## 3 Results and Discussion  
Selenium functionalized compounds, especially diselenides, have been widely used as oxidative catalysts due to their responsive redox behavior [15]. Herein, we introduced diselenide functional groups into a polymer chain which offered the possibility of reuse. For this, diselenide functionalized monodisperse polystyrene (DSe-PS) was synthesized by soap-free emulsion polymerization of styrene using FVPDSe and DVB as the crosslinkers. After the DSe-PS was oxidized by hydrogen peroxide, Se-PS containing selenium acid was formed to catalyze the oxidation of acrolein. Firstly, the oxidation behavior of the diselenide bond was investigated by using FVPDSe as a small molecule model. The \({}^{77}\)Se NMR spectrum of FVPDSe was characterized before and after oxidation. The results are summarized in Figure 1. It shows that the selenium signal at \(\delta\) = 373 ppm in deiselenide was shifted to 1204 ppm which, corresponding to selenium acid after oxidation by excessive H\({}_{2}\)O\({}_{2}\) (30 times that of FVPDSe) at room temperature. The chemical shift at \(\delta\) = 1244 ppm could be from a small amount of a selenium derivative with a higher oxidation state. Such results indicated the successful oxidization of diselenide in FVPDSe under mild conditions. The formation of an oxidized selenium structure could be used to selectively oxidize organic compounds [28]. Then, a diselenide group was introduced into polymer particles by using FVPDSe as the crosslinker in soap-free emulsion polymerization of DSe-PS in an aqueous medium at 75 \({}^{\circ}\)C. The polymerizations were carried out by using different amounts of crosslinker. Two crosslinker, e.g., FVPDSe and DVB, were used in preparing polymer particles for the consideration of possible fragmentation of diselenide in FVPDSe after oxidization. The results are summarized in Table 1. It shows that polymer particles could be adjusted by varying the concentration of crosslinker and the amount of water. Polymeric particles with a diameter of 141-190 nm could be obtained in these conditions. The morphology of the obtained particles was characterized by SEM, as shown in Figure 2a-c. The results showed that regular spherical particles were obtained after polymerization. The particle size almost showed monodispersity, as identified by DLS analysis (Figure 2d). \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Sample** & **St (g)** & **FVPDSe (g)** & **DVB (g)** & **KPS (g)** & **SLS (g)** & **H\({}_{2}\)O (mL)** & **Particle Size (nm) 1** \\ \hline Se-1-D-2-20 & 1.0 & 0.066 & 0.132 & 0.02 & 0.005 & 20 & 190 \\ Se-1-D-2-40 & 1.0 & 0.066 & 0.132 & 0.04 & 0.01 & 40 & 166 \\ Se-1-D-2-60 & 1.0 & 0.066 & 0.132 & 0.04 & 0.01 & 60 & 141 \\ Se-1-D-1-40 & 1.0 & 0.100 & 0.100 & 0.04 & 0.01 & 40 & 148 \\ Se-1-D-3-40 & 1.0 & 0.05 & 0.15 & 0.04 & 0.01 & 40 & 149 \\ Se-1-D-4-40 & 1.0 & 0.04 & 0.16 & 0.04 & 0.01 & 40 & 167 \\ \hline \end{tabular} \({}^{1}\) determined by DLS.  
\end{table} 
Table 1: A series of selenium-containing DSe-PS microspheres with different particle sizes or diselenide content. Figure 1: \({}^{77}\)Se NMR spectra of FVPDSe before and after oxidation (red-before oxidation; black-after oxidation). After obtaining these polymer particles, the oxidization of diselenide in DSe-PS was investigated. Polystyrene microspheres with different selenium contents (mass ratio of DVB:FVPDSe = 1:1, 2:1, 3:1, 4:1) were oxidized by 5 wt% H\({}_{2}\)O\({}_{2}\) overnight at room temperature. The polystyrene microspheres before and after oxidation were characterized by DIS, XPS and SEM. The results showed in Figure 3 indicated that the morphology of particles remained as a regular sphere after oxidization.