Kinetic investigations of hydrolysis and condensation of the glycidoxypropyltrimethoxysilane/aminopropyltriethoxy-silane system by means of FT-Raman spectroscopy I

Fourier transform Raman spectra with laser excitation in the near infrared were recorded during the base-catalyzed sol-gel reaction of the system 3-glycidoxypropyl-trimethoxysilane (GPTS)/3-aminopropyl-triethoxysilane (APTS), This combination of organo-(alkoxy)silanes is used for the synthesis of hybrid polymers. Raman bands of the trimethoxysilyl- and the epoxy-moieties were used to monitor the kinetic behaviour of the hydrolysis reaction and the ring cleavage as a function of temperature. A decrease of the rate of hydrolysis of GPTS at elevated temperatures is attributed to a decrease of the pH caused by temporarily accumulating silanol groups. After the start of the condensation reactions, the pH increases and forces hydrolysis to accelerate. The results indicate the existence of a pentacoordinated transition state with a negative charge at the silicon atom during base catalyzed hydrolysis. (C) 1998 Elsevier Science B.V. All rights reserved.