This study provides a comprehensive understanding of the polymeric properties of lignin-based non-isocyanate poly(imine-hydroxyurethane)s (LNIPUs). The properties of the LNIPUs are affected by changes in the stoichiometric feed ratios of the bis(6-membered cyclic carbonate) (BCC) and levulinate enzymatic hydrolysis lignin (LEHL). The results showed that the LNIPUs exhibited a short relaxation time and excellent thermal repair and degradation properties. With a change in the LEHL content in the LNIPUs to 45.53%, a relaxation time of only 9 s was achieved, and the thermal repair rate of the scratches reached 93%. Furthermore, the tensile strength of the LNIPUs decreased with an increase in the LEHL content after two hot-pressing processes, while a higher than 75% tensile strength was maintained after the second hot-pressing treatment. The LNIPUs exhibited thermoresponsive shape memory property with deformation and shape fixing at 80℃. In addition, the as-synthesized LNIPUs were soluble in ethylene glycol in the absence of any organic solvents. This work demonstrates the synthesis of LNIPUs with self-healing, reprocessing, shape memory, and degradation properties.

In this study, an environmentally friendly and non-toxic route to synthesize lignin-based non-isocyanate poly(imine-hydroxyurethane)s networks was explored. Specifically, the NH₂-terminated polyhydroxyurethanes (NPHUs) prepolymer was first synthesized from bis(6-membered cyclic carbonate) (BCC) and diamine via the ring-opening reaction. Subsequently, the corresponding lignin-based non-isocyanate polyurethanes (NIPUs) with tunable properties were synthesized from NPHUs and levulinate lignin derivatives containing ketone groups via the Schiff base reaction. The structural, mechanical, and thermal properties of NIPUs with different stoichiometric feed ratios of BCC and levulinate lignin were characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA). The results indicated that the tensile strength, Young's modulus, toughness, storage modulus, glass transition temperature, and thermal stability of lignin-based NIPUs gradually increased with increasing lignin content, and the highest Young's modulus of 41.1 MPa was obtained when lignin content reached 45.53%. With good reprocessing properties, this synthetic framework of lignin-based NIPUs also provides sustainable non-isocyanate-based substitutions to traditional polyurethane networks.