Synergy of Dynamic Covalent Bonds and Hydrogen Bonds Enables Dual Dynamic Recyclable Helical Polymers
Biopolymers such as proteins exhibit both stability and dynamic properties, reflected in precise conformational adaptability and reversibility within cells. Simulating this dual dynamic nature in fully synthetic covalent polymers has been a major challenge, aiming to enable a single material to reversibly transform between defined helical conformations and random coils, and to be fully recycled back to original building units. Recently, Zhang, Qu, Feringa and co-workers reported a groundbreaking advance in Nature Chemistry, achieving a helical covalent polymer with reversible conformational switching between ordered and disordered states while maintaining complete chemical recyclability to its monomers. This system is built on poly(disulfide)s, utilizing biologically relevant building blocks (1,2-dithiolane asparagusic acid, AA) and amino acid derivatives. Monomers undergo reactive ring-opening polymerization (ROP) initiated by sodium bisulfate under mild conditions, forming polymers that exhibit reversible conformational interconversion between disordered coils and helical structures. Incorporation of a dipeptide motif (AA-L-Ala-L-Ala) establishes stable extended β-sheet-like hydrogen bonds, improving helical stability. Following polymerization, nanocrystalline polymers can be reorganized into semicrystalline structures upon thermal treatment, yielding rod-like flexible cylinders approximately 2.1 nm in diameter and 25 nm in length. Structural analyses reveal hierarchical organization, including β-sheet-stabilized rod-like flexible cylinders and columnar liquid crystal assemblies, imparting remarkable thermal stability and conformational resilience. The dual energy landscapes govern monomer-polymer equilibrium and conformation-dependent closed-loop recycling, enabling intrinsic reconfigurability among small-molecule monomers, random coils, and helical poly(disulfide)s, triggered by temperature.