Quantitative determination of base-catalyzed hydrolysis kinetics of methyltrimethoxysilane by in-situ Raman spectroscopy

Abstract

A thorough understanding of the hydrolysis reaction of alkoxysilanes is of great significance to the synthesis of silicone resins, however, the determination of the reaction kinetics is pretty hard. This is because the hydrolysis of alkoxysilanes is fast under the alkaline conditions, especially methyltrimethoxysilane (MTMS), and the reaction is difficult to terminate. Meanwhile, there is a reverse hydrolysis reaction in the system. In this work, we developed a fast and quantitative method by applying in-situ Raman spectroscopy to determine the base-catalyzed hydrolysis kinetics of MTMS. The short measuring time, high sensitivity, and low water interference enable Raman spectroscopy to be a powerful tool for the real-time monitoring of rapid hydrolysis reaction. In order to avoid the influence of the reverse reaction and condensation reaction, the initial rate method was employed to determine the reaction kinetic parameters. The reaction orders with respect to MTMS, H2O, and NH4OH are 0.8, 0.9, and 0.7, respectively. The activation energy (Ea) and pre-exponential factor (A) are 26.02 kJ/mol and 1088.94 (mol/L)−1.4·min−1, respectively. Furthermore, the solubility of MTMS in H2O was measured, and a mathematical model of the heterogeneous hydrolysis process of MTMS microdroplets was established. This model can predict the time required for the disappearance of MTMS microdroplets, thereby providing quantitative guidance for the process design and product quality control.