Influence of the Stereochemical Structure on The Physicochemical Properties of Polymers Prepared by Ring-Opening Polymerization of Chiral Heterocyclic Monomers

Physico-chemical properties of polymers prepared by ringopening polymerization of heterocyclic chiral monomers with different enantiomeric composition are compared. Two general kinds of behaviour were observed for products with a monosubstituted carbon in the chain: when the substituent group is not bulky the properties of polyenantiomers and their racemic mixture are very similar ; when the substituent is a bulky group, e. g. t-butyl, many of the properties (m.p., crystalline structure, solubility, etc.) are very different for the same polymers. The corresponding statistical stereocopolymers are amorphous. For polymers with disubstituted asymmetric carbon atoms the statistical stereocopolymers are crystalline and their melting behaviour varies with the enantiomeric purity. In some cases a strong dependence of the mechanical and biological properties on the enantiomeric purity of stereocopolymers is reported

L'historien et le document [Remarques sur l'utilisation des archives]

Oleg Khlevniuk. The historian and the document. This article examines some problems related to the opening of archival sources pertaining to Soviet history. It deals mainly with the misuse of archives by historians: falsification of documents, distortion of their contents. It then raises the question of the degree of preservation of documents, their partial destruction in the past, and the completeness of the collections' informational contents. It concludes with the prospects of research based on the archives.Oleg Hlevnjuk. L 'historien et le document. Cet article examine certains problèmes soulevés par l'ouverture des documents d'archives relatifs à l'histoire de la période soviétique. Il traite principalement de l'exploitation néfaste des archives par certains historiens : falsification des documents et déformation de leur contenu. Il pose ensuite la question du degré de conservation des archives, de la destruction partielle des documents dans le passé, de l'intégrité des collections de documents et donc de leur potentiel d'information. En dernier lieu, il mentionne les perspectives ouvertes aux chercheurs par ces nouvelles sources.Hlevnjuk Oleg, Spassky Nicolas. L'historien et le document [Remarques sur l'utilisation des archives]. In: Cahiers du monde russe : Russie, Empire russe, Union soviétique, États indépendants, vol. 40, n°1-2, Janvier-juin 1999. Archives et nouvelles sources de l'histoire soviétique, une réévaluation Assessing the new Soviet archival sources. pp. 101-111

Influence of the Stereochemical Structure on The Physicochemical Properties of Polymers Prepared by Ring-Opening Polymerization of Chiral Heterocyclic Monomers

Physico-chemical properties of polymers prepared by ringopening polymerization of heterocyclic chiral monomers with different enantiomeric composition are compared. Two general kinds of behaviour were observed for products with a monosubstituted carbon in the chain: when the substituent group is not bulky the properties of polyenantiomers and their racemic mixture are very similar ; when the substituent is a bulky group, e. g. t-butyl, many of the properties (m.p., crystalline structure, solubility, etc.) are very different for the same polymers. The corresponding statistical stereocopolymers are amorphous. For polymers with disubstituted asymmetric carbon atoms the statistical stereocopolymers are crystalline and their melting behaviour varies with the enantiomeric purity. In some cases a strong dependence of the mechanical and biological properties on the enantiomeric purity of stereocopolymers is reported

Les fonds personnels des dirigeants soviétiques [Histoire de leur formation et état actuel]

Rogovaja Larisa, Košeleva Lidija, Spassky Nicolas. Les fonds personnels des dirigeants soviétiques [Histoire de leur formation et état actuel]. In: Cahiers du monde russe : Russie, Empire russe, Union soviétique, États indépendants, vol. 40, n°1-2, Janvier-juin 1999. Archives et nouvelles sources de l'histoire soviétique, une réévaluation Assessing the new Soviet archival sources. pp. 91-99

Étude de la tacticité du poly(oxyde de propylène) par RMN pulsée du carbone 13

L’examen des spectres du carbone 13, en résonance magnétique nucléaire puisée, de divers échantillons de poly(oxyde de propylène) synthétisés à l’aide de différents amorceurs à partir de monomère optiquement actif ou racémique, conduit à une interprétation des spectres en fonction des différences de régularité d’enchaînement dans les polymères. Une évaluation approchée de la pureté optique du monomère peut être déterminée à partir de la stéréorégularité du polymère obtenu en utilisant la potasse comme amorceur. Le système d’amorçage diéthylzine-eau ne paraît pas provoquer les irrégularités d’enchainements décrites auparavant

300 MHz 1H-NMR study of poly(propylene sulfide)

An 1H 300-MHz NMR spectroscopic study of deuterated poly(propylene sulfide) shows that methylene protons are sensitive to triad effects. It was possible to distinguish i, hi, s, and hs triads. Experimental values found for different polymers are in good agreement with theoretical amounts obtained from statistical probability calculation. The methyl groups are also slightly stereosensitive. By using optically active deuterated monomers with different R/S ratios it was possible to confirm the assignment of peaks and the tacticity. Nondeuterated polymers give very complicated spectra, and only the highly stereoregular polymer could be analyzed through its ABCX3 spin system

Synthesis and rheological study of some maleic acid and fumaric acid stereoregular polyesters, 10 - Synthesis and characterization of alpha,omega-dihydroxyoligo(alkylene maleate)s

alpha,omega-Dihydroxyoligo(alkylene maleate)s with molecular weights ranging from 1500 to 4000 were prepared by polycondensation, in 1-methyl-2-pyrrolidone at 105 degrees C, of potassium maleate and 1,4-dibromobutane, 1,6-dibromohexane or 1,8-dibromooctane in the presence of 2-bromoethanol. The structure of oligomers was checked by H-1 and C-13 NMR spectroscopy. In most cases the mean functionality of oligomers is reasonably close to two

Synthesis and rheological study of some maleic acid and fumaric acid stereoregular polyesters - 8. Unsaturated polyester fibers

First unsaturated polyester fibers were prepared starting from stereoregular, macromolecular poly(octamethylene fumarate). Fibers obtained from octamethylene copolyesters of fumaric and terephthalic acids manifested improved mechanical properties and higher melting points. All unsaturated polyester fibers prepared in the study, based on the homopolymer and on copolymers of fumaric acid, even those containing as low as 10% of fumaric acid residues, are able to be covalently bonded to an unsaturated polyester matrix