Supramolecular chemical ligation of helical polymers.

Abstract

Chemical ligation of polymer segments is an essential approach to extend the length of synthetic polymers. Ligating individual polymer chains at the molecular level remains a formidable challenge owing to the entropically disfavoured collision probability between reactive end groups, and the need to overcome the activation barrier. Here we report a pathway to chemical ligation of synthetic polymers via folding-driven supramolecular polymerization followed by dynamic covalent polycondensation. Our strategy, which does not require thermal activation, uses hydrogen bonds that induce conformational folding to rigidify the polymer backbone while providing sticky ends for supramolecular pre-organization. This promotes base-catalysed covalent exchange between terminal groups (in our case, thiolate-disulfide groups). We obtain mechanistic insight in the ligation process by engineering side-chain units that determine conformational foldability and intermolecular H-bonding pre-organization. The resulting extended helical polymers fold into hierarchical globular architectures in solution and exhibit thermo-responsive macromolecular entanglements in bulk films. The combination of noncovalent assembly and dynamic covalent polymerization offers a supramolecular pathway for non-thermal and controllable polycondensation of dynamic polymers with secondary structures.