Self-assembly of a bridged silsesquioxane containing a pendant hydrophobic chain in the organic bridge

ROMEO H. E.; FANOVICH, M. A.; WILLIAMS, R. J. J.; MATÌJKA, L.; PLEšTIL, J.; BRUS, J.

MACROMOLECULES

Año: 2006

0024-9297

Bridged silsesquioxanes are a family of organic-inorganic hybrid materials prepared by the polycondensation of monomers containing an organic bridging group joining two (or eventually more) trialkoxysilyl or trichlorosilyl groups. The aim of this study was to synthesize and characterize the self-assembly of a new family of bridged silsesquioxanes containing a hydrophobic pendant chain on the organic bridge. The precursor of this hybrid was obtained by the reaction of glycidoxypropyl(trimethoxysilane) (GPMS) (2 moles) with dodecylamine (1 mol). Polycondensation was produced with formic acid, either in mass or using tetrahydrofuran or isopropanol as solvents. A glassy material was obtained that was characterized by 29Si NMR, FTIR, SAXS, WAXS, SEM and HRTEM. 29Si NMR, FTIR and WAXS revealed the formation of a ladder configuration of the inorganic domains.  SAXS and WAXS spectra showed the presence of a correlation distance of 34 Å between the scattering inorganic domains that corresponds to the length of a tail-to-tail association of two dodecylamine chains. Based on these results a model of the self-assembled structure was proposed. A basic unit with an H-shape structure is generated by the piling up of precursor molecules due to the self-assembly by tail-to-tail associations of hydrophobic chains (central part of the H). In turn, these H-shape structures are self-assembled by the interaction among the inorganic domains present in the extremes. The reaction of neighboring SiOH groups produces the ladders that covalently bond the self-assembled structures. Due to the presence of pendant hydrophobic chains, the precursor of this new type of organic-inorganic hybrid material may be used for the dispersion and nanostructuration of hydrophobic molecules or of nanoparticles stabilized by hydrophobic chains.