The placement of main-group functionalities within polymers represents a strategy to access a wide catalog of materials but is limited by poor understanding of the catalyst selection criteria and polymerization mechanism when moving down the periodic table. Here, we study a series of new heterobimetallic carbon dioxide and carbon disulfide/epoxide copolymerization catalysts that allow for a comparative mechanistic understanding of two ring-opening copolymerization processes. We reveal that the distinct roles each metal plays are preserved from carbon dioxide to carbon disulfide, maintaining activity and selectivity across copolymerizations. Experimental and computational studies show that carbon disulfide/epoxide copolymerization can be understood as a series of structurally related insertion events that are interlinked by a central oxygen/sulfur scrambling reaction at the propagating chain end. This facilitates the synthesis of new carbon dioxide-/carbon disulfide-/epoxide-derived terpolymers with improved degradability over the parent carbon dioxide/epoxide copolymers at low levels of sulfur incorporation.
