Monomer‐Dependent Selectivity in Sulfur‐Containing Ring‐Opening Copolymerisation: Bimetallic Catalysis for Predictive Design of Degradable Polymers

Sulfur-containing polymers offer unique opportunities for advanced materials due to their inherent degradability, high refractive indices, and potential for chemical recyclability. Yet, synthetic strategies for their precise construction remain underdeveloped and monomer selection rules to achieve this are elusive. Herein, we achieve the first comprehensive evaluation of sulfurated ring-opening copolymerisations (ROCOP) performed under unified conditions using a single heterobimetallic Cr(III)/Rb(I) catalyst platform. Although such catalysts are largely unexplored in sulfur-based ROCOP, our study demonstrates their remarkable synergistic performance in controlling both activity and selectivity across diverse heteroallene/epoxide systems. We identify carbonyl sulfide (COS) as the most promising monomer, enabling perfectly alternating copolymers under mild conditions on kinetic grounds. As a close second, PhNCS emerges as a viable, easier to handle, alternative that offers selective access to sulfur-containing copolymers. In contrast, thioanhydrides and CS₂ show progressively lower selectivity, with increasing O/S scrambling and small molecule byproduct formation. This study provides the first predictive framework linking sulfur monomer identity to selectivity and reactivity under unified conditions, enabling rational design of degradable sulfur-rich polymers.