Synthesis and characterization of intrinsically flame retardant functional ionogel thermoplastic polyurethane

Brominated (Br) and phosphorus (P) based flame retardants are effective for thermoplastic polyurethane (TPU). However additive approaches suffer from incompatibility, and sustainability issues, which reactive strategies effectively address. Two novel ionic liquid chain extenders, 1,3-bis [(1-(2-hydroxyethyl) imidazolium) methyl] benzene dibromide ionic liquid (Br₂IL) and 1,3-bis [(1-(2-hydroxyethyl) imidazolium) methyl] benzene bromide diphenyl phosphate ionic liquid (BrPIL), were synthesized to prepare intrinsically flame-retardant functional ionic TPUs (TPUBr₂IL and TPUBrPIL). The bulky ion pairs facilitate a more uniform linear structure through steric hindrance. Furthermore, the resultant oligomers act as efficient internal plasticizers, concurrently reducing the glass transition temperature (T_g) and improving the overall fire safety of the functional ionic TPUs. For TPUBr₂IL with 10.75 wt% Br, the LOI reached 27.2%, while the pHRR and THR decreased by 36.9% and 32%, respectively. Under Br/P synergy, TPUBrPIL showed an LOI of 25.0%, with pHRR and THR reduced by 40.8% and 21.2%, respectively. The functional ionic TPUs maintained tensile strengths above 17.4 MPa. These findings underpin the design of intrinsically flame-retardant and environmentally compatible ionically functionalized polyurethanes and expand their application.