Silsesquioxane-Based Nanoparticles Formed via Hydrolytic Condensation of Organotriethoxysilane Containing Hydroxy Groups

Abstract

Silsesquioxanes-based nanoparticles synthesized by hydrolytic condensation of a functionalized precursor, N,N-di(2,3-dihydroxypropyl)(aminopropyl)triethoxysilane, (HOCH2CH(OH)CH2)2NCH2CH2CH2Si(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 ≥ 0.5 at 10 ≥ n ≥ 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.