Supramolecular organogel of polyureas containing POSS units in the main chain: dependence on the POSS and comonomer structures

para-Substituted bis(3-aminopropyl)hexaisobutyl-cage octasilsesquioxane (T8 cage) (1) was polymerized with several diisocyanates; methylenediphenyl 4,4’-diisocyanate (2a), 4,4’-diisocyanato-3,3’-dimethylbiphenyl (2b), m-xylene diisocyanate (2c), 1,3-bis(isocyanatomethyl)cyclohexane (2d), tolylene-2,4-diisocyanate (2e), and tolylene-2,6-diisocyanate (2f), at room temperature to prepare T8-polyureas (3). Gel formation was observed immediately during the addition of 2 to the solution of 1 when above the critical gel concentrations (Cgs). T8-polyureas with phenylurea moieties, 3a, 3b, 3e, and 3f, promoted organogel formation in comparison with T8-polyureas with nonphenylurea moieties, 3c and 3d. The substitution of methyl groups at the ortho position of the phenylurea groups provided lower Cgs. FT-IR analysis suggests that increasing the intermolecular hydrogen bonding between the ureido groups in T8-polyurea enhanced the organogel formation. We also studied the POSS structure-dependent properties of the polyureas, in which the T8 cages were replaced by double-decker-shaped phenyl-substituted silsesquioxane (DDSQ) units. Polymerization was conducted at various concentrations, and it was found that no organogels were formed below the solubility limit of the monomers except when 2f was used. This observation suggests that the polyureas containing the isobutyl-substituted T8 units promoted organogel formation in comparison with those containing DDSQ units.