Ein Synergetischer Effekt bei Chlorierungen von Silicagel bzw. Metakaolin mit gasförmigen,Aluminiumchlorid enthaltenden Chlorierungsmitteln

A Synergetic Effect in Chlorination of Silicagel and Metakaolin with Aluminium Chloride Containing Chlorinating Agents The reactivity of silicagel with CCl₄, C₂Cl₆, C₂Cl₄, COCl₂, S₂Cl₂/Cl₂, and Cl₂/carbon is low up to 1000 K. Aluminium chloride under these conditions is a little more reactive above 600 K. But gaseous mixtures of aluminium chloride with CCl₄, C₂Cl₆, and S₂Cl₂/Cl₂ resp., show a synergetic effect: They attain conversion grades much higher than the sum of those obtained with each of the single components. The reactivity of aluminium chloride/CCl₄ mixtures with silicagel in dependence on temperature and partial pressure has been followed. Metakaolin is reacted by such a mixture synergetically and with increased silicate conversion. Practical consequences of this effect are demonstrated and essential phenomena involved in metakaolin chlorination are explained. A mechanistic model of the synergetic effect has been developed.     

A cyclographic approach to the vertices of plane curves

For a closed plane curve the centers of distance functions are considered satisfying the condition that the function attains at least two absolute minima along. From the topology of the closure of this set some information on specific vertices of the curve can be obtained. If a simply closed curve has a finite number of vertices only, then the structure of this set is given by a tree, composed from regular arcs, such that the end points of this tree belong to minimal osculating circles of, which entirely are located in the interior of. Furthermore, the curve can be reconstructed from this set as the envelope of a suitable family of circles. These relations are used to give alternative proofs and extensions of several known vertex theorems for closed curves.Dedicated to N. Stephanidis on occasion of his 65. birthday     

Thermische Beständigkeit von linearen Polyisoprenen unterschiedlicher Kettenlänge

Zusammenfassung An einer polymerhomologen Reihe von linearen Polyisoprenen mit Molekulargewichten zwischen 40000 und > 10⁷ wurde im Festzustand und in L?sung die Abh?ngigkeit der thermischen Stabilit?t von der jeweiligen Kettenl?nge untersucht. Es zeigte sich, da? die zum Zerbrechen der Makromoleküle notwendigen Temperaturen mit steigendem Molekulargewicht deutlich abnehmen und für Polyisoprene mit Molekulargewichten > 10⁷ bei Raumtemperatur liegen.

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Summary The dependence of thermal stability from the molecular weight of linear macromolecules was tested using polyisoprenes with m. w. between 40000 and > 10⁷. We could demonstrate that the temperatures at which molecular fractures occur, decrease with increasing chain length and approach room temperature at molecular weights of about 10⁷.

     

Electron-transfer polymers. XXXIV. Redox polyurethanes from p-benzoquinone-2,5-diols and diisocyanates

It is possible to prepare polyurethanes from p-benzoquinone-diols and diisocyanates by using dibutyltin diacetate catalyst at room temperature or below, since the benzoquinone group does not react with isocyanate under these conditions. This permits preparation of new redox polymers. In preparing the polyurethanes excess isocyanate groups must be destroyed at the end of the reaction time in order to prevent crosslinking during work-up. These polymers are readily reduced by aqueous hydrosulfite. Good viscosity numbers are obtained; and, in general, upon reduction the viscosity increases over that of the oxidized form. There is no evidence of crosslinking. When oxidized and reduced forms of these polymers are mixed there is no evidence of charge transfer.     

Soft vesicles formed by diblock codendrimers of poly(benzyl ether) and poly(methallyl dichloride)

The synthesis of a block codendrimer (g3-PBE-b-g3-PMDC), composed of a third-generation poly(benzyl ether) (PBE) monodendron and an aliphatic polyether (PMDC) monodendron is reported. In THF/diiospropyl ether (1:1) the PMDC block functions as a "hydrophilic" block, while the PBE acts as a "hydrophobic" block. The codendrimer can form interdigitated layers leading to vesicle formation. Tapping mode atomic force microscopy (AFM), dynamic light scattering (DLS), and transmission electron microscopy (TEM) were used to characterize the vesicles. The effect of molecular architecture on the formation of the interdigitated layers and vesicles was studied.