COMPOSITES OBTAINED BY THE HYDROLYSIS OF TETRAACETOXYSILANE IN THE PRESENCE OF POLY(ETHYLENE GLYCOL) AS A MACROMOLECULAR MATRIX

Composites based an PEG and polysilicic acid were prepared by the hydr olysis of tetraacetoxysilane in benzene solutions of PEC as a macromol ecular template. In dilute solutions of PEG, the reaction products pre cipitate. The precipitate incorporates the entire amount of polysilici c acid formed and, depending on the initial molar ratio z between PEG and tetraacetoxysilane, all PEG or only a part of it. At z > 2, the pr oduct composition corresponds to a molar ratio between PEG and polysil icic acid equal to two, whereas excess PEG stays in solution, At z < 2 , the product composition corresponds to the composition of the initia l mixture. In semidilute solutions of PEG, the reaction proceeds via g elation, which takes place when the amount of water added to the syste m is sufficient to hydrolyze similar to 40% of the SiOAc bonds, The hy drolysis of tetraxetoxysilane proceeds in a stepwise manner and is lim ited by the absorption of water from the gas phase. Two PEG fractions were identified in the composites obtained. One fraction decomposes at 150 degrees C, whereas the other fraction decomposes at significantly higher temperatures than pure PEG (220 degrees C). The structure of t he obtained composites is discussed.