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Two chemical routes were employed to prepare Si−Ti polymers, using acetylacetone (acacH) and acetic acid (HOAc) as modifying agents. The homogeneous and transparent sols were studied at different aging times. The characterization techniques were29Si NMR, FTIR, UV-Vis and TGA. When HOAc was used, the oligomeric species in the first stages of polymerization were assigned by29 Si NMR. The Ti−O−Si bond vibration was detected by FTIR in the 950–960 cm−1 region. UV-Vis spectroscopy showed bands of acac bonded to Ti at 300 nm and 365 nm, and OAc− bonded to Ti was found at 320 nm. The TGA study allowed the establishment of the xerogel formulas. [ABSTRACT FROM AUTHOR]