Supramolecular flame retardants towards fire safe polycarbonate with high thermal stability and smoke-suppression properties

• Thermally stable supramolecule is designed by metal-ligand coordination. • DPPA@Co can meet PC processing requirements and enhance its thermal stability. • 2.5 wt% DPPA@Co allows PC to achieve a UL-94 V-0 rating with a high LOI of 32.7%. • 2.5 wt% DPPA@Co endows PC with good smoke suppression and flame retardancy. • The tensile and impact strength of the PC-DPPA@Co composite are well maintained. Polycarbonate (PC) is highly attractive as an engineering plastic for high-end products in aviation/aerospace, electrical/electronic, and sensor fields, due to its good mechanical and electrical properties. To adapt to the requirements in such fields, PC is required to achieve higher thermal stability and satisfactory fire retardancy, while maintaining its mechanical strength. However, most existing flame retardants suffer from low thermal stability and poor interfacial compatibility with the PC. In this study, we rationally design a novel supramolecular compound (DPPA@Co) combining P and Co elements via a metal-ligand coordination reaction of diphenylphosphonic acid and cobalt acetylacetonate. The resultant supramolecular DPPA@Co exhibits good thermal stability and strong interfacial interaction within the PC matrix owing to the metal-ligand coordination and π-π stacking interaction. Particularly, the incorporation of DPPA@Co into PC enhances its thermal stability and impact strength. Besides, 2.5 wt.% DPPA@Co endows PC with a limiting oxygen index value of 32.7% and self-extinguishing property (V-0 rating according to UL-94). Owing to the excellent char-forming ability, DPPA@Co also leads to a 64.1% reduction in the peak CO release rate and a 13.9% reduction in the total heat release. This study provides a practical approach to the development of advanced PC in many industrial applications.