bluuebunny/crossref_metadata_2025_split huggingface dataset:
Identification of free radicals produced by the radiolysis of poly(methyl methacrylate) and poly(methyl acrylate) at 77°K
Authors: Geuskens G. , David C. 
Published: April 2003

AbstractThe evolution of the ESR spectra of poly(methyl methacrylate) (PMM) and poly(methyl acrylate) (PMA) gamma irradiated at liquid nitrogen temperature has been studied as a function of temperature between 100°K and 320°K. In both cases, six radicals have been identified which are already present at 100°K. Some of these are a direct consequence of high energy irradiation while others are due to subsequent hydrogen transfer reactions. The results are discussed on the basis of a mechanism previously proposed for the radioysis of PMM.
Caractérisation de réactions primaires de dégradation oxydante au cours de l'autoxydation des polyoxyéthylènes à 25°C: Étude en solution aqueuse avec amorçage par radiolyse du solvant. IV. Diéthylèneglycol: Produits d'oxydation et schéma cinétique
Authors: Decker Christian , Marchal Jean 
Published: April 2003

AbstractL'autoxydation du diéthylèneglycol (DEG) en solution aqueuse, amorcée B 25°C par les radicaux HO• provenant de la radiolyse de l'eau, conduit aux produits primaires suivants : hydroperoxydes organiques, eau oxygénée, aldéhyde du DEG, monoformiate de glycol, formaldéhyde, acide formique, éthylèglycol et glycolaldèhyde. La presence de ces produits indique que les réactions d'hydroperoxydation et d'oxydation de la fonction alcool terminale sont en compétition avec des réactions de degradation oxydante provoquant des coupures de la molécule de DEG. Ces coupures résultent de la décomposition monomoléculaire des deux types de radicaux peroxyles secondaires selon des mécanismes à 4 et à 6 centres. Les radicaux alcoxyles primaires libérés par ces réactions participent à la propagation des chaînes d'autoxydation et assurent leur terrninaison.
Solvent systems with required optical and thermodynamic properties and their application in light scattering from dilute solutions of copolymers or polymer mixtures
Authors: Kratochvǐal Pavel , Sedláček Blahoslav , Straková Dagmar , Tuzar Zdeněk 
Published: April 2003

AbstractSometimes, it is desirable in light scattering measurements on copolymers (or polymer mixtures) that the solvent has definite refractive and thermodynamic properties. Such solvents can, e.g., mask optìcally one copolymer component and be theta solvents for the polymer system studied. This enables the other copolymer component to be measured directly by light scattering. These solvent systems have to be generally ternary mixtures. Some optical and thermodynamic properties of mixed solvents are discussed. The application of ternary solvent systems is illustrated by measurements of butadiene/styrene block copolymers ((poly)butadiene‐b‐styrenes)) in acetophenone/cyclohexane/ethanol mixtures. The experimental limitations of this approach are demonstrated on the example of poly(styrene‐co‐methyl methacrylate).
The reactions of hydroxymethylated 2‐methoxy‐4,6‐diamino‐s‐triazine in an acidic aqueous solution
Authors: Tashiro Tatsuo 
Published: April 2003

AbstractThe kinetics of the reaction of hydroxymethylated 2‐methoxy‐4,6‐diamino‐s‐triazine (II) was studied at 35°C in aqueous solution at pH‐values between 2,8 and 1,8. The average degree of formaldehyde substitution of II was 3,39. The reactions were found to proceed through both cleavge and methylene bond formation of the methylol groups under elimination of formaldehyde and water, respectively. The reaction rates were determined by measuring methylol groups and liberated formaldehyde with iodometric and sodium sulfite methods. The rate constant km of methylene bond formation became maximum at [H3O⊕] = [H2O]/K1 (K1: the equilibrium constant of the conjugated acid formed from the reaction of II with acid). The rate constant kc of cleavage increased with decreasing pH. The activation energies of cleavage (Ec) and of methylene bond formation (Em) were calculated at 20,4 and 21,4 kcal·mole−1, respectively.
The structure of molecular aggregates in dilute solutions of poly(vinyl chloride) in tetrahydrofuran
Authors: Lyngaae‐J∅︁rgensen J∅︁rgen Helge 
Published: April 2003

AbstractThe structure of the aggregates found in dilute solutions of PVC with tacticity 0,53 in THF has been investigated. It is shown that a model of an aggregate describing it as a composition of 10 to 15 single molecules bound together by a crystalline nucleus, is in accordance with the experimental evidence from light‐scattering and GPC analysis.
The interactions between polymerization initiators and inhibitors in solution V. The reaction between benzoyl peroxide and p‐benzoquinone in carbon tetrachloride; some observations on the induced decomposition of the peroxide
Authors: Yassin Ahmady. A. 
Published: April 2003

AbstractThe reaction between benzoyl peroxide and p‐benzoquinone in CCl4 was investigated by isolation and identification of the reaction products. At peroxide/quinone ratios ≥ 3 only quinonoid products of the spontaneous decomposition of the peroxide are formed. At ratios < 3 the peroxide undergoes induced decomposition by both trichloromethyl and phenyl radicals. The induced decomposition involves the formation of radical intermediates which undergo intermolecular disproportionation, but not intramolecular rearrangement to form p‐trichloromethylbenzoyloxy radicals, p‐phenylbenzoyloxy radicals, and their corresponding acids. The p‐trichloromethylbenzoyloxy radicals are captured by benzoquinone to form 2‐(p‐trichloromethylbenzoyloxy)‐1,4‐benzoquinone and a considerable amount of quinonoid resins. A correlation between the electron‐donating or accepting property of a radical and its capability to induce the decomposition of the peroxide was developed.
On the possibility of molecular weight fractionation during isothermal crystallization
Authors: Kamide Kenji , Ogata Takashi 
Published: April 2003

AbstractAn attempt is made to clarify the possibility of molecular weight fractionation during isothermal crystallization studied by computer simulation technique and experiments on Marlex 50 by differential scanning calorimetry. The basic equation: [dC(t)/dt]t=τ = F(τ) of the KAWAI theory (where, dC(t)/dt is the rate of crystallization, F(τ) is the distribution function of retardation time τ) can only be valid when the broadness of F(τ), as defined by the ratio of maximum τ to minimum τ is 102 or greater. The isothermal crystallization curve (ICC) was calculated for Marlex 50 at various temperatures Tc assuming different degree of fractionations, x, which is the weight fraction of the polymer obeying the complete fractionation. When partial fractionation occurs, even to a very small extent, during isothermal crystallization, (1) ICCs are not superimposable, even when the exponent n in the AVRAMI's equation is identical for mono‐disperse polymer components having different molecular weight, and (2) n decreases with time, this tendency becomes more significant at higher Tc for larger x and at the final stage of crystallization. By comparing the experimental data with the theoretical curves, x = 0,15–0,25 was obtained. This implies that the fractionation with respect to molecular weight occurs, though partially, during isothermal crystallization.
Conformational studies of optically active poly(oxyisobutylidenecarbonyl) [poly(L‐α‐hydroxyisovaleric acid)] and its oligomers
Authors: Matsuo Shunji , Tohara Akifumi , Iwakura Yoshio , Iwata Kaoru 
Published: April 2003

AbstractOptical rotatory dispersion (ORD) and circular dichroism (CD) of poly(oxyisobutylidenecarbonyl) (II) were investigated and compared with those of its optically active oligomers (III). The two‐term DRUDE equation was applied to analyze the ORD curves using n‐π*‐ and π‐π*‐transition bands as the critical wavelengths, λ0 and λ1, respectively. No drastic difference in ORD curves between the polymer and oligomers was detected in chloroform, which suggests that the polymer has no special conformation. On the other hand, in dioxane and acetonitrile λ1 of the polymer II shows a red shift in comparison with that of its oligomers.
Structure of oligourethane, 5. Micro structure of solution grown crystals
Authors: Nagura Masanobu , Tagawa Hiroyuki , Wada Eiichi 
Published: April 2003

AbstractTo study the dependence of the micro structure of oligomer crystals on the degree of polymerization, the small and wide angle X‐ray scattering of the oligomer α‐acetoxy‐ω‐methoxyoligo(oxypentamethyleneiminocarbonyl), CH3CO[O(CH2)5NHCO]nOCH3, having strictly homogeneous molecular weight, and of the corresponding polymer were investigated, together with the IR absorption spectra, the density and the thermal properties.The solution grown crystals of oligomers and of the polymer are composed of the two‐phase structure. One is the crystalline phase having the ordered high density, and the other one is the intercrystalline phase of low density occupied by mobile molecular chain ends. The structure of the crystalline phase above trimer is similar to that of the dimer crystal, and the molecular motion in the intercrystalline phase is the local mode motion. This twophase structure could be illustrated by one dimensional density distribution having trapezoidal profile.
Mathematical properties of polydisperse systems, 1. General relations
Authors: Greschner G. S. 
Published: April 2003

AbstractIn the present paper the connection between an arbitrary polydisperse property and the molecular weight distribution is investigated using exact mathematical methods. On the basis of the superposition principle a general equation is derived which can be applied e.g. to the polydispersity problems connected with the Gel Permeation Chromatography, to the light scattering from dilute solutions of high polymers, or the ultracentrifuge. From this point of view, each of these phenomena is described by help of a linear operator with a special kernel, the analytical or numerical inversion of the operator yielding the molecular weight distribution of the system by help of an uniform algorithm.
Berechnung der ungestörten dimensionen von vinylpolymeren mit unterschiedlichen seitenketten. Poly(propyläthylen), poly(äthyläthylen), polystyrol
Authors: Biskup U. , Cantow H.‐J. 
Published: April 2003

AbstractFür Poly(propyläthylen) (Poly‐n‐penten‐1), Poly(äthyläthylen) (Poly‐n‐buten‐1) und Polystyrol wurden mit dem FLORY‐Modell der rotationsisomeren Zustände die ungestörten Dimensionen 〈r〉/nl2 sowie deren Temperaturkoeffizienten berechnet. Sowohl für ataktische wie auch für isotaktische Konfigurationen stimmen die berechneten Werte von 〈r〉/nl2 gut mit den in der Literatur angegebenen Meßwerten überein. Die zur übereinstimmung mit den experimentellen Daten einzusetzenden Parameterwerte des Modells ändern sich in sinnvoller Weise mit der Länge der Seitenkette. Die experimentall ermittelten Temperaturkoeffizienten werden nur für ataktische Polypentene und Polybutene durch das FLORY‐Modell befriedigend beschrieben.
Über aziridinylchinone und ihre polymeren
Authors: Manecke Georg , Kretzschmar Hans‐Jürgen 
Published: April 2003

AbstractDurch Addition von Aziridin an Mono‐ und Divinyl‐p‐chinone unterschiedlichen Redoxpotentials werden N‐substituierte Aziridinverbindungen dargestellt. Die Redoxpotentiale der Monomeren, ihr Polymerisationsverhalten und die Eigenschaften der Redoxpolymeren werden untersucht.
Polymérisation par ouverture de cycle, 1. Polymérisation du bicyclo[6.1.0] nonène‐4
Authors: Pinazzi Chr. P. , Cattiaux J. , Brosse J. C. 
Published: April 2003

AbstractLe bicyclo[6. 1. 0]nonène‐4 soumis à l'action des catalyseurs de métathèse, conduit avec des rendements quantitatifs, à des polymères de masse moléculaire moyenne en nombre 5000. Les études spectroscopiques montrent que la structure des polymères correspond à celle d'un poly(butadiène‐1,4) dont une double liaison sur deux est remplacée par un cyclopropane. Une faible proportion de motifs de structure différente a été mise en évidence dans certains des polymères obtenus. L'étude systématique de la polymérisation du bicyclo [6. 1. 0] nonène‐4 en milieu cationique et en présence des complexes des métaux de transition, a permis de montrer que ces motifs correspondent à une polymérisation transannulaire qui apparait comme réction secondaire au cours de la polymérisation par métathèse.
Vinyl polymerization, 297. Polymerization of acrylonitrile initiated by the system of tetramethyl‐2‐tetrazene and pyruvic acid
Authors: Sugiyama Kazuo , Hatanaka Hideo , Nakaya Tadao , Imoto Minoru 
Published: April 2003

AbstractThe polymerization of acrylonitrile (AN) initiated by the system of 1,1,4,4‐tetramethyl‐2‐tetrazene (TMT) and pyruvic acid (PA) was investigated in dimethylformamide (DMF). The TMT/PA system could polymerize AN more easily than TMT alone. The polymerization was confirmed to proceed by a radical mechanism. The rate of polymerization was proportional to [TMT]0,52, [PA]0,59, and [AN]1,63. The over‐all energy of activation of the polymerization was found to be 7,7 kcal · mol−1 within the temperature range of 50 to 70,5°C. The reaction of TMT with PA in benzene gave products whose analysis corresponded to nitrogen, hydrogen, carbon dioxide, tetramethylhydrazine, and N,N‐dimethylacetamide. From these results and from the data of the ESR measurement of the TMT/PA system, a possible initiation mechanism is proposed.
A nuclear magnetic resonance study on the conformation and molecular interaction of polyelectrolyte model compound in alcohol/water mixtures
Authors: Miyamoto T. , Cantow H.‐J. 
Published: April 2003

AbstractThe conformation and molecular interaction of polyelectrolyte model compound (2,4‐dimethylglutaric acid) in alcohol/water mixtures were investigated by using high resolution NMR spectroscopy.It is shown that the local conformation of meso‐isomer in alcohol/water mixtures slightly changes with the mole fraction of ethanol. The difference in the chemical shifts of two methylene protons and the chemical shift of carboxyl protons are comparably dependent of the mole fraction of ethanol. These results, however, do not always mean that the change in the viscosity of poly(acrylic acid) or poly(methacrylic acid) in alcohol/water mixtures is due to the change of such local conformation as estimated by NMR. On the contrary, it is probably true that such change in the viscosity curve is mainly due to the long‐range interaction between non‐adjacent segments.It is also shown that the local conformation of meso‐isomer depends upon the use of the solvents, leading to the conclusion that its local conformation varies with the solvent.
Polymerisation of ethylene by catalysts formed from π‐ and σ‐bonded transition metal carbon compounds and silanols
Authors: Ballard D. G. H. , Heap N. , Kilbourn B. T. , Wyatt R. J. 
Published: April 2003

AbstractSoluble halogen free polymerisation catalysts have been prepared by reacting tetrabenzyl zirconium and related compounds with silanols. The combination of tetrabenzyl zirconium and 1,1,3,3‐tetraphenyldisiloxane‐1,3‐diol (VI) was found to be particularly active. Structural analysis of VI shows that the SiOSi angle is linear, which may account for this compound behaving as a monodentate ligand. The relationship between structure and activity in these soluble systems and the transition metal polymerisation centres, prepared by reacting transition metal alkyls with silica and alumina, is discussed.
Cationic copolymerization of tetrahydrofuran with diketene. NMR analysis of copolymer microstructure
Authors: Okada Masahiko , Yokoyama Yasuaki , Sumitomo Hiroshi 
Published: April 2003

AbstractCationic copolymerization of tetrahydrofuran and diketene (4‐methylene‐2‐oxo‐oxetane) with triethyloxonium tetrafluoroborate as initiator was carried out and the microstructure of the products was investigated. The diad fractions determined by NMR analysis showed that both monomer units were distributed randomly along the copolymer chain, and that the propagating species of tetrahydrofuran added to both the carbon‐carbon double bond and the ring‐oxygen atom of diketene. The fraction of the former mode of addition was estimated to be 0,37–0,41, in notable contrast to the corresponding values observed in the copolymerization of 1,3‐dioxolane with diketene. The difference in the selective reactivities of the growing ions was discussed.
Eine blockierungsmethode zur darstellung molekular‐einheitlicher hydroxyphenylenmethylen‐verbindungen
Authors: Kämmerer Hermann , Rausch Werner , Söhle Ingrid 
Published: April 2003

AbstractHydroxyphenylenmethylen‐Verbindungen wurden nach verschiedenen Verfahren dargestellt. Dabei wurden folgende Ausgangsprodukte verwendet: p‐Kresol und Formaldehyd (Gl. (i)) oder p‐Kresol und 2,6‐Bis(hydroxymethyl)‐p‐kresol (4) (Gl. (ii)), (Duplikations‐Verfahren), 2‐Chlor‐6‐(3′‐chlormethyl‐2‐hydroxy‐5′‐methylbenzyl)‐p‐kresol (5) und 2‐Chlor‐p‐kresol (Gl. (iii)), (schrittweise Synthese) oder 2‐Chlor‐6‐chlormethyl‐p‐kresol (8) und p‐Kresol (Gl. (iv)) (Blockierungsmethode). Die nach den verschiedenen Methoden entstandenen Reaktionsprodukte wurden papierchromatographisch aufgetrennt und identifiziert unter Berücksichtigung der bei der Analyse auftretenden Nebenreaktionen.
Investigations on conformational transitions in polymer chains in dilute solution
Authors: Dondos Anastasios , Rempp Paul , Benoit Henri 
Published: April 2003

AbstractTemperature dependence of light scattering and viscosity data was studied on three polymers: poly(4‐bromophenylethylene) [poly‐p‐bromostyrene], poly[1‐(methoxycarbonyl)‐1‐methylethylene] [poly(methyl methacrylate)] and poly(2‐pyridylethylene) [poly(vinylpyridine)] in dilute solution. It was observed that over a narrow range of temperature sharp changes of second virial coefficients, unperturbed dimensions and scattered intensities do occur. This phenomenon can be accounted for by assuming that in the chosen solvents the conformation of the chain undergoes changes, increasing temperature causing a higher flexibility.These conformational changes disappear entirely on addition of minute amounts of well solvating, polar solvents, which confirms that the observed transition is only concerned with short range interactions along the chain.
Über den photochemischen abbau von polyurethanen
Authors: Schultze Hartmut 
Published: April 2003

AbstractEinwirkung von Licht und Sauerstoff bei Raumtemperatur auf Polyurethane, die aus aromatischen Diisocyanaten und Diolen hergestellt wurden, führt zur Bildung von primären aromatischen Amino‐ und Hydroperoxy‐Gruppen. Oxidation der NH2‐Gruppen und Radikalreaktionen beim Zerfall der HOO‐Gruppen führen zur Verfärbung des Hochpolymeren. Die Bildung der NH2‐Gruppen und HOO‐Gruppen kann durch die Qualität der Ausgangs‐verbindungen, Reaktionsführung und geeignete Zusätze eingeschränkt werden. Diese Gruppen lassen sich durch Alkylierungsmittel bzw. Trioxo‐s‐triazin (Isocyanurat) abfangen. Polyurethane, die aus aliphatischen Diisocyanaten hergestellt wurden, unterliegen ebenfalls der Alterung.
Radical reactions initiated by chelate complexes of transition metals, 11. Effect of pyridine on the styrene polymerization initiated by the system bis[(—)‐ephedrine]copper(II) chelate/carbon tetrachloride
Authors: Bartoň Jaroslav. , Werner Peter , Vlčková Jana 
Published: April 2003

AbstractThe ability of the system bis[(—)‐ephedrine]copper(II) chelate (Cueph)/carbon tetrachloride/pyridine (Py) to initiate the styrene polymerization was studied. In the region near to an equal mole ratio [CCl4] : [Py] the rate of polymerization depends linearly on the concentration of pyridine. At a mole ratio [CCl4] < [Py] an inhibition period is observed which is inversely dependent on the concentration of CCl4. The rate of polymerization decreases with increasing inhibition period. On the basis of spectrophotometric investigations in the UV region the formation of an adduct of Cueph with Py is to be assumed. The effect of this adduct on the course of the styrene polymerization initiated by the system Cueph/CCl4/Py is discussed.
Zur kinetik der anionischen polymerisation von methyl‐methyacrylat in tetrahydrofuran bei −75°C
Authors: Löhr G. , Schulz G. V. 
Published: April 2003

AbstractDie anionische Polymerisation von Methylmethacrylat (MMA) in Tetrahydrofuran (THF) verläuft bei −75°C mit Cumylcäsium bzw. oligomerem α‐Methylstyrylcäsium als Initiatoren ohne erkennbare Nebenreaktionen analog der anionischen Polymerisation von unpolaren Monomeren in ätherischen Lösungsmitteln. Als Beweis wird hauptsächlich die enge Molekulargewichtsverteilung der unter diesen Bedingungen hergestellten Polymethylmethacrylate angeführt.Bei −75°C betragen die Geschwindigkeitskonstanten für die Monomeranlagerung an das Ionenpaar kw(±) = 80 dm3 mol−1 s−1 und an das freie Anion etwa kw(−) ≈︁ 6 · 104 dm3 mol−1 s−1. Leitfähigkeitsmessungen ergeben, daß die Dissoziationskonstante des Polymethylmethacrylcäsiums bei dieser Temperatur bei 10−9 mol dm−3 liegt.
Polymer modification and synthesis using sulphenyl derivatives, 1. Preparation of poly(ß‐chlorothioethers)
Authors: Cameron G. Gordon , Stachowiak Stephen A. 
Published: April 2003

AbstractThe preparation and characterization of some novel poly(ß‐chlorothioethers), from reaction of 4,4′‐biphenyldisulphenyl chloride (1) or benzene‐1,3‐disulphenyl chloride (2) with diolefins, are described.
Über die elementarreaktionen der radikalischen polymerisation von benzylmethacrylat
Authors: Mayer Gunter , Schulz G. V. 
Published: April 2003

AbstractDurch Kombination stationärer und instationärer Methodik (rotierender Sektor) werden die Absolutwerte der Geschwindigkeitskonstanten von Kettenwachstum und Kettenabbruch von Benzylmethacrylat unter dem Einfluß verschieden viskoser Lösungsmittel bestimmt.Die Radikalausbeute f hängt von der Viskosität des Lösungssystems und der Art der Monomeren, dagegen nicht (oder fast nicht) von der Konzentration des Monomeren und der Geschwindigkeit der Radikalerzeugung ab. Daraus wird geschlossen, daß ein merklicher Anteil von Zwillingsrekombinationen außerhalb des primären Lösungsmittelkäfigs stattfindet.Die Geschwindigkeitskonstante kw des Kettenwachstums stimmt praktisch überein mit der des Methylmethacrylats und zeigt ebenfalls einen leichten Anstieg mit der Lösungsmittel‐viskosität. Die Geschwindigkeitskonstante ka des Kettenabbruchs nimmt etwas schwächer als proportional der reziproken Viskosität der Monomer‐Lösungsmittel‐Viskosität zu. Es wird auf den möglichen Einfluß der inneren Viskosität hingewiesen.
Photopolymerization of acrylamide sensitized by sodium chloroaurate in aqueous solution
Authors: Imamura Kazuyoshi , Asai Michihiko , Tazuke Shigeo , Okamura Seizo 
Published: April 2003

AbstractPhotopolymerization of acrylamide (AM) sensitized by NaAuCl4·2H2O in aqueous system was investigated under irradiation at 365 nm. The rate of polymerization (Rp) was strongly influenced by the change of the pH and the chloride concentration. The results were interpreted assuming different initiating efficiencies for various hydrolyzed species of Au(III). From the dependence of Rp on the wavelength, the effective photoabsorption was confirmed to be due to the excitation of the CTTM (charge transfer to metal) band of Au(III). The monomer participated in the photodecomposition of Au(III), eventually leading to Au(0). Under thermal conditions the polymerization was greatly accelerated by the addition of reducing agents, indicating that active species were produced during the reduction of Au(III) to lower valency states. The kinetic expression of photopolymerization was the expected one for a radical polymerization.