Silsesquioxane-based nanoparticles formed via hydrolytic condensation of organotriethoxysilane containing hydroxy groups

Silsesquioxanes-based nanoparticles synthesized by hydrolytic condensation of a functionalized precursor, N,N-di(2,3-dihydroxypropyl)(aminopropyl)triethoxysilane, (HOCH2CH(OH)CH2)(2)NCH2CH2CH2Si(OCH2CH3)(3), were characterized using MALDI-TOF MS, NMR, elemental analysis, FT-IR, transmission electron microscopy (TEM), and scanning force microscopy (SFM). MALDI-TOF MS analysis indicated that the product consists of many species having 12-18 Si atoms with different numbers of intramolecular cyclizations, and Si-O-C bonds are formed through the reaction of SiOH (or SiOEt) groups with the hydroxyl functionalities of an organic moiety bonded to a Si atom. The species having high number of intermolecular cyclization (f greater than or equal to 0.5 at 10 greater than or equal to n greater than or equal to 7) were predominantly detected, suggesting that the product mainly consists of complete and incomplete cagelike structures. The chemical composition of the product was consistent with that calculated from the structure, (R-SiO1.5)(n), indicating that the nanoparticles belong to a family of silsesquioxanes characterized by a ratio of 1.5 between the silicon and oxygen atoms. Reasonable NMR and FT-IR spectra were observed, corresponding to the structure assuming that majority of the alkyl chain attached on a Si atom was intact during the hydrolytic condensation. The resulting particles have relatively narrow size distribution with average particle diameter less than 3.0 nm, as confirmed by TEM and SFM.