The effect of temperature on the kinetics of diacrylate photopolymerizations studied by real-time FTIR spectroscopy

Real-time FTIR spectroscopy was used to study the effect of temperature on the kinetics of photopolymerization from room temperature up to 160 degrees C. A highly viscous epoxy diacrylate and tripropylene glycol diacrylate (TPGDA) as systems of lower viscosity were used to study the influence of viscosity on the polymerization rate, the induction period, and the ultimate conversion. Different behaviour was observed at temperatures below and above ca. 90 degrees C. In the epoxy diacrylate, the polymerization rate first distinctly increases with temperature due to the drop of viscosity, whereas in TPGDA the polymerization rate only little increases or is even independent of temperature depending on the photoinitiator used. The induction period decreases due to the decreasing solubility of oxygen in the reactive formulation. At higher temperatures, termination processes lead to a decrease of the polymerization rate if morpholino ketones are used for initiation. Simultaneously, the induction period re-increases. In contrast, systems initiated by a hydroxy alkylphenone or benzildimethyl ketal continue the trends from below 90 degrees C. (C) 2000 Elsevier Science Ltd. All rights reserved.