Morphology Control in Metallocene Polymerization; Organic Supports vs. Non-aqueous Emulsion Polymerization

Nano-sized latex support in metallocene polymerization is known to be able to avoid fuming or leaching and leads to a powder-like and well-processable polymer. Focus has been put on the fragmentation behaviour of the particles, a key parameter to morphology control. To study the different behaviour of the new systems as classical inorganic supported metallocenes, e.g. SiO₂, a wide range of analytical methods were applied. Fluorescence microscopy, polymerization videomicroscopy, as well as kinetic studies led to a better understanding of the process. The performance of the supports was approved by several phenoxy-imine type catalysts (“FI-Catalyst”), which were combined with a tailored latex support. Ultra high molecular weight polyethylene (UHMWPE) was synthesized without any reactor fouling thereby. A different approach towards the metallocene catalyzed olefin polymerization is also presented. Based on emulsion polymerization, it enables very good control over product morphology. The completely hydrophobic system consists of perfluorinated solvent as a continuous phase and a hydrocarbon solvent as a dispersed phase. In contrast to the already existing water based emulsion polymerization of olefins, very high molecular weights are achieved.     

The K2nCoMo2+nO7+4n family of structures,with n = 2, 3 or 5

The compounds K₄CoMo₄O₁₅ (tetra­potassium cobalt tetra­molybdate), K₆CoMo₅O₁₉ (hexa­potassium cobalt pentamolybdate) and K₁₀CoMo₇O₂₇ (deca­potassium cobalt hepta­molybdate) belong to a series of compounds with closely related crystal structures. In K₄CoMo₄O₁₅, the Co atom and one of the two unique Mo atoms are at sites with threefold symmetry; two of the three unique K atoms lie at sites with symmetry. K₆CoMo₅O₁₉ crystallizes in a new monoclinic structure type. Each [CoO₆] octa­hedron is surrounded by one face‐sharing [MoO₆] octa­hedron and six corner‐sharing [MoO₄] tetra­hedra. All three compounds have this structural unit in common, but differ in the degree of connectivity between these units. They form layers in K₄CoMo₄O₁₅ and zigzag chains in K₆CoMo₅O₁₉, both by sharing [MoO₄] tetra­hedra. In K₁₀CoMo₇O₂₇, the structural units are isolated from each other.     

Giant magnetic anisotropy in tetragonal FeCo alloys

In order to further increase the recording density in hard disk drives, new media materials are required. Two essential parameters of future recording media are a large uniaxial magnetic anisotropy energy (MAE) K(u) and a large saturation magnetization M(s). Based on first-principles theory, we predict that very specific structural distortions of FeCo alloys possess these desired properties. The discovered alloy has a saturation magnetization that is about 50% larger than that of FePt--a compound that has received considerable attention lately-with a uniaxial MAE that can easily be tailored reaching a maximum value that is 50% larger than that of FePt.     

Bag-model form factors and Hartree-Fock approximation to the σωπ model

We evaluate form factors for the scattering ofσ, ω andπ mesons from nucleons described by the MIT bag model. These form factors are then written covariantly and used for nuclear matter in the Hartree-Fock approximation to theσω model of quantum hadrodynamics with pions. For fixed parameters (meson couplings and masses) the inclusion of these form factors results in more binding at a higher saturation density. After refitting the parameters to reproduce the empirical saturation properties, the result is very close to that without form factors.     

Investigation on the influence of particular structure parameters on the anisotropic spin-exchange interactions in the distorted wolframite-type oxides Cu(Mo(x)W(1-x))O4

A spin-dimer analysis of the anisotropic spin-exchange interactions in the distorted wolframite-type oxides CuWO4, CuMoO4-III, and Cu(Mo(0.25)W(0.75))O4 was performed by Koo and Whangbo (Inorg. Chem. 2001, 40, 2161-2169). For Cu(Mo(0.25)W(0.75))O4, a magnetic structure with a magnetic unit cell doubled along the a and b axes has been predicted, but neutron powder diffraction on Cu(Mo(0.25)W(0.75))O4 did not confirm such a magnetic structure. In the present work, a detailed spin-dimer analysis, considering the influence of particular atomic structure parameters, finally revealed that a wrong coordinate transformation of the Cu z coordinate of the Cu(Mo(0.25)W(0.75))O4 structure is responsible for the prediction of the new, hypothetical magnetic structure. The deviation from the correct value is too small to be recognized by unreasonable bond lengths or angles but is sufficient to change one specific calculated value that is responsible for the prediction of the hypothetical magnetic structure.