CO₂ and Lignin‐Based Sustainable Polymers with Closed‐Loop Chemical Recycling

Abstract This work highlights the conversion method of chaining up greenhouse gas CO₂ with biomass lignin to develop new sustainable, recyclable polymers from abundant and non‐food based renewable resources. A cyclic carbonate monomer has synthesized using a cost‐effective, non‐phosgene‐based, and greener approach under atmospheric pressure and room temperature. The fully programable ring‐opening polymerization is accomplished by varying the catalyst (DBU and TBD), catalyst loading (0.5–5.0%) and reaction time (2–40 min). The best polymer is obtained in 1% TBD with a 30‐min reaction. The precise characterization of the synthesized cyclic carbonate monomer and polymers' structure are established using spectroscopic analyses including ¹H, ¹³C, and 2D HSQC NMR, FT‐IR, and GPC. The new polymers exhibit high molecular weights (M_n: 120.34–154.58 kDa) and adequate thermal stabilities (T_d5%: 244–277 °C from TGA and T_g: 33–52 °C from DSC), rendering them advantageous for practical applications. Significantly, the CO₂ and lignin‐based polymers have successfully recycled to the monomer for a circular plastic economy by heating at 90 °C for 12 h in the presence of DBU. This process yields original monomers for another polymerization without unwanted changes in chemical structures, presenting an ultimate sustainable solution.