as well as all-oxygen carbonate (-O-C(=O)-O-OOO) and thioether links are always obtained in addition to small molecule by-products, such as different cyclic (thio)carbonates, thiiranes and COS instead of the expected poly(dithiocarbonates) from alternating ROCOP as demonstrated, assigned and rationalised by the groups of Wan, Zhang and Darensbourg. Polymer selectivities versus cyclic heterocarbonates range from 30 to 80% in which dithiocarbonate links from alternating copolymerisation make up the minor (typically 0 -30 %) fraction. Product distribution and polymer composition strongly depend on the exact reaction conditions making material properties unpredictable and necessitating time-consuming purification steps. The process behind the formation of the different linkages has been termed O/S-scrambling and is suspected to originate from the attack of metal-alkoxide chainends (formed from epoxide/oxetane ring-opening alike intermediate A in Figure ) into dithiocarbonate linkages in place of propagation with CS2 (forming metal-dithiocarbonate chain ends alike DTC in Figure ). Notably this sideprocess extends to related polymerisations and causes linkage scrambling and small molecule byproducts. Previously it has been shown for alloxygen ROCOP that cooperative catalysts can control the reactivity of alkoxide intermediates and limit or even productively regulate side reactions. Williams and co-workers in particular showed that a heterobimetallic Co(III)K catalyst can limit back-biting side reactions originating form alkoxides in CO2/epoxide ROCOP which lead to excellent polymer and linkage selectivities. Relatedly, we found in a comparative study on CO2/epoxide vs. CS2/epoxide ROCOP employing a series of heterobimetallic Cr(III)-alkalimetal complexes based on a bis-methoxy substituted SalcyCr(III) complex that cooperativity is maintained moving from CO2 to CS2 ROCOP. Yet these catalysts still yielded product mixtures in which the OSS link from alternating ROCOP represented the minor product calling for further catalyst development. In terms of targeted polymer structures, we hypothesized that linkage control is particularly important for unsubstituted monomers (such as ethylene oxide or oxetane) as the material properties of the resulting polymers are predominantly determined by the chemical nature of the linkages. In these case of oxetane (OX) previous reports by Darensbourg and Zhang showed that sulfur enhances semi-crystallinity is observed in the COS/OX copolymers while the same was not the case for the CS2/OX copolymers. We inferred this to stem from the uncontrolled microstructure of this polymer as a consequence of the O/S scrambling process. Hence this monomer combination represents an opportunity for selective catalysis to potentially control material properties which we report in this contribution.