Direct Synthesis of Polyurea Thermoplastics from CO₂ and Diamines

The transformation of CO₂ into polymeric materials is an important and hot research topic from the viewpoint of renewable resources and environmental effects. Herein, a series of polyureas have been synthesized by polycondensation from CO₂ with diamines of 1,12-diaminododecane (DAD) and/or 4,7,10-trioxa-1,13-tridecanediamine (TTD). The properties of polyureas synthesized were characterized by FTIR, ¹H NMR, ¹³C NMR, XRD, DSC, TGA, and DMA. The polyureas synthesized from CO₂ with a mixture of diamines presented high performances compared to those of polyureas synthesized from CO₂ with a single diamine. The thermal and mechanical properties were improved largely by the variation in the crystallization and the chain flexibility depending on the changes in the density and/or intensity of hydrogen bonds. With increasing amounts of TTD from 0 to 100% in weight, the melting (T_m), crystallization (T_c), and glass transition (T_g) temperatures decreased from 207 to 116 °C, from 181 to 54 °C, and from 66 to -34 °C, respectively. When the TTD content was increased from 0 to 50 wt %, the Young's modulus decreased from 1170 to 406 MPa, and the tensile strength decreased from 53.3 to 42.9 MPa. However, the elongation at break increased from 13 to 330%. Furthermore, the chain length of aliphatic diamines and polyetheramines had a significant effect on the mechanical properties. The initial decomposition temperature (T_d,5%) is >295 °C, about 110 °C higher than the T_m (116-207 °C), which is advantageous for the postprocessing. The mechanical properties of the polyureas synthesized herein are superior to those of polycarbonate and polyamide 6. Thus, polyureas synthesized from the renewable and cheap resources, CO₂ and diamines, will find wide potential applications in the field of polymeric materials.