Analyse par résonance magnétique nucléaire des polycondensats urée–formol

The oligomer reaction products between urea and formaldehyde were preliminarily studied by 60-MHz NMR spectroscopy. This analytical method was extended to urea–formaldehyde copolymers and provided means to attempt to determine their molecular stucture. Prior to NMR analysis, dilution water was removed by freeze drying in order to avoid degradation and advancement of the resin. Lithium chloride was found to enhance polycondensate solubility in deuterated dimethylsulfoxide and to improve resolution of the spectra by reducing overlapping of the signals. It was then possible to proceed to a qualitative and quantitative analysis of urea–formaldehyde copolymer structure. Structural differences appeared between one-step synthesized resins and those involving a second urea addition; in the latter case, the percentage of unreacted urea was calculated. The shape of the unresolved broad signal assigned to the various methylene groups yielded further information on the resins. A particular shoulder on the methylene signal gives evidence for polyoxymethylene sequences occurring in polycondensates synthesized from concentrated aqueous formaldehyde solutions.     

Etude calorimétrique de la rétention de l'eau par les résines novolaques

Moisture retention in various substituted novolake resins has been investigated by differential scanning calorimetric analysis. Water molecules leave the polymer network in a two step drying process. The first one occurs at T > T_g, the second at T < T_g and requires an external energy supply. The energy recorded in the second drying step indicates the presence of a dipolar link.     

Interprétation cinétique des mesures d'ignition dans le cas des systèmes réactionnels gaz-solide

A quantitative interpretation of the ignition phenomenon is proposed which allows the determination of the kinetic parameters of exothermic chemical reactions of the type: gas + solid → gas. Two kinetic methods are presented for the case of unsteady state reaction and their application in practice is discussed. The first method is characterized by a gas-solid heat transfer coefficient different in each experiment, the second one by a constant heat transfer coefficient. The reaction kinetics are determined from the experimental conditions at ignition. Both methods are then applied successfully to a reacting system of complex geometry, hydrodynamics and kinetic mechanism: the catalysed oxidation of carbon black, measured by thermogravimetry.     

Polymerisation du chlorure de vinyle par les systèmes Ti(OR)y Cl4–y–AlRxCl3–x en milieu CCl4

Vinyl chloride polymerizations by Ti(OR)_yCl_4–y–AlR_xCl_3–x systems, using carbon tetrachloride as solvent, obey a radical mechanism. Free radicals are generated from alkyl aluminum by way of decomposition of an organometallic compound of tetravalent titanium; the latter is formed either by direct reaction between aluminum and titanium compounds, or after reoxidation by CCl₄ of a compound of trivalent titanium. The organometallic compound so obtained contains organic groups more complex than the alkyl group initially bond to aluminum.     

Etude des propriétés des films préparés par evaporation des solutions d'un polymére dans différents solvants

Films of a plasticized random terpolymer were prepared by evaporation of solutions in several solvents. The glass transition temperatures of the films were determined and were found to follow the Fox's equation. Their tensile modulus, measured just below the glass transition temperature, was found to depend on the residual solvent content of the films.     

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.     

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 de copolymères greffés ABS (Acrylonitrile-Butadiène-Styrène). III. Vitesse de polymérisation dans la réaction de greffage – Retardation – Solvatation préférentielle par les promoteurs

The author has studied copolymers of styrene and maleic anhydride, which have been produced continuously or batchwise and in which the styrene and maleic anhydride units were in a non alternating distribution, with regard to the molecular weight distribution and the distribution of the maleic anhydride units as function of the molecular weight. Surprisingly, the products obtained continuously or batchwise showed only slight differences. It is believed that this is caused by the fact that since the temperature of the reaction was very high and thus the reaction proceeded very rapidly the course of the reaction was determined by the kind and smoothness of mixing.     

Règies de construction et d'extrapolation des réacteurs auto-agités par jets gazeux

An analysis is made of the agitation mechanism in a spherical reactor which is self-stirred by means of gas jets; it is made on the double assumption of an internal recycling and of a turbulent free jet. Extrapolation laws have been developed and verified experimentallly by means of the residence time distribution in several reactors of volumes varying between 501 and several cubic centimeters, the passage times varying from 0.6 to 7.5 seconds: the experiments involved several gases and different temperatures.     

Synthèse et propriétés de polyuréthannes réticulés par des cycles isocyanurates

The reaction of α-ω-hydroxy-terminated polyethers or polybutadienes and diphenyl methane diisocyanate in presence of a basic catalyst, such as triethylene or dibutyl tin dilaurate gives polyurethane networks. IR spectroscopy shows that the networks contain isocyanurate rings. These rings are stable at high temperature showing a constant rubbery modulus from T_g up to 160°C. It is noted that the modulus varies with the formulation, the nature of the prepolymer and its molecular weight, the rate of diisocyanate and the catalyst as well as the possibility of introducing butanediol into the formulation.     

Etude cinétique de la déshydrtation du sulfate de cuivre par thermogravimétrie et thermogradientimétrie

A new type of thermobalance has been built, Sample temperatures have been determined by a new technique called “thermogradientimetry”. A special crucible assembly allows control of the atmosphere surrounding the sample. Kinetic results for the three successive stages in the dehydration of copper sulphate indicate that the reactions involved are of zero order. The apparent activation energy for each stage of the dehydration has been avaluated under isobaric conditions for different water vapor pressures.     

Etude PAR spectroscopie de la deshydratation de dérivés de l'alcool polyvinylique: Mise en evidence d'une répartition séquentielle des substituants

The dehydration of sulfopropylic and alkyl derivatives of poly(vinyl alcohol), with varying degrees of substitution, was observed using ultraviolet and visible spectroscopy. The dehydration reactions were carried out in a KHSO₄/heptane system kept under nitrogen at 100°C. Spectroscopic results show that definite sequences of conjugated double bonds are formed. The distribution of the number and length of these conjugated sequences was determined and compared with the theoretical values obtained assuming statistical distribution of the substituents. From this work it is concluded that: (1) the grafting of propane-sultone onto poly(vinylalcohol) molecules does not follow a random, statistical pattern, rather the reaction is sequential, i.e., of a “zip” type. The product molecules contain blocks of sulfopropylic-substituted vinyl alcohol groups. (2) The grafting of alkyl groups onto the poly(vinyl alcohol) molecules also occurs in a sequential manner. Results obtained show that the polymer chains contain at least two unreacted hydroxyl functions between each substituent alkyl group; this is in agreement with x-ray studies of these derivates. Further evidence of an ordered distribution of the substituents along the polymer chain is given by the heterogeneity in the compositions of the substituted polymers. The difference in the observed structures of the two substituted polymers demonstrates the importance of the nature of the substituents in determining the reaction mechanism. It is concluded that the structural differences observed are due to differences in the solubility of the sulfopropylic and alkyl reactants in the original reaction medium, and the hydrophilic and hydrophobic character of the sulfopropylic and alkyl substituents in the polymer.     

Greffages mecanochimiques sur le polychlorure de vinyle. III. Stabilitéa thermique des polymègeres modifiéas

The mastication of poly(vinyl chloride) (PVC) in presence of monomers causes important changes of the thermal stability of the polymer when the last one possesses a basic character (e.g., 2-vinylpyridine). The dehydrochlorination rate is greatly increased, even if the monomer is present in only small amounts. In the most cases (styrene, acrylic ester) a better thermal stability is observed with respect to the acceleration of the dehydrochlorination, which is retarded or even suppressed. Infrared spectroscopy and differential thermal analysis show that the improved stability is due to an improved crystalline organization. When mastication causes the polymerization of the monomer (methyl methacrylate), degradation of the PVC part and depolymerization of the rafted part are observed simultaneously; this fact supports a radical mechanism for the thermal degradation of the PVC.     

Etude de copolymères greffés ABS (acrylonitrile-butadiène-styrène) V. Mécanisme et cinétique de la réaction de greffage

A new low-pressure-capillary-viscosimeter is described. It is designed for measurements of low-viscos solutions at low shear gradients. The change of hydrostatic pressure during the measuring experiment is automatically compensated by a simple device. By the aid of this viscosimeter absolute viscosities can be measured exactly without applying any corrections. The range of applicable shear stress lies between 0.15 and 3.75 Pa.     

Comparaison des méthodes de fractionnement par chromatographie de perméation et par gradient d'elution pour la détermination des répartitions moléculaires des polypropylénes

Molecular weight distributions for polypropylene samples have been determined by a permeation fractionation method (GPC). Porous silica beads were used as a packing material for the columns. The set of columns allows a good separation of the polypropylene macromolecular chains in a range of molecular weights from 5000 to 1.5 × 10⁶, and the thermal and mechanical stabilities of these beads are very good. The calibration has been carried out with fractions of polypropylene of narrow molecular weight distribution prepared by a large-scale column fractionation. The molecular weights M?_w and M?_n and the ratios M?_w/M?_n calculated from the GPC curves show, in general, good agreement with the ones calculated from the column fractionation curves. However, the M?_w/M?_n ratios are always highter in the case of GPC fractionation. This could be due to diffusion phenomena.