The metal atom net charge correlation(MANCC) method was developed in prediction of catalyst activity of asymmetric late-transition metal complexes,2-quinoxalinyl-6-iminopyridine Ni(Ⅱ),2-imino-1,10-phenanthroline Co(Ⅱ) and 2-methoxycarbonyl-6-iminopyridine Pd(Ⅱ) complexes,from the net charge of the metal atom for ethylene polymerization.Dreiding force field was modified according to the X-ray diffraction data.We found that the asymmetric structure of the complexes resulted in a charge differ-ence between two halogen atoms coordinated to the metal atom.In order to remove such contribution we introduced the effective charge Qeff,which was obtained by the charge equilibration(QEq) approach.The results verified the successful introduction of Qeff and showed that the catalytic activities of different complexes are related to central metal atom effective charge.
Atomistic detailed hydration structures of poly(vinyl methyl ether)(PVME) have been investigated by molecular dynamics simulations under 300 K at various concentrations. Both radial distribution functions and the distance distributions between donors and acceptors in hydrogen bonds show that the hydrogen bonds between the polymer and water are shorter by 0.005 nm than those between water molecules. The Quasi-hydrogen bonds take only 7.2% of the van der Waals interaction pairs. It was found the hydrogen bonds are not evenly distributed along the polymer chain,and there still exists a significant amount(10%) of ether oxygen atoms that are not hydrogen bonded to water at a concentration as low as 3.3%. This shows that in polymer solutions close contacts occur not only between polymer chains but also between chain segments within the polymer,which leads to inefficient contacts between ether oxygen atoms and water molecules. Variation of the quasi-hydrogen bonds with the concentration is similar to that of hydrogen bonds,but the ratio of the repeat units forming quasi-hydrogen bonds to those forming hydrogen bonds approaches 0.2. A transition was found in the demixing enthalpy at around 30% measured by dynamic testing differential scanning calorimetry(DTDSC) for aqueous solutions of a mono-dispersed low molecular weight PVME,which can be related to the transition of the fractions of hydrogen bonds and quasi-hydrogen bonds at ～27%. The transition of the fractions of hydrogen bonds and quasi-hydrogen bonds at ～27% can be used to explain the demixing enthalpy transition at 30% at a molecular scale. In addition,at the concentration of 86%,each ether oxygen atom bonded with water is assigned 1.56 water molecules on average,and 'free' water molecules emerge at the concentration of around 54%.
