Double helical conformation of polymer chains is widely observed in biomacromolecules and plays an essential role in exerting their biological functions, such as molecular recognition and information storage. It has remained challenging however to prepare synthetic helical polymers, and those that exist have mainly been limited to single stranded polymers or short oligomeric double helices. Here, we report the synthesis of covalent helical polymers, with high molecular weight, from the achiral monomer hexahydroxytriphenylene through spiroborate formation. Polymerization and crystallization occurred simultaneously under solvothermal conditions, forming single crystals of the resulting helical covalent polymers. Characterization by single-crystal X-ray diffraction shows that each crystal consists of pairs of mechanically entwined polymers. No strong non-covalent interactions are observed between the two helical polymers forming a pair; instead, each strand interacts with neighbouring pairs through hydrogen bonding. Each individual crystal is made up of helical polymers of the same handedness, but the crystallization process produces a racemic conglomerate, with equal amounts of right-handed and left-handed crystals.

Single crystals of mechanically entwined helical covalent polymers

ACS Fall 2021

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