## 3 Results and Discussion
### Polystyrene Nanoparticle Synthesis  
#### 3.2.1 Influence of Surfmer Concentration Below the CMC on Nanoparticle Size  
For the surfmer **2a**, we selected four different surfmer concentrations below the CMC, and synthesized polystyrene nanoparticles **3a-d** in an emulsion polymerisation (Figures 1 and 3a,b). We used potassium persulfate as a radical initiator and added small amounts of divinyl benzene to enable cross linking. The emulsion polymerizations were performed for 24 h at 80 \({}^{\circ}\)C for maximum conversion of the monomers. At this temperature the surfmer **2a** was still completely soluble and the cloud point wasn't reached. The degree of conversion was analysed by headspace GC-MS on the final latex. Here 0.73 wt % monomer were detected (see Figure S7), which is in the range of commercial polystyrene latexes [31]. All starting material concentrations and initial conditions were kept constant for these reactions with different surfmer concentrations (Table 2).  
Figure 2: Surface tension as function of the surfmer concentration in water (\(n\) = number of repeating units in the oligoglycidol moiety of the surfmer; intersection of regression lines at critical micelle concentration (CMC)).  
Emulsion polymerisation with **2a** at a concentration of 0.24 mmol\(\cdot\)L\({}^{-1}\) and a surfmer:monomer ratio of 1:1984 resulted in spherical particles **3a** with an average diameter of 247 nm and a narrow size distribution with a PDI of 0.015 (Figure 3a,b and Table 3). The particle size was analysed by dynamic light scattering (DLS) and was confirmed by scanning electron microscopy (SEM, Table 3). The average particle diameter obtained from SEM images was with 235 nm slightly smaller than the average diameter obtained via DLS (Table 3). A zeta potential of \(-\)37.7 mV was measured for polystyrene particles **3a**, which illustrates that surface bound sulphate groups of the initiator offer additional charge stabilisation. Increasing the surfmer concentration to 0.88 mmol\(\cdot\)L\({}^{-1}\) and the surfmer:monomer ratio to 1:545 leads to a reduction in particle size and an average nanoparticle diameter of 173 nm with a PDI of 0.004 (as determined by DLS; **3b**, Figure S8, Table 3). A further increase in surfmer concentration yielded nanoparticles **3c** and **d** with even smaller diameters of 163 and 137 nm (determined by DLS, Figures S9 and S10, Table 3) respectively. Both nanoparticles **3c** and **d** showed a narrow size distribution with PDI of 0.009 and 0.010 respectively (Table 3). Hence the overall trend showed that an increase in surfmer concentration led to a reduction in particle size if all other reaction parameters are kept constant (Figure 3c). As previously reported [16], below the CMC homogeneous nucleation of surfmer molecules reacting with the initiator drives the polymerisation. Therefore an increase in surfmer concentration led to a higher nucleation rate and therefore to smaller particles. All synthesized nanoparticles showed a narrow size distribution in DLS as well as SEM analysis and similar zeta potential (Table 3).  
Figure 3: (**a**) Overview and (**b**) high resolution SEM image of nanoparticles **3a** synthesized with 0.24 mmol\(\cdot\)L\({}^{-1}\) of oligoglycidol6 (**2a**) as surfmer, and (**c**) average particle size (determined by dynamic light scattering (DLS)) as a function of the surfmer concentration (surfmer **2a** with 6 repeating units in all experiments).