Competitive polymerization between organic and inorganic networks in hybrid materials

Hybrid organic-inorganic materials derived from 3-glycidoxypropyltrimethoxysilane have been synthesized via sol-gel using BF3 etherate as a catalyst of organic polymerization. Different amounts of BF3 etherate have been used, from B/Si = 0.01 up to B/Si = 0.1, to prepare powder samples. The materials have been characterized by Fourier transform infrared spectroscopy (FTIR) and multinuclear solid-state NMR spectroscopy. FTIR and NMR spectra have shown that with a B/Si = 0.03 molar ratio a complete opening of epoxy in 3-glycidoxypropyltrimethoxysilane is achieved. The different amounts of BF3 etherate employed have been found to affect the degree of inorganic cross-linking and the length of the ethylene oxide chains. Larger amounts of BF3 enhance the inorganic network crosslinking and give oligo(ethylene oxide) derivatives. Boron has been found to remain in the matrix as a network former of the inorganic side. The formation of Si-O-B bonds has been observed by the FTIR spectra.