Organofunctional silica aerogels

Abstract

Abstract. Organically modified silica aerogels were prepared from mixtures of tetramethoxysilane (TMOS) and organofunctional alkoxysilanes RSi(OMe)3 with R = mercaptopropyl, diphenylphosphinoethyl and chloropropyl. The base catalyzed hydrolysis and condensation reactions, followed by supercritical drying with liquid carbon dioxide were investigated. Starting from 9 : 1 mixtures of TMOS and RSi(OMe)3, incorporation of the functional moieties succeeded quantitatively. Increasing the percentage of RSi(OMe)3 to 20% or 40% leads to an incomplete condensation of the RSiOI,s units to the SiO2 network. Compared with an unmodified silica aerogel, the microstructure of the resulting hybrid aerogels is nearly uninfluenced for the 9 : 1 mercapto-and chloro-modified samples, while in the phosphino-modified sample the typical pore radii distribution is disturbed by the bulky organic groups. The organofunctional aerogels decompose between 210 and 650~

Influence of silica derivatizer and monomer functionality and concentration on the mechanical properties of rapid synthesis cross-linked aerogels

“…7d), all peaks associated with the organics nearly vanished, indicating that the derivatizing moiety and polymer were completely oxidized and burned off. Weight loss was of about 10% in sample N1 due to desorption of water adsorbed on the hydrophilic silica surfaces [36], and, possibly, to solvent residues [37]. Sample D6 exhibited a weight loss of about 80%.…”

Hydrolysis–condensation reactions of diethylphosphato-ethyltriethoxysilane with tetraethoxysilane studied by 29Si-NMR: Solvent and phosphonate catalytic effect

“…Moreover, organo-modified alkoxysilanes have been attracting considerable attention because of the potential applications they offer as they represent a very direct manner to introduce organic functions in a silica network during sol-gel synthesis [7][8][9][10]. For example, Hüsing et al [11] prepared organically modified silica from mixtures of TMOS and organofunctional alkoxysilanes RSi(OMe) 3 with R = mercaptopropyl, diphenylphosphinoethyl and chloropropyl. They evidenced the influence of the functional groups on the condensation reaction and on the porosity of the final silica.…”

Silicone‐Based Organic–Inorganic Hybrid Aerogels and Xerogels

“…However, increasing the MTMS ratio to >40 % decreases the degree of condensation, and >80 % MTMS did not give any monolithic gels. Organofunctional aerogels were prepared in a base‐catalyzed manner from similar co‐precursor systems containing a mercaptopropyl, diphenylphosphinoethyl or chloropropyl functional group on the tri‐functional alkoxysilane . In these cases, a quantitative incorporation of organic groups was confirmed when 10 % of an organotrialkoxysilane is involved, and increasing ratios discourage polycondensation and decrease the transparency, except for the case of the chloropropyl group.…”