Polynorbornene-Based Polyelectrolytes with Covalently Attached Metallacarboranes: Synthesis, Characterization, and Lithium-Ion Mobility

Boron cluster leveraged polymeric building blocks

Boron cluster compounds (BCCs) are inorganic molecules characterized by their unique physical and chemical properties. Polymeric materials incorporating BCCs exhibit significant chemical and thermal stability, making them valuable for applications in biomedical fields, energy storage, ultrahigh stability materials, and π-conjugated luminochromic polymers. This review article aims to explore the primary methods for integrating these distinctive clusters into traditional carbon-based polymers. Both boron and carbon atoms possess catenation abilities, enabling the formation of extensive macromolecular structures. While carbon forms long linear chains, boron typically leads to three-dimensional polyhedral clusters. We first examine hybrid nanostructures, focusing on weak non-covalent interactions such as dihydrogen bonding, hydrophobic, and chaotropic effects between boron clusters and polymer chains. We then discuss classical chemical bonding approaches. Despite their inorganic nature, boron clusters can undergo exoskeletal substitution akin to organic counterparts, allowing their attachment as side groups to polymer repeating units. Additionally, polyhedral boron clusters can be incorporated into polymer backbones primarily through polycondensation reactions, resulting in hybrid macromolecules with exceptional physical and chemical attributes. Finally, we summarize the applications of BCC-containing polymeric materials, including their use in boron neutron capture therapy (BNCT), solid polymer electrolytes (SPEs) for metal ion batteries, and as electron acceptor groups in stimuli-responsive luminescent materials. In summary, BCC-containing polymeric materials are increasingly considered viable alternatives to traditional hydrocarbon-based polymers for biomedical applications, ion-conducting materials, luminescent materials, and temperature-resistant materials.

Tetracyanocyclopentadienide-Based Stable Poly(aromatic) Anions

Polyelectrolytes, a class of polymer with ionized functional groups in their repeating units, are widely used in various applications. Many ionized groups have been incorporated into polyelectrolytes, but aromatic anions are rarely investigated. Here, we first successfully incorporate a stable tetracyanocyclopentadienide (TCCp) aromatic anion into polynorbornene (PNb)-based electrolytes (PNb-TCCp) through ring-opening metathesis polymerization (ROMP) with controllable molecular weight and low polydispersity. PNb-TCCp shows a high ionic conductivity of 4.5 × 10^-5 S/cm in thin films. Due to its highly stable aromatic anion groups and favorable interactions with aromatic cations, it could improve thermal stability of doped conjugated polymers. Pairing with doped poly(3,4-ethylenedioxythiophene) (PEDOT) through salt metathesis, the generated poly ion complex PEDOT:PNb-TCCp retains its conductivity up to 180 °C.