## 3 Results and Discussion
### Randomly CuAAC-Grafted Arborescent Copolymers from G1 and G2 Substrates  
The linear side chains with terminal azide functionalities were also grafted onto arborescent G1 PBG and G2 PBG substrates randomly functionalized with alkyne groups using CuSO\({}_{4}\)/NaAsc. The characteristics of the randomly CuAAC-grafted arborescent copolymers derived from the G1 and G2 substrates are summarized in Table 3. The grafting yield varied between 8-27% in most cases, except for G1 PBG-\(g\)-PEO which had a yield of 57%, while the synthesis of G2 PBG-\(g\)-P(HEA-TMS) was unsuccessful. These relatively low grafting yields were expected due to steric hindrance arising from the compact structure of the arborescent PBG substrates, as previously observed for random grafting reactions via carbodiimide activation [16]. The higher grafting yield observed for G1 PBG-\(g\)-PEO may be linked to the more open structure of G1 PBG, together with the high flexibility of the PEO chains. A similar effect was observed previously for carbodiimide-promoted coupling, in that the only successful grafting reaction with a randomly-functionalized G3 PBG substrate was for the PEO side chains, with a grafting yield of 58% [16]. The molecular weight distribution of all the arborescent copolymers obtained was relatively narrow (\(M_{\mathrm{w}}/M_{\mathrm{n}}\leq 1.14\)). The SEC traces for the purified copolymers with P(HEA-TMS), PGly and PEO side chains, the G1 PBG and G2 PBG substrates are compared in Figure 6, except for the G2 PBG-\(g\)-P(HEA-TMS) sample where only the crude product was recovered since the reaction failed. Relatively symmetrical peaks are observed for all the purified arborescent copolymers, indicating that no degradation occurred during CuAAC grafting. Figure 5: SEC traces in DMF with 0.1% LiCl for (top to bottom) G0 PBG-\(g\)-P(HEA-TMS), G0 PBG-\(g\)-PGly, G0 PBG-\(g\)-PEO after 24 h using CuSO\({}_{4}\)/NaAsc, and G0 PBG. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Copolymer**\({}^{\mathbf{a}}\)} & \multicolumn{3}{c}{**PBG Substrate**} & \multicolumn{3}{c}{**Graft Copolymer**} \\ \cline{2-7}  & \(M_{\mathbf{n}}\) **(g/mol)**\({}^{\mathbf{b}}\) & \% Alkyne**\({}^{\mathbf{c}}\) & & \(M_{\mathbf{n}}\) **(g/mol)**\({}^{\mathbf{b}}\) & \(M_{\mathbf{w}}/M_{\mathbf{n}}\)**\({}^{\mathbf{b}}\) & \(f_{\mathbf{n}}\)**\({}^{\mathbf{e}}\)** & **\% Shell**\({}^{\mathbf{f}}\) \\ \hline G1 PBG-\(g\)-P(HEA-TMS) & 322,000 & 19 & 27 & \(1.2\times 10^{6}\) & 1.14 & 80 & 73 \\ G2 PBG-\(g\)-P(HEA-TMS) & \(1.1\times 10^{6}\) & 32 & & & Reaction Failed & & \\ G1 PBG-\(g\)-PGly & 322,000 & 19 & 20 & 734,000 & 1.09 & 58 & 56 \\ G2 PBG-\(g\)-PGly & \(1.1\times 10^{6}\) & 32 & 13 & \(2.8\times 10^{6}\) & 1.03 & 234 & 60 \\ G1 PBG-\(g\)-PEO & 322,000 & 19 & 57 & \(1.2\times 10^{6}\) & 1.13 & 166 & 72 \\ G2 PBG-\(g\)-PEO & \(1.1\times 10^{6}\) & 32 & 8 & \(1.8\times 10^{6}\) & 1.08 & 140 & 38 \\ \hline \hline \end{tabular}  
* All reactions done with a 1:1 azide to alkyne ratio; \({}^{\mathbf{b}}\) absolute values from SEC-MALLS in DMF; \({}^{\mathbf{c}}\) functionalization level determined from \({}^{1}\)H NMR analysis; \({}^{\mathbf{d}}\) grafting yield: fraction of side chains attached to the substrate; \({}^{\mathbf{e}}\) branching functionality: number of side chains added in the last grafting cycle; \({}^{\mathbf{f}}\) weight fraction of shell material, from the difference in absolute molecular weights of the copolymer and the substrate.  
\end{table} 
Table 3: Characteristics of arborescent G1 and G2 copolymers obtained by random CuAAC-grafting. Dynamic Light Scattering Measurements  
DLS measurements were performed on the arborescent copolymers in DMF and in aqueous phosphate-buffered saline (PBS) to characterize their solution properties. To obtain a water-soluble PHEA shell, removal of the labile TMS protecting group was achieved by simply adding a few drops of a dilute HCl solution into the DMF solution containing the G1 PBG-\(g\)-P(HEA-TMS) sample and stirring for a few minutes.