(43b) A Fully Renewable and Recyclable Polymer Platform from CO? and Biomass Lignin

The rapid growth of the plastics industry has contributed to a worsening global crisis involving plastic waste, environmental degradation, and increased greenhouse gas emissions. This study presents a sustainable strategy to address these issues by combining carbon dioxide (CO₂) and biomass-derived lignin to create recyclable polymers from abundant, non-food-based renewable resources. A lignin- and CO₂-based cyclic carbonate monomer was synthesized using an environmentally friendly, phosgene-free method conducted at room temperature and atmospheric pressure. The polymerization of this monomer was carried out through ring-opening polymerization (ROP), with tunable conditions involving different catalysts—1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD)—catalyst loadings (0.5–5.0%), and reaction times (2–40 minutes). The optimal polymer was obtained using 1% TBD with a 30-minute reaction time. The structures of both the monomer and resulting polymers were confirmed using 1H, 13C, and 2D-HSQC NMR spectroscopy, FT-IR, and gel permeation chromatography (GPC). The synthesized polymers exhibited high molecular weights (Mn: 120.34–154.58 kDa) and good thermal stability (Td₅%: 244–277 °C by TGA; Tg: 33–52 °C by DSC), making them suitable for practical use. Importantly, these CO₂- and lignin-based polymers can be depolymerized back into their original monomer form by heating at 90 °C for 12 hours in the presence of DBU, enabling true chemical recycling. The regenerated monomers retain their chemical structure and are suitable for re-polymerization, supporting a closed-loop recycling system. This work demonstrates a novel and fully biomass-based polymer platform that integrates sustainable synthesis with efficient monomer recovery, offering a promising alternative to conventional petroleum-derived plastics and contributing to a circular plastic economy.