Circular High-Value Utilization of Low-Boiling Components from Waste Lithium-Ion Battery Electrolytes: Diamino Carbamate-Mediated Synthesis of Sustainable Nonisocyanate Polyurethanes

This study proposes an eco-friendly synthesis route for polyurethane by utilizing low-boiling components (LBCs) from discarded lithium-ion battery electrolytes to react with aromatic diamines, producing diamino carbamates and subsequently synthesizing nonisocyanate polyurethane (NIPU). This method aims to achieve high-value utilization of waste electrolytes and replace the toxic phosgene/isocyanate route commonly used in traditional polyurethane (PU) production with the composition of waste electrolytes, which has the advantages of environmental friendliness. Through systematic screening of four aromatic diamines (1,8-naphthalenediamine, 1,5-naphthalenediamine, 1,4-phenylenediamine, and 1,3-phenylenediamine) for LBC reactions, experiments revealed that under the composite catalyst TBD-DBU-CH3ONa (TBD: 1,5,7-triazolane-4,4,0-diketide, DBU: 1,8-diazabicyclo[5.4.0]decane-5-en), 1,8-naphthalenediamine (1,8-NDA), and 1,4-phenylenediamine (1,4-PDA) could efficiently convert into diamino carbamates: 1,8-naphthalenedicarbamate (1,8-NPDC) and 1,4-benzenedicarbamate (1,4-BDC). Combined density functional theory and kinetic analysis demonstrated the thermodynamic spontaneity and first-order kinetic characteristics of the reaction, consistent with the experimental results. Furthermore, using 1,8-NPDC and 1,4-BDC as hard segment monomers, the NIPU prepolymer was successfully synthesized through copolymerization with 1,6-hexanediol (1,6-HDO), proving its potential for NIPU production. Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy confirmed the structural accuracy of diamino carbamate and NIPU. Differential scanning calorimetry analysis demonstrated that its glass transition temperature (Tg) and viscosity-average molecular weight (Mη) measurements align with prepolymer characteristics. Thermogravimetric analysis results showed that the prepolymer has excellent thermal stability. This study represents the first full-chain validation process for synthesizing NIPU from waste electrolyte using the carbamate method to prepare diamino carbamate intermediates; it solves the problems of high toxicity, easy leakage, and strong sensitization of phosgene and isocyanate in traditional PU synthesis and provides a way for high value utilization of waste electrolyte to avoid environmental and safety risks caused by direct treatment of hazardous waste.