Controlling polymer composition starting from mixtures of monomers is an important, but rarely achieved, target. Here a single switchable catalyst for both ring-opening polymeri-zation (ROP) of lactones and ring-opening copolymerization (ROCOP) of epoxides, anhydrides and CO2 is investigated, using both experimental and theoretical methods. Different combinations of four model monomers: -caprolactone, cyclohexene oxide, phthalic anhydride and carbon dioxide are investigated using a single dizinc catalyst. The catalyst switches between the distinct polymerization cycles and shows high monomer selectivity resulting in block sequence control and predictable compositions (esters and car-bonates) in the polymer chain. The understanding gained of the orthogonal reactivity of monomers, specifically con-trolled by the nature of the metal-chain end group, opens the way to engineer polymer block sequences.