## 3 Results and Discussion
### Effect of TEMPO Content on Polymerization Rate and Molecular Weight Development  
Cases 3, 4, 7, and 8 of Table 1, all of them with [DVB] = 1 wt.%, were used to analyze the effect of controller (TEMPO) content on the NMC of STY/DVB at T = 120 \({}^{\circ}\)C and P = 207 bar. It is observed in Figure 8 that increasing TEMPO content in the reacting mixture results in decreased polymerization rates (slower conversion versus time profiles), a result which is expected in RDRPs. It is shown in Figure 9 that the M\({}_{\rm n}\) versus conversion (x) profiles for Cases 7 and 8 follow linear trends, with the case with lower TEMPO content reaching slightly higher molecular weights. Figure 8: Effect of controller (TEMPO) content on polymerization rate for the NMC of STY/DVB in scCO\({}_{2}\) at [DVB] = 1 wt.%, T = 120 \({}^{\circ}\)C, and P = 207 bar. Figure 7: Effect of DVB content on the development of the SI for the NMC of STY/DVB in scCO\({}_{2}\) at [TEMPO]/[BPO] = 1.1, T = 120 \({}^{\circ}\)C, and P = 207 bar. Figure 10 shows profiles of M\({}_{\rm w}\) versus x. At first sight, the data points do not seem to show clear trends. However, when each profile is analyzed individually, the expected trends are revealed. In the case at [TEMPO]/[BPO] = 1.1, only two data points (triangles) are observed in Figure 10; one of them (x = 0.1) seems to correspond to an increasing profile for the pre-gelation period, and the other (x = 0.33) to a decreasing profile for the post-gelation period (see solid black trending lines). This indicates that the gelation point for Case 4 occurs between 15 and 25% monomer conversion. In the case at [TEMPO]/[BPO] = 1.6, there are three data points at conversions lower than 20% monomer conversion, which shows an increasing trend that agrees with the increasing trend of a crosslinking system for the pre-gelation period. The data point at x = 0.3 seems to correspond to a decreasing profile for the post-gelation period. This behavior is illustrated with the short-dashed red trending lines. The gelation point for Case 7 occurs between 15 and 28% monomer conversion. In the system at [TEMPO]/[BPO] = 3 (Case 8), although the data points are scattered, all of them seem to follow the increasing trend of a profile during the pre-gelation period. As indicated by the long-dashed green trending line, it seems that the gelation point was not reached before 24 h, which was the maximum time where samples were taken. Figure 10: Effect of controller (TEMPO) content on the evolution of M\({}_{\rm w}\) versus conversion for the NMC of STY/DVB in scCO\({}_{2}\) at [DVB] = 1 wt.%, T = 120 °C, and P = 207 bar. Figure 9: Effect of controller content on the evolution of M\({}_{\rm n}\) versus conversion for the NMC of STY/DVB in scCO\({}_{2}\) at [DVB] = 1 wt.%, T = 120 °C, and P = 207 bar. Figure 11 shows the profiles of gel percentage versus conversion. As expected, gelation is delayed as the amount of TEMPO is increased. From the data points at low conversions, it can be inferred that the gelation point in the absence of a controller (Case 3) occurs very early during the polymerization (no data point available); gelation occurs between 5 and 10% monomer conversion for Case 4 and between 13 and 25% for Case 7. The colored trending lines of Figure 11 provide an easier way to visualize these results. The results of the SI versus conversion shown in Figure 12 confirm that gelation did not take place during the time that the polymerization was monitored in Case 6, the one with [TEMPO]/[BPO] = 3 (green trending line and green squares). On the other hand, the SI for Case 7 increased abruptly and then decreased between 20 and 30% monomer conversion, which indicates that gelation took place in that interval, in agreement with what was observed in Figures 10 and 11 (see red trending line and red diamonds). Figure 11: Effect of controller (TEMPO) content on the evolution of gel percentage versus conversion for the NMC of STY/DVB in scCO\({}_{2}\) at [DVB] = 1 wt.%, T = 120 \({}^{\circ}\)C, and P = 207 bar.