bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanismus der NCA‐Polymerisation, 4. Synthese und Reaktionen von N‐Acyl‐NCA
Authors: Kricheldorf Hans R. 
Published: April 2003

AbstractVarious N‐acyl NCAs (8a–c, 14, 15) were prepared by reaction of N‐acyl‐N‐trimethylsilylglycine trimethylsilyl esters (7a–c) with phosgen or by addition of NCAs or of N‐thiocarboxylic acid anhydrides (NTAs) on chlorosulfonyl isocyanate. Furthermore, the direct acylation of 4,4‐dimethylglycine NCA and of several NTAs could be achieved with 3,5‐dinitrobenzoyl chloride and triethylamine, a reaction, that involves NCA‐anions 3 as intermediates, in analogy with the sulfenylation and silylation of NCAs 1. N‐Acyl NCAs (3‐acyloxazolidine‐2,5‐diones) react with nucleophils exclusively at the carbonyl group C‐5. The addition of N‐acyl NCAs to a NCA‐polymerization initiated by a tertiary amine enhances the rate of the polymerization, but lowers the polymerization degree, because any N‐acyl NCA starts a growing chain by reaction with the NCA‐anions 3. The NCA‐polymerization with high ratios of N‐acyl NCA/NCA (1:4) yields, therefore, oligopeptides 20, which show an acyl and an NCA endgroup in the IR‐ and the 1H NMR spectrum. If the NCA‐polymerization initiated by a tertiary amine is carried out in the presence of isocyanates, polypeptides with an urea and an NCA endgroup are obtained (25). These results prove, that the so called “activated monomer mechanism” is predominating in the case of the polymerization of N‐unsubstituted NCAs 1 initiated by a tertiary amine. Pyridine as a weak base gives in high concentrations the same results as the strong base triethylamine. No evidence is found for a “zwitterionic mechanism” as with N‐alkyl NCAs 2 described in Part 3 of this series. For the polymerization of four different NCAs 1 initiated with pyridine the relationships between reduced viscosity (ηsp/c) and conversion were established. These curves show for a 0 to 95% conversion a kinetic behaviour similar to a “living polymerization”; but from 95 to 100% conversion the viscosity increases exponentially due to condensation steps. The concentration of NCA end groups decreases by condensation and termination reactions even after 100% conversion of the monomers 1. Various initiation, propagation, and termination reactions are discussed.
Synthèse de polymères ω‐hydroperoxyde
Authors: Catala Jean‐Marie , Riess Gérard , Brossas Jean 
Published: April 2003

AbstractThe general conditions are described for the synthesis of ω‐hydroperoxy polymers by reaction of oxygen with CLi bonds of anionic living polymers. Secondary reactions as interchain coupling and the formation of alcohols are also discussed. In order to obtain a quantitative hydroperoxydation the following experimental parameters must be observed: (a) slow addition of the living solution to a polar solvent saturated by oxygen; (b) low concentration of living ends; (c) bulky terminal units; (d) lowest possible temperature.
Mechanism of the formation of macrocycles during the cationic polymerization of cyclotrisiloxanes. End to end ring closure versus ring expansion
Authors: Chojnowski Julian , Ścibiorek Marek , Kowalski Józef 
Published: April 2003

AbstractStudies of the distribution of cyclic oligomers formed in the first step of the cationic polymerization of hexamethylcyclotrisiloxane disclosed a correlation between the kinetically controlled concentrations of cyclic species and the statistical conformations adopted by the corresponding acyclic chains. The correlation found experimentally is in good agreement with the theoretical one predicted by the macrocyclization theory for non‐equilibrium chemical system and can be taken as evidence for the formation of macrocycles (even those containing about 100 atoms in the skeleton) by the intramolecular reaction between chain ends, a process which competes with the linear growth of the macromolecule. This approach may be useful in solving mechanistic problems involving polyreactions.
Polymerization of propadiene by some η‐allylic derivatives of rhodium(III)
Authors: Giarrusso Antonino , Gronchi Paolo , Ingrosso Giovanni , Porri Lido 
Published: April 2003

AbstractAn investigation has been carried out on the polymerization of propadiene (allene) by several η‐allylic derivatives of rhodium(III). Polymers of a high structural regularity were obtained, along with liquid oligomers, at ca. 70°C. The results are compared with those obtained using complexes of rhodium(I) as catalysts. The catalytic cycle is interpreted on the basis of the formation of a complex of rhodium(III) in the initiation and of a complex of rhodium(I) in the termination.
Polymerization of acrylamide photoinitiated by cobalt ammine complexes
Authors: Bhaduri Ramananda , Aditya Sukumar 
Published: April 2003

AbstractThe kinetics of polymerization photoinitiated by pentaammineoxalatocobalt(III) and tetraamminebis(oxalato)cobalt(III)complexes were investigated in aqueous and mixed solvents by irradiation of these complexes in the charge‐transfer bands at 35°C. Radiation of wavelength 420 nm was employed and the kinetics were followed by measurement of the rate of monomer disappearance (gravimetrically) and chain lengths of polymer formed (viscometrically). The dependence of the rate of polymerization and of the chain lengths on factors like absorbed light intensity, light absorption fraction, monomer concentration, initiator concentration, hydrogen ion concentration, viscosity of the medium, and the nature of the outer anion were studied in detail. A kinetic scheme is proposed and discussed in the light of experimental results, involving (i) a primary photo‐chemical act of excitation of the complex, followed by dark reaction of electron transfer within the complex, producing free radicals and bivalent Co2+ ions, (ii) initiation of polymerization by the free radicals generated, and (iii) termination of the active chain by a mixed process, namely mutual termination of macroradicals as well as termination by the complex depending on experimental condition.
Polymer‐cosolvent systems, 1. Polystyrene in acetone/cyclohexane mixtures
Authors: Deb Pramil C. , Prasad Jagdish , Chatterjee Satya R. 
Published: April 2003

AbstractAttempts were made to explain the cosolvency or the solubilisation of polystyrene in cyclohexane/acetone mixtures at 30°C. Cyclohexane is a Φ‐solvent for polystyrene at 35°C. and acetone is a non‐solvent. The effective interaction parameter χms of Scott has been determined for the optimum solvent composition from the slope of a Stockmayer‐Fixman plot as modified by Yamakawa. The value of unperturbed dimension obtained for polystyrene at this solvent composition coincides very well with that obtained in cyclohexane (Θ‐solvent). The binary interaction parameter χ12, between the two liquids obtained from χms shows a certain amount of incompatibility between them. The values of λ*, the preferential adsorption coefficient, were calculated for the entire solvent spectrum assuming the binary interaction parameters χij as being independent of solvent composition. The inversion point (λ* = 0), the optimum solvent composition yielding [η]max, and the importance of χ123, the ternary interaction parameter, are discussed.
The flexibility of poly(2,4,5‐trichlorophenyl methacrylate)
Authors: Hadjichristidis Nikos 
Published: April 2003

AbstractLight scattering in benzene and intrinsic viscosities [η] in tetrahydrofuran, chloroform, 1,4‐dioxane, and benzene of poly(2,4,5‐trichlorophenyl methacrylate) (PTCPh) were measured in dilute solutions. Relations between [η], z‐average root‐mean‐square end‐to‐end distance (r2z)1/2, and molecular weight M̄w were established. The unperturbed dimensions, calculated from viscometric and light scattering data by different methods, are in excellent agreement with one another. PTCPh has a lower flexibility factor (σ = 2,37) than poly(phenyl methacrylate) (σ = 2,5), in spite of the higher bulkiness of the side group of PTCPh. It seems, therefore, reasonable to suggest that the presence of the chlorine atoms hinders partly the interactions between the aromatic groups.
The 13C NMR spectra of poly(1‐pentenylene) and poly(1,3‐cyclopentylenevinylene)
Authors: Ivin Kenneth J. , Laverty D. Theodore , Rooney John J. 
Published: April 2003

Abstract13C NMR spectra were obtained for polymers made by ring‐opening polymerization of cyclopentene and bicyclo[2.2.1]hept‐2‐ene respectively. The fraction of cis double bonds could be determined with much greater precision from 13C NMR spectra than from IR spectra and varied from 0,66 to 0,31 for the samples of poly(1‐pentenylene), (2), and from 1,0 to 0,14 for the samples of poly(1,3‐cyclopentylenevinylene), (4). This is the first time an all‐cis polymer of 4 has been reported.The spectra of 2 showed a cis (upfield) and trans (downfield) peak for each of CH and α‐CH2, but only one peak for β‐CH2. The spectra of 4 showed multiple fine structure, the main splittings corresponding to a cis (upfield) and trans (downfield) peak for α‐CH, and a reverse line order for the other three carbons; subsidiary splittings were observed for all but the olefinic carbons, interpreted in terms of sensitivity of the chemical shifts to the cis/trans structure at the next nearest double bond. A complete interpretation of the line orders in 4 is given in terms of steric compression effects. The possibility that ring tacticity accounts for some of the fine structure cannot be entirely discounted.The stereochemistry of 4 is discussed in relation to the four possible modes of addition of monomer to a carbene chain carrier during polymerization.
Phénomènes cinétiques associés à la transition vitreuse du polyisoprène de structure 1,4 prépondérante
Authors: Prud'homme Jacques , Goursot Paul , Laramée André 
Published: April 2003

AbstractThe thermal behavior of polyisoprene with a high content of 1,4 structures prepared by anionic polymerization has been investigated in the glass transition interval by means of differential scanning calorimetry (DSC). This polymer is of particular interest since it has a low glass transition temperature Tg and shows a substantial increase in heat capacity in the glass transition interval. When the thermal history of the polymer is fixed by linear cooling, the dependence of Tg (measured at the inflexion point of the experimental curve) on heating rate q, can be expressed by q=constant × exp{−E/(RTg)} where E varies from 127 to 144 kJ/mol when the cooling rate decreases from 80 to 1.25 K/min. It is shown that this behavior is consistent with a kinetic model for glass transition involving a simple relaxation process characterized by an energy of activation close to E.
Heats of mixing of polyriboadenylic acid and polyribouridylic acid in aqueous NaCl solution
Authors: Baba Yoshihiro , Tanaka Shigeyuki , Kagemoto Akihiro 
Published: April 2003

AbstractThe heats of mixing of polyriboadenylic acid (Poly A) and polyribouridylic acid (Poly U) in various proportions by changing the mole ratio n = [Poly U]/[Poly A] in 0,001, 0,1, and 0,5 molar NaCl solutions containing 0,1 molar tris‐HCl buffer solution were measured. Constant values for the heats of mixing of the (Poly A+n Poly U) system are found for n ≤ 1 and n ≥ 2. From the results of UV and CD spectra, it may be considered that the mixing of Poly A and n (Poly U) leads to the formation of Poly(A+U) for n ≤ 1, and to that of Poly(A+2U) for n ≥ 2, even at [NaCl] = 0,001 mol/l.The enthalpies of formation of Poly(A+U) and that of Poly(A+2U) depend on the concentration of NaCl. This dependence may be attributed to the differences in conformation of Poly(A+U) in NaCl solution.
Die bestimmung der molekulargewichtsverteilung von nichtkristallisierenden polymeren mit dem elektronenmikroskop, 7. Präparation durch verdampfung des lösungsmittels aus lösung
Authors: Koszterszitz G. , Schulz G. V. 
Published: April 2003

AbstractA preparation method is described by means of which it is possible to transfer individual molecules of a high molecular weight polymer on a support, in order to determine their mass and therefrom their molecular weight distribution, using our previously published electron microscopic method.The advantages of the new procedure as compared to the previously described freeze‐drying are 1 that the range of solvents, which can be used is much larger, and 2 that the preparation is performed by evaporation from a dilute solution, which means that the molecules are distributed statistically on the support. The risk of formation of associates is avoided by keeping the polymer concentration correspondingly low and the rate of evaporation high. As examples the results for three samples of poly(methyl methacrylate) and one sample of natural rubber are reported and discussed.
Polymerization of vinyl acetate with 1,1′‐diacetoxy‐1,1′‐diphenylazoethane
Authors: Može Adolf , Vizovišek Ivan , Lapanje Savo 
Published: April 2003

AbstractThe kinetic and thermal parameters for the decomposition of 1,1′‐diacetoxy‐1,1′‐diphenylazoethane were determined using differential scanning calorimetry (DSC). The activation energy for decomposition is 145,1 kJ/mol, the heat of decomposition is −231,6 kJ/mol, and the rate constant (kd in s−1) obeys the relation in kd = 40,43 − (17460 K/T). This compound was used as initiator for the bulk polymerization of vinyl acetate. The polymerization was studied at 50, 55, 60, and 65°C. The rate of polymerization was followed dilatometrically. The per cent shrinkage was calculated from the partial specific volumes of polyvinyl acetate in vinyl acetate. The partial specific volumes were determined by means of an automatic digital densimeter. The number average of polymerization was obtained from viscosity data. The reaction order with respect to initiator concentration is smaller than 0,5 (between 0,27 and 0,31). The deviation is explained in terms of primary radical termination.The bulk polymerization of vinyl acetate at 65°C using both 1,1′‐diacetoxy‐1,1′‐diphenylazoethane and 2,2′‐azodiisobutyronitrile as initiators was also investigated by DSC technique. The data were used for obtaining various kinetic parameters.
Polymere ester von säuren des phosphors, 6. Ringöffnende polymerisation cyclischer phosphite und phosphonite durch michaelis‐arbuzov‐reaktion.–Theorie zur struktur der hauptkette
Authors: Vogt Walter 
Published: April 2003

AbstractThe hypothesis of Harwood and Patel, suggesting for the polymerization of 2‐phenyl‐1,3,2‐dioxaphospholane a type of insertion reaction to explain the formation of ethylenediphosphinic ester structures besides the normal 2‐hydroxyethyl(phenyl)phosphonic ester structures is extended to similar monomers and its theoretical consequences are examined. It is shown that in such a system mutual transformations between ω‐hydroxyalkyl‐P‐acid and alkylenedi(P‐acid)structures should occur, establishing a dynamic equilibrium and leading to a sort of azeotropic polymer, in which only one unique composition is kinetically stable. Equations relating to different kinetic parameters are deduced.
Polymerization of lactams, 21. effect of activating agents on the anionic polymerization of 2‐pyrrolidone
Authors: Roda Jan , Kušková Marie , Králíček Jaroslav 
Published: April 2003

AbstractThe activated anionic polymerization of 2‐pyrrolidone (1a) was studied by using N‐potassium‐2‐pyrrolidone (1e) as initiator in a 1:1 mole ratio with N‐acetyl‐ (1b), N‐benzoyl‐ (1c), and N‐pivaloyl‐2‐pyrrolidone (1d), N‐benzoyl‐8‐octanelactam (2a) or N‐benzoyl‐12‐dodecanelactam (2b) as activators in the heterogeneous stage of the polymerization process under isothermal conditions.
The unperturbed dimensions of poly(2‐hydroxyethyl methacrylate)
Authors: Fort Richard J. , Polyzoidis Theodoros M. 
Published: April 2003

AbstractValues of the unperturbed dimensions of poly(2‐hydroxyethyl methacrylate) have been determined in five non‐ideal solvents using viscometric data and a number of different theoretical treatments. Values of the steric factor σ, the characteristic ratio C∞ and the expansion factor α were also calculated. There was some variation of all these parameters with solvent but on the whole they were comparable to values for polymethacrylates with non‐polar side groups of a similar size.
Étude de la gélification d'un système triol/diacide/monoacide avec effect de substitution sur le triol
Authors: Durand Dominique , Bruneau Claude‐Marcel 
Published: April 2003

AbstractUsing a new general formulation of Flory's gelation criterion, a critical transition equation is derived for the trimethylolpropane (2,2‐bis(hydroxymethyl)‐1‐butanol)/adipic acid/lauric acid system having a substitution effect on the hydroxyl groups of the triol. The successive reactivity of the hydroxyl groups present in the trimethylolpropane has been formulated by the study of the condensation of the triol with the monoacid, lauric acid. From GPC measurements of the reaction medium for various degrees of conversion, the distribution curves of the different molecular species are plotted. Examination of these distribution curves has shown a non‐equireactivity of the sites of the polyol, which may be assigned to a positive substitution effect. Comparison of experimental distribution curves with the results of the kinetic analysis allows one to quantify the substitution effect. The gelation equation shows that a positive substitution effect on the hydroxyl groups of the triol decreases the extent of reaction necessary for the gelation. The difference between the experimental gelation curves and the theoretical curves with substitution effect may be assigned to intramolecular reactions.
Synthèse par voie radicalaire de polymères à extrémités hydroxylées, 6. Etude des réactions de transfert
Authors: Brosse Jean‐Claude , Legeay Gilbert , Lenain Jean‐Claude , Bonnier Maryvonne , Pinazzi Christian 
Published: April 2003

AbstractRadical polymerizations in an alcohol, initiated by hydrogen peroxide were found to afford polymers with hydroxyl end groups. The constants of chain transfer to the initiator and to the alcohol were determined for the polymerization of vinyl acetate, isoprene, and butadiene. The results show the influence of the initiator and the nature of the alcohol in the polymerization mechanism.
Polymere aus Nitrilen, 5. Anionische polymerisation von fumaronitril. Kinetik und Mechanismus zur synthese eines molekulareinheitlichen oligomeren
Authors: Helling Günter , Wöhrle Dieter 
Published: April 2003

AbstractFumaronitrile can polymerize quantitatively under mild conditions with anionic initiators. With the initiator butyllithium the kinetics is examined with the help of the 1H NMR method. The mechanism of the polymerisation is described which is different in polar and unpolar solvents. In THF an electrontransfer mechanism is responsible for a molecularly uniform oligomer of structure 5 which does not contain the initiator. In benzene or hexane normal anionic addition of the initiator to the CN‐group of the monomer leads to oligomer 7.
Dynamic mechanical behaviour of linear polyamides with different degree of unsaturation in the chain
Authors: de Candia Francesco , Maglio Giovanni , Palumbo Rosario , Tortorella Vincenzo , Vittoria Vittoria 
Published: April 2003

AbstractThe dynamic mechanical behaviour of polyamide systems containing different degrees of unsaturation was analyzed. The results do not show any simple relation between unsaturation and mechanical response. Particular attention was given to the α‐transition, that is a glass transition, and experimental data suggest that the generally accepted mechanism for this transition requires a more extensive study.
X‐Ray diffraction and iodine adsorption of acid modified cellulose fibers
Authors: Shinouda Hakim Grace , Kinawi Anwar , Abdel‐Moteleb Mohamed Magdy 
Published: April 2003

AbstractThe crystallinity of acid modified fibers prepared from viscose rayon and cotton cellulose is determined by x‐ray diffraction and iodine adsorption methods. The results are analysed and interpreted in the light of the definition of each method. In addition, the role of low fractions as well as the effect of vacuum drying on the measured crystallinity are discussed. The literature shows a lack of consistency between crystallinity determined for cellulosic fobers using different methods. The present work is an attempt to analyse the crystallinities of hydrocellulose residues determined by the x‐ray diffraction and the iodine adsorption methods.
Interferenzmikroskopische Charakterisierung von Faserstrukturen, 2. Der Einfluß des Schrumpfes beim Thermofixieren von Polyäthylenterephthalat‐fasern mit extrem unterschiedlicher radialer Struktur
Authors: Kühnle Gerhard , Schollmeyer Eckhard , Herlinger Heinz 
Published: April 2003

AbstractThe change of the radial structure during the thermofixation of poly(ethylene terephthalate), [poly(oxyethyleneoxyterephthaloyl)], fibres with and without shrinkage is studied.The fibre structure is described by interferometric measurements, which allow statements about order and orientation as a function of the fibre radius. The fibre interferograms are interpreted by an analytical model, which has been developed in the first part of this series.
Interaction between dyes and polyelectrolytes, 9. Effect of polyanions on alkaline fading reaction of methylene blue
Authors: Shirai Masamitsu , Yamashita Makoto , Tanaka Makoto 
Published: April 2003

AbstractThe effect of polyanions poly(potassium vinyl sulfate) (PVS), poly(sodium acrylate) (PANa), and poly(potassium p‐styrenesulfonate) (PSS), on the alkaline fading reaction of methylene blue (1) was investigated. The fading rate of 1 was extremely retarded on addition of polyanions. The binding type of 1 to polyanions was investigated spectrophotometrically by following the changes in the molar absorption coefficient (ε) at 664nm band. The relationship between the binding type and the fading rate of 1 in aqueous alkaline solution of polyanions is discussed.
Stufenweise Darstellung von Cyclo{quater[(5‐alkyl‐2‐hydroxy‐1,3‐phenylen)methylen]}en und ihr Vergleich mit linearen phenolischen Mehrkernverbindungen
Authors: Kämmerer Hermann , Happel Günter 
Published: April 2003

AbstractThe stepwise syntheses of cyclo{quater[(5‐alkyl‐2‐hydroxy‐1,3‐phenylene)methylene]}s (5) are described and compared with a one‐flask reaction procedure. The structures of the cyclic compounds 5 are analytically confirmed and their properties were compared with those of linear phenol formaldehyde condensates which have very similar structures and molecular weights.
Crystallization of glycine/β‐benzyl‐L‐aspartate copolymer in the course of polymerization
Authors: Kim Kea Yong , Kōmoto Tadashi , Kawai Tohru 
Published: April 2003

AbstractIn order to examine the structure and growth mechanism of copolymer crystals formed during polymerization, the heterogeneous copolymerization of glycine N‐carboxy anhydride and β‐benzyl‐L‐aspartate N‐carboxy anhydride, initiated by butylamine, was studied in acetonitrile. In all the copolymerization systems, the crystal growth took place through formation of the cross‐β structure, i.e., the introduction of glycine residues into the poly(β‐benzyl‐L‐aspartate) chain during this particular copolymerization broke the α‐helix of poly(β‐benzyl‐L‐aspartate). The growth mechanism of the copolymer crystals was compared with that for poly(β‐benzyl‐L‐aspartate) crystals reported previously.