They plotted the conversion of each X-Y-DOT as a function of total monomer conversion. The consumption of unmodified DOT (in black) follows a trajectory similar to, albeit slightly higher than that of a random copolymerization depicted by a dashed line. In contrast, fluorine and thioether substituents increase the reactivity of X-Y-DOT relative to styrene, whereas methoxy substituents decrease its reactivity. We thus employed our computational method to verify the correlation between the experimental values obtained by the Johnson group and our results, and thus to validate that our approach effectively captures the trend of substituent effects on the reactivity of this thionolactone with styrene. The kp/ktr computed values for the different X-Y-DOT are reported on Figure . Using our DFT computational method, theoretical values that follow the same trend as the experimental ones were obtained. The electronic nature of the substituent at the para positions of the aryl groups influences the reactivity of the thionolactones. Among the various X-Y-DOT structures, Johnson et al. prepared functional derivatives bearing one or two functional groups that could not be used to discriminate the effect of the substituent on either the aromatic group in α position of the thiocarbonyl moiety or on the group that stabilizes the ring-opened radical. In order to decorrelate the effects, we performed various DFT calculations by substituting either side with different groups having distinct electronic effects and determined the various kinetic rate constants in the case of copolymerization with styrene. These results are presented in Figure . We first observed different effects depending on whether the substitution is made on the aromatic group in the α position of the thiocarbonyl moiety or on the group that stabilizes the ringopened product. Specifically, focusing on the aromatic group in the α position of the thiocarbonyl moiety (Figure ), we see that substitution influences both addition/reverse addition and β-scission. Regarding the addition rate constant, the more electron-withdrawing the substituent, the more the radical addition is favored. This is in good agreement with the data already observed on RAFT agents. Conversely, a lower reverse addition rate constant is observed when the substituent is an electronwithdrawing group. For β-scission, we also notice a significant effect: the more electron-donating the substituent, the more βscission is favored. If we focus on the group stabilizing the ringopened radical, we observe that only the beta-scission rate constant is affected, also in agreement with the reactivity of RAFT agents. Specifically, the rate constant kβ increases with a more electron-withdrawing substituent. Conversely, the addition rate constant is hardly affected. We can thus separate the impact of substituents based on whether they are on the aromatic at the α position of the thiocarbonyl moiety or on the aromatic at the site that stabilizes the ring-opened radical. For example, the superior reactivity of SPr-F-DOT compared to other molecules can be explained by the additive effect of its two substituents. Both the fluorine and SPr groups increase β-scission without significantly reducing the addition rate constant. This leads to a higher transfer rate constant and a lower kp/ktr ratio, making this molecule more reactive in copolymerization. It can also be explained that the F2-DOT molecule is slightly less reactive in copolymerization with styrene than the SPr-F-DOT molecule. By substituting the aromatic ring in the α position of the thiocarbonyl with an F instead of an SPr, beta-scission rate slightly decreases, which reduces the transfer constant and results in a higher kp/ktr ratio for F2-DOT compared to SPr-F-DOT. Similarly, it can be explained that the SPr-DOT molecule is more reactive than F-DOT, and that F-DOT is more reactive than DOT in copolymerization with styrene. The beta-scission rate constant increases with the introduction of these groups on the aromatic ring in the α position of the thiocarbonyl: the kβ value of SPr is higher than the one of F-DOT, which is itself higher than the one of DOT. This leads to an increase in the transfer rate constant in this order (SPr-DOT > F-DOT > DOT), and therefore a higher reactivity of SPr-DOT. Similarly, the low reactivity of the OMe2-DOT molecule is explained by the additive effect of the two electron-donating groups in the para position of the aromatic rings. The effect of the OMe group in the ring in α position of the thiocarbonyl fraction increases β-scission but decreases the addition rate constant and significantly increases the reverse addition constant. For the group stabilizing the ring-opened product, the OMe group does not significantly change the addition constant and does not increase β-scission, which remains low. Overall, beta-scission slightly increases, the addition rate constant slightly decreases, and the reverse addition constant increases significantly. This resulted in a lower ktr than that of DOT and a higher kp/ktr ratio, making OMe2-DOT less reactive in copolymerization with styrene. The good agreement between our theoretical results and the experimental findings of the Johnson's group 17 prompted us to apply this DFT computational method to adjust the structure of another thionolactone, POT, and thus its reactivity in copolymerization with vinyl monomers (styrene and acrylate), using electron-withdrawing or electron-donating groups. Several groups on the para position of the aromatic ring with distinct electronic effects, ranging from highly electron-donating to highly electron-withdrawing according to their Hammett parameters, were compared using this DFT computational method at 80°C without solvent. Different trends can be distinguished when dealing with an electron-withdrawing group versus an electron-donating group.