Simulation of conversion profiles within dimethacrylate thick material during photopolymerization. Validation of the simulation by thermal analysis data. Application to the synthesis of a gradient structure material

In a previous paper, a new synthesis method of gradient structure materials from a homogeneous system of monomers was described. 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 consisted in setting the obtained gradient by a thermal crosslinking reaction. Here, we focussed our attention on the first step, i.e. the creation of the conversion gradient. The knowledge of this gradient is of fundamental importance to predict the final properties of the material. Unfortunately, the measurement of this parameter all over the thickness during the photopolymerization is impossible because no suitable technique is available. A numerical simulation based on the general heat equation transfer was developed on a dimethacrylate model system to calculate this conversion gradient. To describe the true conditions of kinetic experiments, some necessary parameters were measured, like conversion, reaction rate, spectral irradiance of the Hg vapour lamp, dimethacrylate spectral absorbance. The validation of the model by comparison between numerical simulation and experimental temperature results was checked. Finally, influence of physical and chemical parameters on the conversion gradient was discussed.