## 3 Results and Discussion  
Scheme 3 displays our proposed mechanism for two-step, one-pot switching of the polymer topology from linear to branched via tuning of the solubility of the copper complex. At the beginning of this process, we mixed a more-active initiator (EBiB), Cu(I)/L, a monomer (St), and an inner (VBC). Condition under which the copper complex retained poor solubility were employed to perform irreversible initiation of the atom transfer radical reaction from EBiB; the initiating site of the VBC monomer or P(St-_co_-VBC) copolymer could not be activated efficiently as a result of precipitation of the deactivators. This atom transfer reaction induced a conventional free radical polymerization process (named herein as AT-FRP) and resulted in a linear structure. During the AT-FRP procedure, the reaction medium contained mainly the propagating linear polymer with a pendent initiating site (_i.e._, benzyl chloride), poorly dispersed Cu(II)/L deactivator, and the rest of the monomers and inimers. In the second step, the conditions were changed to increase the solubility of the deactivator (_i.e._, increasing the temperature or the solvent polarity). The propagating chains and re-dissolved deactivators guided the recovery of the balance between activation and deactivation. Namely, the linear polymer with a pendent initiating site, Cu(I)/Cu(II) species, the monomer, and the inimer could undergo a typical SCVP procedure, resulting in a branched polymer. **Scheme 3. ** Control over polymer topology through one-pot AT-SCVP with catalyst phase transfer. To examine this proposed concept, we selected a poorly soluble and less-effective copper complex. We first examined the solubilities of CuBr/Bpy and CuBrz/Bpy in toluene (T) and anisole (A), prior to performing the catalyst-phase-switchable AT-SCVP. We performed the solubility tests using the (co)solvents at a thermostatted temperature. As displayed in Figure 1a, the solubilities of CuBr/Bpy in T were approximately an order of magnitude lower than those of CuBr/Bpy in A at the various temperatures. Compared to the case in T alone, the solubility of CuBr/Bpy in the cosolvent [_i.e._, T/A, 1:1 (_v/v_)] was approximately five times greater at 50 or 70 \({}^{\circ}\)C. CuBrz/Bpy (Figure 1b) exhibited verylimited solubilities in T, even at 110 \({}^{\circ}\)C (_ca._ 40 ppm). The solubilities of CuBr\({}_{2}\)/Bpy in the higher-polarity solvent (A) were over an order of magnitude greater than those in T. The solubility of CuBr\({}_{2}\)/Bpy in the cosolvent also increased by over five times at 50 or 70 \({}^{\circ}\)C. These results indicated that both the temperature and the solvent polarity could tune the solubility of these copper complexes, with increased solvent polarity providing significant improvements. Table 1 summarizes the results. The radicals generated through C-X bond hemolysis of the alkyl halides (RX) activated by Cu(I)/L species were trapped irreversibly by the stable nitroxide radical to yield the corresponding alkoxyamines (_i.e._, R\({}_{y}\)-TEMPO in Scheme S1). This method has been used frequently to measure the activation rate constants (\(k_{\mathrm{act}}\)) during ATRP [62]. Previous studies have indicated that TEMPO functions only as a radical trap; the measured rate constants were nonrelated to the concentration of excess TEMPO. To further understand the related activation rate constants (\(k_{\mathrm{act}}\)), we examined the effect of a high molar ratio difference between the initiators EBiB and BzCl (herein, EBiB/BzCl = 1:16), which have similar initiating moieties to the reagents in Scheme 3. We employed systematic model conditions for the trapping reactions of the atom transfer radical with TEMPO (AT-TEMPO). We monitored (GC) the reactions by following the consumptions of the initiators. Figure 2 displays the kinetic results obtained using various temperatures (50, 70, and 110 \({}^{\circ}\)C) and solvents [T (hollow symbols in Figure 2a-c) and A (solid symbols in Figure 2d-f)]. By fitting plots of \(\ln[1-(C_{0}/I_{0})\times X]-\ln(1-X)\)