## 2 Materials and Methods
### Characterization  
Proton nuclear magnetic resonance (\({}^{1}\)H NMR) spectroscopy served to estimate the degree of polymerization of the linear poly(\(\gamma\)-benzyl L-glutamate) PBG chains, to determine the deprotection level of the PBG substrates, and to investigate the ability of randomly grafted arborescent copolymers to form micelles. The instrument used was a Bruker 300 MHz spectrometer (Bruker, Milton, ON, Canada). Fluorine nuclear magnetic resonance (\({}^{19}\)F NMR) spectroscopy was also performed on the Bruker 300 MHz instrument to determine the chain end primary amine functionality,\(f_{\mathrm{NH2}}\), of the polymers used in the grafting reactions, by a procedure developed by [PERSON] et al. [(29)].  
Analytical SEC, for the characterization of the arborescent PBG substrates of generations G0-G2 and of the copolymers, was carried out on a Viscotek GPCmax unit (Malvern Panalytical, Westborough, MA, USA) equipped with a VE 2001 SEC Solvent/Sample Module, a Viscotek double detector array with refractive index and dual-angle light scattering detectors, and two Agilent Technologies (Mississauga, ON, Canada) PLgel 5 \(\upmu\)m MIXED-C and PLgel 10 \(\upmu\)m MIXED-B organic mixed bed columns, with dimensions of 7.5 mm (ID) \(\times\) 300 mm (L). The system was operated at a flow rate of 0.5 mL/min at 70 \({}^{\circ}\)C, using dimethyl sulfoxide (DMSO) with LiBr (0.05 M) as the mobile phase. Analysis of the chromatograms was performed with the OmniSEC 4.6.1 software package.  
Preparative SEC was conducted on a system with a Waters (Mississauga, ON, Canada) M45 HPLC pump, a 2-mL sample injection loop, a Waters R401 differential refracometer detector, and a Jordi Gel DVB 1000 A 250 mm \(\times\) 22 mm preparative SEC column (Jordi Labs, Mansfield, MA). \(N\),\(N\)-Dimethylformamide (DMF) with 0.2 g/L LiCl served as the mobile phase. The concentration of polymer injected was 25 mg/mL. The system was operated at a flow rate of 3 mL/min at room temperature (25 \({}^{\circ}\)C).  
Light scattering measurements were performed on a Zetasizer Nano ZS90 (Malvern Panalytical) equipped with a 4 mW He-Ne laser operating at 633 nm and 25.0 \({}^{\circ}\)C, at a scattering angle of 90\({}^{\circ}\). The samples were dissolved in phosphate-buffered saline (PBS), DMF, or water for at least 12 h before analysis.  
Absorption spectra were obtained on a Cary 100 Bio UV-Vis spectrophotometer (Agilent) with a spectral bandwidth (SBW) of 2 nm, operated with the Cary Varian UV Scan Application (v3.001339). The absorption peak at 483 nm for doxorubicin and a molar extinction coefficient \(\varepsilon\) = 10,240 M\({}^{-1}\)-cm\({}^{-1}\) was used to calculate the doxorubicin loading in the DOX-micelle samples.  
The dendritic micelles were imaged with a Philips CM10 electron microscope operated at 60 kV. Samples for the TEM measurements were prepared by the following method: One drop of solution (0.05 mg\(\cdot\)mL\({}^{-1}\)) was cast onto a 300-mesh Formvar(r) carbon-coated copper TEM grid placed on filter paper and the excess solution was wicked off with filter paper. After 1 min, one drop of 2% (\(w/v\)) phosphotungstic acid was added to the grid and the excess staining solution was wicked off with filter paper. Finally, the grid was transferred to a new piece of filter paper in a Petri dish and left to dry overnight at room temperature.  
Atomic force microscopy images were recorded in the tapping mode on a Nanoscope III instrument (Veeco, Plainview, NY, USA, model MMAFM-2, scan stage J). The polymer solutions were prepared at concentrations ranging from 0.01 to 0.05 mg.mL\({}^{-1}\). A 20 \(\upmu\)L aliquot of the solution was deposited on the mica substrate and spun at about 3000 revolutions per minute (rpm) for 60 s under ambient conditions. The images were analyzed using the Nanoscope v 1.40 software. The scan rate was typically between 0.7 and 1.2 Hz, at a scan angle of 0\({}^{\circ}\), acquiring 512 samples/line.