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

The base catalyzed sol-gel process in the system 3-glycidoxypropyltrimethoxysilane (GPTS)/3-aminopropyltriethoxysilane (APTS) is highly interesting for the synthesis of hybrid (inorganic-organic) polymers. FT-Raman spectroscopy with excitation in the near infrared as a versatile tool for in situ measurements was used to monitor the kinetic behavior of the hydrolysis reaction. An unexpected slow-down of the hydrolysis of GPTS recorded at higher temperatures can be attributed to a decrease of the pH-value during hydrolysis caused by silanol groups. After condensation has started, the pi-I-value reincreases and forces hydrolysis to reaccelerate. The results strongly suggest the existence of a pentacoordinated transition state with a negative charge at the silicon atom during base catalyzed hydrolysis.