Bio-based photo-reversible self-healing polymer designed from lignin†
Lignocellulose-derived p-hydroxycinnamic acids possess the photo-responsive reversible α,β-unsaturated ester moiety, a reactive structural feature that functions as the basis of the photo-reversible [2 + 2] cycloaddition reaction. To explore the potential of these naturally occurring compounds in the field of self-healing materials, novel bio-based photo-crosslinkable lignin- and glycerol-derived polyfunctional monomers having cinnamate groups were produced using a sustainable process from vanillin and syringaldehyde, two compounds readily obtained from the oxidation of lignin. Through a Structure–Activity Relationship (SAR) study, the structural design of these bio-based monomers was optimized with regards to the crosslinking/decrosslinking extent and the self-healing capacity of the corresponding polymer material. The lignin- and glycerol-derived tri-functional monomer with 4-O-propyl-ferulate moieties has facilitated the design of a new family of bio-based, environment-friendly and reversible self-healing materials for widespread applications. Computational density-functional theory (DFT) and time-dependent DFT calculations were further used for the verification of the SAR study in terms of dimerization energy of the synthesized monomers.