bluuebunny/crossref_metadata_2025_split huggingface dataset:
Trans→cis photoisomerization of the stilbene residues in the side chains of copolymers from 2‐hydroxyethyl methacrylate and monomer containing stilbene residue
Authors: Mikeš František , Štrop Petr , Kálal Jaroslav 
Published: April 2003

AbstractThe rate of the trans→cis photoismerization of the stilbene residue was compared in the copolymer 3 from 2‐hydroxyethyl methacrylate (1) and trans‐N‐4‐(4‐nitrostyryl)phenylmethacrylamide (2a) with its low molecular weight analogue trans‐N‐4‐(4‐nitrostyryl)phenylisobutyramide (2b) in methanol, 2‐ethoxyethanol and in the binary solvents propanol/water and tert‐butyl alcohol/water. It was observed that the trans→cis photoisomerization of the stilbene residues was more rapid at 20°C in the side chains of the copolymer than for 2b in most solvents. This result may be interpreted on the basis of the quantum yield dependence for the trans→cis isomerization on the polarity of the medium where the isomerization takes place. Acceleration of the trans→cis isomerization of the stilbene residues in the side chains of the copolymer results from a decrease in the polymer microenvironment polarity as compared to the polarity of the solvent itself. This interpretation is supported by direct measurement of the polarity of the polymer chain microenvironment, based on the Kosower semi‐empirical polarity scale. The course of the trans→cis isomerization of 2b and 3 does not obey the equilibrium, first‐order reaction for all the solvents mentioned. The effect of preferential sorption of one of the components in binary solvents on the polymer coil and the effect of temperature on the photochemical trans→cis isomerization are discussed in connection with the experimental results.
13C‐kernresonanzspektren von ligninen, 2. Buchen‐ und fichten‐björkman‐lignin
Authors: Lüdemann Hans‐D. , Nimz Horst 
Published: April 2003

AbstractAuf der Grundlage der in der ersten Mitteilung dieser Reihe beschriebenen Modellsubstanzen werden die Signale der 13C‐NMR‐Spektren von Buchen‐ und Fichten‐Björkman‐Lignin zugeordnet. Die Spektren liefern detaillierte Konstitutionshinweise, die im Einklang mit den Vorstellungen über die Biosynthese des Lignins und mit den Ergebnissen des Ligninabbaus sind. Die beiden Spektren zeigen außerdem charakteristische Unterschiede, die die 13C‐Spektroskopie zu einer geeigneten Methode für die Klassifizierung von Ligninen verschiedener pflanzlicher Herkunft macht.
Lösefraktionierapparatur für makromolekulare stoffe
Authors: Craubner Hans 
Published: April 2003

AbstractEs wird eine Lösefraktionierapparatur für makromolekulare Stoffe beschrieben. Sie kann mit Schutzgas bei konstanten hohen und tiefen Temperaturen (bis 300°C), bei normalem oder erhöhtem Druck, sowie unter Vakuum betrieben werden.Die Apparatur wurde durch Lösefraktionierung von Polyamid 6 (PA 6; [η] = 104cm3/g, Tm = 220°C, N = 12,4%) experimentell getestet. Mit Lösungsmitteln steigender Lösekraft (u.a. konz. Ameisensäure zwischen 20 und 90°C) wurde PA 6 in Fraktionen zerlegt. Bei einer Rückgewinnung von 100,0% beträgt der mittlere Trennfaktor φα = 1 und der Fraktionierwirkungsgrad Φ>99%. Die Viskositätszahl‐ und Schmelztemperaturverteilungen sind ungewöhnlich eng. In Verbindung mit einer linearen Lorenzkurve besteht für N Konzentrationsgleichverteilung.
Polymerisation of tetrahydrofurfuryl methacrylate in solution
Authors: Zafar Mukhtar Mohammed , Mahmud Ruqia 
Published: April 2003

AbstractRadical polymerisation of tetrahydrofurfuryl methacrylate (1b) in chloroform benzene, bromobenzene, methyl benzoate, α‐bromonaphthalene, 1,2‐dimethylethylene phthalate, and in bulk at 60°C showed that only bromobenzene, methyl benzoate, α‐bromonaphthalene, and 1,2‐dimethylethylene phthalate have a rate‐enhancing effect. The values of kp, kt, and Ri, calculated from k/kt, kp/kt, and the measurement of the rate of polymerisation, have shown that probably kp is dependent on the nature of the solvent, whereas kt is related to the viscosity (kt.ηmix=constant) of the solvent/monomer mixture. There is on effect of solvent on the rate of initiation.
Some kinetic aspects regarding the solid state polymerisation of trioxane
Authors: Voigt‐Martin Ingrid 
Published: April 2003

AbstractAn attempt is made to correlate crystallographic changes arising during the radiation induced polymerisation of trioxane with the morphological changes observed during this process. Particular emphasis is placed on the differences which are noted with changing polymerisation time and temperature, so that both nucleation and growth could be discussed.
La fusion et la cristallisation du polypivalolactone
Authors: Prud'Homme Robert E. , Marchessault Robert H. 
Published: April 2003

AbstractDes fibres orientées de polypivalolactone (PPL) ont été fondues dans un calorimètre enthalpique différentiel (DSC). Deux pics sont alors obtenus à des températures de 507 et 512 K. Ils correspondent à des phases formées de chaǐnes hélicoïdales et zig‐zag planaires respectivement, tel que démontré par la méthode des rayons‐X. Après la fonte et la recristallisation des ces měmes échantillons, deux pics de fusion sont révélés à des températures de 495 et 507 K. Ils correspondent à deux modifications cristallines différentes du PPL. Suivant les conditions de cristallisation et de recuit, chacune de ces deux modifications peut ětre isolée, ou un mélange des deux peut co‐exister.
Chemische charakterisierung des kettenaufbaus und kristallisationsverhaltens von copolymeren aus 3,3‐bis(chlormethyl)oxetan und β‐propiolacton
Authors: Wiemers Norbert , Wegner Gerhard 
Published: April 2003

AbstractAus 3,3‐Bis(chlormethyl)oxetan (1) und β‐Propiolacton (2) wurden durch kationische Polymerisation Copolymere hergestellt, in denen Propiolactoneinheiten bis zu einem Molenbruch von 0,16 eingebaut sind. Das Copolymerisationsverhalten wurde untersucht, und die Copolymerisationsparameter wurden bestimmt.Die Copolymeren wurden kristallisiert und die Einkristalle hinsichtlich ihrer Zusammensetzung und Morphologie charakterisiert. Durch selektive Umesterung in den amorphen Bereichen der suspendierten Einkristalle wurde die Verteilung der aus β‐Propiolacton gebildeten Einheiten (PL) über den Kristall untersucht, und die Ergebnisse mit Abbauversuchen an den gelösten Copolymeren wurden verglichen. Bei der Polymerisation entstehen Copolymere, in denen Blöcke aus 3,3‐Bis(chlormethyl)oxetan‐Einheiten((—BCMO)n—) mit heterogen aus BCMO‐ und PL‐Einheiten zusammmengesetzten Sequenzen abwechseln. Die durchschnittliche Länge der homogenen BCMO‐Blöcke ist im untersuchten Mischungsbereich unabhängig von der Zusammensetzung der Monomermischung. In den lamellaren Einkristallen bilden die homogenen BCMO‐Blöcke die kristalline Phase, die BCMO‐PL‐Sequenzen werden in diè amorphen Bereiche gedrängt.
The cationic polymerization of ketene acetals and the preparation and characterization of poly(1,3‐diketones)
Authors: Dunn David J. , Plesch Peter H. 
Published: April 2003

AbstractVarious ketene acetals (1a–d) were prepared and their cationic polymerization under homogeneous and heterogeneous conditions, in bulk and in solution between ca. 100 and −100°C were investigated.Most of the reaction products formed in solution were viscous pale yellow fluids or sticky red solids, whereas those formed in bulk with solid, sparsely soluble initiators were white waxes or powders. For all systems for which solubility of product permitted DP determinations, the highest DPs (ca. 20) were found from bulk polymerization with solid CdCl2. With a wide range of soluble initiators in different solvents over a wide range of concentrations, DPs greater than about 8 were exceptional.It is suggested that there are at least five chain‐breaking reactions involving the growing dialkoxycarbenium ion \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}\hbox{---} {\rm CH}_2 \hbox{---} \mathop {\rm C}\limits^ \oplus \left( {{\rm OR}} \right)_2 $\end{document} and evidence is presented which accounts for the high rate of chain‐breaking compared with that for other olefinic monomers.Acid hydrolysis of the polymers yielded the corresponding poly(1‐oxoethylenes) (poly‐(1,3‐diketone)) (4a, b), and various derivatives of both the keto and enol forms of these were prepared.
Crystallization kinetics of natural rubber under stress
Authors: de Candia Francesco , Romano Gennaro , Vittoria Vittoria 
Published: April 2003

AbstractIn the present paper the crystallization kinetics of two networks of natural rubber was analyzed. The two networks were prepared following two different vulcanization techniques, as usual the first, and under swelling conditions the second.The results are discussed at the molecular level and give some important information about the well known deviations from the Gaussian theory on rubber elasticity.
Synthèses de polyisoprènes et polybutadiènes téléchéliques à extrémités hydroxyles allyliques
Authors: Brossas Jean , Clouet Gilbert 
Published: April 2003

AbstractDes polymères de bas poids moléculaire possédant des fonctions alcools allyliques aux extrémités des chaǐnes ont été synthétisés. Pour cela, nous avons préparé des polydiènes α,ω‐dicarbanioniques en utilisant le naphthalène‐lithium comme amorceur, et en effectuant la réaction de terminaison par addition d'oxygène. Afin de vérifier les structures obtenues, nous avons identifiées les dimères alcadiéniques correspondants. Par oxydation directe des extrémités carbanioniques, nous avons obtenu avec un bon rendement des polyalcadiènes α,ω‐diols à hydroxyles allyliques.
Polymerization of aromatic aldehydes, 11. Polymerization of 3‐(o‐formylphenyl)propionaldehyde and o‐phenylenediacetaldehyde
Authors: Tagami Sanae , Kunitake Toyoki 
Published: April 2003

AbstractPolymerization of 3‐(o‐formylphenyl)propionaldehyde (4) and o‐phenylenediacetaldehyde (5) were performed with several ionic catalysts. The cationic polymerization of 4 yielded polyacetals which contained a seven‐membered cyclic unit (7) in mole fractions of 0,3–0,5. The uncyclized unit (6) contained the pendant aromatic aldehyde. Apparently, the aromatic aldehyde group reacted during the course of the intramolecular cyclization.Polymerizations of 5 with BF3·O(C2H5)2, lithium tert‐butoxide, or Al(C2H5)3‐TiCl4 as catalysts, similarly gave polyacetals containing a seven‐membered cyclic unit (10) in mole fractions of 0,5–0,8. The extent of cyclization decreased with increase in temperature in the cationic polymerization, resulting in a difference of −7,5 kJ mol−1 (−1,8 kcal mol−1) between the activation energy of intramolecular cyclization and that of intermolecular propagation. The polymerization with Al(C2H5)3 as catalyst gave a polyester via propagation involving a hydride shift.
A chain folding model for poly(decamethylene oxide)
Authors: Fernandez‐Bermudez Salvador , Baltá‐Calleja Francisco José , Hosemann Rolf 
Published: April 2003

AbstractThe present paper deals with a small angle X‐ray diffraction study of poly(oxydecamethylene) [poly(decamethylene oxide)] (1) regarding the influence of the chemical nature of the macromolecule on the fold length value. Four fractions of 1 with different molecular weights, were crystallized and the highly diluted solutions of the crystals were deposited in layers just a few microns (μm) thick. These layers were investigated by means of X‐ray diffractometry. In all fractions the X‐ray long spacing, L, exhibits characteristic values which differs in the ratio of monomeric lengths. The crystal thickness predominantly corresponds to n=2 and 3 times half the value of the unit cell (13,75 Å), for crystallization temperatures Tc≤20°C. At higher temperatures these values increase to n=6. However, at Tc≈︁50°C n changes to n=7 or 8 and recovers the value n=6 at higher crystallization temperatures if the substance is still able to crystallize at these temperatures. The multiples of 13,75 Å obtained can be explained by a specific lateral packing of stems according to a proposed model which preserves the unit cell, excludes the oxygen atoms from the folds, and favours the idea of a regularly folded surface layer (4–5 atoms per fold, 2–3 Å thick) and of an ordered three dimensional suprastructure of oxygen atoms within the lattice. Similarly, the increase of the fold length on annealing occurs in steps equal to a whole number of repeating units along the molecular chain.
Studies on functional micelles, 2. Micellar effect on the preparation of cyclic dipeptide from thioalanine S‐dodecyl ester
Authors: Kawabata Yasuziro , Kinoshita Masayoshi 
Published: April 2003

AbstractThe condensation reaction of thioalanine S‐dodecyl ester (1a), catalyzed by pyridine, sodium hydroxide or alkyl amines, was carried out in aqueous media to give 3,6‐dimethyl‐2,5‐piperazinedione (2a) in good yield, although thioalanine S‐ethyl ester (1b) gave under the same reaction conditions only traces of cyclic dipeptide 2a. The specific accelerating effect was explained by a supposed matrix reaction on the micelle surface.
Gel permeation chromatography in mixed eluents. Effects of sorption on porasil gels
Authors: Berek Dušan , Bakoš Dušan , Bleha Tomáš , Šoltés Ladislav 
Published: April 2003

AbstractThe gel chromatographic behaviour of polystyrene standards in single and mixed eluents was compared using the polar inorganic carriers of the Porasil type. It was confirmed that the changes of the elution volume with injected polymer concentration are dependent on the thermodynamic quality of the solvent. In theta mixtures the elution volume changes only little in the studied range of injected concentrations.Further it was shown that sorption phenomena in the system can play an important part. This fact is demonstrated by different courses of universal calibration curves for single good solvents and mixed theta solvents. Besides the adsorption of polymer onto carrier also the selective sorption of a mixed eluent component on gel and/or into polymer coils can take place, and this may lead to the change of the corresponding elution volume.
The proton chemical shifts and the stereochemical structures of poly(vinyl chloride)
Authors: Ando Isao , Nishioka Atsuo , Asakura Tetsuo 
Published: April 2003

AbstractThe proton chemical shifts of dyads, triads and tetrads of poly(vinyl chloride) were calculated as a function of racemic unit fraction in a chain by taking account of the diamagnetic contribution, magnetic anisotropy effect and polar effect, based on Pople's approximation. The electron densities on the hydrogen atoms in each of the model compounds for the dyad, triad and tetrad units were calculated by the CNDO/2 method. The statistical weights of the preferred conformations for any specified stereochemical configuration were calculated by generating a set of 100 Monte Carlo chains using Flory's matrix method. Thus the proton chemical shifts of methylene and methyne groups in each of the dyad, triad and tetrad units were calculated by averaging over the preferred conformations. Fairly good agreement between the calculated and the experimental values of the proton chemical shifts for the dyad and triad units were obtained, but some discrepancies were found in the case of tetrads especially mrm tetrads. The dependences of the proton chemical shifts of the dyad, triad and tetrad units upon the racemic unit fraction and on the temperature were discussed.
Polymere aus 6‐Acryloylamino‐2,3‐diphenylchinoxalin
Authors: Braun Dietrich , Quarg Gunter 
Published: April 2003

Abstract6‐Acryloylamino‐2,3‐diphenylchinoxalin (5a) und 6‐Methacryloylamino‐2,3‐diphenylchinoxalin (5b) werden durch Umsetzung von 6‐Amino‐2,3‐diphenylchinoxalin (3) mit den entsprechenden Säurechloriden dargestellt. Die radikalische Polymerisation von 5a in Dioxan bei 60°C liefert Polymere mit Erweichungstemperaturen von 270–280°C. Die Polymerisationsgrade sind relativ niedrig.Das Monomere 5a wird mit Methylmethacrylat radikalisch copolymerisiert. Die Copolymerisationsparameter betragen unter den oben genannten Polymerisationsbedingungen für 5a r1 = 3,09, für Methylmethacrylat r2=0,89. Die dargestellten Monomeren und Polymeren werden durch IR‐, NMR‐ und UV‐Spektren charakterisiert.
The photolysis of copolymers of methyl methacrylate and methyl acrylate
Authors: Grassie Norman , Scotney Alan , Davis Thomas I. 
Published: April 2003

AbstractThe photolysis of copolymers of methyl acrylate and methyl methacrylate, covering the entire composition range, is studied with the copolymers in the form of film and in solution, under vacuum and in an atmosphere of oxygen. In film under vacuum, copolymers with high acrylate contents become insoluble, and cross‐linking and chain scission may be separated by application of the Charlesby‐Pinner equation to sol‐gel separation data. Otherwise, the polymer remains soluble, chain scission predominates and may be measured by the changes in number average molecular weight. Differences in the characteristics of chain scission under the four sets of conditions are accounted for in terms of physical factors, such as glass transition temperatures and “cage” recombination of radicals, and chemically in terms of the alternative reactions available to the primary radicals involved.
Vinyl polymerization by metal complexes, 20. Initiation by vinylamine/vinyl alcohol copolymer · copper(II) systems
Authors: Kimura Keiichi , Inaki Yoshiaki , Takemoto Kiichi 
Published: April 2003

AbstractThe polymerization of acrylonitrile (AN) and of methyl methacrylate (MMA) initiated by various copper(II) chelates was studied in the presence of carbon tetrachloride. Several vinylamine (VAm)/vinyl alcohol (VA) copolymers with different contents of NH2 and OH bearing monomeric units were chosen as polymer ligands as well as polyvinylamine (PVAm)/poly(vinyl alcohol) (PVA) mixtures (of equal NH2 and OH group contents as the corresponding copolymers), PVAm, and PVA. The activity of the used polymer chelates to initiate the AN and the MMA polymerization was compared at various pH values of the reaction systems. For the polymerization of MMA, the VAm/VA copolymer systems showed a higher activity than the PVAm chelate containing the same amount of NH2 groups, contrary to the case of the polymerization of AN, where the polymerization activity showed a reverse behavior. The initiation mechanism is discussed.
Hydrolysis kinetics of terephthalic and 5‐sulfonatoisophthalic acid esters
Authors: Grobe Heinrich , Nissen Dietmar , Rossbach Volker 
Published: April 2003

AbstractThe saponification reaction of bis(2‐hydroxyethyl) terephthalate (3) and sodium 3,5‐bis(2‐hydroxyethoxycarbonyl)benzenesulfonate (6) was followed under pH‐stat conditions in the alkaline pH range (pH 8 to 10 at 50 to 80°C) to determine the consecutive reaction rate constants for the hydrolysis of the diesters and the intermediate monoesters. The observed overall reaction rate constants were split into the individual rate constants for the hydrolysis catalyzed by the solvent, the OH− ions, the SO groups and the COO− groups (k0, kOH−, kSO, kCOO−, respectively). No intermolecular catalysis by either the sulfonato or the carboxylato groups and no “autocatalysis” by the solvent was found. The activation parameters for the hydrolysis of the corresponding esters of both acids are equal; for the diesters 3 and 6: ΔH† = 73,7 (72,0) kJ mol−1 [17,6 (17,2) kcal mol−1], ΔG† = 103,8 (104,7) kJ mol−1 [24,8 (25,0) kcal mol−1], ΔS† = −89,6 (−97,6) J mol−1 K−1 [−21,4 (−23,3) cal mol−1 K−1]; for the monoesters [terephthalic acid mono(2‐hydroxyethyl) ester and 5‐sodiumsulfonatoisophthalic acid mono(2‐hydroxyethyl) ester]: ΔH† = 80,4 (78,7) kJ mol−1 [19,2 (18,8) kcal mol−1], ΔG† = 109,3 (109,7) kJ mol−1 [26,1 (26,2) kcal mol−1], ΔS† = −86,3 (−93,0) J mol−1 K−1 [−20,6 (−22,2) cal mol−1 K−1]. It is concluded that disorders in the fine structure of polyester fibers modified with sulfonato group containing comonomers may primarily be responsable for their lower hydrolytic stability and not any catalytic effects of these groups.
Preparation of graft and block copolymers by means of amide linkages
Authors: Gupta Satyendra Nath , Nandi Umashankar 
Published: April 2003

AbstractBased on the reaction between acid chlorides and amines, two techniques were developed to prepare graft and block copolymers. In the first method poly(methyl methacrylate), (PMMA), containing chloroformyl groups was reacted with 2,2′‐azodiisobutyramidine (1) or 2,2′‐azobis[2‐(2‐imidazolin‐2‐yl)propane] (2) to give a polymeric initiator which, on thermal activation in the presence of acrylamide, produced graft and block copolymers, according to the position of the chloroformyl group on the PMMA backbone. In the second method, PMMA containing one terminal chloroformyl group was directly reacted with polyacrylonitrile containing two terminal amidine groups to produce a block copolymer.
Die Autoxidation von Cumol in Gegenwart von Chelaten monomerer und polymerer Schiffscher basen
Authors: Kurusu Yasuhiko , Storck Winfried , Manecke Georg 
Published: April 2003

AbstractEs wurden einige Übergangsmetallchelate 2a–e, 4a,b und 6a,b monomerer und polymerer Schiffscher Basen (1, 3 und 5) aus Salicylaldehyd und 2‐Aminophenol, bzw. 2,4‐Diamino‐5‐hydroxyphenol, sowie aus 2,5‐Dihydroxyterephthalaldehyd und (2,4‐Diamino‐5‐hydroxyphenol) dargestellt und ihre katalytischen Eigenschaften für die Autoxidation von Cumol untersucht. Die Aktivität nimmt in der Reihenfolge Mn>Co>NI>Cu>Zn sowie mit steigendem Molekulargewicht der Schiffschen Base ab. Die Verbindungen katalysieren auch die Zersetzung von Cumolhydroperoxid; am wirksamsten erwiesen sich auch hier die Manganchelate.
Darstellung einiger oligomerer Cyclo{oligo[(2‐hydroxy‐1,3‐phenylen)methylen]}e. Spektroskopische Untersuchung ihrer Pseudorotation
Authors: Happel Günter , Mathiasch Bernd , Kämmerer Hermann 
Published: April 2003

AbstractEs wird die Darstellung von Cyclo{tris[(2‐hydroxy‐5‐methyl‐1,3‐phenylen)methylen]‐(2‐hydroxy‐5‐tert‐butyl‐1,3‐phenylen)methylen} (4a), Cyclo{bis[(2‐hydroxy‐5‐methyl‐1,3‐phenylen)methylen]‐bis[(2‐hydroxy‐5‐tert‐butyl‐1,3‐phenylen)methylen]}(4b) und Cyclo‐{pentakis[(2‐hydroxy‐5‐methyl‐1,3‐phenylen)methylen]} (4c) beschrieben. Die IR‐Spektren zeigen, daß die phenolischen Hydroxygruppen der Vierringverbindungen 4a und 4b intramolekulare, vom Lösungs(CCl4)‐ oder Zerteilungsmittel (KBr) weitgehend unabhängige Wasserstoffbrücken bilden, die bei der pentameren Ringverbindung 4c schwächer sind. Anhand der 1H‐NMR‐Spektren läßt sich bei diesen Verbindungen eine Pseudorotation nachweisen. Die Massenspektren von 4a und 4b sind für verhältnismäßig hoch beständige Verbindungen charakteristisch, während die pentamere Verbindung 4c leicht einen Grundbaustein abspaltet und so wahrscheinlich eine Ringverengung eingeht.
Transition conformationnelle de certains polymères vinyliques en solution dans de solvants binaires
Authors: Gargallo Ligia 
Published: April 2003

AbstractLe comportément viscosimétrique de poly(vinyl‐1 pyrrolidone‐2), de poly(méthacrylate de p‐tert‐butylphényle) et de poly(méthacrylate de p‐tert‐butylcyclohexyle) a été étudié dans des mélanges de dioxanne‐1,4/chloroforme à des differentes compositions.Dans le cas du poly(méthacrylate de p‐tert‐butylcyclohexyle), on a trouvé l'existence d'un comportement irrégulier qui a été interprété en termes de transitions conformationnelles de la chaîne polymérique due au changement de la composition du mélange binaire. L'interprétation est basée sur une modification produite par le passage d'une conformation ordonnée, stabilisée par le dioxanne‐1,4 dans un milieu de concentration chloroformique faible, vers une conformation moins ordonnée de la chaîne qui serait plus stable et energétiquement favorisée dans un milieu riche en chloroforme.Une évidence spectroscopique de ces transformations a été aussi détectée. Le déplacement et modification de l'intensité des bandes d'absorptionne pourraient pas être dues à une interaction du type polymére‐solvant ce qui suggére une interaction intramoléculaire des groupements chromophores du polymére qui sérait différente pour chaque conformation.