# Doped Epoxy Resins as an Alternative to Luminescent Optical Sensors
## 2 Materials and Methods  
The set of investigated samples contained one of two derivatives of bisphenol A epoxy diacrylate EB150 or EB600 (CYTEC, Viesbaden, Germany) doped with photoluminescence dopants: fluorescein (ALDRICH, Warsaw, Poland) or 2.7-dihydroxy naphthalene with epichlorohydrin (the substance synthesized at the Department of Polymer Chemistry, UMCS, Lublin, Poland), was obtained by photopolymerization. The structures of all substances used are shown in Figure 1. The acrylates used vary in viscosity; therefore, it was possible to investigate the influence of a changing viscosity, by adding the active solvent N-vinyl-pyrrolidone (NVP) (Fluka AG, Buchs, Switzerland), on obtained material properties. The detailed information about the synthesis of 2.7-dihydroxy naphthalene with epichlorohydrin (2.7-NAF.EP) was presented in Refs. [39; 40]. To obtain studied compositions, bisphenol A epoxy diacrylate derivative was dissolved in NVP. The process was conducted in the three-necked flask equipped with a stirrer and a water condenser. During the whole process, temperature (80 \({}^{\circ}\)C) was controlled by the thermometer placed in one of the flask neck. After the acrylate derivative was completely dissolved, a photoluminescence dopant was added. The concentration of dopant in all prepared samples was 1 wt.%. Detailed information about compositions used in the syntheses is given in Tables 1 and 2. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{**EB150/wt.\%**} & \multirow{2}{*}{**NVP/wt.\%**} & \multicolumn{2}{c}{**Dopant/wt.\%**} & \multirow{2}{*}{**Polymerization Time/s**} \\ \cline{3-4}  & & & **2.7-NAEEP** & & \\ \hline Sample No.1-15 & 75 & 25 & - & - & 15 \\ Sample No.1-30 & 75 & 25 & - & - & 30 \\ Sample No.1-60 & 75 & 25 & - & - & 60 \\ \hline Sample No.2-15 & 75 & 25 & 1 & - & 15 \\ Sample No.2-30 & 75 & 25 & 1 & - & 30 \\ Sample No.2-60 & 75 & 25 & 1 & - & 60 \\ \hline Sample No.3-15 & 75 & 25 & - & 1 & 15 \\ Sample No.3-30 & 75 & 25 & - & 1 & 30 \\ Sample No.3-60 & 75 & 25 & - & 1 & 60 \\ \hline Sample No.4-15 & 67 & 33 & - & - & 15 \\ Sample No.4-30 & 67 & 33 & - & - & 30 \\ Sample No.4-60 & 67 & 33 & - & - & 60 \\ \hline Sample No.5-15 & 67 & 33 & 1 & - & 15 \\ Sample No.5-30 & 67 & 33 & 1 & - & 30 \\ Sample No.5-60 & 67 & 33 & 1 & - & 60 \\ \hline Sample No.6-15 & 67 & 33 & - & 1 & 15 \\ Sample No.6-30 & 67 & 33 & - & 1 & 30 \\ Sample No.6-60 & 67 & 33 & - & 1 & 60 \\ \hline Sample No.7-15 & 50 & 50 & - & - & 15 \\ Sample No.7-30 & 50 & 50 & - & - & 30 \\ Sample No.7-60 & 50 & 50 & - & - & 60 \\ \hline Sample No.8-15 & 50 & 50 & 1 & - & 15 \\ Sample No.8-30 & 50 & 50 & 1 & - & 30 \\ Sample No.8-60 & 50 & 50 & 1 & - & 60 \\ \hline Sample No.9-15 & 50 & 50 & - & 1 & 15 \\ Sample No.9-30 & 50 & 50 & - & 1 & 30 \\ Sample No.9-60 & 50 & 50 & - & 1 & 60 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Experimental parameters of the syntheses for EB150. Figure 1: Substances used in the study: (**a**) EB150, (**b**) EB600, (**c**) Fluorescein, (**d**) 2.7-NAF.EP, (**e**) NVP. All compositions were polymerized with UV light in the presence of 1 wt.% of 2,2-dimethoxy-2-phenylacetophenone (Irgacure 651, ALDRICH, Warsaw, Poland) for 15, 30 and 60 s. The curing process was carried out at room temperature in a chamber in which 8 UV lamps (OSRAM, DULUX L BL UVA 18 W/78, UVA radiation in the range of 315-400 nm) were placed. The atmosphere of the photopolymerization reaction is very important, which is why during the entire process the chamber was washed with inert gas, argon, to prevent oxygen inhibition. The oxygen molecule is a radical, which is why it is highly reactive. Atmospheric oxygen can extinguish radicals generated from the initiator at the very beginning of photopolymerization, i.e., at the initiation stage. In the next step, unreactive peroxydricals may be formed. This causes the active part of the chain to \"freeze\" and thus generally inhibit the reaction.