## 3 Results and Discussions  
### Synthesis of Polymer-Grafted Nanoparticles  
Scheme 1 shows the synthesis pathway of bare silica, amino-modified, initiator-modified silica nanoparticles, and polymer-grafted nanoparticles. Firstly, SiO\({}_{2}\) nanoparticles were synthesized by the Stober method [32]. The nanoparticles were then modified by 3-aminopropyltrimethoxysilane (APTMS) and then by 2-bromoisobutyryl bromide (BiBB) to obtain silica nanoparticle initiator, SiO\({}_{2}\)-Br. Next, SI-ATP was employed to graft oligoethylene glycol methyl ether methacrylate (OEGMA) and/or tert-butyl acrylate (tBA) monomers onto SiO\({}_{2}\)-Br. By this, we prepared SiO\({}_{2}\)-\(g\)-POEGMA, SiO\({}_{2}\)-\(g\)-PtBA, and SiO\({}_{2}\)-\(g\)-P(OEGMA-_stat_-tBA) nanoparticles. SiO\({}_{2}\)-\(g\)-PtBA and SiO\({}_{2}\)-\(g\)-P(OEGMA-_stat_-tBA) were then hydrolyzed to obtain SiO\({}_{2}\)-\(g\)-PAA and SiO\({}_{2}\)-\(g\)-P(OEGMA-_stat_-AA), respectively. For SiO\({}_{2}\)-\(g\)-P(OEGMA-_stat_-AA), three nanoparticles containing different ratios of OEGMA and tBA monomers were prepared (Table 1). After hydrolysis, SiO\({}_{2}\)-\(g\)-P(OEGMA\({}_{30}\)-_stat_-AA\({}_{70}\)), SiO\({}_{2}\)-\(g\)-P(OEGMA\({}_{50}\)-_stat_-AA\({}_{50}\)) and SiO\({}_{2}\)-\(g\)-P(OEGMA\({}_{70}\)-_stat_-AA\({}_{30}\)) were obtained. The nanoparticles were characterized by TEM, and the images of the polymer-grafted nanoparticles clearly show that the nanoparticles have a silica core and a polymer shell (Figure 1). The diameter of SiO\({}_{2}\) is 40 nm, calculated based on the TEM images. The thickness of the polymer shell of SiO\({}_{2}\)-\(g\)-POEGMA and SiO\({}_{2}\)-\(g\)-PAA is approximately 5 nm and 3 nm, respectively. For SiO\({}_{2}\)-\(g\)-P(OEGMA\({}_{30}\)-_stat_-AA\({}_{70}\)), SiO\({}_{2}\)-\(g\)-P(OEGMA\({}_{50}\)-_stat_-AA\({}_{50}\)), and SiO\({}_{2}\)-\(g\)-P(OEGMA\({}_{70}\)-_stat_-AA\({}_{30}\)) particles, the thickness of the polymer shells are similar, approximately 2.5 nm. These results indicate that the polymers were successfully grafted onto the silica nanoparticle. \begin{table}
\begin{tabular}{c c c c} \hline
**OEGMA (m)** & **tBA (n)** & **m/n** & **SiO\({}_{2}\)-\(g\)-P(OEGMA-_stat_-tBA) Nanoparticles** \\ \hline
2.04 mmol & 4.76 mmol & 30/70 & SiO\({}_{2}\)-\(g\)-(OEGMA\({}_{30}\)-_stat_-tBA\({}_{70}\)) \\
3.40 mmol & 3.40 mmol & 50/50 & SiO\({}_{2}\)-\(g\)-(OEGMA\({}_{50}\)-_stat_-tBA\({}_{50}\)) \\
4.76 mmol & 2.04 mmol & 70/30 & SiO\({}_{2}\)-\(g\)-(OEGMA\({}_{70}\)-_stat_-tBA\({}_{30}\)) \\ \hline \end{tabular}
\end{table} 
Table 1: Ratio of OEGMA and tBA monomers for preparation of SiO\({}_{2}\)-\(g\)-P(OEGMA-_stat_-tBA) nanoparticles. Figure 1: TEM images of bare SiO\({}_{2}\) (**a**), SiO\({}_{2}\)-\(g\)-POEGMA (**b**), SiO\({}_{2}\)-\(g\)-PAA (**c**), SiO\({}_{2}\)-\(g\)-P(OEGMA\({}_{30}\)-_stat_-AA\({}_{70}\)) (**d**), SiO\({}_{2}\)-\(g\)-P(OEGMA\({}_{50}\)-_stat_-AA\({}_{80}\)) (**e**), and SiO\({}_{2}\)-\(g\)-P(OEGMA\({}_{70}\)-_stat_-AA\({}_{30}\)) (**f**). The bare silica and the polymer-grafted nanoparticles were also characterized by FT-IR (Figure 2). For the bare silica nanoparticles (Figure 2a), the absorption peaks at 1100 cm\({}^{-1}\) and 465 cm\({}^{-1}\) belong to the stretching and bending vibration of the Si-O groups, respectively. In addition, the absorption peaks at 945 cm\({}^{-1}\) and 800 cm\({}^{-1}\) belong to the bending vibration of the Si-OH and Si-O-Si groups, respectively. Figure 2b shows a new absorption band at 1536 cm\({}^{-1}\) corresponding to the bending vibration of N-H in the amide group that appears in the spectrum of the SiO\({}_{2}\)-Br nanoparticles, indicating the silica nanoparticles were successfully functionalized with the initiator. For SiO\({}_{2}\)-\(g\)-POEGMA nanoparticles, the absorption peak at 1730 cm\({}^{-1}\) was observed (Figure 2c), belonging to the stretching vibration of the -O-C=O group, indicating the successful grafting of the POEGMA polymer chains onto the silica surface by SI-ATRP.