A relatively new rROP monomer family are thionolactones, which were discovered simultaneously by Roth and Gutekunst 27 focusing on dibenzo[c,e]oxepine-5(7H)-thione (Figure , DOT). These authors showed that DOT is able to copolymerize with the vinyl monomer (classes) acrylonitrile, acrylates, acrylamides, maleimides derivatives, S-vinyl and P-vinyl monomers, leading to (co)polymers with a thioester functionality within the polymer backbone. However, its copolymerization with styrene, methacrylate derivatives and vinyl acetate were not successful, at least initially. The compatibility of DOT with styrene and isoprene was only reported later on, and Destarac et al. as well as Guillaneuf et al. reported ε-thionocaprolactone (thCL) as a second thionolactone monomer compatible with less activated monomers such as vinyl ester derivatives. In the same approach, Gutekunst et al. reported the efficient copolymerization of cyclic thionocarbamate with N-vinyl pyrrolidone (NVP), N-vinyl carbazole (NVC), and N-vinyl caprolactam (NVCl).