The integration of a low number of cleavable bonds into polymers backbone via a comonomer approach is a promising way for meeting the contemporary challenges of polymer durability. Indeed, this allows to conserve the polymer main structure so that there is no need to investigate or modify the main mechanical, thermal, etc. properties of the new designed durable materials, which is important for their practical use. Thus, combining already known and registered materials with the possibility to fragmentate the polymer chain at a molecular level opens new prospects for the design of polymers with improved end of life options, i.e. biodegradation and chemical recyclability. Such approach is today applied to all polymerization techniques from ionic polymerization to ring-opening metathesis polymerization (ROMP). In the radical polymerization field, the radical ring-opening polymerization (rROP) of a cyclic monomer with a common vinyl monomer is the main technique for producing this kind of "smart" materials. Among the various families of cyclic monomers used in rROP, cyclic ketene acetals (CKA), which were proposed and extensively studied by Bailey et al. in the 1980s are maybe the most famous but suffered from important drawbacks such as low stability in the presence of protic compounds and low reactivity with more active monomers (MAM) that could lead to compositional drift during the polymerization process. In 2019, the Roth and Gutekunst groups introduced thionolactones as efficient cyclic monomer for rROP. In particular they both showed that dibenzo[c,e]oxepane-5-thione (DOT) is efficient in copolymerization with acrylate and acrylamide derivatives as well as with acrylonitrile. Few years later, the Guillaneuf and Johnson 17 groups showed that the same monomers could be applied to styrene copolymerization (Figure ). Although DOT is compatible with styrene and acrylate-based copolymerization, the reactivity ratios between these comonomer pairs is not ideal whatever the feed composition. A slight difference in reactivity ratios has an impact on the random incorporation of the cleavable bonds in the polymer backbone and thus will have an impact on the molar mass distribution of the degraded oligomers. Designing new structures to tune the reactivity ratios between thionolactones and vinyl monomers is highly desirable to improve the results in this field. We previously proposed to investigate the reactivity of thionolactones in radical copolymerization with various vinyl monomers using DFT calculations combined with the calculation of some kinetic rate constant such as kp/ktr (defined below). With this approach we found first better experimental conditions for the copolymerization of DOT and styrene and later developed a new thionolactone, the 7-phenyloxepane-2-thione (POT) able to copolymerize with styrene with reactivity ratios close to 1. Since both DOT and POT have aromatic moieties, they are prone to modification via insertion of electron-withdrawing or electron-donating groups that are expected to slightly affect the reactivity of the monomers. In this work, we thus focused on DOT and POT-functional structures and compared their theoretical and experimental reactivity in the radical copolymerization of styrene and acrylate derivatives.