Preparation and properties of flame retardant epoxy resin modified by additive nitrogen-containing POSS-based molecule with eight DOPO units

Octa-N-phenylaminopropyl-POSS (Octa-NAPA-POSS), DOPO and paraformaldehyde were used to synthesize Octa-DOPO-POSS through the Kabachnik-Fields reaction. It was added into epoxy resin with different ratio to prepare a series of modified epoxy resin composites. The results proved that the addition of flame retardant Octa-DOPO-POSS significantly improved the thermal property, flame retardant performance and moisture resistance of epoxy resin without weakening the mechanical properties. When the addition amount of Octa-DOPO-POSS was 5 wt%, the LOI value of the cured EP/Octa-DOPO-POSS composite increased to 33.9%. Its UL-94 level reached V-0 rating, and the THR and PHRR were significantly reduced. Meanwhile, the flexural modulus and breaking elongation were improved. Moreover, as the adding amount increased the residual char yield of EP/Octa-DOPO-POSS composites also increased, while the maximum thermal weight loss rate gradually decreased. The real-time FTIR and SEM analysis of the char residue after high temperature pyrolysis proved that Octa-DOPO-POSS could promote the char formation and produce a denser char layer. Overall, the combination of POSS and DOPO at a molecular level rather than physical mixing has a positive and significant effect on the flame retardancy of epoxy resin.