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Five novel vanadium(III) complexes [PhN = C(R2)CHC(R1)O]VCl2(THF)2 (4a: R1 = Ph, R2 = CF3; 4b: R1 = t‐Bu, R2 = CF3; 4c: R1 = CF3, R2 = CH3; 4d: R1 = Ph, R2 = CH3; 4e: R1 = Ph, R2 = H) have been synthesized and characterized. On activation with Et2AlCl, all the complexes, in the presence of ethyl trichloroacetate (ETA) as a promoter, are highly active precatalysts for ethylene polymerization, and produce high molecular weight and linear polymers. Catalyst activities more than 16.8 kg PE/mmolV h bar and weight‐average molecular weights higher than 173 kg/mol were observed under mild conditions. The copolymerizations of ethylene and norbornene or 1‐hexene with the precatalysts were also explored, which leads to high molecular weight copolymers with high comonomer incorporation. Catalyst activity, comonomer incorporation, and polymer molecular weight as well as polydispersity index can be controlled over a wide range by the variation of precatalyst structure and the reaction parameters such as Al/V molar ratio, comonomer feed concentration, and polymerization temperature. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2038–2048, 2008

A black hole X-ray binary produces hard X-ray radiation from its corona and disk when the accreting matter heats up. During an outburst, the disk and corona co-evolves with each other. However, such an evolution is still unclear in both its geometry and dynamics. Here we report the unusual decrease of the reflection fraction in MAXI J1820+070, which is the ratio of the coronal intensity illuminating the disk to the coronal intensity reaching the observer, as the corona is observed to contrast during the decay phase. We postulate a jet-like corona model, in which the corona can be understood as a standing shock where the material flowing through. In this dynamical scenario, the decrease of the reflection fraction is a signature of the corona’s bulk velocity. Our findings suggest that as the corona is observed to get closer to the black hole, the coronal material might be outflowing faster.

Vanadium(III) complexes bearing tridentate salicylaldiminato ligands (2a-f) [OC 6 H 4 CHdNL]-VCl 2 (THF) (L ) CH 2 CH 2 OMe, 2a; CH 2 CH 2 NMe 2 , 2b; CH 2 C 5 H 4 N, 2c; 8-C 9 H 6 N (quinoline), 2d; 2-MeSC 6 H 4 , 2e; 2-Ph 2 PC 6 H 4 , 2f) and tridentate β-enaminoketonato ligands [OC 6 H 8 CHdN-2-Ph 2 PC 6 H 4 ]VCl 2 (THF) (2g) and [O(Ph)CdCHCHdN-2-Ph 2 PC 6 H 4 ]VCl 2 (THF) (2h) were prepared from VCl 3 (THF) 3 by treating with 1.0 equiv of the deprotonated ligands in tetrahydrofuran (THF). These complexes were characterized by FTIR and mass spectrometry as well as elemental analysis. Structures of complexes 2e, 2f, and 2h were further confirmed by X-ray crystallographic analysis. These complexes were investigated as catalysts for olefin polymerization in the presence of organoaluminum compounds. On activation with Et 2 AlCl, complexes 2a-h exhibited high catalytic activities toward ethylene polymerization (up to 20.64 kg PE/mmol V • h • bar) even at high temperature, suggesting these catalysts possess high thermal stability. Moreover, high molecular weight polymers with unimodal molecular weight distribution can be obtained, indicating the single site behavior of these catalysts. The copolymerizations of ethylene and norbornene or 1-hexene with catalysts 2a-h were also explored in the presence of Et 2 AlCl, which led to high molecular weight poly(ethylene-co-1-hexene)s (M w up to 138 000) and poly(ethyleneco-norbornene)s (M w up to 164 000). Catalytic activity, comonomer incorporation, and polymer molecular weight can be controlled in a wide range by the variation of catalyst structure and the reaction parameters such as Al/V molar ratio, comonomer feed concentration, and polymerization reaction temperature.

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The reversible addition–fragmentation chain transfer (RAFT) polymerization of acrylonitrile (AN) mediated by 2‐cyanoprop‐2‐yl dithiobenzoate was first applied to synthesize polyacrylonitrile (PAN) with a high molecular weight up to 32,800 and a polydispersity index as low as 1.29. The key to success was ascribed to the optimization of the experimental conditions to increase the fragmentation reaction efficiency of the intermediate radical. In accordance with the atom transfer radical polymerization of AN, ethylene carbonate was also a better solvent candidate for providing higher controlled/living RAFT polymerization behaviors than dimethylformamide and dimethyl sulfoxide. The various experimental parameters, including the temperature, the molar ratio of dithiobenzoate to the initiator, the molar ratio of the monomer to dithiobenzoate, the monomer concentration, and the addition of the comonomer, were varied to improve the control of the molecular weight and polydispersity index. The molecular weights of PANs were validated by gel permeation chromatography along with a universal calibration procedure and intrinsic viscosity measurements. 1H NMR analysis confirmed the high chain‐end functionality of the resultant polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1272–1281, 2007

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