High-efficiency flame retardency of epoxy resin composites with perfect T8 caged phosphorus containing polyhedral oligomeric silsesquioxanes (P-POSSs)

Phosphorus containing polyhedral oligomeric silsesquioxanes (P-POSSs) of perfect T8 caged structures was designed as a new class of flame retardant. Phosphorus containing POSS combine several advantages from phosphorus based flame retardant and nanostructure inorganic-organic hybrid materials. Three phosphorus containing POSSs were synthesized by the addition reaction of octa vinyl POSS with diphenylphosphine (DPP), diphenylphosphine oxide (DPOP), and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), respectively. The impacts of DPP-POSS, DPOP-POSS, and DOPO-POSS on the pyrolysis and fire behavior of an epoxy resin (DGEBA/DDS) were investigated under temperature programmed heating (TGA-FTIR), forced flaming conditions (cone calorimeter) and small flame conditions (LOI and UL-94). The flame retardant performance and mechanisms of DPP-POSS, DPOP-POSS, and DOPO-POSS were assessed and discussed in detail based on TGA-FTIR, XPS, and FTIR. The main flame retardant activity of DPP-POSS, DPOP-POSS, and DOPO-POSS are in the especially strong condensed phase activity through charring and intumescence due to the synergistic between phosphorus and silicon in these POSSs.