| Abstract: | Structure–property relationships were investigated for the diglycidly methacrylate derivative of bisphenol-A crosslinked by electron beam irradiation. This material, commonly called bis-GMA, is a viscous liquid at room temperature which crosslinks to form a glassy network. The major parameters which were systematically varied in this study were radiation dosage, dose rate, aging time after irradiation, and post-cure annealing at higher temperatures. Measurements were conducted to quantify the crosslinking reaction and to characterize the physical properties of the resulting networks. Solvent extraction was done to determine the relative degree of network formation through the equilibrium swelling and the gel weight fraction after drying. Another method utilized FTIR to monitor the disappearance of double bonds as the crosslinking reaction proceeded. To characterize the thermal and physical properties, differential scanning calorimetry (DSC) and dynamic mechanical spectroscopy were utilized. Network density was found proportional to the irradiation dosage, with an upper limit reached above some critical dosage. Over the range of dose rate studied, this variable was not found to influence the degree of cure greatly. The crosslinking reaction became diffusion limited as vitrification occurred. These phenomena were discussed in terms of the well-known time–temperature–transformation diagram. Free radicals trapped in these reacting networks due to vitrification exhibited a finite lifetime. Post-curing could be achieved by annealing at a temperature above the Tg of the initially cured network, as shown by the increase of the glass transition temperature from both DSC and dynamic mechanical results. |
