Reinforcement of Optically Healable Supramolecular Polymers with Cellulose Nanocrystals

We report the preparation and characterization of light-healable nanocomposites based on cellulose nanocrystals (CNCs) and a metallosupramolecular polymer (MSP) assembled from a telechelic poly(ethylene-co-butylene) that was end-functionalized with 2,6-bis(1'-methylbenzimidazolyl) pyridine (Mebip) ligands and Zn(NTf2)(2). The polymer absorbs incident ultraviolet (UV) radiation and converts it into heat, which causes dissociation of the metal ligand motifs. This process liquefies the material, and small defects are readily filled. When the UV light is switched off, the MSP reassembles and the original properties matrix leads to a significant increase of the stiffness and strength, from 52 and 1.7 MPa for the neat polymer to 135 and 5.6 MPa upon introduction of 10% w/w CNCs. The Zn2+ ions bind to the CNCs which means the metal:ligand ratio of the MSP must be adjusted accordingly. In nanocomposites thus made, deliberately introduced defects can be efficiently healed.