Hydrolysis and condensation kinetic studies of mercaptopropyl trimethoxysilane using in-situ Raman spectroscopy

The hydrolysis and condensation kinetic parameters of mercaptopropyl trimethoxysilane (MPTMS, HS(CH2)3Si(OCH3)3) have rarely been quantitatively studied due to the fast reaction rate with the presence of catalysts. In this work, we employed the in-situ Raman spectroscopy to monitor the hydrolysis and condensation reactions of MPTMS in real time. First, with CH3OH as the solvent and NH4OH as the catalyst, the hydrolysis kinetics of MPTMS was investigated via the initial rate method. The reaction orders with respect to MPTMS, H2O, and NH4OH are 1.0, 1.0, and 1.0, respectively. The activation energy (Ea) and pre-exponential factor (A) of MPTMS hydrolysis reaction are (28.4 ± 1.1) kJ/mol and 938.1 (mol/L)-2·min−1, respectively. Then, an ‘acid-catalyzed hydrolysis and base-catalyzed condensation’ two-step strategy was employed to decouple the hydrolysis and condensation reactions. With the hydrolysates, trihydroxy silanols HS(CH2)3Si(OH)3, as the starting reactant, the early-stage condensation reaction kinetics was studied. The reaction orders with respect to HS(CH2)3Si(OH)3 and NH4OH are 1.4 and 2.8, respectively. The activation energy (Ea) and pre-exponential factor (A) of the condensation reaction are (52.2 ± 0.4) kJ/mol and 7.5 × 1013 (mol/L)-3.2·min−1, respectively. The kinetic parameters determined in this work could provide quantitative guidance for the design and control of MPTMS reaction process.