Synthèse de copolymères greffés à base de polyéthylène—1

Polyethylene macromolecular free radical initiators, obtained by ozonization, are used to prepare graft copolymers with methyl methacrylate, styrene and vinyl chloride. The reactions parameters are the number of initiator groups (found by DPPH), peroxide and hydroperoxide proportions (respectively 36 and 64%), decomposition rate (K_d at 90° 10⁻¹sec⁻¹) and monomer concentration. The molecular structure of these copolymers is defined.     

Nouveaux Élastomères de polyuréthanes dérivés d'aminoacides

Synthesis and characterization of new polyurethane elastomers with rigid blocks derived from aminoacids have been achieved by polycondensation using poly(tetramethylene oxide) (PTMO) as a soft segment. Aminotelechelic oligopeptides or pseudopeptides were used in the hard block, eventually in association with lysine diisocyanate (ethyl 2, 6-diisocyanatohexanoate, LDI). Physicochemical characteristics of the so obtained materials, especially good filmmaking properties, allow their use as biomaterials of reduced toxicity.     

Structure moléculaire et propriétés moléculaires de quatre isomères de formule C8H10N4

The molecular structures of the three Meyer isomers [3-methyl-3-(5′-amino-3′-methyl-l-pyrazolyl)acrylonitrile; acetylacetonitrile azine; 2,5-dimethyl-7-aminopyrazolo[1,5-a]pyrimidine] have been compared with that of the fourth isomer, 2,7-dimethyl-5-amino-pyrazolo[1,5-a]pyrimidine. The CNDO/2 and CNDO/S calculations utilizing these geometries have been accomplished. These include electronic transitions, dipole moments, ionisation potentials, charge densities, bond ordres and total energies. The calculated values have been compared to some experimental data. Uv spectra, ¹³C chemical shifts, ¹H-¹H coupling constants and relative stability of the four isomers are included.     

Synthèse et polymérisation de monomères chlorofluorés allyliques vinyliques et acryliques

Synthesis, polymerization and copolymerization of allylic, vinylic and acrylic monomers containing chlorinated or chlorofluorinated substituents were studied. The reactivity of terminal alcohols or acids is influenced by their neighbouring group. By products and their mechanism of formation were studied.La synthèse et la polymérisation d'acrylates fluorés, a donné lieu à de nombreux travaux. Une première méthode d'obtention de ces composés consiste à faire réagir un alcool fluoré avec un chlorure d'acide insaturé. Les acrylates obtenus sont de la forme :

     

Étude par rayons X de copolymères téléchéliques butadiène acide méthacrylique

The telechelic polybutadiene–methacrylic acid copolymer (Hycar CTB) containing 2 mole percent acid and neutralized (5–100%) by alkali ions, Na⁺, K⁺, and Cs⁺, has been studied by small-angle x-ray scattering. Salt groups form clusters, and the average value of the radii of gyration is approximately 8 Å; this value seems to be independent of the nature of the cation and the degree of neutralization. The existence of a low-angle maximum in the scattering intensity gives evidence of a mean distance of 80 Å between clusters in the fully neutralized sample. This distance increases slightly with a decreasing degree of neutralization. A more precise analysis of the small-angle scattering curve gives further information on the cluster structure: the ionic groups may form small bilayer disks while the polymer chains maintain a regular distance of 80 Å between the disks.     

Importance Relative des Isomères de I'Ion Moléculaire de Dérivés Substitués Polycycliques du Benzodioxinne 1,4

The existence of different isomers of phenyl benzocyclobutene derivatives of specifically deuterium labelled 1,4-benzodioxin molecular ions have been demonstrated. The number of differently labelled benzoyl and formyl radicals being lost facilitated the determination of the relative importance of the various molecular ion isomers.     

Étude de la cotacticité des copolymères acrylonitrile-méthacrylate de methyle par resonance magnetique nucléaire—haute resolution

A study of the NMR spectra of acrylonitrile–methyl methacrylate copolymers (PAM) with very low percentages of methyl methacrylate (M) allows quantitative determinations of AMA, and MMA or AMM triad sequences from the methoxy resonances. The resolution of the complex α-methyl resonances of the isolated M units in seven components has been attempted. If our assignments are correct, the analysis of the cotactic pentad sequences (with a M in central position) has revealed that the configurations of the copolymer chain do not follow the Bernouillian or the first-order Markoffian statistics.     

Contributions au fractionnement des copolymères. II. Copolymères ternaires acrylonitrile–acétate de vinyle–α-méthylstyréne

Acrylonitrile, vinyl acetate, and α-methyl styrene copolymers, were synthesized in aqueous solution, and the resulted products were studied viscometrically by fractionation and by cloud-point titration. The values of the intrinsic viscosities of the polymers in DMF at 20°C are not influenced by the overall composition of the copolymers and the distribution mode of the comonomers. The solubility of the products is directly dependent on the composition, namely, it increases as the acrylonitrile content decreases. The differential fractionation curves are influenced by the chemical composition and by the mode of distribution of the monomers along the macromolecular chain. The successive precipitation method for the fractionation of the ternary copolymers is recommended.     

Propriétés themodynamiques des mélanges binaires. Chaleurs de mélange des n-alcanes ainsi que de leurs isomères

The following heats of mixing have been measured: the five isomers of hexane with n-dodecane at 10°, 20° and 30°C, and with n-hexadecane at 20°C, as well as the systems dodecane-hexene-1 at 20°C, and dodecane-methyl-2-pentene-1 at 10° 20° and 30°C.     

L'indice de rétention des alcanes isomères en chromatographie en phase gazeuse

A method, using the radiolysis of an alkane, for the obtention of a great number of branched hydrocarbons is given. The retention index at 100° as well as its variation with temperature is determined on Apiezon L for 200 alcanes containing between seven and twenty four carbons. It is shown that for branched hydrocarbons the decrease of the retention index is mainly due to the length of the substituent group but also to its position on the chain. Some rules between retention index and molecular structure are deduced that allow the determination of the index of higher branched hydrocarbons. It is also shown that the variation of the retention index with temperature is only a function of the length of the substituent group.     

Nouvelle méthode de détermination des taux de réativité des copolymères par résonance magnétique nucléaire: Application aux poly(méthacrylate de méthyle–chlorure de vinylidène)

Constant-composition copolymers of methyl methacrylate and vinylidene chloride produced by radical copolymerization are studied by ¹H-NMR at 60 and 250 MHz. The different methods of the literature for the derivation of reactivity ratios from either the copolymer composition or the sequence average lengths, or even the diad distribution, are applied but lead to rather dispersed results. A new graphical method is proposed, based on the use of peculiar values of the triad distribution functions. It allows us to detect a penultimate effect for the vinylidene chloride-rich region. In the same range, a change in tacticity of the diads and triads on the methylmethacrylate sequences, as compared with homopolymers, is observed; it suggests that the anomaly is caused by the competition of the depropagation reaction.