Intrinsically Flame-Retardant and Recyclable Adhesives from <i>N</i> -Phosphorylated Aziridine-Based Inverse Vulcanized Polymers

Adhesives are widely used in both industrial and daily applications, with growing demands for multifunctional properties such as flame retardancy and recyclability. Herein, we present a strategy that incorporates N-phosphorylated aziridine as a comonomer in the inverse vulcanization of 1,3-diisopropenylbenzene (DIB) with elemental sulfur, affording intrinsically flame-retardant polysulfides with enhanced adhesive performance. The ring-opening reactivity of N-phosphorylated aziridine with sulfur was confirmed under both organocatalytic and catalyst-free thermal conditions. Subsequent terpolymerization with DIB and sulfur yielded the desired polysulfides, whose structures were characterized by FT-IR, XPS, and SEM-EDS mapping analyses. The resulting polymers exhibited outstanding adhesion, achieving lap-shear strengths of up to 5.8 MPa on aluminum and 7.3 MPa on steel, significantly surpassing poly(DIB-r-S) analogs without a diphenyl phosphoramidate group. Moreover, the incorporation of phosphorus conferred inherent flame retardancy, with the best-performing sample reaching the highest UL-94 V-0 classification. This work demonstrates an efficient approach for designing recyclable, high-performance flame-retardant adhesives while providing a sustainable route for the utilization of elemental sulfur.