## 3 Results and Discussion
Furthermore, as Sn(EH)\({}_{2}\) is not able to initiate polymerization, the ARGET ATRP should allow synthesis of pure block copolymers, not contaminated by a fraction of homopolymers. Last but not least, the use of a reducing agent in the ARGET ATRP allows removal of residual oxygen from the polymerization system. Thanks to this, the degassing procedure before the polymerization does not have to be so restrictive. We tested three types of catalytic system with three ligands (L) differing in their activities in ATRP: N,N\({}^{\prime}\),N\({}^{\prime\prime}\),N\({}^{\prime\prime}\)-pentamethyldiethylenetriamine (PMDETA), 2,2\({}^{\prime}\)-Bipyridyl (bpy) and tris[2-(dimethylamino)ethyl]amine (Me\({}_{6}\)TREN). All polymerizations were carried out using a very low concentration of Cu(II) salt (CuCl\({}_{2}\) or CuBr\({}_{2}\)) (9 ppm (_u/v_)). In all cases, the same molar ratio of PNIPAM-Br: St:CuX\({}_{2}\):L:Sn(EH)\({}_{2}\) was applied 1:400:0.006:0.1:0.1. The reactions were carried out at 90 \({}^{\circ}\)C or 110 \({}^{\circ}\)C.  
The conditions under which the polymerizations of styrene were performed are presented in Figure 1:0 The obtained conversions of styrene and characteristics of the prepared block copolymers, from SEC, are also given in Figure 1:1  
As can be seen, the highest conversion (\(>\)50%) was attained for CuCl\({}_{2}\)/Me\({}_{6}\)TREN catalytic system after 24 h of polymerization which was conducted at 110 \({}^{\circ}\)C. However, the polymers with a broad MWD (PDI = 2.01) were prepared in this way. The application of the CuBr\({}_{2}\)/bpy system caused the polymerization to proceed significantly slower but MWDs of the synthesized polymers were still not satisfactory. Finally, the employment of CuCl\({}_{2}\)/PMDETA as a catalytic system resulted in relatively low polydispersities (PDI \(<1.5\)) \begin{table}
\begin{tabular}{c c c c c c c c} \hline \multirow{2}{*}{**Entry**} & **Starting** & **Catalytic** & **T** & **Conv 1 ** & **\(M_{\mathrm{n}}\) [Da] 2 ** & **\(M_{\mathrm{n}}\) [Da] 3 [FOOTNOTE:3]Footnote 3: \(M_{\mathrm{n}}\) [Da] & **PDI =** \\  & **PNIPAM** & **System** & **[\({}^{\circ}\)C]** & **[\%]** & **PNIPAM** & **b [FOOTNOTE:3]Footnote 3: \(M_{\mathrm{n}}\) [Da] & **PDI =** \\ \hline PNPS1 & P5 & CuCl\({}_{2}\)/PMDETA & 46 & 110 & 37.5 & 4900 & 2600 & 1.33 \\ PNPS2 & P2 & CuCl\({}_{2}\)/PMDETA & 4 & 90 & 10 & 2200 & 3000 & 1.35 \\ PNPS3 & P2 & CuCl\({}_{2}\)/PMDETA & 8 & 90 & 28.4 & 2200 & 4300 & 1.35 \\ PNPS4 & P4 & CuBr\({}_{2}\)/bpy & 48 & 110 & 38.7 & 4100 & 11100 & 1.7 \\ PNPS5 & P5 & CuCl\({}_{2}\)/Me\({}_{6}\)TREN & 24 & 110 & 54.8 & 4900 & 19500 & 2.01 \\ \hline \end{tabular}
\end{table} 
Table 3: The conditions under which the chain extensions of PNIPAM-Br with styrene via ARGET ATRP were conducted; the obtained monomer conversions (Conv), number-averaged molecular masses (\(M_{\mathrm{n}}\)) of both blocks in the polymers’ chains and polydispersity indices determined from SEC analyses. Figure 7 shows a \({}^{1}\)H NMR spectrum recorded for one of the prepared copolymers, denoted in Table 3 as PNPS2. The spectrum reveals the presence of both blocks in the prepared copolymer. From the proton integration of the signals at 6.25 ppm to 7.25 ppm (characteristic for aromatic protons in the PS block and NH proton in the PNIPAM block) and 4.01 ppm for isopropyl proton (CH(CH\({}_{3}\))\({}_{2}\)) of the PNIPAM block, the ratio of the repeated units in both blocks may be estimated as 1:0.7 PNIPAM:PS. It is in a good agreement with the results from SEC (see Table 3). The \({}^{1}\)H NMR of other synthesized copolymers can be found in in the Supplementary Material (Figure S2). It is worth mentioning that in all post-polymerization mixtures, except for the prepared block copolymers, an admixture of polystyrene was present. Albeit the polystynenes, obtained as by-products, can be easily separated from the prepared copolymers simply by washing the solid mixtures with toluene.