Facile preparation of ladder aluminosilsesquioxanes with high flame retardancy for polycarbonate

A ladder aluminosilsesquioxanes (Al-L-PPSQ) was synthesized using AlCl₃ as an auxiliary catalyst. The chemical structure of Al-L-PPSQ was confirmed by FTIR, ¹H, ¹³C, ²⁹Si-NMR, and MALDI-TOF MS. The well characterized Al-L-PPSQ was used for flame retardant polycarbonate (PC), and the PC/Al-L-PPSQ composite with 6 wt.% Al-L-PPSQ reached UL-94 V-0 rating (1.6 mm), with an oxygen index of 36.6 % and a decrease of 61.2 % in p-HRR. The smoke release of composite materials has also decreased. By analyzing the condensed and gaseous products during the thermal degradation process of PC/Al-L-PPSQ composite materials, it is demonstrated that Al-L-PPSQ can promote the early decomposition of PC into carbon and quickly form a stable and dense char layer to protect the internal substrate during combustion, thereby improving the flame retardancy of PC.