxyéthylèneoxyadipoyl) (PAE, M̄n = 2350) en solution dans le toluène ou le dioxanne, et pour un rapport constant [NCO]/[OH] = 2. Il est possible d'obtenir, dans des conditions expérimentales bien déterminées, des «prépolymères» porteurs de groupements terminaux isocyanate. Ces «prépolymères» présentent cependant une stabilité limitée dans le temps, qui se manifeste par un accroissement de la masse moléculaire moyenne et de la fonctionnalité, résultant de la formation de liaisons allophanate intermoléculaires. Ce processus est en particulier accéléré dans le cas des POE.La polycondensation en solution homogène entre «prépolymère» PAE ω.ω′‐diisocyanate et POE conduit à des copolymères séquencés linéaires, dans lesquels le nombre moyen de séquences (3 à 20) et la longueur de la séquence POE (2750 ≤ M̄n ≤ 10600) peuvent varier dans un assez large domaine. L'architecture de ces macromolécules est caractérisée par l'alternance régulière de séquences hydrophobes PAE et hydrophiles POE reliées entre elles par des charnières uréthane. Ces matériaux constituent des modèles intéressants dans le domaine des copolymères séquencés cristallisables doués de propriétés amphipatiques, et dans celui des élastomères polyuréthane.