## 3 Results and Discussion
### Chain End CuAAC-Grafted Arborescent Copolymers  
Chain end-grafted copolymers derived from arborescent PBG substrates were previously synthesized using peptide coupling techniques [16]. It was shown that chain end grafting provided improved yields and solution properties relatively to random grafting. A similar trend was, therefore, expected for the CuAAC approach.  
\begin{table}
\begin{tabular}{l c c c c c c} \hline \multirow{2}{*}{**Copolymer**} & \multicolumn{3}{c}{**PBG Core (DMF) a**} & \multicolumn{3}{c}{**Graft Copolymer (DMF) a**} & \multicolumn{3}{c}{**Graft Copolymer (PBS) b**} \\ \cline{2-7}  & \(d_{\text{h1}}\) (nm) c & \(d_{\text{h2}}\) (nm) d & \(d_{\text{h1}}\) (nm) c & \(d_{\text{h2}}\) (nm) d & \(d_{\text{h1}}\) (nm) c & \(d_{\text{h2}}\) (nm) d \\ \hline G1 PBG-\(g\)-PHEA & \(11.7\pm 1\) & \(10.4\pm 1\) & \(61.8\pm 1\) & \(47.6\pm 1\) & \(128\pm 1\) & \(104\pm 1\) \\ G1 PBG-\(g\)-PGly & \(11.7\pm 1\) & \(10.4\pm 1\) & \(78.5\pm 1\) & \(65.8\pm 1\) & \(221\pm 1\) & \(199\pm 1\) \\ G2 PBG-\(g\)-PGly & \(18.7\pm 1\) & \(17.5\pm 1\) & \(39.0\pm 1\) & \(35.1\pm 1\) & \(94.9\pm 1\) & \(67.4\pm 1\) \\ G1 PBG-\(g\)-PEO & \(11.7\pm 1\) & \(11.4\pm 1\) & \(24.2\pm 1\) & \(20.5\pm 1\) & insoluble \\ G2 PBG-\(g\)-PEO & \(18.7\pm 1\) & \(17.5\pm 1\) & \(30.4\pm 1\) & \(27.8\pm 1\) & insoluble \\ \hline \end{tabular}  
* DMF with 0.05% LiC1 to prevent aggregation; b phosphate-buffered saline (pH 7.4); c hydrodynamic diameter from 1 st order analysis of the correlation function; d diameter from second-order analysis.  
\end{table}
Table 4: DLS measurements for randomly CuAAC-grafted arborescent copolymers.  
CuAAC grafting reactions of P(HEA-TMS) with both the G1 PBG and G2 PBG chain end-functionalized substrates were attempted but failed, as less than 3% grafting was observed in both cases. The reactions worked for the \(\alpha\)-azido PGly and \(\omega\)-azido PEO chains, however, and the characteristics of the copolymers obtained are summarized in Table 5. The grafting yields observed for the arborescent copolymers using PGly follow the expected trend, with yields decreasing as the substrate generation number increases. The copolymers with PEO had lower grafting yields than those containing PGly. The G1 PBG-_eg_-PEO and G2 PBG-_eg_-PEO samples also had significantly larger polydispersities of 1.30 and 1.23, respectively, which may lead to inaccurate absolute molecular weight determinations by the SEC-MALLS detector. The SEC traces obtained for the arborescent copolymers and the PBG substrates are compared in Figure 7. Repeat SEC measurements and syntheses for both G1 PBG-_eg_-PEO and G2 PBG-_eg_-PEO yielded results similar to those in Table 5. It is obvious that the elution volumes for G1 PBG-_eg_-PEO and G2 PBG-_eg_-PEO are lower than expected, suggesting that either cross-linking has taken place, aggregation or some other artefact is present in the SEC measurements. Since no reliable molecular weight values could be obtained by SEC analysis of the G1 PBG-_eg_-PEO and G2 PBG-_eg_-PEO samples, the grafting yields were not calculated for these reactions. The \(M_{\text{n}}\) and the weight fraction of the shell material in the copolymers could be estimated from their known composition (determined by \({}^{1}\)H NMR analysis) along with the known \(M_{\text{n}}\) value of the PBG substrate as described earlier [16], but in this case the signal from the PBG core is lost (due to its reduced mobility) in the \({}^{1}\)H NMR analysis. Therefore, the grafting yields were determined from the area ratio of the peaks obtained with the DRI detector. In this approach the graft copolymer peak area is divided by the total peak area for the graft copolymer and the unreacted side chain peaks. The grafting yields thus obtained are unfortunately overestimated, since a fraction of the graft copolymer peak response is due to the PBG core, which has a higher \(\text{d}n/\text{d}c\) value than PEO (PBG \(\text{d}n/\text{d}c=0.099\) versus PEO \(\text{d}n/\text{d}c=0.044\) in DMF).