Based on the switchable feature of this catalytic method, we next synthesized various sulfur-containing block copolymers in one pot via ROP and ROCOP two steps (Table , Figs. ). Using BnOH and BDM as initiators, we delivered diblock copolymers P1 to P4 and triblock copolymers P5 to P8 (PLA block in the middle), respectively, by ROP first and then ROCOP. Conversely, by ROCOP first and then ROP, we synthesized triblock polymers P9 to P12 (polythiocarbonate block in the middle). The switch between ROP and ROCOP is through simple inflation and deflation operations (Supplementary Information). By changing the amount of monomer and initiator added, we could easily regulate the molecular weight and the length of each block. The resulting block copolymers have high Mn up to 144.8 kDa (Ð ~ 1.1).