Thionolactones have been recently introduced as new promising monomers for radical ring-opening polymerization. Nevertheless only two structures were really efficient and only one (dibenzo[c,e]-oxepane-5-thione (DOT)) could be used for the activated monomers (styrene, acrylate, acrylamide derivatives). In this work, we showed that DFT calculation help to understand the peculiar reactivity of thionolactones and to design a new efficient thionolactone, i.e. the 7-phenyloxepane-2-thione (POT). An experimental study confirmed the good copolymerization behavior of this thionolactone with styrene and methyl acrylate as a model for acrylate derivatives. A detailed kinetic analysis led to reactivity ratios of rS = 0.7 and rPOT = 0.9 during the solution copolymerization of POT and Styrene at 80 °C initiated with 0.5 mol% AIBN and rIBA = 0.2 and rPOT = 0.9 for the solution copolymerization of POT and isobornyl acrylate at 80 °C initiated with 0.5 mol% AIBN. With these reactivity ratios, a more homogeneous incorporation of thioesters into the polymer chains could be obtained. Good chemical degradation profile was demonstrated with the addition of a new efficient oxidative degradation procedure using mCPBA in THF at RT. The good degradation properties of the obtained copolymers are an indirect proof of the random incorporation of thioester moieties into the backbone that is essential for a homogeneous degradation.