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 lambda 1) connected by a spacer including at least one photocleavable unit (irradiation wavelength lambda 2 not equal lambda 1) 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 lambda 1, then the subsequent degradation or modification of crosslinked resins under an actinic light (lambda 2) was evaluated by DMA for formulations including these new monomers. These new monomers were shown, in resin formulation, to readily rigidify the material upon lambda 1 irradiation and for most of them the subsequent photolysis of their internal linkers at lambda 2 irradiation was followed by a decrease of the hardness at low temperature (-20 degrees C). For one of them (compound 6) lambda 2 illumination at room temperature provoked the decrease of the mechanical properties of the solid material making it of interest for dental applications. (C) 2012 Elsevier Ltd. All rights reserved.