Supramolecular organogel formation behaviors of beads-on-string shaped poly(azomethine)s dependent on POSS structures in the main chains

Beads-on-string-shaped polymers incorporating cage silsesquioxanes in the main chain, especially double-decker-shaped phenyl-substituted silsesquioxanes (DDSQ), have received significant attention in the past few decades. Difunctionalized isobutyl-substituted cage octasilsesquioxanes (T 8 ) have also been generating this type of polymer architecture. However, direct comparisons between main-chain-type polymers comprising phenyl-substituted DDSQ and isobutyl-substituted T 8 units have seldom been reported. In this study, we prepared bis(3-aminopropyl)-DDSQ ( 6 ) via the hydrosilylation of 3,13-dihydrooctaphenylhexacyclodecasiloxane (dihydro-DDSQ) with t -butyl N -allylcarbamate and deprotection with trifluoroacetic acid. Both para -bis(3-aminopropyl)hexaisobutyl-substituted T 8 cage ( 1 ), which was developed by us, and 6 were polymerized with terephthalaldehyde ( 2a ), isophthalaldehyde ( 2b ), and 4,4′-oxydibenzaldehyde ( 2c ) to produce the corresponding T 8 -poly(azomethine)s ( 3a-c ) and DDSQ-poly(azomethine)s ( 7a-c ), respectively. Although precipitates were observed when the polymerization solution of 7 was concentrated under reduced pressure, 3 underwent organogel formation. Solubility test results for heptaisobutyl-hydride-POSS ( 8 ) and dihydro-DDSQ ( 9 ) as model compounds for the POSS units in 3 and 7 , respectively, suggested that the wider solubility spectrum of the isobutyl-substituted T 8 moieties in 3 may provide a suitable balance for organogel formation, and the narrower spectrum of solubility for the phenyl-substituted DDSQ moieties in 7 may prevent the existence of a specific solvent region for suitable balanced gel formation. The concentration ( c ) dependences of zero shear relative viscosity ( η 0,r ) for the polymerization solutions of 3a-c , containing various linker structures were well described by an equation with a single value of the characteristic exponent using different values of gelation threshold concentration. Organogel formation was observed for isobutyl-substituted cage octasilsesquioxane (T 8 ) in the main-chain type polyazomethines, while precipitates instead of gel formation were observed for phenyl-substituted double-decker-shaped silsesquioxanes (DDSQ)-poly(azomethine)s.