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.