Silicon-Stille coupling

Further elements of the periodic system will be incorporated into the core, branches, and periphery of dendrimers. High-purity dendritic silicones still appear to be absent. Whereas purely aromatic dendritic hydrocarbons have been described, aliphatic CxHy dendrimer are hardly known. This will require efficient non-symmetrical C-C coupling reactions posing a challenge to develop fundamentally new synthetic approaches yielding minimal amounts of byproducts. 

Probably the most efficient flame retardant system ever discovered for a polymer is platinum, which at 1 ppm flame retards silica-filled silicones and increases unbumed residue (Fig. 6). In a very thorough study by MacLaury at GE (37), platinum was shown to exert a catalytic action to induce coupling between chains and with the filler. The detailed mechanism is still uncertain nevertheless, the remarkable efficacy of platinum in this system supports the idea that very efficient f.r. agents may be designed by using catalysis principles. 

Oscillations have been observed in chemical as well as electrochemical systems [Frl, Fi3, Wol]. Such oscillatory phenomena usually originate from a multivariable system with extremely nonlinear kinetic relationships and complicated coupling mechanisms [Fr4], Current oscillations at silicon electrodes under potentio-static conditions in HF were already reported in one of the first electrochemical studies of silicon electrodes [Tul] and ascribed to the presence of a thin anodic silicon oxide film. In contrast to the case of anodic oxidation in HF-free electrolytes where the oscillations become damped after a few periods, the oscillations in aqueous HF can be stable over hours. Several groups have studied this phenomenon since this early work, and a common understanding of its basic origin has emerged, but details of the oscillation process are still controversial. 

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