bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymérisation anionique de l'acroléine, 3. Analyse des microstructures par 1H NMR et 13C NMR et mécanisme de polymérisation
Authors: Gulino Danièle , Pascault Jean Pierre , Pham Quang Tho 
Published: April 2003

AbstractWe have synthesized anionic polyacroleins using various initiators (naphthalene complex, tert‐butyllithium) in different solvents (tetrahydrofuran, toluene). We have studied the 1H NMR and 13C NMR spectra of the polymers and assigned monomeric units and diads by comparison with spectra of four compounds corresponding to the different microstructure arrangements. By this method, we have clearly proved the presence of 1,4‐ as well as 3,4‐ and 1,2‐units. But numerous cyclisations occur on the 1,2‐units. Using only the 1H NMR method, a first estimation of the microstructure was obtained. 13C NMR gave further information and permitted the estimation of the (1,4‐cis)/(1,4‐trans) ratio. Furthermore the presence of hydroxyl groups along the chains has also been established. A satisfactory determination of the 1,2,3,4‐ and 1,4‐structure percentages of several polyacroleins has been obtained using 1H NMR and 13C NMR simultaneously. A mechanism of acrolein polymerization, based on two different living ends is proposed. The microstructure indicates the existence of several complexation phenomena. When the living end/metal and monomer/metal complexations are weak (with Na+ e.g.), the polymer consists mainly of 1,4‐ and 3,4‐units. On the other hand, with Li+, the microstructure has a high 1,2‐content. Moreover, the living end/Li+ complexation would decrease with the chain length, because of the increasing attraction of the cation by the other complexing sites on this chain.
Conformation des polyacrylamides partiellement hydrolyses en solution aqueuse
Authors: Schwartz Thierry , François Jeanne 
Published: April 2003

AbstractA series of hydrolyzed commercial polyacrylamide samples were fractionated by successive precipitation fractionation. The radius of gyrationRGand the intrinsic viscosity [η] of the fractions were measured as a function of the molecular weight and the NaCl concentrationcs. The fractions were found to present the classical behaviour of polyelectrolytes with a conformation of expanded coils atcs= 0,1 mol/l. By increasing the salt concentration, the dimensions of the coils were found to become those of the unhydrolyzed, less expanded, polyacrylamide molecules.
Asymmetric induction in the radical copolymerization of mono and di‐l‐menthyl fumarate with styrene
Authors: Kurokawa Masahiro , Yamaguchi Hidemasa , Minoura Yuji 
Published: April 2003

AbstractRadical copolymerizations of mono‐ and di‐l‐menthyl fumarate (1 and 2) with styrene (St) were carried out, and the copolymers were hydrolyzed with potassium hydroxide. The products show still optical activity even after the removal of the optically active side chain, because of an introduction of asymmetry into the main chain of the copolymer. The specific rotation per one of the diad sequences of hydrolyzed poly(1‐co‐St) was the same as that of hydrolyzed poly(2‐co‐St). The mechanism of asymmetric induction and the position of the new asymmetric center are discussed based on the measurements of UV spectra, optical rotation, and circular dichroism.
Stereoregularity of polystyrene derivatives, 3. Poly(methylstyrene)s Obtained by Anionic Catalysts
Authors: Kawamura Tokiji , Uryu Toshiyuki , Matsuzaki Kei 
Published: April 2003

AbstractThe stereoregularity of the polymers of ortho‐, meta‐, and para‐methylstyrenes prepared with various anionic catalysts was determined by means of 13C NMR spectroscopy. The substituent effect on the stereoregularity was discussed comparing with that of polystyrenes obtained under the same polymerization conditions. Syndiotactic‐rich poly(methylstyrene)s were prepared with butyllithium in toluene and the syndiotacticity increased in the order of para‐, meta‐, and ortho‐derivatives. Although the structure of the polymers prepared with sodium‐naphthalene (Na‐naph.) in THF did not change with the position of the substituent, in toluene, however, the methyl group at ortho‐position influences the stereoregularity. The trend of the stereoregularity of the polymers produced by potassium‐naphthalene was almost the same as that of poly(methylstyrene)s prepared by Na‐naph. Nearly random polymers were obtained with the cesium ion as catalyst.
Structural characterization of unsaturated polyesters
Authors: Paci Maurizio , Crescenzi Vittorio , Supino Nicola , Campana Francesco 
Published: April 2003

AbstractA few unsaturated polysters prepared by melt polycondensation of maleic anhydride, phthalic anhydride, and aliphatic glycols in different proportions have been characterized. The salient features of the 1H and 13C NMR spectra of the polyesters and of model compounds are compared. It appears that from 15 to 20% of maleic acid residues have reacted with excess glycol to yield branching points while the remaining free olefinic double bonds have undergone cis → trans isomerization almost quantitatively along the oligomeric chains.
Die kristallstruktur von cycloalkanen
Authors: Trzebiatowski Thomas , Dräger Martin , Strobl Gert R. 
Published: April 2003

AbstractAn X‐ray structure analysis was performed on single crystals of the cycloalkane (CH2)36. The lattice belongs to the space group Aa and is arranged in layers. The unit cell has the dimensions α = 1,033 nm, b = 0,824 nm, c = 4,22 nm, β = 107, 1° and contains four molecules. The molecules consist of two stretched stems which are linked by sharp folds at each end. The folds have the conformation …t(g g t g g) t… lying parallel to the b‐axis. Raman measurements suggest that the stems are slightly twisted. A comparison of the homologous series (CH2)n, n = 36, 48, 60, and 72 using X‐ray powder methods showed that the (CH2)36‐structure, including the fold conformation, is also representative for the longer chain cycloalkanes.
Inhibition of radical polymerization by polyconjugated polymers with anthracene repeating units
Authors: Schopov Ivan , Jossifov Christo 
Published: April 2003

AbstractThe thermal and the benzoyl peroxide initiated polymerizations of styrene and methyl methacrylate in presence of three polyconjugated polymers with anthracene repeating units are investigated. Participation in the inhibition reaction of the polymer methylene end groups is shown. A charge transfer complex formation between the polyconjugated polymers as donors and the propagating radicals was assumed as another factor determining inhibition activity.
Living anionic stereospecific polymerization of 2‐vinylpyridine, 3. Structure of models of active centres and mechanism of polymerization
Authors: Soum Alain , Fontanille Michel 
Published: April 2003

AbstractThe mechanism of the stereospecific polymerization of 2‐vinylpyridine initiated by organomagnesium compounds in non‐polar solvents, was studied. Triad and pentad data were found to be consistent with a first‐order Markov‐polymerization process. 1H and 13C NMR studies on model molecules of the active species showed an sp3 hybridization of the carbanion and a coordination of the Mg cation by the last and the penultimate pyridine rings of the living chain. The NMR characterization of the monomer coordination with the Mg cation of the active species indicates that two transition states are possible. For steric reasons, only one of them is highly probable, leading to isotactic linkages.
Synthèse et propriétés du poly(p‐triméthylsilystyrène)
Authors: Chaumont Philippe , Beinert Gérard , Herz Jean E. , Rempp Paul 
Published: April 2003

Abstractp‐Trimethylsilylstyrene was found to be polymerisable anionically. When the reaction is carried out at low temperature in THF as solvent the polymer—poly(p‐trimethylsilylstyrene)—is obtained in a quantitative yield and exhibits a low polydispersity. The glass transition temperature, viscosity‐molecular weight relationships, and 1H and 13C NMR spectra were investigated in order to compare the influence of the trimethylsilyl group located at the benzene nucleus with respect to polystyrene and some other p‐subtituted polystyrenes. The presence of the trimethylsilyl group in para position of the aromatic nucleus results in an increase of the rigidity of the polymer chain and in an increase of the glass transition temperature.
2‐tert‐butyl‐6‐vinylnaphthalene polymers, 2. Steric effects of tert‐butyl group on intramolecular energy transfer from naphthalene to anthracene chromophore
Authors: Nakahira Takayuki , Sasaoka Tatsuya , Iwabuchi Susumu , Kojima Kuniharu 
Published: April 2003

AbstractPoly(2‐vinylnaphthalene) and poly(2‐tert‐butyl‐6‐vinylnaphthalene) having small fractions of 2‐vinylanthracene were prepared to examine the effect of bulky tert‐butyl groups on the intramolecular singlet energy transfer from naphthalene to anthracene chromophore. The steric interactions of the tert‐butyl groups were found not only to reduce excimer formation and thereby increase the donor lifetime, but to suppress energy migration through the donor chromophores, giving a significant reduction of the overall transfer efficiency.
Anionic polymerization of oxiranes and cyclic siloxanes initiated with potassium salt‐crown ether systems
Authors: Koinuma Hideomi , Naito Katsuyuki , Hirai Hidefumi 
Published: April 2003

AbstractPotassium carboxylates and 18‐crown‐6 form initiator systems for the anionic polymerization of oxiranes to afford polyethers with an acyloxy group at one of the chain ends. Because of the slow initiation as compared to the propagation step, the resulting polymers have wide molecular weight distributions (Mw/Mn ≈ 4,0). The presence of a small amount of water in the catalysts accelerates the initiation to give polymers with narrow molecular weight distributions (Mw/Mn ⩽ 1,2). The polymerization of methyloxirane is accompanied by a significant chain‐transfer reaction to the monomer, especially at high temperatures. Hexamethylcyclotrisiloxane is also polymerized by the same initiators. Furthermore, potassium salts of carboxylic acids initiate the polymerizations in the presence of a crown ether.
Die polymerisation von N‐ethylaziridin, seine copolymerisation mit N‐(2‐hydroxyethyl)aziridin und die überführung der copolymeren in die N‐(2‐chlorethyl)‐analoga
Authors: Kern W. , Mannschott Ch. , Höcker H. 
Published: April 2003

AbstractN‐Ethylaziridine (1) was polymerized in water with HCl as initiator and copolymerized with N‐(2‐hydroxyethyl)aziridine (2). Rapid propagation and termination reactions were observed. The maximum yield increases with the initiator concentration, whereas the molecular weight decreases. This is due to the difference in basicity between the tertiary N‐atoms of the two monomers and the tertiary and the terminal secondary N‐atoms of the polymers, which causes tranfer and termination reactions. Macrocycles with a side chain on a quaternary N‐atom are formed. During the copolymerization, the more basic 1 is preferentially incorporated into the copolymer chain. The copolymerization parameters can be estimated roughly on the basis of basicity considerations: r1 > 1; r2 < 1. The ratio of the rate constants (propagation to termination) is lower for 1 than for 2. This is due to the fact that the basicity difference between the monomer and the tertiary N‐atoms of the polymer is higher for 1 than for 2. By reaction of thionyl chloride with the copolymers the desired hydrochlorides of the N‐(2‐chloroethyl) derivatives are obtained. The neutralisation with alkali did not result the free bases, since the products formed are rather due to side reactions.
Kinetics of free radical oligomerization, 2. Cooligomerization of styrene and methyl methacrylate in carbon tetrachloride
Authors: Chen Show‐An , Hwang Cheng‐Chuan 
Published: April 2003

AbstractA mechanism for the cooligomerization of styrene and methyl methacrylate in CCl4 is proposed that includes: (a) the primary radicals decomposed from the initiator (benzoyl peroxide) first react with carbon tetrachloride (TX) to form the radical T*; (b) T* then reacts with styrene and successively propagates with styrene or methyl methacrylate; (c) only the cooligomer radicals ended with styrene units undergo chain transfer reaction with TX; (d) the T* radicals can also combine with each other to form the termination product T – T. From the proposed mechanism a simple scheme for predicting monomer conversion, number average molecular weight, and cooligomer composition is obtained. Values of the kinetic constants can be determined easily from the conversion data. The coolligomer composition equation developed is the same as that of Tsuchida, even though the detailed mechanism is different. Agreement of the simplified theory with the experimental data is reasonable.
Polymer conformation and NMR chemical shifts, 6. Alternating copolymer of α‐methylene‐γ‐butyrolactone with styrene
Authors: Koinuma Hideomi , Sato Kota , Tanabe Tsuneaki , Hirai Hidefumi 
Published: April 2003

AbstractIn view of the structural resemblance of α‐methylene‐γ‐butyrolactone to methyl methacrylate, conformation and NMR chemical shifts of poly(α‐methylene‐γ‐butyrolactone‐alt‐styrene). are calculated and compared with those of poly(methyl methacrylate‐alt‐styrene). The conformational energy surfaces for the dyad sequence models of the both copolymers are analogous to each other, as is expected from the similarity in the constituting monomeric units. Agreement of calculation with observation is satisfactory with respect to the cotacticity‐dependent splittings in the 13C NMR spectra and is improved by the fixation of a substituent in poly(α‐methylene‐γ‐butyrolactone‐alt‐styrene). Calculation of 1H chemical shifts gives an alignment of NMR signals which is in accordance with the observation.
Comparative DSC technique — application to studies of melting of branched polyethylene
Authors: Pakula T. 
Published: April 2003

AbstractA version of DSC technique is proposed which ensures good accuracy in comparing the melting behaviour of two apparently similar samples. The information is obtained in the form of comparative thermograms recorded during simulataneous melting of both samples. The method is applied to observe the influence of cooling conditions and annealing on melting behaviour of low‐density polyethylene.
Dynamic NMR studies of equilibria involving active species in the polymerization of cyclic acetals. Reaction of the methoxymethyl cation with 5‐, 6‐, and 7‐membered cyclic acetals
Authors: Szymański Ryszard , Penczek Stanislaw 
Published: April 2003

AbstractThe cyclic acetals 1,3‐dioxolane (4a), 1,3‐dioxane (4b), and 1,3‐dioxepane (4c) give in their reactions with the methoxymethyl cation (1) a mixture of two isomeric tertiary oxonium ions: the simple products of cationation 5a‐c and the cationated rings 6, 7, 9, enlarged by two atoms. The equilibria for the studied monomers are shifted to the side of the oxonium ions as shown in the reaction schemes 2, 4, 5, and 6 (SbF‐6 or SbCIF‐5 being the corresponding anions). In the case of 4a the equilibrium is displaced almost completely to the enlarged ring 6, whereas for the other two cyclic acetals 4b and 4c the first cationated products 5b and 5c dominate. Application of the dynamic 1H NMR method allows the determination of the equilibrium constants of the reaction of 4a with 1.
Polymere charge‐transfer‐komplexe auf der basis von polyvinylalkoholacetalen, 4
Authors: GeißLer Ulrich , Schulz Rolf C. 
Published: April 2003

AbstractPartially acetalisized poly(vinyl alcohol)s with degrees of acetalization between 39 and 60% were prepared by reaction of poly(vinyl alcohol) with 9‐isobutyl‐3‐carbazolealdehyde (5a) or 3‐formyl‐9‐((S)‐2‐methylbutyl)carbazole (5b). Complex formation constants and ε‐values of the charge‐transfer complexes with ethylenetetracarbonitrile, 2,5‐cyclohexadien‐1, 4‐diylidenedimalonodinitrile, 2,4,5,7‐tetranitro‐9‐fluorenone, and 2,4,7‐trinitro‐9‐fluorenone were determined. Circular dicroism measurements of the optically active CT‐complexes indicate two distinct CT‐transitions.
Oxidative polymerization of 2‐(2‐butenyl)‐ and 2‐(3‐methyl‐2‐butenyl)‐6‐methylphenol
Authors: Nishide Hiroyuki , Minakata Takashi , Tsuchida Eishun , Yamada Shigetoshi 
Published: April 2003

Abstract2‐(2‐Butenyl)‐6‐methylphenol (1a) and 2‐(3‐methyl‐2‐butenyl)‐6‐methylphenol (1b) were oxidatively polymerized in the presence of a copper‐pyridine catalyst to yield poly[oxy‐2‐(2‐butenyl)‐6‐methyl‐1, 4‐phenylene] (2a) and poly[oxy‐2‐(3‐methyl‐2‐butenyl)‐6‐methyl‐1,4‐phenylene] (2b) with molecular weights >104. The polymerization rates were in the order 1b > 1a > 1a > 2,6‐dimethylphenol (3), and this order agreed with those of the rate constant of the electron‐transfer step and of the redox potential. The 2‐butenyl and 3‐methyl‐2‐butenyl group in 2 showed enough chemical reactivity for addition of bromine and epoxidation.
Cellulosic microcapsules for drug delivery, 1. Hydrocortisone release
Authors: Singh Maninder , Bala Kiran , Vasudevan Padma 
Published: April 2003

AbstractCellulose acetate was used as an encapsulating material for preparing microcapsules by the technique of coacervation for sustained drug delivery. The condition of formation of such capsules containing hydrocortisone as drug, and its subsequent release from such depots, are described. The scanning electron micrographs show the formation of good, nearly spherical capsules in the range 10–20 μm. The release of hydrocortisone from the microcapsules sustains up to 7 days.
Contribution à l'étude de la métallation de structures polyisoprène, 1. Mèthode de dosage
Authors: Brosse Jean‐Claude , Maidunny Zainul Abdin Bin , Soutif Jean‐Claude 
Published: April 2003

AbstractSqualene, as a model compound, and polyisoprene were metalated by the complex of sec‐butyllithium (sec‐BuLi) with N,N,N′,N′‐tetramethylenediamine. The rate of metalation was determined indirectly by further reaction with a deactivating reagent. Amongst the various agents tested, a solution of chlorotrimethylsilane (Me3SiCl) in diethyl ether was preferred, as deactivation by this reagent does not lead to secondary reactions. The rate of silylation of sec‐BuLi by Me3SiCl was found to be influenced by the solvent and the temperature. The presence of diethyl ether, as solvent of silylation, and a reaction temperature of 0°C are suitable conditions for the reaction between lithiated polymers and Me3SiCl.
Functionalization of polymeric organolithium compounds. Carbonation
Authors: Quirk Roderic P. , Chen Wei‐Chih 
Published: April 2003

AbstractThe carbonation reactions of polymeric organolithium compounds with high purity, gaseous carbon dioxide have been investigated in benzene and benzene/tetrahydrofuran (75/25) solutions. The polymers investigated were poly(styryl)lithium, poly(isoprenyl)lithium, and poly(styrene‐b‐isoprenyl)lithium. In Benzene solution the products are a mixture of the carboxylic acid and the ketone (dimer). No tertiary alcohol product (trimer) was observed. In benzene/tetrahydrofuran solution, the quantitative carboxylation of chain ends was observed.
Propene polymerization with a magnesium chloride‐supported ziegler catalyst, 1. Principal kinetics
Authors: Keii Tominaga , Suzuki Eiichi , Tamura Masanori , Murata Masahide , Doi Yoshiharu 
Published: April 2003

AbstractThe main kinetic behavior of the slurry polymerization of propene with a MgCl2‐supported TiCl4/C6H5COOC2H5 catalyst, activated by Al(C2H5)3, was studied, Examination of the dependence of the polymerization rate on temperature and concentrations of Al(C2H5)3 and of propene resulted in a Langmuir‐Hinshelwood rate law with the number of polymerization centers dependent on time. The Polymerization rate as function of the polymerization temperature shows a maximum, which is compatible with the rate law. The analysis of the phenomenon of an optimum temperature gave 15 KJ. mol−1 and 36 KJ. Mol −1 for the activation energy of the rate determining step and the adsorption energy of Al(C2H5)3, respectively. Examination of the rapid decay of the polymerization rate showed that the main part of the decay is represented by a second order decay independent of the amount of polymer produced, which can be understood by a second order decay of surface sites by Al(C2H5)3. The number of active centers of the catalyst in gas phase polymerization was estimated applying the inhibition method with carbon monoxide. The results show a constant value for the propagation rate constant, Kp, during the second order rate decay. The observed polymerization kinetics strongly suggest the existence of two kinds of polymerization centers (isotactic and atactic).
Synthesis and phase behaviour of liquid crystalline polyacrylates
Authors: Portugall Michael , Ringsdorf Helmut , Zentel Rudolf 
Published: April 2003

AbstractThe synthesis and phase behaviour of a series of polymers having liquid crystalline sidechains and a poly(acrylic acid) backbone are described. These polymers show a dependence of the phase transition temperatures on molecular weight. In copolymers of two liquid crystalline acrylic esters, induced smectic phases occur. A comparison of the phase transitions of the different polyacrylates, with those of liquid crystalline polymethacrylates and polysiloxanes, published elsewhere, establishes that the spacer group achieves partial “decoupling” of liquid crystalline and polymer properties.
The influence of molecular interaction on polymerization, 7. Copolymerization of monomethyl itaconate with styrene
Authors: Boudevska Hrissanta , Platchkova Svetla , Todorova Olga 
Published: April 2003

AbstractThe copolymerization of monomethyl intaconate (MMI) with styrene (St) initiated with 2,2′‐azoisobutyronitrile in solvents differing in dielectric constants and capability to form hydrogen bonds was investigated. The IR‐ and 1H NMR spectroscopic studies of the monomer mixtures in four solvents have shown an influence of the solvent on the formation of hydrogen bonds and of other donor‐acceptor associates. The reactivity ratios of the monomer pairs in the different solvents are as follows: in chloroform, rMMI = 0,09 ± 0,05 and rSt = 0,14 ± 0,00; in acetonitrile, rMMI = 0,26 ± 0,10 and rSt = 0,36 ± 0,01; in dioxane, rMMI = 0,28 ± 0,01 and rSt = 0,55 ± 0,00; in acetone: rMMI = 0,18 ± 0,05 and rSt = 0,49 ± 0,00. The changes in the values of the reactivity ratios are connected with the ability of the solvents to govern the formation of hydrogen bonds among the MMI molecules and between the MMI and the solvent on the one hand and the formation of donor‐acceptor associates between both monomer molecules on the other. The increase of the concentration of associated monomer molecules which occur in chloroform leads to a decrease of the r‐values.
Polymer‐supported dinitrogen complexes of manganese. Coordination of molecular nitrogen in solid‐gas phase reaction under mild conditions
Authors: Kurimura Yoshimi , Ohta Fumihiko , Gohda Junko , Nishide Hiroyuki , Tsuchida Eishun 
Published: April 2003

AbstractA copolymer (PC‐1) was synthesized from a mixture of 1,2‐and 1,3‐isomers of tricarbonyl‐(methylvinylcyclopentadienyl)manganese (1) and styrene (St) crosslinked with 1,4‐divinylbenzene, and a membrane (PM–1) consisting of the 1/St copolymer. A polymer‐supported dinitrogen complex (PC‐4) was prepared from the tetrahydrofuran (THF) complex of PC‐1 and molecular nitrogen in a solid‐gas phase reaction under moderate conditions. The dinitrogen complex membrane (PM–4) was readily obtained directly from PM‐1 by a “one‐step reaction” on UV light irradiation under normal pressure of nitrogen at room temperature. A prominent feature of polymer‐supported dinitrogen complexes, PC‐4 and PM‐4, is their high stability as compared with the corresponding low molecular weight analogues. The coordinated nitrogen can be substituted by carbon monoxide in a PC‐4/THF mixture. The mechanism of nitrogen co‐ordination to PC‐1 and PM‐1 was investigated by means of IR and/or absorption spectrometry.