Etude de copolymères ABS (acrylonitrile–butadiène–styrène): Solvatation préférentielle du polybutadiène par les promoteurs

ABS resins formed by copolymerization of styrene and acrylonitrile (AN) in presence of polybutadiene, consist of a mixture of SAN graft copolymer on polybutadiene (PBut) and of ungrafted SAN copolymer (styrene-co-acrylonitrile). The kinetic study was completed by showing a preferential solvation of polybutadiene by the initiator. This solvation effect was studied as a function of the concentration ratio SAN/PBut and in relation with the type of initiator. The adsorption of initiator appeared to be maximum when its solubility parameter (σ) is close to that of polybutadiene. As a function of the polybutadiene characteristics, this selective adsorption can be given by where I₁ is the quantity of initiator in the polybutadiene medium, I is the total amount of peroxide, [PBut] is the concentration of polybutadiene, and M?_n its molecular weight. It has been shown furthermore that the preferential solvation of polybutadiene by the benzoyl peroxide can be increased by addition of SAN or acrylonitrile. The consequences of this solvation effect on the characteristics of the grafting reaction, more precisely on the molecular weight of grafted and ungrafted SAN and on the rate of polymerization, were examined.     

Polymérisation anionique des diènes. III. Etude thermodynamique de la propagation du butadiène et de i'isoprène par les organo-alcalins

The present work is concerned with the influence of the polymerization temperature on the propagation mechanisms of polyisoprenyl- and polybutadienyl-alkali metals. The thermodynamic parameters of the contact ion pairs and free ions propagations have been calculated. With Li⁺ in dioxane solvent, the vinyl propagation is stereospecific (for isoprene, the propagation is mainly 4–3). In comparison with benzene, the vinyl propagation of the polydienyl-Li contact ions pairs should be due to complexation of Li⁺ by dioxane, an electron donor having a weak dielectric constant. In general, the stereospecificity of the propagation of contact ion pairs decreases with increasing counterion size; little difference has been observed with K⁺ and Cs⁺ ion pairs in dioxane and benzene media. For isoprene, the methyl substituant should have chiefly a steric effect in the propagation of free ions, whereas it should confer a polar character to the isoprene molecule in the presence of ions pairs.     

Contributions au fractionnement des copolymères. II. Copolymères ternaires acrylonitrile–acétate de vinyle–α-méthylstyréne

Acrylonitrile, vinyl acetate, and α-methyl styrene copolymers, were synthesized in aqueous solution, and the resulted products were studied viscometrically by fractionation and by cloud-point titration. The values of the intrinsic viscosities of the polymers in DMF at 20°C are not influenced by the overall composition of the copolymers and the distribution mode of the comonomers. The solubility of the products is directly dependent on the composition, namely, it increases as the acrylonitrile content decreases. The differential fractionation curves are influenced by the chemical composition and by the mode of distribution of the monomers along the macromolecular chain. The successive precipitation method for the fractionation of the ternary copolymers is recommended.     

Copolymérisations radicalaires sous haute pression. Influence de la pression sur les rapports de réactivité

The pressure effect upon the reactivity of the radicals in copolymerizations can be important. The present work reports the pressure dependence of the reactivity ratios for some radical copolymerizations involving monomers of various polarities and proposes an interpretation concerning their variations with pressure based upon the Q—e scheme (or Alfrey–Price scheme). The direction as well as the magnitude of the pressure effect can thus be predicted.     

Propriétés électriques du trioxyde de tungstène a proximité de sa composition stoechiométrique. Influence des conditions thermodynamiques de préparation et phénomènes de trempe

The experimental study of variations in electrical conductivity of WO_3−x vs oxygen partial pressure and temperature shows evidence of interstitial W⁶_i· as being the major defect. Under certain conditions, point defects can order themselves in extended defects. The behavior of electrical conductivity can be interpreted in terms of thermodynamic equilibrium between point defects and extended defects, the latter leading to structural modifications beyond a certain departure from stoichiometry. Moreover, WO_3−x shows evidence of quenching phenomena allowing it to keep electrical features characteristic of high temperatures down to room temperature. These properties may explain discrepancies between previous data.     

Polymérisation “basse pression” de l'ethylène en préasence de noir de carbone

The polymerization of ethylene with Ziegler-Natta catalysts in the presence of carbon black has shown three characteristic features both with a heterogeneous catalyst, AlBu₃? TiCl₄, and with a soluble catalyst, Cl₂Ti(C₅H₅)₂? AlEt₂Cl. They are, in order of increasing importance: reactivity of the organoaluminum derivatives with surface chemical groups of the carbon black, adsorption of a certain amount of organoaluminum compounds on the carbon black surface, and influence of the specific surface of carbon black, which controls the dispersion degree of the catalytic system. Furthermore, it was possible to obtain polyethylene by this procedure, containing different amounts and different types of carbon black.     

Évaluation ab initio de la couleur de diaryléthènes présentant un pont maléimide

We have investigated the visible spectra of closed-ring diarylethenes based on maleimide bridges. Our simulations have been performed with an ab initio time-dependent density functional theory approach that takes into account bulk environmental effects. The computed λ_max almost quantitatively agree with experimental data, with a mean absolute error limited to 13 nm for the 26 investigated photochroms.     

Oligomérisation anionique de l'ethylène. I. Etude cinétique

A kinetic study of ethylene oligomerization in hexane, in the presence of n-BuLi–TMEDA complexes, allowed us to suggest a new mechanism for anionic ethylene oligomerization. n-BuLi and n-Bu(CH₂CH₂)Li species have the same reactivity. The RLi–TMEDA complex in a 1-to-1 stoichiometry is the active species. The following kinetic equation has been established: It reflects the intervention of associated species (n-BuLi–TMEDA)₂ as well as the influence of the concentration of the complexing agent on the kinetics of oligomerization.     

Polymérisation radicalaire du pentadiène-1,3. II. Microstructure des résidus pentadiéniques dans les homo- et copolymères des cis et trans pentadiènes-1,3 avec l'acrylonitrile

The microstructure of diene units was investigated in radical homopolymers of the cis and trans isomers of 1,3-pentadiene and copolymers with acrylonitrile, synthetized in bulk and emulsion. Experiments were carried out by infrared spectroscopy, 100 MHz ¹H-NMR, and 25 MHz ¹³C-NMR studies. No difference between the bulk and emulsion samples was noted. The microstructure of poly(1,3-pentadiene) is practically independent of the cis or trans configuration of the diene monomer and is as follows: 56–59% trans-1,4, 15–17% cis-1,4, 16–20% trans-1,2 7–10% cis-1,2 and 0% 3,4. On the other hand, up to about 30% of incorporated acrylonitrile (10% in the feed), the microstructure of the pentadiene fraction in the copolymers is not affected. This finding suggests that the penultimate unit has very little influence on the polymerization process involving the terminal pentadienly unit. Beyond 10% of acrylonitrile in the feed, the proportions of the structural units were linearly dependent upon the acrylonitrile content: trans-1,4 content increased whereas the amounts of cis-1,4 trans-1,2 and cis-1,2 decreased (except the cis-1,2 fraction, constant in the copolymers from the cis-diene). These results are discussed on the assumption that the microstructure of pentadiene residues is strongly associated with the acrylonitrile comonomer in the feed.     

Nucléosides de synthèse XIV. Du choix des paramètres réactionnels pour l'obtention préférentielle de nucleosides en série benzoazole par réaction de fusion

By a judicious choice of the fusion reaction parameters, mainly the percentage of catalyst, we have obtained the corresponding benzotriazole and benzimidazole nucleosides substituted at N-2. We have also obtained the α N-1 anomers. Thus, we have shown it is possible, to confer some selectivity to the acid-catalyzed fusion-reaction.     

Polymérisation anionique de l'isoprène: Nature de la paire d'ions et stéréospécificité. II. Influence de la nature du solvant

The present work reports some new results on the dependence between the stereospecificity of the anionic propagation of isoprene and the nature of the active centers. The stereospecificity of the propagation of macroheterobicylce separated ion pairs does not depend on the nature of the alkali counterions, and the microstructure of the polyisoprenes obtained does not differ from that of those produced by free ions. Variations in the microstructure were observed in the propagation of contact ion pairs, depending on the nature of the cation and the solvent used. These variations are likely to be related to the degree of intimacy of the contact ion pairs. There are two main factors which affect the stereospecificity of the propagations in different ways: the size of the cation and the donating power of the solvent. Finally, the external solvation of the propagation ions pairs was confirmed by the microstructure of polyisoprenes synthesized in mixed (inert + donor) solvents.     

Polymérisation anionique de l'isoprène: Nature de la paire d'ions et stéréospécificité

With accumulated HR-NMR spectra of anionic polyisoprenes, it has been possible to study the influence of the nature of the propagating species on the microstructure of the obtained polymers If free ions are responsible for the propagation, the microstructure (1,4-: 25%, 1,2-: 33%, 3,4-: 42%) does not depend on the nature of the cations. But with contact ion pairs, the different addition modes are governed by the size of the alkali metal counterions. Mechanisms of anionic propagations via diene–cation coordination are proposed.     

Fluorénacènes et fluorénaphènes synthèses dans la série des indéno-fluorènes,XVII. Dérivés méthylés du cis-fluorénacène,du trans-fluorénacène et du trans-fluorénaphène

By condensation of the chlorides of the three 9-oxo-fluorene-2-, -3-, and -4-carboxylic acids with 4-bromo-1,2-xylene on one side, and of the chlorides of o-bromobenzoic acid, 2-bromo-4-methyl-benzoic acid and 2-bromo-4,5-dimethyl-benzoic acid with fluorene, 2-methylfluorene and 3-methylfluorene on the other side, followed by direct or indirect cyclisation and by final reduction, several new methyl derivatives of the indenofluorenes I, II and IV are synthesized.     

Effect solvatant des copolymères styrène–macromère a chaîne polyoxyéthylène. Influence du support polymère

Polyoxyethylene macromers were used to prepare functionalized linear and crosslinked copolymers with styrene and divinylbenzene. Gel or macroporous resins were prepared. These copolymers and resins were used as anionic activators for the Williamson reaction of potassium phenoxide and alkyl bromides under solid–liquid or solid–liquid–liquid (triphase) conditions. In contrast to similar resins obtained from chemical grafting of polyoxyethylene onto chloromethylated styrene–divinylbenzene polymers, the activity factors were strongly dependent on the composition of the resins and their morphology: an optimum activity was obtained for a 0.05M fraction of macromers in soluble copolymers and crosslinked resins. In addition, a macroporous resin with large pores was more efficient than a gel-type resin of similar composition. These effects are discussed in terms of accessibility of the activating group and compatibility of the support with the medium.     

Fluorénacènes et fluorénaphènes Synthèses dans la série des indéno-fluorènes XIV [1] Nouvelle synthèse du trans-fluorénacène

A new synthesis of 6, 12-dihydro-indeno [1,2-b] fluorene (trans-fluorenacene) in 9 steps starting from fluorene (overall yield 24,5%) is recorded. By partial oxidation of the hydrocarbon its 6-oxo derivative is also obtained.