Bio‐renewable polymers based on lignin‐derived phenol monomers: Synthesis, applications, and perspectives

In recent decades, the continuous depletion of fossil fuels and the increasingly serious environmental issue have aroused wide attention on the development of biopolymers based on renewable biomass. Lignin is the second most abundant organic bio-based macromolecule second to cellulose, and it can be widely found in plants. Furthermore, various phenol derivatives can be obtained by their depolymerization processes. The development of bio-renewable polymeric materials originating from lignin-derivative phenol monomers, such as vanillin, syringaldehyde, eugenol, vanillyl alcohol, vanillic acid, and ferulic acid, will not only valorize the bio-sourced materials but also effectively reduce petroleum resource consumption and mitigate the environmental pollution. Therefore, an updated overview of the synthesis processes of these bio-based polymers developed in the past decade, which includes both thermosets and thermoplastics such as epoxy, phenolic, polyimine, polybenzoxazine, polyurethane, and polyesters, are elucidated. In addition, the applications of these bio-based polymers and their composites in flame-retarded materials, degradable and reprocessable materials, dielectric materials, optoelectronic materials, as well as smart responsive materials are also intensively discussed. In line with the gradual development of synthesis technologies, we believe that derivatives of lignin will turn into one of the most promising materials to be considered for the preparation of high-performance and functional bio-based polymer materials.