Greffages mecanochimiques sur le polychlorure de vinyle. II. Éatude des copolymègres grefféas

The copolymers obtained by mastication of poly(vinyl chloride) (PVC) in presence of methyl methacrylate and styrene monomers, and their fractions, were studied by using infrared spectroscopy, NMR, and flash pyrolysis. The degree of alternation between vinyl chloride and methyl methacrylate or styrene units is very low, and the copolymers are heterogeneous in composition. The results suggest that the mastication medium involves three kinds of domains: the inner part of the elementary grains of PVC is very slightly penetrated by the monomers. The polymerization initiated by the polymeric free radicals created by the rupture of bonds, begins in the surface layers of the grains and cause the formation of a true copolymer which accounts for 5–10% of the material. Light radicals arising from transfer reaction migrate into the third external domain which consists practically entirely of pure monomers and initiate polymerization.     

Greffages mecanochimiques sur le polychlorure de vinyle. I. Polyméarisations amorcéaes par le malaxage

The grafting of methyl methacrylate and of methacrylic esters on poly(vinyl chloride) by mechanicochemical synthesis can be performed in the Brabender Plastograph. These monomers possess sufficient intermolecular plasticizing power to bring the poly(vinyl chloride)-monomer system into the viscoelastic state required for the formation of free radicals by homolytic scission of polymeric chains. Nevertheless several other monomers (among them the styrene) have interstructural plasticizing ability and can be grafted by mechanicochemical synthesis by addition of an intermolecular plasticizer or a monomer of the first class (methyl methacrylate). Also, except for basic monomers, the monomers stabilize poly(Vinyl chloride) during the mastication, probably because they act as free-radical scavengers.     

Sur la dégradation thermique du polychlorure de vinyle. V. Stabilité thermique de polyméres semicristallins

The thermal dehydrochlorination of semicrystalline, but rather low molecular weight, PVC fractions, prepared by ionic polymerization catalyzed by tert-butylmagnesium chloride was studied under an inert atmosphere and compared with that of commercial polymer. When the samples are in powder form, the crystallinity of some fractions, which are insoluble at room temperature in all the usual solvents for PVC, induces a tremendous thermal stability, which is observed so long as the temperature is under the melting point of the sample. In dilute solution, the dehydrochlorination of all the samples is much slower, but the differences between the samples are less important; besides, a catalytic effect of some metallic impurities is observed. This catalytic effect is chiefly relative to a process of intermolecular condensation which causes the formation of a labile tertiary chlorine structure and so initiates or accelerates the purely thermal chain dehydrochlorination. It is suggested that, besides the crystallization and the catalytic effects, the configuration of the structural units could be an important factor in the course of the dehydrochlorination process.     

Sur la dégradation thermique du polychlorure de vinyle. VI. Etapes initiales—etude générale préliminaire

A differential conductimetric apparatus allowing the continuous titration of HCl carried by a stream of gas with a limit sensitivity of 40 nanograms is described and applied to study the initial steps of poly(vinyl chloride) thermal degradation. The powdered sample is placed in a quartz cell which may be closed and detached and placed at a chosen time interval in a reflexion diffuse UV spectrometer. The dehydrochlorination process begins just above T_g; the isotherms under argon show, after a variable time, a steady state with a zero order and an activation energy of 22 kcal. For a dehydrochlorination ratio (DR) less than 1000 ppm, the shape of the UV visible spectrum does not depend on the DR, and for the same DR it does not depend on the degradation temperature. A plot of the reflectance ratio versus the DR shows a coloration process in two steps: a rapid step followed by a slower step. The phenomenon, which does not depend on the physical state of the sample, tends to disappear if the amount of polymer is lowered and if the rate of flow of the gas is increased. It suggests that the HCl formed upon the dehydrochlorination process remains partly dissolved in the polymer. Further proof of the dissolution of HCl in the polymer is given, and a through method of titration is proposed. It is suggested that the initial steps of the dehydrochlorination follows an ionic mechanism, and might be partially reversible and diffusion controlled, although the autocatalysis which involves a rather high dehydrochlorination ratio and the presence of a large amount of dissolved HCl might initiate the radical process.     

Etude de l'action des acides de lewis sur les polymères. Application au greffage de macromolécules sur les surfaces solides

The interaction between a solid surface (metal oxides, carbon blacks…) and macromolecules carrying a carbenium ion formed by a Lewis acid attack, results in a significant insolubilization of the polymer on the surface. Physical modifications of hydrocarbon polymers under the action of Lewis acids have been followed. Saturated (polyethylene, polypropylene, polyisobutylene), unsaturated (polybutadiene, polyisoprene, styrene-butadiene and isoprene-isobutylene copolymers) and styrene polymers have been investigated. Lewis acids generally extract a hydrid ion or add a proton to the double bond of a polymer. In both cases, a polymeric cation is formed: its evolution depends essentially on its stability and on the vicinity of chemical groups on the backbone of the polymer. The carbenium ion reacts with the surface hydroxyl groups. The amount of polymer irreversibly fixed on the solid surface exceeds the one required for the formation of the monolayer. It depends both on the concentration of polymeric cations and on the accessibility of the surface groups to the Lewis acid.     

Un modèle de points chauds fondé sur l'implosion de la porosité microstructurale

A Hot Spot Model Based on Microstructural Pores Collapse We present the basic equations of a hot spot model based on the viscoplastic strains of the explosive around the microstructural voids collapsing under the effects of shock or compressive waves. This model itself is a good theoretical tool for the analysis of the phenomena involved in the mechanical initiation of heterogeneous explosives. An original method to determine the viscosity of the explosives, which is a fundamental parameter of the model, is proposed. Two versions of the model are presented. The reference one needs a numerical integration of the motion and heat transfer equations. The second one is an analytical model which can be easily implemented in a hydrodynamic code and associated to a grain burning law in order to build up a kinetic able to simulate accurately the shock-to-detonation transition phenomena.     

Etude par résonance magnétique nucléaire des polychlorures de vinyle polymérisés par les systémes titanate de butyle–alcoyles-aluminium

NMR analysis of the chain ends of samples of poly(vinyl chloride) prepared using a Ti(OBu)₄–alkylaluminum system in CCl₄ reveals that the mechanism of the formation of free radicals depends on whether the alkylaluminum used is chlorinated or not. In the first case, some of the radicals are reactive in the initiation step of the polymerization, while in the latter case theses radicals first undergo transfer to CCl₄, then the CCl₃· formed initiates the polymerization of vinyl chloride. The poly(vinyl chloride) radicals are chiefly stopped by transfer to CCl₄ (chlorine abstraction) or to alkylaluminum (hydrogen abstraction). In transfer reactions between growing radicals and alkylaluminum, the radicals formed have to react with CCl₄ before reinitiating the polymerization of vinyl chloride.     

Plastification sélective dans le cas d'alliages de polymères II) Systèmes ternaires — Rôle de l'adhésion interfaciale

Polymerization of methly methacrylate (MMA) was carried out in the presence of nylon-6 with different content of amino end groups and water. The more the content of amino end groups of the nylon molecule, the lower is the conversion of MMA. The rate of polymerization, R_p, is proportional to the amount of nylon. However, as for the amount of MMA, the rate increased at first amount of MMA, but then became independent of the amount of MMA. These kinetical behaviours suggest a model of an enzyme-like reaction. MICHAELIS -MENTEN'S equation was found to be able adequately to be applied. The polymerization was confirmed to proceed through a radical mechanism. By the activation analysis, it was found that the nylon used here contained a slight amount of copper (5 – 8 · 10^?7 g Cu/g fiber). When the nylon was dissolved in formic acid and reprecipitated by adding hot water, the nylon was found to lose the activity for the polymerization. However, when a trace of CuCl₂ was absorbed on the nylon, the nylon was confirmed to regain the activity. As a conclusion, an assumed mechanism similar to an enzymatic reaction in which nylon plays as enzyme and copper as coenzyme was proposed. In the second part of the present paper, a study on the polymerization in the presences of carbon tetrachloride was made. Regardless of the content of the NH_2? end groups, the conversion was always near to quantitative yield. The mechanism was found to be a radical one. An initiation mechanism, in which a complex of nylon, CCl₄, H₂O and MMA is formed, was proposed.     

Effet du diamètre de l'agitateur et de la largeur des chicanes sur le niveau d'agitation en régime continu et sur la puissance dissipée

The system studied is made of a vertical cylindrical tank with a coaxial turbine agitator and baffles. The feed is in the bottom of the tank, the outlet at the surface, and both are coaxial with the agitator. A model proposed by Cholette and Cloutier, in which the parameters m and n are involved, was used to evaluate the effect of different variables. At a given agitator speed, the level of mixing is decreased when baffles are present, proportionally to the width of the latter. A lowering of the short-circuit is also observed. The torque varies with the level of mixing; it increases when baffles are present, and more so for large agitator diameters. The authors propose a flow pattern to explain the experimental results.     

Comparaison du modèle des réservoirs imparfaitement agités en série avec le modèle de dispersion axiale

The transfer function of the model of imperfectly mixed tanks in series, involving the three parameters p, m and n, is presented. It is thus possible to evaluate easily the residence time distribution curve E(θ) and the output response for a given input. This model is compared to the axial dispersion model, through the variance of the curve for E(θ) and the average absolute error between theoretical values and experimental data. A graphical representation relates the Péclet number of the axial dispersion model to the parameters of the p, m, n model and also to the variance of the curve for E(θ). The p, m, n model gives a good approximation of experimental data; it is shown to be more versatile than the axial dispersion model.     

Étude de l'étirage à froid des fibres de polymères synthétiques dans les agents organiques

The cold drawing of synthetic polymers is generally carried out through necking at a short collar between the drawn part and the undrawn part of the fiber; if the drawing is carried out in certain organic liquids, the lengthening is realized through thousands of simultaneous necks which permit the fiber to be penetrated by a dye dissolved in the liquid. The stress–strain curves for the drawing in liquid show an important decrease in the force at the time the multiple necking are produced. This decrease is the result of an increase in the mobility of the macromolecular chains through the penetration of the organic liquid to the level of the shoulder of the necks. A morphological study has been carried out through the observation of cuts by optical microscopy, along with a utilization of the techniques of x-ray diffraction, IR spectroscopy, and electron microscopy. It was found that the liquid penetrates t?he fiber to the level of the necking via a rupture of the interchain bonds which takes place during the change of structural following the drawing. The bonds are maintained ruptured as long as the liquid is not squeezed out by the aligning of the chains; they reform later to produce a new highly crystalline structure.     

Etude par chromatographie liquide haute pression de polyoléfines et de polyéthylènes modifiés

The high speed liquid chromatography behaviour of polyolefins with different crystallinities, of various branched chain polyolefins (high and low density polyethylene, ethylene-propylene copolymer, polypentene) as well as modified polyethylenes either in bulk (chlorination) or on the surface (chlorination, chlorophosphorylation, oxidation) was studied. The samples consisted of glass beads (44–50 μm) which were coated by deposition of the polymers. The study was carried out on one hand in an apolar mobile phase (cyclohexane) with phenol, ortho-, meta-, and para-nitrophenol as solutes, on the other hand in a polar mobile phase (water-methanol mixtures) with benzene, chlorobenzene, and orthodichlorobenzene as solutes. The influence of a swelling agent for the polymer and the temperature effect were investigated. The obtained results show the possibility of liquid chromatography to study interactions between polymers and a given solventsolute.     

Influence de la quantité d'un sel de sulfonium sur la coupure des liaisons O?Si et sur la solubilité d'un mélange renfermant le sel et le poly(p-triméthylsiloxystyrène) et irradié par des UV

If coating solutions obtained by dissolving poly(p-trimethylsiloxystyrene) together with one of the salts (C₆H₅)₂(C₆H₅SC₆H₄)SSbF₆ or (C₆H₅)₃SAsF₆ in a solvent such as 3-pentanone are aged, the percentage of O? Si(CH₃)₃ bonds cleaved by irradiation at a given intensity (λ = 254 nm) and after post-annealing depends on the amount of salt introduced. The same result is observed with respect to the solubility of the resist when it is treated with the basic solvent MF-319.     

Polymérisation des méthacrylates d'ethers glycériques par le peroxyde de benzoyle: Accélération de la polymérisation par les sulfinates d'amines tertiaries

The kinetic study of the radical polymerization of phenyl glyceric ether methacrylate, taken as model of the corresponding derivative of bisphenol A, initiated by the system benzoyl peroxide/dimethyl p-toluidine p-toluene sulfinic acid salt, was performed. The effect of hydroxylic groups of the monomer on the polymerizability was established. The system used as initiator allows rapid polymerization of the monomer in presence of stabilizers.     

Étude cinétique du greffage de polystyrène anionique sur les silices. Contraction des macromolécules sur la surface solide

The kinetic study of the grafting reaction of anionic polystyrene on silica has been investigated in order to control the surface coverage model described previously. The amount of polymer fixed, or the grafting ratio, is related to the physicochemical characteristics of the silica as well as to the properties of the anionic polymer solution. The influence of the surface area(S), the silica concentration (Cs) and the surface concentration (A = S · Cs) has been followed. In dilute solution, the grafting ratio is proportional to the surface area if A is kept constant. This result is in favour of the proposed model. In concentrated solution, the grafting ratios are mostly dependend on the properties of the polymer solution, such as concentration, molecular weight and nature of the solvent. From the experimental results, it is possible to obtain informations about the contraction of the statistical coil fixed on the solid surface.     

Photovieillissement d'un copolymère d'éthylène et d'acétate de vinyle en présence de sueur artificielle. II. Evolution morphologique

An artificial photoaging cell was arranged with the goal to study the behaviour of polymers partly immersed in artificial sweat. A poly(ethylene-co-vinyl acetate) (EVA) was photoaged in this cell. On the other hand, photoaging was realized without artificial sweat in order to understand the action of this substrate. Similar studies were carried out with light stabilized EVA. The morphological evolution of the crystalline structures of the polymer was studied by differential scanning calorimetry, mainly the evolution of the melting temperatures, and secondly those of the glass transition temperatures and of the melting enthalpies. Thus, it was possible to understand the reorganization of two crystalline structures contained in the fresh EVA, the first one rich in poly(vinyl acetate) and the second one in rich in polyethylene.