Degree of Conversion Analysis by FTIR-ATR

The degree of conversion was assessed by Fourier transform infrared spectroscopy (Spectrum One, Perkin Elmer) coupled to an attenuated total reflectance (ATR) device consisting of a diamond crystal of 2 mm in diameter (Diamond ATR, Perkin Elmer). For analysis, 0.05 g of each experimental composite sample (n = 5) was directly dispensed onto the diamond crystal and the absorbance spectrum of the unpolymerized condition was obtained. After, the composite was photoactivated as described and the absorbance spectrum of the polymerized condition was obtained. Thirty-two coaddition scans were made at 10 kHz velocity and 4 cm⁻¹ resolution. The ratio of the absorbance peak corresponding to the aliphatic carbon-carbon double bond (1637 cm⁻¹ peak height) with that of the internal standard, the aromatic carbon-carbon bond (1608 cm⁻¹ peak height) of polymerized and unpolymerized condition, was determined [13 (link), 21 (link), 24 (link)]. Degree of conversion (DC) was calculated using the follow equation: $\begin{array}{c}\mathrm{D}\mathrm{C}\hspace{0.17em}\hspace{0.17em}\left(\%\right)=\mathrm{100}\times \left[\mathrm{1}-\left(\frac{R\text{\hspace{0.17em}\hspace{0.17em}polymerized}}{R\text{\hspace{0.17em}\hspace{0.17em}non-polymerized}}\right)\right].\end{array}$ R represents the ratio between the absorbance bands at 1637 cm⁻¹ and 1608 cm⁻¹.