Flame retardant polycarbonate with ultralow loading 1,3-benzenedisulfonate

Polycarbonate (PC) is one of the major engineering plastics. For the flame retardant PC, there are still obstacles to the development of high performance thin-walled PC. 1,3-Benzenedisulfonic acid dipotassium salt (KSP) was successfully synthesized by the electrophilic reaction of octaphenylsilsesquioxane (OPS) with excess chlorosulfonic acid (ClSO₃H), and the structure of KSP was characterized using Fourier-transform infrared (FTIR), nuclear magnetic resonance (NMR), and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) measurements. PC/KSP composites with different KSP contents were prepared. It is obtained that the PC with only 0.01 wt% KSP exhibits superior flame retardant properties: the thin-walled PC (1.1 mm) sample reached UL-94 Vertical burn tests V-0 rating, the peak heat release rate (p-HRR) decreased by 16.2% and the limiting oxygen index (LOI) increased to 32.5%, while maintaining the mechanical properties. By analyzing the condensed-phase and gas-phase products during the thermal degradation of the PC/KSP composites, it is demonstrated that KSP can promote the early decomposition of PC into carbon and rapidly form a stable carbon layer to protect the internal substrate during combustion.