Reactions de condensation interpolymeriques a l'etat fondu

Condensation reactions between the anhydride groups of a copolymer containing maleic anhydride links and OH groups on different molecules were carried out in a plastograph, the copolymer being in the molten state. If dihydroxylated molecules or even telomers were used, the progress of reaction is easily followed by the rising of the consistency of the melt. The ester bridges formed between two copolymer molecules may be disrupted by methanolic transesterification in basic solution. Study of the reactivity of a series of monohydroxylated polymers of increasing DP showed that the compatibility of these hydroxylated polymers with maleic anhydride copolymer in the molten state is of outstanding importance for a good yield.     

Proprietes viscoelastiques des reseaux a l'etat caoutchoutique

The dynamic properties and the stress relaxation of vulcanisates of natural rubber, cis-polybutadiene and a butadiene (76,5)-styrene (23,5) copolymer are analysed in order to determine the influence of some structural parameters on the shape and position on the time scales of the rheological functions characterizing their viscoelasticity.The persistence of the energy loss at low frequencies and the corresponding high level of the distribution of relaxation times are all the more marked as these polymer networks are less cross-linked or contain a larger amount of carbon black HAF. Undoubtedly closely related to the “viscoelastic plateau” of linear polymers, this anomaly is interpreted in terms of an extension of the Rouse theory derived for bulk polymers or their concentrated solutions.     

Effet de longueur d'onde et controle par la geometrie de l'etat fondamental de la photoisomerisation de derives de l'hexatriene-1,3,5

Irradiations at different wavelengths (313, 254, 229 and 214 nm) of the 4 geometric isomers of 5-phenyl-1,3,5-heptatriene show that the photochemical behaviour of these trienes is mainly controlled by their ground state equilibrium.     

Copolymerisation a l'etat cristallise des acides acrylique et methacrylique

Acrylic acid (A Ac) and methacrylic acid (MA Ac) form a eutectic mixture for the equimolecular composition; its melting point is ?30°. Most polymerization experiments were carried out at ?37° with gamma-ray initiation. The irradiation of the eutectic mixture generates a random copolymer with a narrow distribution of compositions and containing 80% MA Ac. In solid mixtures which contain an excess of MA Ac with respect to the eutectic, the reaction product is essentially the same copolymer as generated in the eutectic, the rate of polymerization in MA Ac crystals being negligible as compared with the reaction in the eutectic. When A Ac is in excess, the phenomena are more complex. A pronounced minimum is observed in the rate vs composition curve at ca 20 mole % MA Ac. Fractionation of the reaction product demonstrates the presence of a block copolymer built by sequences of A Ac and of random copolymer. An interpretation is suggested to account for the various results.     

Criteres d'evaluation de la position de l'etat de transition dans les additions conjuguees

The conjugate addition of substituted aryacetonitrile anions to α-enones implies a reagent-like transition state; it is insensitive to conjugation loss but slightly sensitive to steric factors.     

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.     

Transposition des oxirannes-ethanols par l'intermediaire d'alcoxyetains. Influence de la configuration de l'oxiranne

The transposition of oxirane-ethanols, through alkoxytin compounds, into oxetane-2-methanols and/or oxolan-3-ols (tetrahydrofuran-3-ols) is dependent upon the oxirane configuration. Cis configuration is more suitable for the formation of the smallest ring. Steric hindrance is not sufficient enough to explain the results.     

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.     

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.     

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.     

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.     

Etude comparative de l'alkylation des tetraphenylporphyrines de l'etain et de leurs formes reduites par les reactifs de grignard

A comparative study of alkylation by Grignard reagents of PSn(OH)₂ (P = tetraphenylporphyrin (TPP), tetraphenylchlorine (TPC), tetraphenylisobacteriochlorine (TPiBC)) shows that dialkylstannylisobacteriochlorines are the most easily obtained. The presence of transition metals in the magnesium crystals directs the reaction towards reduction of the macrocycle instead of alkylation on tin. This is supplementary proof for the intervention of a single electron transfer mechanism (SET) in alkylation of a macrocycle by Grignard reagents.These results fit very well with earlier electrochemical experiments and the measurements of the reduction potentials of the Group IVB metalloporphyrins and their reduced forms.     

Influence des solvants sur la copolymérisation de l'acrylamide avec l'acrylonitrile

The copolymerization of acrylamide with acrylonitrile was investigated in various solvents, which can be put into three groups according to their influence on molecular associations; (1) solvents autoassociated by hydrogen- bonds (acetic acid, methanol, water, dimethylformamide); (2) polar solvents which can associate with the NH group of acrylamide (acetonitrile, dioxane, acetone); (3) inert solvents (toluene, benzene, hexane). The reaction kinetics and the compositions of the copolymers are different for each group of solvents. The composition of copolymers formed in solvents of group 1 vary widely, depend- ing on the solvent. Copolymers formed in all solvents of group 2 have the same composition which is that of copolymers formed in bulk. The amount of acrylamide is highest in copolymers formed in inert solvents of group 3. Such parameters as the degree of conversion, the reaction temperature, the mode of initiation and the extent of dilution only slightly affect the composition of copolymers. Homopolymerizations of acrylamide and acrylonitrile were investigated in all solvent used.The results suggest that the effects of solvents on the copolymerization of acrylamide with acrylonitrile are consequences of the various modes of molecular association of acrylamide. The solvents affect the equilibrium between auto- association of acrylamide and its association with solvent and thereby affect the reactivity of the monomer.     

Sur la reactivite des organomagnesiens derivant de l'addition d'organomagnesiens allyliques sur l'isoprene

Contrary to a recent report, it is shown that allylic Grignard reagents prepared by treating allylic Grignard reagents with isoprene and a catalytic amount of Cp₂TiCl₂ react normally with carbon dioxide and carbonyl compounds: a complete allylic rearrangement is observed.