Structure–Property Relationships in Metallosupramolecular Poly(<i>p</i>-xylylene)s

The self-assembly polymerization of ditopic monomers via metal–ligand binding is a facile route for the preparation of metallosupramolecular polymers. Here this approach was used for the synthesis of supramolecular poly­(<i>p</i>-xylylene)­s based on 2,6-bis­(1′-methylbenzimidazolyl)­pyridine (Mebip) end-capped telechelic oligomers with a <i>p</i>-xylylene core and different metal salts. These polymers can be readily processed from solution and merge the ease of processing of supramolecular materials with the good thermal stability of the <i>p</i>-xylylene core. The nature of the metal cation (Fe²⁺, Zn²⁺, La³⁺) and counteranion (ClO₄^–, OTf^–, NTf₂^–) was systematically varied, and a tetrafunctional supramolecular cross-linker was used to probe how these modifications influence the materials’ properties. Interestingly, and in contrast to other metallosupramolecular polymers, where the nature of the metal salt plays a critical role, only minor property differences were observed for the materials studied. Instead, the properties of the supramolecular poly­(<i>p</i>-xylylene)­s investigated appear to be primarily governed by the crystalline nature of the telechelic oligomer. We note that minor impurities in the latter can exert a significant influence on the metallosupramolecular polymer’s properties and report a new protocol for the synthesis and purification of Mebip-end-capped <i>p</i>-xylylene telechelic oligomers

Optically healable supramolecular polymers

Polymers with the ability to repair themselves after sustaining damage could extend the lifetimes of materials used in many applications. Most approaches to healable materials require heating the damaged area. Here we present metallosupramolecular polymers that can be mended through exposure to light. They consist of telechelic, rubbery, low-molecular-mass polymers with ligand end groups that are non-covalently linked through metal-ion binding. On exposure to ultraviolet light, the metal–ligand motifs are electronically excited and the absorbed energy is converted into heat. This causes temporary disengagement of the metal–ligand motifs and a concomitant reversible decrease in the polymers’ molecular mass and viscosity, thereby allowing quick and efficient defect healing. Light can be applied locally to a damage site, so objects can in principle be healed under load. We anticipate that this approach to healable materials, based on supramolecular polymers and a light–heat conversion step, can be applied to a wide range of supramolecular materials that use different chemistries