## 3 Results and Discussion
### Polystyrene Nanoparticle Synthesis
#### 3.2.3 Influence of Oligoglycidol Chain Length on Nanoparticle Size  
Additionally, we analysed the influence of the oligoglycidol chain length on the average polystyrene particle size whilst keeping the surfmer concentration constant. Therefore, we synthesized, in addition to the previously described particles, polystyrene nanoparticles **5** with 0.96 mmol-L\({}^{-1}\) oligoglycidol\({}_{20}\) (**2c**). Keeping all other reaction parameters constant led to nanoparticles with an average particle diameter of 405 nm and a narrow size distribution with a PDI of 0.037 (as determined by DLS, Figure S14, Table 3). As for the other surfmers, **2c** was still completely soluble in water at 80 \({}^{\circ}\)C. Furthermore we performed a control experiment using previously described reaction parameters without the addition of surfmer. Here, polystyrene nanoparticles **6** with an average diameter of 365 nm and a PDI of 0.18 (as determined by DLS, Figure S15, Table 3) were obtained. The nanoparticles **6**, synthesized without surfactant, showed a very large size distribution. In SEM analysis particles with diameters ranging from approximately 50 to 500 nm were observed (see Figure S15). With this experiment we could show that latex particles can be stabilized solely by the sulphate group of the used initiator, but that the stabilization is not enough to get good control over the particle size. Therefore a large range of differently sized particles was obtained. Comparing nanoparticles of all three oligoglycidol surfmers **2a-c** with a concentration of approximately 1 mmol-L\({}^{-1}\) and a surfmer:monomer ratio around 1:500, a clear trend was visible (Figure 5). It can be observed that an increase in the chain length led to an increase in the average particle size (Figure 5). Furthermore, comparing the average particle size of latexes synthesized with and without surfmer it can be seen that the use of **2c** as surfmer led to nanoparticles with a similar average diameter as using no surfmer. Together with the surface tension measurements, which suggest that an increase in the oligoglycidol chain length leads to an increase in hydrophobicity, it can be proposed that with increased chain length the oligoglycidol macromolecules have an increased tendency to be located inside the polystyrene nanoparticles instead of at the surface. This tendency, caused by increased hydrophobicity, would lead to less amount of surfactant being available to stabilize the nanoparticles and therefore larger particles. Another factor, which may influence the resulting particle size, is the reactivity of the oligoglycidol surfmer. As described in a previous article [16], the reaction mechanism of emulsion polymerisation of styrene with oligoglycidol as a surfmer goes via a homogeneous nucleation mechanism, when the surfmer concentration is below the CMC. Here, in the initial stage of the polymerisation the rate of nucleation is determined by the reactivity of the oligoglycidol-functionalised surfmer. A change in oligoglycidol chain length can influence the reactivity due to, e.g., larger steric hindrance of the vinyl group. Furthermore surfmer **2c** is at a concentration of 1 mmol-L\({}^{-1}\) already above the CMC, whereas surfmers **2a** and **b** are still below. Therefore the difference in reaction mechanism will also have an influence on the different particle sizes. Nevertheless additional experiments investigating the hydrophobicity of the different oligoglycidol surfmers and the nucleation rate of emulsion polymerisations using those surfmers at various concentrations are necessary for a better understanding.  
Figure 4: Average particle size (determined by DLS) dependant on surfactant concentration for oligoglycidol\({}_{10}\) (**2b**). At a concentration of 1.55 mmol-L\({}^{-1}\) (dashed line) the CMC is reached.