Polymerisation radiochimique de l'acide acrylique en solution dans l'alcool isopropylique et le dimethylformamide

The radiation-induced polymerization of acrylic acid in isopropyl alcohol and dimethylformamide solutions was investigated between?196°and40°. Mixtures which form glasses at low temperatures exhibit a maximum in the rate of polymerization at 30° and 50° above the glass transition temperature (T_g). The difference between the most favourable temperature for polymerization and T_g is larger than in systems studied previously. This fact could be due to the presence of H-bonded aggregates.The study of the polymerization of acrylic acid in dimethylformamide solution at 20° led to a correlation between this reaction and the presence of plurimolecular aggregates. The very high polymerization rate and the syndiotacticity of the resulting poly(acrylic acid) confirm the earlier assumption of a favourable orientation for propagation of the molecules of acrylic acid in these aggregates.     

Etude cinetique de la polymerisation cationique du cyclopentadiene amorcee par l'hexachloroantimoniate de triphenylmethyle

A study of cyclopentadiene polymerization, initiated by φ₃C⁺SbCl₆^? in methylene chloride solution, has been carried out at temperatures between ?70 and +20° using a dilatometric method. An overall external second order with respect to monomer has been found. At very low temperature (?70°), the concentration of active centres remains low and roughly constant, in agreement with a quasi-stationary state assumption. Between ?50 and + 10°, experimental determination of (k_p. M^*), obtained from variation of v_p and [M] with time, shows that the concentration of centres goes through a maximum, sharper and more rapidly reached as the temperature is raised. Initiation is slower than propagation and active centres are rapidly destroyed when termination becomes faster than initiation. This explains the partial conversions and the observed maximum for concentration of active centres. Propagation and unimolecular termination rate constants have been determined at each temperature: activation energies are E_p = ?8 ± 0·5 kcal mole^?1 and E_p = ?0·3 ± 0·1 kcal mole^?1. These negative values can be explained by an exothermic process of solvation of active centres, leading to more reactive propagating species.     

Copolymeres du chlorure de vinyle et de l'acrylate de glycidyle

A study of the radical copolymerization of vinyl chloride (C) and glycidyl acrylate (A) at 60° in dichloroethane solution leads to the following reactivity ratios r_c = 0·14 ± 0·02 and r_A = 7·4 ± 0·3According to the nature of the solvent, the reaction of protonic acids may cause either cationic polymerization of epoxy groups or addition of HCl or water onto the same groups. The HCl addition is observed during the thermal degradation of the copolymers so that HCl evolution is greatly delayed.     

Copolymerization de l'acenaphtylene avec le n-vinylcarbazole

The copolymerization of acenaphthylene (ANA) with N-vinylcarbazole (NVC) was investigated at 60° in the melt with 1% AIBN and in benzene solution at 20° with gamma ray initiation. In the melt at 60°, the polymerization rate gradually decreases with the amount of NVC in the mixture. The following reactivity ratios were determined: r_NVC = 0.12; r_ANA = 7.0. The copolymers have a fairly narrow distribution of compositions but contain small amounts of poly NVC. Gamma ray initiation at 20° gives rise to the free radical copolymer together with significant amounts of poly NVC which results from a cationic mechanism. In addition, acenaphthylene cyclodimerizes in the process.     

Polymerisation cationique de l'indene amorcee par le tetrachlorure de titane-II Influence de la temperature sur la vitesse de polymerisation

Polymerization rates in the indene-titanium tetrachloride-methylene chloride system, using rigorously dried reagents, have been measured at various temperatures. At sufficiently high temperatures (above ?10°C), polymerization yields may be incomplete and cocatalytic phenomena have been observed; at low temperatures, yields are always complete. The reaction order in monomer is unity at ?70°C, which may be explained by a constant concentration of active centres during the major part of the reaction. At ?70°C, the reproducibility shows that residual water has no cocatalytic effect. The measured values of polymerization initial rates at various temperatures show that the apparent overall activation energy is negative. Various interpretations of this result are discussed, but it may be more easily reconciled with both the existence of a quasi-stationary state and an equilibrium between different types of active species.     

Étude thermodynamique de la complexation de l'argent par la pipérazine et quelques-uns de ses derives en milieu eau—ethanol

The stability constants of the complexes of Ag⁺ ion with piperazine and its 2-methyl-, 2-methyl-1-m-tolyl-, 2-methyl-1-p-tolyl- and 1-(p-methoxyphenyl)-2-methyl-derivatives are obtained at 25°C in water—ethanol (52%, w/w) solvent and KNO₃ 0.1 M ionic strength, by means of corresponding metal-complex electrodes.The enthalpies of formation are determined by direct calorimetry, in the same conditions of temperature and medium.The comparison of the thermodynamic functions ΔG_n°, ΔH_n°, ΔS_n° allows a discussion about the ability of each amine to coordinate, in terms of nature and position of the entering group.     

Contributionàl'étude du système formépar l'étain,le soufre et l'iode. Mise enévidence des deux variétés de l'iodosulfure stanneux Sn2SI2: Comportement thermique etétude structurale

We have found a new compound Mn₈O₁₀Cl₃. It is prepared by oxidation of anhydrous or hydrated MnCl₂ in streaming (N₂ + O₂) at temperatures less than 680°C. At room temperature the compound is tetragonal, a = b = 9.2898 Å, c = 13.0247 Å. The more symmetric space group is $\text{I4}\text{mmm}$. Mn₈O₁₀Cl₃ becomes cubic at 360°C with the c-axis as cubic parameter. In air, DTA and GTA have shown that Mn₈O₁₀Cl₃ is transformed at 580°C into Mn₂O₃ which gives Mn₃O₄ at 960°C. The exact formula has been determined only by crystal structure analysis.     

Nombre de transport et conductivité cationique dans l'oxyde de nickel: NiO

Ionic transport number measurements have been made on single crystals of NiO over the temperature range 900–1300°C and for oxygen partial pressures varying from 10^?8 to 1 atm. At 1000°C and in air, t_Ni ～ 2 × 10^?7. The variation in cationic conductivity as a function of oxygen partial pressure suggests that V′_Ni is the dominant defect at high temperature and low oxygen pressure and that V″_Ni is the dominant defect at low temperature and high oxygen pressure.     

Etude calorimetrique et analytique de l'adsorption du cyanogene sur la silice

The adsoprtion of C₂N₂ on well outgassed specimens of SiO₂ at temperatures from 35 to 913°C has been studied by heat flow calorimetry, volumetry, and mass spectrometry.Small amounts of cyanogen are adsorbed at low temperature: reversibly by hydrogen bonding with the silanol groups, and irreversibly on strained siloxane bridges or Lewis acid sites. Above 200°C cyanogen reacts, with silanol groups, leading to the formation of HCN (partly reversibly adsorbed on non-reacted silanol groups) and silyl isocyanate:

. The process is complete at 418°C and the measured enthalpy for the reaction

is ΔH = ?12.2 ± 0.3 kcal mole^?.Above 500°C, HCN and C₂N₂ react with ordinary siloxane bridges. At higher temperature, the pyrolysis of

produces CO₂ with CO and N₂ (in smaller quantities), showing that a large proportion of N-atoms are bonded on the surface.     

Alcoylation par l'iodure de butyle,de l'enolate de tetrabutylammonium de l'acetylacetone; nature de l'entite reagissante

The alkylation of tetrabutylammonium acetylacetonate with butyl iodide was studied in order to specify the nature of the reactive anionic species during the nucleophilic reaction of an ambident anion, under similar conditions to those of phase transfer catalysis. The C/O alkylation ratio changes with neither the solvents nor the enolate concentration; however k_obs, varies with the solvent but does not depend on the énolate concentration. The results and spectrophotometric UV data show that only one reactive species, the ion-pair, is involved.     

Etudes calorimetriques en milieu solvant organique. V. Enthalpies de dissolution de l'alanate de sodium,NaAlH4, dans le tetrahydrofuranne

The enthalpies of dissolution of sodium tetrahydridoaluminate NaAlH₄ in THF have been determined for different concentrations. The enthalpies of dissolution and dilution are exothermic from 1 to 7 · 10^?3 M. The enthalpy of dissolution at infinite dilution has been calculated: ΔH^∝_diss = ?6.38 kcal mole^?1.     

Étude conformationnelle et spectres infrarouges de l'acide glycyl aminométhylphosphonique

Glycyl aminomethylphosphonic acid (Gly AMPh) is studied by X-ray diffraction and IR spectrometry in the solid state. It is shown to exist as the monohydrated zwitterion

,H₂O. Its conformation in the crystal (Pbca space group) is defined by ψ₁ = ?162°, Φ₂ = ?110° and ψ₂ = ?58°. Energy calculations by a semi-empirical method for the isolated zwitterion shows two stable conformations for ψ₁ = ?75°, Φ₂ = ?120° and ψ₁ = +75°, Φ₂ = +120°, gave for ψ₂, = ?60°, the most probable value. Infrared spectra are analysed by means of normal mode calculations.     

Etude de l'equilibre entre l'oxyde de nickel et l'oxygene. Essai d'interpretation des lois de variation de la conductivite electrique en fonction de la temperature

In a previous paper we have shown that at 740°C and under an oxygen pressure less than 1,3 torr the electrical conductance G of a NiO powder reaches rapidly an apparently stabilized signal G_i which sharply decreases after a sufficiently long time to a G₀ value independent of P_O2.From this observation we have studied the influence of the temperature successively on the electrical conductance G_i and G₀. The Arrhenius law is only verified for the G₀ = f(T) curve. G₀ appears as the representative value of the gas-solid equilibrium.     

Influence des associations moleculaires sur la copolymerisation de l'acide acrylique avec l'acide methacrylique et avec l'acrylate de methyle

The copolymerization of acrylic acid with methacrylic acid in bulk is investigated at 40 and 60°. It is confirmed that a “matrix effect” occurs only for high contents of acrylic acid. The critical concentration beyond which the matrix effect disappears is shifted towards lower acrylic acid contents for higher temperatures. The copolymer composition is independent of temperature. The copolymerization of acrylic acid with methyl acrylate is investigated in a mixture which determines an “exaltation of the matrix effect” in the homopolymerization of acrylic acid (molar fractions: m_Monomers = 0.34; m_n-Hexane = 0.52; m_Methanol = 0.14). The resulting copolymers are found to contain a much larger fraction of acrylic acid residues than the copolymers formed in bulk or in toluene or DMF solutions.     

Dosage de l'hydrogene,de l'azote et de l'oxygene dans le monocarbure d'uranium

A method is described for the determination of hydrogen, oxygen and nitrogen in uranium monocarbide. Hydrogen and oxygen are determined by the classical or modified “Platinum flux” method at 2000° with a coefficient of variation of 10%. Nitrogen is determined at 2000° by the modification of the “Platinum flux” technique. The results obtained are in agreement with those found by Kjeldahl analysis. The coefficient of variation is about 10%. A procedure for the simultaneous determination of the 3 gases is given.     

Étude de l'oxydation et de la réduction électrochimiques de l'or par ellipsométrie avec excitation de plasmons de surfaces (SEW)

We studied the variation of optical parameters of voltage-sweep oxidized films on gold electrodes (evaporated gold on glass; 0.5 M H₂SO₄; 0<V<1.8 V/ENH; dV/dt=0.03 V s^?1). By ellipsometry with surface plasmons, we can measure large variations of Δ and ψ with oxygen coverage (20° for Δ; 10° for ψ). By associating optical and coulometric data, and assuming different values for the thickness d_f⁰ of diatomic Au₂O₃ layer corresponding to V=1.6 V, θ=1.2 (2 Å<d_f⁰<10 Å) we calculate at each coverage, the complex dielectric constant ?~, during oxidation and reduction steps. Anodic sweep: if 1.3 V<V<1.45 V (0<θ<0.38), ε₂?0. Only chemisorbed oxygen is present on the surface. If 1.45<V<1.60 V (0.38<θ<1.2) ε₁ and ε₂ increase according to the generalized Lorenz-Lorentz equation applied to a model of lateral growth of Au₂O₃ nuclei. If V>1.6 V, ε₁ and ε₂ have very slight variations with θ. Cathodic sweep: the slight variation of ε₂ with coverage for θ≥0.6 is in agreement with a model of uniform reduction of oxidized film until the Au₂O₃ layer becomes monoatomic. Optical, crystallographic, and coulometric data make us consider d_f⁰=3.7 Å to be the most likely value.     

Etude cinetique de l'oligomerisation de l'ethylene amorcee par le complexe butyl-lithium tertiaire NNN′N′ tetramethylethylenediamine (tBuLi-TMEDA)

tButyl-lithium in the presence of TMEDA progressively adds ethylene molecules to produce a linear alkyl-lithium compound. This oligomerization has been studied at low pressures (0–1 atm) and temperature (0°). The rate of consumption of ethylene depends on the pressure, tBuLi concentration, and TMEDA concentration. By varying the molar ratio r, (TMEDA/|tBuLi|₀), from 0–1 to 4·3, the rate of consumption increased up to r = 1, where it becomes independent of r. A mechanism for the addition reaction is proposed.     

Influence de la temperature et du gradient de vitesse sur la viscosite des solutions diluees de xanthane

The dependence of the relative viscosity of a dilute xanthan solution (0.4 g·l^?1) has been studied as a function of temperature (20–70°) and of the ionic strength of the solvent. When the rate of shear exceeds 100 sec^?1, the viscosity can be expressed as γ&#x030A; the exponent (n ? 1) varies with the polymer conformation. In aqueous solution in the absence or in the presence of added salt at a temperature above the melting temperature T_M (depending on the ionic strength of the solvent), the exponent (n ? 1) is ?0.285 and corresponds to the unordered conformation; at temperatures below T_M, the local helical conformation is rigid and (n ? 1) is ～ ?0.44 almost independent of the temperature.     

Synthese,structure cristalline et analyse vibrationnelle de l'hexathiohypodiphosphate de lithium Li4P2S6

The crystalline compound Li₄P₂S₆ is obtained either by devitrification of Li₄P₂S₇ glass at 450°C with sulfur formation or by crystallisation at 450°C of a Li₂S, P and S melt. The structure determination has been solved by X-ray diffraction on a monocrystal. The unit cell is hexagonal $\text{P6}{}_3\text{mcm}$ with a = 6.070(4), c = 6.577(4) Å, V = 209 ų, Z = 1. Intensities were collected at 293°K with Kα (λ = 0.71069 Å) Mo radiation on an automatic Nonius CAD-4 diffractometer. The structure was solved under the assumption of random disorder of P atoms over two sites (occupancy factor of 0.5). Anisotropic least-squares refinement with W = 1 gave R = 0.047 for 90 independent reflections and 9 variables. The structure is built according to an ABAB sequence sulfur packing. Per unit cell, four out of six octahedral sites are occupied by Li ions, and the other two are statistically filled (0.5) by PP pairs. The PP central bond (2.256(13) Å) links two staggered PS₃ groups (PS = 2.032(5) Å) to form the D_3d symmetry P₂S^4?₆ anion. Infrared and Raman spectra show features very similar to those of Na₄P₂S₆, 6H₂O and M^IIPS₃ compounds. A new assignment in terms of symmetry species is proposed for the P₂S₆ internal modes, which is confirmed by a normal coordinate calculation using a valence force field; the stretching force constants f_PP and f_PS are equal to 1.6 and 2.7 mdyne Å^?1, respectively.     

Structure cristalline et expansion thermique de l'iodure de nickel hexahydrate

The structure of NiI₂, 6 H₂O has been determined by X-ray diffraction techniques. The dimensions of the hexagonal unit cell are: a = 7.638 ± 0.005 Å and c = 4.876 ± 0.005 Å, with Z = 1. The space group is $\text{P}\text{3}\text{m1}$. The structure was deduced from Patterson and Fourier syntheses and refined by least-squares method to a final R value of 0.09. It is almost a layer structure, each layer is composed by n complex ions [Ni(H₂O)₆]²⁺ surrounded by 2 n ions I^?; this is in agreement with the good cleavage of crystals and with the marked anisotropy in the thermal expansion. But the structure may also be regarded as a derivation of NiAs structure, with only $\text{1}\text{8}$ of octahedral holes occupied. A structural classification of compounds MX₂, 6 H₂O is proposed.