Optically transparent and flame-retarded polycarbonate nanocomposite based on diphenylphosphine oxide-containing polyhedral oligomeric silsesquioxanes

Series of phosphorus-containing polyhedral oligomeric silsesquioxane (DPOP-POSSs) have been synthesized through hydrolytic condensation reactions. FTIR, NMR, and MALDI-TOF-MS were used to identify the structures of the DPOP-POSSs, which including T8, T9, and T10 cage structures. Excellent optically transparent polycarbonate PC/DPOP-POSSs nanocomposites can be achieved through simple twin-screw extrusion. The % transmittance of the PC control (83%) was decreased by 3–5% in the PC/DPOP-POSSs nanocomposites. The pyrolysis and fire behavior of PC/DPOP-POSSs nanocomposites have been investigated by TGA-FTIR, cone calorimetry, LOI and UL-94. PC/DPOP-POSSs-6 nanocomposites showed LOI values of 30.1% and V-0 rating. The flame-retardant performance and mechanisms of DPOP-POSSs have been assessed based on TGA-FTIR, XPS, and FTIR results and are discussed in detail. The main flame-retardant activity of DPOP-POSSs is due to formation of a framework of silicon and phosphorus in the condensed phase, which can improve the thermal stability, strength, and integrity of the char layer.