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911.
912.
Po‐Sheng Chen Yi‐Chang Liu Chia‐Her Lin Bao‐Tsan Ko 《Journal of polymer science. Part A, Polymer chemistry》2010,48(16):3564-3572
Two novel sulfonate phenol ligands—3,3′‐di‐tert‐butyl‐2′‐hydroxy‐5,5′,6,6′‐tetramethyl‐biphenyl‐2‐yl 4‐X‐benzenesulfonate (X?CF3, LCF3 ‐H, and X?OCH3, LOMe ‐H)—were prepared through the sulfonylation of 3,3′‐di‐tert‐butyl‐5,5′,6,6′‐tetramethylbiphenyl‐2,2′‐diol with the corresponding 4‐substituted benzenesulfonyl chloride (1 equiv.) in the presence of excess triethylamine. Magnesium (Mg) complexes supported by sulfonate phenoxide ligands were synthesized and characterized structurally. The reaction of MgnBu2 with L‐H (2 equiv.) produces the four‐coordinated monomeric complexes ( LCF3 )2Mg ( 1 ) and ( LOMe )2Mg ( 2 ). Complexes 1 and 2 are efficient catalysts for the ring‐opening polymerization of ε‐caprolactone (ε‐CL) and trimethylene carbonate (TMC) in the presence of 9‐anthracenemethanol; complex 1 catalyzes the polymerization of ε‐CL and TMC in a controlled manner, yielding polymers with the expected molecular weights and narrow polydispersity indices (PDIs). In ε‐CL polymerization, the activity of complex 1 is greater than that of complex 2 , likely because of the greater Lewis acidity of Mg2+ metal caused by the electron‐withdrawing substitute trifluoromethyl (? CF3) at the 4‐position of the benzenesulfonate group. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3564–3572, 2010 相似文献
913.
Przemys?aw Górka 《Nonlinear Analysis: Theory, Methods & Applications》2010,72(6):2852-2858
We study the Cauchy problem for a 1D nonlinear wave equation on R. The nonlinearity can depend on the unknown function and its first order spatial derivative. Using the fixed point theorem we prove the existence of a classical solution. Moreover, the existence of periodic and almost periodic solutions are shown. 相似文献
914.
915.
《中国化学会会志》2017,64(8):896-917
β‐Cyclodextrin (β‐CD ), a naturally occurring supramolecular structure, is an effective catalyst for the synthesis of heterocyclic compounds. Its ubiquity, high performance, nontoxicity, ease of separation, and reusability have drawn the attention of green chemists. Here we present the synthetic procedures of heterocyclic compounds catalyzed by β‐CD in water and compare them with those using organic solvents. In many cases, using water as the solvent shows better efficiency than conventional organic solvents with regard to catalytic activity and simplicity of recycling procedures. This review highlights the applications of β‐CD in catalysis covering the years 2004–2016. 相似文献
916.
G. Spavieri V. Guerra R. De Abreu G. T. Gillies 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,47(3):457-463
Propagation of Aharonov-Bohm matter waves and light waves in moving media is
characterized by the interaction electromagnetic momentum. Thus, recent
models of light propagation in moving rarefied media justify and call for an optical experiment of the Mascart-Jamin type,
capable of testing the
modern interpretations of ether drift experiments. 相似文献
917.
918.
We introduce the notions of a pre--set and a pre-V-set in a topological space. We study the fundamental properties of pre--sets and pre-V-sets and investigate the topologies defined by these families of sets. 相似文献
919.
Bruno Sévennec 《Mathematische Annalen》2002,324(1):195-211
We improve – roughly by a factor 2 – the known bound on the multiplicity of the second eigenvalue of Schr?dinger operators
(i.e. Laplace plus potential) on closed surfaces. This gives four new topological types of surfaces for which Colin de Verdière's
conjecture relating the maximal multiplicity to the chromatic number of the surface is verified. The proof goes by defining
a space of "nodal splittings” of the surface, equipped with a double covering to which a Borsuk-Ulam type theorem is applied.
Received: 19 June 2001; revised version: 18 March 2002 /Published online: 17 June 2002 相似文献
920.
Michael Capalbo 《Combinatorica》2002,22(3):345-359
For all positive integers N and k, let denote the family of planar graphs on N or fewer vertices, and with maximum degree k. For all positive integers N and k, we construct a -universal graph of size . This construction answers with an explicit construction the previously open question of the existence of such a graph.
Received July 8, 1998
RID="*"
ID="*" Supported by NSF grant CCR98210-58 and ARO grant DAAH04-96-1-0013. 相似文献