Polyaluminocarbosilane (PACS) was synthesized directly by the one-pot reaction of polydimethylsilane (PDMS) with aluminum acetylacetonate [Al(acac)(3)] in an autoclave. In this closed system, all the aluminum in Al(acac)(3) was converted into PACS. Therefore, the content of aluminum could be readily controlled quantitatively. On the basis of Fourier transform infrared, H-1-NMR, C-13-NMR, Si-29-NMR, and Al-27 magic-angle spinning NMR analysis, the reaction mechanism was proposed as follows: PDMS dissociated during pyrolysis to generate silicon free radicals, and then they reacted with Al(acac)(3) to yield PACS containing (Si-O)(n)Al groups (n = 4, 5, or 6). Mean while, these reactions resulted in the cleavage of O-C and/or O=C bonds in Al(acac)(3). Some of the free-radical fragments generated by this cleavage continued to react with the silicon free radicals and were incorporated into the structural units of PACS; the rest of them may have been converted into small oxygen-containing compounds, which were removed in the subsequent processing after the reactions. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113:3725-3731, 2009