Pyrolyse eclair de polyacrylonitriles entre 400 et 800°

Flash pyrolysis of radical and anionic polyacrylonitriles between 400 and 800° and in the absence of oxygen leads to various degradation products, the most characteristic being cyanhydric acid,. cyanogen, acrylonitrile and two dimers α-methyleneglutaronitrile and a cyanopicoline. Two important parameters have been studied: molecular weight ($\text{4 × 10}{}^3\text{<}\text{M}{}_{\mathrm{<mtext>w</mtext>}}\text{< 1·6 × 10}{}^6$) and branching density (0 < N/X < 0·6). At 400°, the yields in acrylonitrile and α-methylene glutaronitrile increase with branching density. All the experimental results may be interpreted on the basis of random chain scission, hydrogen transfer reactions and cyclization of the nitrile groups.     

Le developement de l'etude de la diffusion de la lumiere et des neutrons par les polymeres a strasbourg

In this paper one recalls the history of the development of scattering studies after the first world war in Strasbourg. Tremendous progress has been made and some examples of this progress are discussed     

Relations entre les caracteristiques physico-chimiques des charges et les proprietes mecaniques des polymeres (PVC) plastifies et charges

Some rheological and mechanical properties of polyvinyl chloride filled with up to 80 phr CaCO₃ have been evaluated with a view to rationalizing results in terms of polymer/filler interfacial interactions. These interactions have been characterized by inverse chromatography using a series of acid-base vapour probes selected from literature classifications. Both pure and industrially pretreated CaCO₃ samples were employed; in addition, one of the pure materials was surface-modified by exposure to selected vapours in a microwave plasma apparatus. Though the data are not adequate to develop exact correlations linking interaction parameters and the physical properties of the filled systems, it is clear that favourable interaction (wetting, adhesion) states at the polymer-filler interface promote ease of dispersion of solids in the molten polymer, enhance mechanical properties (such as elongation at break and the yield stress in the stress/strain curve of the materials) and reduce the rates at which these properties deteriorate when compounds are exposed to weathering. This preliminary work therefore confirms the apparent importance of interfacial effects to property development in filled polymers, suggests the usefulness of acid-base concepts as an index of these effects, and shows inverse chromatography data to be convenient for their quantification. Plasma treatment appears to be a particularly flexible approach to the tailoring of diverse surface properties in filler particles. Detailed development of the various concepts is indicated.     

Relation entre la solvatation preferentielle et la densite en segments de polymeres: Generalisations et limitations

This paper presents results on viscosity and preferential solvation for the ternary systems: polystyrene (PS)-carbon tetrachloride-methanol, PS-benzene-cyclohexane, PS-chloroform-ethanol and poly(2 vinylpyridine)-ethanol-cyclohexane using linear and branched polymers. For a given ternary system the representation Δλ′ (variation of the preferential solvation coefficient) as a function of Δρ (variation of the segment density) already proposed gives a unique curve. This shows that this relation is not sensitive to branching or to molecular weight of the polymer when the dimensions of the polymer in the mixed solvent are lower than in the pure good solvent. However, when the dimensions of the polymer in the mixed solvent are higher than in the pure good solvent, the relation between Δλ′ and Δρ cannot be applied.     

Relations entre la structure et les proprietes des membranes de polytetrafluoroethylene greffe—III. Membranes non-ionisables contenant de la poly-n-vinylpyrrolidone

Equilibrium properties (swelling) and transport phenomena (dialysis) of non-ionizable membranes, obtained by radiation grafting of N-vinylpyrrolidone onto thin PTFE films, were studied. Grafting was conducted by the direct method with monomer solutions in benzene. The overall activation energy of grafting determined between 20 and 50° is high (12.5 kcal mol^?1): the reaction is controlled by the monomer diffusion into PTFE film. The length of grafted chains increases with temperature.The molality of the membranes decreases when the temperature of grafting increases; for a given grafting ratio, the swelling is higher for membranes containing a small number of long grafts than for membranes with numerous short branches. The transfer of both ions and water is a function of the free volume in the films, it depends on the grafting ratio and is not influenced by the preparation conditions.     

Lien experimental entre la viscosité et la longueur de correlation ζ∥ dans les smectiques hexatiques B et F

Abstract

Nous présentons les premières mesures de viscosité en cisaillement parallèle aux couches dans la phase B hexatique du 65OBC (n-hexyl-4′-n-pentyloxybi-phenyle-4-carboxylate) et dans la phase F du 90.4 (4-n-nonyloxybenzilidene-4′-n-butylaniline). Le comportement pseudoplastique observé dans ces deux phases est analysé en termes de couplage entre l'écoulement et les dislocations. Leur viscosité intrinsèque est déduite des mesures à hautes fréquences. Nous montrons qu'elle est proportionnelle à la longueur de cohérence ζ∥ mesurée antérieurement dans les couches par diffraction des rayons X.     

Relations entre la structure et les proprietes des membranes de polytetrafluoroethylene greffe—II. Membranes bifonctionnelles

Bifunctional membranes containing both carboxylic and pyridine groups are obtained by successive grafting of acrylic acid and 4-vinylpyridine onto thin films of PTFE. Homogeneous membranes with a random distribution of grafting chains have been prepared by the direct radiation method. Mosaic membranes containing geometrically well defined acid and basic zones are made by pre-irradiation with X-rays using two absorbing shields; the two monomers are grafted in successive steps. The equilibrium and transport properties of these membranes have been determined. They can either result from the addition of the properties of each component (in the case of conductivity) or give rise to a new properties (e.g. abnormal negative osmosis). Whatever the structure of the bifunctional membrane (homogeneous or mosaic), this negative osmosis occurs within a pH range in which the membrane potential varies greatly i.e. when the ionic character of the membrane changes. Experimental data are discussed on the basis of thermodynamics of irreversible phenomena. The phenomenological coefficients characteristic for a membrane belonging to each of the two types (mono- and bi-functional) have been calculated. The reflection coefficient σ is negative: this suggests a potential application of these membranes in piezodialysis.     

Influence de la solvatation preferentielle sur les dimensions des polymeres en solution dans des melanges de solvants

We have studied the dependence of the intrinsic viscosity number of polymers on the composition of binary solvents. The systems studied are: polystyrene in CCl₄/CH₃OH, C₆H₆/CH₃OH and C₆H₆/heptane and poly-2-vinylpyridine in CHCl₃/CH₃CH₂OH. We have also studied, for the same systems, preferential solvation of the polymers, using light scattering.We have observed that, near the θ point, short polystyrene chains exhibit a higher expansion than long chains. This was explained in terms of the dependence of preferential solvation on molecular weight.For the system poly-2-vinylpyridine/CH₃CH₂OH/CHCl₃, we have established the viscosity increment dependence on solvent composition. The curve describing this increment differs markedly from the theoretical curve based on G^E values (excess free energy) of the solvent mixture. However, taking into consideration the process of preferential solvation, the experimental curve can be corrected and becomes very similar in shape to the theoretical curve but there still remains a quantitative difference between the two curves.     

Polymerisation anionique du methacrylate de methyle par les organoalcalins—II. Polymerisation en milieu solvant protonique et influence de la temperature sur les tacticites des polymeres

Anionic polymerization of methylmethacrylate, initiated by fluorenyl-alkali metals in amine media, gives syndiotactic polymers.With amines having high dielectric constant (NH₃ and MeA) Li⁺, Na⁺ and K⁺ give approximately the same values of differential enthalpies and entropies of activation for iso- and syndiotactic placements.With primary amines having moderate dielectric constant (5 < ? < 7), influence of the nature of the counter-ion has been observed. The syndiotacticity increases with increasing alkali cation radius.For the same ion pair, the syndiotacticity of the propagation depends on the nature of the primary amine. From the absorption peak shifts detected by u.v. spectroscopy, it has been suggested that the living carbanion is solvated by amines. Because of this solvation, the coordination bond between the carboxy group of the living chain-end and the counter-ion is weakened; the syndiotactic placement is thus favoured.The strength of the solvation phenomenon depends on the steric hindrance of the amine molecule. Differences between the stereoconfiguration propagations have been observed for the bulky cyclohexylamine and the smaller and less rigid n-butylamine and ethylamine. With iso-propylamine, the behaviour of the anionic propagation is intermediate.Finally, with free ions or loose ion pairs, the anionic propagation is not affected by solvation of the living carbanion.     

Decomposition des tosylhydrazones cycliques par les organolithiens relations entre la reactivite et la conformation

Tosylhydrazones of a series of cyclanones containing from 7 to 15 carbon atoms are decomposed at room temperature by MeLi or BuLi in ether or hexane, to yield elimination products exclusively. The ratio of cis and trans olefins depends on the size of the ring. These values are analysed in terms of the most likely conformations of the tosylhydrazones.     

Polymerisation en phase homogene du methyl-2 thiiranne amorcee par les thiolates de cadmium et de zinc. Influence des interactions monomere-metal sur la stereoregularite des polymeres

The stereoregularity of polymethylthiiranes initiated by zinc and cadmium thiolates depends upon the nature of the metal, temperature, solvent and the monomer/initiator concentrations ratio. Complexation of the metal with monomer has been studied by (¹³C) and (¹H) NMR on a model molecule, dimethylcadmium. Cryoscopic measurements made on a soluble cadmium thiolate have shown the presence of aggregates. The relationship between these observations and polymer stereoregularity is discussed.     

Relations entre la structure electronique des films de passivation formes sur les aciers inoxydables et la susceptibilite de ces derniers a la corrosion par piqures

The passive films formed on 316L stainless steel in various NaCl solutions have been investigated by capacitance measurements (Mott-Schottky study). Pitting parameters have been determined using the galvanokinetic polarisation method. The obtained results reveal the existence of a shallow and a deep donor level localised in the band gap of the semiconducting oxide film. These energy levels are due to iron ions in the tetrahedral and octahedral positions. It also appears that the participation of the deep donor level affects the electric field. The study developed allows us to compare characteristic parameters of the electronic structure of the passive film to those related to pitting susceptibility.     

Relations entre la structure et les proprietes des membranes de polytetrafluoroethylene greffe—I. Membranes monogreffees carboxyliques ou basiques

We have determined the equilibrium properties (neutralization and swelling and the transport properties: conductivity and dialysis) of hydrophilic membranes obtained by radiation grafting of acrylic acid or 4-vinylpyridine onto thin PTFE films. The presence of strong counter-ion-membrane interaction (PTFE-PAA-K⁺ and PTFE-P4VP-ClO^?₄) has been confirmed in the beginning of neutralization. The grafting ratios of the samples ranged between a few percent and several hundreds percent. The properties have been studied in connection with the average degrees of ionization and the average molalities of the reactive groups throughout the whole thickness of the membrane. The parameters of the synthesis which determine the structure of acid or basic grafted chains also have an influence on the properties of the resulting membranes. For a high dose-rate (> 100 rad min^?1), the properties of carboxylic membranes are related to the degree of cross-linking: for smaller dose rates, the properties are related to the length of the grafted branches and/or to the state of the skeleton of PTFE. For the basic membranes, the properties are controlled by the length of the grafted branches and the importance of the micro-phase-separation between PTFE and the grafted chains; for low dose rates, when the grafted branches are long, separation of hydrophobic and ionizable zones is noticed for grafting ratios higher than 5%. The carboxylic membranes with lower degrees of grafting, prepared with a high dose rate, exhibit very good permselectivity. The pyridinic membranes with a low degree of grafting could be of practical interest, viz. the manufacture of selective electrodes for perchlorate ions.     

Utilisation de l'ultracentrifugeuse pour la mesure des masses et pour l'etude de la polydispersite des polymeres de synthese

After a review of the two techniques based on sedimentation rate and equilibrium in binary medium, more recent methods involving the presence of a second non-macromolecular solute are described. Application of these methods to synthetic polymers is still rare but of increasing interest. The use of computers simplifies the exploitation of the measurements.     

Etude de l'action de la pression sur la pression osmotique des solutions de polymeres

Osmotic pressures of solutions of polymers were measured as a function of pressure. The measurements were made at room temperature at pressures up to 500 bars. The results are as follows:

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-the effect of pressure depends upon the polymer-solvent pair. Depending upon the particular case the effects can be positive, negative or zero. We have given examples for each case.     

Etude de la synthese des zeolites 4A et HS a partir de produits naturels

The crystallization of the zeolite HS was studied during the synthesis of the zeolite 4A using several raw materials like diatomite, kaolin and bentonite. First, these three materials were activated mainly by melting in the presence of caustic soda. The comparison with the pure reagents (solution of sodium silicate and sodium aluminate) as a reference allowed to deduce that an appearance of the zeolite HS during the synthesis is observed with most of the raw materials. Its formation takes place when the concentration of aluminium decreases below the value corresponding to the pure products in the liquid phase. This situation takes place when the reactant gel is heterogeneous, which is characteristic of all the raw materials studied. This seems to be the reason for the formation of zeolite HS.     

Tetrahydro anthraquinones disubstituees en - 1,5: etude de la regioselectivite de la reaction de diels-alder entre des naphtoquinones et des dienes attracteurs.

Diels-Alder reaction of - 2,4 pentadienoïc acid and its methyl ester (electron with-drawing) dienes with juglone and its derivatives is described. High regioselectivity is observed, the adducts have a “head-to-tail” geometry.