Octa(3-mercaptopropyl)octasilsesquioxane – A reactive nanocube of unique self-assembled packing morphology

• The role of thiol moieties in the synthesis of octa(3-mercaptopropyl)octasilsesquioxane is elucidated.
• Rod-like geometry of the molecule and self-assembling of side groups affect crystalline packing morphology.
• Solid-solid and solid-liquid mesomorphic transitions were observed for crystalline octa(3-mercaptopropyl)octasilsesquioxane.

The synthesis of octa(3-mercaptopropyl)octasilsesquioxane (γHS-POSS) was studied with a special regard to factors determining the yield of octahedral product (acidity of the reaction medium and solvation of primary oligomeric species). The role of thiol moieties as effective acidic catalysts accelerating the hydrolysis of (MeO)3SiCH2CH2CH2SH was explained. Nucleophilic thiol groups were also found to be appreciably reactive towards polar aprotic solvents (acetone, acetonitrile). Isolation of γHS-POSS by preparative size exclusion chromatography (SEC) was proposed as an effective and safe purification method.Orthogonal alignment of side 3-mercaptopropyl substituents yields a rod-like geometry of the molecule and affects the packing morphology of crystalline γHS-POSS as revealed by X-ray diffraction. Self-assembling of side groups allows for the formation of a specific nanostructure of a long-range order. Several specific solid-solid (rotor phase and crystallographic transition) and solid-liquid phase transitions were detected for γHS-POSS using thermal (DSC) as well as optical (POM) techniques.

Nucleophilic thiol moieties are involved as catalytic species in the synthesis of octa(3-mercaptopropyl)octasilsesquioxane (γHS-POSS), and exhibit a substantial reactivity towards polar aprotic solvents. Rod-like geometry of the isolated molecules of γHS-POSS and self-assembling of side groups affect crystalline packing morphology and result in specific solid-solid mesophase transitions.Figure optionsDownload as PowerPoint slide