# Doped Epoxy Resins as an Alternative to Luminescent Optical Sensors
## 3 Results and Discussion  
### Double-Bond Conversion  
One of the most important values describing the quality of the obtained polymer, and more precisely indicating the correctness of the polymerization process, is the conversion of double bonds. This value provides information about the number of unreacted functional groups, the cross-linking density and the functionality of monomers used in polymerization. The double-bond conversion was calculated based on IR spectra obtained using the ATR technique using Equation (1). The data obtained in this way are presented in Table 3.  
\[\pi=\left[1-\left(\frac{A_{p}^{810\text{ cm}^{-1}}}{A_{p}^{1720\text{ cm}^{-1}}}\times\frac{A_{0}^{1720\text{ cm}^{-1}}}{A_{0}^{810\text{ cm}^{-1}}}\right)\right]\times 100\%, \tag{1}\]  
where \(A_{p}^{810\text{ cm}^{-1}}\) is the band absorbance at the wavelength 810 cm\({}^{-1}\) derived from the polymer, \(A_{0}^{1720\text{ cm}^{-1}}\) is the band absorbance at the wavelength 1720 cm\({}^{-1}\) derived from the monomer, and \(A_{0}^{1720\text{ cm}^{-1}}\) is the band absorbance at the wavelength 1720 cm\({}^{-1}\) derived from the monomer. The band at wavelength 1720 cm\({}^{-1}\) was used as a reference. This band corresponds to the stretching vibrations of the carbonyl group and does not change during the polymerization process. The band at wavelength 810 cm\({}^{-1}\), which corresponds to the -C=C- in the monomer, was used to calculate the double-bond conversion [41]. When designing the composition that would be best from the optical fiber-technology point of view, both resins, with different viscosities, various exposure times, and two photosensitive substances, were taken into account. The viscosity of EB150 given by the manufacturer and measured at a temperature of 25 \({}^{\circ}\)C is 1400 mPa*s, while for EB600 it reaches the value of 3000 mPa*s, but for this epoxy acrylate, measurements were performed at 60 \({}^{\circ}\)C. This information is important because it affects the course of the polymerization process and explains the use of the active solvent (NVP, viscosity 2.4 mPa*s measured at 20 \({}^{\circ}\)C). When comparing the double-bond conversion values for compositions based on EB150 resin, a significant increase in the discussed value can be observed with an increase in exposure time from 15 to 30 s. At the same time, this tendency is not observed when the exposure time is increased to 60 s (where the conversion most often remained at the same level). Such observations were made for samples No.1-4 and 6, while for samples No.5 and No.7-9, as time increases, the value of double bond conversion increases. It is worth noting that in the case of the highest conversion values, they always exceed 80%, with the exception of sample No.3 (75.9%). Comparing the compositions without the photosensitive dopant (samples No.1, 4, and 7), it can be clearly stated that the addition of an active solvent increases the degree of double-bond reaction. The addition of a photosensitive dopant has different effects depending on the starting composition. In the case of 75 wt.% EB150 content, the addition of fluorescein worsens the conversion rate by approximately 10% (samples No.3-60). A similar tendency is observed when we add 2.7-NAF.EP to the composition containing 67 wt.% of the resin (samples No.5-60). When the resin content is 50 wt.%, the addition of both photosensitive substances slightly improves the conversion of double bonds (samples No.8-60 and No.9-60). For samples based on EB600 resin, an increase in conversion rate is observed with increasing exposure time. The exceptions are samples No.14-60 and No.15-60, where a slight decrease in the discussed value is observed. It is noteworthy that the highest bond-conversion values for these samples exceed 90%. The exceptions are samples No.11 and No.12, where the resin content is the highest (75 wt.%) and where photosensitive compounds have been added.