Reinforcement of Optically Healable Supramolecular\nPolymers with Cellulose Nanocrystals

Abstract

We report the preparation and characterization\nof light-healable nanocomposites based on cellulose nanocrystals (CNCs)\nand a metallosupramolecular polymer (MSP) assembled from a telechelic\npoly­(ethylene<i>-co</i>-butylene) that was end-functionalized\nwith 2,6-bis­(1′-methylbenzimidazolyl) pyridine (Mebip) ligands\nand Zn­(NTf₂)₂. The polymer absorbs incident\nultraviolet (UV) radiation and converts it into heat, which causes\ndissociation of the metal–ligand motifs. This process liquefies\nthe material, and small defects are readily filled. When the UV light\nis switched off, the MSP reassembles and the original properties are\nrestored. The introduction of CNCs into the MSP matrix leads to a\nsignificant increase of the stiffness and strength, from 52 and 1.7\nMPa for the neat polymer to 135 and 5.6 MPa upon introduction of 10%\nw/w CNCs. The Zn²⁺ ions bind to the CNCs which means the\nmetal:ligand ratio of the MSP must be adjusted accordingly. In nanocomposites\nthus made, deliberately introduced defects can be efficiently healed.