Non-symmetrical Bis-silylated Precursor Can (Also) Self-Direct the Assembly of Silsesquioxane Films

International audienceSymmetric α,ω-bis-silylated precursors are the standard building blocks of self-assembled bridged silsesquioxanes, a unique class of robust ordered nanomaterials prepared by sol-gel process without external surfactant. We report an unprecedented approach based on the utilization of a dissymmetric bis-silylated precursor, 1,2-bis(trimethoxysilyl)decane (1), in which the two alkoxy groups are carried by adjacent methylene groups. Extensive characterization—based on X-ray diffraction, real-time fourier transform infrared, electron and optical microscopy, 29Si solid-state nuclear magnetic resonance, thermogravimetry, and molecular modeling—shows surprisingly that such non-symmetrical precursor is highly conducive to achieve highly ordered lamellar mesostructure, able to sustain temperature up to 120 °C. To emphasize the effect of the alkoxy group functionality and position, comparison is made systematically with analogous silsesquioxanes derived from bis-(2) and mono-silylated (3) precursors. The sol-gel polymerization of 1 is unique by its ability to produce a homogeneous film possessing structural characteristic on multiple scales: uniform microcrystallites consisting of nanolamellar organosilica hybrid material. The most likely mesostructure consists of bilayers of slightly interpenetrated trans C8H9 chains, with a single central siloxy-hydrocarbon chain (Si2O(OH)4-C2H3) n . To permit a good lateral chain packing, the hydrocarbon chain of two adjacent silicon atoms point in opposite directions