Method for preparing polyaluminocarbosilane

Abstract

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, 1H‐NMR, 13C‐NMR, 29Si‐NMR, and 27Al 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)nAl groups (n = 4, 5, or 6). Meanwhile, 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. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Synthesis of polyaluminocarbosilane with low branched molecular structure using liquid polysilacarbosilane and aluminum acetylacetonate by high‐pressure method

“…Therefore, only the PACS in solid state are analyzed in this work, and the 27 Al MAS NMR spectra are shown in Figure S3 in the Supporting Information. Three peaks located at about 0, 32 and 55 ppm are observed in the PACS, which are assigned to octahedral AlO 6 , pentacoordinated AlO 5 and tetrahedral AlO 4 , respectively . From the 29 Si‐NMR results and the later analysis, we can infer that the AlO x (x = 4, 5, 6) sites mainly exist via Al‐O‐Si bonds.…”

“…It can also be seen that the Si‐CH 2 ‐Si absorption intensity at 1350 cm −1 gradually increases with reaction time, while Si‐CH 3 at 1410 cm −1 becomes weaker, indicating more Si‐CH 2 ‐Si bonds form during the reaction process. However, the structural information of Al in PACS is not detectable in the spectra, maybe because the content of Al in PACS is too low, or the absorption of Al‐X (X = Si, O or C) overlaps with other existing peaks …”

“…However, the structural information of Al in PACS is not detectable in the spectra, maybe because the content of Al in PACS is too with other existing peaks. [7,11] According to the Lambert-Beer law, the relative contents of Si-H and Si-CH 2 -Si bonds in the polymers can be estimated by the absorption ratios of the peak at 2100 cm −1 (Si-H) and 1020 cm −1 (Si-CH 2 -Si) to the peak at 1250 cm −1 (Si-CH 3 ), respectively. The results are presented in Figure 4.…”

“…The broad peak between −140 and −75 ppm is due to SiO 2 in the glass NMR tube. The signal situated at 5-20 ppm in PACS is attributed to the SiC 3 O group, [11] which may come from the reaction of the formed silicon free radicals and Al (acac) 3 . It can be seen from the figure that the peak for SiC x Si 4-x decreases significantly at the beginning of the reaction, indicating the Si-Si bond cleavage occurs, consistent with the FT-IR and 1 H-NMR results.…”

“…[8][9][10] PSCS is a lowmolecular-weight compound having Si-Si and Si-CH 2 -Si linkage in the backbone, which can be prepared by thermal decomposition of polydimethylsilane (PDMS). PACS can also be synthesized using PDMS [11] or low-softening-point polycarbosilane [12] with Al (acac) 3 in an autoclave, where the sublimation of Al (acac) 3 may be alleviated significantly or even avoided, and the content of aluminum in PACS can be controlled readily. This is important because aluminum plays a role as a sintering aid in densifying the structure and suppressing grain growth of the SiC fiber during pyrolysis and sintering process.…”