Formation of supramolecular gels by self-assembly of dumbbell-shaped polyhedral oligomeric silsesquioxane derivatives linked with bisurea groups

Abstract We studied the supramolecular gelation abilities of dumbbell-shaped polyhedral oligomeric silsesquioxane (POSS) derivatives (3a to e), which were prepared from 3-aminopropyl-heptaisobutyl-substituted POSS (1) with 1,4-phenylene diisocyanate (2a), hexamethylene diisocyanate (2c), 4,4′-methylenebis(phenyl isocyanate) (2d), and 4,4′-methylenebis(cyclohexyl isocyanate) (2e), respectively. Four turbid supramolecular organogels were formed after the homogeneous solution was obtained by heating: 3a in 1,2-dichloroethane (Gel A), 3b in 1-chlorobutane (Gel B), 3d in o-dichlorobenzene (Gel C), and 3d in 1-chlorobutane (Gel D). Xerogels A, B, C, and D were prepared by removing the solvent form Gels A, B, C, and D, respectively. X-ray diffractometry analysis showed that sharper diffraction peaks were observed for Xerogels A, C, and D compared to their corresponding powder states, and a new peak was identified on the small angle region, suggesting the formation of lamellar structures. The wide-angle X-ray scattering measurements of Xerogels C and D exhibited the primary peaks as well as the secondary to quaternary peaks, confirming the formation of stacking-layer structures. Our findings provide a new method for controlling the self-assembly and packing of POSS units.