Organosilicas with Covalently Bonded Groups under Thermochemical Treatment

Abstract

Silica-based hybrid materials having covalently immobilized vinyl (SiO 2 -C 2 H 3 ), chloropropyl (SiO 2 -R-C1), trimethylsilyl (SiO 2 -SiMe 3 ), ethyl sulfonic acid (SiO 2 -R-SO 3 H), and aminopropyl (SiO 2 -R-NH 2 ) groups, as well as the salt of the latter with HNO 3 (SiO 2 -R-NH 2 ·HNO 3 ) were studied by different thermoanalytical methods: thermogravimetry (TGA), differential thermal analysis (DTA), and temperature-programmed desorption mass spectrometry (TDP-MS). It was demonstrated that TPD MS can be successfully used for the investigation of the interfacial layer in such materials. Particularly, it was shown that a side reaction between the grafted group and aromatic solvents is possible during the preparation of SiO 2 -C 2 H 3 and SiO 2 -R-C1. For SiO 2 -SO 3 H the formation of 2-Si-ethanesulfonic, 1-Si-ethanesulfonic, and 2,4-Si-butanesulfonic acid grafted groups with the predominance of the 2-Si isomer was found. The process of SiO 2 -NH 2 ·HNO 3 decomposition at 500 K may be applied for the preparation of silica modified by aldehyde groups. Mechanisms of thermal transformations of bonded layer were established and the key role of the reactions of grafted groups with silanols in such processes was demonstrated. As was found for SiO 2 -R-C1 and SiO 2 -R-NH 2 , the decomposition process with participation of silanols is realized in two stages. The first one occurs in the 400-700 K range and includes the interaction between organic groups and the neighboring silanol. The second decomposition stage occurs above 700 K and includes migration of the bonded groups on the silica surface.