Visible light activation of an epoxy monomer containing methacrylate monomers

The photopolymerization of epoxy monomers is traditionally carried out by UV cure. Recently, epoxy cure is being investigated by the use of visible light through combined use of photo-sensitizing agents and cationic UV initiators. Objectives: The purpose in this study was to determine the heat of cure and conversion during visible light activated polymerization of an epoxy monomer CYRACURE (Dow-Corning) admixed with selected methacrylate monomers. Materials and Methods: The selected monomer mixture was cured using camphoroquinone, ethyl-4-dimethyl amino benzoate (EDMAB) and arylsulfonium hexafluoroantimonate (ASHF) under visible light activation. The effect of addition 20% methacrylate monomers Dipenta erythrytol penta acrylate (DIPENTA), Gylecryl dimethacrylate (GDMA), Ethylene glycol dimethacrylate (EGDMA) and Tri-ethylene glycol dimethacrylate (TEGDMA) to CYRACURE on its heat of cure during visible light polymerization was evaluated. Heat of cure was measured at 37^oC by 60 sec cycles of light activation (using a VIP curing light at 600 mW/cm²) of monomers kept in the sample pan of a TA Instruments DSC model 2910. Conversion was determined using epoxide absorption peak at 970 cm^-1 and -C=C- stretching peak at 1637 cm^-1, using Thermo-electron FTIR Model 370. Results: The heat of cure (J/gm) values due to visible light activation ranged from 147 for TEGDMA to 220 for DIPENTA, and the corresponding molar heats showed significant differences (p<0.05) in the order TEGMA<GDMA<EGDMA≤DIPENTA. Conversion values >80% were observed for both –C=C- double bonds and epoxide ring opening, except in TEGDMA. The heats of cure means showed significant differences (p<0.05) between TEGDMA additive use and those of other monomers. Conclusions: The results indicate effective visible light cure of methacrylate-epoxide monomer systems. Because of their ring opening mechanism of polymerization, epoxy resins are expected to cause low shrinkage during cure, and may be valuable for composite and bonding applications in dentistry.