29Si MAS NMR and FTIR study of inorganic–organic hybrid gels

Inorganic–organic hybrid materials produced by the sol–gel method from Si(OR)4 and R′x−ySi(OR)y (R,R′—CnHm groups) compounds are very interesting materials for new optical techniques. Recognition of the structure of these materials is very important for controlling their production process as well as their properties. Five different hybrid gels were obtained using tetraethoxysilane (TEOS) with addition of the following modifiers: methyltrimethoxysilane (MTMS) (CH3)Si(CH3O)3, vinyltriethoxysilane (VTES) (CH6-point double bond; length half of m-dashCH2)Si(CH3CH2O)3, phenyltriethoxysilane (PhTES) Ph–Si(CH3CH2O)3 (Ph—phenyle group C6H5), diethoxydimethylsilane (DEDMS) (CH3)2Si(C2H5O)2, diethoxymethylvinylsilane (DEMVS) (CH3)(CH6-point double bond; length half of m-dashCH2)Si(C2H5O)2. Copolymerisation of tetraethoxysilane (TEOS) and of the organic modifiers was studied by means of both the 29Si MAS NMR and the FTIR spectroscopy. It has been found that according to the organic modifier used different 29Si MAS NMR chemical shifts were observed. An attempt has been made to assign the signals to the corresponding structure units of gels. The FTIR spectra confirmed the formation of copolymers between TEOS and organic modifiers. Moreover, using 29Si MAS NMR and FTIR spectroscopy the stability of the hybrid structure at the temperatures 100–500 °C was determined.