Synergistic effects of a half‐cage and cage structure phosphorus and nitrogen‐containing POSS with tetrabutyl titanate on flame retardancy of vinyl epoxy resins

To improve the flame retardancy of vinyl epoxy (VE) resins more effectively, a half‐cage and cage structure polyhedral oligomeric silsesquioxanes (P/N‐POSS) containing phosphorus and nitrogen was synthesized by a one‐step Kabachnik‐Fields reaction from paraformaldehyde, 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) and 3‐aminopropyltriethoxysilane. It was then blended with tetrabutyl titanate (TBT) in VE resins to construct a phosphorus‐nitrogen‐silicon‐titanium synergy flame retardant system. P/N‐POSS was well dispersed in the VE matrix at low loadings (≤4 wt%). With the addition of only 4 wt% P/N‐POSS and 0.2 wt% TBT, the LOI value reached 29.2 and the UL‐94 grade passed V‐1 rating. Moreover, compared with VE‐0, the peak heat release rate, total heat release, smoke production rate and total smoke production decreased significantly. The investigations on pyrolysis volatiles and char residue of cured VE composites revealed that the excellent flame retardancy of the VE composites were due to the superior free radical capturing ability, the dilution effect of P/N‐POSS in the gas phase, and the promoting the carbonation effect of P/N‐POSS, the catalyzing char formation ability of TBT in the condensed phase. Meanwhile, VE composites exhibited improved mechanical properties, thermal stabilities and retained the low viscosity and good processability of VE resins.