Ladder macromolecules are an intriguing subset of conjugated polymers due to their high backbone rigidity and lack of torsional disorder, brought by their fully fused skeleton. Such a structural feature is expected to endow ladder polymers with attractive properties, including extraordinarily high thermal and chemical stabilities, together with low entropy penalty when they function as hosts. Guided by these underlying principles, our group has successfully synthesized two novel categories of ladder polymers and explored their potential application as functional materials.<br/>Polyaniline and its derivatives of various redox states represent one of the well known and widely used conductive polymers applied in a large variety of fields. However, rigorous investigation of polyaniline and pernigraniline salts remains much limited due to their steady degradation. To tackle this concern, our group synthesized a series of ladder-type pernigraniline oligomers to incorporate ladder structure into the polyaniline backbone so that its stability could be enhanced. Their optical properties, acid-doping processes, redox and paramagnetism behaviors were explored in a comparison to non-ladder analogues to demonstrate the role of ladder structure in the molecular design. Inspired by the success, the scope of research was extended to their polymer analogue, and it was fabricated into an electrochromic device with vivid color change and desirable reversibility.<br/>The rigid backbone of ladder polymers also lowers their entropy so that the entropy penalty of adsorption is decreased. In this context, our group reported a porous ladder polymer network constructed by thermodynamically controlled ring closing metathesis reaction. Its solid-state structure was unambiguously characterized by various methods, and it showed a high BET surface area up to ~1900 m2/g. Such a high porosity was retained even after harsh treatments, including strong acid, base, oxidant, reductant at high temperature. It showed a remarkably high methane uptake per unit surface area compared to other covalent-organic frameworks and porous hydrocarbons without enthalpic contributions. Such superior performance was elucidated by deriving relevant thermodynamic parameters and it turned out that the reported network possessed a much lower original entropy and had a more favorable adsorption entropy change.  <br/>

Conjugated ladder polymers for robust electrochromism and entropically favorable gas adsorption

ACS Fall 2020 Virtual Meeting

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