The measurements were done in anisole (50 mol%). The reactivity ratios were then evaluated first by fitting the evolution of the feed ratio versus the overall molar conversion (Figure and 7b) using the Skeist equation and a nonlinear leastsquares (NLLS) method (Meyer-Lowry method). We also used the CONTOUR software (see ESI for details) to confirm these values and calculate the 95% joint confidence interval. The experiments with styrene led to reactivity ratios close to unity (rS = 0.84, rPOT = 0.88) showing no compositional drift even at high conversion. In the case of IBA, the values are less ideal at riBoA = 0.27 and rPOT = 1.42, indicating a slight decrease of FPOT with conversion (Figure ). These reactivity ratios are nevertheless greatly improved for styrene and slightly improved for acrylate derivatives compared to DOT. With these reactivity ratios, it is possible to plot the evolution of the instantaneous and the cumulated fraction of inserted thioester bonds into the polymer backbone versus the overall monomer conversion (see ESI for details). Such plot is represented in Figure -d for an initial feed ratio of 5 mol% in thionolactone. It is interesting to visualize the compositional drift that occurred during the reaction. The same plot for DOT in the same copolymerization system is also reported in the same Figure . The impact of POT compared to DOT is clearly apparent especially for styrene and is less pronounced for acrylate derivatives. In all cases (DOT and POT) for the polymerization of acrylate derivatives, the conversion has to be kept below 60-70% conversion to still have insertion of thioester moieties into the polymer backbone.