FT-Raman-spectroscopic investigations of the system glycidoxypropyltrimethoxysilane/aminopropyltriethoxysilane

The base catalyzed sol-gel process in the system 3-glycidoxypropyltrimethox ysilane (GPTS)/3-aminopropyltriethoxysilane (APTS) is highly interesting fo r the synthesis of hybrid (inorganic-organic) polymers. FT-Raman spectrosco py with excitation in the near infrared as a versatile tool for in situ mea surements was used to monitor the kinetic behavior of the hydrolysis reacti on. An unexpected slow-down of the hydrolysis of GPTS recorded at higher temper atures can be attributed to a decrease of the pH-value during hydrolysis ca used by silanol groups. After condensation has started, the pi-I-value rein creases and forces hydrolysis to reaccelerate. The results strongly suggest the existence of a pentacoordinated transition state with a negative charg e at the silicon atom during base catalyzed hydrolysis.