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

Lookup NU author(s): Dr Ross Harrington, Emeritus Professor Bill Clegg

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Abstract

The homologous series of octa-n-alkylsilsesquioxanes (n-alkylPOSS) was prepared by hydrosilylation of octahydrido-octasilses-quioxane H8T8 with terminal n-alkenes in good yields (n = 2-18). The compounds were characterized by NMR spectroscopy (H-1, C-13, Si-29), MALDI-TOF 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-even 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 degrees C. Pyrolysis-gas chromatography/mass spectrometry has been used to elucidate the thermal degradation process of T-8(n-CnH2n+1)(8) (n = 11 and 18). Thermal cracking along the whole alkyl chain was observed rather than simple loss of the complete arm.


Publication metadata

Author(s): El Aziz Y, Bassindale AR, Taylor PG, Stephenson RA, Hursthouse MB, Harrington RW, Clegg W

Publication type: Article

Publication status: Published

Journal: Macromolecules

Year: 2013

Volume: 46

Issue: 3

Pages: 988-1001

Print publication date: 01/02/2013

ISSN (print): 0024-9297

ISSN (electronic): 1520-5835

Publisher: American Chemical Society

URL: http://dx.doi.org/10.1021/ma302229v

DOI: 10.1021/ma302229v


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