The polymerization mechanism of the ternary thiol-allyl ether-methacrylate monomer system has been investigated. The effects of various factors including the thiol concentration, functionality, and structure on the polymerization mechanism, the polymer network structure, and mechanical properties were examined. The thiol-allyl ether-methacrylate ternary system uniquely exhibits two different polymerization regimes: a methacrylate homopolymerization dominated regime coupled with chain transfer to thiol followed by a second thiol-ene polymerization dominated regime. This polymerization mechanism is primarily due to the chemical nature of the methacrylate and allyl ether double bonds. Because methacrylate homopolymerization with chain transfer reactions to thiols dominates the initial stage of polymerization (up to 60% of the methacrylate conversion), the concentration and structure of the thiol significantly affect the polymerization processes and polymer network structure. The methacrylate chain length significantly decreases from 20 to 1.5 with increasing thiol content, and the methacrylate conversion rate during the first polymerization regime depends linearly on the [SH](0)/[methacrylate](0) ratio. The overall polymerization rates and glass transition temperature increase significantly with increasing thiol functionality, while the methacrylate final conversion decreases more than 20% due to the formation of the highly cross-linked network.