Fully bio-based monopyrrolidone-containing monomers towards the synthesis of renewable polyesters with high Tg and hydrolyzable closed-loop recycling

Abstract

The development of fully bio-based polyesters with distinguished performance and facile chemical closed-loop recycling in aqueous environments remains challenging. Herein, a series of N-substituted pyrrolidone carboxylic acid monomers (xPCA) were synthesized from renewable itaconic acid (IA) with six amino acids under solvent-free, water-catalyzed conditions. The resulting xPCA monomers were polymerized with ethylene glycol to afford six bio-based homopolyesters with number-average molecular weights (M_n) of up to 37.8 kDa. These polyesters exhibited high glass-transition temperatures (T_g) in the range of 47.8–106.2 °C. Among them, the L-tryptophan-derived polymer achieved the highest T_g (106.2 °C) due to the addition of the indole heterocycle, and this T_g is higher than that of most commercial polyesters, such as polyethylene terephthalate (PET). In addition, these amorphous polyesters exhibit excellent UV shielding performance, with cutoff values of 241–323 nm. The pyrrolidone structure improves the hydrophilicity of the polyester, thereby enabling closed-loop chemical recycling in deionized water at 80 °C using low-toxicity zinc acetate as the catalyst. The recovered monomer can be repolymerized to obtain the original polyesters, which retain their original properties. In addition, these polyesters demonstrate significant tolerance to common organic solvents and long-term stability in water. Overall, this series of fully bio-based polyesters realizes a greener pathway across the entire lifecycle from raw-material synthesis to product preparation and recycling treatment.