In-situ photo-polymerization study of Si-(bis-GMA)/TEGDMA by correlations of PA signals

Abstract
The photo-polymerization reaction of Si-(bis-GMA)/TEGDMA (a bis-GMA modified with silyl groups and mixed with TEDGMA) has been studied by pulsed photoacoustic (PA) and FTIR techniques. The light from a pulsed laser is focused on the surface of the sample for both to activate the chemical reaction and generate PA signals. The in-situ acquisition of the PA signals, during photo-polymerization (PP), in consecutive way, permits to follow changes in its physical properties. The structural changes during polymer formation are recovered by a numerical procedure based on correlation coefficients r_i. This numerical procedure, applied to digitally recorded PA signals, allows the construction of a PP profile dr_i /dT_i, and permits to detect the phase transitions during the whole process including the gel region. The obtained results are in agreement with those obtained from the FTIR analysis, under similar conditions.