Synthesis and Photopolymerization of Thiol-Modified Triazine-Based Monomers and Oligomers for the Use in Thiol-Ene-Based Dental Composites

Thiol-ene photopolymerizations combine the unique features of step-growth reactions and photoinitiated polymerizations, so that they experience a growing interest for applications such as coatings or dental restoratives. Most studies have making use of a relatively flexible ester and the hydrolytically labile derivative pentaerythritoltetra(3-mercaptopropionate) (PETMP) as the thiol component in common. In this study, the performance of hydrolytically stable 1,3,5-tris(3-mercaptopropyl)-1,3,5-triazine-2,4,6-trione (4a), 1,3,5-tris(2-methyl-3-mercapto-propyl)-1,3,5-triazine-2,4,6-trione (4b), and oligomers thereof in thiol-ene photopolymerizations is investigated. The oligomers are prepared via thiol-Michael or thiol-isocyanate additions by using 4a and suitable diacrylates or diisocyanates containing a rigid core structure. Compared with PETMP, the thiol derivative 4a shows better flexural strength and modulus of elasticity in thiol-ene photopolymerizations with 1,3,5-triallyl-1,3,5-triazine-2,4,6-trione (TATATO) as the -ene derivative. This phenomenon becomes especially evident after storage in water at 37 degrees C for 24 h. Furthermore, the performance regarding the flexural strength, the Young's modulus of elasticity, the polymerization shrinkage stress of 4a, and the polyadducts thereof in dental filling composites is evaluated and discussed.