Ferrocene-Based Nonphosphorus Copolymer: Synthesis, High-Charring Mechanism, and Its Application in Fire Retardant Epoxy Resin

Abstract

A novel nonphosphorus copolymer poly((3,3′-diphenyl diacetylethylenediamino)-1,1′-ferrocene) (PDPFDE) was synthesized, with the aim of reducing the fire hazards of epoxy resin (EP), via an aza-Michael addition reaction and was well characterized. A high char yield of about 62.9 wt % was obtained for PDPFDE from thermogravimetric analysis results, and a charring mechanism has been suggested that involves iron-cored carbon nanotubes as catalysts. An EP composite containing 5.0 wt % PDPFDE reached a low limiting oxygen index value of 29.1% and V-1 rating in the UL-94 test. On comparison with neat EP, the peak of the heat release rate and the total smoke production of the composite were reduced by 36.0% and 24.0%, respectively. Scanning electron microscopy and energy dispersive X-ray analysis results indicated the formation of coherent, dense, and nitrogen-rich char residues due to the incorporation of PDPFDE. Furthermore, the addition of an appropriate amount of PDPFDE improved the mechanical properties compared to pure EP.