. Recently, Roth and coworkers proposed a new thionolactone structure, i.e. the 3,3-dimethyl-2,3-dihydro-5Hbenzo[e] [1,4]dioxepine-5-thione (DBT, Figure ) that is reported to homopolymerize, to copolymerize with styrene and methacrylate derivatives but not with tert-butyl acrylate. Nevertheless, the copolymerization with styrene is not ideal with a tendency to polymerize DBT first and styrene in a second time. In the case of methacrylate derivatives, the results are opposite with the incorporation of DBT only at the end of the polymerization. Satoh and Destarac 28 developed in parallel thionolactide (TLD, Figure ) as a new monomer for rROP. This compound copolymerizes with styrene and acrylate derivatives but with a high proportion of ring-retained moieties in the backbone.