Halogen-free and phosphorus-free flame-retarded polycarbonate using cyclic polyphenylsilsesquioxanes

Organic–inorganic hybrid macrocyclic compounds, polyphenylsilsesquioxanes (cyc-PPSQ), have been synthesized through hydrolysis and condensation reactions of phenyl trichlorosilane. PC/cyc-PPSQ flame retardant materials were obtained by melt blending cyc-PPSQ and PC using a twin-screw extruder. The combustion and thermal decomposition behavior of PC/cyc-PPSQ composites were studied using UL-94, LOI, CONE, TG–FTIR and Py–GC/MS, which showed that the presence of cyc-PPSQ could improve flame retardancy and reduce the heat release and smoke release during combustion of PC. Incorporation of 2 wt% cyc-PPSQ produced a PC/cyc-PPSQ-2 composite which displayed LOI 37.5% and UL-94 V-0 (1.6 mm). The presence of cyc-PPSQ not only improved the flame retardancy of PC, but also did not diminish the glass transition temperature, good mechanical properties and transparency of PC. These results combined with those from TG–FTIR analysis suggest that cyc-PPSQ can promote the initial thermal induced chain-breaking reaction of PC, promote the cross-linking and charring of PC, and facilitate the formation of a dense carbon layer and external SiO₂ inorganic barrier layer during combustion. Results from Py–GC/MS indicate that the presence of cyc-PPSQ promotes the generation of phenolic compounds when the composites are pyrolyzed at high temperature.