Influence of zirconium propoxide on the radical induced photopolymerisation of hybrid sol–gel materials

This study emphasizes the role of zirconium propoxide on the free-radical photopolymerisation of hybrid organic–inorganic material based on 3-methacryloxypropyltrimethoxysilane (MAPTMS). By means of atomic force microscopy in pulsed force mode and real-time Fourier-transform infrared spectroscopy, it is shown that the addition of zirconium complex in the hybrid sol–gel material leads to a well-polymerised and hydrophilic surface under UV-illumination. By contrast, sols without zirconium complex exhibit soft and sticky surfaces. The study also demonstrates an unexpected role of oxygen in the photopolymerisation process. Indeed oxygen is well-known being a strong inhibitor of the radical polymerisation. However, in the present case, it interacts with Zr(OPr)4 and participates in a positive way to the photochemical process. During the irradiation, radicals react with O2 to form peroxyl radicals that are generally inert towards the photopolymerisation. By using laser flash photolysis, it was proved that these radicals combine with zirconium propoxide to form new initiating species that contribute to further free-radical photopolymerisation.