Copolymerization kinetics of dental dimethacrylate resins initiated by a benzoyl peroxide/amine redox system

The copolymerization of four dental dimethacrylates initiated by a benzoyl peroxide/4‐ N,N ‐dimethylamino phenethyl alcohol redox system at 37°C was studied with differential scanning calorimetry. The studied dimethacrylates were viscous bisphenol A glycidyl dimethacrylate (Bis‐GMA), bisphenol A ethoxylated dimethacrylate (Bis‐EMA), and urethane dimethacrylate (UDMA), which were characterized as base monomers, and low‐viscosity triethylene glycol dimethacrylate (TEGDMA), which was characterized as a diluent. Also, three series of dimethacrylate copolymers were prepared by incremental additions (12.5 wt %) of TEGDMA to a base comonomer (Bis‐GMA, UDMA or Bis‐EMA). The maximum rate of homopolymerization of the dimethacrylates followed the order of Bis‐GMA > UDMA > TEGDMA > Bis‐EMA, and the final degree of conversion of the corresponding homopolymers followed the order of TEGDMA > UDMA > Bis‐EMA > Bis‐GMA. A reaction–diffusion‐controlled termination region was clear in all monomers and started earlier in bulky and rigid Bis‐GMA and Bis‐EMA (followed by the more flexible UDMA and TEGDMA) but lasted longer in the Bis‐EMA polymerization. The maximum rate of copolymerization and degree of conversion of copolymers of a base monomer with TEGDMA changed monotonically with an increase in the TEGDMA content in the initial comonomer mixture. A synergistic effect was clear only in the final double‐bond conversion of Bis‐GMA/TEGDMA.