bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multimerization: Association and aggregation, 14. Distinction between open and closed associations
Authors: Elias Hans‐Georg , Šolc Karel 
Published: April 2003

AbstractOpen and closed molecule‐based associations with experimentally incompletely accessible concentration dependencies of the apparent molecular weights can be distinguished by plotting the apparent weight average molecular weight, (Mw)app, versus the inverse apparent number average molecular weight, (Mn). For closed associations, straight lines are observed for theta‐systems and concave ones for non‐theta‐systems of associating rods. Open associations in these cases give convex lines for both, theta and non‐theta‐systems. Loops can be expected for both types of associations for non‐theta‐systems at high concentrations. A similar plot can be based on apparent z and weight average molecular weights.
Contribution à l'étude de la structure des polytéréphtalates de quelques polyméthylèneglycols
Authors: Joly Adrien M. , Nemoz Guy , Douillard Alain , Vallet Georges 
Published: April 2003

AbstractL'étude des domaines cristallins au moyen de la diffraction des rayons X de fibres étirées bien cristallisées a montré que les polytéréphtalates d'éthylèneglycol (1a), de butanediol‐1,4 (1b), de pentanediol‐1,5 (1c) et d'hexanediol‐1,6 (1d) cristallisent dans le système triclinique. L'évolution des paramètres ne se fait pas régulièrement en fonction de la longueur du motif monomère. La connaissance du réseau cristallin et de la structure chimique nous a conduit à proposer des conformations permettant aux chaǐnes de s'arranger dans le réseau et de proposer ainsi des hypothèses de structure pour les polyesters étudiés.Ces résultats sont confirmés par l'examen des spectres IR des échantillons cristallins qui présentent des bandes caractéristiques de conformation trans très importantes pour les polyesters 1a et 1d alors que les polyesters 1b et 1c présentent des bandes de structure gauche importantes. L'étude du taux de cristallinité par différentes méthodes (rayons X, calorimétrie différentielle, spectres IR et colonne à gradient de densité) confirme la valeur proposée pour le volume de la maille du polyester 1d.
Optically active hydrocarbon polymers with aromatic side chains, 7. Synthesis and properties of copolymers of vinyl aromatic monomers with chiral α‐olefins
Authors: Carlini Carlo , Chiellini Emo 
Published: April 2003

AbstractOptically active alkyl‐α‐olefins such as (R)‐3,7‐dimethyl‐1‐octene (1), (S)‐4‐methyl‐1‐hexene (2), and (S)‐5‐methyl‐1‐heptene (3) were copolymerized with styrene (4), 1‐vinylnaphthalene (5) or 2‐methylstyrene (6) by Ziegler‐Natta catalysts based on VCl4, TiCl4 or TiCl3 “ARA” and Al[CH2CH(CH3)2]3 or Al(C2H5)3.Fractionation by solvent extraction as well as optical rotation and differential dichroic absorption (Δε) demonstrate unequivocally the formation of copolymer macromolecules. The isotactic enchainment of the units is supported by IR and X‐ray spectra.A remarkable contribution to optical rotation by aromatic units is observed in the copolymers of 1. In addition circular dichroism data relative to the lowest energy π→π* electronic transition of aromatic nuclei show that aromatic units, when inserted in optically active copolymer macromolecules, assume a preferential chiral conformation.
Synthesis of polyurethanes containing imide groups in the main chain from a mixture of isomeric N,N‐bis(isocyanatotolyl)pyromellitimides and α,ω‐diols
Authors: Matsuda Hideaki 
Published: April 2003

AbstractThe reaction of pyromellitic dianhydride (1) with 2,4‐tolylene diisocyanate (2) was investigated. It was found that N,N′‐bis(isocyanatotolyl)pyromellitimide (3) is formed, which contained three stereoisomers.Polyurethanes containing imide groups in the main chain were synthesized by a polyaddition reaction of the diimide 3 with α,ω‐diols. The polymers obtained were yellow or yellow brown powders with inherent viscosities (in DMF) of 14–28 cm3/g. DMF, DMSO and m‐cresol were found to be good solvents for these polymers. The results of TG of these polymers were discussed.
Characterization of the structure of the stereocomplex of poly(methyl methacrylate) in solution from NMR relaxation data
Authors: Spěváček Jiří , Schneider Bohdan 
Published: April 2003

AbstractFrom the values of relaxation times T2 determined on a pulse spectrometer, and from the shape of bands in high resolution (HR‐) and broad line (BL‐) NMR spectra, two types of protons, different in mobility, were found to exist in the associated stereocomplex of isotactic (it‐) and syndiotactic (st‐) poly(methyl methacrylate) (PMMA). From the analysis of NMR spectra, measured at magic angle rotation (MAR‐NMR), the mobility of the ester groups in the stereocomplex is shown to be greatly hindered. Temperature changes of HR‐NMR spectra of mixed solutions of it‐ and st‐PMMA in benzene indicate that the associated segments of the stereocomplex can be characterized as junctions of a network of nonassociated sequences.
Zum Mechanismus des Abbaus von Polymeren in Lösung durch Ultraschall
Authors: Basedow Arno M. , Ebert Klaus H. 
Published: April 2003

AbstractDie Abbaureaktion von Dextran durch Ultraschall wurde im Molekulargewichtsbereich von 30 000 bis 90 000 in verschiedenen Lösungsmitteln untersucht. Die Abbauprodukte wurden durch ihre Molekulargewichtsverteilungen, die mit Hilfe von Chromatographie an porösem Glas bestimmt wurden, charakterisiert. Aus den Ergebnissen der Untersuchungen konnte abgeleitet werden, daß die Abbaureaktion nach erster Ordnung verläuft, die Abbaukonstante proportional dem Molekulargewicht ist, und die Moleküle bevorzugt in zwei nahezu gleichgroße Bruchstücke zerfallen. Die Art des Lösungsmittels hat dabei einen erheblichen Einfluß auf die Abbaukonstanten; es wurde gefunden, daß diese der molaren Verdampfungsenthalpie des Lösungsmittels direkt proportional sind. Der Einfluß der Konformation des Polymeren auf die Abbaukonstanten wurde studiert, wobei sich ergab, daß mit einer Aufweitung der Polymerknäuel die Abbaukonstanten größer wurden.Die Ergebnisse bestätigen die allgemeine Auffassung, daß die Kavitäten, die bei der Ultrabeschallung entstehen, für die Abbaureaktion verantwortlich sind. Eine eindeutige Entscheidung, ob die inhomogenen Strömungsfelder oder die Stoßwellen, die bei der Implosion der Kavitäten entstehen, für den Molekülbruch letztlich maßgebend sind, kann mit den bisher vorliegenden Ergebnissen nicht getroffen werden. Der Befund, daß aufgeweitete Knäuel leichter abgebaut werden, spricht für den Stoßwellenmechanismus. Andererseits wird ein Modell für die Abbaureaktion angegeben, in dem beide Effekte insoweit zusammenwirken, daß die inhomogenen Strömungsfelder das Polymerknäuel zunächst strecken und die nachfolgende Stoßwelle den Molekülbruch bewirkt.
Study by 19F nuclear magnetic resonance spectroscopy of the cationic polymerization of tetrahydrofuran initiated by PF5
Authors: Andruzzi Fulvio , Pescia Aldo , Ceccarelli Giulio 
Published: April 2003

AbstractBy means of 19F‐NMR spectroscopy it was possible to detect and estimate the hexafluorophosphate ion (PF) in the THF polymerization, initiated by PF5 in methylene dichloride at 25°C. The observed variations with time of [PFPF], [PF5·THF], and [PPF] were analysed kinetically, and by means of the resulting equations, the rate constants for initiation, propagation and termination were evaluated. Comparison of our kp value with those of others indicates that our method is sound, and we conclude that it should be applicable to other similar systems.
Flash pyrolysis of poly(propylene) stereoisomers
Authors: Audisio Guido , Bajo Giuseppe 
Published: April 2003

AbstractStereoirregular, isotactic, and syndiotactic poly(propylene) were decomposed by the gaschromatographic pyrolysis technique. Some components of the tetramer fraction were identified and resolved into the two possible diastereomers. The relative intensities of these vary according to the tacticity of the decomposed polymer. The hydrogenation is a source of perturbation in the tacticity measurement as well as the partial isomerization.
Evaluation of triads in methyl methacrylate/methacrylic acid copolymers by 1H‐NMR in different solvents and 13C‐NMR
Authors: Klesper Ernst , Johnsen Andreas , Gronski Wolfram , Wehrli Felix W. 
Published: April 2003

AbstractThe probabilities of compositional‐configurational triads in tactic and atactic methyl methacrylate/methacrylic acid copolymers are evaluated. After verification of the assignment of syndiotactic and isotactic triads in the 1H‐NMR spectra of tactic methyl methacrylate/methacrylic acid copolymers in three NMR solvents, the chemical shifts of the heterotactic triads are postulated by shift increments. The postulated assignment of the heterotactic triads is supported by comparison of the experimental 1H‐NMR peak intensities of atactic methyl methacrylate/pentadeuteromethacrylic acid copolymers and atactic pentadeuteromethyl methacrylate/methacrylic acid copolymers in three NMR solvents with calculated triad probabilities. The compositional and configurational parameters needed for the calculation of triad probabilities are determined. It is shown how the peak areas obtained from the two partially deuterated, atactic copolymers in different solvents may be combined to determine the probabilities of all compositional‐configurational triads in atactic copolymers. Possibilities for the evaluation of triad probabilities from the 13C‐NMR spectra of tactic and atactic methyl methacrylate/methacrylic acid copolymers are presented.
Strukturuntersuchungen an Adsorptionsschichten makromolekularer Stoffe, 2. Haftstellenzahlen linearer Polyester an wasserfreien γ‐Aluminiumoxidoberflächen und ihre Beeinflussung durch Poly(oxyäthylen)e und Wasser als Konkurrenzadsorptive
Authors: Joppien Günter Richard 
Published: April 2003

AbstractDie Struktur der Adsorptionsschichten von linearen, gesättigten, aliphatischen Polyestern, adsorbiert aus Lösung in CCl4an die Oberfläche von wasserfreiem, pyrogenem γ‐Aluminiumoxid, wird durch IR‐spektroskopische Bestimmungen der Bruchteile spezifisch gebundener Kettencarbonylgruppen (Haftstellenzahlen) und der adsorbierten Mengen beschrieben. Durch verschieden starke H‐Brückenbindung der Carbonylgruppen an oberflächenständige Aluminolgruppenpaare und anwenigstens zwei Arten isolierter Alumisolgruppen, die sich durch die Zahl ihrer O2—‐Nachbarn unterscheiden, wird die IR‐Bande der CO‐Valenzschwingung nach drei kleineren Wellenzahlen verschoben. Die energetische Heterogenität der Adsorptionsplätze an der wasserfreien Al2O3‐Oberfläche bewirkt, daß sich nach rasch erfolgender Adsorption die Gleichgewichts‐Schlaufenstrukturen in den Polyesterschichten sehr langsam ausbilden. Die Geschwindigkeit der Langzeit‐Orientierungsprozesse ist von der absorbierten Menge, vom Molekulargewicht der Adsorptive und von der Polyesterstruktur, nicht dagegen von der chemischen Natur der Endgruppen der Polyester abhängig. Mit einer Monoschicht Wasser bedeckte Al2O3‐Oberflächen haben energetisch homogene Adsorptionsplätze, und Polyester‐Gleichgewichtsstrukturen kleiner Schlaufengröße bilden sich daran rasch aus. Coadsorption von Polyäthylenglykolen [Poly(oxyäthylen)en] bewirkt keine Desorption von Polyestermolekeln, sondern ein merkliches Ansteigen der adsorbierten Polymermengen in den sich ausbildenden Mischadsorptionsschichten, die aus großen Adsorptionsschlaufen bestehen. äthergruppen der Polyäther können offenbar gebundene Kettencarbonylgruppen der Polyester nur von Aluminolpaaren und von isolierten Aluminolgruppen ohne O2−‐Nachbarn, nicht dagegen von Aluminolgruppen mit vier oder drei O2−‐Nachbarn verdrängen.
A general method of the synthesis of “step‐ladder” polymers
Authors: Korshak Vasiliy V. , Rusanov Alexander L. , Iremashvili Tsiala G. , Plieva Larisa Kh. , Lekae Tat'yana V. 
Published: April 2003

AbstractA new general method for the synthesis of “step‐ladder” polymers was developed. It involves the interaction of aromatic diamines, containing in o‐positions aromatic heterocycles with reactive hydrogen atoms, with aromatic dicarboxylic acids or their derivatives. This general method was used for the preparation of new classes of thermally stable polymers of type 27, 28, 29 and 30, containing 1,2,4‐triazole‐, 1,2,4‐triazolo[4,3‐c]‐quinazoline‐, benzimidazole‐ or benzimidazolo[1,2‐c]quinazoline‐rings. Physical properties of these polymers were determined together with those of corresponding model compounds.
Determination of compositional heterogeneity of styrene‐methyl methacrylate block copolymers
Authors: Kotaka Tadao , Uda Taichiro , Tanaka Takeshi , Inagaki Hiroshi 
Published: April 2003

AbstractDeterminations of compositional heterogeneity of anionically prepared block copolymers of styrene (S) and methyl methacrylate (M) were attempted by three different methods: thin‐layer chromatography (TLC), cross‐fractionation, and by a computer simulation method. To this end the TLC elution behavior of diblock and triblock copolymers of SM‐ and MSM‐type were compared with those of their statistical copolymers. A new TLC method was devised which does not require any reference samples as TLC elution standards. The compositional distributions determined by the three methods were in good agreement with one another, and found to be unexpectedly broad. The implication of such a result was discussed on the basis of the polymerization mechanism of the block copolymers.
On the formation of tert‐butyl radicals after irradiation of polymers containing tert‐butoxycarbonylthioethylene units
Authors: Mönig Hans , Ringsdorf Helmut , Wessel Silvia 
Published: April 2003

AbstractThe formation and the behaviour of radiation induced free radicals in poly[1‐(tert‐butoxy carbonylthio)ethylene] (2) and in a statistical copolymer 4 from O‐tert‐butyl S‐vinyl thiocarbonate (1) with N‐vinylpyrrolidone (1:1) was studied, using ESR spectroscopy. After γ‐irradiation at 77 K, tert‐butyl radicals and other species were detected in the polymers. The yield for the homopolymer was evaluated to be Gtert‐butyl = 0.18. Investigations on the behaviour of radicals with an annealing procedure revealed, that at first the tert‐butyl radicals disappear with increasing temperature and that a further warming up leads to a concentration rise of this radical species. A radical cation localized at the carboxy group is assumed as precursor of this reaction. Further reactions are discussed.
Determination of copolymerization parameters in steady state
Authors: Penchev Pencho 
Published: April 2003

AbstractIn the proposed method copolymerization is carried out in an agradient flow reactor where a steady state is established. For the homogenous radical process the following copolymerization equation holds

where r1 and r2 are the reactivity ratios; a0, b0 and a, b are the feed (with index) and steady mole ratios of monomers to an internal standard. Experimentally the relative substance quantities in the reaction system can be measured with the help of gas‐chromatography. It is possible to calculate statistically the most probable values for r1 and r2 as parameters of the linear form of the above equation. As an example the reaction of styrene and methyl methacrylate in toluene initiated by benzoyl peroxides at 100°C was used. The results are r1 =0,582±0,044 and r2 =0,530±0,004; they agree well with literature values.
Single crystals of linear polyesters
Authors: Girolamo M. , Keller A. , Stejny J. 
Published: April 2003

AbstractThe influence of chemical groups regularly spaced along a polymer chain on structure and behaviour of chain folded single crystals was studied on linear aliphatic polyesters with different lengths of repeating unit. Poly(oxytetramethyleneoxysebacoyl) (or polyester 4,10), poly(oxyhexamethyleneoxysebacoyl) (or polyester 6,10), and poly(oxydecamethyleneoxysebacoyl) (or polyester 10,10) single crystals were grown from solution and their structure and annealing behaviour were examined. Chain folded lamellae with two different structures were formed depending on the chemical composition of polyester. Although in both structures the chains are perpendicular to the lamella surface, the ester group planes {00l} are parallel to the lamella surface in polyester 4,10 as opposed to the polyester 10,10 where the ester group planes are inclined.In spite of the fact that the chain folded lamellae are of about 100Å thick and can accommodate only few crystallographic repeats along, the lamella thickness of all three polyesters increases continuously with crystallization temperature. A picture of chain folded lamellae containing folds of different but quantized lengths mixed in different proportions is proposed in order to explain the continuous increase of lamella thickness.On annealing, the lamella thickness of polyester 4,10 and 6,10 increases in discrete steps suggesting that a rearrangement of folds leading to a more uniform fold length mixture takes place. In contrast, in polyester 10,10 the lamella thickness increases continuously on annealing which is attributable to the inclination of the ester group planes to the lamellar surface and to the ensuing non‐equivalence of the folds which distinguishes it from the other two polyesters. Some generalizations about fold length changes are being made.
The rôle of organometallic co‐catalysts in catalytic ziegler‐natta systems
Authors: Zakharov Vladimir A. , Bukatov Gennadii D. , Yermakov Yurii I. 
Published: April 2003

AbstractThe influence of triphenylphosphine and organoaluminium additives of various composition on the activity of titanium dichloride in polymerization of ethylene and propene as well as on the structure of the polypropylene obtained is studied. When these additives are introduced into highly active samples of TiCl2, the polymerization rate decreases, whereas the stereospecificity of the catalytic system increases. On the basis of these and earlier data, conclusions are drawn about the composition of active centers and about the role of organometallic cocatalysts in formation of active centers, in chain propagation, and in formation of stereoregular polymer.
Polyanion—polycation interaction, 2
Authors: Ghosh Amit Kumar 
Published: April 2003

AbstractThe interactions of the basic proteins, ribonuclease, γ‐globulin, and lysozyme with the polyanion potassium hyaluronate at varying pH were studied conductometrically and turbidometrically. The effect of a lowering of pH is most marked in the case of the lysozyme/hyaluronate system, but not to that extent in the case of ribonuclease/hyaluronate or γ‐globulin/hyaluronate interactions. This difference is not obvious. This interaction is also dependent on the nature of the polyanion.Titrations are dependent on the pH of the system not only because of the increasing cationic sites of a protein with lowering of pH, but also due to the simultaneous decrease in the dissociation of the anionic groups of the polyanion; the latter cause is more operative in the weak polyanions like hyaluronate which contain only carboxylate groups.
Hydrophobic environmental effects on oxygenation of polymeric hemochrome in aqueous solution
Authors: Tsuchida Eishun , Honda Kenji , Sata Hiroshi 
Published: April 2003

AbstractThe reversible oxygenation of a synthetic polymeric pyridine‐hemochrome was studied in aqueous solution at room temperature. The polymeric hemochrome was synthesized by coordination of partially quaternized poly(4‐vinylpyridine), (QPVP), to the axial site of protoheme in water. The equilibrium constants of hemichrome and hemochrome were 2,60.102 and 2,77.104dm3 mol−1, respectively, and the coordination number of axial ligands (pyridine groups) both in the complexation of heme and hemin was approximately 1,0.The kinetics of the elementary processes of oxygenation, i.e. “adsorption of O2” and “irreversible oxidation of the resulting oxygen complex”, were studied as a function of the local field around heme. The rate of the irreversible oxidation process of the heme oxygen complex was greatly lowered as a result of situating the active site of heme inside the hydrophobic environment formed by shrinking QPVP with adding a salt {sodium chloride, sodium dodecylsulfate, and poly[1‐(sodium sulfonatophenyl)‐ethylene]} or by complexing QPVP with poly(methacrylic acid). The redox potential of the central metal ion of heme was lowered by increasing the hydrophobicity around heme. On the other hand, the rate of the adsorption process was approximately constant, regardless of the microenvironmental change around heme.
Studies on polymerizations initiated by syncatalytic systems based on aluminium organic compounds, 2. The interactions of the reactants in the absence of polymerization
Authors: Priola Aldo , Cesca Sebastiano , Ferraris Giuseppe , di Maina Marcello 
Published: April 2003

AbstractIn the course of studies on polymerizations of isobutene (1) by syncatalysts consisting of ethylaluminium halides and halogens, it became necessary to study the separate reactions between the components of the reaction mixtures. The results showed: (a) that in general alkyl chlorides do not react with halogens in the dark at −35°C and below, but do react in the light; (b) that at low temperatures 1 and its dimers react with chlorine more easily by substitution than by addition; (c) that ethylaluminium halides react with halogens by forming aluminium halides, ethyl halides and ethylene.The findings of the present study enabled us to design polymerization conditions and procedures which minimize undesirable side‐reactions in the polymerization of 1 with syncatalysts.The experiments with the dimer of 1 (i.e. 2,4,4‐trimethyl‐1‐pentene), which is a non‐polymerizable model compound for 1, supported our view that initiation occurs by a halonium ion.
Studies on polymerizations initiated by syncatalytic systems based on aluminium organic compounds, 3. Polymerization and copolymerization of isobutene initiated by diethylaluminium iodide and iodine
Authors: Giusti Paolo , Priola Aldo , Magagnini Pier Luigi , Narducci Piero 
Published: April 2003

AbstractThe polymerization of isobutene and its copolymerization with isoprene, initiated by diethylaluminium iodide + iodine was studied in pentane, dichloromethane, and chloroethane, and the influence of the concentrations of the reagents and of the temperature on the copolymer yield and molecular weight was investigated. In the homopolymerization of isobutene initiated by diethylaluminium iodide+iodine the initiation is a comparatively slow process leading to non‐stationary reactions. The interaction between initiator and co‐initiator in the absence of monomer produces products (most probably ethylaluminium diiodide) which, on addition of monomer, cause fast, incomplete polymerization of isobutene.