Thermal Properties of the Homologous Series of 8-fold Alkyl-Substituted Octasilsesquioxanes

The homologous series of 8-fold alkyl-substituted octasilsesquioxane has been prepared by hydrosilation of alkenes with octakis(hydridosilsesquioxane) (HSiO3/2)8. Ethene, propene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, and 1-decene were employed either in bulk or in toluene solution. The homologous series of 1,3,5,7,9,11,13,15-octaalkylpentacyclo[9.5.1.13,9.15,15.17,13]octasiloxanes, which are interesting model compounds for silsesquioxane-based materials was characterized by 1H, 13C, and 29Si NMR spectroscopy, IR and mass spectroscopy, and elemental analysis. Melting points of the compounds were studied by DSC, revealing a strong decrease of the melting point from the octapropyl-substituted T8 to the octapentyl derivative. Melting points for derivatives with longer n-alkyl chains showed an odd−even effect. TGA evidenced thermal stability under nitrogen up to temperatures between 200 and 400 °C and under air up to temperatures between 200 and 250 °C.