Résumé : The inherent skeletal and thermal features to forge polymers by step-growth polymerization are conflicting with any depolymerization strategies via cascade back-biting reactions that necessitate adequate ceiling temperature, spacers and functionalities to create cyclic compounds. Here, we report the edition of step-growth poly(carbonate-urea)s and poly(carbonate-amide)s that are depolymerized on demand into their native precursor or added-value offspring oxazolidinones, together with a hemiacetal cyclic carbonate. The unprotected in-chain secondary amide or urea functionalities of the polymers trigger their degradation via cascade ring-closing events upon a thermal switch (from 25 to 80°C) in the presence of an organic base as catalyst. Although most studies are realized in solution for understanding the deconstruction process, the polymers are also fully degraded in 2 h in the neat without any catalyst at 150°C. At 80°C, the organic base is required to accelerate the process. On the road to sustainability and circularity, we validate the concept by exploiting monomers designed from waste CO2 and upcycled commodity plastics. Ultimately, these polymers are selectively depolymerized from plastic mixtures composed of commodity polyethylene terephthalate and polycaprolactone, offering new options for recycling plastics waste mixtures while delivering high value-added chemicals.