Synthesis and properties of new photosensitive triazene and o-nitrobenzene methacrylates

New photoactive polymerizable monomers were synthesized in order to photomodulate the mechanical properties of photocurable materials. These monomers are end-capped by at least two polymerizable units (using irradiation wavelength λ1) connected by a spacer including at least one photocleavable unit (irradiation wavelength λ2 ≠ λ1) i.e. aryltriazene or 2-nitrobenzyl core. The photochemical behaviour of these systems was studied in solution and in resin formulations. Their ability to promote the hardening and crosslinking of a curable resin at λ1, then the subsequent degradation or modification of crosslinked resins under an actinic light (λ2) was evaluated by DMA for formulations including these new monomers. These new monomers were shown, in resin formulation, to readily rigidify the material upon λ1 irradiation and for most of them the subsequent photolysis of their internal linkers at λ2 irradiation was followed by a decrease of the hardness at low temperature (-20 °C). For one of them (compound 6) λ2 illumination at room temperature provoked the decrease of the mechanical properties of the solid material making it of interest for dental applications.