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91.
Jing Chen Ludovic Dumas Jannick Duchet‐Rumeau Etienne Fleury Aurélia Charlot Daniel Portinha 《Journal of polymer science. Part A, Polymer chemistry》2012,50(16):3452-3460
Novel H‐bond donor copolymers were designed by a versatile “click type” grafting reaction of unprotected mercaptoalcohols onto poly(2,3,4,5,6‐pentafluorostyrene) (PPFS). As demonstrated by 19F NMR and Fourier transform infrared spectroscopy (FTIR) analyses, the reaction appears to be chemoselective as the SH groups solely react onto the para‐fluoro position of the PFS units. The nucleophilic substitution was successfully performed with two mercaptoalcohols bearing either one or two hydroxyl groups. By carefully selecting the experimental conditions, a library of copolymers with various degree of substitution up to 95% was obtained in a reasonable timescale through kinetic control. By turbidity analysis, the ability of these functional polymers to form in solution interpolymer complexes with poly(4‐vinyl pyridine) was shown to be tunable by adjusting the molecular characteristics. FTIR, X‐ray photoelectron spectroscopy, and Differential scanning calorimetry evidence that different types of blends (immiscible, partially or totally miscible, and complex) can be achieved, and that the driving force of the interaction originates from H‐bond. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
92.
Mateo Alajarín Prof. Carmen López‐Leonardo Dr. Ángel Álvarez‐García Pilar Llamas‐Lorente Dr. Pilar Sánchez‐Andrada Dr. José Berná Dr. Aurelia Pastor Dr. Delia Bautista Dr. Peter G. Jones Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(12):3728-3735
A series of N,P,P‐trisubstituted aminophosphanes react with diphenylcyclopropenone to afford an easily separable mixture of two diastereomeric α,β‐diphenyl‐β‐phosphinoyl carboxamides in good yields. X‐ray crystal structures reveal that these compounds associate into dimers, formed from two enantiomeric units linked by two bifurcated hydrogen bonds, whereby the oxygen atom of the phosphoryl group acts as a dual acceptor for the vicinal NH and CH of a carbonyl group of a neighbouring molecule. Studies on the interconversion between diastereomeric phosphinoyl carboxamides in basic solution show that the thermodynamically most stable isomer depends on the nature of the substituent at the nitrogen atom. Simple computational calculations explain this phenomenon. 相似文献
93.
The present review presents the state of the art of the developments, key strategies and analytical applications of chemiluminescence detection coupled to CE (CE‐CL). Different parts considering the most common CL systems have been included, such as the tris(2,2′‐bipyridine)ruthenium(II) system, the luminol and derivatives reaction, the peroxyoxalate CL or direct oxidations. New advances in homemade configurations and applications in different fields such as clinical, pharmaceutical, environmental and food analysis have been included. The focus is on studies which appeared from 2000 to the end of 2009. 相似文献
94.
Alajarín M Pastor A Orenes RA Martínez-Viviente E Pregosin PS 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(3):877-886
Compounds formed by linking two tris(ureidobenzyl)amine modules with a hexamethylene tether are described. These compounds self-assemble to form bicapsular aggregates featuring two rings of six hydrogen-bonded ureas. (1)H and (1)H/(1)H ROESY NMR spectroscopy, together with pulsed gradient spin echo (PGSE) NMR diffusion measurements, have been used to characterize the dimers in solution. The results have been compared with energy-minimized structures. The new compounds are kinetically stable on the NMR timescale, and their thermodynamic stabilities are comparable to other capsular aggregates derived from tris(ureidobenzyl)amines. 相似文献
95.
Ugo Boscain Grégoire Charlot Francesco Rossi 《Proceedings of the Steklov Institute of Mathematics》2010,270(1):43-56
We consider the problem of reconstructing a curve that is partially hidden or corrupted by minimizing the functional $
\smallint \sqrt {1 + K_\gamma ^2 ds}
$
\smallint \sqrt {1 + K_\gamma ^2 ds}
, depending both on the length and curvature K. We fix starting and ending points as well as initial and final directions. For this functional we discuss the problem of
existence of minimizers on various functional spaces. We find nonexistence of minimizers in cases in which initial and final
directions are considered with orientation. In this case, minimizing sequences of trajectories may converge to curves with
angles. We instead prove the existence of minimizers for the “time-reparametrized” functional $
\smallint ||\dot \gamma (t)||\sqrt {1 + K_\gamma ^2 dt}
$
\smallint ||\dot \gamma (t)||\sqrt {1 + K_\gamma ^2 dt}
for all boundary conditions if the initial and final directions are considered regardless of orientation. In this case, minimizers
may present cusps (at most two) but not angles. 相似文献
96.
97.
98.
The electronic structure of an icosaedral cluster of 13 nickel atoms is studied using an Extended Hückel method. Near the highest occupied level at ?7.65 eV, h and t orbitals are accidentally degenerate so that the fundamental state possesses a high spin multiplicity (2S + 1 = 9) accounting for the magnetism of the particule. We have considered several geometries for a hydrogen molecule approaching the cluster at a minimum distance of 1.47 Å. In all cases the H-H bond is weakened because of electron transfer from the nickel towards the hydrogen atoms and partial filling of the antibonding orbital of h2. During the increase of the H-H distance the weakening is easier than in the absence of a nickel catalyst leading to the dissociative adsorption of the molecule. The activation mechanism of H2 requires participation of both the s and d orbitals of the metal and leads to a lowering of the spin multiplicity. Finally, we have shown that a dissociative adsorption is obtained when the H2 molecule approaches a triangular face. After breaking of the H-H bond, the more stable system corresponds to atomic H adsorption on two opposite vertices. 相似文献
99.
100.
Cristofor I. Simionescu Geta David Vasile Paraschiv Aurelia Ioanid Sorin Manolache Bogdan C. Simionescu 《Journal of polymer science. Part A, Polymer chemistry》1996,34(15):3071-3076
The kinetic study of the photochemical polymerization of methacrylic acid (MAA) in aqueous dilute solution in the presence of poly(N-acetyliminoethylene) (PNAI) oligomers evidenced template features. The process proceeded in two stages, depending on [PNAI]/[MAA]0 ratio and polymerization duration, two different complexes being formed, both by a “zip” chain-growth mechanism. Computing and transmission electron microscopy data revealed that this aspect is due to the replacing of the initial PNAI template by the newly formed poly(methacrylic acid) daughter polymer, as a result of the structural peculiarities of the latter as a component of the primary complex. Its specific mode of packing in a complex aggregate was considered to be the main reason for the reported behavior. © 1996 John Wiley & Sons, Inc. 相似文献