Synthesis and characterization of water-soluble silsesquioxane-based nanoparticles by hydrolytic condensation of triethoxysilane derived from 2-hydroxyethyl acrylate

A new family of silsesquioxane-based nanoparticles was synthesized by hydrolytic condensation of a triethoxysilane precursor, R-Si(OCH2CH3)3, R = -CH2CH2CH2N(CH2CH2COOCH2CH2OH)2, derived from 2-hydroxyethyl acrylate. Condensation of the triethoxysilane precursor proceeded as a homogeneous system in methanol in the presence of hydrofluoric acid (HF) to afford water-soluble silsesquioxane-based nanoparticles, as confirmed by NMR, FT-IR, and elemental analyses. Scanning force microscopy (SFM) measurements indicated the formation of nanoparticles having a relatively narrow size distribution with an average particle diameter of less than 2.0 nm without aggregation. The size of the nanoparticles (1.7 nm) was determined by X-ray diffraction (XRD). The narrow polydispersity (Mw/Mn = 1.08) and a reasonable molecular weight (Mn = 3300), corresponding to species having 6-12 silicon atoms, were also confirmed by size-exclusion chromatography. Co-condensation of tetraethoxysilane (TEOS) with the triethoxysilane precursor was carried out under different feed ratios, and water-soluble products were obtained in the cases of TEOS molar ratios up to 70%. Thermal stability and the char yield were found to increase with increasing TEOS content in the feed, as determined by thermogravimetric analysis. The isolated nanoparticles distributed homogeneously without any aggregation were visualized by SFM, when the product was prepared at TEOS/triethoxysilane precursor = 50/50 mol %.