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

摘要

The synthesis of polyaluminocarbosilane (PACS) using liquid polysilacarbosilane (PSCS) and aluminum acetylacetonate [Al (acac)(3)] by a high-pressure method is reported for the first time. The effects of reaction time, temperature and feed ratio on the structure of PACS are investigated in detail by gel permeation chromatography, Fourier transform-infrared, H-1-NMR, Si-29-NMR and Al-27-NMR methods. It was found that the molecular weight and its polydispersity, as well as the branching degree of the molecular structure of PACS, increase with reaction time and temperature. Increasing the weight percentage of Al (acac)(3) has a similar effect as temperature. Combined with the gas chromatography-mass spectroscopy results, the reaction mechanism is proposed, which contains three main reactions: (i) cleavage and rearrangement reaction of PSCS; (ii) silicon-free radicals react with Al (acac)(3), leading to cleavage of O=C and/or O-C bonds and formation of AlOx ligands; and (iii) conversion reaction of Al ligands from AlO6 into AlO5 and AlO4. It is also found that PACS prepared by high-pressure method has a lower branched molecular structure in comparison to its analog prepared under ambient pressure conditions, and it is achieved to increase the molecular weight and ceramic yield of PACS, which is beneficial for the processing and overall quality of the final product.