Abstract
The spectra of photo-polymerised composite resins, measured by the micro-Raman spectroscopy, are analysed in the frequency region of the C O carbonyl stretching bands. The band intensities at about 1700 and 1715 cm −1 (the peak frequencies of the hydrogen bonded and free C O bands, respectively) decrease with the irradiation time and with the methacrylate monomer conversion. Consequently, a degree of apparent conversion (DAC) can be defined. It is shown that the intensity variations conserve the band-shape and allow the DAC measurements via the single frequency intensity ratio. Both the bands give rise to DAC values which exhibit a one-to-one dependence on the degree of C C conversion, in partial disagreement with previous results. The microscopic mechanisms, associated to the intensity decrease, are critically revised and discussed on the basis of the experimental findings.
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