# Doped Epoxy Resins as an Alternative to Luminescent Optical Sensors
## 3 Results and Discussion
### Thermal and Spectroscopic Analysis
As is the case with compounds with a benzyl group, most often formed as a result of \(\alpha\)-cleavage, in the mass spectra an ion with mass \(m/z=\) 91 is observed. In most cases, this ion quickly rearranges to the more stable tropylium ion. It, in turn, losing a neutral acetylene molecule (ion \(m/z=\) 26), decays to form the ion \(m/z=\) 65 (C\({}_{5}\)H\({}_{5}\)\({}^{+}\)) and in the next stage, also as a result of the loss of C\({}_{2}\)H\({}_{2}\), it is transformed into the ion \(m/z=\) 39 (C\({}_{3}\)H\({}_{3}\)\({}^{+}\)). The presence of these ions proves that the resin used has decomposed. Other ions indicating the decomposition of benzene, i.e., the resin used and photosensitive dopants, are also present: \(m/z=\) 50 (C\({}_{4}\)H\({}_{2}\)\({}^{+}\)), \(m/z=\) 51 (C\({}_{4}\)H\({}_{3}\)\({}^{+}\)), \(m/z=\) 52 (C\({}_{4}\)H\({}_{4}\)\({}^{+}\)), \(m/z=\) 63 (C\({}_{5}\)H\({}_{3}\)\({}^{+}\)), \(m/z=\) 64 (C\({}_{5}\)H\({}_{4}\)\({}^{+}\)), \(m/z=\) 77 (C\({}_{6}\)H\({}_{5}\)\({}^{+}\)), \(m/z=\) 78 (C\({}_{6}\)H\({}_{6}\)\({}^{+}\)), \(m/z=\) 78 (C\({}_{6}\)H\({}_{7}\)\({}^{+}\)), \(m/z=\) 78 (C\({}_{6}\)H\({}_{7}\)\({}^{+}\)), \(m/z=\) 92 ((C\({}_{6}\)H\({}_{5}\)\({}^{+}\))CH\({}_{2}\)+ H), \(m/z=\) 93 ((C\({}_{6}\)H\({}_{5}\)\({}^{+}\))O), \(m/z=\) 94 ((C\({}_{6}\)H\({}_{5}\)\({}^{+}\))O+H), \(m/z=\) 104 ((C\({}_{6}\)H\({}_{5}\)\({}^{+}\))CHCH\({}_{2}\)), \(m/z=\) 105 ((C\({}_{6}\)H\({}_{5}\)\({}^{+}\))CHCH\({}_{3}\)), and \(m/z=\) 111 (molecular ion of the active solvent). The remaining part of the mass that did not decompose up to the temperature of 600 \({}^{\circ}\)C ranges from 9 to 13 wt.% (Table 4) for the analyzed samples. There were no observations that would indicate that the initial composition or exposure time would affect the residual mass. In the case of samples with a higher content of active solvent (samples No.4-9, where the NVP content is 33 wt.% and 50 wt.%), the first recorded mass loss (1 wt.% Table 4) is slightly shifted towards lower temperatures (values mostly below 100 \({}^{\circ}\)C) compared to the previously discussed samples. Analyzing the mass spectra, only the presence of ions responsible for water physically adsorbed on the surface was found (\(m/z=17\) and 18). Figure 2: Ion current for: (**a**) sample series No.1–3; (**b**) sample series No.4–6; (**c**) sample series No.7–9; (**d**) sample series No.10–12; (**e**) sample series No.13–15; (**f**) sample series No.16–18. The hygroscopic properties of the analyzed samples should be considered. The lowest temperatures were recorded for samples with the highest NVP content (sample No.7 with 50 wt.% NVP content and without the addition of photosensitive dopants). In the case of samples No.4-15, No.4-30 and No.4-60, the first maximum recorded on the DTG curve is in the temperature range 134-144 \({}^{\circ}\)C, and is, as mentioned, related to the presence of ions \(m/z=17\) and 18. The second maximum for the first two samples occurs at a temperature of approximately 188 \({}^{\circ}\)C and, based on the mass spectra, is related to the presence of ions \(m/z=15\), 17-19, 28, 29, 41-44, and 56. In the case of samples No.4-60 the same set of ions is observed, but it should be noted that the second maximum of the DTG curve is recorded at the temperature of 237.3 \({}^{\circ}\)C. Therefore, although the sample hardened for 60 s shows a similar mechanism of decomposition of the first molecules released from the polymer structure (most likely NVP), the process itself, seems to be slower, as indicated by the shift in the decomposition maximum towards higher temperatures. At the same time, the double-bond conversion of samples No.4-30 and No.4-60 is at a similar level, which may indicate that this does not affect the final structure of the obtained polymer. Of course, the appearance of the mentioned ions is related to the endothermic effects recorded on the DSC curves (temperatures slightly shifted towards lower values).