**4. Conclusions**

Structural, thermal, mechanical, and electrochemical characterization of novel epoxysilica and PMMA-silica hybrid coatings have shown that their properties are extremely dependent of the hybrid precursors proportion, time and temperature of synthesis, and addition of fillers. After a careful adjustment of the preparation conditions, these homogeneous and transparent hybrid coatings present a defect-free very smooth surface, low porosity, a highly cross-linked silica network, excellent adhesion to the metallic substrate, elevated thermal stability, and especially an excellent anticorrosive performance. Epoxysilica and PMMA-silica films with thicknesses of less than 10 μm exhibit a dense and highly reticulated nanostructure, resulting in enhanced thermal stability combined with high corrosion resistance and long durability in saline environment. Exceptional barrier properties, especially on aluminum alloy, were found for PMMA-silica hybrids prepared at a 8MMA:1MPTS:2TEOS molar ratio, 4 h/80°C of synthesis, and BPO/MMA molar ratio of 0.01. This coating highlights a corrosion resistance of about 50 GΩ cm<sup>2</sup> and a lifetime of more than 18 months in saline solution. Nanofillers have been successfully added to the PMMA-silica matrix to improve the anticorrosive performance and to reinforce the hybrid structure. Carbon nanotubes and graphene oxide incorporated into the PMMAsilica matrix resulted in a multifunctional material, which combines an excellent anticorrosive performance with improved adhesion, anti-scratch and heat-resistant properties, thus extending the application range of these coatings to abrasive environments. Furthermore, it has been shown that added Ce(IV) ions act as oxidation agents during the formation of the hybrid matrix, leading to densification process that improves the barrier property of the coatings. In addition, the active corrosion inhibition provided by formation of insoluble cerium species in regions affected by corrosion, known as self-healing ability, resulted in a prolonged the lifetime of the coatings. The great progress achieved in the last couple of years in the development of organic-inorganic hybrids makes these materials very promising candidates for new-generation high-performance protective coatings.
