Thiol−Allyl Ether−Methacrylate Ternary Systems. Evolution Mechanism of Polymerization-Induced Shrinkage Stress and Mechanical Properties

The evolution of the polymerization-induced shrinkage stress and mechanical properties of thiol−allyl ether−methacrylate ternary systems and their relationship to the polymerization kinetics have been investigated. Because of the two distinct polymerization regimes of the ternary systems a methacrylate homopolymerization regime followed by a thiol−ene polymerization dominated regime the mechanism for the evolution of polymerization induced shrinkage stress is unique as compared to other thiol−ene and methacrylate systems. During the first polymerization stage, only intermediate molecular weight methacrylate oligomers are produced, resulting in delayed gelation and near zero shrinkage stress. Immediately following the first polymerization stage, the allyl ether begins to polymerize, and shrinkage stress increases in correspondence with the increased allyl ether conversion. It is observed that the shrinkage stress of the ternary systems exhibits ∼50% of the shrinkage stress of the current dental restoration systems. Also, because of the two polymerization regimes, the mechanical properties evolve uniquely as compared to other ternary systems. It is noted that glass transition temperatures of the ternary systems (∼100 °C) are much higher than traditional thiol−ene polymers and comparable to the current polymeric composites for dental restorations, indicating that the thiol−allyl ether−methacrylate systems are an excellent candidate for dental restorations.