The most used rROP monomer family, as also clear from a more developed library of monomer reactivity ratios and kinetic parameters, is those of CKAs, which produces under homopolymerization conditions polyesters (Figure , example with 2-methylene-1,3dioxepane (MDO) as CKA). Various CKA compounds with diverse ring-sizes and substituents have been already synthesized and evaluated for their rROP ability. The exploitation of CKAs has led to the preparation of a wide variety of (bio)degradable materials, however, displaying a rather low (absolute) reactivity compared to many industrially relevant vinyl-based monomers, limiting industrial implementation demanding high yield reactions in a rapid manner. Other structures such as cyclic allyl sulfides or allyl sulfones have been prepared but their long and tedious synthetic procedures impede their practical usage.