Hansen Solubility Parameters for Octahedral Oligomeric Silsesquioxanes

The Hansen Solubility Parameters (HSP) for several polyhedral oligomeric silsesquioxane (POSS) compounds were successfully determined, demonstrating the applicability of the HSP approach for selected types of organic–inorganic compounds. As commonly practiced with organic polymers, a set of simple “pass/fail” tests for complete solubility at a fixed concentration (100 mg/mL) was conducted for an array of five octameric POSS compounds, octa(phenethyl), octa(styrenyl), octa( iso butyl), octakis(hexafluoro iso butyl), and (1-naphthyl)heptaphenyl), and 45 test solvents. Group contributions for the octameric POSS cage were determined using three different approaches, which produced similar results. The best cage contribution estimate for the dispersive, polar, and hydrogen-bonding components δ D, δ P,, and δ H of the total solubility parameter was determined to be δ D = 22 (J/cc) 1/2, δ P = 19 (J/cc) 1/2, and δ H = 15 (J/cc) 1/2, with an estimated uncertainty of approximately 5 (J/cc) 1/2 . The utility of the HSP approach was demonstrated by successfully identifying mixtures of poor solvents that provided significantly enhanced solubility for octa( iso butyl) POSS, and by successfully estimating the HSP of octakis(trifluoropropyl) POSS from group contributions derived solely from aromatic POSS compounds.