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121.
Margarita Acevedo Alain Fradet 《Journal of polymer science. Part A, Polymer chemistry》1993,31(3):817-830
2,2′-Bis(4,4-dimethyl-5(4H)-oxazolone) ( B3 ) and 2,2′-(1,2-ethylene)-bis(4,4-dimethyl-5(4H)oxazolone) ( B4 ) have been reacted in the bulk with α, ω-diamino polyamide-12 ( PA12 ) of M?n = 1000. The reactions have been studied by SEC, and 1H- and 13C-NMR and resulting polymers characterized by DSC and TGA. The chain coupling reaction is fast and gives high molar mass polymers within 10 min at 200°C with B4 while some side reactions occur with B3 leading to polymers of lower molar mass. The crystallinity of resulting polymers is lower than that of starting oligomer. However, the thermal stability is higher. Model reactions using B3 or B4 and hexamethylene diamine or 1-dodecanamine have been carried out and studied. An intramolecular cyclodehydration giving 2-imidazolin-5-ones takes place during the reactions. Higher cyclization extent is found in the presence of amino group excess. 2-Imidazolin-5-one heterocyclic structures are also observed in the chains of the polymers obtained from PA12 and B3 or B4 . © 1993 John Wiley & Sons, Inc. 相似文献
122.
Jean-Luc Decout Alain Lablache-Combier Claude Loucheux 《Journal of polymer science. Part A, Polymer chemistry》1980,18(7):2371-2390
Vinylpyridine-N-oxide units were introduced in polymeric chains in order to study their photocrosslinking. Copolymers of styrene and 4-vinylpyridine-N-oxide were especially synthesized and studied. The methods used for characterization of photocrosslinked films were a “photoresist test” or the measurement of the insolubility and of the swelling ratio. The Cleavage of the N-oxide bond was responsible for the photocrosslinking. The competitive formation of carbonyl compounds took place and decreased the rate of photocrosslinking. This last reaction is favored by triplet-state quenchers. The photosensitivity of the copolymers was determined as a function of the wavelength of the radiation used. When the photocrosslinking proceeded, a film of the copolymeric material became transparent in the 280–320-nm range. Thick films could therefore be completely photocrosslinked when irradiated in this range of wavelength. 相似文献
123.
Recherches théoriques sur la structure électronique de molécules contenant des atomes hybridés en sp
Alain Pellégatti 《Theoretical chemistry accounts》1967,8(2):128-137
Résumé La structure de la molécule d'allène est étudiée à l'aide de la méthode LCAO améliorée. On met en évidence la nécessité d'introduire d'une part l'interaction des systèmes et
avec les liaisons C-H et d'autre part un déplacement d'électrons dans les liaisons C-H. La distance interatomique C1-C2 est alors bien retrouvée et les charges nettes, presque nulles, sont en accord avec ce que suggère la réactivité chimique de la molécule. La transition permise A
1 B
2 est trouvée en bonne place; les trois autres étant un peu basses. Le problème de la réduction des intégrales faisant intervenir la couche 1s est abordé.
Nous tenons à remercier ici M. le Professeur André Julg (Laboratoire de Chimie Théorique, Faculté des Sciences, Marseille) pour les nombreuses discussions que nous avons eues avec lui sur ce sujet, et qui a bien voulu relire le manuscrit.
Les calculs numériques ont été effectués par nos soins sur l'ordinateur PB 250 du Centre de Calcul Numérique de la Faculté des Sciences de Marseille. 相似文献
The improved LCAO theory is used to study the structure of the allene molecule. We show that we must introduce on the one hand the interaction of the and systems with the C-H bonds and on the other hand an electrons displacement in the C-H bonds. The bond distance C1-C2 is then found in good agreement with the experimental value and the net charges, almost null, are in agreement with what suggests the chemical reactivity of the molecule. The allowed transition A 1 B 2 is found at the right place; the other three being a little low. The problem of the integrals reduction, making to intervene the 1s shell, is approached.
Zusammenfassung Die Struktur von Allen wird mit Hilfe der verbesserten LCAO-Methode untersucht. Es wird gezeigt, daß eine Wechselwirkung zwischen - und -System mit den C-H-Bindungen und eine Elektronenverschiebung längs der C-H-Bindungen eingeführt werden müssen. Der C1-C2-Bindungsabstand stimmt mit der Erfahrung überein. Die Nettoladungen sind fast Null, wie die chemische Reaktivität zeigt. Der erlaubte Übergang A 1 B 2 wird gut plaziert angegeben; aber die drei anderen liegen ein wenig zu tief. Das Problem der Integralreduktion mit 1s-Atomorbitalen wird behandelt.
Nous tenons à remercier ici M. le Professeur André Julg (Laboratoire de Chimie Théorique, Faculté des Sciences, Marseille) pour les nombreuses discussions que nous avons eues avec lui sur ce sujet, et qui a bien voulu relire le manuscrit.
Les calculs numériques ont été effectués par nos soins sur l'ordinateur PB 250 du Centre de Calcul Numérique de la Faculté des Sciences de Marseille. 相似文献
124.
Spadini L Schindler PW Charlet L Manceau A Vala Ragnarsdottir K 《Journal of colloid and interface science》2003,266(1):1-18
The surface properties of ferrihydrite were studied by combining wet chemical data, Cd(K) EXAFS data, and a surface structure and protonation model of the ferrihydrite surface. Acid-base titration experiments and Cd(II)-ferrihydrite sorption experiments were performed within 3<-log[H(+)]<10.5 and 0.5<[Cd(t)]<12 mM in 0.3 M NaClO(4) at 25 degrees C, where [Cd(t)] refers to total Cd concentration. Measurements at -5.5triple bond Fe-OH(-1/2),logk((int))=-8.29, assuming the existence of a unique intrinsic microscopic constant, logk((int)), and consequently the existence of a single significant type of acid-base reactive functional groups. The surface structure model indicates that these groups are terminal water groups. The Cd(II) data were modeled assuming the existence of a single reactive site. The model fits the data set at low Cd(II) concentration and up to 50% surface coverage. At high coverage more Cd(II) ions than predicted are adsorbed, which is indicative of the existence of a second type of site of lower affinity. This agrees with the surface structure and protonation model developed, which indicates comparable concentrations of high- and low-affinity sites. The model further shows that for each class of low- and high-affinity sites there exists a variety of corresponding Cd surface complex structure, depending on the model crystal faces on which the complexes develop. Generally, high-affinity surface structures have surface coordinations of 3 and 4, as compared to 1 and 2 for low-affinity surface structures. 相似文献
125.
Vladimir A Escobar Barrios Alain Petit Rafael Herrera Nájera 《European Polymer Journal》2003,39(6):1151-1167
Three types of butadiene-styrene copolymers, diblock, triblock and random, were partially hydrogenated in their elastomeric units in order to determine the influence of hydrogenation extent on their thermal properties. The hydrogenation reactions were carried out using a Ziegler-Natta type catalyst and the extent of hydrogenation was evaluated by FTIR spectroscopic technique. The percentage of crystallinity was determined by differential scanning calorimetry (DSC), considering the low density polyethylene (LDPE) as reference since the saturation of elastomeric units with low content of 1,2-vinyl bonds gives a structure which resembles to LDPE, thus semi-crystalline polymers were obtained. On the other hand, the glass transition temperature (Tg) for the hydrogenated and non-hydrogenated copolymers as well as their heat of fusion, were also determined by DSC. An equation to evaluate the Tg of partially hydrogenated random copolymers is proposed considering both the saturated and unsaturated fractions. The thermo-oxidative behaviour of certain hydrogenated and non-hydrogenated copolymers was evaluated by thermogravimetric analyses (TGA). The results obtained by TGA suggest that a minimum saturation level is necessary in order to improve the thermo-oxidative resistance of the polymers. 相似文献
126.
The stability and electronic properties of highly packed 1-hexyl-naphthalene (HNap) molecular wire on Si(0 0 1) have been studied with first principles DFT method. HNap assembles into a 1D arrangement on the Si(0 0 1)[2 × 1] surface on which molcules adopt a commensurate structure along a dimer row with an intermolecular distance of 3.8 Å. HNap is attached to the surface through the hexyl chain, and stands normal to the surface. This highly packed structure leads to the formation of delocalized π-orbitals over the entire wire but essentially localized on the naphthalene counterpart, and well separated from the Si surface states. Cohesion energy within the wire arises from a significant attraction between hexyl chains, and to a weaker stabilizing π–π interaction between naphthalenes. 相似文献
127.
128.
Enamino- and Halogenoacetylenic sugars Traitment of an aldehydosugar ( 1 ) with secondary amines gave in an essentially quantitative yield the expected enamines ( 4–6 ). Chloro- and bromo-acetylenic sugars ( 11–14 ) were obtained in good yields by reacting with lithium methylphenylamide the corresponding gem-dihalo-olefinic sugars ( 7–10 ), whereas a Z-gem-fluoro-enamine ( 17 ) was formed when the difluoro-olefinic sugar 15 was submitted to the same reaction. The fluoro-enamine 17 is a useful synthetic intermediate allowing the preparation of several kinds of C-glycosylic compounds bearing heterocycles like isoxazole, chromone or coumarin. 相似文献
129.
Alain J.P. Alix 《Journal of Molecular Structure》1976,33(1):137-139
Microwave spectra of CH18 OCOOH, CHOC18 OOH, CHOCO18 OH, 13 CHOCOOH and CHO13 COOH are reported and have been used in combination with data on CHOCOOH and CHOCOOD to determine the molecular structure as r(C=O)ald. = 1.174 ± 0.006 Å, r(C=O)acid = 1.203 ±0.006 Å, r(C—O) = 1.313 ± 0.010 Å, r(C—C) = 1.535 ± 0.005 Å, r(O—H) = 0.948 ± 0.004 Å, r(C—H) = 1.104 ±0.010 Å, ald. = 123.7 ± 0.4<, 相似文献
130.
Hartl F Mahabiersing T Chardon-Noblat S Da Costa P Deronzier A 《Inorganic chemistry》2004,43(22):7250-7258
IR, UV-vis, and EPR spectroelectrochemistry at variable temperatures and in different solvents were applied to investigate in situ the formation of electroactive molecular chains with a nonbridged Os-Os backbone, in particular, the polymer [Os(0)(bpy)(CO)(2)](n) (bpy = 2,2'-bipyridine), from a mononuclear Os(II) carbonyl precursor, [Os(II)(bpy)(CO)(2)Cl(2)]. The one-electron-reduced form, [Os(II)(bpy(.)(-))(CO)(2)Cl(2)](-), has been characterized spectroscopically at low temperatures. This radical anion is the key intermediate in the electrochemical propagation process responsible for the metal-metal bond formation. Unambiguous spectroscopic evidence has been gained also for the formation of [[Os(0)(bpy(*)(-))(CO)(2)](-)](n), the electron-rich electrocatalyst of CO(2) reduction. The polymer species are fairly well soluble in butyronitrile, which is important for their potential utilization in nanoscience, for example, as conducting molecular wires. We have also shown that complete solubility is accomplished for the monocarbonyl-acetonitrile derivative of the polymer, [Os(0)(bpy)(CO)(MeCN)(2)Cl](n). 相似文献