2.4. Real-Time FT-IR

Real-time FT-IR spectroscopy was used to monitor the epoxy band absorption as a function of exposure of irradiation in the resins. An Hg lamp adapted to the FT-IR spectrometer by means of a light guide was used to adjust the light intensity to 18.4 mW/cm² and to irradiate the resins. PBG (2 mol %) was added to the corresponding monomers and well-mixed by ultrasonic vibration for 10 min (Thioxanthone (TX) was dissolved in 0.3 mL acetone firstly). Before the photopolymerization, the mixture was dried under vacuum for 30 min at room temperature in order to remove the solvent. The thickness of the mixture film was adjusted by a 120 μm film applicator (BYK, Wesel, Germany). Polymerization profiles were recorded during 1000 s irradiation at room temperature. For each sample, the measurements were tested more than three times. The polymerization kinetics were measured by monitoring the disappearance of thiol and epoxy band, and the conversion was calculated using the formula:

where A_t is the area of the epoxy and thiol characteristic absorbance peak at 915 and 2568 cm⁻¹ at time t, and A₀ stands for the initial area of this peak.