Adaption of the Mechanism of Emulsion Polymerization to New Experimental Results

Summary: New experimental investigations of the 'classical' batch ab-initio emulsion polymerization of styrene reveal the important role of monomer droplets for the whole process. Monomer droplets with a size between a few and some hundreds of nanometers, which are formed by spontaneous emulsification as soon as styrene and water are brought into contact, have a strong influence on the particle nucleation, the particle morphology, and the swelling of the particles. Experimental results confirm that micelles of low molecular weight surfactants are not a major locus of particle nucleation. Brownian dynamics simulations show that the capture of matter by the particles (monomer or radicals) strongly depends on the polymer volume fraction and the size of the captured species (primary free radicals, oligomers, single monomer molecules, or clusters).     

The copolymer route to new luminescent materials for LEDs

The synthesis of the highly fluorescent mono‐ and bis‐silylated poly(1,4‐phenylene vinylene) derivatives 1 and 2 is reported. The Gilch dehydrohalogenation polycondensation and the Horner synthesis of strictly alternating copolymers have been used to prepare the copolymers 8‐11 and 14, 16‐18 , respectively, in which the tunability of various optoelectonic properties may be examined systematically.     

A note on mixed graphs and directed splitting off

We give counterexamples to two conjectures of Bill Jackson in Some remarks on arc-connectivity, vertex splitting, and orientation in graphs and digraphs (Journal of Graph Theory 12 (3):429–436, 1988) concerning orientations of mixed graphs and splitting off in digraphs, and prove the first conjecture in the (di-) Eulerian case(s). Beside that we solve a degree constrained non-uniform directed augmentation problem for di-Eulerian mixed graphs. © 1998 John Wiley & Sons, Inc. J Graph Theory 27: 213–221, 1998     

Enantioselective Allylic Substitution of Cyclic Substrates by Catalysis with Palladium Complexes of P,N-Chelate Ligands with a Cymantrene Unit

Mechanistic considerations made a decisive contribution to the development of new chiral P,N ligands L* containing tricarbonylcyclopentadienylmanganese (cymantrene). These ligands induce very high enantioselectivities (>99:1) in allylic substitutions of cyclic substrates 1 with formation of 2 (2-Bp=2-biphenylyl).     

Aminosubstituted disilanes: Synthesis by unsymmetrical and symmetrical reductive coupling

The reductive coupling of chlorotris(diorganylamino)silanes 1 with chlorotrimethylsilane by the action oflithium in THF provides for steric reasons, an easy access to unsymmetrical aminosubstituted disilanes (R₂N)₃Si-SiMe₃ 3. Similarly, cross-coupling to give pentakis(diethylamino)disilane 4 is observed between 1a and bis(diethylamino)chloro-hydridosilane 2a on treatment with lithium. In reactions of the less bulky bis(diorganylamino)chlorohy-dridosilanes 2 with ClSiMe₃ and Li, however, thesymmetrical coupling is preferred and affords SiH-functional substituted (R₂N)₃₂HSi-SiH(NR₂)₂ 5. Aminosubstituted disilanes 3–5 are useful starting materials for modification of disilanes or syntheses ofsilicon heterocycles via generation and trapping of aminosilylenes, as exemplified by diethylaminosilacyclopent-3-ene 6a. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:311–316, 1998