The evolution of the longitudinal modulus during the photo-polymerisation of a bis-GMA/TEGDMA resin by pulsed photoacoustic technique

Abstract
A pulsed photoacoustic (PA) technique was implemented to study the evolution of the longitudinal modulus, C₁₁, during the polymerisation of a methacrylate co-monomer system, induced by UV light. A laser pulse was used as a standard source of ultrasound waves to monitor the changes in the longitudinal velocity of the acoustic signal during the photo-polymerisation (PP) a bis-GMA/TEGDMA co-monomer system (70/30 %w/w) containing camphorquinone as photo-initiator, and N,N-dimethyl-p-toluidine as reducing agent. C₁₁ was determined on real time conditions after irradiating the system for predetermined periods. The kinetics of the PP reaction was also studied by infrared spectroscopy in order to compare the evolution of C₁₁ with the rate of conversion of the double bounds of the methacrylate groups. The evolution of C₁₁ reflects the whole polymerisation process: The technique permits to determine the transitions of the resin during polymerisation from viscous to viscoelastic state and further to a glassy polymer.