# Doped Epoxy Resins as an Alternative to Luminescent Optical Sensors
## 3 Results and Discussion
### Thermal and Spectroscopic Analysis
It is worth noting that compared to the substances with 25 wt.% NVP content, compositions containing 33 wt.% addition of active solvent between temperatures of 100 \({}^{\circ}\)C and 200 \({}^{\circ}\)C are characterized by a maximum of mass loss of 2. Due to the assumption that the first one concerns only physically adsorbed water, it should be stated that compared to sample No.1, sample No.4 is characterized by higher thermal resistance. Additionally, samples No.4-60 register the maximum mass loss related to the decomposition of the substance well above 200 \({}^{\circ}\)C, so they can be considered as the best in the series. The situation is the same for the entire series of samples No.6, where at around 140 \({}^{\circ}\)C a mass loss is recorded only due to the presence of ions \(m/z=17\) and 18, and the next maximum is above 200 \({}^{\circ}\)C. In the case of sample No.5, no clear maximum related to the presence of ions \(m/z=17\) and 18 is recorded. The evaporation of water is so extended in time that in the temperature range of 100-200 \({}^{\circ}\)C only one maximum with ions \(m/z=14\)-18, 28, 29, 42-44 is recorded (which corresponds to one endothermic effect, the maximum of which is at lower temperatures). Based on the results of mass loss and ions associated with it, it can be concluded that for samples doped with photosensitive substances, the addition of an active solvent improves thermal properties (comparing 25 wt.% with 33 wt.% NVP content). Above 200 \({}^{\circ}\)C, the discussed samples show two maxima (except for series No.5, where only one is recorded, related to the proper decomposition of the sample, based on which it can be concluded that this series has better thermal properties), the first one in the temperature range 230-242 \({}^{\circ}\)C, and the second 431-437 \({}^{\circ}\)C. Endothermic peaks appear in DSC curves in similar temperature ranges. Based on the results obtained from mass spectroscopy, it can be concluded that the mass ion profile for sample series No.4 and No.6 looks similar. Around the temperature of 240 \({}^{\circ}\)C, the presence of ions \(m/z=15\), 17, 18, 26-29, 30 (CH\({}_{2}\)NH\({}_{2}\)+), 31 (CH\({}_{3}\)NH\({}_{2}\)+), 41-44, 52-56, 68, 82-85, and 111 is recorded. Ions 68 (C\({}_{4}\)H\({}_{4}\)O\({}^{+}\)) and 82-85 (C\({}_{4}\)H\({}_{4}\)NO\({}^{+}\), C\({}_{4}\)H\({}_{5}\)NO\({}^{+}\), C\({}_{4}\)H\({}_{6}\)NO\({}^{+}\), C\({}_{4}\)H\({}_{6}\)NO\({}^{+}\), C\({}_{4}\)H\({}_{7}\)NO\({}^{+}\)) are also associated with NVP decomposition, but appear in the case of samples with higher solvent content (33 wt.% and 50 wt.%). Analyzing mass spectra at temperatures of 320-350 \({}^{\circ}\)C (i.e., in the range where subsequent endothermic effects are recorded), we find that no new ions appear. Only the change in their intensity is noticeable (Figure 2). In the case of samples in series No.5, a slightly different ion profile can be observed. Up to a temperature of approximately 275 \({}^{\circ}\)C (the DSC maximum shifted towards higher temperatures compared to the series of samples No.4 and No.6), only ions \(m/z=14\), 15, 17, 18, 27-29, 31, 40, and 44 are present. At the temperature of about 340 \({}^{\circ}\)C the ion \(m/z=56\) and \(m/z=111\) does appear. It should be concluded that the structure of the polymers obtained in this series is more homogeneous. Ions resulting from the NVP decomposition appear in mass spectra at higher temperatures, and the fact that fewer effects are recorded is an additional advantage. As a rule, the smaller the maximum on the DTG and DSC curves, the more homogeneous the structure. The greater complexity of the structure for series No.5 is evidenced by the multiple peaks on the DSC curve in the temperature range of the proper sample decomposition. But, from the optical fiber-technology point of view, this is much less important, because in this temperature range the polymer fibers are not drawn out.