2. Chemical aspects of sol-gel polymerization

Although sol-gel polymerization can be carried out using precursors other than alkoxides (e.g. halides), since these are the subject of 95% of the work described in the literature, we will restrict ourselves here to their study. Sol-gel polymerization can be "hydrolytic", i.e. require the addition of water and therefore include one or more hydrolysis steps, or, on the contrary, be "non-hydrolytic" when carried out without water. The case of hydrolytic gels is by far the most important and widespread [2] .