Abstract Ring‐opening copolymerizations have emerged as a powerful approach towards the creation of sustainable polymers. Typical H‐bonding catalysts for ring‐opening are subject to a single catalytic site. Here we describe a H‐bond‐donor/Lewis‐acidic‐boron organocatalyst featuring two distinct catalytic sites in one molecule. The ring‐opening copolymerization of epoxides with anhydride mediated by these modular, and tunable catalysts achieves high selectivity (>99?% polyester selectivity) and markedly higher activity compared to either of the di‐thiourea analogues or any combinations of them. Calculations and experimental studies reveal that the superior catalytic performance arises from tug‐of‐war between two differentiated catalytic sites: thiourea pulls off the propagating chain‐end from boron center, simultaneously enhancing the role of monomer activation and also nucleophilicity of the propagation intermediates.
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