The sequential arrangement of multiple monomer units in a polymer chain remains a major challenge in synthetic chemistry.Here we describe a versatile route to the novel polyester-polythiocarbonate block copolymer from commercially available lactones,epoxides,and carbonyl sulfide (COS).A bicomponent organocatalyst combining triazabicyclodecene (TBD) with triethyl borane (TEB) generates two types of tunable active sites,i.e.,TBD-capped alcohol via hydrogen bond and TEB-capped alcohol via O→B coordination bond,which can successively catalyze ring-opening polymerization of lactones and ring-opening copolymerization of COS and epoxides from mixed monomers in one pot.Because of the reversible activated propagating anions and fast activity exchange between the active and dormant species,all of the polymer chains are enchained with both polyester and polythiocarbonate blocks.Kinetic determination quantitatively confirms the proposed mechanism.This method enables diverse lactones and epoxides to form sulfur-containing block copolymers with readily tunable structures.