Synthesis, characterization, and polycondensation of new stable α,ω-organo(bis-silanediols)

The synthesis and characterization of stable bis(dihydroxymethylsilyl) derivatives are described. These compounds were obtained as microcrystalline powders by controlled hydrolysis in a biphasic medium (ethyl ether – water) of the corresponding bis(dimethoxymethylsilyl) organic precursors containing phenyl, biphenyl, stilbenyl, diphenyl acetylene, and diphenylbut-1,3-diyne groups. All the solids obtained exhibited a layered structure. Condensation of the bis-silanediols could be effected by fluoride catalysis in solution at ambient temperature or simply by heating in solid state. The polysiloxanes obtained from the bis-silanediols have been compared with those obtained by hydrolysis–polycondensation of the corresponding bis-dimethoxysilanes. The thermal route led to highly polycondensed solids arranged into thin plates as evidenced by TEM analysis; furthermore, in the case of the longer spacer, the organization was controlled by the arrangement of the Si-O-Si layers instead of the spacer. The X-ray study of these materials clearly evidenced the drastic influence of the length of the organic spacer, the polycondensation route and the nature of the leaving group (hydroxy or methoxy) on the short-range organization of the solids.