Bromine-containing copolymer polycarbonate for simultaneous thermal stability, transparency, and thin-wall flame-retardant polycarbonate

The incorporation of traditional low molecule bromine flame retardants can enhance the flame retardancy of polycarbonate (PC), yet their poor compatibility with PC impairs its transparency and mechanical properties. Here, brominated polycarbonate (B₅₀PC) was synthesized by interfacial polycondensation method using bisphenol A, tetrabromobisphenol A, and triphosgene. The number average molecular weight (M_n) of B₅₀PC reached 14,600, and compared to the low molecule bromine flame retardant tetrabromobisphenol A (TBBPA), its initial decomposition temperature increased by 38.7 % under air atmosphere. The PC composites containing 5 wt% B₅₀PC achieved the V-0 rating in the UL-94 test, with LOI increased by 10.3 %. At the same time, the peak heat release rate (PHRR) was decreased by 28.6 % and the ignition time (TTI) was delayed by 21.3 %. Compared with that of samples with TBBPA, the composite with the same amount of B₅₀PC maintained the original elongation at break of PC and the transmittance remained at 84.9 %. In summary, the composites with B₅₀PC maintains outstanding transparency and mechanical properties while enhancing the flame retardancy. This work has developed a high molecular bromine flame retardant that combines flame retardancy and transparency, offering a strategy for expanding the application of PC in the electronics, construction, and aerospace sectors.