Self-healing polymers emerge from the first use of pnictogen bond crosslinks

Scientists in China have created the first polymer networks crosslinked using pnictogen bonds. 

Crosslinking polymer chains is a common way to tailor a material’s mechanical and functional properties. While permanent covalent bonds lock a structure in place, crosslinks made from reversible bonds let a system reorganise itself in response to changing conditions. This topological adaptability is ideal for materials designed to self‑heal or respond to external stimuli.

A variety of supramolecular interactions can be harnessed to build crosslinked polymers, and many have been tried and tested. Hydrogen‑bonded networks are the best known, but their weak bonding strength and limited solvent compatibility restrict their application. Chalcogen and halogen bonding offer promising alternatives for dynamic polymer materials, but finding the right balance of properties remains a challenge.

Pnictogen bonding was only recently defined as ‘a subset of the attractive interactions between an electrophilic region on a pnictogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity.’ Now, a team led by Wei Wang from Zhengzhou University in China, has taken advantage of this bonding motif to produce materials with controllable self-healing properties, including when under water.

The new materials rely on interactions between antimony and pyridine-functionalised polymer chains, with antimony having been chosen for its strong Lewis acidity relative to other pnictogens. By varying the oxidation state of the antimony, the researchers could further tune the system, as the pnictogen bond strengths differ between Sb(iii) and Sb(v) centres.

Because pnictogen bond donors typically have more accessible σ‑holes than other non‑covalent donors, they enable stronger bonding directionality and greater structural complexity in the polymer, and therefore more control over the properties. Additionally, the excellent water tolerance of pnictogen bonds also broadens the potential applications of such polymers.