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 degrees 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 (BisGMA, UDMA or Bis-EMA). The maximum rate of homopolymerization of the dimethacrylates followed the order of Bis-GMA > UDMA > TEGDMA > Bis-E AA, 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. (c) 2008 Wiley Periodicals, Inc.