A Non-Hydrolytic Sol–Gel Route to Organic-Inorganic Hybrid Polymers: Linearly Expanded Silica and Silsesquioxanes

Condensation reactions of chlorosilanes (SiCl(4) and CH(3)SiCl(3)) and bis(trimethylsilyl)ethers of rigid, quasi-linear diols (CH(3))(3)SiO–AR–OSi(CH(3))(3) (AR = 4,4′-biphenylene (1) and 2,6-naphthylene (2)), with release of (CH(3))(3)SiCl as a volatile byproduct, afforded novel hybrid materials that feature Si–O–C bridges. The precursors 1 and 2 were characterized using FTIR and multinuclear ((1)H, (13)C, (29)Si) NMR spectroscopy as well as single-crystal X-ray diffraction analysis in case of 2. Pyridine-catalyzed and non-catalyzed transformations were performed in THF at room temperature and at 60 °C. In most cases, soluble oligomers were obtained. The progress of these transsilylations was monitored in solution with (29)Si NMR spectroscopy. Pyridine-catalyzed reactions with CH(3)SiCl(3) proceeded until complete substitution of all chlorine atoms; however, no gelation or precipitation was found. In case of pyridine-catalyzed reactions of 1 and 2 with SiCl(4), a Sol–Gel transition was observed. Ageing and syneresis yielded xerogels 1A and 2A, which exhibited large linear shrinkage of 57–59% and consequently low BET surface area of 10 m(2)⋅g(−1). The xerogels were analyzed using powder-XRD, solid state (29)Si NMR and FTIR spectroscopy, SEM/EDX, elemental analysis, and thermal gravimetric analysis. The SiCl(4)-derived amorphous xerogels consist of hydrolytically sensitive three-dimensional networks of SiO(4)-units linked by the arylene groups. The non-hydrolytic approach to hybrid materials may be applied to other silylated precursors, if the reactivity of the corresponding chlorine compound is sufficient.