Layered assembly of alkoxy-substituted bis(trichlorosilanes) containing various organic bridges via hydrolysis of Si-Cl groups

Monoalkoxy derivatives of bis(trichlorosilanes) containing methylene, ethylene, and phenylene bridges (Cl₃Si-R′-SiCl ₂OC₁₆H₃₃, R′ = -CH₂-, -C ₂H₄-, -C₆H₄-) were synthesized and self-assembly of the amphiphilic hydrolyzed species ((HO)₃Si- R′-Si(OH)₂OC₁₆H₃₃) was investigated. Hydrolysis of all Si-Cl groups was confirmed by liquid-state ²⁹Si and ¹³C NMR while the alkoxy groups were retained. The self-assembly was induced either by casting the hydrolyzed solutions on glass substrates or by cooling. The structures of the products were characterized by X-ray diffraction (XRD), electron microscopies (TEM and SEM), and solid-state ²⁹Si and ¹³C NMR. The products obtained from methylene- and ethylene-bridged monomers have lamellar structures consisting of bridged polysilsesquioxane layers and all-trans hexadecanol layers, which means that alkoxy groups were cleaved during polycondensation. The large difference in the d values of these hybrids (5.84 nm and 3.40 nm) suggests the variation in the arrangement of hexadecanol molecules within the layers. In contrast, the phenylene-bridged monomer afforded a lamellar solid (d = 5.14 nm) consisting of monomeric species, where both silanol groups and alkoxy groups mostly remain intact. This is attributed to the relatively stronger interaction and hydrogen-bonding networks between hydrolyzed species.