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61.
62.
Nicolas Spassky Vesna Simic Liliane G. Hubert-Pfalzgraf Maurizio S. Montaudo 《Macromolecular Symposia》1999,144(1):257-267
The polymerization of (D,L)-Lactide at room temperature in solution using Y(OCH2CH2OiPr)3 and Ln5(μ-O)(OiPr)13 with Ln = La, Sm, Y, Yb as initiators was studied. According to kinetic data, a controlled type polymerization is observed for most of the systems. La μ-oxoisopropoxide is the most reactive initiator, but leads to a substantial broadening of molecular weight distribution at high conversions. The nature of transesterification reactions was studied by SEC, 13C NMR and MALDI-TOF MS techniques. For Sm and Y-μ-oxo initiators only limited intermolecular ester exchange occurs, while with La μ-oxoinitiator and with Y(OCH2CH2OiPr)3 initiator, but after a long time of the polymerization reaction, both inter and intramolecular transesterification occur with formation of cyclics. 相似文献
63.
64.
Alain Le Borgne Valrie Vincens Muriel Jouglard Nicolas Spassky 《Macromolecular Symposia》1993,73(1):37-46
Bifunctional telechelics with defined structure can be prepared by oligomerization of oxiranes, β-butyrolactone and L-lactide using aluminium Schiff's base complexes as initiators. Chiral initiator (SALCENAlCl) shows a stereoelective character leading to preferential oligomerization of one enantiomer from a racemic monomer mixture. The reaction with β-butyrolactone proceeds through O-alkyl cleavage. Alkoxy Schiff's bases aluminium complexes are used for oligomerization of L-lactide. All the prepared oligomers were fully characterized by IR, elemental analysis, 1H and 13C NMR and GPC. 相似文献
65.
Nevena Manolova Milena Ignatova Iliya Rashkov Maurice Sepulchre Nicolas Spassky 《Macromolecular Symposia》1997,122(1):281-286
Some new poly(ether-ester)s (PEEs) and poly(ether-amide)s (PEAs) with polyether sequences linked by tartrate units have been synthesized. Derivatives bearing residues from the synthetic plant-growth regulator 1-naphthylacetic acid (NAA) as pendent groups and end-groups have been prepared by esterification of PEEs and PEAs with NAA. Polymers bearing residues from pyridine-2, 6-dicarboxylic acid (a herbicide) in the main chain have been prepared. The hydrolysis has been found to depend on the structure of the polymer carrier, on pH of the medium and on the ability of the polymers to form complexes with polyacids. The phytosanitary activity of the new polymers has been related to the particular features of their hydrolysis behaviour. 相似文献
66.
Nicolas Spassky Christian Pluta Vesna Simic Mohamedou Thiam Muriel Wisniewski 《Macromolecular Symposia》1998,128(1):39-51
The stereochemical aspects of controlled polymerization of lactide and β-butyrolactone are discussed. The physicochemical and thermal properties of these polymers are shown to be depending on the stereochemical structure of the macromolecular chain. Different types of processes involving change of enantiomeric composition in the course of the polymerization reaction are examined in function of different initiators used. The formation of stereocomplexes from stereocopolymers of various enantiomeric compositions is reported. 相似文献
67.
Philippe Dumas Nicolas Spassky Pierre Sigwalt 《Journal of polymer science. Part A, Polymer chemistry》1979,17(6):1595-1604
The kinetics of enantiomerically enriched t-butyl thiirane was studied. The stereoelectivity and the kinetic behavior are not changed when a monomer of an initial enantiomeric composition lower than a defined limit value is used. When the enantiomeric composition is higher than this value, the stereoelectivity increases. In agreement with kinetic results, a mechanism is proposed involving, in a first step, the complexation of monomer on preexisting sites of the initiator with formation of highly selective chiral active species on which propagation occurs. 相似文献
68.
Philippe Dumas Nicolas Spassky Pierre Sigwalt 《Journal of polymer science. Part A, Polymer chemistry》1979,17(6):1605-1610
The effect of temperature on stereoelective polymerization of t-butyl thiirane was studied. Although the overall kinetic scheme was not modified by a change of temperature, a strong effect on the stereoelectivity ratio was observed. Very high optical yields were obtained for polymerizations run below 0°C. On the other hand, at temperatures higher than 120°C, the stereoelection is inversed; i.e., the opposite enantiomer is chosen. The stereoselectivity ratio varies with temperature according to an Arrhenius relationship. 相似文献
69.
L. I. Galanina N. S. Zelenskaya V. M. Lebedev N. V. Orlova A. V. Spassky 《Bulletin of the Russian Academy of Sciences: Physics》2017,81(6):702-709
All even components of the spin-tensors of a density matrix reconstructed by means of angular correlation for 12С nuclei in the 2+ state (4.44 MeV), produced during the inelastic scattering of α particles with energies of 16 to 25 MeV in scattering angle range θα(lab) = 20°–90°, are presented. The energy dependences of its orientation characteristics (i.e., the population of magnetic substates and the orientation tensors of multipole moments) are determined. Experimental results are compared to calculations using the coupledchannel method and the compound nucleus model. 相似文献
70.
L. I. Galanina N. S. Zelenskaya A. V. Ignatenko V. M. Lebedev N. V. Orlova O. I. Serikov A. V. Spassky 《Physics of Atomic Nuclei》2005,68(12):1957-1967
The results are presented that were obtained by measuring the differential cross sections for the reaction 10B(d, p)11B occurring at E d = 15.3 MeV and leading to the production of a 11B nucleus in the ground state (3/2?) and in the lowest two excited states (the 1/2? state at 2.125 MeV and the 5/2? state at 4.445 MeV). The energy dependence of the differential cross section for this reaction was measured for several proton emission angles in the energy range E d = 12–15.3 MeV. The double-differential cross sections for the reaction 10B(d, pγ)11B were measured for the 5/2? state of the 11B nucleus at 4.445 MeV, and the angular dependences of the even spin-tensor components of the density matrix were reconstructed on the basis of these data. The angular dependences of the populations of magnetic sublevels are also given. The experimental results in question are compared with their theoretical counterparts obtained under the assumption of various reaction mechanisms (neutron stripping, heavy-particle stripping, and a two-step mechanism that takes into account the delay of interaction). On the basis of this comparison, the deformation parameters of the boron nuclei were found to be β 2(10B) = ?0.55 and β 2(11B) = 0.4. 相似文献