Gradient structure materials from homogeneous system induced by UV photopolymerization

This work deals with the synthesis of a gradient structure material from a homogeneous system of monomers. This new synthesis involved hydroxyethylmethacrylate, a hydroxytelechelic polybutadiene, and 4,4′-methylene-bis(cyclohexylisocyanate). These materials were made in two steps. The first one consisted in creating a photopolymerization gradient in methacrylic double bonds under UV exposure thanks to the decay of UV light intensity through the sample thickness. The second one involved a thermal crosslinking reaction leading to the formation of a polyurethane network in order to set the obtained gradient. Using FTIR and UV spectroscopies, the required experimental conditions to obtain and keep the gradient were investigated. Thus, these parameters enabled us to obtain a 20% hydroxyethylmethacrylate double bonds conversion gradient in the ultimate 5 mm thick material. Further DMA analysis well revealed a difference of structures between the two sides of the material.