The decrease in the band intensity at 1643 cm -1 , corresponding to the stretching vibration of C=C in methacrylate group, is evidence for the reaction of the unsaturated functional groups during the photopolymerization. Additionally, due to the reaction of methacrylate functional groups, a new band appears at 1634 cm -1 , corresponding to the resultant C-C bond. For the case of materials that were cured under air atmosphere, we note that the signal at 1643 cm -1 is more pronounced, which is likely due to oxygen inhibition.