IADR Abstract Archives
Thiol–Ene Networks with Improved Thermomechanical, Chemical, and Aesthetic Properties
Objectives: This study aims to examine the deficiencies of thiol–ene polymerizations that curtail their clinical acceptability for composite dental restorative materials, such as their typically low glass transition temperatures, the potential hydrolysis of thiol monomer-borne ester functional groups, and the malodor associated with volatile thiol compounds. We hypothesize that these deficiencies are not inherent to thiol–ene systems; rather, they can each be addressed by utilizing appropriately-designed precursor monomers.
Methods: Thiol–ene resins were formulated using vinyl-bearing monomers incorporating inflexible moieties and either ester-bearing or ester-free, tetrathiol monomers. Photopolymerization kinetics studies of these thiol–ene formulations were performed using Fourier transform infrared (FT-IR) spectroscopy, and the resultant polymers were subject to dynamic mechanical analysis (DMA) to determine their glass transition temperatures and temperature-dependent storage moduli.
Results: Thiol–ene resins formulated with tetramercaptoalkylsilanes photopolymerized rapidly at rates approaching those formulated with conventional, ester-bearing tetrathiols. The glass transition temperatures (Tgs) of the generated polymers were significantly raised with increased cross-linking density and polymer backbone stiffness. The co-reaction of off-stoichiometric mixtures of tetramercaptoalkylsilane and rigid norbornylic monomers yielded oligomeric thiols that, upon subsequent thiol–ene polymerization, afforded cross-linked polymers with high Tgs.
Conclusions: The radical-mediated thiol–ene addition reaction is an appealing polymerization mechanism for composite dental restoratives; however, its utilization has been hindered by the often poor mechanical properties of the resultant polymers, potential hydrolysis of thiol monomer-borne esters, and the malodor of volatile thiols. Once these deficiencies are addressed, thiol–ene resins will be viable for clinical use as the continuous phase of composite dental restorative materials.
Methods: Thiol–ene resins were formulated using vinyl-bearing monomers incorporating inflexible moieties and either ester-bearing or ester-free, tetrathiol monomers. Photopolymerization kinetics studies of these thiol–ene formulations were performed using Fourier transform infrared (FT-IR) spectroscopy, and the resultant polymers were subject to dynamic mechanical analysis (DMA) to determine their glass transition temperatures and temperature-dependent storage moduli.
Results: Thiol–ene resins formulated with tetramercaptoalkylsilanes photopolymerized rapidly at rates approaching those formulated with conventional, ester-bearing tetrathiols. The glass transition temperatures (Tgs) of the generated polymers were significantly raised with increased cross-linking density and polymer backbone stiffness. The co-reaction of off-stoichiometric mixtures of tetramercaptoalkylsilane and rigid norbornylic monomers yielded oligomeric thiols that, upon subsequent thiol–ene polymerization, afforded cross-linked polymers with high Tgs.
Conclusions: The radical-mediated thiol–ene addition reaction is an appealing polymerization mechanism for composite dental restoratives; however, its utilization has been hindered by the often poor mechanical properties of the resultant polymers, potential hydrolysis of thiol monomer-borne esters, and the malodor of volatile thiols. Once these deficiencies are addressed, thiol–ene resins will be viable for clinical use as the continuous phase of composite dental restorative materials.