PROBLEMS OF SYNTHESIS OF TETRAHEDRAL ORGANOSILSESQUIOXANES - HYDROLYTIC CONDENSATION OF HEXAFUNCTIONAL BRANCHED ORGANOTETRASILOXANES

The hydrolytic condensation of methyltris(methyldichlorosiloxy)silane (Ib), methyl(la), and vinyltris(methyldiethoxysiloxy)silanes (Ic) in dilute homogeneous solutions was studied. It was found by X-ray diffraction and H-1 NMR methods that, irrespective of reaction conditions, only octaorganooctasilsesquioxanes (T-8), namely, octamethyloctasilsesquioxane and 1,4-divinylhexamethyloctasilsesquioxane, were obtained instead of the expected tetraorganotetrasilsesquioxanes (T-4). These data suggest that the condensation processes involved in the hydrolysis of 1a-c are predominantly intermolecular, and the molecules of the starting oligomers do not undergo rearrangements. Probably, the formation of T-4, whose molecules are built of four strained six-membered organosiloxane cycles, is less favorable thermodynamically than the formation of their homologs (T-8) built of eight-membered organosiloxane cycles.