X-ray Crystal Structures, Packing Behavior, and Thermal Stability Studies of a Homologous Series of n-Alkyl-Substituted Polyhedral Oligomeric Silsesquioxanes

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• 作者：Youssef El Aziz ; Alan R. Bassindale ; Peter G. Taylor ; Richard A. Stephenson ; Michael B. Hursthouse ; Ross W. Harrington ; William Clegg
• 刊名：Macromolecules
• 出版年：2013
• 出版时间：February 12, 2013
• 年：2013
• 卷：46
• 期：3
• 页码：988-1001
• 全文大小：790K
• 年卷期：v.46,no.3(February 12, 2013)
• ISSN：1520-5835

文摘

The homologous series of octa-n-alkylsilsesquioxanes (n-alkylPOSS) was prepared by hydrosilylation of octahydrido-octasilsesquioxane H₈T₈ with terminal n-alkenes in good yields (n = 2鈥?8). The compounds were characterized by NMR spectroscopy (¹H, ¹³C, ²⁹Si), MALDI鈥揟OF and ESI MS. Most of them have also been characterized using X-ray crystallography, including some polymorphs. The packing systems of the octa-n-alkylsilsesquioxanes are reported. Two types of packing have been observed, rod-like and disk-like (interdigitated). Some n-alkylPOSS crystals were formed in which the chains are tilted away from the axes of the cubic core. It was also observed that as alkyl-chains are flexible they can take up a variety of conformations. Melting points of the homologous series showed an odd鈥揺ven alternating effect for alkyl chains longer than four CH₂ units. The TGA of n-alkylPOSS under nitrogen showed that the thermal stability temperatures are between 200 and 400 掳C. Pyrolysis-gas chromatography/mass spectrometry has been used to elucidate the thermal degradation process of T₈(n-C_nH_2n+1)₈ (n = 11 and 18). Thermal cracking along the whole alkyl chain was observed rather than simple loss of the complete arm.