Study of the hydrolysis and condensation of c-Aminopropyltriethoxysilane by FT-IR spectroscopy

The hydrolysis and condensation reactions of c-APS have been studied in different acid content aqueous solution by using Fourier Transform infrared (FT-IR) spectroscopy. The hydrolysis of c-APS under the studied conditions can be followed by the increase of the ethanol band located at 882 cm–1 and the decrease of the band due to the q(CH3) of c-APS molecules located at 959 cm–1. Hydrolysis reaction is faster by increasing both H2O and acid concentrations, and it is completed when 3 moles of H2O per mole of c-APS are used. The increase of the vibrational band located at 1146 cm–1 shows that condensation of the hydrolysed c-APS molecules take place forming linear chains in poorly cross-linked structures. Besides, both 8-membered cyclic siloxane formations and poorly cross-linked structures are formed and increase as the water and acid content are increased. On the other hand, highly connected cross-linked structures do not appear due to the steric hindrance of the non-hydrolysable aminopropyl group. The silanol band shows that hydrolysis is faster than condensation except for samples with the lowest H2O content.