Single-Crystal Helical Covalent Polymers with Organic Counter Cations.

Abstract

Helical polymers, central to many bioactive molecules and polymers, offer distinctive functional properties, yet the precise synthesis and atomic-level characterization of artificial helical covalent polymers (HCPs) remain challenging. Here, we demonstrate that soft organic counter cations, combined with dynamic spiroborate chemistry, enable the rapid synthesis of hydrogen-bonded, single-crystal HCPs, significantly reducing polymerization times compared with analogous systems containing alkali metal cations. Single-crystal X-ray diffraction of HCPs prepared from amines or pyridine with their conjugate acid pKa values ranging from 4.63 to 10.71 revealed closely related hydrogen-bonded helical backbones associated with nearby organic counter cations. Importantly, counter-cation acidity strongly influences polymerization kinetics and the resulting helical architectures, establishing a previously underexplored strategy for controlling HCP formation. Beyond structural control, these materials exhibit promising solid-state proton-conducting properties, with HCP-TFEA achieving a proton conductivity of 2.8 × 10-3 S cm-1 at 70°C and 97% relative humidity. These findings demonstrate that rational counter-cation selection provides an effective approach to accelerate HCP synthesis while simultaneously tuning polymer structure and function, offering new opportunities for the design of dynamic helical polymeric materials.