that showed moderate to high ring-retaining propagation. We thus applied the same methodology on three of the six originally prepared thionolactones to validate our approach (Table ). As previously, we used B3LYP/6-31G(d) as method of DFT calculation because we already showed that the reactivity of CKA and thionolactones was well described with this method and that the use of more sophisticated levels of theory was at the expense of thecalculation cost without better correlation with the experimental data. As done already in our previous papers, we used tabulated pre-exponential factors, instead of the one that can be obtained using DFT calculations. Even if the entropy associated for certain vibrations is correct, hindered rotations occurring in cyclic molecules cannot be properly taken into account. In particular for radical addition reaction, we used Aadd = 10 8 L mol -1 s -1 as recommended by Fischer and Radom 31 and for the unimolecular β-fragmentation, a value of Aβ = 10 13 L mol -1 s -1 was used for the β-scission and inverse radical addition. The result of the DFT calculations as well as the ktr values and the ratio kp/ktr are summarized in Table . The first observation is that in agreement with the study of Roth, 15 DOT is the most efficient thionolactone since its kp/ktr value is roughly close to unity compared to values that are higher by 2-5 order of magnitude for thionolactones 1, 2 and 5. Since many approximations (gas phase, model molecules, etc.) were used during these calculations, it is interesting to note that only relative values between different structures are of interest. Besides this preliminary finding, other conclusions could be done. First, the addition rate constant kadd is dictated as expected by the group in a position to the thionocarbonyl, with values one order of magnitude higher when an aromatic group is present (structure 1 compared to 2-5 and DOT). The presence of a stabilizing group on the released radical do not affect such value (structures 2 and 5). For the β-scission, we could observe a drastic increase of the kβ between 2 and 5 that is due to the stabilizing properties of the ethyl group. It is more difficult to see the influence of the group in a position to the thionocarbonyl since both groups were changed between 1 and 5. We already showed experimentally using thCL and thDL that an alkyl group inserted on the released radical did not drastically improve the efficiency of the radical ringopening polymerization. The kp/ktr for DBT is very instructive. Its value for styrene is two orders of magnitude lower than the one for DOT and lower than unity, meaning that PS macroradical is more prone to add on DBT than on styrene thus indicating higher reactivity of DBT than DOT on styrene. This theoretical result is in good agreement with the experimental since DBT polymerizes non-randomly with DBT reacting first and styrene latter. The kp/ktr for DBT and acrylate derivative is also very interesting since this value is one order of magnitude lower than the one with styrene. We could then expect an even more pronounced inhomogeneous incorporation that is observed experimentally with only poly(DBT) that is produced without any polymerization of the acrylate derivative. These preliminary results are interesting but the structural diversity (ring size, presence of a stabilizing group either or both in α to the thionocarbonyl and on the released radical) of the structures (1,2,5, DBT and DOT) that have been prepared by Roth and coworkers impede to clearly understand the key parameters to design efficient thionolactones. and the ratio between ktr and the propagation rate constant kp of styrene and acrylate derivatives calculated using the same approach for in-silico designed thionolactones Other structures were then calculated that will only differ in one feature to investigate in more details the reactivity of the thionolactone family. These structures and their calculated rate constants are presented in Table . We first designed and calculated a thionolactone bearing an aromatic group in a position to the carbonyl moiety and a phenyl stabilizing group on the released radical ( ) and compared it to the DOT structure. Indeed, in this case both compounds will have a stabilizing group for the radical addition and for the released radical.