We consider the weight ${{u(x) = x^{\gamma} e^{-x^{-\alpha}-x^{\beta}}}}$ , with ${{x \in(0,+\infty)}}$ , α > 0, β > 1 and γ ≥ 0 and prove Remez-, Bernstein–Markoff-, Schurand Nikolskii-type inequalities for algebraic polynomials with the weight u on (0, + ∞). 相似文献
The kinetics of the ethylene‐norbornene copolymerization, catalyzed by rac‐Et(Ind)2ZrCl2/MAO, 90%rac/10%meso‐Et(4,7‐Me2Ind)2ZrCl2/MAO and rac‐H2C(3‐tert‐BuInd)2ZrCl2/MAO was followed by sampling from the reaction mixture at fixed time intervals. Catalyst activity, copolymer composition and molar mass were studied as a function of time. The polymers showed an unusually low polydispersity and a significant increase in their molar mass with time, suggesting a quasi‐living polymerization. 相似文献
Unbridged zirconium and titanium catalysts, where a seven-or eight-membered ring fused to a cyclopentadiene is associated
with a phenyl substituent in position 2, were tested in propylene polymerization in order to investigate the possibility of
observing a “fluxional behavior” and to obtain stereoblock polypropylene, even in the absence of the aromatic ring, usually
present in this kind of catalysts, by introducing the conformational flexibility of the saturated ring as a new parameter.
The microstructure, molecular properties, and thermal behavior of the polymers obtained showed that it is possible to observe
a “fluxional behavior” even by replacing the basic indenyl structure with a slightly flexible saturated ring. Furthermore,
this structural feature sensibly increases the stability of the complexes, thus making it possible to observe for the first
time the oscillating behavior in titanocenes.
The text was submitted by the authors in English. 相似文献
Summary: Model chains of ethylene‐norbornene copolymers were built up using the results of 13C NMR spectral analysis of copolymer samples synthesized with metallocene‐based catalysts. Our models statistically reproduce the microstructure, composition, and tacticity of the copolymer chains of experimental samples. They were used to test if MD simulations are suitable to investigate the relationships between microstructure and macroscopic properties. In particular, MD simulations were applied to calculate the glass transition temperature and to study the chain flexibility by the analysis of ACF of specific virtual bonds. Plots of specific volume versus temperature computed for models of four copolymer samples having different microstructures and norbornene contents yield Tg values in good agreement with experiments. Moreover, comparison of the ACFs provides some qualitative indications about the relationship between chain stereochemistry and Tg.
ACF functions of the virtual bonds with microstructures NENE (bottom) and ENNE (top). 相似文献
A series of ethylene‐norbornene copolymers were synthesized in the presence of zirconocenes with different symmetries and ligand patterns and at different norbornene (N)/ethylene (E) mole ratios. Copolymers were characterized by 13C NMR spectroscopy; Inadequate NMR sequences were used also. The comparison of 13C NMR spectra of copolymers prepared with different norbornene content and the correlation between 13C NMR chemical shifts and conformational structures of the chain on the basis of molecular mechanics calculations were performed. Preliminary assignments were revised and new comonomer sequences such as ENNE which contain meso and racemo NN dyads were assigned. 相似文献