Functionalized polystyrene as a versatile support for olefin polymerization catalysts

Heterogeneous polyolefin catalysts based on metallocenium salts of weakly coordinating anions can be prepared via a series of simple reactions from lightly crosslinked chloromethylated polystyrene beads. Catalytic sites are distributed homogeneously throughout the polystyrene particles. The nonporous nature of these catalysts affords a high degree of control over the olefin uptake rate, avoiding problems of premature catalyst fragmentation that often plague high‐surface‐area heterogeneous catalysts based on highly reactive species. The choice of amine as the means of binding or templating allows catalysts based on a wide variety of metallocenes to be readily prepared by the same synthetic approach. The dative interactions between the metallocene cation and the amine functionality of the support material are sufficient to prevent extraction under polymerization conditions to yield excellent particle morphology of the polyolefin product, but they are not so strong as to affect the nature of the polyolefin produced. The polymer‐supported catalysts have been used effectively for the polymerization of ethylene and polypropylene. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2979–2992, 2000     

Untersuchung des Wassers

Ohne Zusammenfassung     

Vanadiummetall

Ohne Zusammenfassung     

Gravitation in the Fractal D = 2 Inertial Universe: New Phenomenology in Spiral Discs and a Theoretical Basis for MOND

A particular interpretation of Mach's Principle led us to ask if it was possible to have a globally inertial universe that was irreducibly associated with a non-trivial global matter distribution, Roscoe [1]. This question received a positive answer, subject to the condition that the global matter distribution is necessarily fractal, D = 2. The present paper shows how gravitational processes can arise in this universe. We begin by showing how classical Newtonian gravitation arises from point-source perturbations of this D = 2 inertial background. We then use the insights gained from this initial analysis to arrive at a general theory for arbitrary material distributions. We illustrate the process by using it to model an idealized spiral galaxy. One particular subclass of solutions, (the logarithmic spiral) has already been extensively tested (Roscoe [2, 3]), and shown to resolve large samples of optical rotation curve data to a very high statistical precision. These analyses also led to the discovery of a major new phenomenology in spiral discs—that of discrete dynamical classes, [3]. In this paper, we analyse the theory more comprehensively, showing how this phenomenology has a possible explanation in terms of an algebraic consistency condition which must necessarily be satisfied.Of equal significance, we apply the theory with complete success to the detailed modelling of eight Low Surface Brightness spirals (LSBs) which, hitherto, have been successfully modelled only by the MOND algorithm (Milgrom [5–7]. We are able to conclude that the essence of the MOND algorithm must be contained within the presented theory.     

The multi-functional aspect of scanning holographic microscopy: a review(Invited Paper)

Recent developments in scanning holographic microscopy that offer the prospects of new quantitative tools and imaging modalities in bio, micro, and nano sciences are reviewed. The versatility of the method is emphasized. Scanning holography can operate in an incoherent mode for fluorescence imaging, in a coherent mode for quantitative phase imaging, or in a tomographic mode for axial sectioning and rejection of the out-of-focus haze. Possible applications are illustrated with examples, and future prospects ...     

The reaction of O(3P) with H2O2

The rate constant for the reaction of O(³P) with H₂O₂ was measured as a function of temperature and the [H₂O₂]₀/[O]₀ ratio. The numerical solution of the appropriate rate equations was used to arrive at a mechanism which adequately describes our results and the rather divergent data in the literature. A recommended expression for the temperature dependence of the absolute rate constant is presented from consideration of the available experimental data.     

Minor processes in the photolysis of azomethane at low pressure: An upper limit for the rate of the unimolecular elimination of H2 from vibrationally excited ethane

The photolysis of azomethane in the near UV has been studied at room temperature and pressures from 10 mtorr to 10 torr. The main products, C₂H₆ and N₂, accounted for more than 99% of the reaction. Minor hydrocarbon products observed were (with quantum yields) C₃H₈ (3.5 × 10^?3), C₂H₄ (3.2 × 10^?4), CH₄ (3 × 10^?3), and n-C₄H₁₀ (trace). Quantum yields of H₂ of 4 × 10^?5 and 2 × 10^?5 were measured at azomethane pressures of 0.1 and 1.0 torr, respectively. The minor hydrocarbon products can be accounted for by reactions of CH₃ and C₂H₅ radicals following hydrogen abstraction from azomethane by CH₃. The H₂ product observed represents an upper limit for the H₂ elimination from vibrationally excited C₂H₆ formed by CH₃ combination in the system, corresponding to a rate of elimination ca. 5 × 10^?5 times the competing rate of dissociation to 2CH₃. Assuming a frequency factor of 10¹³ s^?1 for the H₂ elimination, a lower limit of about 90 kcal mol^?1 was estimated for the energy barrier.