## 3 Results and Discussion
### Synthesis of Randomly Grafted Arborescent Copolymers
It is nonetheless clear that these values represent differently weighted means of the size distributions, and indeed size distribution analysis (Figure 3) shows that all the G1 PBG-\(g\)-PEO copolymers exhibit a small quantity (16-34%) of aggregated structures with a diameter of 70-160 nm in their _intensity_ distributions, while no aggregation is detected in neither the _number_ nor the _volume_ distributions. Size distribution analysis of the G2 PBG-\(g\)-PEO copolymers likewise yielded a small quantity (17-32%) of aggregated structures with a diameter of 160-230 nm in the _intensity_ distributions, while no aggregation was detected in neither the _number_ nor the _volume_ distributions (Figure S6, Supplementary Materials). These results indicate that even though the vast majority of randomly grafted arborescent copolymer molecules exist as stable, isolated unimolecular micelles, a minute amount of aggregation occurs that is only detectable in the intensity-weighted distributions, due to the extremely high sensitivity of the scattering intensity to large particles [34]. Arborescent copolymers of the same generation yielded similar hydrodynamic diameters by DLS analysis even though their core structure was different. For example, when comparing the micelles formed by G2 PBG\({}_{15}\)-\(g\)-PEO and G2 PBG\({}_{65}\)-\(g\)-PEO, there is only a 4 nm difference in the number-average diameter, confirming that the core only has a minor influence on the overall micelle size. Since the hydrophobic PBG cores should collapse to minimize their unfavorable interactions with the aqueous solution (as determined by \({}^{1}\)H NMR analysis) and the G1 and G2 cores have a similar molecular weight in each series, their contribution to the overall size of the micelles should be minimized in comparison to the more soluble PEO shell. The morphology and size of the unimolecular micelles were investigated by TEM, after staining with phosphotungstic acid on a carbon-coated copper grid, as well as by AFM (Figure S7 in the Supplementary Materials for the G1 copolymers, Figure 4 for the G2 copolymers). The unimolecular micelles have a fairly uniform size distribution and a spherical shape in all cases. The average micelle diameter measured by TEM was 15 \(\pm\) 2, 14 \(\pm\) 3, and 16 \(\pm\) 2 nm for G1 PBG\({}_{15}\)-\(g\)-PEO, G1 PBG\({}_{29}\)-\(g\)-PEO, and G1 PBG\({}_{65}\)-\(g\)-PEO, respectively. In contrast, the average micelle diameter was 29 \(\pm\) 3, 30 \(\pm\) 2, and 35 \(\pm\) 3 nm for G2 PBG\({}_{15}\)-\(g\)-PEO, G2 PBG\({}_{29}\)-\(g\)-PEO, and G2 PBG\({}_{65}\)-\(g\)-PEO, respectively. All the measurements were based on 15-30 particles within the same micrograph. The TEM measurements confirmed the trends in the DLS measurements in terms of increasing micelle size for higher generations. The diameter of these unimolecular micelles appears to be within the ideal size range for therapeutic nanocarriers to be used in cancer treatment [35]. The size of the micelles measured by TEM was somewhat smaller than by DLS analysis. Because TEM yields the diameter of the dry, somewhat flattened micelles on the TEM grid surface, while DLS measures their hydrodynamic (solvated) diameter, discrepancies are to be expected between these methods. The results obtained are therefore considered to be in good agreement.