DFT mechanistic study of the H2‐assisted chain transfer copolymerization of propylene and p‐methylstyrene catalyzed by zirconocene complex

DFT computations have been performed to investigate the mechanism of H₂‐assisted chain transfer strategy to functionalize polypropylene via Zr‐catalyzed copolymerization of propylene and p‐methylstyrene (pMS). The study unveils the following: (i) propylene prefers 1,2‐insertion over 2,1‐insertion both kinetically and thermodynamically, explaining the observed 1,2‐insertion regioselectivity for propylene insertion. (ii) The 2,1‐inserion of pMS is kinetically less favorable but thermodynamically more favorable than 1,2‐insertion. The observation of 2,1‐insertion pMS at the end of polymer chain is due to thermodynamic control and that the barrier difference between the two insertion modes become smaller as the chain length becomes longer. (iii) The pMS insertion results in much higher barriers for subsequent either propylene or pMS insertion, which causes deactivation of the catalytic system. (iv) Small H₂ can react with the deactivated [Zr]?pMS?PP_n facilely, which displace functionalized pMS?PP_n chain and regenerate [Zr]? H active catalyst to continue copolymerization. The effects of counterions are also discussed. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 576–585     

Unique continuation along curves and hypersurfaces for second order anisotropic hyperbolic systems with real analytic coefficients

In this paper we prove the following kind of unique continuation property. That is, the zero on each geodesic of the solution in a real analytic hypersurface for second order anisotropic hyperbolic systems with real analytic coefficients can be continued along this curve.

     

Crystallographic report: Bis(norfloxacin)dilead(II) tetranitrate, [Pb2(H‐Norf)2(ONO2)4]

The centrosymmetric binuclear structure of [Pb₂(H‐Norf)₂(ONO₂)₄]shows the geometry around each lead(II) atom to be distorted trigonal bipyramidal with Pb–O distances ranging from 2.357(3) to 2.769(4) Å. Copyright © 2003 John Wiley & Sons, Ltd.     

Degree Sums and Covering Cycles

It is shown that if in a simple graph G of order n the sum of degrees of any three pairwise non-adjacent vertices is at least n, then there are two cycles (or one cycle and an edge or a vertex) of GF that contain all the vertices. © 1995 John Wiley & Sons, Inc.     

Vanishing Shear Viscosity Limit in the Magnetohydrodynamic Equations

We study an initial boundary value problem for the equations of plane magnetohydrodynamic compressible flows, and prove that as the shear viscosity goes to zero, global weak solutions converge to a solution of the original equations with zero shear viscosity. As a by-product, this paper improves the related results obtained by Frid and Shelukhin for the case when the magnetic effect is neglected. Supported by NSFC (Grant No. 10301014, 10225105) and the National Basic Research Program (Grant No. 2005CB321700) of China.     

Preparation of Nanoelectrode Ensembles by Assembly of Nano—Silver Colloid on Gold Surface

A novel method for preparing silver nanoelectrode ensembles(SNEEs) and gold nanoelectrode ensembles (GNEEs) has been developed. Silver colloid particles were first absorbed to the gold electrode surface to form a monolayer silver colloid. N-hexadecyl nercaptan was then assembled on the electrode to form a thoil monolayer on which hydrophilic ions cannot be transfered. The SNEEs was prepared by removing thiol from silver colloid surface through applying and AC voltage with increasing frequency at 0.20V(vs.SCE). Finally,GNEEs was obtained by immersing a SNEEs into 6 mol/L HNO3 to remove the silver colloid particles. By comparison with other methods such as template method ect., this method enjoys some advantages of lower resistance, same diameter,easy preparation,controllable size and density.     

Prompt Gamma-Ray Analysis of Rats

Prompt -ray analysis with the internal monostandard method was used to organs taken from rats. After B or Cd was administered, the B/H and Cd/H contents ratios were determined in the brain, kidney, and liver to study their distribution and metabolism. Boron was distributed in all organs but metabolized quickly. Cd was slowly accumulated in the liver and kidneys during the 65 hours studied but no Cd was detected in the brain.     

Use of diode-array detectors for the simultaneous spectrophotometric determination of calcium and magnesium by flow injection

A method for the simultaneous flow injection spectrophotometric determination of calcium and magnesium with Arsenazo III based on the use of diode-array detector and merging zones is described. The method is applicable to the resolution of mixtures in which the chromogenic reagent has a high absorbance and its spectrum strongly overlaps those of its complexes. In resolving the mixtures, the excess reagent is considered as another component. Quantitation is based on the normal absorbance and first-derivative absorbance spectra. The method is applied to 0.2–1.5 μg ml^?1 Ca and 0.1–1.0 μg ml^?1 Mg. The analysis rate is 50 h^?1.