Kinetic Study of Alkoxysilane Hydrolysis under Acidic Conditions by Fourier Transform Near Infrared Spectroscopy Combined with Partial Least-Squares Model

Abstract

Fourier transform near-infrared (FT-NIR) spectroscopy combined with a partial least-squares (PLS) model was successfully employed to study the hydrolysis kinetics of dimethyldiethoxysilane, methyltriethoxysilane, and tetraethoxysilane in an acid-catalyzed EtOH system. The high scanning speed and high sensitivity of FT-NIR spectroscopy enabled the new method to catch the rapid changes of the H2O and EtOH concentrations without delay, allowing the kinetic behaviors of the hydrolysis reactions of the specified alkoxysilanes to be investigated. The hydrolysis processes were found to follow second-order reactions. The hydrolysis rate constants, activation energies, and Arrhenius frequency factors were obtained. The FT-NIR PLS results were in good agreement with those determined by Fourier transform midinfrared spectroscopy. However, the FT-NIR PLS method was found to be more accurate, because of the powerful data processing ability of PLS. All of the results suggest that the FT-NIR PLS model is a valuable tool for performing kinetic research.

Kinetics of Alkoxysilanes and Organoalkoxysilanes Polymerization: A Review

“…The rate constants could be in the ratio (4:3:2:1) [6], or they could have completely different values depending on the catalyst and solvent, as in the case of γ-glycidoxypropyltrimethoxysilane (GPS) [26]. Some articles, however, reported a single overall rate constant, k h , for the hydrolysis process [36,37].…”

“…Different catalysts, such as ammonia, were used to improve the polymerization process to prepare monodisperse nanoparticles (Stöber method) [36,42,43,50,51,52]. Mineral acids, such as HCl [30,37,53,54,55,56,57,58], phosphoric acid [38], and hydrofluoric acid [59], as well as organic acids, such as acetic acid [2,23,26,45,60,61,62,63], chloroacetic acid [24], p -toluene sulphonic acid [22], and methane sulphonic acid [21], were also used. Researches also looked at the use of other organic compounds, such as tin alkyl esters [24,28], while boron-based catalysts were used to overcome the toxicity of the tin compounds.…”

“…They also reported that the transesterification (solvolysis) of some nitrogen bearing trialkoxysilanes with methanol and ethanol as solvents, in the absence of water and catalysts, depends on the chemical structure of the organo groups [23]. The hydrolysis rate of the (CH 3 ) x –Si–(OC 2 H 5 ) (4 – x ) silanes increased with increasing the substituent, x , which ranged from 0 to 2 in an acidic medium, which could have been due to an inductive effect [37]. Nearly the same results were obtained by Altman and co-workers [46].…”

Polymerization of 3‐cyanopropyl (triethoxy) silane: A kinetic study using gas chromatography

“…These findings are in line with previous reports on the determination of the activation energy and frequency factor of methyl triethoxysilane (MTES) in alkaline and acidic media. According to these reports, the activation energies are 50.09 and 97.84 kJ mol −1 in alkaline and acidic media, respectively . They also found that the activation energy and frequency factors decreased with decreasing the pH in an acidic medium …”

“…According to these reports, the activation energies are 50.09 and 97.84 kJ mol −1 in alkaline and acidic media, respectively . They also found that the activation energy and frequency factors decreased with decreasing the pH in an acidic medium …”