Anion-binding can regulate anion transport in chloride channels via dynamic non-covalent interactions, which gives insights into the designing of new organocatalytic transformations, but is surprisingly unexplored in polymerization catalysis. Herein, we describe an effective unimolecular anion-binding organocatalysis where 4-(dimethylamino)pyridine is anchored to a thiourea for ring-opening polymerization of O-carboxyanhydrides (OCAs), which well addresses the formidable challenge of synthesizing high molecular weight (MW) stereoregular polyesters. Ring-opening polymerization of PheOCA (OCA from phenylalanine) mediated by unimolecular anion-binding organocatalyst generates highly isotactic poly(phenyllactic acid) (Ph-PLA) with MW up to 150.0 kDa. Specifically, high MW Ph-PLA exhibits 30-fold increase in the elongation at break in comparison to its low MW congener. Moreover, active species of the polymerization are moisture-tolerant and can be conducted in unpurified solvent, facilitating facile synthesis of high MW stereoregular polyesters with pendant functional groups. Calculations and experiment studies indicate a dynamic cooperative anion-binding mechanism where the dynamic anion-binding interaction of thiourea moiety to propagating species facilitates efficient chain propagation and the synergetic decarboxylation retains high selectivity for OCA ring-opening over side reactions (e.g., cyclization, epimerization and transesterification).

Unimolecular anion-binding catalysts for selective ring-opening polymerization of O-carboxyanhydrides

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