Chemical modification of silica gels

Highly porous pure and polyethyleneglycol (PEG)-doped silica gels have been prepared from tetraethyl orthosilicate (TEOS) in ethanol using NH4OH base-catalysis. Addition of PEG to the SiO2-systemincreases the average particle size and most frequent pore diameter of the resultant gels while their total surface areadecreases. The viscosity of the solincreases with PEG concentration and passes through a maximum with increasing molecular weight at PEG 200. Results obtained indicate a definite interaction of the polymer with SiO2 and that this interaction is not as a result of direct formation of Si−O−C linkage, but is more likely to be, due to hydrogen bonding between the hydrated PEG and the Si−O−Si network. Structure-process correlations are considered.