Monitoring structural evolution of organosilicate species during sol-gel processes by electrospray ionization mass spectrometry

RATIONALE: Electrospray ionization mass spectrometry (ESI-MS) has been employed to study species distribution in controlled acid-catalyzed hydrolysis and condensation of (3-chloropropyl) trimethoxysilane (CPTMS), which is frequently used in the synthesis of hybrid silica-based materials. METHODS: The conditions of analysis for reaction products, i.e. organosilicate oligomers, were optimized by using various capillary temperatures and solute concentrations. The structures of organosilicate oligomers were shown to vary with reaction duration and the molar ratio of water to siloxane (r), with multiple types of oligomers attributed to linear, cyclic and hydroxylated species. RESULTS: The evolution of oligomeric structures was elucidated from the ESI-MS spectra. The number and intensity of cyclic oligomers increase with an increase in the r-value or reaction length, at the expense of linear species, indicating the trend to formation of cross-linked polysiloxane structures. CONCLUSIONS: Overall, this work demonstrates that ESI-MS is an indispensable tool for the comprehensive characterization of the correlation between properties and structure of hybrid silica-based materials. Copyright (C) 2016 John Wiley & Sons, Ltd.