Elaboration of gradient structure materials from homogeneous system combining UV and thermal processes

A new synthesis of a gradient structure material from a homogeneous system of monomers is described. This synthesis involved 1,6-hexanediylbis[oxy(2-hydroxy-3,1-propanediyl)]bisacrylate, a hydroxytelechelic polybutadiene, and 4,4′-methylene-bis (cyclohexylisocyanate). In a first step, an acrylic double bonds photopolymerization gradient is created under UV exposure thanks to the decay of UV light intensity through the sample thickness. In a second step, a thermal crosslinking reaction is realised to form a polyurethane network in order to set the obtained gradient. The required experimental conditions to obtain and keep the gradient were investigated by FTIR and UV spectroscopies. Thus, a 50% 1,6-hexanediylbis[oxy(2-hydroxy-3,1-propanediyl)]bisacrylate double bonds conversion gradient was obtained in the ultimate 5 mm thick material. DMA and swelling analysis well revealed a difference of structures between both sides of the material, and a change in polarity was observed by contact angle measurements.